LIBRARY 

V 

X\i    *  °F  THE 

UNIVERSITY  OF  CALIFORNIA. 
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m 


Works  of  ALFRED  I.  COHN 

PUBLISHED   BY 

JOHN  WILEY  &  SONS. 


Indicators  and  Test-papers. 

Their  Source,  Preparation,  Application,  and  Tests  for 
Sensitiveness.  With  Tabular  Summary  of  the  Applica- 
tion of  Indicators.  Second  Edition.  Revised  and  En- 
larged, i 2mo,  ix  -f-26?  pages.  Cloth,  $2.00. 

Tests  and  Reagents, 

Chemical  and  Microscopical,  known  by  their  Authors' 
Names:  together  with  an  Index  of  Subjects.  8vo,  iii-H83 
pages.  Cloth,  $3  oo. 

Fresenius'  Quantitative  Chemical  Analysis. 

New  Authorized  Translation  of  the  latest  German 
Edition.  In  two  volumes.  By  Alfred  I.  Cohn. 
Recalculated  on  the  basis  of  the  latest  atomic  weights, 
and  also  greatly  amplified  by  the  translator.  8vo,  2vols., 
upwards  of  2000  pages,  280  figures.  Cloth,  $12.50. 


QUANTITATIVE 
CHEMICAL  ANALYSIS 


BY  THE  LATE 


DE.  C.  KEMIGIUS  FRESENIUS 

PRIVY  AULIC  COUNSELLOR; 
DIRECTOR  OF  THE  CHEMICAL  LABORATORY  AT  WIESBADEN 


AUTHORIZED  TRANSLATION  OF  THE  GREATLY  AMPLIFIED  AND 
REVISED  SIXTH  GERMAN  EDITION 

BY 

ALEBED   I.   COHN 

AUTHOR  OF  "INDICATORS  AND  TEST-PAPERS,"  AND  "TESTS  AND  REAGENTS.1" 

MEMBER  OF  THE  AMERICAN  CHEMICAL  SOCIETY;  SOCIETY  OF 

CHEMICAL  INDUSTRY:  VEREIN  DEOTSCHER 

CHEMIKER:  ETC. 


NEW  YORK 

JOHN  WILEY   &   SONS 

43-45    EAST   NINETEENTH    STREET 

1904 


< 

9 

C^~~ 


GtNERAL  :      > 

Copyright,  1903, 

BY 
ALFRED  I.  COHN. 


ROBERT  DRUMMOND.    PRINTER,   NEW  YORK. 


CONTENTS. 


PART  I.— GENERAL. 

DIVISION  I. 
THE  EXECUTION  OF  ANALYSIS.     SECTION  VI. 

PACK1 

ORGANIC  ANALYSIS,  §  171 I 

I.  Qualitative  examination  of  organic  substances,  §  172 4 

1.  Testing  for  nitrogen 4 

2.  Testing  for  sulphur 5 

3.  Testing  for  phosphorus 7 

4.  Testing  for  iodine,  bromine,  and  chlorine 7 

5.  Testing  for  inorganic  substances g 

IL  Determination  of  the  elements  in  organic  substances,  §  173 9 

A.  Analysis  of  substances  containing  carbon  and  hydrogen  only,  or 

carbon,  hydrogen,  and  oxygen 11 

a.  Solid  substances ., 12 

a.  Readily  combustible  and  non-volatile 12 

Combustion  with  cupric  oxide 12 

1.  LIEBIG'S  method,  §  174 12 

(1)  Apparatus  and  preparation  required 12 

(2)  Performance  of  the  analytical  process 22 

2.  BUNSEN'S  modification  of  LIEBIG'S  method,  §  175 30 

ft.  Difficultly  combustible  non-volatile  substances 33 

(1)  Combustion  with  lead  chromate,  §  176 33 

(2)  Combustion  with  cupric  oxide  and  potassium  chlorate 

or  perchlorate,  §  177 36 

(3)  Combustion  with  cupric  oxide  and  oxygen,  §  178.  ...  37 
f.   Hygroscopic  or  volatile  compounds,  or  such  as  undergo 

changes  when  heated  at  100°,  §  179 44 

6.  Fluid  bodies 46 

a.  Volatile  liquids,  §  180 46 

3.   Non-volatile  liquids,  §  181 49 

Supplement  to  A,  §  174-§  181 51-5°, 

Modified  apparatus,  §  182 51 

v 


L02 


VI  CONTENTS. 

PACT! 

1.  For  connecting  the  chloride  of  calcium  tube  to  the  com- 

bustion tube 51 

2.  For. the  absorption  of  water 51 

3.  For  the  absorption  of  carbonic  acid 53 

B.  Analysis  of  compounds,  containing  carbon,  hydrogen,  oxygen, 

and  nitrogen 56 

a.  Determination  of  the  carbon  and  hydrogen  in  nitrogenous  sub- 

stances, §  183 56 

b.  Determination  of  nitrogen  in  organic  compounds 58 

a.  Determination  of  the  nitrogen  by  volume 58 

1.  Relative  determination  of  the  nitrogen  by  volume,  §  184  59 

aa.  LIEBIG'S  method 59 

66.   BUNSEN'S  method 62 

cc.    MARCHAND'S  method  modified  by  GOTTLIEB 65 

2.  Absolute  determination  of  nitrogen  by  volume,  §  185.  ..  66 

aa.  DUMAS'  method 66 

66.   SIMPSON'S  method 69 

cc.    W.  GIBBS'  method 74 

P.  Determination  of  nitrogen  by  conversion  into  ammonia. 

Method  of  VARRENTRAPP-WILL,  §  186 82 

Y.  PELIGOT'S  modification  of  VARRENTRAPP- WILL'S  method, 

§187 91 

C.  Analysis  of  organic  substances  containing  sulphur,  §  188 95 

I.  Methods  in  the  dry  way 96 

1.  Method  suitable  for  determining  sulphur  in  non- volatile 

substances  poor  in  sulphur 96 

2.  Method  adapted  for  non-volatile  or  difficultly  volatile 

substances  containing  more  than  5  per  cent,  sulphur.  .  97 

3.  Method  adapted  for  volatile  and  non- volatile  substances  98 

4.  Method  adapted  for  solid  and  liquid  volatile  compounds .  99 

5.  Methods  based  upon  combustion  in  oxygen  gas 100 

6.  Method  of  determining  sulphur  in  coal  and  coke 115 

II.  Methods  in  the  wet  way 116 

D.  Determination  of  phosphorous  in  organic  substances,  §  1C9.  .  .  .  120 

E.  Analysis  of  organic  compounds  containing  chlorine,  bromine, 

and  iodine,  §  190 121 

I.  Methods  in  the  dry  way 123 

II.  Methods  in  the  wet  way 126 

F.  Analysis  of  organic  substances  containing  inorganic  compounds, 

§191 129 

Supplement  to  §  174-191,  §  192 131 

A.  Methods  for  the  direct  estimation  of  oxygen,  §  192 131 

a.  BAUMHAUER'S  method 131 

6.  STROMEYER'S  method 135 

c.  MITSCHERLICH'S  method 137 

d.  LADENBURG'S  method 139 


CONTENTS.  V 

PAGE 

e.  MAUMENE'S  method 139 

/.   CRETIER'S  method 140 

B.  Methods  of  organic  analysis  which  differ  from  the  ordinary  pro- 
cess, without  including  a  direct  estimation  of  oxygen 140 

a.  CLOEZ'  method 140 

6.  WARREN'S  method 145 

c.  Method  of  WHEELER,  F.  SCHULZE,  and  T.  SCHLOSING 145 

d.  ULLGREN'S  modification  of  BRUNNER'S  method 145 

HI.  Determination  of  the  equivalent  of  organic  compounds.  . 145 

1.  From  its  combination   with  acids,  bases,  etc.,  §  193 146 

2.  Determination  of  the  vapor  density  of  the  compound,  §  194 147 

A.  DUMAS'  process 147 

B.  HOFMANN'S  process 151 

C.  GRABOWSKI  and  LANDOLT'S  processes 155 

D.  BUNSEN'S  process 156 

E.  Process  of  DEVILLE  and  TROOST 156 

3.  From  its  products  of  decomposition,  §  195 157 


DIVISION  II. 
CALCULATION  OF  ANALYSIS. 

I.  Calculation  of  the  constituent  sought  from  the  compound  obtained  in  the 

analytical  process,  and  conversion  of  the  result  in  per  cents. ,  §  196.     158 

1.  When  the  substance  sought  has  been  separated  in  the  free 

state 158 

a.  Solid,  liquid,  and  gaseous  substances  which  have  been 

determined  by  weighing,  §  197 158 

b.  Gases  which  have  been  determined  by  measuring, 

§198 159 

2.  When  the  substance  sought  has  been  separated  in  com- 

bination, §  199 164 

3.  Calculation  of  the  results  of  indirect  analysis,  §  200 166 

SUPPLEMENT  TO    I. 

I.  Remarks  on  loss  and  excess  in  analyses,  and  on  taking  the  mean, 

§  201 168 

II.  Deduction  of  empirical  formulas.  §  202 170 

HI.  Deduction  of  rational  formulas,  §  203 173 

IV.  Calculation  of  the  vapor  density  of  volatile  substances,  §  204 177 


CONTENTS. 


.      PART  II.— SPECIAL. 

PAGE 

I.  ANALYSIS  OF  WATER. 

A.  Examination  of  potable  water,  §  205 185 

I.  The  water  is  clear 185 

II.  The  water  is  not  clear 214 

Appendix  to  A.,  Estimation  of  hardness 215 

B.  Analysis  of  Mineral  waters,  §  206 221 

1.  The  analytical  process 222 

A.  Operations  at  the  spring  or  well 222 

I.  Apparatus  and  other  requisites,  §  207 222 

II.  Special  analytical  processes,  §  208 224 

B.  Operations  in  the  laboratory 242 

I.  Qualitative  analysis 242 

II.  Quantitative  analysis,  §  209 242 

Examination  of  the  dissolved  gases,  §  210.  .  . . 265 

Modifications  required  in  the  case  of  saline  waters,  §  211.  268 

Remarks  on  the  analysis  of  sulphuretted  waters,  §  212 ...  272 

2.  Calculation,  control,  and  arrangement  of  the  results  of  analyses 

of  mineral  waters,  §  213 274 


II.  ANALYSIS  OF  SOME  TECHNICAL  PRODUCTS  AND  MINERALS,  WITH  PRO- 
CESSES FOR  DETERMINING  THEIR  COMMERCIAL  VALUE 284 

1.  Determination  of  free  acid — acidimetry 284 

A.  Estimation  by  specific  gravity,  §  214 284 

B.  Estimation  by  saturation  of  the  acid  with  an  alkaline  liquid  of 

known  strength,  §  215 293 

C.  KIEFER'S  modification  of  B,  §  216 315 

D.  Estimation  by  weighing  the  carbonic  acid  expelled  by  the  free 

acid  from  sodium  bicarbonate,  §  217 316 

E.  Methods  relating  to  particular  acids 317 

2.  Determination  of  free  alkali  and  of  alkali  carbonate — alkalimetry.  .  319 

A.  Determination  of  potassa,  soda,  or  ammonia,  potassium  car- 

bonate, or  sodium  carbonate  from  the  specific  gravity  of 

their  solutions,   §  218 319 

B.  Determination  of  the  total  amount  of  carbonated  and  caustic 

alkali  present  in  a  substance 323 

I.  Volumetric  methods — methods  of  titration 323 

a.  DESCROIZILLES  and  GAY-LUSSAC'S  method  slightly  modi- 

fied, §  219 323 

b.  MOHR'S  method,  §  220 329 

II.  Gravimetric  method  of  FRESENIUS  and  WILL,  §  221 331 


(§225 341 


CONTENTS.  IX 

MOB 

C.  Determination  of  the  caustic  alkali  which  is  present  along  with 

the  carbonate,  §  222 332 

Determination  of  sodium  carbonate  in  presence  of  potassium 

carbonate 333 

3.  Estimation  of  alkaline  earths  by  the  alkalimetric  method,  §  223 334 

4.  The  most  important  technical  potash  compounds 336 

A.  Potash  or  pearlash,  §  224 336 

B.  Potassium  chloride    ) 

C.  Potassium  sulphate 

D.  Potassium  nitrate,  §  226 ._ 346 

E.  Analysis  of  gunpowder  (Appendix  to  D.),  I  227 349 

F.  Potassium  bitartrate  (tartar),  §  228 357 

5.  Sodium  compounds 360 

A.  Soda,  §  229 360 

B.  Sodium  chloride  (common  salt) ,  §  230 371 

C.  Sodium  sulphate  (salt-cake),  §  231 373 

6.  Barium  compounds 375 

Heavy  spar  (Barium  sulphate),  §  232 375 

7.  Calcium  compounds 376 

A.  Calcium  phosphate  (phosphorite).   See  V.  Analysis  of  manures  376 

B.  Chlorinated  Lime,  §  233 376 

A.  PENOT'S  method 379 

B.  MOHR'S  modification  of  PENOT'S  method 381 

C.  lodometric  methods 382 

D.  OTTO'S  method 383 

C.  Calcium  acetate,  §  234 387 

D.  Analysis  of  limestones,  dolomites,  marls,  cements,  etc.,  §  235.  393 

8.  Aluminium  compounds 403 

A.  Clays.     (See  silicon  compounds,  §  238,  p.  413.) 

B.  Aluminium  sulphate,  §  236 403 

9.  Silicon  compounds 405 

A.  Analysis  of  native,  and  more  particularly  of  mixed  silicates, 

§  237. 405 

B.  Analysis  of  clays,  §  238 413 

10.  Chromium  compounds.     Analysis  of  chrome  iron  ore,  §  239 421 

11.  Zinc  compounds 428 

A.  Calamine 


B.  Electric  calamine  i  * 

C.  Zinc  blende,  §  241 430 

D    Zinc  ores  generally 435 

I.  Volumetric  determination  of  zinc,  §  242 435 

II.  Electrolytic  determination  of  zinc  in  zinc  ores,  §  243 ....  448 

E.  Metallic  zinc,  §  244 450 

F.  Zinc  dust,  §  245 452 

12.  Manganese  compounds 456 

A.  Black  oxide  of  manganese,  §  246 456 


CONTENTS. 

PAGE 

I.  Drying  the  sample 457 

II.  Determination  of  the  manganese  dioxide  present,  §  247. . .  458 

III.  Determination  of  moisture  in  manganese,  §  248 468 

IV.  Determination  of  the  amount  of  hydrochloric  acid  required 

for  the  complete  decomposition  of  the  manganese  ore, 

§  249 469 

B.  Manganese  ores  generally. 

Determination  of  their  metallic  manganese  content,  §  250 470 

Electrolytic  determination 472 

13.  Nickel  compounds 474 

A.  Nickel  ores,  "nickelstein,"  and  other  intermediate  products 

of  nickel  manufacture,  §  251 474 

B.  Commercial  metallic  nickel,  §  252 483 

14.  Iron  compounds 486 

A.  Iron  ores 486 

I.  Methods  for  complete  analysis,  §  253 486 

a.  Hematite 488 

b.  Brown  iron  ore  (limonite) 488 

c.  Bog  iron  ore 493 

d.  Magnetic  iron  ore 494 

e.  Spathic  iron  ore 494 

II.  Determination  of  the  iron  in  iron  ores,  §  254 495 

1.  Volumetric  methods 495 

2.  Gravimetric  methods 499 

B.  Analysis  of  various  kinds  of  iron 501 

I.  Cast  iron,  §  255 501 

II.  Steel  and  wrought  iron 548 

C.  Pyrites,  §  256 553 

15.  Uranium  compounds,  §  257 567 

16.  Silver  compounds,  §  258 568 

A.  Silver  ores 568 

B.  Silver  alloys 569 

17.  Lead  compounds 574 

A.  Galena,  §  259 574 

B.  Varieties  of  metallic  lead 584 

C.  Oxides  and  salts  of  lead 597 

18.  Mercury  compounds,  §  260 601 

A.  Mercury  ores 601 

B.  Metallic  mercury 602 

19.  Copper  compounds 605 

A.  Copper  ores,  §  261 605 

Electrolytic  determination  of  copper 61 1 

3.  Other  methods  of  determining  copper 624 

B.  Varieties  of  copper 633 

I.  Cement  copper,  §  262 633 

II.  Coarse  copper,  refined  copper,  §  263 636 


CONTENTS.  XI 


C.   Copper  alloys,  §  264 , 655 

I.  Brass 655 

II.  Nickel  coinage  metal 659 

III.  German  silver  (Argentan) 660 

20.  Bismuth  compounds,  §  265 661 

A.  Ores  of  bismuth 661 

B.  Bismuth  alloys 665 

C.  Bismuth  salts 666 

21.  Antimony  compounds,  §  266 669 

A.  Antimony  ores 669 

B.  Antimony  alloys 674 

22.  Tin  compounds,  §  267 675 

A.  Tin  ores 675 

I.  Tinstone 675 

II.  Tin  pyrites 676 

B.  Varieties  of  tin 677 

C.  Alloys  of  tin 680 

I.  Alloys  consisting  chiefly  of  copper  and  tin  (bronzes,  etc.) . .  680 

II.  Alloys  consisting  chiefly  of  lead  and  tin  (solders) 683 

III.  Alloys  consisting  chiefly  of  antimony  and  tin  (pewters) 685 

IV.  Alloys  used  for  bearings  (bearing  metal) 686 

D.  Preparations  of  tin 689 

23.  Arsenic  compounds,  §  268 690 

Detection  and  estimation  of  arsenic  in  organic  matter,  §  268a. . .  693 

24.  Phosphorus  compounds,  §  269 700 

25.  Sulphur  compounds,  §  270 703 

A.  Commercial  sulphur 703 

B.  Fuming  sulphuric  acid 706 

26.  Nitrogen  compounds,  §  271 710 

A    "Nitrose" 710 

B.  Chamber  acid,  etc 715 

27    Carbon  compounds,  §  272 717 

A.  Graphite 717 

B.  Coal  and  coke 721 

28.  Hydrogen  compounds,  §  273 728 

Hydrogen  peroxide 728 

SUPPLEMENT   TO    DIVISION   II. 

L  Determination  of  grape  sugar  (dextrose},  fruit  sugar  (levulose),  in- 
vert-sugar, maltose,  milk  sugar,  cane  sugar  (saccharose),  starch, 

and  dextrin.  .    730 

A.  Methods  based  upon  the  reduction  of  cupric  oxide  to 

cuprous  oxide,  §  274 732 

B=  Methods  based  upon  the  reduction  of  mercury  compounds, 

§  275 749 


i  CONTENTS. 

PAGE 

C.  Methods  based  upon  the  decomposition  of  sugar  by  alco- 

holic fermentation,  §  276 754 

D.  Determination  of  cane  sugar,  dextrin,  and  starch,  §  277 .  .  757 

1.  Cane  sugar 757 

2.  Dextrin  and  starch 760 

II.  Determination  of  alcohol,  §  278 763 

III.  Determination  of  tannin 767 

A.  LOWENTHAL'S  method,  §  279 767 

B.  HAMMER'S  method,  §  280 775 

C.  Gravimetric  modification  of  HAMMER'S  method,  §  281 780 

D.  Other  methods  for  estimating  the  tanning  principle 780 

IV.  Estimation  of  anthracene,  §  282 785 


HI.  ESTIMATION  OF  THE  INORGANIC  CONSTITUENTS  OF  PLANTS,  §  283 ...     787 

A.  Ash  analysis 789 

I.  Preparation  of  the  ash,  §  284 790 

II.  Analysis  of  the  ash,  §  285 798 

a.  Qualitative  analysis. 799 

b.  Quantitative  analysis 800 

a.  Ashes  in  which  the  carbonates  of  the  alkalies  or  alkaline 

earths  predominate,  and  in  which  all  the  phosphoric 
acid  may  be  assumed  to  be  combined  with  ferric 
oxide,  §  286 800 

/?.  Ashes  decomposable  by  hydrochloric  acid,  and  in  which 
a  further  quantity  of  phosphoric  acid  is  present  above 
that  combined  with  iron,  §  287 806 

f.  Ashes  not  decomposed  by  hydrochloric  acid,  §  288 ....     808 

B.  Supplementary  determination  of  certain  other  inorganic  substances 

in  plants,  §  289 810 

C.  Arrangement  of  the  results,  §  290 813 


IV.  ANALYSIS  OF  SOILS,  §  291 815 

A.  Collecting  the  Sample,  §  292 816 

B.  Mechanical  Analysis,  §  293 817 

a.  Purely  mechanical  method,  §  294 819 

6.  SCHLGSING'S  method,  §  295 824 

C.  Chemical  analysis,  §  296 825 

1.  Determination  of  the  moisture 827 

2.  Determination  of  the  chemically  combined  water 827 

3.  Estimation  of  the  substances  soluble  in  water,  §  297 827 

4.  Estimation  of  the  substances  soluble  in  hydrochloric  acid, 

§298 831 

5.  Examination  of  that  portion  of  the  earth  insoluble  in  cold 

hydrochloric  acid,  §  299 835 


CONTENTS.  Xiii 

PAGE 

6.  Examination  of  the  residue  insoluble  in  sulphuric  acid, 

§  300 836 

7.  Determination  of  the  carbon  contained  in  organic  com- 

pounds, §  301 837 

a.  Determination  of  the  total  organically  combined  carbon.  838 

b.  Determination  of  humus 840 

c.  Determination  of  waxy  and  resinous  substances 842 

8.  Determination  of  the  nitrogenous  constituents  of  the  soil, 

§  302. .  . '. 842 

a.  Determination  of  nitric  acid 842 

6.  Determination  of  ammonia 842 

c.   Determination. of  the  nitrogen  in  organic  compounds. ..  846 

9.  Supplementary  determinations,  §  303 847 

10.  Statement  of  the  results,  §  304 848 


V.  ANALYSIS  or  MANURES 850 

A.  General,  §  305. 850 

B.  Sampling,  §  306 851 

C.  Analysis  of  manures  the  value  of  which  depends  entirely  or  almost 

entirely  upon  their  phosphoric  acid  content 853 

I.  Those  containing  the  whole  of  the  phosphoric  acid  in  the 

form  of  compounds  insoluble  in  water,  §  307 853 

1.  Determination  of  the  moisture 854 

2.  Estimation  of  the  phosphoric  acid 854 

a.  Dissolving  the  substance,  §  308 854 

6.  The  determination 856 

a.  Molybdenum  method,  §  309 856 

/?.  GLASER'S  method,  §  310 860 

II.  Manures  containing  phosphoric  acid  partly  in  the  form  of 

water-soluble  compounds,  §  311 862 

1.  Determination  of  the  moisture 863 

2.  Determination  of  the  phosphoric  acid 863 

a.  Determination  of  the  phosphoric  acid  hi  the  three  con- 
ditions in  which  it  may  occur  in  superphosphate 863 

a.  Determination  of  the  water-soluble  phosphoric  acid, 

§  312 863 

aa.  Preparation  of  the  solution 863 

66.   Determining  the  content  of  the  solution,  §  313 . .  864 

aa.  Gravimetric  method 864 

pp.  Volumetric  uranium  method 864 

ff.  Acidimetric  method,  §  314 866 

/?.  Determination  of  the  "reverted,"  and  of  the  unat- 

tacked  phosphoric  acid,  §  315 869 

6.  Shortened  methods  of  determining  the  values  of  super- 
phosphate   870 


CONTENTS. 

PAGE 

a.  Determination  of  "soluble"  phosphoric  acid,  §  316 .  .  870 
ft.  Determination    of    the    citrate-soluble    phosphoric 

acid,  §  317 871 

c.   Determination  of  the  total  phosphoric  acid  in  super- 
phosphates, §  318 873 

D.  Analysis  of  manures,  the  value  of  which  depends  wholly  or  almost 

wholly  upon  their  potassium  content,  §  319 873 

E.  Analysis  of  manures,  the  value  of  which  depends  solely  or  nearly 

altogether  upon  the  nitrogen  they  contain 875 

I.  Chili  saltpetre,  §  320 875 

II.  Ammonium  salts 883 

a.  Distillation  method,  §  322 883 

6.  Azotimetric  method,  §  322 835 

III.  Substances  containing  nitrogen  organically  combined. .  . .  894 

a.  Modified  VARRENTRAPP-WILL  method,  §  323 894 

6.  KJELDAHL'S  method,  §  324 897 

a.  KJELDAHL'S  original  method,  §  325 899 

p.  Modifications  of  KJELDAHL'S  method,  §  326 902 

F.  Analysis  of  manures  containing  two  or  more  manurial  substances  907 

I.  Usual  mode  of  procedure,  §  327. 908 

1.  Determination  of  the  water 908 

2.  Total  fixed  constituents 908 

3.  Constituents  both  soluble  and  insoluble  in  water 908 

4.  Fixed  constituents  singly 908 

5.  Total  carbon 909 

6.  Sulphur  compounds 909 

7.  Total  nitrogen,  §  328 909 

a.  Preparatory  treatment 910 

6.  The  analytical  process 910 

a.  DUMAS'  method 910 

ft.  JODLBAUER'S  modification  of  KJELDAHL'S  method.  910 

f.  VARRENTRAPP-WILL' s  method  and  its  modifications  911 

8.  Nitrogen  in  its  different  forms  of  combination,  §  329. .  .  .  914 

a.  In  ammoniacal  compounds 914 

ft.  In  the  form  of  nitric  acid 914 

f.  In  organic  combination 915 

IL  Analysis  of  commercial  manures 916 

1.  Bone  preparations,  §  330 916 

a.  Bone  meal 917 

b.  Animal  charcoal  or  bone  black 918 

c.  Bone  ash 920 

d.  Precipitated  calcium  phosphate  from  bones 920 

e.  Superphosphate  from  bone 920 

2.  Guano  (Peruvian  guano),  §  331 921 

a.  Crude  guano 921 

b.  Decomposed  guano 925 


CONTENTS.  XV 


3.  Fish  guano,  "granat"  guano,  horn-meal,  tendon-meal, 

and  flesh-meal  manure,  §  332 926 

4.  Mixed  manures,  §  333 926 


VI.  ANALYSIS  OF  ATMOSPHERIC  AIR 928 

A.  Determination  of  the  water  and  carbonic  acid 929 

I.  BRUNNER'S  method,  §  334 929 

II.  PETTERSSON'S  method,  §  335 932 

B.  Determination  of  carbonic  acid  alone 938 

I.  PETTENKOFER'S  original  process,  §  336 938 

II.  Modification  of  PETTENKOFER'S  process 941 

1.  SONDEN'S  modification,  §  337 941 

2.  SPRING  and  ROLAND'S  modification,  §  338 942 

3.  Modifications    in  the   manner  of  titrating  the  baryta 

water,  §  339 945 

III.  Process  proposed  by  MOHR,  and  employed  by  HLASIWETZ 

and  v.  GILM,  §  340 946 

C.  Determination  of  oxygen  and  nitrogen,  §  341 948 


PART  III. 

EXERCISES  FOR  PRACTICE 953 

A.  Simple  determinations  in  the  gravimetric  way,  intended  to  teach 

the  student  the  more  common  analytical  operations 955 

B.  Complete  analysis  of  salts  in  the  gravimetric  way;    calculation  of 

the  formulae  from  the  results  obtained 964 

C.  Separation  of  two  bases  or  two  acid  radicals  from  each  other,  and 

determinations  hi  the  volumetric  way 969 

D.  Analysis  of  alloys,  minerals,  industrial  products,  etc.,  in  the  gravi- 

metric and  volumetric  way 976 

E.  Determination  of  the  solubility  of  salts 981 

F.  Determination  of  the  solubility  of  gases  hi  liquids,  and  analysis  of 

gaseous  mixtures 982 

G.  Organic  analysis,  and  determinations  of  the  equivalents  of  organic 

compounds;    also  analyses  hi  which  organic  analysis  has  to  be 

employed 984 

ANALYTICAL  EXPERIMENTS 985 


XVi  CONTENTS. 


APPENDIX  I. 

PAGE 

OFFICIAL  METHODS  OF  ANALYSIS  ADOPTED  BY  THE  ASSOCIATION  OF 

OFFICIAL  AGRICULTURAL  CHEMISTS 1017 

I.  Methods  for  the  analysis  of  fertilizers 1017 

1.  Preparation  of  sample 1017 

2.  Determination  of  moisture 1017 

3.  Determination  of  phosphoric  acid 1017 

a.  Gravimetric  method 1017 

b.  Optional  volumetric  method 1020 

4.  Determination  of  nitrogen 1021 

a.  KJELDAHL  method 1021 

b.  GUNNING  method. 1024 

c.  KJELDAHL  method  modified  to  include  the  nitrogen  of 

nitrates 1024 

d.  GUNNING  method  modified  to  include  the  nitrogen  of 

nitrates 1025 

e.  Absolute  or  cupric-oxide  method 1025 

/.   Ruffle  method 1027 

g.  Soda-lime  method 1028 

h.  Magnesium  oxide  method 1029 

i.   ULSCH  method  modified  by  STREET 1029 

j.   Zinc-iron  method 1030 

5.  Determination  of  potash 1030 

a.  LINDO-GLADDING  method 1030 

&.  Optional  method 1031 

c.  Factors 1032 

II.  Methods  for  the  analysis  of  foods 1032 

1.  Preparation  of  sample 1032 

2.  Determination  of  moisture 1032 

3.  Determination  of  ash 1032 

4.  Determination  of  ether  extract 1033 

.    a.  Preparation  of  anhydrous  ether 1033 

b.  Determination 1033 

5.  Determination  of  crude  protein 1033 

6.  Determination  of  albuminoid  nitrogen  by  STUTZER'S  method  1033 

7.  Determination  of  crude  fibre  and  carbohydrates 1034 

8.  Official  methods  for  the  determination  of  carbohydrates  in 

grains  and  by-product  cattle  foods 1034 

a.  Determination  of  reducing  sugars  (estimated  as  dex- 
trose)     1034 

6.  Determination  of  sucrose 1034 

c.  Determination  of  starch  in  commercial  starches  and 

potatoes 1034 

d.  Diastase  method  for  starch.  .  .1034 


CONTENTS.  XVU 

PAGE 

e.  Provisional  methods  for  the  determination  of  pento- 

sans  by  means  of  phloroglucin 1035 

/.   Method  for  estimating  galactan 1036 

g.  Determination  of  crude  fibre 1036 

HE.  Methods  for  the  determination  of  soluble  carbohydrates 1037 

1.  Determination  of  water 1037 

a.  By  drying 1037 

(1)  In  sugars 1037 

(2)  In  massecuites,  molasses,  honeys,  and  other  liquid 

and  semi-liquid  products 1037 

(3)  Provisional  method  for  drying  molasses  with  quartz 
sand 1037 

6.  Aerometric  methods 1038 

2.  Ash 1040 

a.  Determination  of  ash 1040 

b.  Quantitative  analysis  of  the  ash 1041 

3.  Determination  of  nitrogen 1041 

4.  Determination  of  reducing  sugars 1042 

a.  Preparation  of  reagents 1042 

6.  Volumetric  methods 1042 

c.  Gravimetric  methods 1044 

5.  Determination  of  sucrose 1049 

a.  Optfcal  methods 1049 

6.  Optical  methods  by  inversion 1050 

6.  Determination  of  lactose 1051 

a.  Optical  method  for  the  determination  of  lactose  in 

milk 1051 

b.  SOXHLET'S  method  using  alkaline  copper  solution 1052 

IV.  Methods  for  the  analysis  of  dairy  products. .' 1054 

1.  Butter  analysis 1054 

a.  Preparation  of  sample 1054 

6.  Determination  of  water 1054 

c.  Determination  of  ether  extract 1054 

d.  Determination  of  casein,  ash,  and  chlorine 1054 

e.  Determination  of  salt 1054 

/.   Determination  of  volatile  acids 1055 

LEFFMANN-BEAM  method 1057 

g.  Determination  of  soluble  and  insoluble  acids 1059 

h.  Determination  of  saponification  equivalent 1060 

i.   Determination  of  the  refractive  index 1061 

/.   Determination  of  iodine  absorption-number 1063 

k.  Determination  of  specific  gravity 1065 

1.    Determination  of  melting-point 1066 

m.  Microscopic  examination 1068 

2.  Milk  analysis 1068 

a.  Determination  of  water .   1068 


xviii  CONTENTS. 

PAGE 

b.  Determination  of  fat 1069 

c.  Determination  of  total  nitrogen 1069 

d.  Determination  of  ash 1070 

e.  Determination  of  sugar 1070 

3.  Cheese  analysis 1070 

a.  Preparation  of  sample 1070 

b.  Determination  of  water 1071 

c.  Determination  of  fat 1071 

d.  Determination  of  nitrogen 1071 

e.  Determination  of  ash 1071 

/.    Determination  of  other  constituents 1072 

g.  Provisional  method  for  the  determination  of  acidity 

in  cheese 1072 

V.  Methods  for  the  analysis  of  fermented  and  distilled  liquors 1072 

1.  Determination  of  specific  gravity 1072 

2.  Determination  of  alcohol 1072 

a.  In  fermented  liquors 1072 

b.  In  distilled  liquors 1072 

3.  Determination  of  extract 1078 

a.  In  distilled  liquors,  dry  wines,  beers,  ales,  etc 1078 

b.  In  sweet  wines 1078 

4.  Determination  of  total  acidity 1078 

5.  Determination  of  volatile  acids 1078 

6.  Determination  of  glycerin 1078 

a.  In  dry  wines 1078 

b.  In  sweet  wines 1078 

7.  Determination  of  reducing  sugars 1078 

8.  Polarization 1078 

a.  In  white  wines 1078 

b-  In  red  wines 1079 

c.  In  sweet  wines 1079 

d.  Application  of  analytical  methods 1079 

9.  Determination  of  tannin  and  coloring  matter 1081 

10.  Determination  of  potassium  bitartrate 1082 

11.  Determination  of  tartaric  acid 1082 

12.  Determination  of  tartaric,  malic,  and  succinic  acids 1083 

13    Detection  of  coloring  matter 1084 

14.  Determination  of  ash 1085 

15.  Determination  of  potash 1085 

16    Determination  of  sulphurous  acid 1085 

17.  Detection  of  salicylic  acid 1085 

18,  Detection  of  gum  and  dextrin 1086 

19    Determination  of  fusel  oil 1086 

20.  Determination  of  aldehydes ; 1087 

21.  Determination  of  ethereal  salts. .                                             .  1088 


CONTENTS.  XIX 

PAGE 

VI.  Methods  for  the  analysis  of  soils 1088 

1.  Preparation  of  sample 1088 

2.  Determination  of  moisture 1089 

3.  Determination  of  volatile  matter 1089 

4.  Determination  of  acid-soluble  materials 1089 

a.  Acid  digestion  of  the  soil 1089 

6.  Determination  of  ferric  oxide,  alumina,  and  phos- 
phoric acid,  collectively 1090 

c.  Determination  of  manganese 1090 

d.  Determination  of  calcium 1091 

e.  Determination  of  magnesium 1091 

/.   Determination  of  ferric  oxide 1091 

g.  Determination  of  phosphoric  acid 1092 

h.  Provisional  method  for  determining  available  phos- 
phoric acid 1092 

t.   Provisional  method  for  determination  of  more  active 

forms  of  phosphoric  acid  in  soils 1093 

j.    Determination  of  sulphuric  acid 1093 

k.  Determination  of  potash  and  soda 1094 

5.  Determination  of  acid-insoluble  materials 1094 

6.  Determination  of  total  alkalies 1094 

7.  Identification  of  lithium,  caesium,  and  rubidium 1095 

8.  Determination  of  total  nitrogen 1095 

9.  Determination  of  carbon  dioxide 1095 

10.  Determination  of  humus 1095 

11.  Determination  of  humus  nitrogen 1095 

12.  Statements  of  results 1096 

VII.  Methods  for  the  analysis  of  ashes 1096 

1.  Preparation  of  the  ash 1096 

2.  Solution  and  determination  of  carbon,  sand,  and  silica 1097 

3.  Determination  of  manganese,  calcium,  and  magnesium 1097 

4.  Determination  of  phosphoric  acid 1098 

5.  Determination  of  sulphuric  acid  and  alkalies 1 098 

6.  Determination  of  carbon  dioxide  .    1098 

7.  Determination  of  chlorine 1098 

VIII.  Methods  for  the  analysis  of  tanning  materials 1099 

1.  Preparation  of  sample 1099 

2.  Quantity  of  material 1099 

3.  Moisture 1099 

4.  Total  solids 1099 

5.  Soluble  solids 1099 

6.  Non-tannins 1099 

7.  Tannins 1 1 00 

8.  Testing  hide  powder 1100 

9.  Testing  non-tannin  filtrate 1 100 


XX  CONTENTS. 


APPENDIX  II. 

PAGE 

SOME  PRINCIPLES  AND  METHODS  OF  ROCK  ANALYSIS 1101 

PART  I.  Introduction 1101 

I.  Importance  of  complete  analysis 1101 

II.  Object  and  scope  of  the  treatise 1106 

III.  Statement  of  analyses 1107 

IV.  Time  needed  for  analysis 1109 

V.  Two  useful  aids  in  chemical  manipulation 1109 

VI.  Limits  of  allowable  error 1111 

VII.  Quality  of  reagents 1111 

VIII.  Preliminary  qualitative  analysis 1112 

PART  II.  Methods 1112 

I.  Introductory  remarks 1112 

II.  Specific  gravity 1113 

III.  Preparation  of  sample  for  analysis 1116 

IV.  Water-hygroscopic,  zeolitic,  crystal 1117 

Apparatus  for  direct  determination  of  water  at  dif- 
ferent temperatures 1121 

V.  Water— total  or  combined 1122 

Arguments  against  "loss"  on  ignition  method 1122 

Direct  weighing  of  the  water  without  use  of  absorption 

tubes — PENFIELD'S  methods 1122 

VI.  Silica,  separation  from  alumina,  etc 1131 

Alternative  methods  of  decomposition 1131 

Decomposition  of  refractory  silicates  by  hydrochloric 

acid  under  pressure 1132 

Boric-oxide  method  of  JANNASCH  and  HEIDENREICH.  .   1132 

Sodium-carbonate  method 1134 

Subsequent  treatment 1135 

VII.  Metals  precipitable  by  hydrogen  sulphide 1137 

VIII.  Aluminium.     Total  iron 1137 

Indirect  method  for  aluminium 1137 

Precipitation  of  aluminium,  iron,  etc 1138 

Ignition  of  precipitate 1139 

Estimation  of  iron  in  the  alumina  precipitate,  etc 1140 

Determination  of  the  true  value  for  ferric  iron 1141 

Methods  aiming  at  the  more  or  less  direct  estimation 
of  aluminium  after  first  removing  iron  as  sulphide ...    1 141 

By  extraction  with  a  fixed  caustic  alkali 1142 

Direct  precipitation  of  alumina 1143 

IX.  Manganese,  nickel,  cobalt,  copper,  zinc 1143 

Manganese  and  zinc 1143 

Nickel,  cobalt,  and  copper 1144 

X.  Calcium  and  strontium  (barium) 1144 


CONTENTS.  Xxi 

PAGE 

Separation  of  strontium   (barium)  from  calcium  by 

ether-alcohol 1145 

Behavior  of  barium 1145 

Separation  of  barium  from  strontium 1146 

XI.  Magnesium 1146 

Precipitation 1146 

Methods  of  collecting  and  igniting  the  precipitate.  .  .  .  1148 

Contamination  by  and  removal  of  barium  and  calcium  1149 

XII.  Titanium 1149 

Colorimetric  estimation  with  hydrogen  peroxide  (WEL- 

LER'S  method) 1149 

Alternative  mode  of  preparing  the  solution 1150 

Colorimetric  apparatus  and  its  use 1151 

GOOCH'S  gravimetric  method 1152 

GOOCH'S  method  not  directly  applicable  to  rocks  con- 
taining zirconium 1154 

Superiority  of  Colorimetric  and  GOOCH  methods  over 

older  ones , 1154 

BASKERVILLE 's  method 1154 

XIII.  Barium  (zirconium,  total  sulphur) 1155 

XIV.  Zirconium 1156 

HILLEBRAND'S  method 1156 

Other  methods  of  separating  zirconium 1158 

XV.  Rare  earths  other  than  zirconia 1158 

XVI.  Phosphorus 1159 

Procedure  when  material  is  ample 1159 

Procedure  when  material  is  scanty 1159 

XVII.  Chromium 1160 

Gravimetric  method 1160 

Colorimetric  method 1161 

XVIII.  Vanadium  (chromium)  and  molybdenum 1162 

Distribution  of  vanadium  and  molybdenum 1162 

Description  of  method 1163 

Application  of  the  method  in  presence  of  relatively 

much  chromium 1 165 

Condition  of  vanadium  in  rocks 1167 

XIX.  Ferrous  iron 1 168 

Comparison    of    sealed -tube    and    hydrofluoric -acid 
methods — comparative  worthlessness  of  the  former 

in  rock  analysis 1168 

Modified  MITSCHERLICH  method 1170 

Hydrofluoric-acid  method 1171 

PRATT' s  modification  of  the  hydrofluoric-acid  method.  1173 
Influence  of  sulphides,  vanadium,  and  carbonaceous 
matter  on  the  determination  of  ferrous  iron  by  the 

hydrofluoric-acid  method 1173 


XX11  CONTENTS. 

PAGE 

Uncertainties  of  the  ferrous-iron  determination 1175 

XX.  Alkalies 1175 

LAWRENCE-SMITH  method 1175 

Lithium 1178 

GOOCH  method  for  separating  lithium 1178 

Separation  of  alkalies  by  other  methods 1179 

XXI.  Carbon  dioxide.     Carbon 1180 

XXII.  Chlorine 1182 

XXIII.  Fluorine 1182 

XXIV.  Sulphur 1184 

XXV.  Boron 1185 

XXVI.  Nitrogen 1186 

XXVII.  Special  operations 1187 

Detection  of  nepheline  in  presence  of  olivine 1187 

Estimation  of  soluble  silica 1187 

XXVIII.  Estimation  of  minute  traces  of  certain  constituents.  .      .1188 


TABLES  FOR  THE  CALCULATION  OF  ANALYSES 1190  et  seq. 

Table  I.  Equivalents  of  the  elements 1190 

Table  II.  Composition  of  the  bases  and  oxygen  acids 1191 

Table  III.  Reduction  of  compounds  found,  to  constituents  sought,  by 

simple  multiplication  or  division 1195 

Table  IV.  Amount  of  the  constituent  sought  for  every  unit  of  weight 

of  the  compound  found 1197  et  seq. 

Table  V.  International  atomic  weights,  1903 1211 

Table  VI.  Specific  and  absolute  weights  of  some  gases 1212 

Table  VII.  Comparison  of  degrees  of  the  mercurial  thermometer  with 

those  of  the  air-  or  hydrogen-thermometer 1213 

INDEX..  .  1215 


QUANTITATIVE  ANALYSIS, 


SECTION  VI. 
ORGANIC  ANALYSIS. 

§  171. 

ORGANIC  compounds  contain  comparatively  but  few  of  the  ele- 
ments. A  small  number  of  them  consist  simply  of  2  elements,  viz., 

C  and  H; 
the  greater  number  contain  3  elements,  viz.,  as  a  rule, 

C,  H,  and  O; 
most  of  the  rest  4  elements,  viz.,  generally, 

C,  H,  O,  and  N; 
a  small  number  5  elements,  viz., 

C,  H,  O,  N,  and  S; 
and  a  few  elements,  viz., 

C,  H,  O,  N,  S,  and  P. 

This  applies  to  all  the  natural  organic  compounds  which  have 
as  yet  come  under  our  notice.  But  we  may  artificially  prepare 
organic  compounds  containing  other  elements  besides  those  enu- 
merated; thus  we  know  many  organic  substances  which  contain 
chlorine,  iodine,  or  bromine;  others  which  contain  arsenic,  anti- 
mony, tin,  zinc,  platinum,  iron,  cobalt,  etc.;  and  it  is  quite  impos- 
sible to  say  which  of  the  other  elements  may  not  be  similarly 


2  ORGANIC    ANALYSIS.  [§    17l» 

capable  of  becoming  more  remote  constituents  of  organic  com- 
pounds (constituents  of  organic  radicals). 

With  these  compounds  we  must  not  confound  those  in  which 
organic  acids  are  combined  with  inorganic  bases,  or  organic  bases 
with  inorganic  acids,  such  as  tartrate  of  lead,  for  instance,  silicic 
ether,  borate  of  morphine,  etc.;  since  in  such  bodies  any  of  the 
elements  may  of  course  occur. 

Organic  compounds  may  be  analyzed  either  with  a  view  simply 
to  resolve  them  into  their  proximate  constituents;  thus,  for  in- 
stance, a  gum-resin  into  resin,  gum,  and  ethereal  oil;  or  the  analy- 
sis may  have  for  its  object  the  determination  of  the  ultimate  con- 
stituents (the  elements)  of  the  substance.  The  simple  resolution 
of  organic  compounds  into  their  proximate  constituents  is  effected 
by  methods  perfectly  similar  to  those  used  in  the  analysis  of 
inorganic  compounds;  that  is,  the  operator  endeavors  to  sepa- 
rate (by  solvents,  application  of  heat,  etc.)  the  individual  constitu- 
ents from  one  another,  either  directly  or  after  having  converted 
them  into  appropriate  forms.  We  disregard  here  altogether  this 
kind  of  organic  analysis — of  which  the  methods  must  be  nearly  as 
numerous  and  varied  as  the  cases  to  which  they  are  applied — and 
proceed  at  once  to  treat  of  the  second  kind,  which  may  be  called 
the  ultimate  analysis  of  organic  bodies. 

The  ultimate  analysis  of  organic  bodies  (here  termed  simply 
organic  analysis]  has  for  its  object,  as  stated  above,  the  determi- 
nation of  the  elements  contained  in  organic  substances.  It  teaches 
us  how  to  isolate  these  elements  or  to  convert  them  into  com- 
pounds of  known  composition,  to  separate  the  new  compounds 
formed  from  one  another,  and  to  calculate  from  their  several 
weights,  or  volumes,  the  quantities  of  the  elements.  Organic 
analysis,  therefore,  is  based  upon  the  same  principles  upon  which 
rest  most  of  the  methods  of  separating  and  determining  inorganic 
compounds. 

The  conversion  of  most  organic  substances  into  distinctly 
characterized  and  readily  separable  products  the  weights  of  which 
can  be  accurately  determined,  offers  no  great  difficulties,  and 
organic  analysis  is  therefore  usually  one  of  the  more  easy  tasks 


§   171.]  ORGANIC    ANALYSIS.  3 

of  analytical  chemistry;  and  as,  from  the  limited  number  of  the 
elements  which  constitute  organic  bodies,  there  is  necessarily  a 
great  sameness  in  the  products  of  their  decomposition,  the  analyti- 
cal process  is  always  very  similar,  and  a  few  methods  suffice  for  all 
cases.  It  is  principally  ascribable  to  this  latter  circumstance  that 
organic  analysis  has  so  speedily  attained  its  present  high  degree  of 
perfection — the  constant  examination  and  improvement  of  a  few 
methods  by  a  great  number  of  chemists  could  not  fail  to  produce 
this  result. 

An  organic  analysis  may  have  for  its  object  either  simply  to 
ascertain  the  relative  quantities  of  the  constituent  elements  of  a 
substance — thus,  for  instance,  woods  may  be  analyzed  to  ascertain, 
their  heating  power,  fats  to  ascertain  their  illuminating  power — or 
to  determine  not  only  the  relative  quantities  of  the  constituent 
elementary  atoms,  but  also  the  number  of  atoms  of  carbon,  hydro- 
gen, oxygen,  etc.,  which  constitute  1  molecule  of  the  analyzed 
compound.  In  scientific  investigations  we  have  invariably  the 
latter  object  in  view,  although  we  are  not  yet  able  to  achieve  it  in 
all  cases.  These  two  objects  cannot  well  be  attained  by  one  opera- 
tion; each  requires  a  distinct  process. 

The  methods  by  which  we  ascertain  the  proportions  of  the  con- 
stituent elements  of  organic  compounds  may  be  called  collectively 
the  ultimate  analysis  of  organic  bodies,  in  a  more  restricted  sense; 
whilst  the  methods  which  reveal  to  us  the  absolute  number  of 
elementary  atoms  constituting  the  molecule  of  the  analyzed  com- 
pound may  be.  styled  the  determination  of  the  molecular  weight  of 
organic  bodies. 

The  success  of  an  organic  analysis  depends  both  upon  the. 
method  and  its  execution.  The  latter  requires  patience,  circum- 
spection, and  skill;  whoever  is  moderately  endowed  with  these 
gifts  will  soon  become  a  proficient  in  this  branch.  The  selection 
of  the  method  depends  upon  the  knowledge  of  the  constituents  of 
the  substance,  and  the  method  selected  may  require  certain  modifi- 
cations, according  to  the  properties  and  state  of  aggregation  of  the 
same.  Before  we  can  proceed,  therefore,  to  describe  the  various, 
methods  applicable  in  the  different  cases  that  may  occur,  we  have 


4  ORGANIC    ANALYSIS.  [§   172. 

first  to  occupy  ourselves  here  with  the  means  of  testing  organic 
bodies  qualitatively. 

[.  QUALITATIVE  EXAMINATION  OF  ORGANIC  BODIES. 

§172. 

It  is  not  necessary  for  the  correct  selection  of  the  proper 
method  to  know  all  the  elements  of  an  organic  compound,  since, 
for  instance,  the  presence  or  absence  of  oxygen  makes  not  the 
slightest  difference  to  the  method.  But  with  regard  to  other  ele- 
ments, such  as  nitrogen,  sulphur,  phosphorus,  chlorine,  iodine, 
bromine,  etc.,  and  also  the  various  metals,  it  is  absolutely  indis- 
pensable that  the  operator  should  know  positively  whether  either 
of  them  is  present.  This  may  be  ascertained  in  the  following 
manner: 

1.  Testing  for  Nitrogen. 

Substances  containing  a  tolerably  large  amount  of  nitrogen 
evolve  upon  combustion,  or  when  intensely  heated,  the  well-known 
odor  of  singed  hair  or  feathers.  No  further  test  is  required  if 
this  smell  is  distinctly  perceptible;  otherwise  one  of  the  following 
experiments  is  resorted  to: 

a.  The  substance  is  mixed  with  potassium  hydroxide  in  powder 
or  with  soda-lims  ( §  66,  4)  and  the  mixture  heated  in  a  test-tube. 
If  the  substance  contains  nitrogen,  ammonia  will  be  evolved, 
which  .may  be  readily  detected  by  its  odor  and  reaction,  and  by 
the  formation  of  white  fumes  with  volatile  acids.  Should  these 
reactions  fail  to  afford  positive  certainty,  every  doubt  may  be 
removed  by  the  following  experiment:  Heat  a  somewhat  larger 
portion  of  the  substance  in  a  short  tube,  with  an  excess  of  soda- 
lime,  and  conduct  the  products  of  the  combustion  into  dilute 
"hydrochloric  acid;  evaporate  the  acid  on  the  water-bath,  dissolve 
the  residue  in  a  little  water,  add  platinic  chloride  to  the  solution, 
evaporate  nearly  to  dryness  on  a  water-bath  and  treat  the  residue 
Avith  alcohol.  If  the  residue  dissolves  and  leaves  no  precipitate 


§   172.]    QUALITATIVE    EXAMINATION    OF    ORGANIC    BODIES.         5 

of  ammonium  platinic  chloride,  the  substance  may  be  considered 
free  from  nitrogen. 

b.  LASSAIGNE  has  proposed  another  method,  which  is  based 
upon  the  property  of  potassium  to  form  potassium  cyanide  when 
ignited  with  a  nitrogenous  organic  substance.     The  following  is 
the  best  mode  of  performing  the  experiment: 

Heat  the  substance  under  examination  in  a  test-tube,  with  a 
small  lump  of  potassium,  and  after  the  complete  combustion  of 
the  potassium,  treat  the  residue  with  a  little  water  (cautiously); 
filter  the  solution,  add  2  drops  of  solution  of  ferrous  sulphate  con- 
taining some  ferric  sulphate,  digest  the  mixture  a  short  time,  and 
add  hydrochloric  acid  in  excess.  The  formation  of  a  blue  or 
bluish-green  precipitate  or  coloration  proves  the  presence  of 
nitrogen. 

Both  methods  are  delicate :  a  is  the  more  commonly  employed,, 
and  suffices  in  almost  all  cases;  b  does  not  answer  so  well  in  the 
case  of  alkaloids  containing  oxygen  (e.g.,  morphine,  brucine). 

c.  In   organic   substances   containing  oxides   of  nitrogen,   the 
presence  of  nitrogen  cannot  be  detected  with  certainty  by  either  a 
or  6,  but  it  may  be  readily  discovered  by  heating  the  substance  in 
a  tube,  when  red  acid  fumes,  imparting  a  blue  tint  to  potassium- 
iodide    starch    paper,    will    be    evolved,   accompanied   often    by 
deflagration. 

2.  Testing  for  Sulphur. 

a.  Solid  substances  are  fused  with  about  12  parts  of  pure  po- 
tassium hydroxide  and  6  parts  of  potassium  nitrate,  or  they  are 
intimately  mixed  with  some  pure  potassium  nitrate  and  sodium 
carbonate;  potassium  nitrate  is  then  heated  to  fusion  in  a  porce- 
lain crucible,  and  the  mixture  gradually  added  to  the  fusing  mass. 
The  mass  is  allowed  to  cool,  then  dissolved  in  water,  and  the  solu- 
tion tested  with  barium  chloride  after  acidifying  with  hydrochloric 
acid.  Special  care  must  be  taken  that  the  reagents  be  free  from 
sulphuric  acid.  The  sulphur  compounds  present  in  coal  gas  may 
even  give  rise  to  error,  hence  in  exact  experiments  the  fusion  muF^r 
be  effected  over  an  alcohol  lamp. 

6.  Fluids  are  treated  with  fuming  nitric  acid  free  from  sulphuria 


6 


ORGANIC    ANALYSIS. 


[§  172. 


&cid,  or  with  a  mixture  of  nitric  acid  and  potassium  chlorate,  at 
first  in  the  cold,  finally  with  application  of  heat;  the  solution  is 
tested  as  in  a. 

c.  On  heating  a  small  quantity  of  a  dry  organic  compound 
{containing  sulphur)  with  a  small  fragment  of  sodium  in  a  glass 
tube  sealed  at  one  end,  the  sulphur  is  converted  into  sodium  sul- 
phide, which  dissolves  on  treating  the  fragments  cf  the  lower  part 
of  the  tube  with  water,  and  may  be  detected  by  one  of  the  methods 
detailed  under  d  (SCHONN  *). 

d.  As  the  methods  a,  6,  and  c  serve  simply  to  indicate  the  pres- 
ence of  sulphur  in  a  general  way,  but  afford  no  information  regard- 
ing the  state  or  form  in  which  that  element  may  be  present,  I  add 
here  another  method,  which  serves  to  detect  only  the  sulphur  in 
the  non-oxidized  state  in  organic  compounds. 

Boil  the  substance  with  strong  solution  of  potassa  and  evapo- 
rate nearly  to  dryness.  Dissolve  the  residue  in  a  little  water,  and 
bring  the  solution  into  a  flask,  Fig.  1,  provided 
with  a  loosely-fitting  stopper,  through  which 
passes  a  funnel  tube  reaching  nearly  to  the 
bottom  of  the  flask.  Suspend  from  the  lower 
surface  of  the  stopper  within  the  flask  a  strip 
of  paper  dipped  first  in  lead-acetate,  then  in 
ammonium-carbonate  solution.  Add  slowly 
dilute  sulphuric  acid  through  the  funnel  tube, 
c,  and  observe  whether  the  lead  paper,  b,  be- 
comes brown ;  or  test  the  first  alkaline  solution 
with  a  solution  of  lead  oxide  in  soda  lye,  or 
by  means  of  a  polished  surface  of  silver,  or 
by  nitroprusside  of  sodium,  or  by  just  acidi- 
fying the  dilute  solution  with  hydrochloric  acid  and  adding  a  few 
drops  of  a  mixture  of  ferric  chloride  and  potassium  ferricyanide 
(see  "Qual.  Anal.,"  §  187,  WELLS'  translation,  published  by  JOHN 
WILFT  &  SONS,  New  York). 


FIG.  1. 


*  Zeitschr.  f.  analyt.  Chem.,  viu,  52. 


§  172.]   QUALITATIVE    EXAMINATION    OF   ORGANIC   BODIES.         7 

3.  Testing  for  Phosphorus. 

The  methods  described  in  2,  a  and  b,  may  likewise  serve  for 
phosphorus.  The  solutions  obtained  are  tested  for  phosphoric  acid 
with  magnesium  sulphate,  ammonium  chloride,  and  ammonia; 
or  with  ferric  chloride,  with  addition  of  sodium  acetate;  or  best 
with  solution  of  ammonium  molybdate  in  nitric  acid  (comp.  "Qual. 
Anal.")-  In  method  6,  the  greater  part  of  the  excess  of  nitric  acid 
must  first  be  removed  by  evaporation. 

b.  In  some  cases  the  following  method  by  SCHONN  *  may  be 
advantageously  employed:  Carbonize  the  organic  matter  in  a 
covered  crucible,  powder  the  charred  mass  and  mix  it  with  half  its 
volume  of  magnesium  powder,  introduce  the  mixture  into  the 
lower  part  of  a  thin-walled  glass  tube  sealed  at  the  lower  end,  and 
heat  quite  strongly  while  shaking  the  tube,  so  as  to  avoid  having 
the  mixture  driven  out.  If  the  substance  contained  phosphorus, 
the  upper  part  of  the  tube  will  appear  luminous  in  the  dark,  and 
at  times  some  yellow  or  amorphous  phosphorus  will  be  observed 
oii  the  sides.  The  remainder  of  the  phosphorus  will  be  in  the 
residue  as  magnesium  phosphide.  On  breaking  off  the  lower  end 
of  the  tube,  moistening  the  contents  with  a  little  water,  and 
heating,  hydrogen  phosphide  develops,  and  is  recognized  by  its 
characteristic  odor. 

4.  Testing  for  Iodine,  Bromine,  and  Chlorine. 

As  regards  the  testing  of  organic  substances  for  iodine,  bromine, 
or  chlorine,  I  refer  to  §  190.  I  give  here  only  two  methods  which 
suffice  for  most  cases. 

a.  Sprinkle  the  organic  substance,  if  dry,  on  the  bottom  of  a 
test-tube  heated  to  redness.  Iodine  may  be  frequently  recognized 
by  the  color  of  the  vapor.  On  introducing  the  inverted  tube  into 
a  larger  one  containing  a  little  water  and  ammonia,  hydriodic, 
hydrobromic,  or  hydrochloric  acid  may  be  detected  in  the  liquid 
after  a  time,  by  the  usual  methods  (see  "Qual.  Anal.").  In  the 
case  of  a  liquid  organic  substance,  fill  into  a  small  bulb-tube  such 
as  is  used  in  organic  analysis  (§  180),  insert  the  open  and  down- 

*  Zeitschr.  f.  analyt.  Chem.,  VTII,  55. 


8  ORGANIC   ANALYSIS.  [§   172. 

wardly  directed  tube  in  a  test-tube,  ignite  the  bottom  of  the  latter, 
and  then  cause  some  of  the  liquid  to  flow  out  by  warming  the 
bulb  (ERLENMEYER  *). 

6.  BEILSTEIN  f  ignites  some  powdered  cupric  oxide  in  the  loop 
of  a  platinum  wire,  moistens  with  water,  and  ignites  again.  If 
the  flame  remains  uncolored,  the  cupric  oxide  is  eligible  for  use. 
Some  of  the  substance  to  be  tested  is  now  taken  up  with  the  cupric 
oxide  and  held  in  the  flame  of  a  bunsen-burner  near  the  lower  and 
inner  margin.  The  carbon  burns  first,  but  immediately  after- 
wards the  characteristic  blue  or  green  color  is  seen  if  chlorine, 
bromine,  or  iodine  is  present  (see  "Qual.  Anal."). 

5.  Testing  for  Inorganic  Substances. 

A  portion  of  the  substance  is  heated  on  platinum  foil,  to  see 
whether  or  not  a  residue  remains.  When  acting  upon  difficultly 
combustible  substances,  the  process  may  be  accelerated  by  heating 
the  spot  which  the  substance  occupies  on  the  platinum  foil  to  the 
most  intense  redness,  by  directing  the  flame  of  the  blow-pipe  upon 
it  from  below.  Occasionally  complete  combustion  is  best  effected 
by  adding  mercuric  oxide  to  the  residue  left  on  ignition,  and  re- 
igniting.  The  residue  is  then  examined  by  the  usual  methods. 
That  volatile  metals  in  volatile  organic  compounds — e.g.,  arsenic 
in  cacodyl — cannot  be  detected  by  this  method  need  hardly  be 
mentioned. 

These  preliminary  experiments  should  never  be  omitted,  since 
neglect  in  this  respect  may  give  rise  to  very  great  errors.  Thus, 
for  instance,  taurin,  a  substance  in  which  a  large  proportion  of 
sulphur  was  afterwards  found  to  exist,  had  originally  the  formula 
C4N2H14010  assigned  to  it.  The  preliminary  examination  of  organic 
substances  for  chlorine,  bromine,  and  iodine  is  generally  unneces- 
sary, as  these  elements  do  not  occur  in  native  organic  compounds, 
and  as  their  presence  in  compounds  artificially  produced  by  the 
action  of  the  halogens  requires  generally  no  further  proof.  Should 
it,  however,  be  desirable  to  ascertain  positively  whether  a  substance 


*  Zeitschr.  f.  analyt.  Chem.,  iv,  137.  Mbid.,  xn,  95. 


§   173.]  ELEMENTS    IN    ORGANIC    BODIES.  9 

does  or  does  not  contain  chlorine,  iodine,  or  bromine,  this  may  be 
done  by  the  methods  given  in  §  190. 


II.  DETERMINATION  OP  THE  ELEMENTS  IN  ORGANIC  BODIES.* 

§173. 

It  is  not  my  intention  to  detail  the  history  of  the  development 
of  organic  analysis;  I  shall  confine  myself  to  a  description  of  those 
methods  which  are  considered  to  be  the  best,  and  shall  not  touch 
upon  the  others.  The  more  simple  methods,  which  usually  are 
followed  by  the  student  in  the  study  of  organic  analysis,  I  shall 
describe  fully;  the  more  complicated  ones  will  be  treated  of  more 
briefly,  since  the  chemist  who  uses  them  is  presupposed  to  possess 
a  more  advanced  knowledge  of  the  general  manipulations  of  organic 
analysis.  In  the  selection  of  the  methods,  consideration  has  also 
been  paid  to  the  varied  requirements  of  the  purely  experimental 
as  well  as  practical  operator,  since  it  is  evident  that  methods  based 
upon  the  use  of  complicated  apparatus  may  be  most  suitable  for 
laboratories  wherein  organic  analyses  are  daily  made,  without  being 
adapted  for  those  chemists  who  make  such  an  analysis  only  occa- 
sionally. For  the  latter  those  methods  requiring  simple  apparatus 
are  naturally  the  most  suitable. 

Since  the  accuracy  of  the  results  depends  just  as  much  upon 
the  proper  construction  and  arrangement  of  the  apparatus  as  upon 
the  execution  of  the  method  itself,  I  would  lay  special  stress  upon 
the  fact  that  equal  care  must  be  bestowed  upon  both;  and  that 
the  rules  here  given  may  not  be  deviated  from  without  impunity, 
as  they  are  the  results  of  long  experience  and  numberless  experi- 
ments on  the  part  of  the  most  distinguished  chemists. 

In  order  to  afford  a  clear  survey  over  the  extensive  subject, 
the  matter  to  be  treated  of  is  presented  here  in  tabular  form,  show- 
ing the  order  in  which  the  different  methods  are  treated. 


*  For  Prof.  WARREN'S  admirable  methods  we  must  refer  to  his  original 
papers  in  Am.  Journ.  Sci.,  2d  ser.,  xxxvin,  387,  XLI,  40,  and  XLII,  156. 


10  ORGANIC    ANALYSIS.  [§   173. 

A.  SUBSTANCES  CONSISTING  OF  CARBON  AND  HYDROGEN,   OR 

OF  CARBON,  HYDROGEN,  AND  OXYGEN. 

a.  Solid  bodies. 

a.  Readily   combustible,   non-volatile  bodies.      Com- 
bustion with  cupric  oxide. 

1.  LIEBIG'S  Method,  §  174. 

2.  BUNSEN'S  Modification,  §  175. 

ft.  Difficultly  combustible,  non- volatile  bodies. 

1.  Combustion  with  lead  chromate  (and  potas- 

sium bichromate),   §  176. 

2.  Combustion  with  cupric  oxide  and  potassium 

chlorate  or  perchlorate,  §  177. 

3.  Combustion  with  cupric  oxide  and  oxygen  gas, 

§178. 
7*.  Volatile  bodies,  or  such  as  undergo  alteration  at 

100°,  §179. 
5.  Liquid  bodies. 
a.  Volatile,  §  180. 
P.  Non-volatile,  §  181. 

Supplement  to  A  (§§174-182),   §182.     Modified 
apparatus. 

B.  COMPOUNDS  CONSISTING  OF  CARBON,  HYDROGEN,  OXYGEN, 

AND  NITROGEN. 

a.  Estimation  of  Carbon  and  Hydrogen,  §  183. 

b.  Estimation  of  Nitrogen. 
a.  From  the  volume. 

1.  Relative  Method,  §  184. 
aa.  According  to  LIEBIG. 
bb.  According  to  BUNSEN. 

cc.  According  to  MARCHAND  and  GOTTLIEB. 

2.  Absolute  nitrogen  estimation,  §  185. 
aa.  According  to  DUMAS. 

bb.  According  to  SIMPSON. 

^.  Estimation  of  nitrogen  by  conversion  into  ammonia, 
according  to  VARRENTRAPP  and  WILL,  §  186. 


§  173.]  ELEMENTS    IN    ORGANIC    BODIES.  11 

;-.  PELIGOT'S    modification    of    VARRENTRAPP-WILL'S 
method,  §  186. 

C.  ANALYSIS  OF  ORGANIC  COMPOUNDS  CONTAINING  SULPHUR, 

§188. 

D.  ESTIMATION  OF  PHOSPHORUS  IN  ORGANIC  COMPOUNDS,  §  189. 

E.  ANALYSIS*  OF  ORGANIC  COMPOUNDS  CONTAINING  CHLORINE, 

BROMINE,  OR  IODINE,  §  190. 

F.  ANALYSIS  OF  ORGANIC  COMPOUNDS  CONTAINING  INORGANIC 

SUBSTANCES,  §  191. 
Supplement  to  §§  174-191. 

Direct  estimation  of  oxygen  in  organic  substances, 
and  methods  of  organic  analysis  differing  from 
those  ordinarily  used,  §  192. 

A,  ANALYSIS  OF  COMPOUNDS  WHICH  CONSIST  SIMPLY  OF  CARBON 
AND  HYDROGEN,  OR  OF  CARBON,  HYDROGEN,  AND  OXYGEN. 

The  principle  of  the  method  which  serves  to  effect  the  quanti- 
tative analysis  of  such  compounds,  and  which  was  first  proposed 
in  its  present  form  by  LIEBIG,  is  exceedingly  simple.  The  sub- 
stance is  burned  to  carbonic  acid  and  water;  these  products  are 
separated  from  each  other  and  weighed,  and  the  carbon  of  the 
substance  is  calculated  from  the  weight  of  the  carbon  dioxide,  the 
hydrogen  from  that  of  the  water.  If  the  sum  of  the  carbon  and 
hydrogen  is  equal  to  the  original  weight  of  the  substance,  the 
substance  contains  no  oxygen ;  if  it  is  less  than  the  weight  of  the 
substance,  the  difference  expresses  the  amount  of  oxygen  present.* 

The  combustion  is  effected  either  by  igniting  the  organic  sub- 
stance with  oxygenized  bodies  which  readily  part  with  their  oxy- 
gen (cupric  oxide,  lead  chromate,  etc.)  or  at  the  expense  both  of 
free  and  combined  oxygen. 

*  The  methods  proposed  for  directly  estimating  oxygen  in  organic  sub- 
stances have  so  far  had  no  important  influence  on  organic  analysis.  They 
will  be  described  in  §  192. 


112  ORGANIC    ANALYSIS.  [§    174. 

a.  SOLID  BODIES. 

a.  Readily  combustible,  non-volatile  bodies  (e.g.,  sugar,  starch, 
tartaric  acid,  etc.).* 


COMBUSTION  WITH  CUPRIC  OXIDE. 
1.  LIEBIG'S  METHOD. 

§174. 

I.  APPARATUS  AND  PREPARATIONS  REQUIRED  FOR  THE  ANALYSIS. 

1.  THE  SUBSTANCE. — This  must  be  most  finely  pulverized  and 
perfectly  pure  and  dry ; — for  the  method  of  drying,  I  refer  to  §  26. 
Substances  which  on  drying  in  the  air  are  liable  to  change,  must 
be  heated  in  a  current  of  dry  carbon  dioxide  or  of  hydrogen  (RocH- 

LEDER  f). 

2.  A  TUBE  IN  WHICH   TO  WEIGH  THE  SUBSTANCE. — 
A  small,  perfectly  dry  glass  tube,  4  to  5  cm.  long  and  about 
1  cm.  bore,  Fig.  2.     It  should   be  provided  either  with  a 
light  ground-glass  stopper  or  with  a  cork  wrapped  in  tin 
foil.     The  weight  of  the  tube  with  its  stopper   must   be 
accurately  known  to  0.01  grm.     It  is  advisable  -to  keep 
the  tube,  together  with  the  substance,  in  the  drying  closet 
until  the  analysis  is  undertaken.     It  is  either 
laid  on  the  balance  or  placed  in  a  small  foot 
made  of  tin,  Fig.  3. 

3.  THE   COMBUSTION    TUBE.— A  tube  of 

difficultly  fusible  glass  (potassa  glass),  about  2  mm.  thick  in  the 
glass,  about  90  cm.  in  length,  and  from  12  to  14  mm.  inner  diameter 

*  It  need  scarcely  be  mentioned  that  readily  combustible  substances  may 
be  treated  also  by  the  methods  given  for  difficultly  combustible  substances; 
and  in  fact  these  latter  methods,  because  of  the  greater  certainty  afforded  as 
regards  completeness  of  combustion  of  the  carbon,  are  generally  preferred 
nowadays  to  the  older  methods,  which  are  distinguished  by  their  simplicity. 

f  Zeitschr.  /.  Analyt.  Chem.,  vi,  235. 


§  174.] 


COMBUSTION    WITH    CUPRIC    OXIDE. 


13 


is  first  cleaned  with  paper  or  linen  tied  to  the  end  of  a  wire  or  string, 
then  softened  in  the  middle  before  a  glass-blower's  lamp,  while 
being  constantly  rotated,  drawn  out  as  represented  in  Fig.  4, 


FIG.  4. 

and  finally  apart  at  6.  The  fine  points  of  the  two  pieces  are  then 
sealed  and  thickened  a  little  in  the  flame,  and  the  sharp  edges  of 
the  open  ends,  a  and  c,  are  slightly  rounded  by  fusion,  care  being 
taken  to  leave  the  aperture  perfectly  round.  The  posterior  part 
of  the  tube  should  be  shaped  as  shown  in  Fig.  5,  and  not  as  in 
Fig.  6. 


FIG.  5.  FIG.  6. 

Two  perfect  combustion  tubes  are  thus  produced.  The  one 
intended  for  immediate  use  is  cleaned  with  linen  or  paper  attached 
to  a  piece  of  wire,  and  then  thoroughly  dried.  This  is  effected 
either  by  laying  the  tube,  with  a  piece  of  paper  twisted  over  its 
mouth,  for  some  time  on  a  sand-bath,  with  occasional  removal  of 
the  air  from  it  by  suction,  with  the  aid  of  a  glass  tube,  or  (rapidly) 
by  moving  the  tube  to  and  fro  over  the  flame  of  a  gas  or  spirit 
lamp,  heating  its  entire  length,  and  continually  removing  the  hot 
air  by  suction  through  the  small  glass  tube  (Fig.  7).  The  suction 


FIG.  7. 

may  be  most  conveniently  effected  by  the  water-pump,  but  failing 
this,  with  the  mouth. 


14  ORGANIC    ANALYSIS.  [§   174. 

The  combustion  tube,  when  quite  dry,  is  closed  air-tight  with 
a  cork  and  kept  in  a  warm  place  until  required  for  use. 

In  default  of  glass  tubes  possessed  of  the  proper  degree  of 
infusibility,  thin  brass  or  copper  foil,  or  brass  gauze,  is  rolled 
round  the  tube,  and  iron  wire  coiled  round  it. 

4.  THE  POTASH  BULBS  (Fig.  8). — This  apparatus,  devised  by 
LIEBIG,  is  filled,  to  the  extent  indicated  in  the  engraving,  with  a 
clear  solution  of  caustic  potassa  of  1-27  sp.  gr.  (§66,  6*).  The 
introduction  of  the  potassa  solution  into  the  apparatus  is  effected 
by  plunging  the  end  a  into  a  beaker  or  dish  into  which  a  little  of 

fc 


FIG.  8.  FIG.  9. 

the  solution  has  been  poured  out,  and  applying  suction  to  6,  best 
and  safest  by  means  of  a  caoutchouc  tube,  as  in  Fig.  9.  The  two 
ends  are  then  wiped  perfectly  dry  with  twisted  slips  of  paper,  and 
the  outside  of  the  apparatus  with  a  clean  cloth. f 

5.  THE  CALCIUM-CHLORIDE  TUBE. — Fig.  10  shows  the  simplest 
and  original  form.  It  is  filled  in  the  following  manner:  In  the  first 
place,  the  aperture  a  of  the  tube  b  a  is  loosely  stopped  with  a  small 
cotton  plug  extending  about  1  cm.  into  the  tube;  this  is  effected 
by  introducing  a  loose  cotton  plug  into  c  and  applying  a  sudden 

*  If  the  potassa  solution  is  pure,  i.e.,  if  it  is  free  or  nearly  free  from  alu- 
mina and  silica,  a  much  more  concentrated  solution  may  be  employed  without 
danger  of  its  frothing.  J.  LOWE  (Zeitschr.  f.  analyt.  Chem.,  ix,  220)  rec- 
ommends a  solution  prepared  by  dissolving  1  part  of  good  potassium 
hydroxide  (containing  80  per  cent.  KOH)  in  1  part  of  water.  Potash 
bulbs  filled  with  this  solution  may  be  used  for  a  number  of  combustions 
without  requiring  refilling. 

+  For  other  potash  bulbs  which  may  replace  the  LIEBIG  bulbs,  see  §  182, 


§  174.] 


COMBUSTION    WITH    CUPRIC    OXIDE. 


15 


and  energetic  suction  at  b.     The  bulb  is  then  filled  with  lumps  of 
calcium  chloride  (§66,  7,  a),  and  the  tube  c  d  up  to  e  with  smaller 


FIG.  10. 


FIG.  11. 


FIG.  12. 

fragments,  intermixed  with  coarse  powder  of  the  same  substance; 
a  loose  cotton  plug  is  then  inserted  and  the  tube  finally  closed  with 
a  perforated  cork  into  which  a  small  glass  tube  is  fitted;  the  pro- 
truding part  of  the  cork  is  cut  off  and  the  cut  surface  covered  over 
with  sealing-wax;  the  edge  of  the  little  tube  fg,  Fig.  11,  is  slightly 
rounded  by  fusion  at  g. 

The  tube  illustrated  in  Fig.  12  is  still  more  convenient  to  use, 
as  a  considerable  quantity  of  water  condenses  hi  the  empty  bulb  a, 
and  at  the  close  of  the  experiment  may  be  poured  out.  The  oper- 
ator is  thus  enabled  to  test  it  as  to  reaction,  etc.,  and  also  to  use 
the  same  tube  far  oftener  without  fresh  filling  than  when  using 
a  tube  not  provided  with  an  empty  bulb. 

Another  form  of  tube,  more  convenient  for  weighing,  is  that 
of  MARCHAND,  Fig.  13.  In  this  also  the  bulb  a  next  to  the  com- 
bustion tube  remains  empty.  VOLHARD  *  recommends  the  form 
shown  in  Fig.  14  as  avoiding  the  use  of  perforated  stoppers. 
Finally  the  two  last  forms  may  be  combined,  as  shown  in  Fig.  14 
(H.  FRESENIUS  f). 

In  order  to  be  quite  certain  that  the  calcium-chloride  tubes 
absorb  water  only,  and  not  small  quantities  of  carbonic  acid  besides 
(as  the  salt  usually  has  a  slightly  alkaline  reaction),  conduct 
through  the  filled  tubes  a  slow  stream  of  dry  carbonic-acid  gas 

*  Annal.  der  Chem.,  CLXXVT,  339.;  Zeitschr.  f.  analyt.  Chem.,  xiv,  333. 
t  Zeitschr.  f.  analyt.  Chem.,  xiv,  334. 


16  ORGANIC    ANALYSIS.  [§  174. 

and  follow  by  a  current  of  dry  air  until  the  carbonic-acid  gas  has 
been  completely  expelled  from  the  tubes. 

6.  A  SMALL  TUBE  OF  VULCANIZED  INDIA-RUBBER. — This  must 
be  so  narrow  that  it  can  only  be  pushed  with  difficulty  over  the 
tube  g  of  the  calcium-chloride  tube  on  the  one  hand,  and  over  the 
end  a  of  the  potash  bulbs  on  the  other  hand;  in  which  case  there  is 


r; 


FIG.  13.  FIG.  14.  FIG.  15. 

no  need  of  binding  with  silk  cord.  If  the  rubber  tube  should  be 
a  little  too  wide,  it  must  be  tied  round  with  silk  cord  or  with 
ignited  piano  wire.  It  is  self-evident  that  the  narrow  end  g  of  the 
calcium-chloride  tube  should  be  of  the  same  width  as  the  tube  a  of 
the  potash  bulbs.  The  india-rubber  tube  is  purified  from  any 
adherent  sulphur  and  dried  in  the  water-bath  previous  to  use. 

7.  CORKS. — These  should  be  soft  and  smooth,  and  as  free  as 
possible  from  visible  pores.  A  cork  should  be  selected  which,  after 
careful  squeezing,  fits  perfectly  tight  and  screws  with  some  diffi- 
culty to  one-third  of  its  length,  at  the  most,  into  the  mouth  of  the 
combustion  tube;  a  perfectly  smooth  and  round  hole,  into  which 
the  end  b  a  of  the  calcium-chloride  tube  must  fit  perfectly  air- 
tight, is  then  carefully  bored  through  the  axis  of  the  cork.  The 
cork  is  then  kept  for  an  hour  or  two  in  the  water-bath.  It  is 
advisable  always  to  have  two  corks  of  this  description  ready. 
Instead  of  ordinary  corks,  caoutchouc  stoppers  may  be  used  with 
great  advantage,  according  to  SONNENSCHEIN,*  who  recommends 
them  as  being  durable,  tight-fitting,  and  non-hygroscopic,  f  They 
are  now  frequently  used  instead  of  corks. 

*  Journ.  f.  prakt.  Chem.,  LXVII,  153. 

f  Cornp.  DIBBITS,  Zeitschr,  /.  analyt.  Chem.,  xv,  157. 


§   174.]  COMBUSTION    WITH    CUPRIC    OXIDE.  17 

8.  A  MIXING  MORTAR. — A  porcelain  mortar  of  greater  width 
than  depth  and  provided  with  a  lip.      It  should  not  be  glazed 
inside,  and  it  should  be  free  from  indentations  and  cracks.     Before 
use  it  should  be  cleaned  by  washing  with  water;  it  is  then  set 
aside  in  a  warm  place  to  dry  until  required. 

9.  A  SUCTION  TUBE.— The  best 
form  for  this  is  shown  in  Fig.  16. 
The  aperture  a  is  closed  by  a  cork 
into  the  perforation  of  which  the 
tube  b  of  the  potash  bulb  is  fitted. 

A  caoutchouc  tube,  however,  may 

FIG.  16. 
also  be  made  to  serve  well.* 

10.  A  GLASS  TUBE,  open  at  both  ends  and  about  60  cm.  long, 
and  wide  enough  to  be  pushed  over  the  tail  of  the  combustion  tube ; 
it  is  supported  in  place  by  a  filter-stand,  f 

11.  A  SHEET  OF  GLAZED  PAPER  with  cut  edges. 

12.  CUPRIC  OXIDE. — A   Hessian   crucible   of    about    100    c.c. 
capacity  is  nearly  filled  with  copper  oxide  prepared  as  directed 
in  §  66,  1 ;   the  crucible  is  covered  with  a  well-fitting  overlapping 
lid  and  heated  to  dull  redness  with  charcoal,  or  in  a  suitable  gas- 
furnace;  1  it  is  then  allowed  to  cool,  so  that  by  the  time  the  cupric 
oxide  is  required  for  use,   the  hand  can   only  just   bear  contact 
with  it. 


*  An  aspirator  is  nowadays  generally  used  instead  of  the  mouth,  which 
was  formerly  used  for  effecting  suction. 

t  This  tube  is  now  generally  replaced  by  a  system  of  tubes  containing 
soda-lime  and  calcium  chloride. 

t  If  the  copper  scales  employed  in  making  the  copper  oxide  contain  lime, 
digest  them  first,  for  some  time,  with  water  and  a  little  nitric  acid,  then  wash 
and  treat  them,  either  immediately  or  after  ignition  in  a  muffie,  with  chlo- 
rine-free nitric  acid.  Copper  oxide  containing  copper  chloride  is  best  purified, 
according  to  E.  ERLENMEYER,  by  igniting  first  in  a  current  of  moist  air  and 
then,  when  the  vapors  no  longer  redden  litmus  paper,  in  a  current  of  dry 
air,  by  which  treatment  all  the  nitrogen  oxides  present  are  also  removed. 
Copper  oxide  perfectly  free  from  injurious  impurities  may  also  be  obtained 
by  dissolving  galvanically  precipitated  copper  in  perfectly  pure  nitric  acid, 
evaporating,  and  igniting  the  cupric  nitrate  (C.  REISCHAUER,  Zeitschr.  f. 
analyt.  Chem.,  n,  197. — J.  LOWE,  ibid.,  ix,  217). 


18  ORGANIC    ANALYSIS.  [§    174. 

13.  AN  AIR-PUMP  WITH  CALCIUM-CHLORIDE  TUBE.  —  See  Fig.  24. 
For  the  manner  of  performing  an  organic  analysis  without  this 
apparatus,  see  §§  176,  178,  and  179. 

14.  HOT  SAND.  —  This  is  taken  either  from  the  sand-bath,  or  it 
must  be  specially  heated  for  the  purpose.     Its  temperature  should 
be  above  100°,  but  not  so  high  as  to  singe  paper. 

15.  A  WOODEN  TROUGH  for  the  sand.     See  Fig.  24. 

16.  A  COMBUSTION  FURNACE.  —  Some  time  ago  the  only  one 

used  was  LIEBIG'S,  in  which  char- 
coal is  the  fuel.  Recently  gas 
combustion  furnaces  have  been 
introduced  into  most  laboratories, 
because  they  are  more  cleanly  and 
convenient. 

a.  LIEBIG'S  combustion  furnace  is  of  sheet  iron.  It  has  the 
form  of  a  long  box,  open  at  the  top  and  behind.  It  serves  to  heat 
the  combustion  tube  with  red-hot  charcoal.  Fig.  17  represents 
the  furnace  as  seen  from  the  top. 

It  is  from  50  to  60  cm.  long,  and  from  7  to  8  deep;  the  bottom, 
which,  by  cutting  small  slits  in  the  sheet  iron,  is  converted  into 
a  grating,  has  a  width  of  about  7  cm.  The  side  walls  are  inclined 
slightly  outward,  so  that  at  the  top  they  stand  about  12  cm.  apart. 
A  series  of  upright  pieces  of  strong  sheet  iron,  having  the  form 
shown  in  D,  Fig.  18,  and  riveted  on  the  bottom  of  the  furnace  at 
intervals  of  about  5  cm.,  serves  to  support  the  combustion  tube. 
They  must  be  of  exactly  corresponding  height  with  the  round 
aperture  in  the  front  piece  of  the  furnace  (Fig.  18,  A). 


w 


FIG.  18.  FIG.  19. 

This  aperture  must  be  sufficiently  large  to  admit  the  com- 
bustion tube  easily.  Of  the  two  screens  used,  one  has  the  form 
shown  in  Fig.  19,  the  other  is  a  single  plate  precisely  like  the  end 
piece  of  the  furnace  (Fig.  18).  The  openings  cut  into  the  screens 
must  be  sufficiently  large  to  receive  the  combustion  tube  without 


§   174.]  COMBUSTION   WITH   CUPRIC    OXIDE.  19 

difficulty.  The  furnace  is  placed  upon  two  bricks  resting  upon 
a  flat  surface,  and  is  slightly  raised  at  the  farther  end  by  insert- 
ing a  piece  of  wood  between  the  supports  (see  Fig.  26).  The 
apertures  of  the  grating  at  the  anterior  end  of  the  furnace  must 
not  be  blocked  up  by  the  supporting  bricks.  In  cases  where  the 
combustion  tubes  are  of  good  quality,  the  furnace  may  be  raised 
by  introducing  a  little  iron  rod  between  the  furnace  and  the  sup- 
porting brick.  Placing  the  tube  in  a  gutter  of  Russia  sheet  iron 
tends  greatly  to  preserve  it,  but  contact  of  the  glass  and  iron  must 
be  prevented  by  an  intervening  layer  of  asbestos.  A  charcoal 
furnace  with  a  regulator  for  the  air  access  has  been  recommended 
by  GAWALOWSKI.* 

b.  Gas  combustion  furnaces  of  the  most  varied  descriptions 
have  been  proposed.!  Fig.  20  represents  one  form  that  is  fre- 
quently employed,  t 

The  apparatus  consists  of  two  parts,  the  system  of  burners 
and  the  stand.  The  former  consists  of  15  to  25  BUNSEN 
burners,  each  of  which  is  provided  with  a  separate  cock  and  a 
ring  for  regulating  the  air  access.  The  burners  are  screwed 
on  to  a  tube  48  to  78  cm.  long  and  25  mm.  wide,  connected 
with  the  gas-supply  tube.  The  orifices  of  the  burner  tubes  are 
flattened  to  form  slits.  The  iron  stand  shown  in  Fig.  20  is  that 


*Zeitschr.  f.  analyt.  Chem.,  xiv,  309. 

f  Compare  the  papers  by  v.  BAUMHAUER  (Annal.  d.  Chem.  u.  Pharm., 
xc,  21). — HOFMANN  (ibid.,  xc,  235). — SONNENSCHEIN  (Journ.  f.  prakt. 
Chem.,  LV,  478). — MAGNUS  (ibid.,  LX,  32). — WETHERILL  (LiEBio-Kopp's 
Jahresb.,  1855,  828). — PEBAL  (Annal.  d.  Chem.  u.  Pharm.,  xcv,  24)  — J. 
LEHMANN  (ibid.,  en,  180).— v.  BABO  (Ber.  uber  die  Verhandl.  der  Gesellsch. 
/.  Beforderung  der  Naturw.  zu  Freiburg  in  Br.,  1857,  Nos.  22  and  23). — 
HEINTZ  (Pogg.  Annal.,  cm,  142).— G.  J.  MULDER  (Scheik.  Verhandl.  en 
Onderzaek,  n  decl.  2,  stuk.  Ondez.  289). — A.  W.  HOFMANN  (Annal.  d.  Chem. 
u.  Pharm.,  cvii,  37). — BERTHELOT  (Compt.  Rend.,  XLVIII,  469). — ERLEN- 
MEYER  (Annal.  d.  Chem.  u.  Pharm.,  cxxxix,  17;  and  Zeitschr.  f.  analyt. 
Chem.,  vi.  110). — LEOPOLDER  (Zeitschr.  f.  analyt  Chem.,  vm,  198). — DONNY 
(ibid.,  cxvin,  200). — GLASER  (Annal.  d.  Chem.  u.  Pharm.,  Suppl.,  vii,  213; 
also  Zeitschr.  f.  analyt.  Chem.,  ix,  932). 

+  Comp.  also  the  Preisverzeichniss  der  BUNSEN'SCHEN  Apparate  vom 
Universitdtsmechanikus  DESAGA  in  Heidelberg,  1873,  p.  36. 


20 


ORGANIC    ANALYSIS. 


[§  174. 


devised  by  v.  BABO  and  improved  by  ERLENMEYER.*  The  flames 
enter  through  a  slit-shaped  opening,  surround  the  combustion  tube, 
and  escape  above  also  through  a  slit.  The  combustion  tube  is 
laid  upon  magnesia  or  asbestos  in  a  sheet-iron  trough,  or  in  a  fire- 


FIG.  20. 

clay  trough  in  which  LOWE  recommends  a  number  of  small  per- 
forations to  be  made.  LOWE  f  also  covers  the  tube  with  a  fire- 
clay channel,  so  that  the  glass  tube  is  completely  surrounded  by 
fire-clay. 

The  heat  is  confined  and  reverberated  by  the  fire-clay  tiles, 
which,  placed  on  each  side,  form  a  dome.  The  tiles  on  one  side 
are  immovably  fastened;  those  on  the  other 
side  are  movable.  The  tube  on  which  the 
burners  are  screwed,  and  also  the  channels  in 
which  the  fire-clay  tiles  are  supported,  may  be 
raised  or  lowered  to  enable  the  distance  between 
the  combustion  tube  and  the  burners  to  be 
regulated. 

HEINTZ'S  apparatus  has    also    been    highly 
lauded.      It    is    illustrated    in    HUGERSHOFF'S  FIG.  21. 

price-list  (Leipzig,  1874,  p.  55).  I  have  had  no  personal  experience 
with  it.  A.  W.  HOFMANN'S  J  furnace,  much  used  in  England, 

*  Annal.  d.  Chem.  u.  Pharm.,  cxxxix.  70;   Zeitschr  f.  analyt   Chem.,  vi, 


110. 


f  Zeitschr.  f.  analyt.  Chem.,  ix,  222. 

J  Annal.  cL  Chem.  u.  Pharm.,  evil,  39. 


§  174.] 


COMBUSTION    WITH    CUPRIC    OXIDE. 


21 


differs  materially  from  the  above.  It  yields  excellent  service, 
although  with  a  greater  gas  consumption.  Its  arrangement  is 
shown  in  Fig.  21  and  Fig.  22. 


FIG.  22. 

Into  the  brass  tube  a,  about  90  cm.  long  and  2  cm.  wide ,  Fig.  21, 
connected  with  the  gas-supply  tube,  there  are  screwed  30  to  34 
tubes,  b,  each  provided  with  an  air-regulator,  stop-cock,  and  carry- 
ing a  cross-tube,  c  c.  Each  of  these  crossrtubes  bears  5  ordinary 
fish-tail  burners,  each  consuming  4  cubic  feet  of  gas  per  hour,  and 
over  which  a  corresponding  number  of  clay  burners  may  be  placed. 
These  clay  burners,  d  d,  are  simply  well-burnt,  hollow  cylinders 
of  pipe-clay  or  similar  material,  8-5  cm.  high,  2  cm.  external,  and 
1  cm.  internal  diameter.  They  are  closed  at  the  top,  and  the  side 
walls  are  perforated  with  numerous  small  pin-holes.  A  cylinder 
of  the  above  dimensions  has  10  rows  of  15  perforations  each.  The 
middle  row  of  burners  are  only  4- 5  cm.  high  and  have  70  to  80  per- 
forations; it  serves  as  a  support  for  the  combustion  tube,  /,  which 
is  thus  bedded  in  a  clay  channel.  Stability  is  imparted  to  the 
entire  system  of  burners  by  a  stout  iron  frame,  g  g,  resting  on  two 
cast-iron  feet,  h  h,  screwed  into  an  iron  plate,  i.  The  iron  frame,  g  g, 
is  in  addition  provided  with  a  groove  in  which  the  clay  side  plates, 
k  k,  are  movable.  These  plates  are  of  the  same  height  as  the 
burners,  but  as  they  are  supported  on  the  frame,  they  overtop  the 
burners  by  about  1  •  5  cm.  The  side  plates,  I,  are  likewise  of  clay, 
and  are  movable.  The  whole  apparatus  is  figured  in  Fig.  22. 
In  the  fore  part  of  the  apparatus  to  which  the  potash  bulbs  are 


22  ORGANIC    ANALYSIS.  [§   174. 

affixed,  the  side  and  top  plates  are  left  off  in  order  to  give  a  view 
of  the  clay  burners  in  position. 

During  the  combustion  all  the  burners  are  to  be  inclosed,  as 
shown  at  the  other  end  of  the  apparatus.  The  most  suitable  dis- 
tance between  the  individual  burners  is  3  mm.  As  it  is  important, 
in  order  to  maintain  a  constant  temperature,  that  the  distance 
between  the  several  burner-arms  be  perfectly  equal,  their  distance 
from  each  other  is  more  especially  assured  by  corresponding  holes 
in  the  iron  frame,  g  g,  Fig.  21. 

In  conclusion  I  also  mention  here  the  gas  furnace  constructed 
on  DONNY'S  principle  by  C.  GLASER  in  conjunction  with  KEKULE. 
This  furnace,  like  HOFMANN'S,  saves  the  combustion  tubes,  but 
consumes  even  more  gas  than  ERLENMEYER'S.  Its  characteristic 
feature  is  that  the  combustion  tube  is  borne  by  a  number  of  iron 
supports  pierced  with  holes  covered  by  perforated  clay  covers. 
The  hot  combustion  gases  which  first  heat  the  iron  supports  of 
the  tube  are  compelled  to  pass  through  both  systems  of  perfora- 
tions, hence  the  tube  is  heated  on  all  sides,  even  from  above.  Since 
the  iron  supports  are  movable,  the  heat  may  be  lessened  somewhat 
by  separating  the  supports  slightly.  The  furnace  is  made  by 
C.  GERHARDT,  of  Bonn.  As  this  furnace  is  particularly  serviceable 
in  analyses  requiring  a  current  of  oxygen,  the  detailed  description 
will  be  given  in  §  178. 

II.  PERFORMANCE  OF  THE  ANALYTICAL  PROCESS. 

a.  Weigh  first  the  potash  apparatus,  then  the  calcium-chloride 
tube.  Introduce  about  0-35-0-6  grm.  of  the  substance  under 
examination  (more  or  less,  according  as  it  is  rich  or  poor  in  oxygen) 
into  the  weighing  tube,*  which  must  be  no  longer  warm,  and  weigh 
the  latter  accurately  with  its  contents  after  inserting  the  stopper. 
The  weight  of  the  empty  tube  with  its  stopper  being  approximately 
known,  it  is  easy  to  take  the  right  quantity  of  substance  required 
for  the  analysis.  Close  the  tube  then  with  a  smooth  cork. 

*  Care  must  be  taken  that  no  particles  of  the  substance  adhere  to  the 
sides  of  the  tube,  at  least  not  at  the  top. 


§  174.]  COMBUSTION    WITH    CUPRIC    OXIDE.  23 

b.  The  filling  of  the  combustion  tube  is  now  effected  as  follows : 
Spread  the  sheet  of  glazed  paper  on  a  clean  table  and  place 
on  it  the  still  rather  warm  mortar.  Rinse  both  the  mortar  and 
the  still  warm  combustion  tube  with  a  little  of  the  warm  cupric 
oxide,  which  is  then  emptied  out  (and  put  by),  and  the  tube  filled 
up  to  the  mark  b,  Fig.  23,  with  cupric  oxide  directly  from  the 


FIG.  23. 

crucible,  using  either  the  tube  itself  as  a  shovel  or  by  aid  of  a  small 
warm  copper  funnel  and  a  German-diver  spoon.  A  portion  of  the 
cupric  oxide  is  now  transferred  from  the  tube  to  the  mortar,  and 
the  substance  to  be  analyzed  added,  taking  care  to  thoroughly 
shake  out  the  last  particles  from  the  small  tube  in  which  it  was 
weighed  by  tapping  it,  then  re-stopper  the  tube  and  lay  it  aside 
carefully,  as  it  must  be  re- weighed.  Now  mix  the  substances  in  the 
mortar  intimately  by  diligent  trituration,  avoiding  too  strong 
pressure,  however;  then  add  almost  all  the  cupric  oxide  in  the 
tube,  leaving  a  layer  of  only  about  3  to  4  cm.,  and  mix  again  inti- 
mately. Now  remove  the  pestle  from  the  mortar  after  freeing  it 
from  particles  of  the  mixture  by  tapping  it,  and  transfer  the  mix- 
ture to  the  tube,  using  the  latter  as  a  scoop.  The  remainder  in 
the  mortar  is  poured  out  on  a  piece  of  smooth  cardboard  and 
likewise  transferred  to  the  tube.  Then  rinse  the  mortar  out  with 
a  new  small  portion  of  cupric  oxide  which  in  turn  is  brought  into 
the  tube  until  the  latter  is  filled  up  about  to  the  mark  a,  Fig.  23, 
and  finally  fill  with  pure  cupric  oxide  to  within  3  or  4  cm.  of  the 
mouth,  in  which  then  place  a  plug  of  copper  turnings  oxidized  by 
ignition  in  air,  and  lastly  stopper  temporarily  with  a  cork.  The 
filling  of  the  tube  is  effected  over  the  glazed  paper  so  that  should 
any  of  the  mixture  be  spilled  it  may  be  readily  recovered.* 

*  In  G.  J.  MULDER'S  laboratory  I  saw  the  filling:  accomplished  differently, 
yet  not  less  satisfactorily.  The  mixture,  prepared  in  a  small  copper  mortar, 
was  transferred  by  means  of  a  smooth,  warm,  copper  funnel  into  the  com- 
bustion tube,  which  was  held  upright  in  a  retort  holder,  the  operation  being 
performed  easily  and  rapidly.  The  anterior  part  of  the  tube  is  filled  with 


24 


ORGANIC    ANALYSIS. 


[§  174, 


c.  A  few  gentle  taps  on  the  table  will  generally  suffice  to  shake 
together  the  contents  of  the  tube,  so  as  to  completely  clear  the 
tail  from  oxide  of  copper  and  leave  a  free  passage  for  the  evolved 
gas  from  end  to  end,  as  shown  in  the  cut,  Fig.  24.  Should  this 


FIG.  24. 

fail,  as  will  occasionally  happen,  owing  to  malformation  of  the  tail, 
the  object  in  view  may  be  attained  by  striking  the  mouth  of  the 
tube  several  times  against  the  side  of  a  table.  Now  place  the 
tube  in  the  wooden  trough  D,  Fig.  24,  and  connect  it  by  means  of 
a  cork  with  the  calcium-chloride  tube  B,  which  is  in  turn  connected 
with  an  air-pump.  Next  completely  cover  the  tube  throughout 
its  length  with  hot  sand,  after  which  pump  out  the  air  slowly  (if 
the  pumping  is  quickly  and  incautiously  done  some  of  the  mixture 
will  be  drawn  over  into  the  calcium-chloride  tube) ;  now  open  the 
cock  a  and  allow  a  fresh  supply  of  air  (dried  by  its  passage  through 
the  calcium-chloride  tube)  to  enter,  and  again  pump  put  as  before, 

a  layer  of  at  least  2  dm.  of  granular  cupric  oxide  well  packed,  and  the  cany- 
ing  away  of  any  particles  by  gas  was  prevented  by  a  plug  of  copper  turnings. 
Comp.  Zeitschr.  /.  analyt.  Chem.,  i,  7. 


§   174.]  COMBUSTION    WITH    CUPRIC    OXIDE.  25 

repeating  the  process  some  10  or  12  times,  thus  insuring  perfect 
removal  of  any  moisture  which  the  cupric  oxide  may  have  taken 
up  during  the  operation  of  mixing.  If  a  water  air-pump  is  used 
insert  between  it  and  the  calcium-chloride  tube  B  a  fork-shaped 
tube,  Fig.  25,  connecting  a  with  the  calcium-chloride  tube  and 
the  end  b  with  the  pump,  while  c  is  closed  by 
means  of  a  short  rubber  tube  provided  with  a  a 

pinch-cock.      After   each  exhaustion  admit  air 

FIG.  25. 

through  c. 

d.  Connect  the  end  b  (Fig.  26)  of  the  weighed  calcium-chloride 
tube  with  the  combustion  tube  by  means  of  a  dried  perforated 
cork,  lay  the  furnace  upon  its  supports,  with  a  slight  inclination 
forward,  and  place  the  combustion  tube  hi  it;  connect  the  end 
of  the  calcium-chloride  tube,  by  means  of  a  vulcanized  india- 


PIG.  26. 

rubber  tube,  with  the  end  ra  of  the  potash  apparatus,  and,  if  neces- 
sary, secure  the  connection  with  silk  cord,  taking  care  to  press 
the  joint  of  the  two  thumbs  close  together  whilst  tightening  the 
cords,  since  otherwise ,  should  one  of  the  cords  happen  to  give  way, 
the  whole  apparatus  might  be  broken.  Rest  the  potash  appara- 
tus upon  a  folded  piece  of  cloth.  Fig.  26  shows  the  whole  arrange- 
ment. 

e.  To  ascertain  whether  the  joinings  of  the  apparatus  fit  air- 
tight, put  a  piece  of  wood  about  the  thickness  of  a  finger  (s),  or  a 
cork,  or  other  body  of  the  kind,  under  the  bulb  r  of  the  potash 
apparatus,  so  as  to  raise  that  bulb  slightly  (see  Fig.  26).  Heat  the 
bulb  ra,  by  holding  a  piece  of  red-hot  charcoal  near  it,  until  a 
certain  amount  of  air  is  driven  out  of  the  apparatus;  then  remove 


26  OKGANIC   ANALYSIS.  [§   174. 

the  piece  of  wood  (s),  and  allow  the  bulb  m  to  cool.  The  solution 
of  potassa  will  now  rise  into  the  bulb  m,. filling  it  more  or  less;  if 
the  liquid  in  m  preserves,  for  the  space  of  a  few  minutes,  the  same 
level  which  it  has  assumed  after  the  perfect  cooling  of  the  bulb, 
the  joinings  may  be  considered  perfect;  should  the  fluid,  on  the 
other  hand,  gradually  regain  its  original  level  in  both  limbs  of 
the  apparatus,  this  is  a  positive  proof  that  the  joinings  are  not  air- 
tight. (The  few  minutes  which  elapse  between  the  two  observa- 
tions may  be  advantageously  employed  in  reweighing  the  little 
tube  in  which  the  substance  intended  for  analysis  was  originally 
weighed.) 

/.  Let  the  mouth  of  the  combustion  tube  project  3  to  4  cm. 
beyond  the  furnaee;  suspend  the  single  screen  over  the  anterior 
end  of  the  furnace,  as  a  protection  to  the  cork;  put  the  double 
screen  over  the  combustion  tube  about  two  inches  farther  on  (see 
Fig.  26),  replace  the  little  piece  of  wood  (s)  under  r,  and  put  small 
pieces  of  red-hot  charcoal  first  under  that  portion  of  the  tube 
which  is  separated  by  the  screen;  surround  this  portion  gradually 
altogether  with  ignited  charcoal,  and  let  it  get  red-hot;  *  then  shift 
the  screen  an  inch  farther  back,  surround  the  newly  exposed  por- 
tion of  the  tube  also  with  ignited  charcoal,  and  let  it  get  red-hot; 
and  proceed  in  this  manner  slowly  and  gradually  extending  the 
application  of  heat  to  the  tail  of  the  tube,  taking  care  to  wait 
always  until  the  last  exposed  portion  is  red-hot  before  shifting  the 
screen,  and  also  to  maintain  the  whole  of  the  exposed  portion  of 
the  tube  before  the  screen  in  a  state  of  ignition,  and  the  projecting 
part  of  it  so  hot  that  the  fingers  can  hardly  bear  the  shortest  con- 
tact with  it.  The  whole  process  requires  generally  from  f  to  1  hour. 
It  is  quite  superfluous,  and  even  injudicious,  to  fan  the  charcoal 
constantly ;  this  should  be  done  however  when  the  process  is  draw- 
ing to  an  end,  as  we  shall  immediately  have  occasion  to  notice. 

The  liquid  in  the  potash  bulbs  is  gradually  displaced  from  the 
bulb  m  upon  the  application  of  heat  to  the  anterior  portion  of  the 
combustion  tube,  owing  simply  to  the  expansion  of  the  heated  air. 

*  In  using  a  gas  furnace  the  individual  burners  are  of  course  lit  one  after 
another. 


§   174.]  COMBUSTION    WITH    CUPRIC    OXIDE.  27 

As  soon  as  the  heat  reaches  the  cupric  oxide,  which  was  used  to 
rinse  out  the  mortar,  a  little  carbonic  acid  and  aqueous  vapor  are 
evolved  which  drive  out  the  air  in  the  apparatus  and  force  it  through 
the  potash  bulbs  in  the  form  of  large  bubbles.  The  evolution  of 
gas  proceeds  with  greater  briskness,  however,  when  the  heat  begins 
to  reach  the  actual  mixture;  the  first  bubbles  are  only  partly 
absorbed,  as  the  carbonic  acid  contains  still  an  admixture  of  air; 
but  those  which  follow  are  so  completely  absorbed  by  the  potassa 
that  only  a  solitary  air-bubble  escapes 
from  time  to  time  through  the  liquid. 
The  process  should  be  conducted  in  a 
manner  to  make  the  gas-bubbles  follow 
each  other  at  intervals  of  from  J  to  1 
second.  Fig.  27  shows  the  proper  posi-a 
tion  of  the  potash  bulbs  during  the  opera- 
tion. 

It  will  be  seen  from  this  that  an  air- 
bubble   entering   through   m  passes   first 

into  the  bulb  6,  thence  to  c,  from  c  to  d,  and  passing  over  the 
solution  in  the  latter  escapes  finally  into  the  bulb  /,  through  the 
fluid  which  just  covers  the  mouth  of  the  tube  e. 

g.  When  the  tube  is  in  its  whole  length  surrounded  with  red- 
hot  charcoal,  and  the  evolution  of  gas  has  relaxed,  fan  the  burning 
charcoal  gently  with  a  piece  of  cardboard.  When  the  evolution  of 
gas  has  entirely  ceased,  adjust  the  position  of  the  potash  bulbs  to  a 
level,  remove  the  charcoal  from  the  farther  end  of  the  tube,  and 
place  the  screen  before  the  tail.  The  ensuing  cooling  of  the  tube 
on  the  one  hand,  and  the  absorption  of  the  carbonic  acid  in  the 
potash  bulbs  on  the  other,  cause  the  solution  of  potassa  in  the 
latter  to  recede,  slowly  at  first,  but  with  increased  rapidity  from 
the  moment  the  liquid  reaches  the  bulb  m.  (If  you  have  taken 
care  to  adjust  the  position  of  the  potash  bulbs  correctly  you  need 
not  fear  that  the  contents  of  the  latter  will  recede  to  the  calcium- 
chloride  tube.)  When  the  bulb  m  is  about  half  filled  with  solution 
of  potassa,  break  off  the  point  of  the  combustion  tube  with  a  pair 
of  pliers  or  scissors,  whereupon  the  fluid  in  the  potash  bulbs  will 


28 


ORGANIC    ANALYSIS. 


[§  174. 


immediately  resume  its  level.  Restore  the  potash  bulbs  once  more 
to  their  original  oblique  position,  and  place  the  glass  tube  mentioned 
in  §  174,  10,  over  the  tail,  supporting  it  against  the  arm  of  a  filter- 
stand  ;  wait  a  few  minutes  so  that  the  carbonic  acid  in  the  calcium- 
chloride  tube  and  combustion  tube  may  be  absorbed  by  the  potassa, 
and  then  slowly  draw  air  through  the  potash  bulbs,  by  means  of 
a  suction  tube  or  rubber  tube,  until  the  bubbles  last  coming  through 
no  longer  diminish  in  size.  The  arrangement  of  the  apparatus  at 
this  point  is  shown  in  Fig.  28.  It  is  better  to  employ  a  small  aspi- 


FIG.  28. 

rator  (Fig.  28)  instead  of  sucking  with  the  mouth.  You  then  know 
the  volume  of  air  that  has  passed  through  the  apparatus.  LIEBIG 
directed  to  draw  not  more  air  through  than  a  volume  equal  to  the 
capacity  of  the  calcium-chloride  tube,  say  about  80  to  100  c.c. 
Nor  may  more  be  safely  drawn  through  if  the  simple  LIEBIG'S 
arrangement  be  used,  as  otherwise  notable  errors  would  be  intro- 
duced. 

This  terminates  the  analytical  process.  Disconnect  the  potash 
bulbs  and  remove  the  calcium-chloride  tube,  together  with  the 
cork,  which  must  not  be  charred,  from  the  combustion  tube;  re- 
move the  cork  also  from  the  calcium-chloride  tube,  and  place  the 
latter  upright,  with  the  bulb  upwards.  After  the  lapse  of  half  an 


§   174.]  COMBUSTION    WITH    CUPRIC    OXIDE.  29 

hour,*  weigh  the  potash  bulbs  and  the  calcium-chloride  tube,  and 
then  calculate  the  results  obtained.  They  are  generally  very  satis- 
factory. As  regards  the  carbon,  they  are  rather  somewhat  too  low 
(about  0-1  per  cent.)  than  too  high.  The  carbon  determination, 
indeed,  is  not  free  from  sources  of  error;  but  none  of  these  inter- 
fere materially  with  the  accuracy  of  the  results,  and  the  deficiency 
arising  from  the  one  is  partially  balanced  by  the  excess  arising 
from  the  other.  In  the  first  place,  the  air  which  passes  through 
the  solution  of  potassa  during  the  combustion,  and  finally  during 
the  process  of  aspiration,  carries  away  with  it  a  minute  amount  of 
moisture.  The  loss  arising  from  this  cause  is  increased  if  the 
evolution  of  gas  proceeds  very  briskly,  since  this  tends  to  heat  the 
solution  of  potassa ;  and  also  if  nitrogen  or  oxygen  passes  through 
the  potash  bulbs  (compare  §  178  and  §  186).  This  may  be  reme- 
died, however,  by  fixing  to  the  exit  end  of  the  latter  a  tube  filled 
with  small  fragments  of  potassa,  or  one-half  filled  with  soda-lime 
and  the  other  half  with  calcium  chloride,  the  end  containing  soda- 
lime  being  connected  with  the  potash  apparatus,  which  is  always 
weighed  along  with  the  appended  tube.  In  the  second  place, 
traces  of  carbonic  acid  from  the  atmosphere  are  carried  into  the 
potash  apparatus  during  the  final  aspiration ;  this  may  be  avoided 
by  connecting  the  tail  of  the  combustion  tube  during  the  aspiration 
with  a  tube  filled  with  potassa  crushed  to  small  lumps,  by  means 
of  a  flexible  tube.  In  the  third  place,  it  may  happen  in  the  analy- 
sis of  substances  containing  a  considerable  proportion  of  water  or 
hydrogen,  that  the  carbonic  acid  is  not  completely  dried  in  passing 
through  the  calcium  chloride;  this  may  be  avoided  by  using  an 
apparatus  filled  with  sulphuric  acid  instead  of  the  calcium-chloride 
tube,  or,  in  conjunction  with  this  latter,  a  U-tube  filled  with  frag- 
ments of  pumice-stone  and  H2SO4;  but  usually  a  calcium-chloride 
tube,  if  filled  for  about  12  cm.  of  its  length  with  not  too  coarsely 

*  LOWE  considers  half  an  hour's  cooling  insufficient,  at  least  when  using 
his  concentrated  potash  in  the  bulbs.  According  to  him  the  weight  of 
the  apparatus  becomes  constant  only  after  2  to  3  hours.  The  open  ends 
of  the  apparatus  are  kept  closed  during  the  cooling  (but  not  while  weighing) 
by  means  of  short  pieces  of  rubber  tubing  and  pieces  of  glass  rod. 


30  ORGANIC   ANALYSIS.  [§  175. 

granulated  calcium  chloride,  will  suffice,  provided  the  combustion 
is  not  pushed  too  rapidly.  Finally,  if  the  mixture  was  not  suffi- 
ciently intimate,  traces  of  carbon  will  remain  unconsumed.  It  is 
therefore  better  to  complete  the  combustion  in  oxygen  gas. 

The  hydrogen  is  usually  too  high — averaging  from  0-1  to  0-15 
per  cent. ;  it  is  due  chiefly  to  the  fact  that  the  final  air  drawn  into 
the  apparatus  conveys  a  little  moisture  into  the  calcium-chloride 
tube;  this  may,  however,  be  easily  avoided  by  connecting  a  tube 
filled  with  potassa  with  the  tail  of  the  combustion  before  applying 
suction. 

I  would  particularly  remark,  however,  that  in  most  cases  it 
is  altogether  unnecessary  to  make  the  operation  still  more  com- 
plicated in  order  to  avoid  these  sources  of  error,  more  particularly 
since  their  influence  on  the  results  is  perfectly  well  known  from 
the  numerous  experiments  made. 

2.  BUNSEN'S  MODIFICATION  OF  LIEBIG'S  METHOD.* 
§175. 

In  this  modification  (which  is  to  be  preferred  when  analyzing 
very  hygroscopic  substances,  or  such  as  may  not  be  mixed  with 
warm  cupric  oxide  without  danger)  the  cupric  oxide  is  allowed  to 
cool  in  a  closed  tube  or  stoppered  flask,  and  the  mixing  of  the 
substance  with  the  cupric  oxide  is  effected  in  the  combustion  tube 
itself,  and  not  in  a  mortar,  thus  effectually  guarding  the  cupric 
oxide  from  taking  up  any  atmospheric  moisture  and  rendering 
the  exhaustion  of  the  tube  unnecessary.  The  dried  substance  is 
weighed  in  a  tube  of  thin  glass  20  cm.  long  and  about  7  mm.  diame- 
ter, one  end  being  sealed  and  the  other  end  closed  by  a  smooth 
cork  during  the  operation  of  weighing. 

Besides  this  tube,  BUNSEN'S  method  requires  a  combustion 
tube,  potash  bulbs,  calcium-chloride  tube,  rubber  tubes,  suction 
tube,  perforated  cork,  combustion  furnace,  and  cupric  oxide  (see 
§  174).  In  addition  to  these  there  is  required  a  wide  glass  tube 

*  KOLBB,  Handworterbuch  der  Chemie,  Supplements,  186. — A.  STRECKER, 
ibid.,  2d  ed.,  i,  852. 


§  175.]  BUNSEN'S  MODIFICATION  OF  LIEBIG'S  METHOD.         31 

sealed  at  one  end,  or  a  FLASK  (Fig.  29),  in  which  the  freshly-ignited 
cupric  oxide  is  allowed  to  cool,  and  from  which  it  is  trans- 
ferred to  the  combustion   tube,  secure  from  the  possible 
absorption  of  moisture  from  the  air. 

The  freshly-ignited  and  still  quite  hot  cupric  oxide  is 
transferred  direct  from  the  crucible  to  this  filling  tube,  or 
flask,  which  is  then  closed  air-tight  with  a  cork.  It  saves 
time  to  fill  in  at  once  a  sufficient  quantity  of  oxide  to  last 
for  several  analyses.  If  the  cork  fits  tight,  the  contents 
will  remain  several  days  fit  for  use,  even  though  a  portion FlG- 29- 
has  been  taken  out,  and  the  tube  repeatedly  opened.  The  filling 
of  the  combustion  tube  is  effected  as  follows:  The  perfectly  dry 
tube  is  rinsed  with  some  cupric  oxide;  a  layer  of  the  oxide  about 
13  cm.  long  is  introduced  into  the  posterior  end  of  the  combustion 
tube  by  inserting  the  latter  into  the  filling  tube  or  flask  containing 
the  cupric  oxide  (Fig.  30),  holding  both  tubes  in  an  oblique  direc- 
tion and  giving  a  few  gentle  taps. 


FIG.  30. 

Shortly  before,  the  cork-stoppered  tube  with  the  substance 
must  be  accurately  weighed.  From  the  tube  containing  the  sub- 
stance next  remove  the  cork  cautiously,  to  prevent  the  slightest 
loss  of  substance;  insert  the  open  end  of  the  tube  as  deep  as  possi- 
ble into  the  combustion  tube  and  pour  from  it  the  requisite  quan- 
tity of  substance  by  giving  it  a  few  turns,  pressing  the  rim  all  the 
while  gently  against  the  upper  side  of  the  combustion  tube,  to 
prevent  its  coming  into  contact  with  the  powder  already  poured 
out;  the  two  tubes  are,  in  this  manipulation,  held  slightly  inclined, 
as  in  Fig.  31. 

When  a  sufficient  quantity  of  the  substance  has  been  thus 
transferred  from  the  weighing  to  the  combustion  tube,  the  latter 
is  restored  to  the  horizontal  position,  which  gives  to  the  former  a 
gentle  inclination  with  the  closed  end  downwards.  If  the  little 
tube  is  now  slowly  withdrawn,  with  a  few  turns,  the  powder  near 


32  ORGANIC    ANALYSIS.  [§   175. 

the  border  of  the  opening  falls  back  into  it,  leaving  the  opening 
free  for  the  cork.  The  tube  is  then  immediately  corked  and 
weighed,  the  combustion  tube  also  being  meanwhile  kept  closed 
with  a  cork.  The  difference  between  the  two  weighings  shows 
the  quantity  of  substance  transferred  from  the  weighing  to  the 
combustion  tube.  The  latter  is  then  again  opened  and  a  quantity 


FIG.  31. 

of  oxide  of  copper  equal  to  the  first  transferred  to  it  from  the 
filling  tube,  or  flask,  taking  care  to  rinse  down  with  this  the  parti- 
cles of  the  substance  still  adhering  to  the  sides  of  the  tube.  There 
is  now  in  the  hind  part  of  the  tube  a  layer  of  cupric  oxide  about 
20  cm.  long,  with  the  substance  in  the  middle. 

The  next  operation  is  the  mixing:  this  is  performed  with  the 
aid  of  the  polished  brass  or  iron  wire  (Fig.  32),  having  a  ring  for  a 
handle  and  a  single  corkscrew  turn  at  the  other,  which  should  taper 
smoothly  to  a  point.  This  wire  is  pushed  down  to  within  3  to  4 
cm.  of  the  end  and  rapidly  moved  about  in  all  directions  until 
the  mixture  is  complete  and  uniform,  the  tube  being  held  nearly 
horizontal.  A  few  minutes  only  suffice  to  effect  so  perfect  a  mix- 
ture that,  in  the  case  of  pulverulent  substances  that  do  not  cake, 
the  eye  can  no  longer  distinguish  the  smallest  particles.  The 
combustion  is  then  effected  as  in  §  174. 

Cupric  oxide  is  then  poured  in  to  within  5  to  6  cm.  of  the  open 
end  and  the  tube  is  corked. 

{Completion  of  *hc  Combustion  by  Oxygen  Gas.  To  insure  the 
oxidation  of  the  last  traces  of  carbon  and  to  leave  the  cupric  oxide 
ready  for  use  again,  it  is  advisable  to  finish  the  combustion  in  a 


§   176.]         COMBUSTION    WITH   LEAD    CHROMATE,    ETC.  33 

stream  of  oxygen.  For  this  purpose  the  tail  of  the  combustion 
tube  must  be  made  rather  stout  and  long.  When  the  potash-lye 
recedes,  slip  tightly  over  the  suitably  cooled  tail  a  caoutchouc 
tube  connected  with  a  source  of  pure  and  dry  0x3  gen  gas,  nip  off 
the  tip  within  this  tube  by  help  of  a  pliers,  and  cautiously  let 


FIG.  32. 

on  the  oxygen  until  the  reduced  copper  is  oxidized  and  the  gas 
traverses  the  potash  bulbs.  Then  replace  the  stream  of  oxygen 
by  one  of  pure  and  dry  air,  to  remove  all  oxygen  from  the  bulbs. 
To  prevent  loss  by  evaporation  from  the  potash-lye,  append  to  the 
potash  bulb  the  additional  absorbing  apparatus  above  mentioned 
(in  §  174). 

The  oxygen  and  purified  air  are  supplied  as  in  the  process 
described  in  §  178.] 

/?.  Difficultly    Combustible    Non-volatile    Bodies — e.g.,   Resinous 
and  Extractive  Matters,  Coal,  etc. 

If  substances  of  this  kind  are  treated  according  to  §§174  and 
175,  small  particles  of  carbon  are  likely  to  escape  combustion. 
In  order  to  avoid  this  the  following  methods  are  employed,  which 
may,  of  course,  be  also  used  for  readily  combustible  substances. 

1.  COMBUSTION  WITH  LEAD  CHROMATE,  OR  WITH  LEAD  CHROMATE 
AND  POTASSIUM  BICHROMATE,  OR  WITH  POTASSIUM  CHRO- 
MATE AND  CUPRIC  OXIDE. 

§176. 

This  is  not  only  a  good  method  for  the  analysis  of  compounds 
mentioned  in  §  174,  but  is  especially  resorted  to  in  the  analysis  of 
salts  of  organic  acids  with  alkalies  or  alkali-earth  metals  (as  the 
chromic  acid  completely  displaces  carbonic  acid  from  their  car- 
bon atss),  and  of  bodies  containing  sulphur,  chlorine,  bromine,  or 


34  ORGANIC    ANALYSIS.  [§   176- 

iodine,  and  also  for  the  combustion  of  substances  containing  car- 
bon in  a  difficultly  oxidizable  form — e.g.,  graphite. 

Of  the  apparatus,  etc.,  enumerated  in  §  174,  all  are  required  ex- 
cept cupric  oxide,  which  is  here  replaced  by  lead  chromate  (§  66, 2). 
A  narrow  combustion  tube  may  be  selected,  as  lead  chromate 
contains-  a  much  larger  amount  of  available  oxygen  in  an  equal 
volume  than  cupric  oxide.  A  quantity  of  the  chromate,  more 
than  sufficient  to  fill  the  combustion  tube,  is  heated  in  a  platinum 
or  porcelain  dish  over  a  gas  or  BERZELIUS  lamp,  until  it  begins  to 
turn  brown;  before  filling  it  into  the  tube,  it  is  allowed  to  cool 
down  to  100°,  and  even  below.  The  process  is  conducted  like  the 
one  described  in  §  174. 

It  was  formerly  believed  that  when  using  lead  chromate  the 
exhaustion  of  the  warmed  tube  could  be  omitted,  as  the  lead  chro- 
mate was  considered  to  be  not  at  all  hygroscopic,  or  at  least  far 
less  so  than  cupric  oxide.  Since  ERDMANN  *  has  shown,  how- 
ever, that  this  opinion  is  unfounded,  and  that  lead  chromate  takes 
up  moisture  just  as  rapidly  as  does  cupric  oxide,  there  is  no  longer 
any  ground  for  neglecting  the  exhaustion. 

If  the  substance  analyzed  contains  a  large  proportion  of  sulphur, 
use  a  rather  long  combustion  tube  (60-70  cm.)  and  place  in  front 
of  the  mixture  10-20  cm.  pure  lead  chromate,  which  should  be 
kept  only  at  a  dull-red  heat  during  the  combustion  (CARIUS). 

One  of  the  principal  advantages  which  lead  chromate  has  over 
cupric  oxide  as  an  oxidizing  agent  being  its  property  of  fusing  at 
a  high  heat,  the  temperature  must,  in  the  last  stage  of  the  process 
of  combustion,  be  raised  (by  fanning  the  charcoal,  etc.)  sufficiently 
high  to  completely  fuse  the  contents  of  the  tube  as  far  as  the 
substance  extends.  To  heat  the  anterior  end  of  the  tube  to  the 
same  degree  of  intensity  would  be  injudicious,  since  the  lead 
chromate  in  that  part  would  thereby  lose  all  porosity,  and  thus 
also  the  power  of  effecting  the  combustion  of  the  products  of 
decomposition  which  may  have  escaped  oxidation  in  the  other 
parts  of  the  tube. 

*  Journ.  f.  prakt.  Chem.,  LXXXI,  180. 


§   176.]  COMBUSTION    WITH    CUPRIC    OXIDE,    ETC.  35 

As  the  lead  chromate,  even  in  powder,  is,  on  account  of  its. 
density,  by  no  means  all  that  could  be  desired  in  this  latter  respect, 
it  is  preferable,  instead  of  filling  with  lead  chromate,  to  fill  the 
anterior  part  of  the  tube  with  coarsely  pulverized  strongly  ignited 
cupric  oxide,  or  with  copper  turnings  which  have  been  superficially 
oxidized  by  ignition  in  a  muffle  or  in  a  crucible  with  access  of  air. 

In  the  case  of  very  difficultly  combustible  substances — e.g., 
graphite — it  is  desirable  that  the  mass  should  not  only  readily 
cake,  but  also,  in  the  last  stage  of  the  process,  give  out  a  little 
more  oxygen  than  is  given  out  by  lead  chromate.  It  is  therefore 
advisable  in  such  cases  to  add  to  the  latter  one-tenth  of  its  weight 
of  fused  and  powdered  potassium  dichromate.  With  the  aid  of 
this  addition,  complete  oxidation  of  even  very  difficultly  com- 
bustible bodies  may  be  effected  (LIEBIG).* 

Good  results  may  also  be  obtained  with  cupric  oxide  and  potas- 
sium dichromate.  GINTL  f  recommends  the  following  process, 
which  is  very  similar  to  that  of  BUNSEX  :  Introduce  into  the  com- 
bustion tube,  first,  a  layer  of  coarse  cupric  oxide  6  cm.  long,  then 
3  cm.  of  potassium  dichromate  (which  has  first  been  fused,  then 
powdered,  and  preserved  from  contact  with  air),  then  the  sub- 
stance, and  finally  another  layer  of  3  cm.  of  cupric  oxide.  Mix 
the  substances  by  aid  of  the  wire,  taking  care,  however,  that  3  cm. 
of  cupric  oxide  remain  at  the  end  of  the  tube  perfectly  free  from, 
chromate.  Now  fill  up  the  tube  fully  with  cupric  oxide  as  usual 
and  proceed  with  the  combustion.  As  the  potassa-lye  towards 
the  end  takes  up  oxygen,  a  little  more  air,  free  from  carbonic  acid 
and  moisture,  must  be  drawn  through  the  apparatus  at  the  close 
of  the  operation.  Further,  the  exit  of  the  potash  bulbs  must  be 
connected  with  a  tube  filled  two-thirds  with  soda-lime  and  one- 
third  with  calcium  chloride,  and  which  is  weighed  with  the  potash 
bulbs. 

*  Experiments  regarding  this  excellent  method  have  been  published  by 
MAYER  (Annal.  d.  Chem.  u.  Pharm.,  xcv,  204). 
f  Zeitschr.  /.  analyt.  Chem.    vii,  302. 


36  ORGANIC    ANALYSIS.  [§    177. 

2.    COMBUSTION  WITH  CUPRIC  OXIDE  AND  POTASSIUM  CHLORATE 
OR  PERCHLORATE. 

§177. 

This  method  requires  all  the  apparatus  enumerated  in  §  174 
or  §  175,  and  in  addition,  a  small  quantity  of  potassium  chlorate 
which  is  freed  from  water  by  heating  it  until  it  fuses,  and  then, 
after  it  has  cooled,  reducing  it  to  a  coarse  powder  and  preserving 
it  in  a  warm  place  until  required  for  use. 

The  process  is  the  same  as  in  §  174  or  §  175,  excepting  that  the 
layer  of  cupric  oxide  in  the  posterior  end  of  the  tube  is  somewhat 
longer  (5  cm.),  and  is  mixed  by  agitation  with  about  one-eighth 
(3  to  4  grm.)  of  potassium  chlorate.  After  this  introduce  2  cm.  of 
pure  cupric  oxide  and  then  the  substance  to  be  analyzed.  When, 
in  heating  the  tube,  the  part  of  the  tube  containing  the  potassium 
chlorate  is  approached,  the  greatest  caution  must  be  exercised  in 
applying  the  hot  charcoal  or  in  turning  on  the  gas  at  the  stop-cocks, 
so  that  the  potassium  chlorate  will  be  only  very  gradually  decom- 
posed; if  this  caution  be  neglected,  a  violent  rush  of  gas  may  drive 
out  some  of  the  potassa  solution  and  entirely  spoil  the  analysis. 

The  oxygen  evolved  from  the  potassium  chlorate  drives  out 
all -the  carbonic  acid  in  the  tube,  effects  the  combustion  of  all 
tmconsumed  particles  of  carbon,  arid  oxidizes  the  reduced  copper. 
Oxygen  gas  cannot  therefore  pass  through  potash  bulbs  until  all 
oxidizable  substances  in  the  tube  have  been  oxidized. 

If,  towards  the  last,  much  gas  passes  through  the  potash  bulbs 
tinabsorbed,  it  is  unnecessary  to  break  off  the  point  and  draw  air 
through  the  tube,  since  the  latter  will  contain  only  oxygen,  and 
neither  carbonic  acid  nor  moisture.  Air  dried  and  free  from  car- 
Iconic  acid  must,  however,  be  drawn  through  the  calcium-chloride 
tube  and  potash  bulbs,  otherwise  these  would  be  weighed  full  of 
oxygen. 

The  decomposition  of  potassium  chlorate  is  somewhat  violent, 
as  is  well  known.  The  perchlorate  obtained  by  heating  the  chlo- 
rate decomposes  much  more  quietly,  however,  and  may  be  em- 
ployed instead  of  the  chlorate,  as  first  recommended  by  BUNSEN, 


§  178.]   COMBUSTION    WITH    CUPRIC    OXIDE    AND    OXYGEN.         37 

The  perchlorate,  while  still  hot  and  in  a  fused  state,  is  introduced 
into  the  posterior  end  of  the  tube,  followed  by  a  loose  plug  of  re- 
cently ignited  asbestos ;  the  tube  is  then  filled  as  usual.  If  BUN- 
SEX'S  method  of  mixing,  as  given  in  §  175,  is  followed,  a  plug  of 
asbestos  must  always  be  used,  even  when  using  potassium  chlorate, 
so  that  on  mixing  the  substance  may  not  come  into  immediate 
contact  with  the  salt  yielding  the  oxygen. 

As  the  dry  oxygen  passing  through  the  potassa-lye  carries  off 
some  moisture  from  the  latter,  the  exit  tube  of  the  potash  bulbs 
should  be  connected  with  a  small  tube,  filled  two-thirds  with  soda- 
lime  and  one-third  with  calcium  chloride;  the  connection  may  be- 
made  by  means  of  a  cork  or  a  short  piece  of  rubber  tubing,  and 
should  be  weighed  with  the  bulbs.  The  increase  of  weight  of  the? 
bulbs  and  this  tube  indicate  the  carbonic  acid  absorbed. 

3.  COMBUSTION*  WITH  CUPRIC  OXIDE  AND  OXYGEN. 
§178. 

Many  chemists  effect  combustion  with  cupric  oxide  in  a  cur- 
rent of  oxygen  supplied  by  a  gasometer.  HESS,  DUMAS  and  STAS, 
ERDMANN  and  MARCHAND,  PIRIA,  STRECKER,  WOHLER,  LOWE, 
GLASER,  and  others  have  proposed  methods  based  upon  this 
principle,  which  they  employ  not  only  for  the  analysis  of  diffi- 
cultly combustible  bodies,  but  also  to  effect  the  determination 
of  the  carbon  and  hydrogen  in  organic  substances  in  general. 

These  processes,  besides  the  others,  have  been  used  in  my 
laboratory  for  years. 

As  these  methods  require,  besides  a  gasometer  filled  with 
oxygen,  arrangements  for  perfectly  drying  the  oxygen  and  free- 
ing it  from  carbonic  acid,  it  may  be  readily  seen  that  the  appara- 
tus required  is  far  more  complicated  than  is  that  used  ir  the  simple 
LIEBIG  or  BUXSEN  method.  They  are  to  be  recommended  espe- 
cially only  when  a  large  number  of  ultimate  analyses  are  to  be 
made,  as  well  as  in  the  analysis  of  substances  which  cannot  be 
reduced  to  powder,  and  which  consequently  cannot  be  intimately 
mixed  with  the  cupric  oxide. 

For  heating  the  combustion  tube,  HESS,  as  well  as  ERDMAXXT 


38  ORGANIC    ANALYSIS.  [§   178. 

and  MARCHAND,  used  alcohol,  but  since  gas  has  come  into  general 
use  for  heating  purposes,  the  older  forms  of  furnaces  have  been 
entirely  superseded.  The  heating  may  also  be  conveniently 
effected  by  means  of  the  charcoal  furnace  shown  in  Fig.  17,  p.  18, 
but  in  this  case  the  furnace  should  be  70  to  80  cm.  long.  The 
various  methods  of  heating  have  no  influence  on  the  operation 
itself  or  on  the  accuracy  of  the  results,  provided  the  heating  can 
be  regulated  at  will  and  increased  to  the  intensity  necessary. 

The  combustion  with  the  aid  of  oxygen  can  be  carried  out  in 
two  ways,  according  as  the  substance  is  mixed  with  cupric  oxide 


FIG.  33. 

or  not.  The  latter  method,  in  which  the  substance  is  placed  in 
a  boat  inserted  into  the  combustion  tube,  is  the  most  convenient 
of  all  the  methods,  because  in  it  the  combustion  tube,  after  the 
analysis  is  finished,  is  immediately  ready  for  a  second  analysis. 
This  method  is  described  under  a;  the  other  method,  that  in  which 
the  substance  is  mixed  with  cupric  oxide,  is  described  under  6. 


§  178.]   COMBUSTION    WITH    CUPRIC    OXIDE    AND    OXYGEN.         39 

Many  forms  of  apparatus  have  been  devised  for  drying  and  puri- 
fying the  air  and  oxygen  which  are  used  in  the  process.  Fig.  33 
shows  one  which  is  durable  and  efficient.  The  bulb  tube  entering 
the  bottle  d  is  connected  with  the  gasometer  by  means  of  a  rubber 
tube.  The  bottle  d  is  half  filled  with  concentrated  sulphuric 
.acid,  through  which  the  gas  or  air  passes  in  bubbles  and  enters 
the  bottom  of  the  cylinder  c.  The  lower  half  of  this  cylinder  is 
filled  with  fragments  of  fused  potash,  the  upper  half  with  calcium 
chloride,  which  is  separated  from  the  potash  by  a  layer  of  asbestos. 
Glass  tubes  provided  with  glass  stop-cocks  enter  the  top  of  each  cylin- 
der through  rubber  stoppers,  and  are  connected  by  means  of  strong 
rubber  tubes  to  the  two  limbs  of  the  forked  tube  b,  so  that  a  regu- 
lated current  of  either  air  or  oxygen  can  be  made  to  enter  the 
combustion  tube  through  a  at  will. 

a.  Combustion  in  a  Boat. 

As  in  this  method  it  is  of  especial  value  to  be  able  to  use  the 
same  tube  for  a  number  of  combustions,  it  is  advantageous  to 
use  a  gas  furnace  which  does  not  destroy  the  tube  too  rapidly, 
e.g.,  such  a  one  as  GLASER'S  improved  DONNY'S  furnace,  or  that 
of  HOFMANN.  Fig.  34  shows  the  entire  furnace  as  described  by 
GLASER.* 

The  ends  of  the  furnace  consist  of  two  upright  iron  supports 
screwed  to  an  iron  plate  and  carrying  two  parallel  iron  bands. 
Directly  over  the  latter  two  iron  rods  are  fixed  into  the  upright 
supports.  The  tiles  are  provided  with  grooves  at  both  top  and 
bottom,  and  may  be  readily  put  in  place  or  removed  from  between 
the  bands  and  rods,  and  serve,  as  seen  in  Fig.  35,  as  supports  for 
the  iron  sections  which,  when  placed  together,  form  the  trough  for 
the  reception  of  the  combustion  tube.  One  of  these  sections  is 
shown  at  the  right  in  Fig.  34. 

The  flames  from  the  gas  burners  beneath  the  iron  sections  heat 
these  first;  a  part  of  the  hot  gases  passes  through  the  apertures 


*  AnnaL  der  Chem.  u.  Pharm.,  Supplementband,  vil,  213;  also  Zeitschr. 
/.  analyt.  Chem.,  ix,  392.  The  apparatus  is  furnished  by  MARQUART  (G. 
GERHARDT),  of  Bonn. 


40 


ORGANIC   ANALYSIS. 


[§  178. 


§   178-]    COAiBLSilON    \ViiH    CUPR1C    OXIDE    AND    OXYGEN.         41 


in  the  sides  of  the  iron  sections,  meets  over  the  combustion  tube, 

and  then  escapes  through  apertures  in  the  clay 

covers  (Fig.  35).    The  shape   of  this  cover  is 

such  as  to  concentrate  the  heat  upon  the  glass 

tube.     By  this  arrangement  the  important  result 

is  secured  in  that  the  tube  is  heated  both  from 

above  and  the  sides,  as  in  the  LIEBIG  charcoal 

fumace.     (In   ordinary   combustions   the    iron 

sections  are  not  placed  close  together,  but  two 

or  three  of  the  sections  are  separated  at  the 

place    where    the   substance    mixed    with   the  FlG- 35- 

cupric  oxide  is.     In  proportion  as  the  combustion  proceeds  these 

sections  may  be  readily  pushed  together  by  means  of  a  pair  of 

tongs,  while  the  combustion  tube,  which  rests  in  a  channel  of  wire 

gauze,  is  held  fast  with  one  hand.) 

The  combustion  tube,  Fig.  36,  is  open  at  both  ends.    From  a 

12cm  > 


to  b  it  is  filled  with  oxidized  copper  turnings  and  granulated  cupric 
oxide,  kept  together  by  plugs  made  of  copper  gauze  at  a  and  6.* 
b  c  contains  an  oxidized  copper  spiral  made  from  rolled  copper 
gauze.  (In  the  analysis  of  substances  containing  chlorine,  bro- 
mine, or  nitrogen,  the  spiral  is  replaced  by  spiral  of  metallic  copper; 
see  below.)  The  platinum  boat  containing  the  substance  is  placed 
at  a  d;  finally,  at  d  e  is  placed  a  metallic  copper  spiral  secured  to 
a  wire.  The  combustion  tube  is  laid  in  a  trough  of  wire  gauze 
placed  in  the  bed  of  the  furnace,  first  removing  three  of  the  iron 
sections  from  the  place  under  the  platinum  boat.  The  fore  part 
of  the  tube  is  now  connected  with  an  unweighed  calcium-chloride 
tube  by  means  of  a  perforated  rubber  stopper;  the  other  end  is 

*  LOWE  (Zeitschr.  f.  analyt.  Chem.,  ix,  218)  uses,  instead  of  these,  hemi- 
spheres of  rather  coarse-meshed  platinum  gauze  the  convex  surfaces  of  which 
are  turned  toward  the  absorption  apparatus. 


42  ORGANIC    ANALYSIS.  [§   178. 

connected  with  the  purifying  and  drying  apparatus  and  gasometers. 
a  and  aA  of  the  purifying  and  drying  apparatus  contain  potassa 
solution,  a  being  connected  by  d  with  the  oxygen  gasometer,  and 
ttj  by  di  with  the  air  gasometer,  b  and  ^  are  two-thirds  filled  with 
soda-lime,  the  upper  third  being  filled  with  calcium  chloride.  The 
U-tube  c  c,  through  which  oxygen  or  air  passes  into  the  combustion 
tube,  contains  calcium  chloride;  it  is  connected  with  the  combus- 
tion tube  by  means  of  a  glass  tube  g,  provided  with  a  glass  stop- 
cock, and  the  rubber  tube  /. 

In  order  to  obviate  all  possibility  of  a  diffusion  of  the  gaseous 
BBga,  ^a-s— -•,   combustion-products  of   the   sub- 

stance into  the  drying  tubes, 
LOWE  *  interposes  between  the 
calcium-chloride  tube  of  the  drying 
apparatus  and  the  combustion 
tube  a  mercury  valve,  as  shown 
in  Fig.  37.  Air  or  oxygen  enters 
FlG-  37-  at  a  and  exits  at  b.  In  the  point 

of  the  tube  c  is  placed  a  little  mercury  into  which  the  tube  a,  drawn 
out  to  a  fine  point,  dips.  The  rubber  stopper  closing  c  is  covered 
with  a  gelatin  solution  to  insure  its  being  air-tight. 

Before  beginning  an  analysis,  first  heat  the  entire  tube  in  the 
combustion  furnace  from  end  to  end,  while  a  slow  current  of  dry 
air  is  passed  through  it,  and  then  allow  it  to  cool  while  the  air  is 
still  passing  through;  then  remove  the  posterior  copper  spiral, 
insert  the  platinum  boat  containing  the  substance  to  be  analyzed, 
replace  the  spiral,  place  in  position  the  iron  disc  seen  in  Fig.  34 
(or  one  of  clay — LOWE),  and  connect  the  fore  part  of  the  com- 
bustion tube  with  the  absorption  apparatus.  The  guard  tube 
(of  which  the  bulb  and  half  the  tube  are  filled  with  calcium  chloride, 
the  other  half  of  the  tube  being  filled  with  soda-lime)  is  not  weighed ; 
it  is  connected  with  the  aspirator  B  by  means  of  a  glass  tube  pro- 
vided with  a  stop-cock.  The  aspirator  consists  of  a  tubulated 
glass  bell-jar  standing  in  a  vessel  filled  with  water.  The  stop- 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  407. 


§   178.]    COMBUSTION    WITH    CUPRIC    OXIDE    AND   OXYGEN.        43 

cock  is  opened  and  the  water  aspirated  up  into  the  jar  until  the 
difference  in  level  is  about  12  to  15  cm.  This  aspirator,  first  de- 
scribed by  PIRIA  *,  serves  to  counterbalance  the  pressure  in  the 
combustion  tube  caused  by  the  potash  bulbs,  and  affords,  besides, 
a  convenient  means  of  testing  the  air-tightness  of  the  apparatus. 

When  everything  has  thus  been  made  ready,  close  the  glass 
cock  of  the  drying  apparatus,  open  that  of  the  aspirator,  and  heat 
the  fore  part  of  the  combustion  tube,  and  the  copper  spiral  in  the 
hinder  end,  to  low  redness;  then  open  the  cock  of  the  drying  appa- 
ratus and  allow  to  pass  in  a  very  slow  current  of  oxygen  gas,  which 
will  be  entirely  absorbed  by  the  copper  spiral  in  d  e,  and  is  only 
intended  to  prevent  the  products  of  combustion  from  entering 
the  hinder  part  of  the  tube. 

The  substance  is  now  heated,  according  to  its  volatility,  either 
by  heat  applied  directly  or  by  radiant  heat,  the  temperature  being 
easily  regulated  by  removing  or  replacing  the  movable  clay  covers. 
When  nothing  more  remains  in  the  platinum  boat  but  carbon, 
allow  the  copper  spiral  in  d  e  to  cool,  and  let  a  stronger  current  of 
oxygen  gas  pass  through,  which  completes  the  combustion  and 
converts  the  reduced  copper  into  cupric  oxide  again.  This  oxida- 
tion is  completed  by  the  current  of  air  which  is  next  passed 
through  the  apparatus  and  drives  out  the  oxygen  from  the  latter. 
Now  turn  off  the  gas,  close  the  cock  of  the  aspirator  and  disconnect 
the  latter  from  the  absorption  apparatus,  allow  this  to  become 
perfectly  cold,  and  weigh. 

The  method  devised  by  CLOEZ  will  be  detailed  in  a  special 
paragraph,  §  192. 

b.  Combustion  of  the  Substance  Mixed  with  Cupric  Oxide. 

This  method  requires  a  tube  about  50  cm.  long,  sealed  behind, 
and  drawn  out  as  in  Fig.  38. 

The  operations  are  at  first  almost  exactly  the  same  as  in  BUN- 
SEN'S  method  (§  175).  First  fill  the  hind  part  of  the  tube  with 
ignited  granular  cupric  oxide  from  a  to  b,  then  fill  the  space  6  to 
c  with  the  substance  and  ignited  powdered  cupric  oxide,  mixed 

*  Cimento,  v,  321 ;  Jahresber.  v.  KOPP  u.  WILL,  1857,  573. 


44  ORGANIC    ANALYSIS.  [§   179. 

by  means  of  the  wire;  from  c  to  d  fill  with  ignited  granular  cupric 
oxide,  and  finally  insert  a  spiral  of  ignited  copper  gauze  in  the 
place  from  d  to  e.  After  the  weighed  absorption  apparatus  is 
now  connected  with  the  tube,  the  combustion  is  effected  as  usual, 


beginning  at  the  fore  part  of  the  tube  and  proceeding  to  the  hinder 
end,  but  before  reaching  the  mixture  of  the  substance  and  cupric 
oxide  heat  the  part  a  b  to  low  redness  to  burn  any  products  of 
distillation  that  may  have  passed  to  the  hinder  end.  When  the 
entire  tube  is  at  a  low  red  heat  and  the  evolution  of  gas  has  ceased, 
let  the  hinder  end  of  the  tube  cool  scmewhat  so  that  the  point  may 
be  comfortably  handled,  and  slip  one  end  of  a  rubber  tube  over 
it,  connecting  the  other  end  with  the  calcium-chloride  tube,  c  c,  of 
the  purifying  and  drying  apparatus,  Fig.  34.  Now  break  off  the 
point  of  the  combustion  tube  within  the  rubber  tubing  and  com- 
plete the  combustion  in  a  slow  current  of  oxygen,  displace  the 
oxygen  by  a  slow  current  of  air,  allow  the  apparatus  to  cool,  and 
then  weigh  the  absorption  apparatus. 

y.  Hygroscopic   or    Volatile   Substances,    or   Bodies   undergoing 
Alteration  at  100°  (losing  Water,  for  instance). 

§179. 

aa.  Hygroscopic  substances,  if  burnt  by  any  of  the  methods 
above  described,  are  very  apt  to  yield  too  high  a  hydrogen  content. 
STEIN  *  hence  recommends  the  following  process  for  their  analysis : 
The  method  is  that  detailed  in  §  178,  a.  The  portion  of  the  tube 
in  which  the  platinum  boat  containing  the  substance  is  situated 
is  unsupported  by  any  part  of  the  trough  or  wire  gauze,-  in  order 

*  Zeitschr.  f.  analyt.  Chem.,  v,  33. 


§  179.]   COMBUSTION   WITH   CUPRIC    OXIDE   AND   OXYGEN.        45 

to  prevent  any  heat  conduction.  The  substance  is  weighed  in 
the  boat  after  being  simply  dried  in  the  air  or  in  the  exsiccator. 
Heat  the  tube  first,  then  cool,  and  test  as  to  ite  tightness,  after 
which  insert  the  boat,  light  one  or  two  burners  some  9  to  12  cm. 
behind  the  boat,  and  pass  a  slow  current  of  dry  air  over  the  sub- 
stance heated  in  this  manner.  Usually  some  water  shows  itself 
in  the  calcium  chloride  very  soon,  but  it  disappears  after  a  tune  and 
does  not  again  appear  even  if  the  air-current  is  heated  somewhat 
more  strongly  and  the  bulb  of  the  calcium-chloride  tube  is  cooled 
by  means  of  ether.  Now  remove  the  absorption  tube,  and  while 
it  is  being  weighed,  pass  a  slow  current  of  cold,  dry  air  through 
the  apparatus.  The  weight  of  the  potash  bulbs  with  the  potash 
or  soda-lime  tube  will  show  whether  any  decomposition  of  the 
substance  has  occurred;  the  increase  of  weight  gives  the  water 
content.  On  repeating  the  drying  in  a  current  of  warm  air  and 
again  weighing  the  calcium-chloride  tube,  the  operator  ascertains 
with  certainty  whether  the  substance  has  been  completely  dried. 
As  soon  as  this  point  is  reached,  begin  the  combustion  of  the  now 
thoroughly  dried  substance. 

In  cases  where  a  higher  temperature  is  required  in  order  to 
expel  chemically  combined  water,  STEIN  suspends  a  piece  of  copper 
foil  by  four  thin  wires  between  the  burners  and  the  tube  at  the 
spot  where  the  boat  is,  places  a  thermometer  between,  and  lights 
a  burner  under  the  foil.  The  temperature  in  the  tube  is,  of  course, 
somewhat  lower  than  that  indicated  by  the  thermometer.  After 
the  drying  is  completed,  the  foil  may  be  readily  removed  by  loosen- 
ing the  wires. 

bb.  Volatile  Substances,  or  such  as  Undergo  Alteration  at  100°, 
e.g.,  lose  Water. 

If  such  substances  are  treated  as  in  §  174,  a  portion  of  the  sub- 
stance or  some  water  would  escape  on  mixing  the  substance  with 
the  warm  cupric  oxide  and  exhausting  the  tube  surrounded  by  the 
hot  sand;  and  the  results  could  not  possibly  be  accurate.  On 
the  other  hand,  were  the  mixing  done  in  the  cold,  the  mixture 
would  absorb  moisture. 


46 


ORGANIC   ANALYSIS. 


[§  180. 


The  process  is  hence  conducted  either  according  to 
§  175  or  as  directed  in  §  178.  Ignited  chromate  of  lead, 
cooled  in  a  closed  tube,  may  also  be  employed  as  oxidizing 
agent,  the  mixing  being  effected  in  the  combus- 
tion tube  by  means  of  a  wire. 

b.  FLUID  BODIES. 

a.  Volatile  Liquids  (e.g.,  ethereal  oils,  alcohol, 
etc.). 

§180. 

1.  The  analysis  of  organic  volatile  fluids  re- 
quires the  objects  enumerated  in  §  174.  The 
ra  combustion  tube  should  be  somewhat  longer  than 
there  mentioned;  it  should  have  a  length  of  50 
or  60  cm.,  according  as  the  substance  is  less  or 
more  volatile.  If  the  combustion  is  not  to  be 
effected  in  a  current  of  oxygen,  as  in  §  178,  a,  the 
process  then  requires  also  a  flask  to  hold  the  cupric 
oxide,  as  in  §  175.  The  process  requires  besides 
several  small  glass  bulbs  for  the  reception  of  the 
liquid  to  be  analyzed.  These  bulbs  are  made  in 
the  following  manner: 

A  glass  tube,  about  30  cm.  long  and  about  8 
mm.  wide,  is  drawn  out  as  shown  in  Fig.  39,  fused 
off  at  a,  and  A  expanded  into  a  bulb,  as  shown 
in  Fig.  40.  The  bulbed  part  is  then  cut  off  at  ft. 
Another  bulb  is  then  made  in  the  same  way,  and 
a  third  and  fourth,  etc.,  as  long  as  sufficient  length  of 
tube  is  left  to  secure  the  .bulb  from  being  reached  by  the 
moisture  of  the  mouth. 

Two  of  these  bulbs  are  accurately  weighed;  they  are 
then  filled  with  the  liquid  to  be  analyzed,  closed  by  fusion f 
and  weighed  again.  The  filling  is  effected  by  slightly 
heating  the  bulb  over  a  lamp  and  immersing  the  point  into  the 
liquid  to  be  analyzed,  part  of  which  will  now,  upon  cooling,  enter 
the  bulb.  If  the  fluid  is  highly  volatile,  the  portion  entering  the 


FIG.  40. 


FIG.  39. 


§  180.]    COMBUSTION    WITH    CUPRIC   OXIDE   AND    OXYGEN.         47 

still  warm  bulb  is  converted  into  vapor,  which  expels  the  fluid 
again;  but  the  moment  the  vapor  is  recondensed,  the  bulb  fills 
the  more  completely.  If  the  liquid  is  of  a  less  volatile  nature, 
a  small  portion  only  will  enter  at  first;  in  such  cases  the  bulb  is 
heated  again,  to  convert  what  has  entered  into  vapor,  and  the 
point  is  then  again  immersed  into  the  fluid,  which  will  now  readily 
enter  and  fill  the  bulb.  The  excess  of  fluid  is  ejected  from  the 
neck  of  the  little  tube  by  a  sudden  jerk ;  the  point  of  the  capillary 
neck  is  then  sealed  in  a  blowpipe  flame.  The  combustion  tube 
is  now  prepared  for  the  process  by  introducing  into  it  from  the 
filling  tube  or  flask  ( §  175)  a  layer  of  cupric  oxide  occupying  about 
6  cm.  in  length.  The  middle  of  the  neck  of  one  of  the  bulbs  is 
slightly  scratched  with  a  file,  the  pointed  end  is  quickly  broken  off, 
and  the  bulb  and  end  are  dropped  into  the  combustion  tube  (see 
Fig.  41).  Another  layer  of  cupric  oxide,  about 
6  to  9  cm.  long,  is  then  filled  in,  and  the  other  bulb 
introduced  in  the  same  manner  as  the  first.  The 
tube  is  finally  nearly  filled  with  cupric  oxide.  A 
few  gentle  taps  upon  the  table  suffice  to  clear  a 
free  passage  for  the  gases  evolved.  (It  is  ad- 
visable to  place  in  the  anterior  half  of  the  com- 
bustion tube  small  lumps  of  cupric  oxide  (comp. 
§  66,  1),  or  superficially  oxidized  copper  turnings, 
which  will  permit  the  free  passage  of  the  gases, 
even  with  a  narrow  channel,  or  no  channel  at  all; 
since  with  a  wide  channel  there  is  the  risk  of  vapors 
passing  unconsumed  through  the  tube.) 

The  combustion  of  highly  volatile  substances 
demands  great  care,  and  requires,  certain  modifica- 
tions of  the  common  method.  The  operation  is 
begun  by  heating  to  redness  the  anterior  half  of  the  tube,  which 
is  separated  from  the  rest  by  a  screen,  or  in  the  case  of  highly 
volatile  substances,  by  two  screens;  ignited  charcoal  is  then  placed 
behind  the  tube  to  heat  the  tail  and  prevent  the  condensation  of 
vapor  hi  that  part.  A  piece  of  red-hot  charcoal  is  now  applied 
to  that  part  of  the  tube  which  is  occupied  by  the  first  bulb;  this 


48  ORGANIC   ANALYSIS.  [§  180. 

causes  the  efflux  and  evaporation  of  the  contents  of  the  latter; 
the  vapor  passing  over  the  cupric  oxide  suffers  combustion,  and 
thus  the  evolution  of  gas  commences,  which  is  then  maintained 
by  heating  very  gradually  the  first,  and  after  this  the  second  bulb; 
it  is  better  to  conduct  the  operation  too  slowly  than  too  quickly. 
Sudden  heating  of  the  bulbs  would  at  once  cause  such  an  impetuous 
rush  of  gas  as  to  eject  the  fluid  from  the  potash  bulbs.  The  tube 
is  finally  in  its  entire  length  surrounded  with  ignited  charcoal 
and  the  rest  of  the  operation  conducted  in  the  usual  way.  If  the 
air  drawn  through  the  apparatus  tastes  of  the  analyzed  substance, 
this  is  a  sure  sign  that  complete  combustion  has  not  been  effected. 

2.  In  the   combustion   of  liquids  of  high  boiling  point    and 
abounding  in  carbon,  e.g.,  ethereal  oils,  unconsumed  carbon  is  apt 
to  deposit  on  the  completely  reduced  copper  near  the  substance; 
it  is  therefore  advisable  to  distribute  the  quantity  intended  for 
analysis  (about  0-4  grm.)  in  3  bulbs,  separated  from  each  other  in 
the  tube  by  layers  of  cupric  oxide. 

3.  In  the  combustion  of  less  volatile  liquids,  it  is  advisable  to 
empty  the  bulbs  of  their  contents  before  the  combustion  begins: 
this  is  effected  by  connecting  the  filled  tube  with  an  exhausting 
syringe  and  rarefying  the  air  in  the  tube  by  a  single  pull  of  the 
handle;    this  will  suffice  to  expand  the  air-bubble  in  each  bulb 
sufficiently  to  eject  the  oily  liquid  from  it,  which  is  then  absorbed 
by  the  cupric  oxide. 

4.  If,  as  frequently  happens,  there  is  reason  to  apprehend  that 
the  cupric  oxide  may  not  suffice  to  effect  the  complete  combustion 
of  the  carbon,  the  process  is  terminated  in  a  stream  of  oxygen  gas 
which,  as  in  §  178,  b,  is  finally  passed  through  the  red-hot  tube 
shown  in  Fig.  38,  or  which  is  evolved  from  some  potassium  chlo- 
rate or  perchlorate  placed  in  the  hinder  end  of  the  tube  (see  §  177). 

5.  If  it  is  intended  to  effect  the  combustion  in  the  apparatus 
described  in  §  178,  a  (using  a  boat  and  oxygen  gas),  place  the  bulb 
or  bulbs,  with  their  points  broken  off,  in  the  boat  in  the  tube  pre- 
viously prepared,  heat  first  the  anterior  end  of  the  tube,  then  the 
hinder  end,  and  thus  burn  the  evaporated  substance  in  a  slow 
current  of  air.     Oxygen  is  then  passed  through,  and  finally  air. 


•§  181.]    COMBUSTION    WITH    CUPRIC    OXIDE    AND    OXYGEN.         49 

This    method    requires    great  care  with  very  volatile  liquids,  as, 
e.g.,  ether,  on  account  of  the  explosions  which  may  take  place. 

ft.  Non-volatile  Liquids  (e.g.,  fatty  oils). 

§181. 

The  combustion  of  non -volatile  liquids  is  effected  either,  1,  with 
lead  chromate,  or  cupric  oxide  with  potassium  chlorate  or  per- 
chlorate,  or  completed  in  a  current  of  oxygen  according  to  §  178,  b; 
or,  2,  in 'the  apparatus  described  in  §  178,  a. 

1.  The  operation  is  conducted  in  general  as  directed,  §  176,  §  177, 
or  §  178,  b.  The  substance  is  weighed  in  a  small  tube  placed  for 
that  purpose  in  a  tin  foot  (see  Fig.  42),  and  the  mixing  effected  as 
follows:  Introduce  into  the  combustion  tube  first  a 
layer,  about  6  cm.  long,  of  chromate  of  lead  or  of 
cupric  oxide,  with  or  without  potassium  chlorate  ac- 
cording to  circumstances;  then  drop  in  the  small 
cylinder  with  the  substance  and  let  the  oil  completely 
run  out  into  the  tube ;  make  it  spread  about  in  various  ~  FIG.  42. 
directions,  taking  care,  however,  to  leave  the  upper  side  (intended 
for  the  channel)  and  the  fore  part,  to  the  extent  of  J  or  J  of  the 
length  of  the  tube,  entirely  clean.  Fill  the  tube  now  nearly  with 
chromate  of  lead  or  cupric  oxide — which  has  previously  been 
cooled  in  the  filling  tube  or  flask — taking  care  that  the  little  cylin- 
der which  contained  the  oil  be  completely  filled  with  the  oxidizing 
agent.  Place  the  tube  in  hot  sand,  which,  imparting  a  high  degree 
of  fluidity  to  the  oil,  leads  to  the  perfect  absorption  of  the  latter 
by  the  oxidizing  agent,  exhaust  if  necessary,  and  proceed  with  the 
combustion  in  the  usual  way.  It  is  advisable  to  select  a  tolerably 
long  tube.  Chromate  of  lead  is  usually  to  be  preferred.  If  it  is 
used,  a  very  intense  heat,  sufficiently  strong  to  fuse  the  contents 
of  the  tube,  is  cautiously  applied  in  the  last  stage  of  the  pro- 
cess. 

Solid  fats  or  waxy  substances  which,  not  being  reducible  to 
powder,  cannot  be  mixed  with  the  oxidizing  agent  in  the  usual 


50  ORGANIC   ANALYSIS.  [§  181. 

way,  are  treated  like  fatty  oils.  They  are  fused  in  a  small  weighed 
glass  boat,  made  of  a  tube  divided 
lengthwise,  Fig.  43;  when  cold,  the 
little  boat  with  its  contents  is  weighed 
and  then  dropped  into  the  combustion 

tube,  which  has  been  previously  filled  to  the  extent  of  about  6  cm. 
with  chromate  of  lead  or  with  cupric  oxide  (mixed,  according  to 
circumstances,  with  potassium  chlorate).  The  substance  is  then 
fused  by  the  application  of  heat  and  made  to  spread  about  in  the 
tube  in  the  same  manner  as  is  done  with  fatty  oils,  the  rest  of  the 
operation  also  being  conducted  oxactly  as  in  the  latter  case.  If 
chromate  of  lead  is  employed,  it  will  be  found  advantageous  to 
add  some  potassium  dichromate  (§  176).  If  cupric  oxide  be  used, 
finish  in  a  stream  of  oxygen. 

2.  If  it  is  intended  to  effect  the  combustion  of  fatty  substances 
or  other  bodies  of  the  kind  in  a  tray,  in  a  current  of  oxygen  gas, 
by  means  of  the  apparatus  described  in  §  178,  a,  the  substance  is 
weighed  in  a  porcelain,  copper,  or  platinum  boat,  which  is  in- 
serted into  the  tube  prepared  as  usual.  The  combustion  must 
be  conducted  with  great  care.  As  soon  as  the  cupric  oxide  in 
the  anterior  and  the  copper  roll  in  the  posterior  parts  of  the  tube 
are  red-hot,  establish  a  slow  current  of  oxygen  and  apply  a  piece 
of  red-hot  charcoal  or  a  hot  tile  to  the  part  occupied  by  the  sub- 
stance. The  volatile  products  generated  by  the  dry  distillation 
of  the  substance  burn  at  the  expense  of  the  cupric  oxide. 

When  it  is  perceived  that  the  surface  layer  of  the  cupric  oxide 
is  reduced,  the  application  of  heat  to  the  substance  is  suspended 
for  a  time  and  resumed  only  after  the  reduced  copper  is  reoxi- 
dized  in  the  stream  of  oxygen  gas.  Care  is  finally  taken  to  insure 
the  complete  combustion  of  the  carbon  remaining  in  the  boat. 


§   182.]  MODIFIED    APPARATUS.  51 

Supplement  to  A,  §§  174-181.* 

§182. 
MODIFIED  APPARATUS. 

1.  For  Connecting  the  Calcium-chloride   Tube   with    the  Com- 

bustion Tube. 

As  is  well  known,  BERZELIUS,  unlike  LIEBIG,  did  not  connect 
the  combustion  tube  with  the  calcium-chloride  tube  by  means  of 
a  cork,  but  drew  the  fore  end  out  into  a  long  point,  which  was  first 
bent  upwards  in  an  obtuse  angle,  then  downwards,  and  connected 
by  means  of  a  rubber  bandage  with  a  peculiarly  shaped  calcium- 
chloride  tube,  into  the  bulb  of  which  it  projected.  This  arrange- 
ment was,  however,  inconvenient  when  the  tubes  were  to  be  charged 
at  the  mouth.  A  similar  arrangement  was  later  recommended 
by  LOWE  f  for  tubes  open  behind.  He  draws  out  the  anterior 
end  to  a  not  too  thin  or  narrow  point,  which  is  slightly  bent  near 
its  orifice,  and  fixes  it  by  means  of  a  perforated  rubber  stopper  into 
the  side  tubulure  of  a  U-shaped  calcium-chloride  tube  bulb.  LOWE 
extols  this  form  of  joint  because  it  does  not  loosen  as  the  tube 
expands,  as  is  usually  the  case,  but  on  the  contrary  it  becomes 
tighter.  AL.  MITSCHERLICH  %  also  draws  out  the  front  end  of  the 
combustion  tube  straight  and  fixes  the  point  by  means  of  a  short 
section  of  rubber  tubing  into  the  water-absorption  apparatus  (a 
tube  filled  with  phosphoric  anhydride). 

2.  For  the  Absorption  of  Water. 

As  is  well  known,  calcium  chloride  is  not  capable  of  completely 
drying  moist  gases,  but  is  surpassed  in  this  respect,  according  to 
the  author's  experiments,§  by  concentrated  sulphuric  acid;  this 
hi  turn  is  surpassed,  although  only  to  a  very  slight  extent,  ||  by 

*  The  methods  of  estimating  oxygen  directly,  and  detailed  under  this 
head  in  the  previous  edition,  are  here  discussed  in  §  192. 
f  Zeitschr.  f.  analyt.  Chem.,  ix,  218. 

J  Elementaranal.  durch  Quecksilberoxyd,  Berlin,  Mittler  u.  Sohn,  1875. 
§  Zeitschr.  f.  analyt.  Chem.,  iv,  177.       ||  Compare  DIBBITS,  ibid.,  xv,  154. 


52  ORGANIC   ANALYSIS.  [§   182. 

phosphoric  anhydride.  Many  chemists  hence  replace  the  calcium- 
chloride  tube  by  one  containing  sulphuric  acid.  For  this  purpose 
email  U-tubes  having  the  forms  shown  in  Figs.  13, 
14,  and  15  answer.  The  tubes  are  filled  with 
pieces  of  ignited  pumice-stone  or  glass  moistened 
with  pure  concentrated  sulphuric  acid.  SCHROT- 
TER  *  recommends  the  form  shown  in  Fig.  44. 
Both  tubes  contain  pumice-stone  moistened  with 
sulphuric  acid,  and  a  small  quantity  of  the  acid 
is  also  introduced  into  the  bulb. 

I  would  point  out  that  when  sulphuric  acid 
is  used  for  absorbing  the  water  generated  during 

the  combustion,  it  must  also  be  used  for  drying 
FIG.  44. 

the  oxygen  and  air  passed  through  the  apparatus, 

because  if  air  dried  by  calcium  chloride  is  passed  into  the  tube 
and  exits  through  sulphuric  acid,  or  vice  versa,  small  errors  will 
result  (compare  the  author's  experiments,  loc.  tit.,  182;  also  DIE- 
BITS,  loc.  tit.,  145).  That  sulphuric  acid  is  likely  to  retain  carbonic 
acid,  as  HLASIWETZ  f  believes  to  have  found,  is  not  to  be  feared 
(compare  the  author's  experminets,  loc.  tit.,  183). 

Tubes  filled  with  phosphoric  anhydride  are  also  very  well 
adapted  for  absorbing  moisture,  and  have  been  recently  strongly 
recommended  by  AL.  MITSCHERLK&  (loc.  tit.).  The  tube  used  by 
him  has  the  form  shown  in  Fig.  45.  It  has  a  bore  of  15  mm. 
and  a  length  of  200  mm.  The 
phosphoric  anhydride  is  confined 
between  two  asbestos  plugs  and 
must  not  contain  the  slightest  trace 

of  admixed  phosphorus.  If,  during  the  analysis,  a  notable  quan- 
tity of  water  has  been  taken  up,  and  if  there  is  any  possibility  that 
chlorine,  hydrochloric  acid,  carbonic  acid,  etc.,  may  have  been 
absorbed,  these  may  be  expelled  by  finally  heating  the  tube  only 
to  such  a  point  that  moist  filter-paper  hisses  when  applied  to  it. 
It  will  then  retain  only  the  water. 

*  Zeitschr.  /.  analyt.  Chem.,  vm,  199.  f  Chem.  CentralbL,  1856,  517. 


§  182.]  MODIFIED    APPARATUS.  53 

The  wide  end  of  the  phosphoric-anhydride  tube  is,  as  above 
mentioned,  connected  with  the  drawn-out  end  of  the  combustion 
tube. 

3.  Far  the  Absorption  of  Carbonic  Add. 

a.  LIEBIG'S  potash  bulbs  have  been  variously  modified.  GEISS- 
LER'S  apparatus,  Fig.  46,  stands  without  support,  and  affords 
greater  certainty  of  action  in  that  the  gas  passes  thrice  through 
the  potassa  solution  and  renders  ejection  of  the  latter  almost 
impossible.  The  filling  and  emptying  of  the  apparatus  is  very 
simple.  In  filling,  a  is  dipped  into  the  potassa  solution  and 
suction  applied  to  b;  in  emptying,  simply  blow  into  6.  One  ob- 
jection to  the  GEISSLER  apparatus  is  that  the  potassa  solution  in 
the  three  bulbs  does  not  communicate;  hence  potassium  bicar- 
bonate is  very  prone  to  form  in  the  first  bulb  and  stop  the  tube. 
On  this  account  the  GEISSLER  apparatus  requires  refilling  much 
more  frequently  than  LIEBIG'S  (J.  LOWE  *). 


FIG.  46.  FIG.  47. 

Fig.  47  shows  E.  MITSCHERLICH'S  apparatus  slightly  modified 
by  AL.  MITSCHERLICH.  a  b  is  first  filled  with  pieces  of  potassa,  and 
b  c  then  filled  with  phosphoric  anhydride,  with  a  plug  of  asbestos 
at  b  and  c.  c  is  now  pushed  over  a  short  piece  of  rubber  tubing 
slipped  over  a  small  glass  tube,  and  the  apparatus  then  filled  with 
potassa  solution  to  such  a  height  that,  when  the  apparatus  is  held 
in  a  slanting  position,  the  gas  passing  through  will  force  some  of 
the  solution  into  the  top  bulb. 

DE  KoxiNCKf  modifies  E.  MITSCHERLICH'S  apparatus  by 
bending  the  tubes  connecting  the  bulbs  and  letting  them  enter 
the  bulbs  laterally. 

*  Zeitschr.  f.  analyt.  Chem.,  vii,  224.  f  Ibid.,  ix,  481. 


54  ORGANIC   ANALYSIS.  [§   182. 

MODIFIED  APPARATUS  FOR  THE  ABSORPTION  OF  CARBONIC  ACID, 
b.  G.  J.  MULDER  *  has  replaced  the  potash  bulbs  altogether  by 
a  totally  different  absorption  apparatus,  in  which  soda-lime  is  used 
instead  of  potassa  solution.    The  calcium-chloride  tube  is  imme- 
diately connected  with  the  sys- 
tem of  U-tubes,  Fig.  48;   a  con- 
tains small  pieces  of  glass,  6  to 
10  drops  concentrated  sulphuric 
acid,    and    at   the    top   asbestos 
plugs,    b  is  filled  to  J  with  granu- 
lated   soda-lime    (say    20    grm.), 
the  remaining  -J  (in  the  2d  limb) 
contains    calcium    chloride    (say 
3  grm.).    Lastly,  c  is  filled  with 

lumps  of  potassa.    a  and  b  are 
FIG.  48. 

weighed  together,  c  serves  as  a 

guard  to  b}  and  is  not  weighed.  The  sulphuric-acid  tube  serves 
to  show  the  rate  of  the  evolution  of  gas;  it  contains  enough  sul- 
phuric acid  when  the  lower  part  is  just  stopped  up.  If  the  process 
goes  on  properly,  the  weight  of  the  tube  does  not  increase  more  than 
0.001  grm.;  generally  the  increment  is  unweighable.  If  the  tube 
is  closed  with  caoutchouc  caps  after  use,  it  may  be  used  over  and 
over  again.  The  sulphuric  acid  possesses  the  advantage  over  other 
fluids  that  it  indicates  whether  the  combustion  was  complete  or 
not;  for  in  the  first  case  it  remains  colorless,  in  the  second  it  be- 
comes brown  from  the  escaping  hydrocarbons,  and  then  the  results 
cannot  be  expected  to  be  perfectly  accurate. 

From  experiments  made  by  me,  it  would  appear  that  the  in- 
crease in  the  sulphuric-acid  tube  is  due  to  the  fact  that  the  air 
dried  only  by  passage  through  calcium  chloride  still  yields  a  trace 
of  moisture  to  sulphuric  acid.  The  sulphuric-acid  tube  may  be 
quite  readily  dispensed  with,  and  all  the  advantages  it  offers  may 
be  obtained  by  using  SCHROTTER'S  sulphuric-acid  tube,  Fig.  44, 
for  absorbing  moisture.  The  absorption  of  the  carbonic  acid  by 

*  Zeitschr.  /.  analyt.  Chem.,  i,  2. 


$   182.J  MODIFIED    APPARATUS.  55 

the  soda-lime  tube  is  as  rapid  as  it  is  complete;  even  when  a  stream 
of  carbonic  acid  is  passing,  with  ten  times  the  rapidity  usual  in 
organic  analysis,  no  trace  of  the  acid  makes  its  escape.  The 
absorption  of  the  carbonic  acid  is  attended  with  warming  of  the 
soda-lime;  if  any  water  evaporates  from  the  soda-lime,  it  is  re- 
tained by  the  calcium  chloride  in  the  second  limb.  The  corks  of 
the  absorption  tubes  are,  like  the  others,  coated  with  sealing-wax. 
A  filled  soda-lime  tube  weighs  about  40  grm.  The  first  time  it  is 
used  alone;  the  second  time  the  same  tube  is  used,  but  as  a  pre- 
cautionary measure  a  second  similarly  rilled  and  separately  weighed 
tube  is  placed  in  front  of  it.  The  second  tube  rarely  increases  in 
weight,  and  unless  it  does,  the  first  tube  can  be  used  a  third  tune, 
but  of  course  in  connection  with  the  second.  If  the  second  tube 
has  gained  in  the  third  operation,  the  first  tube  is  rejected  at 
the  fourth  operation,  and  the  second  is  now  used  alone,  etc. 
If  after  the  combustion  a  stream  of  oxygen  is  transmitted 
through  the  combustion  tube,  the  tubes  are  of  course  at  the  end 
full  of  oxygen.  If,  then,  care  be  taken  that  the  tubes  are  full  of 
oxygen  before  weighing,  the  trouble  of  the  final  transmission  of 
air  may  be  saved.  For  weighing,  MULDER  closes  the  ends  of  the 
glass  tubes  with  caps  made  from  india-rubber  tubing.  According 
to  DIBBITS,*  however,  this  is  not  to  be  recommended. 

MULDER'S  absorption  apparatus  is  peculiarly  suitable  when  the 
carbonic  acid  is  mixed  with  another  gas.  It  insures  complete 
absorption,  precludes  the  evaporation  of  any  water,  and  offers 
perfect  security  in  case  of  the  sudden  occurrence  of  a  too  rapid 
evolution  of  gas. 

If  it  be  desired  to  proceed  strictly  according  to  theory  when 
using  a  sulphuric-acid  tube  for  absorbing  moisture,  the  fore  part 
of  the  soda-lime  tube  must  be  connected  with  a  small  sulphuric- 
acid  tube,  which  is  to  be  weighed  with  it,  to  remove  any  trace  of 
moisture  that  may  not  have  been  absorbed  by  the  soda-lime  and 
calcium  chloride.  Instead  of  soda-lime,  KREUSLER  f  recommends 


*  Zeitschr.  f.  analyt.  Chem.,  xv,  157. 
f  Ibid.,  v,  216. 


56  ORGANIC   ANALYSIS.  [§  183. 

barium  hydroxide,  which  also  absorbs  carbonic  acid  most  com- 
pletely. 

B.  ANALYSIS  OF  COMPOUNDS  CONSISTING  OF  CARBON,  HYDROGEN, 
OXYGEN,  AND  NITROGEN. 

The  principle  of  the  analysis  of  such  compounds  is  in  general 
this :  In  one  portion  the  carbon  and  .the  hydrogen  are  determined 
.as  carbonic  acid  and  water  respectively;  in  another  portion  the 
nitrogen  is  determined  either  in  the  gaseous  form,  or  as  ammonium 
platinic  chloride,  or  by  determining  volumetrically  the  ammonia 
formed  from  the  nitrogen;  the  oxygen  is  calculated  from  the  loss. 

As  the  presence  of  nitrogen  exercises  a  certain  influence  upon 
the  estimation  of  carbon  and  hydrogen,  we  have  here  to  consider 
not  only  the  method  of  determining  the  nitrogen,  but  also  the 
modifications  which  the  presence  of  the  nitrogen  renders  necessary 
in  the  usual  method  of  determining  the  carbon  and  hydrogen. 

a.  DETERMINATION  OF  THE  CARBON  AND  HYDROGEN  IN  NITROG- 
ENOUS SUBSTANCES. 

§183. 

1.  When  nitrogenous  substances  are  ignited  with  cupric  oxide 
or  with  lead  chromate,  a  portion  of  the  nitrogen  present  escapes 
in  the  gaseous  form,  together  with  the  carbonic  acid  and  aqueous 
vapor;  whilst  another  portion,  minute  indeed,  still,  in  bodies 
abounding  in  oxygen,  not  quite  insignificant,  is  converted  into 
nitric-oxide  gas,  which  is  subsequently  transformed  wholly  or 
partially  into  nitrous  or  hyponitric  acid  by  the  air  in  the  apparatus. 
The  application  of  the  methods  described  in  §§  174,  etc.,  in  the 
analysis  of  nitrogenous  substances  would  accordingly  give  too  much 
carbon;  since  the  potash  bulbs  would  retain,  besides  the  carbonic 
acid,  also  the  nitrous  acid  formed  and  a  portion  of  the  nitric  oxide 
(which  in  the  presence  of  potassa  decomposes  slowly  into  nitrous 
acid  and  nitrous  oxide).  This  defect  may  be  remedied  either  by 
intimately  mixing,  slowly  burning,  and,  when  possible,  avoiding 
the  use  of  any  potassium  chromate  or  chlorate  (because  when 


§  183.]     DETERMINATION    OF    CARBON    AND    HYDROGEN.  57 

using  these  and  burning  rapidly  the  evolution  of  nitric  oxide  is 
much  greater  than  when  employing  cupric  oxide  alone  and  slowly 
burning),  or  by  selecting  a  combustion  tube  about  12-15  cm. 
longer  than  those  commonly  employed,  filling  this  in  the  usual 
way,  but  finishing  with  a  loose  layer,  about  9-12  cm.  long,  of  clean, 
fine  copper  turnings  (§66,  5),  or  a  compact  roll  of  copper  wire 
gauze.  The  roll  of  copper  gauze  in  front  of  the  oxide  should  not 
be  previously  oxidized  (as  is  recommended  for  substances  free  from 
nitrogen,  chlorine,  and  bromine),  but  should  be  in  the  metallic  state.* 
The  process  is  commenced  by  heating  these  copper  turnings  to 
redness,  in  which  state  they  are  maintained  during  the  whole  course 
of  the  operation.  These  are  the  only  modifications  required  to 
adapt  the  methods  above  described  for  the  analysis  of  nitrogenous 
substances.  The  use  of  the  metallic  copper  depends  upon  its 
property  of  decomposing,  when  in  a  state  of  intense  ignition,  all 
the  oxides  of  nitrogen  into  oxygen,  with  which  it  combines,  and 
into  pure  nitrogen  gas.  As  the  metal  exercises  this  action  only 
when  in  a  state  of  intense  ignition,  care  must  be  taken  to  maintain 
the  anterior  part  of  the  tube  in  that  state  throughout  the  process, 
and  that  the  operation  is  not  conducted  too  rapidly.f  As  metallic 
copper  recently  reduced  retains  hydrogen  gas,  and,  when  kept  for 
some  time,  aqueous*  vapor  condensed  on  the  surface,  the  copper 
turnings  intended  for  the  process  must  be  introduced  into  the  tube 
hot  as  they  come  from  the  drying  closet  (which  is  heated  to  100°). 
v.  LIEBIG  recommends  to  compress  the  hot  turnings  in  a  tube  into 
a  cylindrical  form,  to  facilitate  their  rapid  introduction  into  the 
combustion  tube.  Spirals  of  copper  gauze  are,  however,  more 
convenient. 

2.  If  it  is  intended  to  burn  nitrogenous  bodies  in  the  apparatus 
described  in  §  178,  a,  a  combustion  tube,  about  80  cm.  long,  must 

*  The  copper  turnings  or  gauze  cannot  be  replaced  by  the  metallic  powder 
obtained  by  the  reduction  of  the  oxide  with  hydrogen,  as  this  obstinately 
retains  hydrogen  and  consequently  decomposes  appreciable  quantities  of 
carbonic  acid  with  formation  of  carbonic  oxide.  SCHROTTER,  LAUTEMANN, 
Journ.  f.  prakt.  Chem.,  LXXVII,  316. 

t  Compare  THORPE,  Journ.  Chem.  Soc.,  1866,  xix,  359;  Chem.  Centrafol., 
1867,  205;  Zeitschr.  /.  analyt.  Chem.,  v,  413. 


58  ORGANIC    ANALYSIS.  [§  183. 

be  used,  and  the  fore  part  filled,  for  a  length  of  15-18  cm.,  with 
clean  copper  turnings  or  a  copper-gauze  spiral  of  similar  length. 
Care  must  be  taken  to  keep  at  least  the  anterior  half  of  the  roll 
from  oxidizing,  both  during  the  ignition  in  the  current  of  air  and 
during  the  actual  process  of  combustion.  When  the  operation 
is  terminated,  and  the  oxidation  of  the  metallic  copper  is  visibly 
progressing,  the  oxygen  is  turned  off,  and  the  cock  of  the  air  gaso- 
meter opened  a  little  instead,  to  let  the  tube  cool  in  a  slow  stream 
of  atmospheric  air. 

3.  Since  the  metallic  copper  is  usually  oxidized  during  each 
combustion  and  must  be  reduced  again,  STEIN  *  uses  silver  instead 
of  copper  (turnings  of  finest  silver  thread).  Silver  has  the  addi- 
tional advantage  that -it  retains  also  chlorine.  According  to  the 
investigations  of  CALBERLA,  silver  at  a  red  heat  reduces  oxides  of 
nitrogen  completely,  while  it  does  not  exercise  the  least  influence 
on  carbonic  acid. 

b.  NITROGEN  DETERMINATION  IN  ORGANIC  COMPOUNDS. 

As  already  indicated,  two  essentially  different  methods  are  in 
use  for  effecting  the  determination  of  the  nitrogen  in  organic  com- 
pounds, viz.,  the  nitrogen  is  either  separated  in  the  pure  form  and 
its  volume  measured,  or  it  is  converted  into  ammonia,  and  this  is 
determined  either  as  ammonium  platinic  chloride,  or  platinum,  or 
volumetrically  by  neutralization. 

a.  Determination  of  Nitrogen  from  the  Volume. 

The  many  methods  recommended  for  effecting  this  purpose 
may  be  arranged  under  two  heads.  The  object  of  the  one  is  to 
collect  all  the  nitrogen  contained  in  a  weighed  portion  of  the  sub- 
stance. In  the  other,  only  the  relative  proportion  between  the 
carbonic  acid  and  nitrogen  evolved  is  determined,  and  from  this 
the  quantity  of  nitrogen  is  calculated,  which  requires  that  the 
quantity  of  carbon  contained  in  the  substance  must  be  previously 
known.  The  methods  based  upon  the  first-named  principle  are 
termed  absolute  or  quantitative;  those  based  on  the  latter  are  desig- 
nated as  relative  or  qualitative.  I  have  selected  from  both  classes 


*  Zeitschr.  f.  analyt.  Chem.,  vin,  83. 


§  184.]  NITROGEN    DETERMINATION.  59 

those  methods  which  are  more  easily  carried  out  and  which  afford 
the  most  accurate  results. 

1.  RELATIVE  DETERMINATION  OF  NITROGEN  FROM  THE  VOLTJM?. 

§  184. 

da.  LIEBIG'S  Method.* 

This  method  is  applicable  only  to  substances  which  do  not  con- 
tain too  small  a  quantity  of  nitrogen  compared  with  their  carbon 
content  (see  also  below).  It  requires  6  to  8  accurately  graduated 
strong  glass  tubes,  each  about  30  cm.  long  and  15  mm.  bore;  also 
a  tall  cylinder  of  strong  glass  widened  at  the  top  (Fig.  50). 

Into  the  sealed  hinder  end  of  a  60-cm.  combustion  tube  in- 
troduce a  6-cm.  layer  of  cupric  oxide,  then  an  intimate  mixture  of 
0-5  grm.t  of  the  very  finely  powdered  substance  with  sufficient 
cupric  oxide  to  about  half  fill  the  tube,  next  another  layer  of  the 
pure  cupric  oxide,  and  finally  enough  copper  turnings  or  a  copper- 
gauze  spiral  to  fill  the  remaining  space  (§  66,  5)  of  at  least 
12  cm.  Connect  the  tube  so  prepared  with  the  delivery  tube,  place 
it  in  the  combustion  furnace,  and  heat  the  anterior  part  to  bright  red- 
ness (which  must  be  maintained  during  the  entire  operation),  while 
that  part  of  the  tube  in  which  the  substance  is  contained  is  pro- 
tected from  the  heat  by  a  screen,  which  is  shifted  back  3  cm.  at  a 
time  as  the  heat  is  gradually  advanced  toward  the  tail  end  of  the 
tube.  When  about  one-fourth  of  the  substance  has  been  decom- 
posed, and  the  combustion  products  have  almost  completely  dis- 
placed the  atmospheric  air  in  the  tube,  invert  one  of  the  graduated 
tubes  filled  with  mercury  %  over  the  mouth  of  the  delivery  tube 
which  dips  into  mercury,  let  it  fill  three-fourths  with  the  gas,  then 
remove  it  from  the  mercury  trough  so  that  the  rest  of  the  mercury 
may  run  out,  and  observe  whether  the  gas  has  acquired  any  color, 
looking  through  the  tube  lengthwise.  If  not  the  slightest  redness 
is  observable,  the  operator  may  be  certain  that  the  gas  contains 

*  Handbook  of  Organic  Analysis,  2d  ed.,  p.  66. 

t  The  weight  need  not  be  more  accurately  known. 

J  In  order  to  fill  a  tube  so  that  no  air-bubbles  will  be  left  in  it,  pour  the 
mercury  into  a  funnel  the  stem  of  which  reaches  to  the  bottom  of  the  tube, 
place  a  finger  over  the  orifice,  and  invert  the  tube,  manipulating  so  that  the 
small  bubbles  may  unite  with  the  large  one,  and  finally  fill  completely  full. 


60 


ORGANIC    ANALYSIS. 


[§  184. 


no  admixed  nitric  oxide.  (This  test  must  be  repeated  near  the 
middle  and  at  the  end  of  the  operation  in  order  to  be  absolutely 
certain  that  no  nitric  oxide  is  present  in  any  of  the  tubes.)  After 
this  preliminary  test,  fill  the  graduated  tubes  one  after  another 
(Fig.  49),  while  the  heating  is  slowly  and  uniformly  continued. 


FIG.  49. 

This  operation  requires  a  stand  capable  of  receiving  and  holding 
6  to  8  tubes,*  or  an  assistant  must  hold  the  tubes.  The  tubes 
should  be  marked  in  the  order  in  which  they  were  filled. 

When  all  the  tubes  are  filled,  the  gaseous  mixture  in  each  is 
determined  in  the  following  manner: 
First  immerse  the  tube  fully  in  the 
mercury  contained  in  the  cylinder, 
Fig.  50,  so  that  the  temperature  of  the 
gases  may  be  uniform  and  correspond 
with  that  of  the  mercury;  next  raise 
the  tube  until  the  mercury  stands 
exactly  at  the  same  level  inside  and 
outside  the  tube,  and  note  the  volume 
(§13,  Vol.  I).  A  small  quantity  of 
potassa  solution  is  now  introduced 
into  the  tube  by  cautiously  blowing 
into  the  pipette,  Fig.  51,  which  is 
filled  with  the  potassa  solution,  and 
the  lower  end  of  which  is  bent  up- 
wards and  inserted  into  the  tube.  The  absorption  of  the  car- 
bonic acid  is  facilitated,  after  removing  the  pipette,  by  moving 


*  Such  a  stand  is  figured  and  described  in  "Das  Chem.  Laboratorium  zu 
Giessen,"  von  J.  P.  HOFMANN,  Heidelberg,  1842. 


§    184.J  NITROGEN    DETERMINATION.  61 

the  firmly  held  tube  up  and  down  in  the  mercury,  while  pressing 
its  mouth  firmly  against  the  side  of  the  cylinder;  finally, 
again  completely  immerse  the  tube,  raise  until  the  mer- 
cury level  is  restored,  and  read  off  the  volume.  (The 
pressure  exerted  by  the  small  column  of  potassa  solution 
may  be  entirely  disregarded.)  The  difference  between  the 
volume  found  on  the  second  reading  (nitrogen)  and  the 

x  IG.  oL . 

volume  first  noted  (nitrogen -f  carbonic-acid  gas)  gives 
the  carbonic-acid  gas  present.  When  the  gaseous  contents  of  one 
tube  have  been  thus  ascertained,  purify  the  mercury  by  washing  it 
with  water  acidulated  with  a  little  hydrochloric  acid,  then  with 
pure  water  and  blotting-paper,  and  proceed  with  the  next  tube. 
As  a  rule,  the  results  obtained  from  the  individual  tubes  agree 
quite  closely;  in  many  cases,  however,  where,  for  instance,  the 
nitrogenous  substance  decomposes  into  decomposition  products  of 
varying  volatility  before  combustion  is  complete,  notable  differences 
are  observed  in  the  individual  tubes.  As  a  rule,  the  arithmetical 
mean  is  taken  as  correct,  and  may  be  considered  the  more  reliable 
the  less  the  differences  between  the  individual  tubes.  Should  the 
first  tubes,  however,  give  a  decidedly  larger  volume  of  nitrogen 
than  those  filled  later,  it  may  be  assumed  that  the  air  had  not  been 
completely  expelled  when  the  first  tubes  were  filled;  in  this  case 
these  tubes  are  not  taken  into  account. 

The  relative  proportion  of  carbonic-acid  gas  to  nitrogen  ex- 
presses directly,  and  without  requiring  further  calculation,  the 
proportion  between  the  equivalents  of  carbonic-acid  gas  and  nitro- 
gen, since  1  eq.  of  carbon  combines  with  2  eq.  of  oxygen  without 
in  any  way  changing  the  volume  of  the  latter,  and  hence  gives 
2  volumes  of  carbonic-acid  gas;  1  eq.  of  nitrogen  gives  similarly 
2  volumes  of  nitrogen  gas. 

Suppose  the  proportion  of  carbonic-acid  gas  to  nitrogen  gas 
had  been  found  to  be  as  4  :  1,  then  the  compound  would  have 
contained  for  every  equivalent  of  nitrogen,  14-04,  4  eq.  of  carbon 
=  4X  12  =  48.  If,  therefore,  we  had  found  in  100  parts  of  analyzed 
substance  52  parts  of  carbon,  the  substance  would  have  contained 
15-21  parts  of  nitrogen,  since  48  : 14-04  ::  52  :z=15-21. 

The  method  of  estimating  nitrogen  above  described  possesses 


62  ORGANIC    ANALYSIS.  [§  184. 

one  inherent  source  of  error,  in  that  the  air  is  not  completely  ex- 
pelled from  the  combustion  tube,  and  this  always  gives  too  high 
a  nitrogen  content.  This  error,  however,  leaves  no  doubt  as  to 
the  correctness  of  the  proportion  if  the  volume  of  nitrogen  is  con- 
siderable. For  instance,  had  the  proportion  been  found  to  be 
1:4-1,  it  would  be  at  once  evident  that  the  correct  ratio  would 
be  1:4.  Where  the  nitrogen  content  is  relatively  small,  however, 
the  results  may  be  rendered  erroneous  by  this  error,  and  experience 
has  shown  that  the  method  is  not  applicable  in  cases  where  the 
substance  contains  less  than  1  eq.  of  nitrogen  to  8  eq.  of  carbon. 
bb.  BUNSEN'S  Method.* 

This  method  gives  more  accurate  results,  but  requires  more 
time  and  trouble,  and  demands  greater  skill  than  that  described 
under  aa. 

First  draw  out  one  end  of  a  tube  of  strong,  difficu  tly  fusible 
3,  about  38  cm.  long  and  2  cm.  wide,  as  shown  in  Fig.  52,  A, 
then  narrow  the  part  a  as  in  Fig.  52,5.  This 
latter  manipulation  is  .necessary  in  order  to 
enable  the  tube  to  resist  the  pressure  exerted 
by  the  gas  within  the  tube  during  ignition.  The 
part  drawn  out  must  be  particularly  stout. 

After  the  tubes  have  been  scrupulously 
cleaned,  introduce  an  intimate  mixture  of  about 
5  grm.  of  loose  ignited  cupric  oxide  with  0-03 
to  0-05  grm.  of  the  substance  to  be  analyzed 
(and  which  need  not  be  more  accurately  weighed), 
PIG.  52.  and  also  a  small  quantity  of  clean  copper  turn- 

ings (§66,  5).  Now  draw  out  the  other  end  about  17  to  20  cm. 
from  the  already  narrowed  part,  and  just  as  was  done  before. 
Volatile  fluids  are  best  introduced  in  capillary  tubes  sealed  at  one 
or  both  ends. 

The  tube,  as  shown  in  Fig.  53,  is  now  connected  at  one  end 
with  the  bulb  B  half  filled  with  sulphuric  acid,  by  which  the 
hydrogen  gas  generated  in  A  is  dried;  the  other  end  is  connected 

*  See  KOLBE'S  paper  on  the  subject  in  the  Handworterbuch  der  Chemie, 
Supplemente  zur  ersten  Auflage,  S.  200. 


§   184.]  NITROGEN    DETERMINATION.  63 

with  the  hand  air-pump,  the  cock  of  which,  p,  is  open,  and  through 
which  the  hydrogen  escapes. 

When  the  hydrogen  has  passed  through  the  apparatus  long 
enough  to  have  rendered  certain  the  expulsion  of  all  the  ah-  in 
it,  close  the  cock  p,  open  A,  compress  c  with  a  screw  pinch-cock, 
rapidly  draw  up  the  piston  of  the  air-pump  and  immediately 


FIG.  53. 

close  the  cock  s.  The  hydrogen  in  the  tube  is  by  this  procedure 
rarefied,  and  the  tube  may  now  be  fused  and  sealed  at  d  with  the 
blowpipe  without  fear  of  any  swelling.  Now  exhaust  as  completely 
as  possible  and  fuse  and  seal  the  tube  at  b  also. 

As  a  tube  so  prepared  would  inevitably  swell  and  blow  out  from 
the  pressure  of  the  evolved  gases  on  being  heated  to  redness  in  the 
usual  manner,  it  is  inclosed  in  a  strong  sheet-iron  mold  shown  in 
Fig.  54. 

This  mold  is  made  in  two  parts  which  accurately  fit  each  other 
and  afford  a  cylindrical  cavity  30  cm.  long  and  5  to  6  cm.  in  diame- 
ter. Fill  the  two  halves  with  freshly  prepared  plaster-of-Paris,  to 
which  has  been  added  a  handful  of  cut  cow's  hair,  press  the  com- 
bustion tube  into  middle  of  one  of  the  halves,  cover  it  with  the 
other  as  soon  as  the  plaster  begins  to  set,  and  clamp  the  two  halves 
together  by  means  of  small  iron  wedges,  as  shown  in  Fig.  55.  Each 


64 


ORGANIC    ANALYSIS. 


L§  184. 


half  of  the  mold  is  provided  with  10  to  12  holes  for  the  escape  of 
aqueous  vapors,  etc. 

After  the  plaster  has  set  completely,  slowly  heat  the  mold  in 
a  suitable  furnace  to  a  dull  redness.    As  soon  as  the  odor  of  burnt 


FIG.  54. 

hair  has  diminished,  and  the  mold  entirely  surrounded  by  live  coal 
is  at  a  red  heat  throughout,  cover  the  coal  with  ashes,  and  con- 
tinue the  heat  thus  for  half  an  hour  longer.  After  cooling,  care- 


FIG.  55. 

fully  remove  the  tube;  it  must  look  dull  and  opaque  and  must 
have  a  blistered  surface — an  evidence  that  it  had  been  completely 
softened  by  the  heat.  If  too  much  substance  is  employed,  or  if 
the  temperature  was  too  high,  the  tube  will  frequently  be  found 
to  have  blown  out  or  swelled  in  some  part.  The  point  of  the  tube 
is  broken  off  under  mercury  in  such  a  manner  that  the  gaseous 
contents  are  received  in  a  graduated  tube  filled  with  mercury  and 
into  which  a  drop  of  water  has  been  introduced  ( §  16) ;  the  already 
moist  gas  is  hereby  fully  saturated  with  aqueous  vapor.  It  is 
unnecessary  to  introduce  the  entire  gaseous  content  of  the  com- 
bustion tube  into  the  measuring  tube,  but  it  is  advisable  to  have 
as  large  a  volume  of  gas  as  possible  for  the  subsequent  analysis. 
Now  make  notes  of  the  barometric  and  thermometric  readings 


§   184.]  NITROGEN    DETERMINATION.  65 

and  the  height  of  the  column  of  mercury  in  the  graduated  tube, 
and  introduce  a  moistened  ball  of  potassa  fused  on  the  end  of  an 
iron  or  platinum  wire  to  absorb  the  carbonic-acid  gas.  Remove 
this  ball  and  introduce  a  second  and  dry  ball,  to  completely  dry 
the  residual  nitrogen,  and  then  measure  the  latter.  Reduce  the 
volume  to  the  same  temperature,  pressure,  and  dryness  and  thus 
ascertain  the  relative  proportion  of  carbonic-acid  gas  to  nitrogen, 
and  consequently  also  the  ratio  of  carbon  to  nitrogen  in  the  analyzed 
substance. 

cc.  MARCHAXD'S  *  process,  modified  by  GOTTLIEB.! 

Draw  out  the  hinder  end  of  a  long  combustion  tube  to  an  open 
point,  then  introduce  an  asbestos  plug,  then  the  mixture  of  0-1 
to  0- 12  grm.  of  the  substance  with  a  large  quantity  of  cupric  oxide, 
then  a  6-cm.  layer  of  pure  cupric  oxide,  next  12  to  14  cm.  of  copper 
turnings,  and  finally  6  cm.  of  coarsely  powdered  fuced  calcium 
chloride.  Now  connect  the  anterior  end  of  the  tube  with  a  delivery 
tube  bent  at  right  angles  and  the  descending  limb  of  which  is 
80  cm.  long,  and  pass  a  current  of  dry  hydrogen  gas  for  two  hours 
through  the  apparatus  by  the  drawn-out  point.  Towards  the  end 
the  tip  of  the  delivery  tube  must  dip  into  a  trough  of  mercury. 
Now  fuse  and  seal  the  hinder  end,  heat  the  pure  cupric  oxide  (the 
oxygen  of  which  combines  with  the  hydrogen,  thus  creating  a 
vacuum),  invert  a  measuring  cylinder  filled  with  mercury  over 
the  end  of  the  delivery  tube  and  proceed  to  effect  the  combustion. 
90  to  100  c.c.  of  gas  are  obtained,  and  of  this  about  one-half  is 
taken  for  the  analysis,  the  remainder  being  used  for  testing  for 
nitric-oxide  gas.  The  results  obtained  by  GOTTLIEB  exhibit  a 
very  satisfactory  degree  of  accuracy.:]: 

dd.  In  SIMPSON'S  §  method  the  combustion  is  carried  out  with 
a  mixture  of  cupric  and  mercuric  oxides.  For  details,  see  the 
original  memoir. 


*  Journ.  /.  prakt.  Chem.,  XLI,  177. 
f  Annal.  d.  Chem.  u.  Pharm.,  LXXVIII,  241. 

%  HEINTZ'S  method  for  the  absolute  estimation  of  nitrogen  is  based  on 
the  same  principle  (Journ.  f.  prakt.  Chem.,  LV,  229). 
§  Annal.  d.  Chem.  u.  Pharm.,  xcrv,  64. 


66 


ORGANIC   ANALYSIS. 


[§  185. 


2.  ABSOLUTE  NITROGEN  DETERMINATION  FROM  THE  VOLUME. 

§185. 

act.  DUMAS'  Method. 

This  method  is  applicable  to  all  organic  nitrogenous  compounds. 
It  requires  a  graduated  glass  cylinder  of  about  200  c.c.  capacity, 
and  which  may  be  closed  by  ground-glass  plate. 

The  combustion  tube  is  about  70  to  80  cm.  long  and  is  sealed 
off  round  at  one  end.  Into  it  introduce  a  layer  of  12  to  15  cm.  of 
pure  dried  sodium  bicarbonate,  then  4  cm.  of  cupric  oxide,  next 
a  very  intimate  mixture  of  the  weighed  substance  (0-3  to  0-6  grm., 
or  in  case  of  substances  poor  in  nitrogen,  still  more)  with  cupric 
oxide,  next  the  oxide  that  has  served  to  rinse  out  the  mortar, 
followed  by  a  layer  of  pure  cupric  oxide,  and  finally  a  15-cm.  layer 
of  metallic  copper  in  the  form  of  a  wire  spiral,  roll  of  thin  sheet 
copper,  or  copper  turnings.*  Make  a  channel  along  the  top  of  the 


FIG.  56. 


tube  by  gentle  tapping,  and  connect  the  tube  with  the  bent  delivery 
tube,  cf,  Fig.  56,  then  place  in  the  furnace.     Now  gradually  heat 


*  MELSENS  (Annal.  d.  Chem.  u.  Pharm.,  LX,  115)  recommends  tubes  of 
1-1  to  1-25  meters  length,  and  fills  them  thus:  Sodium  bicarbonate,  10  cm.; 
coarse  cupric  oxide,  20  cm. ;  the  substance  first  triturated  with  finely  pow- 
dered cupric  oxide,  then  mixed  with  coarser  oxide,  30  cm.;  coarse  oxide, 
30  cm.;  metallic  copper,  20  cm.  STROMEYER  recommends  adding  sodium 
carbonate  to  the  cupric  oxide  in  order  to  prevent  the  formation  of  nitrogen 
oxides  from  the  first  (Annal.  d.  Chem.  u.  Pharm.,  cxvu,  250). 


§   185.]  NITROGEN    DETERMINATION.  67 

to  redness  the  farther  end  of  the  tube  for  a  length  of  about  6  cm., 
while  the  other  parts  are  protected  from  the  heat  by  a  screen. 
The  sodium  bicarbonate  is  decomposed  by  the  heat,  and  the  evolved 
carbonic-acid  gas  drives  out  and  displaces  the  'ah*  in  the  tube. 
When  the  evolution  of  gas  has  proceeded  for  some  time,  immerse 
the  end  of  the  bent  delivery  tube  under  mercury,  invert  over  it 
a  test-tube  filled  with  potassa  solution,  and  advance  the  heat  a 
little  farther  towards  the  fore  part  of  the  tube.  If  the  gas  bubbles 
entering  the  cylinder  are  completely  absorbed  by  the  solution  of 
potassa,  this  is  a  proof  that  the  air  is  thoroughly  expelled  from 
the  tube.  But  should  this  not  be  the  case,  the  evolution  of  carbonic 
acid  must  be  continued  until  the  desired  point  is  attained.  Now 
invert  the  graduated  cylinder,  f  filled  with  mercury  and  J  with  con- 
centrated solution  of  potassa,  over  the  end  of  the  delivery  tube, 
with  the  aid  of  a  ground-glass  plate,*  and  proceed  with  the  com- 
bustion in  the  usual  way,  heating  first  the  anterior  end  of  the  tube 
to  redness  and  advancing  gradually  towards  the  farther  end.  In 
the  last  stage  of  the  process  the  remainder  of  the  sodium  bicar- 
bonate is  decomposed,  so  that  the  whole  of  the  nitrogen  gas  which 
still  remains  in  the  tube  is  forced  into  the  cylinder  by  the  carbonic 
acid  evolved.  Wait  now  until  the  volume  of  the  gas  in  the  cylinder 
no  longer  decreases,  even  upon  shaking  the  latter  (consequently, 
until  the  whole  of  the  carbonic  acid  has  been  absorbed),  then  place 
the  cylinder  in  a  large  and  deep  glass  vessel  filled  with  water,  the 
transport  from  the  mercurial  trough  to  this  vessel  being  effected 
by  keeping  the  aperture  closed  with  a  small  dish  filled  with  mercury, 
or  better,  an  iron  cap  with  sheet-iron  strips  f  riveted  (not  soldered) 

*  The  following  is  the  best  way  of  filling  the  cylinder  and  inverting  it  over 
the  opening  of  the  bent  delivery  tube :  The  mercury  is  introduced  at  first,  and 
the  air-bubbles  which  adhere  to  the  walls  of  the  vessel  are  removed  in  the 
usual  way.  The  solution  of  potassa  is  then  poured  in,  leaving  the  top  of  the 
cylinder  free  to  the  extent  of  about  5  mm. ;  this  is  cautiously  filled  up  to  the 
brim  with  pure  water  and  the  ground-glass  plate  slid  over  it.  The  cylinder 
is  now  inverted  and  the  opening  placed  under  the  mercury  in  the  trough;  the 
glass  plate  is  then  withdrawn  from  under  the  cylinder.  In  this  manner  the 
operation  may  be  performed  easily  and  without  soiling  the  fingers  with  the 
potassa  solution. 

f  REICHARDT,  Zeitschr.  /.  analyt.  Chem.,  v,  67. 


68  ORGANIC    ANALYSIS.  [§   185. 

to  it  (Fig.  57).  The  mercury  and  the  solution  of  potassa  sink  to 
the  bottom  and  are  replaced  by  water.  Immerse  the 
cylinder,  then  raise  it  again  until  the  water  is  inside 
and  outside  on  an  exact  level;  read  off  the  volume  of 
the  gas  and  note  the  temperature  of  the  water  and  the 
state  of  the  barometer;  calculate  the  weight  of  the 
nitrogen  gas  from  its  volume,  after  reduction  to  the 
normal  temperature  and  pressure,  and  with  due  regard 
to  the  tension  of  the  aqueous  vapor  (comp.  "Calcula- 
tion of  Analyses").*  The  results  are  generally  some- 
what too  high,  viz.,  by  about  0 •  2  to  0 •  5  per  cent. ;  this  is 
owing  to  the  circumstance  that  even  long-continued 
transmission  of  carbonic  acid  through  the  tube  fails  to 
expel  every  trace  of  atmospheric  air  adhering  to  the 
cupric  oxide,  and  that  frequently  the  nitrogen  contains 
a  small  quantity  of  admixed  nitric  oxide  (see  below). 
It  is  highly  advisable  before  making  any  nitrogen  determina- 
tions with  this  method  to  subject  a  non-nitrogenous  substance,  e.g., 
sugar,  to  the  same  process.  The  analyst  thereby  acquaints  himself 
with  the  extent  of  the  error  to  which  he  will  be  exposed.  In  such 
.an  experiment  the  quantity  of  unabsorbed  gas  should  not  exceed 
1  or  1-5  c.c. 

To  insure  complete  combustion  of  difficultly  combustible 
bodies,  STRECKER  f  recommends  the  addition  of  arsenous  oxide 
in  powder  to  the  cupric  oxide  with  which  the  substance  is  to  be 
mixed ;  the  arsenous  oxide  is  volatilized  by  the  action  of  the  heat, 
the  fumes  burning  the  whole  of  the  carbon  like  a  current  of  oxygen. 
The  arsenous  oxide  sublimes  in  the  anterior  part  of  the  tube,  and 
arsenic  remains  in  the  copper. 

This  method  has  also  been  modified  in  various  ways. 
THUDICHUM  and  WANKLYN  J  recommend  an  intimate  mixture 
of  5  parts  anhydrous  sodium  carbonate  and   13  parts  of  fused 
potassium  dichromate,  in  powder  form,  for  evolving  carbonic-acid 

*  BROWN  has  given  tables  for  simplifying  the  calculation  (Zeitschr.  f. 
.analyt.  Chem.,  iv,  450). 

f  Handworterbuch  der  Chem.,  2.  AufL,  I,  878. 
J  Journ.  Chem.  Soc.,  xxn,  293. 


§   185.]  NITROGEN    DETERMINATION.  69 

gas.  This  mixture  has  the  advantage  of  containing  no  water. 
These  authors  further  consider  it  necessary  to  adopt  FRANKLAND'S* 
proposal  and  determine  the  nitric  oxide  usually  present  in  small 
quantity  in  the  nitrogen.  This  is  accomplished  by  first  reading  off 
the  volume,  then  admitting  a  small  quantity  of  oxygen,  removing 
the  excess  of  the  latter  not  used  up  in  oxidizing  the  nitric  oxide 
by  means  of  potassium  pyrogallate,  and  then  again  reading  off 
the  volume.  The  difference  gives  the  nitric-oxide  gas;  the  residue 
is  pure  nitrogen.  One  volume  of  nitric  oxide  contains  £  volume 
of  nitrogen.  Finally,  measurement  over  mercury  rather  than 
water  is  preferred,  because  water  by  reason  of  the  slight  quantity 
of  air  it  contains  gives  rise  to  small  errors. 

L.  KESSLER  f  advises  collecting  the  gases  in  a  sulphur-free 
india-rubber  bag  containing  a  little  potassa  solution  and  to  then 
transfer  them  to  the  graduated  tube. 

Instead  of  evolving  the  carbonic  acid  in  the  tube  itself,  it  may 
be  generated  in  a  special  apparatus.  The  combustion  tube  must 
in  such  a  case,  however,  be  open  behind  and  be  provided  with  a 
mercury  valve  shown  in  Fig.  37,  p.  42,  interposed  between  it  and 
the  delivery  tube,  which  must  also  bear  a  glass  or  rubber  stop- 
cock. The  carbonic-acid  apparatus  must  not  allow  the  escape  of 
the  gas  when  the  cock  is  closed,  and  must  deliver  the  gas  at  a 
tension  sufficient  to  readily  overcome  the  pressure  of  the  mercury 
in  the  valve. 

bb.  SIMPSON'S  Method. J 

The  principle  of  this  method,  which  may  be  applied  to  the 
analysis  of  all  nitrogenous  substances,  and  which  affords  accurate 
results  also  in  the  case  of  difficultly  combustible  compounds,  is 
the  same  as  that  of  DUMAS'  method,  but  the  process  embodies 
several  characteristic  differences.  The  carbonic-acid  gas  which 
serves  to  expel  and  displace  the  air  in  the  tube  is  generated  from 
manganous  carbonate;  the  combustion  is  effected  by  a  mixture 
of  cupric  and  mercuric  oxides;  the  free  oxygen  gas  is  removed  by 

*  Phil.  Transact.,  CXLVII,  62;  also  Zeitschr.  f.  analyt.  Chem.,  VTII,  490. 
t  Compt.  rend.,  LXXIV,  683;  Zeitschr.  f.  analyt.  Chem.,  xi,  445. 
J  Annal.  d.  Chem.  u.  Pharm.,  xcv,  74. 


70  ORGANIC   ANALYSIS.  [§   185. 

means  of  copper  in  a  state  of  ignition,  and  the  gaseous  mixture  is 
received  in  a  special  apparatus  in  which  the  carbonic-acid  gas  is 
removed  by  means  of  potassa  solution,  and  the  nitrogen  is  then 
transferred  to  a  graduated  tube  to  be  measured  over  mercury. 

Select  a  strong  combustion  tube  about  80  cm.  long,  and  close 
one  end  by  fusion.  Then  introduce  a  mixture  of  12  grm.  man- 
ganous  carbonate,  dried  at  100°,  with  2  grm.  mercuric  oxide.  (The 
addition  of  the  mercuric  oxide  insures  against  the  possible  forma- 
tion of  any  carbonic-oxide  gas  that  might  otherwise  develop  from 
the  acidulated  admixture  of  organic  matter.)  3  cm.  distant  from 
this  mixture  insert  a  plug  of  recently  ignited  asbestos,  so  that  on 
placing  the  tube  in  a  horizontal  position  a  sufficiently  large  canal 
may  form;  next  introduce  1  grm.  of  mercuric  oxide.  Now  mix 
the  accurately  weighed  substance  (about  0-5  to  0-6  grm.)  with 
45  times  its  weight  of  a  mixture  of  4  parts  freshly  ignited  cupric 
oxide  and  5  parts  mercuric  oxide  (this  mixture  having  been  pre- 
viously prepared  and  dried),  and  introduce  the  mixture  without 
loss  into  the  combustion  tube.  Next  rinse  out  the  mixing  mortar 
with  some  clean  cupric  oxide  and  some  of  the  mixed  cupric  and 
mercuric  oxides,  and  transfer  these  likewise  to  the  tube.  An 
asbestos  plug  is  finally  inserted,  about  30  cm.  distant  from  the 
first  plug,  in  order  that  the  mixture  may  not  form  too  thick  a  layer, 
but  should  leave  a  canal  of  ample  height;  the  plug,  further,  is 
intended  to  remove  any  particles  of  the  mixture  that  may  have 
adhered  to  the  fore  part  of  the  glass  tube,  and  to  push  them  to  the 
rear.  Next  fill  in  a  layer  of  6  to  9  cm.  with  pure  cupric  oxide, 
insert  another  asbestos  plug,  and  fill  in  20  to  24  cm.  with  metallic 
copper  (obtained  by  reducing  granular  cupric  oxide  by  hydrogen 
at  a  relatively  low  temperature).*  The  fore  part  of  the  tube  is 
now  drawn  out  and  connected  by  means  of  a  small  rubber  tube 
with  a  delivery  tube  the  lower  end  of  which  is  bent  at  right  angles 
and  dips  into  the  mercury  in  a  trough. 

When  a  canal  has  been  made  by  tapping  the  tube,  place  the 
latter  in  the  combustion  furnace  and  prepare  the  apparatus 

*  Regarding  the  modifications  required  in  the  process  of  filling  when 
fluids  are  to  be  analyzed,  see  the  original  paper  (loc.  cit.,  p.  83). 


§  185.] 


NITROGEN    DETERMINATION. 


71 


FIG.  58. 


shown  in  Fig.  58  for  the  reception  of  the  gases.  This  apparatus 
should  have  a  capacity  of  about  200  c.c.  and 
should  be  of  sufficiently  strong  glass.  The  upper 
part  should  have  an  external  diameter  of  7  to  8 
mm.  Slip  a  stout  piece  of  rubber  tubing  5  cm. 
long  over  the  point,  leaving  a  piece  of  tubing  pro- 
ject about  3  cm.,  and  tie  it  securely  with  silk  cord; 
then  insert  into  the  projecting  rubber  tube  a  piece 
of  glass  rod  15  mm.  long  and  of  the  same  diameter 
as  the  rubber  tube,  until  it  touches  the  point  of  the 
vessel;  finally,  insert  in  the  rubber  tube  still  left  free  a  very  narrow 
delivery  tube  of  the  same  external  diameter  as  the  glass  rod,  and 
fasten  it  securely  by  tying,  after  which  also  tie  cord  around  the 
part  occupied  by  the  glass  rod,  thus  assuring  an  air-tight  closure 
of  the  vessel.  To  ascertain  whether  the  vessel  is  actually  air-tight, 
partly  fill  it  with  mercury,  invert  it  in  the  trough,  and  observe 
whether  the  mercury  level  falls.  If  the  joints  are  found  to  be 
tight,  fill  the  vessel  with  mercury  and  16  to  17  c.c.  of  concentrated 
potassa  solution,  invert  it  in  the  trough,  and  secure  it  as  shown 
in  Fig.  59. 


FIG.  59. 

Now  screen  off  the  hinder  half  of  manganous  carbonate  by 
means  of  a  screen,  and  heat  it  for  a  few  minutes  with  a  few  pieces 


72  ORGANIC    ANALYSIS.  [§   185.. 

of  red-hot  charcoal,*  until  the  carbonic-acid  gas  evolved  has  com- 
pletely expelled  all  the  air  from  this  part  of  the  tube,  remove  the 
heat  from  the  hinder  end  and  gradually  heat  to  redness  the  other 
half  of  the  manganous  carbonate  as  well  as  the  copper  and  cupric 
oxide  in  the  fore  part  of  the  tube.  That  part  of  the  tube  contain- 
ing the  mixture  must  be  protected  from  the  heat  by  screens.  As 
soon  as  the  evolution  of  carbon  dioxide  ceases,  insert  the  end  of 
the  delivery  tube  (which  from  the  beginning  had  dipped  into  the 
mercury)  into  the  orifice  of  the  gas  apparatus,  but  without  lifting 
it  above  the  surface  of  the  mercury,  and  now  heat  the  mix- 
ture, begininng  at  the  fore  end  and  slowly  proceeding  to  the  hinder. 
During  the  entire  combustion  the  fore  part  of  the  tube,  as  well  as 
that  containing  the  exhausted  manganous  carbonate,  must  be 
maintained  at  a  red  heat.  When  the  combustion  is  at  an  end, 
decompose  the  manganous  carbonate  behind  the  screen  to  drive 
out  all  the  nitrogen  from  the  tube  into  the  gas  receiver  by  means  of 
the  carbonic-acid  gas  evolved.  As  soon  as  all  the  gas  bubbles  are 
completely  absorbed  by  the  potassium  solution  the  delivery  tube 
may  be  removed. 

The  nitrogen  collected  in  the  apparatus  is  now  transferred  to 
the  measuring  tube  by  means  of  a  tube  having  the  form  shown 
in  Fig.  58,  and  which,  immersed  in  the  mercury,  is  fitted  into  the 
tubulure  of  the  gas  vessel  by  means  of  a  perforated  cork.  The 
entrance  of  air  with  the  cork  is  best  prevented  by  moistening  the 
cork  with  a  solution  of  mercuric  chloride.  Now  pour  mercury 
into  the  tube  so  that  its  level  will  be  considerably  higher  than  that 
in  the  gas  vessel,  and  let  the  whole  stand  for  two  hours,  so  that 
all  the  carbonic-acid  gas  may  be  absorbed. 

In  the  meantime  fill  the  gas-measuring  tube  with  mercury, 
after  first  introducing  a  drop  of  water,  and  then  invert  in  the 
trough. 

Now  bring  the  end  of  the  tube  connected  with  the  gas  appara- 
tus under  the  measuring  tube,  untie  the  cord  from  around'the  glass 

*  The  heating  may  be  effected,  of  course,  in  a  gas  furnace  instead  of  a 
charcoal  furnace. 


§  185. 


NITROGEN    DETERMINATION. 


rod,  and  pour  mercury  into  the  perpendicular  tube  as  shown  in 
Fig.  60. 


FIG.  60. 

When  the  gas  has  thus  almost  entirely  been  driven  over,  the 
mercury  must  be  added  by  drops,  until  the  potassa  solution  be- 
comes just  visible  in.  the  gas-delivery  tube.  By  this  procedure 
just  exactly  as  much  nitrogen  is  kept  out  of  the  tube  as  air  had 
first  entered  (from  the  delivery  tube).  When  pouring  hi  the 
mercury  care  must  be  taken  that  it  carries  along  with  it  no  air. 
The  upright  tube  should  hence  be  kept  quite  full  from  the  begin- 
ning and  the  glass  rod  inserted  in  the  rubber  tube  should  be  of 
such  a  dimension  as  to  oppose  considerable  resistance  to  the  passage 
of  the  gas.  After  taking  barometric  and  thermometric  readings, 
measure  the  moist  gas  and  calculate  its  weight.  The  results 
obtained  by  SIMPSON  in  analyses  of  alkaloids,  saltpeter,  and  am- 
monium chloride  are  very  satisfactory. 

It  is  advisable  before  proceeding  to  calculate  the  nitrogen,  to 
test  it  for  oxygen  and  nitric  oxide. 


74  ORGANIC   ANALYSIS.  [§  185. 

cc.  W.  GIBBS'  Method. 

Subsequent  to  the  publication  by  E.  FRANKLAND  and  H.  E. 
ARMSTRONG  *  of  their  method  of  estimating  carbon  and  nitrogen 
in  the  organic  matter  of  potable  water  (which  method  also  included 
the  determination  of  nitrogen),  depending  on  exhausting  the  air 
from  the  combustion  tube,  both  before  and  after  combustion, 
with  a  SPRENGEL  air-pump,  W.  GIBBS  f  also  published  a  method 
in  which  the  SPRENGEL  air-pump  is  used.  This  method,  which  is 
a  combination  of  both  the  FRANKLAND-ARMSTRONG  and  the  SIMP- 
SON methods,  differs  nevertheless  from  these  in  a  number  of  par- 
ticulars. In  the  determination  of  the  nitrogen  in  asparagin  and 
allantoin  it  gave  excellent  results.  Regarding  the  construction 
of  the  meroury  air-pump  used  by  GIBBS,  and  which  is  less  fragile 
than  that  described  by  FRANKLAND  and  ARMSTRONG,  I  refer  to 
the  original  paper.  The  operation  is  carried  out  as  follows: 

Into  a  rather  short  combustion  tube  introduce  first  a  few  grammes 
of  magnesium  carbonate,  then  the  substance  mixed  with  plumbic 
chromate  and  5  or  6  grm.  of  mercurous  chromate.  Then  fill  the 
fore  part  of  the  tube  with  freshly  reduced,  finely  divided  metallic 
copper.  Now  connect  the  tube  with  the  mercury  air-pump  by 
means  of  a  perforated  rubber  stopper  bearing  a  glass  tube,  one  end 
of  which  is  connected  with  the  iron  T-piece  of  the  pump.  Next 
test  the  tightness  of  the  entire  apparatus  by  operating  the  pump 
for  a  few  minutes  and  then  allowing  the  whole  to  stand,  and  ob- 
serving whether  the  height  of  the  mercurial  column  remains  un- 
changed. Now  completely  exhaust  the  combustion  tube,  which 
requires  5  to  10  minutes,  and  cautiously  heat  the  magnesium 
carbonate  until  the  entire  apparatus  is  filled  with  carbonic-acid 
gas  and  the  pressure  within  the  tube  is  equal  to  that  without. 
The  combustion  is  then  effected  in  the  ordinary  manner.  When 
completed,  set  the  pump  again  in  operation  until  a  complete 
vacuum  is  obtained.  SIMPSON'S  receiver,  Fig.  58,  simply  filled 


*Journ.  Chem.  Soc.,  1868,  xxi,  77;  Zeitschr.  /.  analyt.  Chem.,  vin,  489. 
t  Amer.  Journ.  of  Sciences  and  Arts,  XLVIII;   Zeitschr.  /.  analyt.  Chem., 
XI,  206. 


§   185.]  NITROGEN    DETERMINATION.  75 

with  mercury,  serves  to  collect  the  gas.  When  the  operation  is 
at  an  end,  absorb  the  carbonic-acid  gas  with  50  c.c.  of  potassa 
solution,  of  1  -2  sp.  gr.,  transfer  the  nitrogen  to  the  measuring  tube 
and  proceed  as  in  66. 

Another  method  embodying  the  exhaustion  of  the  combustion 
tube  with  an  air-pump,  and  measurement  of  nitrogen  in  SCHIFF'S 
azotometer,  is  described*  as  follows: 

REAGENTS. 

Cupric  Oxide. — "Copper  scale,"  which  may  contain  cuprous 
oxide,  coal  dust,  oil,  etc.,  is  mixed  in  an  iron  pot  with  10  per  cent, 
of  potassium  chlorate  and  enough  water  to  make  a  thin  paste.  The 
mass  is  heated  and  stirred  till  dry;  the  heat  is  then  raised  to  the 
point  of  ignition  and  until  the  mass  does  not  glow  nor  sparkle  when 
stirred. 

The  potassium  chloride  is  washed  out  by  decantation  and  the 
cupric  oxide  is  dried  and  moderately  ignited. 

Metallic  Copper. — Granular  copper  oxide,  or  fine  copper  gauze, 
is  suitable  for  its  preparation.  The  granular  copper  is  most  con- 
venient; copper  gauze  must  be  made  into  rolls  adapted  to  the 
combustion  tube.  The  copper  is  reduced  and  cooled  as  usual  in  a 
stream  of  hydrogen. 

Potassium  Chlorate. — Commercial  potassium  chlorate  is  fused 
in  porcelain  and  pulverized. 

Sodium  Bicarbonate.     It  must  contain  no  organic  matter. 

Solution  of  Caustic  Potash. — Dissolve  commercial  "stick  pot- 
ash" in  less  than  its  weight  of  water,  making  a  solution  so  concen- 
trated that,  on  cooling,  it  deposits  crystals  of  potassium  hydroxide. 

The  same  clear  solution  may  be  used  for  a  number  of  combus- 
tions or  until  the  absorption  of  carbonic-acid  gas  is  not  quite  prompt. 

APPARATUS. 

The  Combustion  Tube  should  be  of  the  best  hard  Bohemian 
glass,  about  2  feet  4  inches  long.  The  rear  end  is  bent  and  sealed 
as  in  Fig.  63. 

*  By  JOHNSON  and  JENKINS,  American  Chemical  Journal,  n,  27. 


76 


ORGANIC    ANALYSIS. 


[§   185. 


It  is  best  to  protect  the  horizontal  part  with  thin  copper  foil. 
The  tube  is  connected  with  the  pump  by  a  close-fitting  rubber- 
cork  smeared  with  glycerin. 

Azotometer. — This  is  a  modification  of  the  apparatus  invented 
and  described  by  SCHIFF,  Fres.  Zeitsckrift,  Bd.  7,  p.  430.  It  is  rep- 
resented in  Fig.  61. 

The  gas  is  measured  in  an  accurately  calibrated  cylinder  (bu- 
rette), A,  of  120  c.c.  capacity,  graduated  to 
fifths  of  cubic  centimetres,  and  closed  at 
the  upper  end  by  a  glass  stop-cock.  The 
lower  end  is  connected,  by  means  of  a  per- 
forated rubber  stopper  about  1J  inches 
long  and  1J  inches  diameter,  with  another 
tube  having  two  arms,  one,  D,  to  receive 
the  delivery  tube  from  the  pump,  the 
other  connected  by  a  rubber  tube  with  a 
bulb  of  200  c.c.  capacity,  F,  through  which 
potassa  solution  is  supplied.  The  gradu- 
ated tube  is  enclosed  in  a  water-jacket 
with  an  external  diameter  of  about  1} 
inches.  Its  lower  end  is  closed  by  the 
caoutchouc  stopper  that  connects  the  two 
parts  of  the  azotometer  described  above. 
The  upper  end  of  the  jacket  is  closed  by 
a  thin  rubber  disc  slit  radially  and  hav- 
ing four  perforations:  one  in  the  centre, 
through  which  the  neck  of  the  graduated  tube  passes,  and  three 
others  near  the  circumference. 

Through  one  of  the  latter  a  glass  tube,  L,  bent  as  in  the  figure, 
reaches  to  the  bottom  of  the  jacket,  another  short  tube  just  passes 
through  the  disc,  and  the  third  hole  is  for  supporting  a  thermom- 
eter. The  azotometer  is  held  upright  and  firm  on  a  stand  by 
rings  fitting  around  the  jacket  and  by  cork  wedges. 

The  bulb  for  potassa  solution  rests  in  a  slotted,  sliding  ring. 
The  Air-pump  used  is  the  SPRENGEL  mercury  pump,  modified 
merely  so  as  to  be  easily  constructed  and  durable.     Its  essential 


61. 


f  185.] 


NITROGEN    DETERMINATION. 


77 


4   LC 


parts  are  sketched  in  Fig.  62.  Some  of  them  are  exaggerated  in 
order  to  show  their  construction  more  plainly.  Through  a  rubber 
stopper  wired  into  the  nozzle  of  the  mercury  reser- 
voir, A,  passes  a  glass  tube,  B,  4  inches  long;  this 
connects  by  a  caoutchouc  tube  with  the  straight 
tube  D,  3  feet  long.  The  rubber  tube  E,  6  inches 
long,  connects  D  with  a  straight  glass  tube  F  of 
.about  the  same  length  as  D. 

G  is  a  piece  of  combustion  tube  1^  inches  long, 
closed  below  by  a  doubly  perforated  soft-rubber 
stopper  admitting  the  tubes  F  and  H,  and  above  by 
a  singly  perforated  rubber  stopper  into  which  a 
tube  /  is  fitted.  The  tube  H  has  a  length  of  45 
inches.  At  the  bottom  it  is  connected  by  rubber 
with  a  straight  tube  of  3  inches,  and  this  again  with 
a  tube  K  of  7  inches.  The  tubes  H  K  should 
have  an  internal  diameter  of  TV  inch,  F  may  be 
T\  inch,  and  D  still  larger. 

We  have  used  for  H  and  F  slender  Bohemian 
glass  tubes  of  ^  inch  exterior  diameter.  Their 
elasticity  compensates  for  their  slenderness.  If 
heavy  barometer  tubes  be  used,  the  stoppers  and 
{JT  must  be  of  correspondingly  larger  dimensions. 

The  joints  at  G  must  be  made  with  the  greatest 
care. 

It  is  best  to  insert  the  lower  stopper  for  half 
its  length  into  G,  having  the  dimensions  of  the  parts 
so  related  that  it  requires  considerable  effort  to 
force  the  slightly  greased  tubes  F  and  H  to  their  places  just 
through  the  stopper.  The  tube  7  must  be  of  stout  glass — a 
decimetre  in  diameter.  It  is  drawn  out  at  either  end  to  a  long 
taper,  and  bent  as  in  the  figure,  in  order  to  bring  its  free 
extremity  to  the  level  of  the  combustion  furnace.  The  hole  in  the 
upper  rubber  stopper  has  a  diameter  of  5  mm.,  just  sufficient  to 
admit  the  narrowed  end  of  the  tube,  which,  after  greasing  or 
moistening  with  glycerin,  is  "screwed  down"  into  the  stopper. 


FIG.  62. 


78  ORGANIC   ANALYSIS.  [§  185. 

These  three  joints  are  the  only  ones  belonging  to  the  pump 
which  have  to  resist  diminished  pressure,  and  require  extreme  care 
in  making. 

If  not  entirely  secure  they  are  to  be  trapped  with  glycerin. 
For  this  purpose  it  is  needful  to  pass  F  and  H  through  a  stopper 
of  half  an  inch  greater  diameter  than  G  and  correspondingly  per- 
forated before  entering  the  latter.  Then,  previous  to  inserting  /, 
a  tube  4  inches  long  is  slipped  over  G  upon  this  wider  stopper. 
When  /  has  been  inserted  and  the  tubes  have  been  secured  to 
their  support,  the  space  between  G  and  the  outer  tube  is  filled 
with  the  most  concentrated  glycerin,  which  is  prevented  from 
absorbing  moisture  by  corking  above. 

The  two  rubber  tubes  are  both  provided  with  stout  screw 
clamps,  to  admit  of  exactly  regulating  the  flow  of  mercury.  The 
tubes,  D,  F,  H,  and  I  are  secured  to  a  vertical  plank  framed  below 
into  a  heavy  horizontal  wooden  foot  on  which  rests  the  mercury 
trough,  and  having  above  a  horizontal  shelf  through  an  aperture 
of  which  passes  the  neck  of  A. 

The  tubes  D,  F,  H,  and  I  are  secured  to  the  plank  at  several 
points  by  wooden  or  cork  clamps  clasping  the  tubes  and  fastened 
by  screws  or  wires. 

These  fastenings  are  made  elastic  by  the  intervention  of  a  thick 
rubber  tube  between  the  glass  and  wood.  The  connections  C  and 
E  should  be  made  of  stout  vulcanized  rubber;  those  at  the  base  of 
HK  of  fine  black  rubber. 

The  latter  should  be  soaked  in  melted  tallow  previous  to  use, 
all  excess  being  carefully  removed  from  the  interior.  The  joints 
should  be  wound  with  waxed  silk. 

A  glass  funnel  is  placed  within  A  to  prevent  spattering  of  the 
mercury  when  it  is  filled. 

OPERATION. 

From  3  to  4  grammes  of  potassium  chlorate,  according  to  the 
amount  of  carbon  to  be  burned,  are  put  into  the  tail  of  the  com- 
bustion tube,  Fig.  63,  followed  by  an  asbestos  plug  just  at  the  bend. 
The  substance  to  be  analyzed  (0  •  6-0  •  8  gramme)  is  well  mixed  in 


§  185.]  NITROGEN   DETERMINATION.  79 

a  mortar  with  enough  cupric  oxide  that  has  been  freshly  ignited 
and  allowed  to  cool  to  make  a  layer  11  or  12  inches  long  in  the 
tube.  The  mixture  is  introduced  through  a  funnel  and  rinsed 
with  enough  cupric  oxide  to  make  a  layer  of  3  inches,  a  second 
asbestos  plug,  and  upon  it  a  layer  of  reduced  copper  of  4  or  5 

MIXTURE          JmNSINGs]         Cu.      jCuOico"  I  ASBESTOS  j 


]8cm.    i          30cm.          i   8cm.    !   12 cm.  :8cmJ3cml    10cm.    ! 

FIG.  63. 

inches  long  are  put  in,  then  a  third  asbestos  plug,  then  2  inches 
of  cupric  oxide,  a  fourth  asbestos  plug,  then  0-8  to  1-0  gramme 
of  sodium  bicarbonate.  The  remaining  space  in  the  tube  is  loosely 
filled  with  asbestos  to  absorb  the  water  which  is  formed  during 
combustion  and  prevent  it  from  flowing  back  upon  the  heated  glass. 
The  anterior  part  of  the  tube  containing  the  cupric  oxide  and  re- 
duced copper  is  wound  with  copper  foil,  leaving,  however,  a  little 
of  the  copper  (Cu  in  Fig.  63)  visible  at  its  rear.  The  combustion 
tube  is  placed  in  the  furnace  at  the  bend  of  the  tube  7  and  connected 
with  the  latter  by  a  close-fitting  rubber  stopper  smeared  with 
glycerin. 

Care  must  be  taken  to  make  the  joint  perfectly  tight.  The 
combustion  tube  has  its  conical  rubber  stopper  partly  inserted, 
and  is  then  forced  and  rotated  upon  the  tapering  and  stout  end  of 
the  tube  7,  the  latter  being  supported  by  one  hand  applied  at  the 
lower  bend. 

PREPARATION   OP  THE   AZOTOMETER. 

Fill  the  bottom  of  the  azotometer  with  mercury  to  about  the 
level  indicated  by  the  dotted  line  G.  Close  the  arm  D  securely 
with  a  rubber  stopper.  Grease  the  stop-cock  H  and  insert  the 
plug,  leaving  the  cock  open. 

Pour  potassa  solution  into  F  till  A  is  nearly  full,  and  there  is 
still  some  solution  in  the  bulb  F.  Raise  the  bulb  cautiously  with 
one  hand,  holding  the  stop-cock  H  in  the  other  hand.  When  the 
solution  in  A  has  risen  very  nearly  to  the  glass  cock,  close  the  latter, 


80  ORGANIC    ANALYSIS.  [§  185. 

avoiding  contact  of  the  alkali  with  the  ground-glass  bearings. 
Replace  the  bulb  in  the  ring  and  lower  it  as  far,  as  may  be.  If  the 
level  of  the  solution  in  the  azotometer  does  not  fall  in  15  or  20 
minutes  it  is  tight.  Place  the  delivery  tube  of  the  pump  K  in  a 
mercury  trough. 

Supply  the  vessel  A  with  at  least  500  c.c.  of  mercury.  Cau- 
tiously open  the  clamps  C  and  E.  If  the  mercury  does  not  start 
at  once  pinch  the  rubber  at  E  repeatedly.  The  mercury  should 
flow  nearly  as  fast  as  it  can  be  discharged  at  K,  without  filling  the 
cylinder  G.  Five  to  ten  minutes'  working  of  the  pump  will  gen- 
erally suffice  to  make  a  complete  exhaustion  of  the  combustion  tube. 
If  most  of  the  mercury  runs  out  before  exhaustion  is  complete, 
close  the  clamp  C,  return  the  mercury  to  A,  and  repeat  the  opera- 
tion. When  there  is  a  complete  exhaustion,  the  mercury  falls 
with  a  rattling  or  clicking  sound.  After  it  has  been  distinctly 
heard  for  half  a  minute,  close  the  clamp  C.  If  the  mercury  column 
in  H  remains  stationary  for  some  minutes,  the  connections  are 
proved  to  be  tight. 

ADJUSTING  THE   AZOTOMETER. 

Remove  the  mercury  trough,  placing  K  in  a  capsule. 

Heat  the  part  of  the  tube  containing  sodium  bicarbonate. 
Water  vapor  and  carbon  dioxide  are  evolved,  which  fill  the  vacuum 
in  H  and  expel  the  mercury.  While  this  is  being  done  place  the 
azotometer  near  by,  remove  the  bulb  F  from  the  ring  and  support 
it  in  a  box  near  the  level  of  D,  so  that  the  stopper  may  be  removed 
from  D  without  greatly  changing  the  level  of  the  mercury  G,  and 
so  that  the  azotometer  can  be  moved  freely  without  disturbing  it. 
When  the  cork  in  D  has  been  removed  fill  D  half  full  or  more 
with  water. 

As  soon  as  the  mercury  has  fully  escaped  from  K  insert  the 
latter  in  D.  Let  a  few  bubbles  escape  through  the  water  and  theti 
pass  the  tube  K  down  so  that  the  escaping  gas  enters  the  azotome- 
ter. It  will  much  facilitate  the  delivery  of  gas  if  the  extremity  of 
the  tube  K  just  touches  the  inside  of  the  azotometer  tube,  and  is 
kept,  as  near  as  possible,  to  the  surface  of  the  mercury. 


§  185.]  NITROGEN    DETERMINATION.  81 

The  carbon  dioxide  is  absorbed  in  passing  through  the  caustic- 
potassa  solution.  In  spite  of  all  precautions  very  minute  bubbles 
of  permanent  gas  will  occasionally  ascend,  but,  as  will  be  seen  on 
observing  the  amount  of  potassa  solution  thus  displaced,  the  error 
thereby  occasioned  is  extremely  small. 


THE    COMBUSTION. 

First  heat  the  anterior  cupric  oxide  to  full  redness,  and  after- 
wards the  copper.  The  fine  gauze  or  pulverulent  copper  com- 
pletely reduces  any  oxides  of  nitrogen  which  might  be  produced 
in  the  combustion,  and  also  retains  any  excess  of  oxygen  which  is 
evolved  at  the  close  of  the  process. 

The  anterior  cupric  oxide  burns  the  traces  of  hydrogen  which 
may  be  held  by  the  reduced  copper,  even  when  the  tube  is  ex- 
hausted, and  also  destroys  the  carbon  monoxide  which  is  usually 

formed  when  steam  and  carbon  dioxide  pass  together  over  reduced 
copper,  if  iron  or  carbon  be  present.  Go  on  with  the  combustion 
as  usual,  bringing  the  heat  up  to  a  fair  redness.  The  flow  of  gas 
may  be  made  quite  rapid,  say  one  bubble  a  second  or  a  little  faster. 

When  the  horizontal  part  of  the  tube  has  all  been  heated,  and 
the  evolution  of  gas  has  nearly  ceased,  heat  the  potassium  chlorate 
so  that  it  boils  vigorously  from  evolution  of  oxygen.  The  reoxidiza- 
tion  of  the  reduced  copper  oxide  and  of  any  unburned  carbon 
proceeds  rapidly. 

When  the  oxygen,  whose  flow  admits  of  easy  regulation,  begins 
to  attack  the  anterior  layer  of  reduced  copper,  stop  its  evolution 
and  lower  the  flames  all  along  the  tube,  keeping  the  reduced  cop- 
per still  faint  red. 

After  a  few  minutes  start  the  pump,  slowly  at  first,  ha^ng  some 
vessel  under  the  tube  D  of  the  azotomer  to  receive  the  mercury. 
A  few  minutes  pumping  suffices  to  clear  the  tube.  Remove  the 
azotometer,  close  the  tube  D  with  its  rubber  stopper,  and  then  raise 
the  bulb  into  its  ring  to  such  a  height  that  the  potassa  solution 
in  it  will  be  at  about  the  same  level  as  that  in  the  graduated 
tube.  Connect  L  at  its  upper  end  with  a  water  supply,  insert  a 


82  ORGANIC   ANALYSIS.  [§  186. 

thermometer  in  the  top  of  the  water-jacket  and  let  the  water  run 
until  the  temperature  and  the  volume  of  gas  are  constant. 

Read  off  the  volume  of  gas  and  temperature,  after  having  accu- 
rately adjusted  the  level  of  the  solution  in  the  bulb  to  that  in  the 
azotometer. 

Read  the  barometer  and  make  the  calculations  in  the  usual  way. 
When  50-per  cent,  potassa  solution  is  used,  no  correction  need  be 
made  for  tension  of  aqueous  vapor,  as  SCHIFF  has  shown. 

The  calculation  is  somewhat  shortened  by  the  use  of  the  table 
in  Journ.  of  Chem.  Soc.,  Vol.  XVIII  (1865),  p.  212. 

Very  fair  results  are  got  by  employing,  with  suitable  precau- 
tion, a  stream  of  carbon  dioxide  to  displace  the  air  of  the  com- 
bustion tube,  but  the  process  is  very  tedious,  the  sources  of  error 
are  more  numerous,  and  the  results  are  apt  to  be  higher  and  not  so 
concordant  as  when  the  mercury  pump  is  used  to  evacuate  the 
tube. 

The  pump  above  described  has  been  in  use  for  eighteen  months 
without  any  repairs,  and  by  its  help  two  or  even  three  analyses 
may  be  performed  in  a  day. 

/?.  Determination  of  Nitrogen  by  Conversion  into  Ammonia. 
VARRENTRAPP  and  WILL'S  Method. 

§186. 

This  method  is  based  upon  the  same  principle  as  the  method 
of  examining  organic  bodies  for  nitrogen  (§  172,  1,  a),  viz.,  upon 
the  circumstance  that,  when  nitrogenous  bodies  are  ignited  with 
an  alkali  hydroxide,  the  latter  is  decomposed,  yielding  water,  the 
oxygen  of  which  combines  with  carbon  to  CO2,  which  remains 
in  combination  with  the  alkali  as  carbonate,  whilst  the  hydrogen 
at  the  moment  of  its  liberation  combines  with  the  whole  of  the 
nitrogen  present  to  form  ammonia. 

In  the  case  of  substances  very  rich  in  nitrogen,  such  as  uric 
acid,  mellon,  etc.,  the  whole  of  the  nitrogen  is  not  at  once  con- 
verted into  ammonia  in  this  process;  a  portion  of  it  combining 
with  part  of  the  carbon  of  the  organic  matter  to  cyanogen,  which 


§  186.]  NITROGEN    DETERMINATION.  83 

then  combines  either  in  that  form  with  the  alkali  metal  or  in  the 
form  of  cyanic  acid  with  the  alkali.  Direct  experiments  have 
proved,  however,  that  even  in  such  cases  the  whole  of  the  nitrogen 
is  ultimately  obtained  as  ammonia,  if  the  alkali  hydroxide  is  pres- 
ent in  excess,  and  the  heat  applied  is  sufficiently  intense. 

As  in  all  organic  nitrogenous  compounds  the  carbon  prepon- 
derates over  the  nitrogen,  and  the  oxidation  of  the  former,  at  the 
expense  of  the  water,  will  invariably  liberate  a  quantity  of  hydro- 
gen more  than  sufficient  to  convert  the  whole  of  the  nitrogen  pres- 
ent into  ammonia;  for  instance, 

CN+  2H20  =  CO2+  NH3+  H. 

The  excess  of  the  liberated  hydrogen  escapes  either  in  the  free 
state  or  in  combination  with  the  not  yet  oxidized  carbon,  accord- 
ing to  the  relative  proportions  of  the  two  elements  and  the  tem- 
perature, as  marsh  gas,  olefiant  gas,  or  vapor  of  readily  condensible 
hydrocarbons,  which  gases  serve  in  a  certain  measure  to  dilute  the 
ammonia.  As  a  certain  dilution  of  that  product  is  necessary  for 
the  success  of  the  operation,  I  will  here  state  that  substances 
rich  in  nitrogen  should  be  mixed  with  more  or  less  of  some  non- 
nitrogenous  body — sugar  recrystallized  from  alcohol,  for  instance — 
so  that  there  may  be  no  deficiency  of  diluent  gas. 

It  was  formerly  supposed  that  this  method  was  applicable  for 
all  nitrogenous  substances  that  did  not  contain  the  nitrogen  in 
the  form  of  nitric  acid,  hyponitric  acid,  etc.  This  supposition, 
however,  is  no  longer  tenable,  as  more  searching  investigations 
have  shown.  Even  though  many  of  the  assertions  regarding  the 
inapplicability  of  the  VARRENTRAPP-WILL  method  are  ascribable 
to  incorrect  procedures  and  the  use  of  impure  soda-lime,  particu- 
larly a  soda-lime  containing  sodium  nitrate,  the  results  obtained 
in  other  cases  cannot  be  ascribed  to  such  causes.  Thus  STRECKER 
found  the  results  too  low  with  guanidin,  and  KONINCK  and  MAR- 
QUART  also  obtained  too  low  results  with  bryonicin.  RITTHAUSEN 
and  KREUSLER  *  similarly  found  the  results  far  too  low  with  leucin, 

*  Zeitschr.  /.  analyt.  Chem.,  x,  350. 


84  ORGANIC    ANALYSIS.  [§  186. 

and  obtained  correct  results  only  when  the  substance  was  burned 
with  an  admixture  of  sugar.  The  applicability  of  the  method  to 
albuminoids  and  allied  substances  has  given  rise  to  an  animated 
discussion.  Thus  NOWACK  and  SEEGEN  state  that  it  is  not  appli- 
cable,* while  KREUSLER  on  the  contrary  firmly  declares  that 
it  is,f  and  considers  the  results  of  the  former  to  be  due  to  tho 
use  of  soda-lime  containing  sodium  nitrate;  again,  ABESSER  and 
MARCKER,J  in  the  estimation  of  nitrogen  in  gluten,  horse  flesh, 
and  blood  albumin,  obtained  results  which  were  0-22,  0-23  and 
0-33  below  the  volumetric  determinations. 

On  the  other  hand,  E.  SCHULZE§  found  that  the  VARRENTRAPP- 
WILL  method,  contrary  to  the  previously  held  supposition,  is 
applicable  also  in  the  case  of  plant  substances  (beets,  tobacco) 
containing  nitrates,  when  the  quantity  of  nitric  acid  does  not 
exceed  a  certain  proportion;  thus  with  from  2  to  3  per  cent,  of 
nitric  acid  the  results  were  quite  accurate,  whereas  with  from  6 
to  7  per  cent,  the  nitrogen  was  0-2  per  cent,  too  low. 

The  determination  of  the  ammonia  formed  in  the  combustion 
with  soda-lime  is 'effected  by  receiving  the  NH3  in  diluted  hydro- 
chloric acid,  converting  the  ammonium  chloride  into  ammonium 
platinum  chloride,  and  either  weighing  this  or  igniting  it  and  cal- 
culating the  ammonia  or  nitrogen  from  the  residual  metal. 

Certain  nitrogenous  organic  compounds  afford  no  ammonia 
on  ignition  with  soda-lime,  but  yield  other  oxygen-free,  nitrogenous, 
volatile  bases.  For  instance,  indigo-blue  yields  aniline;  and 
narcotine,  morphine,  quinine,  and  cinchonine  yield  new  volatile 
bases.  All  these  volatile  bases  have  the  property,  just  like  am- 
monia, of  forming  double  salts  with  hydrochloric  acid  and  plati- 
num chloride.  Were  we  to  weigh  these  double  salts  and,  assuming 
them  to  be  ammonium  platinum  chloride,  calculate  the  nitrogen 
from  the  weight,  we  would  naturally  commit  a  grave  error.  If 
we  ignite  them,  however,  and  calculate  the  nitrogen  from  the 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  324;  xii,  316;  xin,  460. 
f  Ibid.,  xii,  354. 
I  Ibid.,  xii,  447. 
§  Ibid.,  vi,  384. 


§   186.]  NITROGEN    DETERMINATION.  85 

weight  of  the  residual  metal,  all  error  is  avoided,  because  these 
bases,  just  like  ammonia,  contain  2  eq.  of  nitrogen  to  each  equiva- 
lent of  platinum  (LIEBIG).  No  theoretical  explanation  is  necessary 
in  order  to  understand  the  other  part  of  the  process  (collection 
and  determination  of  the  ammonia).  The  process  and  requisites 
arc  as  follows: 
aa.  Requisites. 

1.  THE  SUBSTANCE. — This  must  be  in  the  form  of  finest  pow- 
der, a  condition  not  always  easily  attainable,  as,  for  instance,  with 
albuminoid  substances,  but  which  is,  nevertheless,  indispensable 
for  the   attainment   of   accurate   results   with   many  substances. 
H.  RITTHAUSEN  *  who  has  called  particular  attention  to  this  point, 
gives   methods    of    reducing   albuminoid   substances   to   a   finely 
pulverulent  condition.     After  drying,  the  substance  is  transferred 
to  the  drying  tubes,  in  which  it  is  weighed;  if  the  mixing  with 
soda-lime  is  to  be  effected  in  a  mortar,  such  a  tube  as  shown  in 
Fig.  2  will  serve,  but  if  the  mixing  is  to  be  accomplished  by  means 
of  the  mixing  wire,  a  longer  and  narrower  tube  is  used  (compare 
§  175). 

2.  A  COMBUSTION  TUBE  of  the  kind  described  §  174,  3;  length 
about  40  cm.,  width  about  12  mm.     The  combustion  is  effected  in 
one  of  the  combustion  furnaces  described  in  §  174,  16. 

3.  SODA-LIME  f  (§66,  4). — The  analyst  himself  should  make 
the  caustic  soda  from  the  crystallized  sodium  carbonate  for  the 
preparation  of  the  soda-lime,  as  the  commercial  carbonate  almost 
invariably  contains  sodium  nitrate,  and  the  latter  is  the  source  of 
many  errors,  as  already  pointed  out.     The  soda-lime  is  best  tested 
as  to  its  freedom  from  nitrogenous  matters  by  burning  it  with 
chemically  pure  sugar.     The  soda-lime  should  in  this  case  not  fuse, 
but  simply  cake,  and  on  evaporating  with  hydrochloric  acid  and 
platinum  chloride  and  treating  the  residue  with  alcohol,  no  ammo- 

*  Journ.  f.  prakt.  Chem.,  N.  F.,  vni,  10;  Zeitschr.  /.  analyt.  Chern.,  xin, 
240. 

f  S.  W.  JOHNSON  (Zeitschr.  f.  analyt.  Chem.,  xn,  222,  and  446)  recom- 
mends as  a  substitute  for  soda-lime  a  mixture  of  1  vol.  dry  sodium  carbonate 
or  sulphate  with  1  vol.  dry  calcium  hydrate. 


86  ORGANIC    ANALYSIS.  [§  186. 

nium  platinic  chloride  should  remain.  It  is  advisable  to  gently 
heat  in  a  platinum  or  porcelain  dish  a  quantity  of  the  sandy  or 
granular  soda-lime  sufficient  to  fill  the  combustion  tube,  so  as  to 
have  it  perfectly  dry  for  the  process  of  combustion.  In  the  analysis 
of  non-volatile  substances,  the  best  way  is  to  use  the  soda-lime 
while  still  warm. 

4.  ASBESTOS. — A  small  portion  of  this  substance  is  ignited  in  a 
platinum  crucible  previous  to  use. 

5.  A  VARRENTRAPP  AND  WILL'S  BULB  APPARATUS. — This  may 
be  obtained  from  the  shops.     Fig.  64  shows  its  form.     It  is  filled 


FIG.  64. 

to  the  extent  indicated  in  the  drawing  with  hydrochloric  acid  of 
about  1-07  sp.  gr.  The  acid  is  introduced  either  by  dipping  the 
point  into  the  acid  and  applying  suction  to  d,  or  by  means  of  a 
burette. 

In  order  to  guard  against  the  receding  of  the  acid  into  the 
combustion  tube,  ARENDT  and  KNOP  have  sug- 
gested the  form  indicated  in  Fig.  65. 

PELIGOT'S    U-formed    bulb-tube    also    affords 
good  service  (see  §  187). 

6.  A    soft    well-perforated    CORK    or    rubber 
FIG.  65.          stopper  which  fits  the  combustion  tube  air-tight, 
and  in  which  the  tube  d  of  the  bulb  apparatus  fits  closely.     E. 
MULDER  *  recommends  to  wrap  the  cork  with  tin-foil  in  order  to 
prevent  its  absorbing  ammonia. 

7.  A  SUCTION  TUBE  filled  with  potassa  and  closed  at  the 
anterior  end  by  a  perforated  cork,  in  which  the  point  of  the 
bulb  apparatus  passes;  or,  an  aspirator. 

*  Chem.  CentralbL,  1861,  44;  Zeitschr.  f.  analyt.  Chem.,  i,  98. 


§   186.]  NITROGEN    DETERMINATION.  87 

8.  A  MIXING  MORTAR  (§  174,  8). 

9.  A  sheet  of  GLAZED  PAPER. 

The  reagents  required  in  the  after  treatment  of  the  liquid  ob- 
tained from  the  combustion  will  not  be  detailed  here,  as  it  is  un- 
necessary to  have  them  ready  at  the  beginning  of  the  operation. 

bb.  The  Process. 

The  combustion  tube  is  half  filled  with  soda-lime,  which  is  then 
gradually  transferred  to  the  perfectly  dry,  and,  if  the  nature  of  the 
substance  permits,  rather  warm  mortar,  where  it  is  most  intimately 
mixed  with  the  weighed  substance  (compare  §  174),  forcible  pres- 
sure being  carefully  avoided;  a  layer  of  sandy  soda-lime  occupying 
about  3  cm.  is  now  introduced  into  the  posterior  part  of  the  com- 
bustion tube  and  the  mixture  filled  in  after;  the  latter,  which  will 
occupy  about  18  cm.,  is  followed  by  a  layer  of  about  5  cm.  of  soda- 
lime  which  has  been  used  to  rinse  the  mortar,  and  this  again  by  a 
layer  of  10  cm.  of  pure,  preferably  granulated,  soda-lime,  leaving 
thus  about  4  cm.  of  the  tube  clear.  The  tube  is  then  closed  with 
a  loose  plug  of  asbestos  and  a  free  passage  for  the  evolved  gases 
formed  by  a  few  gentle  taps;  it  is  then  connected  with  the  bulb 
apparatus  by  means  of  the  perforated  cork  or  stopper  and  finally 
placed  in  the  combustion  furnace  (see  Fig.  64). 

To  ascertain  whether  the  apparatus  closes  air-tight,  some  air  is 
expelled  by  holding  a  piece  of  red-hot  charcoal  to  the  bulb  a,  and 
the  apparatus  observed,  to  see  whether  the  liquid  will,  upon  cooling, 
permanently  assume  a  higher  position  in  a  than  in  the  other  limb. 
The  tube  is  then  gradually  surrounded  with  ignited  charcoal,  com- 
mencing at  the  anterior  part  and  progressing  slowly  towards  the 
tail,  the  operation  being  conducted  exactly  as  in  an  ordinary  com- 
bustion (§174).  Care  must  be  taken  to  keep  the  anterior  part  of 
the  tube  tolerably  hot  throughout  the  process,  since  this  will 
almost  entirely  prevent  the  passage  of  liquid  hydrocarbons,  the 
presence  of  which  in  the  standard  acid  would  be  inconvenient; 
on  the  other  hand,  if  the  heat  is  too  high,  the  ammonia  may  be 
decomposed  into  nitrogen  and  hydrogen.  The  stopper  should  be 
kept  sufficiently  hot  to  guard  against  its  retaining  water  and,  with 
this,  ammonia.  The  combustion  should  be  conducted  so  as  to 


88  ORGANIC   ANALYSIS.  [§   186. 

maintain  a  steady  and  uninterrupted  evolution  of  gas;  there  is 
no  fear  of  any  ammonia  escaping  unabsorbed,  even  if  the  evolu- 
tion is  rather  brisk;  but  the  operator  must  constantly  be  on  his 
guard  against  the  receding  of  the  acid,  which  takes  place  the  mo- 
ment the  evolution  of  gas  ceases,  and  this,  in  some  instances,  with 
such  impetuosity  as  to  force  the  acid  into  the  combustion  tube, 
which,  of  course,  spoils  the  whole  analysis.  With  compounds 
very  rich  in  nitrogen,  even  the  greatest  care  during  combustion 
will  be  of  no  avail,  because  of  the  powerful  affinity  of  the  hydro- 
chloric acid  for  the  ammonia  gas  which  almost  completely  fills 
the  tube.  This  difficulty  may  be  readily  met,  however,  by  mixing 
with  the  substance  an  equal  quantity  of  chemically  pure  sugar 
(white  rock  candy  *  recrystallized  from  alcohol),  which  will  give 
rise  to  the  evolution  of  more  permanent  gases  diluting  the  am- 
monia. 

When  the  tube  is  ignited  in  its  whole  length,  and  the  evolu- 
tion of  gas  has  just  ceased,f  the  point  of  the  combustion  tube  is 
broken  off,  and  air  to  the  extent  of  several  times  the  volume  of 
the  gas  in  the  tube  is  sucked  through  the  apparatus,  to  force  all 
the  rest  of  the  ammonia  into  the  acid.  In  order  to  guard  against 
inhaling  the  acid  fumes,  use  a  suction  tube  filled  with  potassa,  or 
else  use  a  small  aspirator.  {  If  the  substance  to  be  analyzed  con- 
tains ammoniacal  salts,  a  loss  of  ammonia  on  triturating  the  sub- 
stance with  the  soda-lime  is  unavoidable.  In  this  case  the  mixing 
must  be  effected  in  the  tube  with  the  mixing  wire  (§175).  Some 
chemists  even  prefer  this  method  in  ordinary  cases  as  well.  § 

Liquid  nitrogenous  compounds  are  weighed  in  small  sealed 
glass  bulbs,  and  the  process  is  conducted  as  directed  in  §  180,  with 
this  difference,  that  soda-lime  is  substituted  for  oxide  of  copper. 


*  Regarding  the  nitrogen  content  of  commercial  sugars,  see  KREUSLER, 
Zeitschr.  f.  analyt.  Chem.,  xn,  362.  White  rock  candy  contains  about  0-012 
per  cent,  of  nitrogen;  fine  white  refined  sugar,  0-055;  and  beet  sugar,  0-039 
per  cent. 

f  This  is  indicated  by  the  white  color  which  the  mixture  reassurr.es  when 
all  the  carbon  deposited  on  the  surface  is  oxidized. 

J  The  suction  may  be  altogether  avoided  by  placing  in  the  hinder  end  of 
the  tube  a  layer  of  calcium  oxalate  dried  at  110°.  as  proposed  by  Bouis. 

§  RITTHAUSEN,  Zeitschr.  f.  analyt.  Chew..  XTTT,  240. 


§186.]  NITROGEN    DETERMINATION.  89 

It  is  advisable  to  employ  tubes  of  greater  length  for  the  combus- 
tion of  liquids  than  are  required  for  solid  bodies.  The  best  method 
of  conducting  the  operation  is  to  heat  first  about  one-third  of  the 
tube  at  the  anterior  end,  and  then  to  force  the  liquid  from  the 
bulbs  into  the  tube  by  heating  the  hinder  end  of  the  latter;  the 
expelled  liquid  will  thus  become  diffused  in  the  central  part  of  the 
tube  without  being  decomposed.  By  a  progressive  application  of 
heat,  proceeding  slowly  from  the  anterior  to  the  posterior  end,  a 
steady  and  uniform  evolution  of  gas  may  be  easily  maintained. 

When  the  combustion  is  terminated,  the  bulb  apparatus  is 
emptied,  through  the  opening  at  the  point,  into  a  beaker,  and  rinsed 
with  water  until  the  rinsings  cease  to  manifest  acid  reaction. 

If  liquid  hydrocarbons  have  formed,  pass  the  liquid  through  a 
moistened  filter  in  order  to  separate  them,  then  evaporate  the  acid 
liquid  containing  the  ammonium  chloride  to  a  small  volume,  add 
pure  *  platinic-chloride  solution  in  excess,  evaporate  to  dryness 
on  the  water-bath,  and  pour  over  the  residue  a  mixture  of  2  vol. 
strong  alcohol  and  1  vol.  ether.  If  the  liquid  acquires  a  bright- 
yellow  color,  it  is  an  evidence  that  sufficient  platinic  chloride  was 
added;  if  it  does  not,  more  must  be  added  (best  in  the  form  of  an 
alcoholic  solution). f  Collect  the  undissolved  platinum  ammo- 
nium chloride  in  a  weighed  filter  dried  at  125°,  wash  it  with  the 
above-mentioned  mixture  of  alcohol  and  ether,  dry,  and  weigh  it 
(compare  §99,  2).  The  dried  filter  should  be  weighed  between 
two  closely  fitting  watch-glasses  held  together  by  a  clamp.  The 
platinum  ammonium  chloride  so  obtained  is  not  always  of  a  fine 

*  If  the  platinic  chloride  contains  potassium  or  ammonium  chloride,  the 
results  for  nitrogen  will  be  too  high;  if  it  contains  nitric  acid,  chlorine  is 
formed  during  evaporation  and  a  portion  of  the  ammonia  will  be  destroyed, 
and  the  results  for  nitrogen  will  hence  be  too  low.  One  should  therefore 
never  neglect  to  test  the  platinic  chloride  most  carefully  as  to  its  eligibility 
for  use. 

f  As  the  platinum  double  salts  of  some  volatile  bases  resulting  from  the 
decomposition  of  certain  organic  substances  (see  above)  are  more  soluble 
in  alcohol  than  the  platinum  ammonium  chloride,  it  is  better  to  employ 
ether  mixed  with  only  a  few  drops  of  alcohol  for  the  washing,  instead  of  the 
alcohol-ether  ordinarily  employed,  if  such  double  salts  are  suspected  as 
being  present  (A.  W.  HOFMANN). 


90  ORGANIC   ANALYSIS.  [§  186. 

yellow  color,  but  is  at  times  darker  and  brownish-yellow.  This 
is  particularly  the  case  with  difficultly  combustible  substances 
rich  in  carbon,  because  with  such  substances  the  formation  of 
liquid  hydrocarbons,  which  bliwjken  the  hydrochloric  acid  during 
the  evaporation,  is  more  difficult  to  avoid.  Direct  experiments 
have  shown,  however,  that  this  darkening  of  the  precipitate  has 
no  perceptible  influence  on  the  result.  The  platinum  ammonium 
chloride  may  be  purified,  particularly  if  the  quantity  is  not  too 
large,  by  dissolving  it  on  the  filter  with  boiling  water,  collecting 
the  filtrate  in  a  weighed  platinum  dish  or  porcelain  crucible,  and 
evaporating  it  together  with  the  washings.  After  drying  at  125°, 
the  increase  in  weight  of  the  dish  or  crucible  gives  the  quantity 
of  the  pure  platinum  ammonium  chloride.  To  test  whether  the 
platinum  ammonium  chloride  is  pure,  convert  it  into  platinum, 
according  to  §  99,  2.  If  volatile  nitrogenous  bases  have  formed 
with  the  ammonia,  the  nitrogen  content  of  the  substance  can  be 
calculated  only  from  the  metallic  platinum  obtained  (compare 
II,  p.  84). 

In  the  analysis  of  such  nitrogenous  substances  for  which  the 
method  is  particularly  adapted  (see  II,  pp.  82-84  *),  and  when  pure 
soda-lime  is  used,  the  results  are  quite  accurate,  being  as  a  rule 
slightly  too  low  rather  than  too  high,  about  in  the  ratio  of  100  :  99  •  5. 
This  may  be  owing  to  the  fact  that  traces  of  the  ammonium-chloride 
vapor  escape  condensation  in  the  absorption  apparatus,  and  are 
carried  off  with  the  permanent  gases  ;f  or  because  the  combustion 
is  not  complete,  i.e.,  nitrogenous  decomposition  products  are 
evolved  which  are  not  preciptated  by  platinic  chloride;  or, 
finally,  because  a  small  quantity  of  the  ammonia  is  decomposed 
into  hydrogen  and  nitrogen.  It  will  be  seen  that  if  in  order  to 
avoid  the  second  source  of  error  a  longer  layer  of  granulated  soda- 
lime  be  employed,  as  recommended  by  E.  MULDER,  there  is  danger 

*  LIEBERMANN  (Annol.  d.  Chem.,  CLXXXT,  103)  in  estimating  the  nitrogen 
content  of  milk  according  to  the  VARRENTRAPP-WILL  method  invariably 
obtained  lower  results  than  with  the  DUMAS  method. 

f  E.  MULDER  on  this  account  replaces  the  bulbs  containing  the  hydro- 
chloric acid  by  a  U-tube  filled  with  broken  fragments  of  glass  moistened 
with  hydrochloric  acid. 


§  187.]  NITROGEN   DETERMINATION.  91 

of  increasing  the  error  from  the  last  source  mentioned  (W.  KNOP  *). 
If  the  results  obtained  are  too  high,  the  cause  is  often  due  to  the 
use  of  impure  platinic  chloride.  Errors  from  this  cause,  or  from 
the  presence  of  ammonia  in  the  hydrochloric  acid,  are  best  guarded 
against  by  taking  such  quantities  of  hydrochloric  acid  and  platinic 
chloride  as  are  used  in  the  analysis,  and  treating  exactly  in  the 
same  manner;  the  small  quantity  of  platinum  ammonium  chloride 
so  obtained,  if  any,  is  deducted  from  the  results  obtained  in  the 
analysis. 

If  soda-lime  is  used  containing  sodium  nitrate  or  nitrite,  not 
only  may  the  results  obtained  be  too  high,  but  also  too  low,  be- 
cause of  the  combustion  of  the  ammonia  by  the  nitrate  or  nitrite 
(KREUSLER  f). 

f.  Peligot's  Modification  of  the  VARRENTRAPP-WILL  Process. 

§187. 

This  modification  consists  in  receiving  the  ammonia  generated 
on  igniting  the  substance  with  soda-lime  in  a  measured  quantity 
of  standard  sulphuric  or  oxalic  acid,  and  then  titrating  the  still 
uncombined  acid  with  standard  sodium  hydroxide  (or  baryta 
water);  the  quantity  of  acid  neutralized  by  the  ammonia,  and 
hence  the  ammonia  itself,  may  thus  be  determined  (compare 
§  99,  3). 

Normal  sulphuric-  or  oxalic-acid  solution  is  most  conveniently 
used  (§215).  10  c.c.  of  the  standard  acid,  containing  respectively 
0-49043  grm.  monohydrated  sulphuric  acid  and  0-63024  grm.  crys- 
tallized oxalic  acid,  and  which  hence  correspond  to  0-1404  grm. 
nitrogen  or  0-17064  grm.  ammonia,  are,  as  a  rule,  sufficient  in  the 
analysis  of  0-5  grm..  a  substance  containing  10  to  20  per  cent, 
nitrogen.  The  acid  may  be  placed  in  the  bulbs  shown  in  either 
Fig.  64  or  65.  In  this  case  place  the  accurately  measured  acid 
in  a  beaker,  suck  up  as  much  as  possible  into  the  bulbs,  and  rinse 
off  the  point.  After  the  combustion  empty  the  bulbs  into  the 

*  Chem.  Centralbl.,  1860,  44. 

t  Zeitschr.  /.  analyt.  Chem.,  xn,  363. 


92  ORGANIC   ANALYSIS.  [§   187. 

same  beaker  again,  carefully  rinse  out  the  bulbs,  and  then  titrate 
the  liquid.  The  receiver  shown  in  Fig.  66  is  more  suitable  for  this 
method.  The  tube  a,  previously  provided  with  a 
perforated  rubber  stopper,  b,  is  first  connected  by 
the  aid  of  a  good  cork  with  the  combustion  tube, 
and  then  the  U-tube  c,  having  been  charged  with 
the  proper  quantity  of  acid  from  a  MOHR  burette, 
is  added.  At  the  termination  of  the  combustion, 
when  air  has  been  drawn  through  the  apparatus, 
the  tube  a  is  rinsed  into  the  apparatus  c,  some 
tincture  of  litmus  added,  and  the  standard  alkali 
FIG.  66.  run  into  the  tube  from  a  second  burette  until  the 

acid  is  almost  blue.  Now  pour  the  contents  into  a  beaker,  rinse 
with  water,  and  complete  the  tit  ration.  With  this  receiver  neither 
receding  nor  spirting  is  possible.  By  not  pouring  out  the  fluid 
until  the  point  of  saturation  is  nearly  attained,  less  water  is  required 
for  rinsing  out  the  tube. 

Of  course  the  form  of  the  receiver  may  be  varied;  thus  in  the 
modification  of  the  VARRENTRAPP-WILL  apparatus,  recommended 
by  J.  VOLHARD,*  the  anterior  bulb  and  point  are  replaced  by  a 
150-c.c.  to  200-c.c.  ERLENMEYER  flask. 

The  standard  sodium-hydroxide  solution  used  must  be  per- 
fectly free  from  carbonic  acid.  I  prefer  to  dilute  it  so  that  3  c.c. 
will  neutralize  1  c.c.  of  the  acid.  Some  chemists  prefer  dilute 
baryta  water.  In  highly  colored  liquids  a  sensitive  litmus  paper 
is  better  than  litmus  tincture  for  recognizing  the  neutrality  point. 

PELIGOT'S  modification  is  particularly  suitable  for  technical 
and  agricultural  investigations.  In  the  hands  of  an  experienced 
operator,  and  using  correct  standard  fluids  and  measures,  this 
method  is  scarcely  inferior  in  accuracy  to  that  described  in  §  186. 

The  results  obtained  by  many  chemists  are,  nevertheless,  even 
in  this  respect,  not  in  accord.  MXRCKER,t  for  instance,  states 
that  titration  gives  lower  results  with  substances  containing  carbon 
and  nitrogen^^gluten)  than  does  the  platinum  method,  because 

*  Annal.  Chem.,  CLXXVI,  282;  Zeitschr.  f.  analyt.  Chem.,  xiv,  332. 
t  Zeitschr.  f.  analyt.  Chem.,  xn,  221. 


§  187.]  NITROGEN   DETERMINATION.  93 

aniline-like  products  form  and  escape  being  titrated.  On  the 
other  hand,  KREUSLER,*  in  analyses  of  meat,  residues  of  meat 
extracts,  and  conglutin,  obtained  results  that  were  almost  identical 
with  both  methods,  and  which  agreed,  moreover,  with  those  afforded 
by  DUMAS'  method. 

[From  the  results  of  a  critical  investigation  of  this  method  by 
JOHNSON  and  JENKINS,!  the  following  facts  may  be  here  added : 

1.  The  efficiency  of  the  ''soda-lime"  mixture  described  §  66,  5, 
is  fully  confirmed.     It  is  easier  to  prepare  than  the  mixture  of 
caustic  lime  and  soda  ( §  66,  4)  formerly  used  for  this  purpose,  and 
does  not,  like  the  latter,  attract  moisture  readily  from  the  air,  and 
is  not  liable  to  swell  and  choke  the  tube  during  combustion. 

2.  Neither  the  highest  heat  possible  to  obtain  in  an  ERLEN- 
MEYER  gas  combustion  furnace,  nor  a  long  layer  of  strongly  heated 
soda-lime,  nor  these  two  conditions  united,  occasion  any  appreciable 
dissociation  of  the  ammonia  formed  in  combustion. 

3.  A  suitable  length  of  the  anterior  layer  of  soda-lime  must  be 
secured  in  order  to  get  a  good  result.     With  0-5  grm.  of  substances, 
such    as   are   encountered   in   agricultural   chemistry,    containing 
less  than  8  per  cent,  of  nitrogen,  a  glass  tube  of  12  to  14  inches  is 
long  enough.     As  the  content  of  nitrogen  increases  to  10  per  cent, 
or  over,  the  tubes  should  be  made  several  inches  longer.     In  the 
combustion  of  dried  blood  or  egg-albumin   a  tube  20-25  inches 
long  is  preferred,   and  the  mixture  of  soda-lime  and  substance 
should  occupy  rather  less  than  half  the  tube,  a  layer  of  pure  soda- 
lime  of  12  or  more  inches  long  being  essential  for  perfectly  destroy- 
ing the  volatile  organic  matters. 

4.  The  long  anterior  layer  of  pure  soda-lime  must  be  brought 
to  a  full  red  heat  before  heating  the  mixture,  and  must  be  so  kept 
throughout  the  combustion. 

5.  No  fumes  or  tarry  matters,  indicative  of  incomplete  com- 
bustion, should  appear  in  bulb-tube  or  receiver. 

6.  When  the  combustion  proper  is  begun  under  the  conditions 

*  Zeitschr.  f.  analyt.  Chem..  xn,  357. 

t  Report  of  Connecticut  Agr.  Exp.  Station,  1878,  p.  111. 


94  ORGANIC   ANALYSIS.  [§  187. 

above  described,  it  can  be  carried  on  quite  rapidly  until  completed. 
The  contents  of  the  tubes  then  show  no  sign  of  unburned  carbon. 

7.  Equally  good  results  are  obtained  whether  the  mixture  is 
made  intimately  in  a  mortar  or  more  roughly  by  stirring  with  a 
spatula  in  a  metallic  capsule  or  scoop,  or  by  mixing  in  the  tube 
with  a  wire.] 

In  using  the  DUMAS  method  in  the  factory,  as,  for  instance,  in 
a  manure  works,  it  is  advantageous  to  replace  the  glass  combustion 
tubes  by  iron  ones.  In  order  to  show  how  this  may  be  done,  the 
process  devised  by  THIBAULT  *  is  here  given.  He  recommends  the 
employment  of  a  wrought-iron  tube  of  20  mm.  bore  and  90  cm. 
length.  It  extends  15  cm.  from  the  furnace  at  each  end.  Both 
orifices  are  closed  by  corks  bearing  narrow  glass  tubes.  A  35-cm. 
layer  of  granular  soda-lime  is  introduced  in  the  fore  part  of  the 
tube  and  is  kept  in  place  by  iron-wire  plugs.  The  substance  to 
be  analyzed  is  mixed  with  pulverulent  soda-lime,  and  is  placed  in 
a  sheet-iron  boat  about  20  cm.  long,  which  is  inserted  into  the  tube 
from  behind.  The  apparatus  used  to  hold  the  acid  is  that  ordi- 
narily employed.  The  operation  is  conducted  as  follows:  First 
heat  the  empty  combustion  tube  to  redness  in  order  to  purify  it, 
and  pass  a  current  of  pure  hydrogen  gas  through  it.  After  the 
tube  has  cooled,  charge  the  fore  part  with  granular  soda-lime,  insert 
the  boat  containing  pulverulent  soda-lime  into  the  hinder  end,  and 
heat  the  tube  to  redness  while  passing  a  current  of  hydrogen  gas 
through  it.  Now  allow  the  hinder  end  to  cool,  withdraw  the  boat 
by  means  of  a  suitable  wire,  remove  some  of  the  soda-lime  from 
the  boat,  mix  the  weighed  substance  to  be  analyzed  with  the  re- 
mainder, and  then  cover  the  mixture  with  the  soda-lime  first 
removed.  Now  replace  the  boat  in  the  tube  and  gradually  heat 
the  mixture  to  redness  while  a  slow  current  of  hydrogen  is  passed 
through  the  tube.  When  the  operation  is  at  an  end,  remove  the 
acid  bulbs  and  the  boat,  and  heat  the  tube  more  strongly  while  a 
more  rapid  current  of  hydrogen  is  passed  through  it  in  order 
to  free  the  layer  of  soda-lime  from  any  hydrocarbons  that  may 
have  condensed  on  it.  The  tube  is  then  ready  for  another  opera- 

*  J.  Pharm.  Chim.,  [4],  xxu,  39;  Journ.  Chem.  Soc.,  CLIX,  433. 


§  188.]  SULPHUR   IN    ORGANIC   COMPOUNDS.  95 

tion,  and  by  using  a  number  of  boats,  a  whole  series  of  analyses 
may  be  uninterruptedly  made. 

C.  ANALYSIS  OF  ORGANIC  COMPOUNDS  CONTAINING  SULPHUR.* 

§188. 

The  usual  method  of  determining  the  carbon  in  organic  bodies 
— viz.,  by  combustion  with  cupric  oxide  or  lead  chromate — would 
give  results  too  high  in  the  analysis  of  compounds  containing 
sulphur,  since — more  especially  if  cupfic  oxide  is  used — a  portion 
of  the  sulphur  would  be  converted  in  the  process  into  sulphurous 
acid,  which  would  be  absorbed  with  the  carbonic  acid  in  the  potash 
bulbs.  In  order  to  avoid  this  error,  LIEBIG  and  WOHLER  interpose 
between  the  calcium-chloride  tube  and  potash  bulbs  a  tube  10  to  20 
cm.  long  and  filled  with  perfectly  dry  lead  dioxide.  According  to 
CARIUS'  t  experiments,  however,  this  means  does  not  suffice  to  retain 
all  the  sulphurous  acid  yielded  by  substances  rich  in  sulphur,  while 
at  the  same  time  it  impairs  the  accuracy  of  the  carbon  determina- 
tion, because  lead  dioxide  has  the  power  to  take  up  quite  a  con- 
siderble  quantity  of  carbonic  acid  (BUNSEN).  CARIUS  recommends 
to  burn  substances  containing  sulphur  in  a  tube  60-80  cm.  long  with 
lead  chromate,  care  being  taken  that  the  anterior  10-20  cm.,  which 
contains  pure  lead  chromate,  are  never  heated  above  low  redness. 
The  lead  chromate  may  be  used  again  three  or  four  times  without 
refusion;  and,  finally,  if  treated  by  VOHL'S  method  (Vol.  I,  p. 
152  J),  it  is  just  as  fit  for  use  as  if  it  had  not  been  employed  for 
the  combustion  of  a  substance  containing  sulphur.  For  the  process 
employed  by  CLOEZ  with  substances  containing  sulphur,  compare 
§192. 

*  The  method  of  qualitatively  determining  sulphur  in  organic  substances 
by  heating  with  sodium,  and  ascribed  to  SCHONN,  was  first  recommended 
by  VOHL  (Zeitschr.  f.  analyt.  Chem.,  n,  442).  [WARREN'S  method  of  deter- 
mining carbon  hydrogen,  and  sulphur  in  one  operation  is  described  in  Am. 
Journ.  Sci.,  XLI,  2d  ser.,  p.  40.] 

f  Annal.  d.  Chem.  u.  Pharm.,  cxvi,  28. 

J  This  is  as  follows :  Wash  first,  if  necessary,  then  fuse  and  powder.  After 
having  been  used  twice,  powder  it,  moisten  with  nitric  acid,  dry,  and  fuse. 
VOHL  states  (Annal.  d.  Chem.  u.  Pharm.,  cvi,  127)  that  lead  chromate  thus 
treated  may  be  used  over  and  over  again  indefinitely. 


96  ORGANIC    ANALYSIS.  [§   188. 

The  presence  of  sulphur  demands  no  modification  in  the 
process  described  in  §§  185,  186,  and  187  for  the  determination  of 
nitrogen.  In  substances  containing  oxygen  in  presence  of  sulphur, 
the  oxygen  is  estimated  from  the  loss. 

As  regards  the  estimation  of  the  sulphur  in  organic  compounds, 
that  element  is  invariably  weighed  in  the  form  of  barium  sulphate, 
into  which  it  may  be  converted  either  in  the  dry  or  in  the  wet  way. 

Both  processes  may  be  carried  out  in  various  ways;  and  as  one 
or  another  of  the  methods  may  be  found  more  easy  of  application, 
or  more  rapid,  according  to  circumstances,  I  feel  it  incumbent  to 
describe  a  number  of  them. 

I.    METHODS  IN   THE   DRY   WAY.* 

1.  Method  suitable,  more  particularly,  to  determine  the  sulphur 
in  non-volatile  Substances  poor  in  Sulphur,  e.g.,  in  the  so-called 
Protein  Compounds  (v.  LIEBIG). 

Put  some  lumps  of  pqtassa  free  from  sulphuric  acid  ( §  66,  6,  c) 
into  a  capacious  silver  dish,  add  J  of  pure  potassium  nitrate,  and 
fuse  the  mixture,  with  addition  of  a  few  drops  of  water.  When 
the  mass  is  cold,  add  to  it  a  weighed  quantity  of  the  finely  pul- 
verized substance,  fuse  over  the  lamp,  stir  with  a  silver  spatula, 
and  increase  the  heat,  continuing  the  operation  until  the  color  of 
the  mass  shows  that  the  carbon  separated  at  first  has  been  com- 
pletely consumed.  Should  this  occupy  too  much  time,  you  may 
accelerate  it  by  the  addition  of  potassium  nitrate  in  small  portions. 
Let  the  mass  cool,  then  dissolve  in  water,  supersaturate  the  solu- 
tion with  hydrochloric  acid  in  a  capacious  beaker  covered  with  a 
glass  dish,  and  precipitate  with  barium  chloride.  Wash  the  pre- 
cipitate well  with  boiling  water,  first  by  decantation,  then  on  the 
filter.  Dry  and  ignite.  Treat  the  ignited  barium  sulphate  as 
directed  in  §  132,  1 ;  if  this  latter  operation  is  omitted,  the  result 
is  almost  always  too  high. 


*  Besides  the  methods  here  given,  many  others  have  been  recommended, 
but  are  here  only  referred  to.  e.g.,  HEINTZ  (POGGEND.  Annal.,  LXXXV,  424); 
Annal.  d.  Chem.  u.  Pharm.,  cxxxvi,  225;  R.  OTTO  (Zeitschr.  f.  analyt.  Chem., 
vii,  117);  W.  F.  GINTL  (ibid.,  vn,  302);  MULDER  (ibid.,  ix,  271),  etc.  AL. 
MITSCHERLICH'S  method  will  be  given  under  §  192. 


§  188.]  SULPHUR    IN    ORGAXIC    COMPOUNDS.  97 

A  suitable  alcohol  lamp  is  preferable  to  a  gas  flame,  since  the 
latter  may  communicate  sulphur  to  the  fused  mass,  and  hence  be 
the  cause  of  error.  As  it  is  by  no  means  easy  to  obtain  the  required 
reagents  perfectly  free  from  sulphur,  it  is  well  to  try  a  parallel 
experiment,  using  the  same  quantities  of  each  that  is  used  for  the 
analysis,  and  if  an  appreciable  amount  of  barium  sulphate  is  ob- 
tained, make  the  necessary  correction  in  the  analysis. 

2.  Method  adapted  more  particularly  for  the  Analysis  of  non- 
volatile or  difficultly  volatile  Substances  containing  more  than  5 
per  cent,  of  Sulphur  (KOLBE  *). 

Introduce  into  the  posterior  part  of  a  straight  combustion  tube  f 
40-54  cm.  long,  a  layer  7-8  cm.  long  of  an  intimate  mixture  of 
8  parts  of  pure  anhydrous  sodium  carbonate  and  1  part  of  pure 
potassium  chlorate;  %  after  this  introduce  the  weighed  substance, 
then  another  layer,  7  or  8  cm.  long,  of  the  same  mixture;  mix  the 
organic  compound  intimately  with  the  sodium  carbonate  and  potas- 
sium chlorate  by  means  of  the  mixing  wire  (Fig.  32,  p.  33,  this 
vol.) ;  fill  up  the  still  vacant  part  of  the  tube  with  anhydrous  sodium 
carbonate  or  potassium  carbonate  mixed  with  a  little  potassium 
chlorate.  Clear  a  wide  passage  from  end  to  end  by  a  few  gentle 
taps,  place  the  tube  in  a  combustion  furnace,  heat  the  anterior  part 
to  redness,  and  then,  progressing  slowly  toward  the  posterior  part, 
proceed  to  surround  with  red-hot  charcoal  the  part  occupied  by  the 
mixture.  In  the  analysis  of  substances  abounding  in  carbon,  it  is 
advisable  to  introduce  into  the  posterior  part  of  the  tube  a  few 
lumps  of  pure  potassium  chlorate,  to  insure  complete  combustion 
of  the  carbon  and  perfect  conversion  into  sulphates  of  the  com- 
pounds of  potassa  with  the  lower  oxides  of  sulphur  that  may  have 
formed.  The  sulphuric  acid  in  the  contents  of  the  tube  is  deter- 
mined as  in  1;  but  the  silica  taken  up  from  the  glass  must  be 
separated  by  first  evaporating  to  dryness  the  liquid  acidulated  with 
hydrochloric  acid. 

*  Supplemente  zum  Handworterbuch  der  Chem.,  1.  edit.,  p.  205. 

f  Sealed  and  rounded  at  the  end  like  a  test-tube. 

t  Instead  of  the  mixture  of  potassium  chlorate  and  sodium  carbonate, 
HOBSON  (Annal.  d.  Chem.  u.  Pharm.,  en,  77)  employs  a  mixture  of  potassium 
chlorate  and  magnesium  carbonate. 


98  ORGANIC    ANALYSIS.  [§  188. 

3.  Method  adapted  for  the  Analysis  both  of  non-volatile  and 
volatile  Substances,  but  more  especially  the  latter  (DEBUS  *). 

Dissolve  1  eq.  (294-42  parts)  of  potassium  dichromate  purified 
by  recrystallization  and  2  eq.  (212-2  parts)  anhydrous  sodium 
carbonate  in  water,  evaporate  the  solution  to  dryness,  reduce  the 
lemon-colored  saline  mass  (K2CrO4+Na2CrO4+Na2CO3)  to  powder, 
heat  to  intense  redness  in  a  Hessian  crucible,  and  transfer  still  hot 
to  a  flask,  Fig.  29,  §  175. f  When  the  powder  is  cold,  introduce 
a  layer  of  it,  7-10  cm.  long,  into  a  common  combustion  tube; 
then  introduce  the  substance,  and  after  this  another  layer,  7-10 
cm.  long,  of  the  powder.  Mix  intimately  by  means  of  the  mixing 
wire,  then  fill  the  still  unoccupied  part  of  the  tube  with  the  saline 
mixture,  and  apply  heat  as  in  an  ordinary  ultimate  analysis.  When 
the  entire  mass  is  heated  to  redness,  conduct  a  slow  stream  of  dry 
oxygen  gas  over  it  for  J- 1  hour.  When  cold,  wipe  the  ash  off  the 
tube,  cut  the  latter  into  several  pieces  over  a  sheet  of  paper,  and 
treat  them  in  a  beaker  with  a  sufficient  quantity  of  water  to  dis- 
solve the  saline  mass.  Add  hydrochloric  acid  (absolutely  free 
from  sulphuric  acid)  in  tolerable  excess,  then  some  alcohol,  and 
apply  a  gentle  heat  until  the  solution  shows  a  beautiful  green  color; 
filter  off  the  chromic  oxide  produced  by  the  combustion  (this  con- 
tains sulphuric  acid);  wash  first  with  water  containing  hydro- 
chloric acid,  then  with  alcohol,  dry,  and  transfer  to  a  platinum 
crucible;  add  the  filter-ash,  mix  with  1  part  of  potassium  chlorate 
and  2  parts  of  potassium  (or  sodium)  carbonate,  and  ignite  until 
the  chromic  oxide  is  completely  converted  into  potassium  chromate. 
Dissolve  the  fused  mass  in  dilute  hydrochloric  acid  and  reduce  by 
heating  with  alcohol;  add  the  solution  to  the  fluid  filtered  from 
the  chromic  oxide,  heat  the  mixture  to  boiling,  and  precipitate  the 
sulphuric  acid  with  barium  chloride  (§  132,  1).  DEBUS'S  test 
analyses  were  very  satisfactory;  thus  he  obtained  99-76  and  99-50 

*  Annal.  d.  Chem.  u.  Pharm.,  LXXVI,  90. 

•]•  The  saline  mass  must  always  first  be  tested  for  sulphur.  For  this 
purpose  a  small  portion  of  it  is  reduced  with  hydrochloric  acid  and  alcohol, 
barium  chloride  added,  and  the  mixture  allowed  to  stand  12  hours  at  rest. 
No  trace  of  a  precipitate  should  be  discernible. 


§  188-]  SULPHUR    IX    ORGAXIC    COMPOUXDS.  99 

of  sulphur  for  100;  again  30-2  of  sulphur  in  xanthogenamide  for 
30-4,  etc. 


4.  Method  equally  adapted  for  the  Analysis  of  Solid  and  Liquid 
Volatile  Compounds  (W.  J.  RUSSELL;  *  suggested  by  BUNSEN). 

Introduce  into  a  combustion  tube,  40  cm.  long,  sealed  at  the 
posterior  end,  first  2-3  grm.  pure  mercuric  oxide,  then  a  mixture 
of  equal  parts  of  mercuric  oxide  and  pure  anhydrous  sodium  car- 
bonate, mixed  with  the  substance,  and  fill  up  the  tube  with  sodium 
carbonate  mixed  with  a  little  mercuric  oxide.  Connect  the  open 
end  of  the  tube  with  a  gas  delivery  tube  dipping  under  water,  to 
effect  the  condensation  of  the  mercurial  fumes.  Place  a  screen  in 
front  of  the  part  of  the  tube  occupied  by  the  substance,  then  heat 
the  anterior  part  to  bright  redness,  and  maintain  this  temperature 
during  the  entire  process.  At  the  same  time,  heat  another  portion 
of  the  tube,  nearer  to  the  end,  but  not  to  the  same  degree  of  inten- 
sity, so  that  there  may  be  alternate  parts  in  the  tube  in  which  the 
mercuric  oxide  is  left  undecomposed.  When  the  part  before  the 
screen  is  at  bright  redness,  remove  the  screen,  heat  the  mixture 
containing  the  substance,  regulating  the  application  of  heat  so  as 
to  insure  complete  decomposition  in  the  course  of  10-15  minutes, 
and  heat  at  the  same  time  the  still  unheated  parts  of  the  tube,  and 
lastly  also  the  pure  oxide  of  mercury  at  the  extreme  end.  The 
gas  must  be  tested  from  time  to  time,  to  ascertain  whether  it  con- 
tains free  oxygen. 

Xext  dissolve  the  contents  of  the  tube  in  a  little  water, 
add  some  mercuric  chloride,  to  decompose  the  sodium  sulphide 
which  may  have  formed,  acidify  with  hydrochloric  acid,  oxidize 
with  potassium  chlorate  the  mercuric  sulphide  which  may  have 
formed,  and  finally  precipitate  the  sulphuric  acid  with  barium 
chloride  (§  132,  1).  W.  J.  RUSSELL  obtained  by  this  method  very 
satisfactory  results  in  the  analysis  of  pure  sulphur,  potassium 
sulphocyanate,  and  carbon  disulphide. 


*  Journ.  f.  prakt.  Chem.,  LXIV,  230. 


100  ORGANIC   ANALYSIS.  [§   188. 

5.  Methods  based  upon  the  Combustion  of  the  Sulphur-containing 
Substance  in  Oxygen  Gas. 

Such  methods  have  been  proposed  by  C.  M.  WARREN,*  W.  G. 
MIXTER,!  A.  SAUER,t  and  G.  BRUGELMANN.§  These  methods 
are  advantageous  in  that  they  yield  the  sulphur  as  sulphuric  acid 
in  a  fluid  containing  little  other  matter,  give  uniformly  good  re- 
sults, and  are  adapted  for  all  kinds  of  organic  substances  containing 
sulphur.  I  would  further  state  here  that  WARREN'S  method  also 
permits  the  carbon,  hydrogen,  and  chlorine  to  be  determined,  while 
BRUGELMANN'S  method  allows  of  the  determination  of  the  sulphur, 
chlorine,  and  phosphorus  in  the  one  portion  of  the  substance. 

a.  WARREN  burns  the  substance  in  a  combustion  tube  open  at 
both  ends,  but  the  hinder  third  of  which  is  bent  upwards  at  an 
obtuse  angle.    The  substance  is  contained  in  this  bent  part,  and  is 
heated  by  a  special  gas  lamp.    The  mixture  of  the  excess  of  oxygen 
gas  with  the  combustion  products  passes  first  through  a  long  layer 
of  asbestos,  then  an  unfilled  space  of  about  6  cm.,  then  a  dense 
asbestos  plug,  next  a  layer  of  pure  asbestos  mixed  with  lead  dioxide 
(which  is  heated  only  just  sufficiently  to  prevent  any  condensation 
of  aqueous  vapors  in  it),  and  finally  another  asbestos  plug.     After 
the  combustion  the  sulphur  is  found  in  the  lead-dioxide  layer  in 
the  form  of  lead  sulphate.     Hence  the  mixture  of  the  latter  with 
the  lead  dioxide  and  asbestos  is  digested  with  a  strong  solution  of 
sodium  bicarbonate  for  twenty-four  hours,  whereby  the  lead  sul- 
phate is  decomposed,  and  the  sulphuric  acid  is  finally  titrated  in  the 
filtrate  according  to  §  132,  1. 

b.  MIXTER'S  method  depends  upon  the  use  of  oxygen  gas  mixed 
with  bromine  vapors,  and  contained  in  a  flask  having  a  capacity 
of  4-10  liters.    The  combustion  tube  used  is  like  that  of  WARREN'S. 
The  apparatus  is  a  closed  one,  so  that  the  oxygen-bromine  mixture 
continuously  circulates  through  it.    The  circulation  is  effected  by 
heating  the  bent-up  portion  of  the  tube  containing  the  substance. 
By  rinsing  out  the  various  parts  of  the  apparatus  a  solution  is 
finally  obtained  which  contains  all  the  sulphur  as  sulphuric  acid, 

*  Zeitschr.  /.  analyt.  Chem.,  v,  169.  t  Ibid.,  xn,  32,  and  xn,  178. 

f  Ibid.,  xii,  212.  §  Ibid.,  xv,  1,  and  xv,  175. 


188.] 


SULPHUR    IN   ORGANIC    COMPOUNDS. 


101 


besides  hydrobromic  acid  and  some  free  bromine;    the  sulphuric 
acid  is  determined  as  in  §  132;  1. 

Both  MIXTER'S  and  SAUER'S  methods  possess  the  advantage 


FIG.  67. 

that  the  sulphur  is  obtained  as  free  sulphuric  acid  in  a  solution 
containing  no  fixed  matter,  and  consequently  in  a  condition  to 
be  easily  and  accurately  determined. 

MIXTER'S  method  is  described  *  as  follows : 

The  apparatus  (Fig.  67)  is  designed  to  effect  the  combustion  in 
a  confined  volume  of  gas,  a  device  resorted  to  on  account  of  the 
difficulty  of  completely  condensing  by  liquid  absorbents  in  U-tubes 
the  dense  white  fumes  of  sulphuric  acid  produced  by  combustion. 
The  bottle  (a)  has  a  capacity  of  from  4  to  10  litres,  according  to 

*  American  Journ.  Sci.  and  Arts,  iv,  90. 


102  ORGANIC    ANALYSIS.  [§  188. 

the  amount  of  oxygen  required.  The  neck  should  be  large  enough 
for  a  stopper  35  to  40  mm.  in  diameter.  /The  condenser  6  is  made 
of  rather  thin  tubing  14  mm.  in  diameter;  at  the  upper  end  it  is 
expanded  to  a  bulb  in  order  to  admit  some  motion  to  the  tube  c  d. 
Below  the  bulb  it  is  surrounded  by  a  water-jacket  22  cm.  high; 
from  the  point  where  it  enters  the  stopper  of  the  bottle  it  is  nar- 
rowed somewhat  for  convenience  of  fitting.  The  combustion  tube 
c  d  is  made  of  hard  glass  of  12-15  mm.  internal  diameter;  the 
portion  c  is  18  cm.  from  curve  to  curve,  and  is  protected  by  a 
sheet-iron  trough  lined  with  asbestos;  the  part  d  is  from  35  to  45 
cm.  in  length.  The  wire  attached  at  /  is  to  sustain  c  in  case  d 
breaks;  c  is  joined  to  b  by  a  collar  of  black  rubber.  The  U-tube  e 
is  connected  with  d  by  a  rubber  collar  drawn  over  the  latter  at  k; 
this  U-tube  is  slightly  inclined,  that  no  liquid  may  run  against  the 
rubber  connectors.  The  tube  /  connects  a  with  e;  it  is  narrowed 
at  both  ends  to  10  mm.  diameter.  Near  the  upper  end  it  is  jointed 
by  a  piece  of  black-rubber  tubing  in  order  that  the  apparatus  may 
be  easily  disconnected  at  k.  The  ends  of  /  extend  2  cm.  or  more 
beyond  the  stoppers.  Through  the  rubber  stopper  i  a  small  glass 
tube  passes  beyond  the  end  of  /,  where  it  is  narrowed  to  an  open- 
ing of  1  mm.  The  double  bulb  tube  j  is  to  accommodate  varia- 
tions of  pressure,  and  to  admit  air  as  the  original  volume  of  gas 
diminishes  during  the  combustion.  The  tubes  6,  c,  d,  and  /  should 
at  no  point  have  an  internal  diameter  less  than  8  mm.  (10  mm.  is 
preferable)  and  the  narrowed  ends  should  be  cut  obliquely  that 
drops  of  water  may  not  obstruct  the  circulation.  The  rubber  stop- 
pers and  connections  should  be  freed  from  adhering  sulphur  by 
heating  in  a  solution  of  soda.  The  joints  of  the  apparatus  are  suffi- 
ciently tight  when  water  will  stand  in  one  limb  of  the  safety  tube. 

The  bottle  a  is  filled  over  water  with  oxygen,  and,  if  necessary, 
rinsed  with  distilled  water;  a  few  drops  of  bromine  are  poured  in, 
the  tubes  adjusted,  and  a  slow  stream  of  water  made  to  flow  through 
the  water-jacket.  The  assay,  if  not  volatile,  is  introduced  into  the 
tube  d  in  a  platinum  tray,*  which  should  not  fill  more  than  half 

*  A  platinum  tray  which  answers  well  may  be  made  10  to  20  cm.  long, 
10  mm.  wide,  and  7  to  10  mm.  deep  by  bending  thin  foil  over  a  glass  tube. 
The  ends  may  be  roughly  bent  together  or  left  open. 


§   188.]  SULPHUR   IN    ORGANIC    COMPOUNDS.  103 

the  bore  of  d,  leaving  space  enough  for  the  free  circulation  of  the 
oxygen.  The  part  c  is  gradually  heated  and  kept  hot  during  the 
combustion.  This  hot  inclined  tube  acts  as  a  chimney;  the  heated 
gases  rise  in  it,  pass  into  the  cold  tube  b  and  fall,  thus  causing  a 
constant  steam  of  gas  to  pass  over  the  assay.  It  is  important  to 
ignite  the  assay  without  distilling  off  any  considerable  portion. 
To  do  this  a  small  splinter  of  wood  may  be  placed  in  contact  with 
that  part  of  the  substance  nearest  I,  or  that  end  of  the  tray  may 
hold  a  thin  layer  of  the  assay,  which  is  heated  as  rapidly  as  safety 
allows  by  a  lamp  held  in  the  hand.  To  insure  a  full  supply  of  gas 
in  the  tube  d  at  the  commencement  of  the  combustion,  oxygen  is 
passed  from  a  gasometer  through  the  tube  i  till  the  white  fume 
which  appears  in  the  condenser  b  passes  into  a.  The  products  of 
combustion  being  denser  falHo  the  bottom  of  the  bottle,  and  for  a 
while  displace  the  oxygen,  thus  increasing  the  circulation.  After 
the  substance  is  ignited,  the  fire  passes  to  the  other  end  of  the  tray. 
The  part  of  the  tube  about  the  tray  is  heated  by  a  lamp  as 
required  to  keep  up  the  combustion.  At  the  end  of  the  operation 
the  heat  is  increased.  If  drops  of  liquid  collect  in  c,  and  are  liable 
to  run  down  to  the  hotter  parts  of  the  tube,  they  should  be  driven 
off  by  heat.  If  carbonic  acid  be  the  principle  product  of  the  com- 
bustion, there  is  little  change  in  the  volume  of  gases  in  the  appa- 
ratus; but  if  water  and  sulphuric  acid  are  formed  in  much  quantity, 
the  volume  is  diminished  and  air  enters  through  the  safety  tube. 

Most  solid  substances  heated  alone  in  the  open  tray  yield  vola- 
tile products  too  rapidly  for  entire  combustion,  but  if  mixed  with 
sand  in  suitable  proportion  they  burn  slowly  and  completely. 
Liquids  should  be  enclosed  in  narrow  tubes  sealed  at  one  end  and 
drawn  out  at  the  other  to  a  capillary  bore  for  two  or  three  inches 
of  length.  Upon  the  point  of  the  tube  a  bit  of  platinum  sponge 
is  fixed  to  assist  the  oxidation.  The  liquid  should  not  fill  more 
than  two- thirds  of  the  wider  part  of  the  tube. 

Before  introducing  very  volatile  substances,  the  10  cm.  of  the 
combustion  tube  I  d  should  be  heated  to  dull  redness.  Oxygen  is 
passed  in  at  i,  the  tubes  are  disjointed  at  k,  and  the  tube  holding 
the  assay  is  then  pushed  in  till  the  platinum  just  reaches  the  heated 


104  ORGANIC    ANALYSIS.  [§   188. 

zone.  The  apparatus  being  connected  at  k,  slow  volatilization  of 
the  liquid  is  effected  by  cautiously  applying  a  flame  under  the 
empty  portion  of  the  tube  containing  the  substance,  so  as  to  main- 
tain the  platinum  sponge  in  a  steady  glow.  As  soon  as  a  cloud  of 
combustion  products  appears  in  the  vessel  a,  oxygen  is  shut  off 
from  i.  When  all  the  liquid  has  distilled  from  the  interior  tube, 
the  tube  c  d  is  cooled  slowly  and  the  apparatus  is  left  for  two  hours 
or  until  the  fume  has  entirely  subsided.  If  no  odor  of  bromine 
be  perceptible  when  the  apparatus  is  disconnected  at  k  to  remove 
the  tray  or  tube,  a  few  drops  of  it  should  be  poured  through  a 
funnel  tube  put  in  the  place  of  /,  and  the  whole  allowed  to  stand 
some  time  to  ensure  complete  oxidation  of  the  sulphur  compounds 
and  deposition  of  the  sulphuric  acid. 

The  tubes  d  and  e  are  then  rinsed  into  a  beaker,  this  water  is 
poured  into  6,  which  is  then  thoroughly  washed  by  the  aid  of 
the  wash-bottle;  the  large  rubber  stopper  is  lifted  from  the  bottle 
and  the  lower  part  of  b  rinsed;  without  removing  the  tube  /  from 
the  stopper,  it  is  rinsed  into  a  beaker,  and  finally  the  bottle  is  care- 
fully washed.  The  solution  obtained,  which  need  not  exceed  500 
c.c.,  is  evaporated  to  a  small  volume,  filtered  if  necessary,  and  the 
sulphuric  acid  is  determined  by  precipitation  with  barium  chloride, 
observing  all  precautions  mentioned  in  §  132,  1.  In  case  the  sub- 
stance leaves  an  ash  or  residue  in  the  tray,  this  must  be  dissolved 
in  aqua  regia,  the  nitric  acid  removed  by  evaporation  with  strong 
hydrochloric  acid,  and  any  sulphuric  acid  it  may  contain  separated 
in  the  usual  manner.  In  the  use  of  this  apparatus  there  is  no 
danger  from  explosions  if  care  be  taken  to  have  the  combustion 
tube  hot  enough  to  ignite  combustible  vapor.  Before  attempting 
to  burn  a  substance  in  the  apparatus,  it  is  best  to  try  it  in  a  large 
inclined  tube  open  at  both  ends,  or  with  oxygen  supplied  at  the 
lower  end.  Such  a  preliminary  trial  will  usually  indicate  the  pre- 
cautions necessary  in  burning  the  substance  in  the  apparatus. 

For  the  determination  of  sulphur  in  substances  rich  in  sulphur, 
0-5  to  0-75  grm.,  requiring  about  4  litres  of  oxygen  may  be  used. 
When  but  little  sulphur  is  present,  a  combustion  of  2  grms.  may 
be  effected  with  9  litres  of  oxygen.  External  heat  is  best  applied 


§  188.]  SULPHUR   IN    ORGANIC    COMPOUNDS..  105 

to  the  part  of  the  tube  containing  the  substance  by  a  BUNSEN  burner 
held  in  the  hand.  The  length  of  time  required  for  the  actual  com- 
bustion seldom  exceeds  20  minutes. 

This  method  gives  very  accurate  results. 

c.  SAUER'S  apparatus  is  comparatively  simple,  and  will  hence 
be  described.  The  substance  is  burned  in  a  current  of  oxygen  and 
the  sulphurous  acid  formed  is  collected  in  hydrochloric  acid  con- 
taining some  bromine;  after  the  greater  part  of  the  hydrochloric 
acid  and  free  bromine  is  evaporated  off,  the  sulphuric  acid  is  esti- 
mated as  in  §  132,  1. 

a.  FOR  SUBSTANCES  WHICH  YIELD  BUT  LITTLE  VAPOR  AND 

PARTICULARLY  No   SULPHUR  ON   HEATING,   e.fa   COKE,  the 

method  is  very  simple.    The  apparatus  used  is  shown  in 
Fig.  68. 


FIG.  68. 


The  substance  is  contained  in  a  porcelain  boat  which  is  placed 
at  b  in  a  combustion  tube  about  60  to  80  cm.  long.  The  brominated 
hydrochloric  acid  is  contained  in  the  receiver  c.  A  current  of 
purified  oxygen  gas  is  passed  through  the  tube,  which  is  then  heated 
to  redness  at  the  point  where  the  boat  is  placed.  The  escaping 
bromine  is  absorbed  by  calcium  hydrate  or  dilute  hydrochloric 
acid,  in  order  to  prevent  any  interference  from  it.  After  the 
combustion,  any  liquid  that  may  have  condensed  is  driven  into 
the  absorption  apparatus  c,  and  the  gaseous  contents  of  the  com- 
bustion tube  finally  displaced  by  a  current  of  oxygen  or  air. 

As  at  times  small  quantities  of  sulphuric  anhydride  remain  in 
the  fore  part  of  the  combustion  tube  even  after  the  passage  of 


106 


ORGANIC   ANALYSIS. 


[§  188. 


oxygen  or  air,  it  is  advisable  to  rinse  the  tube  with  water  and  to 
add  the  washings  to  the  liquid  in  the  receiver  (F.  MUCK  *). 

The  ash  remaining  in  the  boat  may  be  first  weighed  and  then 
treated  with  hydrochloric  acid  for  the  determination  of  the  sul- 
phate contained  in  it,  provided  not  too  much  ferric  oxide  is  present; 
otherwise  it  must  be  fused  with  potassium  and  sodium  carbonates 
(§132,  II). 

SAUER'S  method,  modified  by  MIXTER,!  is  as  follows: 
A  combustion  tube  30  to  40  cm.  in  length  is  drawn  out  quite 
narrow  at  one  end,  and  the  drawn-out  narrow  part  is  bent  down- 
ward at  a  right  angle  and  fitted  by  means  of  a  perforated  stopper 
into  the  U-tube  A,  Fig.  69,  containing  aqueous  solution  of  bro- 


FIG.  69. 


mine  and  also  a  large  drop  of  undissolved  bromine.  The  globule 
of  bromine  is  made  to  rest  at  the  point  /  by  giving  the  apparatus 
a  suitable  inclination.  The  combustion  tube  is  laid  in  a  combus- 
tion furnace,  and  the  substance  contained  in  a  tray  is  pushed  into 


*  Zeitschr.  /.  analyt.  Chem.,  xiv,  16. 
t  Am.  Journ.  Chem.,  n,  396. 


§   188.]  SULPHUR  IN    ORGANIC    COMPOUNDS.  107 

the  open  end  about  15  cm.  This  end  is  then  closed  with  a  stop- 
per, through  which  passes  a  glass  tube.  Pure  oxygen  gas  is  then 
conducted  into  the  combustion  tube,  and  the  part  containing  the 
tray  is  heated  to  redness.  If  during  the  process  the  bromine  in 
solution  becomes  nearly  exhausted  by  the  action  of  sulphurous 
acid,  a  portion  of  the  undissolved  globule  is  shaken  over  into  the 
narrow  part  e  of  the  U-tube,  where  it  is  rapidly  dissolved  by  the 
agitation  caused  by  the  passing  gas-bubbles.  In  order  to  complete 
the  condensation  of  fumes  of  sulphuric  acid  which  may  pass 
through  the  U-tube,  they  are  conducted  by  means  of  the  tube  g 
to  the  bottom  of  the  bottle  B,  which  has  a  capacity  of  about  8 
litres.  The  bottom  of  the  bottle  should  be  barely  covered  with 
water.  During  the  process  of  combustion  a  cloud  of  fumes  may 
be  observed  in  the  lower  part  of  the  bottle,  while  the  air  in  the 
upper  part  remains  perfectly  clear.  After  combustion  is  com- 
pleted, the  tube  g  is  removed  and  the  bottle  with  its  mouth  closed 
is  allowed  to  stand  until  the  visible  fumes  are  absorbed.  The  com- 
bustion tube  is  rinsed  to  remove  sulphuric  acid  which  may  have 
condensed  in  the  part  near  the  U-tube.  The  rinsings  are  added  to 
the  united  solutions  obtained  in  A  and  B.  The  solution  contain- 
ing the  sulphuric  acid  is  now  heated  to  remove  free  bromine,  and 
concentrated  if  the  volume  appears  too  great.  The  sulphuric  acid 
in  it  is  determined  as  in  the  similar  solution  obtained  by  the 
process  described  above  in  1. 

If  the  operator  cannot  procure  a  U-tube  of  the  form  represented 
by  A,  the  more  common  form  shown  by  Fig.  6&  may  be  used.  In 
that  case  it  is  best  to  use  a  saturated  solution  of  bromine  in  hydro- 
chloric acid,  of  which  the  U-tube  should  contain  12  to  15  c.c.  when 
filled  to  extent  indicated  in  Fig.  66.  On  account  of  the  small 
volume  of  liquid  which  can  be  used  in  such  tube,  an  aqueous  solu- 
tion would  hardly  suffice.  The  free  hydrochloric  acid  should  be 
nearly  all  removed  by  evaporation  from  the  final  solution  of  sul- 
phuric acid  before  proceeding  to  precipitate  the  latter  with  barium 
chloride. 

If  inorganic  matter  remains  in  the  tray  after  completing  the 
combustion,  it  is  to  be  treated  as  directed  in  c,  1. 


108  ORGANIC    ANALYSIS.  [§   188. 

(I.  FOR  SUBSTANCES  WHICH  VOLATILIZE  WITH  OR  WITHOUT 
DECOMPOSITION,  the  apparatus  used  is  somewhat  more 
complicated;  it  is  shown  in  Fig.  70. 


r 


FIG.  70. 

A  combustion  tube  about  85  cm.  long  is  narrowed  at  b  to  a 
width  of  5  mm.  The  substance,  which  is  here  assumed  not  to  be 
volatile  unless  heated,  is  contained  in  a  porcelain  boat  d;  the  com- 
bustion tube  is  placed  in  the  furnace;  the  oxygen  is  delivered 
through  the  tube  x  x,  which  is  fixed  to  the  outside  of  the  furnace 
in  order  to  keep  it  cool,  and  which  is  somewhat  widened  at' 6.  The 
rubber  tube  z  may,  according  to  circumstances,  be  connected  with 
an  apparatus  delivering  dry  carbonic-acid  gas,  pure  oxygen,  or 
purified  air.  The  receiver  y  contains  brominated  hydrochloric 
acid,  and  is  connected  with  an  apparatus  containing  calcium 
hydrate  or  dilute  hydrochloric  acid  for  arresting  the  escaping 
bromine.  According  to  SAUER'S  directions,  the  space  in  the  com- 
bustion tube  between  the  boat  and  b  should  remain  unfilled.  I 
believe,  however,  that  it  might  be  advisable  to  at  least  partially 
fill  it  with  ignited  asbestos,  as  recommended  by  WARREN  *  as  well 
as  by  me  f  in  similar  operations. 

After  the  apparatus  has  been  set  up,  the  part  b  is  heated  to 
bright  redness,  a  current  of  oxygen  slowly  passed  through  the  tube 
x  x,  while  a  slow  current  of  air  is  allowed  to  enter  the  rubber  tube  z,  { 

*  Zeitschr.  f.  analyt.  Chem.,  in,  272. 

f  Ibid.,  m,  339. 

j  SAUER  does  not  direct  this  to  be  done,  but  I  consider  it  very  advisable 
because  otherwise  products  of  the  dry  distillation  may  readily  penetrate  as 
far  as  the  stopper  a. 


§   188.]  SULPHUR   IN   ORGANIC   COMPOUNDS.  109 

and  the  substance  then  heated  gradually.  The  evolved  vapors 
meeting  the  oxygen  at  the  strongly  ignited  part  6  are  burned;  as 
soon  as  this  occurs  an  excess  of  oxygen  must  be  supplied. 

When  no  more  gases  are  evolved  and  the  tube  has  been  heated 
to  redness  progressively  from  a  to  b,  the  air  current  is  somewhat 
increased  until  no  more  combustion  is  observed  at  b  and  oxygen 
instead  of  air  is  then  passed  through  the  tube  z,  to  burn  the  residue 
in  the  boat  as  well  as  any  unburned  matter  adhering  to  the  tube. 

Care  must  be  taken  to  so  cautiously  heat  the  substance  that 
no  unburned  tarry  matters  may  collect  in  the  tube  between  b  and 
c.  Should  any  such  have  formed,  however,  they  may  with  proper 
caution  be  finally  burned  in  the  current  of  oxygen. 

It  must  always  be  remembered  that  a  part  of  the  sulphur  may 
remain  in  the  boat  in  the  form  of  sulphates,  and  occasionally  as 
sulphides;  thus,  in  the  analysis  of  vulcanized  caoutchouc,  zinc 
sulphide  is  frequently  found  in  the  residue.  The  residue  in  the 
boat  should  hence  be  dissolved  in  brominated  hydrochloric  acid 
and  the  sulphuric  acid  determined  in  it  alone,  or  along  with  that 
in  the  receiver. 

[With  substances  which  give  off  volatile  matter  at  a  high  tem- 
perature, a  combustion  tube  about  85  cm.  long,  narrowed  at  the 
point  indicated  by  c  in  Fig.  71,  is  employed.  Having  introduced 
the  substance  in  a  tray  (or  if  volatile  at  the  ordinary  temperature 
in  a  bulb  tube  with  capillary  orifice),  the  narrow  part  of  the  combus- 
tion tube  and  also  a  portion  beyond  extending  to  within  10  or  15 
cm.  of  the  end  entering  the  U-tube  is  heated  to  dull  redness  in  a 
combustion  furnace.  Oxygen  gas  is  now  conducted  by  means  of 
the  hard-glass  tube  a  to  the  point  c  beyond  the  tray.  At  the  same 
time  a  very  slow  current  of  carbon  dioxide  is  made  to  enter  through 


FIG.  71. 

the  tube  b  in  order  to  prevent  vapors  from  receding.     Now,  by  a 
cautious  application  of  heat  the  volatile  matter  in  the  tray  is  first 


110  ORGANIC   ANALYSIS.  [§  188. 

distilled  off  and  burned  by  the  constantly  supplied  current  of  oxy- 
gen. Next  the  combustion  of  any  fixed  residue  remaining  in  the 
tray  is  effected  by  transferring  the  supply  of  oxygen  from  a  to  b, 
and  that  of  carbon  dioxide  from  b  to  a.  The  only  use  of  carbon 
dioxide  at  this  stage  is  to  prevent  products  of  combustion  from 
entering  the  tube  a.  The  combustion  tube  during  the  process  is 
connected  with  the  same  absorbing  apparatus  as  used  in  MIXTEK'S 
modification  of  SAUER'S  method  (page  106,  this  vol.).  The  re- 
maining part  of  the  process  is  also  conducted  as  in  the  latter 
method. 

MIXTER  *  obtained  quite  satisfactory  results  with  this  process. 
When  very  volatile  substances,  e.g.,  carbon  disulphide,  are  to  be 
burned,  it  is  necessary  to  apply  heat  very  cautiously  to  the  part  of 
the  tube  containing  the  substance,  so  that  the  flame  produced  by 
the  meeting  of  the  combustible  vapor  with  oxygen  shall  be  a  few 
millimetres  back  of  the  end  of  the  tube  delivering  the  oxygen.] 

7-.  SULPHUR  IN  COAL  GAS  may  also  be  determined  as  in  /?. 
The  apparatus  is  first  filled  with  carbon  dioxide,  then  the  meas- 
ured volume  of  the  coal  gas  is  passed  through  the  tube  and  burned 
at  the  constricted  part  b  with  oxygen.  Finally,  carbon  dioxide 
is  again  passed  through  the  apparatus  until  the  coal  gas  is  all 
expelled  and  burned. 

d.  WHEN  DETERMINING  SULPHUR  IN  READILY  VOLATILE  FLUIDS, 
e.g.,  carbon  disulphide,  weigh  the  substance  in  a  small  glass  tube 
5  to  6  rnm.  wide  and  bent  into  the  form  shown  in  Fig.  72.  First, 

however,  weigh  the  tube  while  empty 
and  open,  then  fill  it,  seal  both  ends, 
and  weigh  again.  Pack  the  hinder 
FlG*  72>  part  of  the  combustion  tube  with 

small  pieces  of  porcelain,  then  fill  the  apparatus  with  carbon 
dioxide,  and  insert  one  limb  of  the  U-shaped  tube  (which  may  be 
drawn  out  thin)  air-tight  into  the  perforation  of  the  stopper.  When 
the  constricted  part  of  the  tube  is  red-hot,  conduct  oxygen  through 
xx,  push  the  U-shaped  tube  further  in  so  that  the  point  is  broken 

*  Am.  Journ.  Chem.,  n,  396. 


§  188.]  SULPHUR   IN   ORGANIC    COMPOUNDS.  Ill 

by  the  pieces  of  porcelain  and  gently  warm  the  fluid  so  that  the 
vapors  reach  the  red-hot  part  of  the  combustion  tube  but  slowly. 
I  consider  it  doubly  necessary  to  place  a  layer  of  asbestos  both  in 
this  as  well  as  in  the  previously  mentioned  process  between  d  and  6. 
When  the  whole  of  the  fluid  has  been  volatilized  and  expelled  from 
the  tube,  insert  the  outer  limb  of  the  latter  into  the  rubber  tube 
connected  with  the  carbon-dioxide  apparatus,  break  off  the  point 
within  the  rubber  tube,  and  pass  a  slow  current  of  carbon  dioxide 
through  the  apparatus  until  combustion  at  b  is  no  longer  observed. 

d.  G.  BRUGELMANN  also  burns  the  substance  in  a  tube  open  at 
both  ends,  but  absorbs  the  combustion  products  hi  a  short  layer 
of  granular  caustic  lime  or  granulated,  pure  soda-lime  *  (4  parts 
pure  lime  and  1  part  pure  sodium  hydroxide) . 

Much  depends  upon  the  quality  of  the  lime.  At  times  the 
ordinary  caustic  lime  from  marble  may  be  employed,  particularly 
if  the  small  quantity  of  sulphur  is  first  determined  and  taken  into 
account.  In  most  cases,  however,  it  is  preferable  for  the  chemist 
to  prepare  the  lime  himself.  For  this  purpose  slack  some  lime 
from  marble  and  add  nitric  acid  until  but  a  small  quantity  of  the 
lime  remains  undissolved,  and  the  reaction  therefore  remains 
alkaline.  Evaporate  without  filtering  over  a  naked  flame  until 
the  boiling-point  reaches  140°.  The  boiling  solution  will  then 
exhibit  a  pellicle  of  calcium  nitrate.  Mix  the  solution  thoroughly 
in  a  beaker  with  two  volumes  of  a  mixture  of  two  volumes  absolute 
alcohol  and  one  volume  ether,  and  let  the  whole  stand  in  a  closed 
flask  for  twelve  hours  to  deposit.  The  ether  and  alcohol  are  now 
expelled  by  carefully  heating  the  pure  calcium-nitrate  solution  in 
a  porcelain  dish,  after  which  evaporate  to  dryness  with  stirring. 
The  calcium  nitrate  so  obtained  must  be  preserved  in  a  well-closed 
bottle.  Heat  a  portion  of  it  to  redness  in  an  unglazed  porcelain 
flask  in  a  suitable  furnace.  As  soon  as  the  calcium  nitrate  is 
decomposed  and  the  evolution  of  gas  has  ceased,  introduce  a  fresh 
quantity  of  the  nitrate  into  the  flask,  and  continue  thus  until  the 
flask  is  filled  with  caustic  lime.  Now  break  the  flask,  separate  the 

*  Zeitschr.  f.  analyt.  Chem.,  xv,  175,  and  xvi,  1. 


112  ORGANIC   ANALYSIS.  [§  188. 

lime  from  the  fragments  of  the  flask,  break  it  into  very  small  pieces 
in  a  porcelain  mortar  until  the  largest  pieces  have  a  diameter  of 
5  mm.  Finally  pass  the  fine  powder  through  a  sieve  of  1  mm.  mesh. 
Commercial  lime  from  marble  which  is  used  without  further  treair- 
ment  is  granulated  similarly. 

The  details  of  the  method  vary  somewhat  according  to  the 
nature  of  the  substance. 

a.  SOLID  SUBSTANCES  OF  ALL  KINDS,  AS  WELL  AS  NON-VOLA- 
TILE COMPOUNDS.  The  combustion  tube  should  be  about  50  cm. 
long  and  12  mm.  in  diameter.  In  the  end  farthest  from  the 
oxygen  gasometer  introduce  a  closely  fitting  roll  of  platinum  foil, 
leaving  an  unfilled  space  of  about  2  cm. ;  then  introduce  a  10-cm. 
layer  of  granulated  caustic  lime  or  soda-lime,  tap  the  tube  so  that 
the  layer  of  lime  settles  well,  clean  the  tube  from  adhering  lime, 
and  keep  the  lime  layer  well  in  place  by  inserting  a  second  roll  of 
platinum  foil,  or,  when  the  substances  contain  phosphorus,  by  a 
layer  of  broken  glass  5  cm.  long.  In  the  case  of  substances  which 
are  likely  to  yield  explosive  gases,  introduce  next  a  layer  of  ignited 
asbestos  15  to  20  cm.  long,  and  then  the  substance,  either  in  pieces 
(e.g.,  parts  of  plants)  or  in  a  boat.  The  last  15  cm.  of  the  tube 
should  remain  unfilled.  Place  the  prepared  tube  in  the  furnace 
so  that  3  cm.  of  the  end  to  be  connected  with  the  oxygen  gasometer 
projects,  and  take  care  that  the  sheet-iron  trough  in  which  the  tube 
rests  underlies  only  that  part  of  the  tube  containing  the  lime, 
platinum  rolls  (or  pieces  of  glass),  and  1  cm.  of  the  asbestos  layer. 
If  the  substance  has  to  be  used  in  large  pieces  (e.g.,  parts  of  plants) 
and  for  which,  therefore,  a  boat  will  not  suffice,  connect  the  tube 
with  the  oxygen  apparatus,  the  delivery  tube  of  which  should  have 
an  aperture  0-5  mm.  wide,  and  regulate  the  current  of  oxygen  so 
as  to  always  ensure  an  excess  of  the  gas,  otherwise  all  the  sulphur 
will  not  be  converted  into  calcium  sulphate  and  obtained  as  such. 
As  a  rule,  100  c.c.  of  oxygen  is  about  the  proper  quantity  to  pass 
through  in  one  minute.  Now  heat  to  redness  5  cm.  of  the  anterior 
layer  of  lime,  then  gradually  also  the  other  5  cm.,  and  finally  the 
substance,  cautiously,  as  directed  below.  If  the  substance  is  to 
be  burned  in  a  boat,  first  heat  to  redness  the  entire  layer  of  lime, 


§  188.]  SULPHUR   IN    ORGANIC    COMPOUNDS.  113 

the  glass  or  platinum  foil,  and  1  cm.  of  the  asbestos,  then  begin  to 
pass  in  the  oxygen,  remove  the  hinder  plug,  insert  the  boat,  and 
rapidly  close  the  tube. 

The  combustion  of  the  substance  is  begun  by  cautiously  heat- 
ing it,  taking  care  that  oxygen  is  always  present  in  excess;  this 
may  be  recognized  by  applying  a  glowing  match  from  time  to  time 
to  the  exit  end  of  the  tube.*  Care  must  also  be  taken  throughout 
the  entire  combustion  that  the  lime  remains  quite  white,  and 
should  the  substance  begin  to  glow  (burning  with  a  flame  is  to  be 
avoided) ,  turn  off  the  heat  from  below  the  substance  until  the  glow 
ceases.  Slight  irregularities  of  combustion  may  be  controlled  by 
diminishing  the  oxygen  current.  Finally,  slowly  heat  to  redness 
the  rest  of  the  tube,  proceeding  from  the  hinder  to  the  anterior 
end.  As  soon  as  this  is  effected,  the  carbon  all  burned,  and  oxygen 
plainly  to  be  detected  at  the  exit  end  of  the  tube,  the  operation  is 
finished.  If  an  asbestos  layer  and  glass  or  platinum  foil  have  been 
interposed  between  the  substance  and  the  lime,  crack  the  hot  tube 
with  a  few  drops  of  cold  water  at  the  point  where  the  glass  or  plati- 
num foil  adjoins  the  asbestos;  if  asbestos  has  not  been  used,  the 
whole  tube  is  treated  as  detailed  below. 

First  clean  the  entire  tube  or  the  piece  of  tube  externally, 
withdraw  the  platinum  foil  from  the  end  of  the  tube,  and  empty 
the  first  2  cm.  of  lime  into  a  small  beaker,  dissolve  it  in  hydro- 
chloric acid,  and  test  it  for  sulphuric  acid.  If  this  is  found,  reject 
the  analysis.  If  absent,  empty  all  the  contents  of  the  tube,  or 
the  piece  of  tube  (excepting  the  platinum  foil  and  boat,  which 
may  be  rinsed  in  the  tube)  into  a  beaker,  treat"  it  with  water  and 
hydrochloric  acid  (if  necessary,  with  the  addition  of  some  bromine) , 
filter,  and  in  the  solution  determine  the  sulphuric  acid  according 
to  §  132,  1. 

/?.  VOLATILE  LIQUIDS  are  weighed  in  a  small  thin-walled  glass 

*  In  the  case  of  substances  the  decomposition  products  of  which  may 
give  rise  to  explosions,  first  heat  in  a  current  of  air  so  that  the  decomposi- 
tion products  may  be  driven  into  the  asbestos  layer  and  then  replace  the 
air  current  by  one  of  oxygen  (Zeitschr.  f.  analyt.  Chem.,  xvi,  1). 


114  ORGANIC    ANALYSIS.  [§   188. 

bulb  with  a  long,  narrow  neck  ( §  180),  and  having  a  total  length  of 
8  cm.  After  the  introduction  of  the  substance  seal  the  point. 
The  combustion  tube  is  charged  as  in  a.  The  asbestos  layer  should 
be  20  cm.  long,  and  when  it  has  been  introduced,  constrict  the  tube 
immediately  behind  it  by  heating  in  the  lamp.  When  the  layer 
of  lime,  the  platinum  foil  or  glass  fragments,  and  1  cm.  of  the 
asbestos  layer  are  red  hot,  introduce  the  sealed  bulb  with  its  point 
towards  the  constricted  part  of  the  tube.  Now  close  the  hinder  end 
of  the  tube  with  a  rubber  stopper  in  the  well-greased  perforation 
of  which  is  inserted  the  delivery  tube  of  the  oxygen  apparatus. 
The  delivery  tube  should  be  of  stout  glass,  the  end  rounded  by 
fusion,  and  the  opening  constricted  to  0-5  mm.  diameter.  Now 
start  the  current  of  oxygen,  and  push  in  the  oxygen  delivery  tube 
so  as  to  break  off  the  point  of  the  bulb.  Push  the  bulb  forward 
so  that  it  will  be  within  4  cm.  of  the  constricted  part  of  the  tube; 
the  oxygen  delivery  tube,  however,  draw  back  to  its  original  posi- 
tion, so  that  its  point  will  extend  only  a  few  mm.  from  the  inner 
end  of  the  stopper.  The  bulb  must  be  heated  very  cautiously  and 
gradually,  and  in  proportion  to  the  volatility  of  the  substance. 
As  soon  as  all  the  liquid  has  been  expelled  from  the  bulb,  crush 
the  latter  by  pushing  in  the  oxygen  delivery  tube,  draw  back  the 
latter  again  to  its  proper  position,  and  finally  heat  the  entire  tube 
to  redness,  proceeding  gradually  from  the  hinder  to  the  fore  part, 
concluding  the  analysis  as  detailed  under  a. 

f.  DETERMINATION  OF  SULPHUR  IN  ILLUMINATING  GAS.  The 
combustion  tube  is  charged  as  in  a.  The  asbestos  layer  should 
be  20  cm.  long.  The  hinder  end  of  the  combustion  tube  is  closed 
by  a  rubber  stopper  carrying  two  glass  tubes  with  narrow  exits; 
the  tubes  should  project  but  a  short  distance  beyond  the  inner 
end  of  the  stopper.  When  the  fore  part  of  the  tube  is  hot,  let  the 
oxygen  enter  by  one  of  the  tubes  (say  about  110  to  120  c.c.  per 
minute),  then  also  the  illuminating  gas  which  had  been  collected 
in  a  glass  globe  of  known  capacity,  or  the  volume  of  which  is  deter- 
mined by  a  gas  meter.  Long  flexible  tubes  should  be  avoided  for 
conducting  the  illuminating  gas;  the  relative  currents  of  the  two 
gases  must  be  so  regulated  that  the  oxygen  will  be  always  in  excess. 


§  188.]  SULPHUR    IN    ORGANIC    COMPOUNDS.  115 

Should  a  small  flame  appear  at  the  exit  end  of  the  combustion 
tube,  the  current  of  illuminating  gas  must  be  reduced  at  once. 
The  combustion  takes  place  at  the  beginning  of  the  heated  part 
of  the  tube,  and  only  when  the  operation  is  carried  on  too  rapidly 
does  it  extend  into  the  asbestos  layer.  About  10  litres  of  gas 
should  be  burned,  and  this  may  be  done  very  well  in  an  hour  and 
a  half  to  two  hours.  Finally,  heat  to  redness  the  entire  asbestos 
layer,  and  conclude  the  operation  as  soon  as  oxygen  can  be  dis- 
tinctly detected  at  the  exit.  The  further  treatment  is  as  described 
under  a.  The  original  paper  gives  all  the  details  as  to  the  manner 
of  measuring  the  gas,  etc. 

6.  Method  of  Determining  Sulphur  in  Coal  and  Coke. 

ESCHKA  *  recommends  the  following  comparatively  simple 
method:  Intimately  mix  about  1  grm.  of  the  substance  in  the 
finest  possible  powder  with  1  grm.  of  calcined  magnesia  and  0-5 
grm.  of  anhydrous  sodium  carbonate  in  a  platinum  crucible  by 
stirring  with  a  glass  rod.  Heat  the  uncovered,  obliquely  placed 
crucible  in  an  alcohol  flame  in  such  a  manner  that  only  the  lower 
half  becomes  red-hot.  In  order  to  promote  the  combustion  which 
according  to  the  nature  of  the  substance  requires  from  three- 
quarters  to  one  hour,  frequently  stir  the  mixture  with  a  platinum 
wire.  After  the  coal  is  burned  and  the  gray  color  has  given  place 
to  a  yellowish  or  brownish,  intimately  mix  with  the  mixture  in 
the  crucible  0-5  to  1  grm.  of  finely  powdered  anhydrous  ammo- 
nium nitrate,  cover  the  crucible  and  ignite  once  more  for  5  to  10 
minutes.  By  this  treatment  the  conversion  into  sulphates  of  sul- 
phites which  may  have  formed  at  first  is  insured. 

Now  transfer  the  mixture,  which  will  have  retained  its  pulveru- 
lent form,  into  a  beaker,  rinse  the  crucible  with  water  into  the 
beaker,  warm  the  whole  (which  may  have  a  volume  of  150  c  c.\ 
filter,  acidulate  with  hydrochloric  acid,  and  precipitate  the  sul- 
phuric acid  with  barium  chloride  (§132,  1).  If  the  calcined  mag- 
nesia or  the  sodium  carbonate  contains  slight  traces  of  sulphates, 
it  is  necessary  to  determine  these  and  deduct  their  weight  from 

*  Zeitschr.  /.  analyt.  Chem.,  xni,  344. 


ORGANIC    ANALYSIS.  [§  188. 

the  total  found.  The  ignition  with  ammonium  nitrate  may  be 
replaced  by  dissolving  the  product  of  the  first  ignition  at  once  in 
brominated  hydrochloric  acid. 

In  this  process  as  well  as  in  all  those  previously  given,  the 
total  sulphur  of  the  coal  (even  that  present  as  calcium  sulphate) 
is  obtained  as  barium  sulphate.  If  only  the  sulphur  exclusive  of 
the  calcium  sulphate  is  desired,  the  finely  powdered  substance 
must  be  continuously  boiled  for  twenty-four  hours  with  an  equal 
weight  of  sodium  carbonate  dissolved  in  water.  By  this  treat- 
ment the  calcium  sulphate  is  decomposed,  while  the  iron  sul- 
phide is  not  attacked.  Filter  off,  wash  with  boiling  water,  and 
use  the  residue  for  the  sulphur  determination.  The  sulphuric 
acid  in  the  calcium  sulphate  so  removed  may  be  determined  in 
the  filtrate  (FR.  GRACE  CALVERT  *). 

II.    METHODS  IN  THE  WET  WAY. 

1.  According  to  BEUDANT,  DAGUIN,  and  RivoTf  the  sulphur 
in  organic  compounds  may  be  readily  determined  by  heating  with 
pure  solution  of  potassa,  adding  2  volumes  of  water  and  conducting 
chlorine  into  the  fluid.     When  the  oxidation  is  effected,  the  solu- 
tion is  acidified  and  freed  from  the  excess  of  chlorine  by  applica- 
tion of  heat,  then  filtered,  and  the  filtrate  precipitated  by  barium 
chloride.     C.  J.  MERZ,  in  my  laboratory,  has  employed  both  this 
method  and  also  LIEBIG'S  (I,  1)  in  the  analysis  of  fine  horn  shav- 
ings.    This  process  appears  convenient  and  exact. J 

2.  CARIUS'S  Method.    .This  chemist  has  made  the  determination 
of  sulphur  (phosphorus,   chlorine,  bromine,  iodine,   arsenic,   and 
other  metals)  the  subject  of  repeated,  most  careful,  and  compre- 
hensive  investigation.     We    owe   to   him    the   following   method 
which  in  expert  hands  is  not  at  all  difficult,  and  which  depends 


*  Chem.  News,  xxiv,  76;  Zeitschr.  f.  anah/t.  Chem.,  xn,  331. 

t  Compt.  rend.,  1853,  835;  Journ.  f.  prakt.  Chem.,  LXI,  135. 

t  Two  experiments  were  made  with  each  method,  on  horn  dried  at  100°. 
The  percentages  obtained  were  as  follows :  By  v.  LIEBIG'S  method,  3 '  37  and 
3'345;  by  the  present  method,  3 '31  and  3 '33. 


§  188.J  SULPHUR   IN    ORGANIC   COMPOUNDS.  11? 

upon  the  oxidation  of  the  substance  in  a  sealed  glass  tube  by  a 
volatile  acid  liquid.  The  very  numerous  test  analyses  leave 
nothing  to  be  desired  so  far  as  accuracy  is  concerned. 

When  CARIUS  first  published  his  method,*  he  recommended  as 
an  oxidizer  25-  to  60-per  cent,  nitric  acid.  As,  however,  many 
sulphur  compounds,  particularly  the  sulphonic  acids,  are  not  com- 
pletely or  are  only  difficultly  oxidized  by  it,  he  neutralized  the 
nitric-acid  solution  first  with  sodium  carbonate  and  then  fused  with 
an  excess  of  sodium  carbonate;  subsequently  f  he  recommended  for 
the  oxidization  of  such  difficultly  oxidizable  sulphur  compounds  po- 
tassium dichromate  and  nitric  acid  of  sp.  gr.  1  -4,  finally  J  returning 
to  nitric  acid,  but  of  sp.  gr.  1-5,  to  the  use  of  which  he  adhered, 
and  which  completely  oxidizes  all  substances  at  temperatures  of 
from  200°  to  320°.  At  this  temperature  the  acid  itself  already 
undergoes  decomposition  to  considerable  extent  into  oxygen, 
water,  and  nitrous  anhydride.  In  order  to  effect  complete  oxidiza- 
tion of  a  substance,  it  suffices  to  employ  one  and  a  half  to  twice 
the  quantity  of  nitric  acid  as  is  theoretically  required;  any  greater 
excess  is  disadvantageous  and  should  be  avoided.  Thus,  for 
0-24  grm.  of  methyl  mercaptan,  one  of  the  substances  requiring 
the  largest  quantity  of  oxygen,  3-3  to  at  most  4-4  grm.  of  nitric 
acid  are  hence  to  be  taken. 

The  ease  with  which  various  organic  substances  are  oxidized 
by  nitric  acid  varies  greatly;  thus  with  some  substances  heating 
for  one  hour  to  150°  to  at  most  200°  suffices;  others,  e.g.,  those  of 
the  aromatic  series,  require  heating  for  one  to  two  hours  at  250° 
to  260°;  difficultly  oxidizable  sulphonic  acids  and  their  derivatives 
again  require  heating  for  several  hours  at  a  temperature  of  250° 
to  260°,  but  are  soon  and  completely  oxidized  at  300°. 

In  carrying  out  the  process  certain  rules  must  be  carefully 
observed. 


*  \nnal.  d.  Chem.  u.  Pharm.,  cxvi,  11. 
f  Ibid.,  cxxxvi,  129;   Zeitschr  f.  analyt.  Chem.,  rv,  451. 
t  Ber.  d.  deutsch.  chem.  Geselkch.,  m,  697;    Zeitschr.    f.  analyt.    Chem., 
x,  103. 


118  ORGANIC    ANALYSIS.  [§   188. 

The  experimental  tube  is  made  of  ordinary  combustion  tubing 
45  to  50  cm.  long,  with  an  inner  diameter  of  13  mm.  and  walls  1-5 
to  2  mm.  thick.     To  avoid  any  risk  of  an  explosion  the 
proportion  of  4  grm.  of  nitric  acid  to  a  tube  capacity  of 
50  c.c.  should  under  no  circumstances  be  exceeded. 

The  substance  is  weighed  in  a  tube  shown  full  size  in 
Fig.  73. 

The  proper  quantity  of  nitric  acid,  according  to 
the  observations  made  above,  is  weighed  out  and  in- 
troduced into  the  experimental  tube  already  containing 
the  small  tube  with  the  substance  inclosed;  the  experi- 
mental tube  is  now  sealed  and  drawn  out  to  a  thick- 
walled  capillary  tube. 

The  intensity  and  duration  of  the  heating  depend 
upon  the  nature  of  the  substance.  One  hour  and  a 
half  is  usually  sufficient  as  a  rule,  if  the  first  half  hour, 
which  is  required  to  raise  the  tube  to  the  proper  tem- 
perature, is  not  counted. 

The  heating  of  the  tubes  is  effected  in  the  sheet- 
iron  air-bath  shown  in  Fig.  74,  the  glass  tubes  being 
inserted  into  the  iron  tubes.     The   latter   are   loosely 
stoppered  in  front,  and  the  ends  directed  towards  the 
wall  of  the  laboratory;  or  better  yet,  cover  the  whole 
with  a  wooden  box,  so  that  no  damage  may  be  caused  should  an 
explosion  take  place. 

When  the  heating  is  over  and  the  tube  is  cold,  cautiously  warm 
the  drawn-out  point  in  order  to  expel  any  liquid  in  it,  and  then 
heat  it  to  redness  so  that  it  may  blow  out  and  allow  the  imprisoned 
gases  to  escape.  If  any  doubt  exists  as  to  the  completeness  of 
the  oxidization,  seal  the  point  again  after  the  gases  have  escaped 
and  heat  once  more.  This  operation  is  recommended  also  when 
it  is  desired  to  heat  difficulty  oxidizable  substances  to  300°,  and 
when  there  exists  a  doubt  as  to  the  ability  of  the  tube  to  with- 
stand the  pressure  of  the  gases  if  the  heating  is  carried  out  all  in  one 
operation. 

Finally  rinse  the  acid  liquid  out  of  the  tube,  dilute,  and  de- 


§   188.]  SULPHUR    IN    ORGANIC    COMPOUNDS.  119 

termine  the  sulphuric  acid  according  to  §  132,  1.  KULZ*  recom- 
mends (when  determining  sulphur  in  bile)  repeatedly  evaporat- 
ing the  contents  of  the  tube  with  concentrated  hydrochloric  acid 
in  order  to  decompose  and  remove  the  nitric  acid,  then  to  treat 


FIG.  74. 

with  water,  filter,  and  precipitate  the  sulphuric  acid  in  the  fil- 
trate with  barium  chloride. 

3.  PEARSON'S  Method. t  Treat  the  weighed  substance  with 
pure  nitric  acid  of  39°  Be.  (sp.  gr.  1-36)  in  a  porcelain  dish,  add 
potassium  chlorate,  and  warm  gently,  first,  however,  covering 
the  dish  with  an  inverted  and  well-fitting  funnel,  the  stem  of  which 
is  bent  into  a  right  angle.  From  time  to  time  add  fresh  quantities 
of  potassium  chlorate  and  continue  the  heat  until  oxidization  is 
complete.  The  quantity  of  potassium  chlorate  required  and  the 
time  required  depend  upon  the  nature  of  the  substance.  For  the 
complete  oxidation  of  1  grm.  potassium  sulphocyanate  5  to  10 
minutes  suffice,  while  1  grm.  of  sulphur  requires  three-quarters 
of  an  hour  to  one  hour.  The  sulphuric  acid  in  the  solution  is 
finally  determined  according  to  §  132,  1.  The  method  is,  of 
course,  not  applicable  to  volatile  substances. 

Substances  which  contain  sulphur  and  leave  an  ash  on  com- 
bustion may  contain  part  of  the  sulphur  present  in  the  form  of 

*  Zeitschr.  /.  analyt.  Chem.,  xi,  353. 
f  Ibid.,  ix,  271. 


120  ORGANIC    ANALYSIS.  [§   189. 

sulphates.  The  sulphur  in  these  must  be  determined  in  a  separate 
sample  of  the  substance  and  deducted  from  the  total  quantity. 
The  method  of  doing  this  in  the  case  of  coal  has  been  given  above 
(pages  115,  116).  In  other  cases  the  object  is  as  a  rule  accom- 
plished by  boiling  the  substance  with  hydrochloric  acid,  whereby 
the  sulphates  are  dissolved,  and  then  determining  the  sulphuric 
acid  in  the  solution  according  to  §  132,  1. 

D.  DETERMINATION  OF  PHOSPHORUS  IN  ORGANIC  COMPOUNDS. 

§189. 

The  phosphorus  in  organic  compounds  is  determined  by  methods 
similar  to  those  employed  for  determining  sulphur  in  organic  com- 
pounds, i.e.,  the  organic  substance  is  oxidized  either  in  the  wet  or 
dry  way,  and  a  solution  is  obtained  in  which  the  phosphoric  acid 
formed  by  oxidization  is  determined. 

For  oxidation  the  methods  given  in  §  188, 1,  1,  2,  4,  and  5  d,  as 
well  as  II,  2,  are  suitable. 

From  the  solution  obtained  phosphoric  acid  is  precipitated, 
either  directly  with  ammonium  chloride,  magnesium  chloride,  and 
ammonia  mixture,  or  with  molybdic-acid  solution,  after  remov- 
ing hydrochloric  acid  by  repeated  evaporation  with  nitric  acid 
(§134,  6,  a,  and  /?). 

The  phosphorus  cannot  be  determined  by  incineration  of  the 
substance  and  examination  of  the  ash.  Vitellin,  which  when 
treated  with  nitric  acid  gives  3  per  cent,  of  phosphoric  acid,  yields 
barely  0-3  per  cent,  of  ash  (V.  BAUMHAUER). 

If  a  substance  contains  phosphorus  both  in  an  unoxidized  state 
and  in  the  form  of  phosphates,  boil  a  separate  portion  with  hydro- 
chloric acid,  filter  if  necessary,  and  determine  the  phosphoric  acid 
in  the  solution.  The  quantity  thus  found  is  deducted  from  the 
total  phosphoric  acid  found  in  the  portion  submitted  to  oxidation 
in  order  to  find  the  amout  which  existed  in  the  compound  in  an 
unoxidized  state. 


§   190.]  HALOGENS    IN    ORGANIC    SUBSTANCES.  121 

E.  ANALYSIS  OF  ORGANIC  SUBSTANCES  CONTAINING  CHLORINE, 
BROMINE,  OR  IODINE. 

§190. 

The  combustion  of  organic  substances  containing  chlorine  with 
cupric  oxide  gives  rise  to  the  formation  of  cuprous  chloride,  which, 
were  the  process  conducted  in  the  usual  manner,  would  condense 
in  the  calcium-chloride  tube,  and  would  thus  vitiate  the  deter- 
mination of  the  hydrogen.  This  and  every  other  error  may  be 
prevented  by  the  employment  of  lead  chromate  ( §  176).  The 
chlorine  is,  in  that  case,  converted  into  lead  chloride,  and  retained 
in  that  form  in  the  combustion  tube. 

If  the  combustion  is  effected  with  cupric  oxide  in  a  current 
of  oxygen,  the  cuprous  chloride  is  decomposed  by  the  oxygen, 
cupric  oxide  and  free  chlorine  being  formed;  the  latter  is  retained 
partly  in  the  calcium-chloride  tube,  partly  in  the  potash  bulbs.  To 
remedy  this  defect,  STAEDELER  *  proposes  to  fill  the  anterior  part 
of  the  tube  with  clean  copper  turnings;  these  must  be  kept  red-hot 
during  the  combustion,  and  the  current  of  oxygen  must  be  arrested 
the  moment  they  begin  to  oxidize.  KEKULE  recommends  placing 
a  few  pieces  of  fused  lead  chromate  in  the  anterior  part  of  the  tube. 
K.  KRAUT  f  observes  with  reference  to  this  process  that  it  is  well  to 
place  a  roll  of  silver  foil  about  15  cm.  long  in  front  of  the  layer  of 
metallic  copper.  In  the  absence  of  the  silver  the  transmission  of 
oxygen  has  to  be  conducted  with  caution,  in  order  that  no  chlorine 
may  be  expelled  from  the  cuprous  chloride  first  formed,  but  by 
adopting  KRAUT'S  recommendation  we  may  continue  passing  the 
gas  without  fear  till  it  escapes  free  from  the  potash  tube.  The 
process  so  modified  is  suitable  also  for  substances  containing  bro- 
mine and  iodine.  [In  the  case  of  substances  containing  iodine, 
it  is  needless  to  employ  metallic  copper  as  well  as  silver  foil.]  The 
silver  may  be  used  over  and  over  again,  but  at  last  requires  ignition 

*  Annal.  d.  Chem.  u.  Pharm.,  LXIX,  335. 
f  Zeitschr.  /.  analyt.  Chem.,  n,  242. 


122  ORGANIC    ANALYSIS.  [§   190. 

in  a  stream  of  hydrogen.  According  to  A.  VOLCKER,*  the  evolu- 
tion of  chlorine  may  be  prevented  by  mixing  the  oxide  of  copper 
with  \  lead  oxide. 

In  the  analysis  of  bodies  containing  bromine  the  above  methods 
do  not  always  answer,  v.  GORUP-BESANEZ  f  satisfied  himself  of 
this  by  analyzing  dibromotyrosin.  Whether  this  body  was  burnt 
with  lead  chromate,  with  a  mixture  of  lead  chromate  and  potassium 
chromate,  -  with  cupric  oxide  and  oxygen  and  an  anterior  layer  of 
lead  chromate,  with  an  anterior  layer  of  copper  turnings,  whether 
mixed  or  in  the  platinum  boat,  in  whichever  way  the  analysis  was 
performed  the  carbonic  acid  always  came  out  several  per  cents, 
too  low,  because  metallic  bromide  was  formed,  which  fused  and 
inclosed  carbon,  thereby  preventing  its  oxidization.  The  follow- 
ing process,  on  the  contrary,  yielded  good  results :  Into  a  combus- 
tion tube  drawn  out  to  a  long  point,  introduce  first  a  layer  about 
9  cm.  long  of  cupric  oxide,  then  a  plug  of  asbestos,  then  a  mixture 
of  the  substance  (finely  powdered)  with  about  an  equal  weight  of 
well-dried  lead  oxide  in  a  porcelain  boat;  again  a  plug  of  asbestos, 
then  granulated  cupric  oxide,  then  lead  chromate  or  copper  turn- 
ings. First  heat  the  anterior  and  then  the  posterior  layers  to  igni- 
tion, and  warm  the  part  where  the  boat  is  very  cautiously  and 
gradually;  everything  combustible  distils  over,  arrives  at  the  cupric 
oxide  in  the  form  of  vapor,  and  is  there  burnt.  In  the  boat  noth- 
ing remains  but  a  mixture  of  lead  bromide  and  oxide.  Complete 
the  combustion  with  oxygen,  taking  care  not  to  heat  the  point 
where  the  boat  is  too  strongly,  nor  continue  the  transmission  of 
oxygen  longer  than  necessary.  If  silver  foil  is  placed  in  the  very 
front  part  of  the  tube  the  hydrogen  will  also  be  correct.  Observe 
also  that  no  copper  bromide  sublimes  into  the  calcium-chloride 
tube. 

The  halogens  themselves  are,  as  a  rule,  determined  according 
to  one  of  the  following  methods: 

*  Chem.  Gaz.,  1849,  CCXLV,  29. 
f  Zeitschr.  f.  analyt.  Chem.,  i,  438. 


§  190.1  HALOGENS   IN    ORGANIC    SUBSTANCES.  123 

I.  METHODS  IN  THE  DRY  WAY. 

1.  Ignition  with  lime  or  soda-lime. 

As  chlorine-free  lime  is  easily  obtainable  (by  burning  marble), 
this  body  is  usually  preferred  to  effect  the  decomposition  of  or- 
ganic substances  containing  chlorine,  bromine,  or  iodine.  It  must 
always  be  tested  for  chlorine  previous  to  use,  and  if  traces  are  found, 
the  quantity  is  determined  in  a  weighed  sample.  The  analysis  is 
made  with  a  weighed  quantity  of  lime,  and  the  chlorine  in  it  is  de- 
ducted from  the  total  found.* 

Introduce  into  a  combustion  tube  about  40  cm.  long,  the  pos- 
terior end  of  which  is  sealed  and  rounded  like  a  test  tube,  a  layer  of 
lime  6  cm.  long,  then  the  substance,  after  this  another  layer  of 
lime  6  cm.  long,  and  mix  with  the  wire;  fill  the  tube  almost  to  the 
mouth  with  lime,  clear  a  free  passage  for  the  evolved  gases  by  a 
few  gentle  taps,  and  apply  heat  in  the  usual  way.  Volatile  fluids 
are  introduced  into  the  tube  in  small  glass  bulbs.  When  the  de- 
composition is  terminated,  dissolve  in  dilute  nitric  acid  and  pre- 
cipitate with  solution  of  silver  nitrate  (§  141).  KOLBE  recom- 
mends the  following  process  to  obtain  the  contents  of  the  com- 
bustion tube:  When  the  decomposition  is  completed,  remove  the 
charcoal,  insert  a  cork  into  the  open  end  of  the  tube,  remove  every 
particle  of  ash,  and  immerse  the  tube,  still  hot,  with  the  sealed 
end  downwards,  into  a  beaker  filled  two-thirds  with  distilled 
water;  the  tube  breaks  into  many  pieces  and  the  contents  are 
then  more  readily  acted  upon.  Now  add  nitric  acid  until  the  lime 
is  dissolved,  filter  off  from  the  separated  carbon,  and  precipitate 
with  silver  nitrate.  As  in  this  method  the  ignition  of  compounds 
abounding  in  nitrogen  may  be  attended  with  formation  of 
calcium  cyanide,!  the  separation  of  the  chlorine,  bromine,  or 

*  Special  methods  for  preparing  pure  lime  free  from  calcium  chloride 
and  sulphide  have  been  given  by  F.  SESTINI  (Zeitschr.  f.  analyt.  Chem.,  iv, 
51),  and  BRUGELMANN  (ibid.,  xv,  5). 

f  The  formation  of  cyanides  may  be  prevented  by  using,  instead  of  lime, 
a  mixture  of  lime  and  soda,  obtained  by  slaking  3  parts  quicklime  in  a  solu- 
tion of  1  part  sodium  hydroxide  (free  from  chlorine)  and  heating  the  mix- 
ture to  dryness  in  a  silver  dish.  ROSE,  Hand,  der  Anal.  Chem.,  6.  Aufl.  von 
FINKENER,  n,  735. 


124  ORGANIC   ANALYSIS.  [§  190, 

iodine,  if  required,  is  to  be  effected  by  the  process  given  in  §  169,  ft 
(NEUBAUER  and  KERNER  *).  If  the  lime  contains  calcium  sulphide 
(F.  SESTINI  f)  the  silver  chloride,  bromide,  or  iodide  must  be  sep- 
arated from  the  silver  sulphide.  It  is  advantageous  to  ust,  soda- 
lime  (free  from  chlorine  or  of  known  chlorine  content)  instead  of 
lime,  as  then  all  the  carbon  is  oxidized  to  carbonic  acid  and  no 
cyanides  form.  J 

In  determining  iodine  by  this  method,  a  little  iodine  set  free 
by  action  of  nitric  acid  must  be  converted  into  hydriodic  acid 
by  adding  a  little  sulphurous  acid  before  precipitating  with 
silver  nitrate.  CLASSEN  §  prefers,  in  the  case  of  substances  con- 
taining iodine,  to  pass  moist  carbonic  acid  over  the  mass  for 
several  hours  after  ignition  with  lime,  then  to  warm  with  water, 
filter  off,  cautiously  neutralize  with  nitric  acid,  and  precipitate 
the  iodine  as  silver  iodide.  In  the  analysis  of  acid  organic  com- 
pounds containing  chlorine  (e.g.,  chlorospiroylic  acid),  the  chlorine 
may  often  be  determined  in  a  simpler  manner,  viz.,  by  dissolving 
the  substance  under  examination  in  an  excess  of  dilute  solution 
of  potassa,  evaporating  to  dryness,  and  igniting  the  residue,  by 
which  means  the  whole  of  the  chlorine,  bromine,  or  iodine  present 
is  converted  into  a  soluble  haloid  salt  (Lowio). 

In  more  readily  decomposable  compounds,  e.g.,  in  the  sub- 
stitution products  of  acids,  the  halogen  may  also  be  determined  by 
decomposing  the  substance  by  contact  during  several  hours  with 
water  and  sodium  amalgam,  acidifying  the  fluid  with  nitric  acid, 
and  precipitating  with  silver  solution  (KEKULE  ||). 

2.  Ignition  with  ferric  oxide  and  iron  (E.  KOPP  ]f). 

The  combustion  tube  used  is  about  60  cm.  long  and  5  to  6  mm. 
wide,  and  is  sealed  at  one  end.  To  more  readily  control  the  decom- 
position, the  organic  substance  is  intimately  mixed  with  pure  ferric 

*  Annal.  d.  Chem.  u.  Pharm.,  ci,  324,  344. 
f  Zeitschr.  f.  analyt.  Chem.,  iv,  51. 

%  Handb.  der.  analyt.  Chem.  von  H.  ROSE,  6  Aufl.  von  R.  FINKENER,  n, 
735. 

§  Zeitschr.  f.  analyt.  Chem.,  iv,  202. 
j|  Jahresb.  v.  KOPP  u.  WILL,  1861,  832. 
f  Zeitschr  f.  analyt.  Chem.,  xv,  107. 


§   190-]  HALOGENS    IN    ORGANIC    SUBSTANCES.  125 

oxide,  prepared  by  igniting  pure  ferrous  sulphate  in  the  air,  and 
the  mixture  introduced  first  into  the  tube.  The  layer  should  be 
loose  and  from  12  to  18  cm.  long.  After  adding  the  rinsings,  in- 
troduce several  closely  wound  spirals  of  rather  fine  iron  wire;  this 
layer  is  to  have  a  length  of  from  20  to  25  cm.  Fill  the  rest  of  the 
space  in  the  tube  with  porous  crusts  of  pure  anhydrous  sodium 
carbonate,  obtained  by  moderately  heating  the  crystalline  salt  in 
a  platinum  dish. 

Now  heat  to  redness  first  that  part  of  the  tube  containing  the 
iron-wire  spirals,  and  then  heat  the  part  containing  the  mixture, 
beginning  at  the  fore  part  and  proceeding  to  the  closed  end.  The 
organic  substance  is  thus  completely  decomposed.  The  halogens 
are  obtained  as  ferrous  compounds;  any  small  quantity  of  these 
that  may  volatilize  is  decomposed  and  retained  by  the  sodium 
carbonate.  After  the  tube  is  cold,  clean  it,  cut  it  into  pieces,  and 
boil  the  whole  for  some  time  with  water.  The  iron-halogen  com- 
pounds are  thus  decomposed  by  the  sodium  carbonate.  Filter, 
wash,  acidulate  cautiously  with  nitric  acid,  and  precipitate  with 
silver  nitrate. 

3.  Combustion  in  a  current  of  oxygen. 

a.  C.  M.  WARREN'S*  process  for  determining  sulphur  (188,  I, 
5,  a),  and  to  which  we  shall  again  refer  in  §  192;  p.  145,  is  also 
employed  for  the  determination  of  chlorine  in  organic  substances. 
The  chlorine  evolved  by  the  combustion  of  the  substance  in  oxygen 
is  absorbed  by  brown  copper  oxide  (obtained  by  precipitating  a 
solution  of  a  copper  salt  with  potassa  and  igniting  over  a  gas  lamp) 
placed  in  the  anterior  part  of  the  tube  between  two  layers  of  as- 
bestos. If  the  carbon  and  hydrogen  are  to  be  also  estimated  with 
the  chlorine  in  the  same  portion  of  substance,  the  fore  part  of  the 
tube  containing  the  cupric  oxide  must  be  so  heated  that,  while  no 
carbonic  acid  or  water  is  retained,  no  chlorine  is  allowed  to  escape. 
WARREN  effects  this  by  surrounding  this  part  with  an  air-bath 
heated  by  a  gas  flame,  and  the  temperature  of  which  is  easily 
regulated. 

*  Zeitschr.  /.  analyt.  Chem.,  v,  174. 


126  ORGANIC   ANALYSIS.  [§  190. 

Difficultly  combustible  substances,  like  chloroform,  require 
different  treatment,  otherwise  a  difficultly  volatile  fluid  condenses 
in  the  unfilled  space  between  the  hinder  asbestos  layer  and  the 
layer  of  cupric  oxide  and  asbestos.  In  such  cases  mix  with  the 
asbestos  in  the  hinder  end  of  the  tube  some  zinc  oxide  (about  3 
grm.),  and  place  in  the  fore  part  of  the  tube  a  mixture  of  zinc  oxide 
(about  1  grm.)  and  asbestos.  The  temperature  of  the  air-bath 
should  not  be  allowed  to  exceed  160°. 

After  the  combustion  the  chloride  with  the  excess  of  oxide  is 
extracted  from  the  asbestos  with  dilute  nitric  acid  and  the  solu- 
tion precipitated  by  adding  silver  nitrate. 

The  test  analyses  given  by  WARREN  are  entirely  satisfactory. 
Whether  the  method  is  also  applicable  for  bromides  remains  to 
be  determined,  although  WARREN  considers  it  probable. 

/?.  G.  BRUGELMANN'S  process  for  determining  sulphur  and 
phosphorus  in  organic  substances,  which  was  detailed  in  §  188  I, 
5,  d,  is  well  adapted  for  the  determination  of  chlorine  (if  chlorine- 
free  lime  be  used);  it  is  also  applicable  for  bromine  and  iodine  if 
the  lime  be  replaced  by  soda-lime.  After  the  combustion  is  ended 
and  the  first  2  cm.  of  the  layer  of  lime  or  soda-lime  have  been  tested 
as  to  their  freedom  from  chlorine,  dissolve  the  main  portion  of  the 
lime  in  very  dilute  nitric  acid  which  had  previously  been  used  to 
rinse  out  the  tube  with,  digest  with  the  dilute  acid  for  a  long  time 
also  the  part  of  the  tube  attacked  by  the  fused  calcium  chloride, 
filter,  and  precipitate  the  solution  with  silver  nitrate. 

The  test  analyses  given  BRUGELMANN  are  very  satisfactory. 
Since  the  decomposition  of  the  substance  is  effected  in  a  current 
of  oxygen,  just  as  in  WARREN'S  method,  it  follows  that  in  the 
analysis  of  difficultly  combustible  chlorine  compounds,  like  chloro- 
form, a  modification  will  be  necessary,  similar  to  that  detailed 
under  a. 

II.  METHODS  IN  THE  WET  WAY. 

1.  Carius'  Method*  Just  as  in  the  method  of  determining 
isulphur,  CARIUS  has  gradually  improved  that  for  determining 

*  Zeitschr.  /.  analyt.  Chem.,  i,  240;  iv,  451;  x,  103. 


§   190.]  HALOGENS    IN    ORGANIC    SUBSTANCES.  127 

chlorine,  bromine,  and  iodine  in  organic  substances,  the  method 
depending  also  upon  the  oxidation  of  the  substance  with  nitric 
acid  in  a  sealed  glass  tube.  The  most  improved  method  is  based 
upon  the  use  of  nitric  acid  of  sp.  gr.  1  •  5,  just  as  in  the  determina- 
tion of  sulphur,  described  under  §  188,  11,  2.  The  additional  use 
of  potassium  dichromate,  which  CARIUS  formerly  recommended, 
is  hence  unnecessary.  The  operation  is  exactly  the  same  as  in  the 
sulphur  determinations,  with  the  single  exception  that  a  small  ex- 
cess of  silver  nitrate  is  placed  with  the  weighed  substance  and  4 
grm.  of  nitric  acid  in  the  tube.  All  the  chlorine,  bromine,  or  iodine 
in  the  substance  is  separated  as  a  silver  salt.  Neither  bromic 
nor  iodic  acid  can  form,  because  these  would  be  reduced  by  the 
nitrous  acid  also  formed.  The  decomposition  of  organic  substances 
is  effected  with  extraordinary  ease  in  the  presence  of  silver  nitrate; 
with  most  substances  in  fact  already  partially  in  the  cold.  In  the 
case  of  the  compounds  of  the  aromatic  series  the  complete  separa- 
tion of  the  halogens  is  more  difficult,  but  even  then  heating  to 
250°  to  260°  always  suffices  for  complete  decomposition.  The 
precipitate  of  silver  chloride,  bromide,  or  iodide  is  filtered  off  and 
weighed.  Before  filtering  off,  CARIUS  recommends  neutralizing 
the  greater  portion  of  the  free  nitric  acid  present  with  pure  sodium 
carbonate.  With  substances  containing  iodine  it  must  be  par- 
ticularly noted  that  silver  iodide  fuses  in  the  hot  tube  with  the  ex- 
cess of  silver  nitrate,  and  forms  a  yellow  compound  which,  on  cool- 
ing, solidifies  to  an  opaque,  yellow  mass.  This  must  be  heated  for 
one  to  two  hours  with  the  dilute  liquid  in  order  to  remove  all  the 
silver  nitrate.  The  silver  iodide  then  obtained  is  perfectly  pure. 

According  to  LINNEMANN  *  the  determination  of  iodine  is  less 
satisfactory  than  that  of  chlorine  or  bromine.  He  observed  losses 
which  he  ascribed  to  the  fact  that  silver  iodide  is  somewhat 
soluble  in  the  liquid  containing  the  silver  nitrate  and  nitric  acid. 
It  is  hence  recommended  to  avoid  too  large  an  excess  of  silver 
nitrate,  i.e.,  to  employ  only  1£  equivalent. 


Zeitschr.  /.  analyt.  Chem.,  xi,  325. 


128  ORGANIC    ANALYSIS.  [§   190. 

2.  In  the  case  of  readily  decomposable  compounds  of  chlorine, 
bromine,  or  iodine,  such  as  the  substitution  derivatives  of  acids, 
the  halogens  may  also  be  determined  by  treating  the  substance 
for  several  hours  with  water  and  sodium-amalgam,  and  (in  the 
case  of  chlorine  and  bromine  compounds)  acidulating  with  nitric 
acid  and  precipitating  with  silver  nitrate.     With  iodine  compounds, 
first  add  to  the  still  alkaline  solution  some  silver  nitrate  and  then 
add  nitric  acid  to  dissolve  the  precipitated  silver  iodide  (KEKULE  *). 

3.  For  determining  the  iodine  in  ethyltropine  hydriodide,  K. 
KRAUT  f  employed  a  very  simple  method  which  is  advantageous 
besides,  in  that  the  substance  is  not  lost.     The  process  was  also 
employed  by  RICH.  MALY  J  for  determining  the  extra-radical  bro- 
mine in  a  substance  obtained  by  the  action  of  bromine  on  thio- 
sinamine. 

Dissolve  an  accurately  weighed  quantity  of  pure  silver  in  nitric 
acid,  dilute  the  solution,  precipitate  with  hydrochloric  acid,  de- 
cant through  a  weighed  filter  to  retain  the  slight  quantity  of  silver 
chloride  in  suspension,  and  wash  the  filter.  Now  add  the  weighed 
substance  to  the  washed  silver  chloride.  After  a  few  minutes' 
standing  and  warming,  all  the  iodine  will  have  combined  with  the 
silver,  while  the  base  will  have  united  with  the  hydrochloric  acid. 
Now  collect  the  silver  iodo-chloride  on  the  weighed  filter  first  used, 
and  from  the  difference  between  the  weight  of  the  precipitate  and 
that  of  the  silver  nitrate  equivalent  to  the  silver  taken  calculate 
the  iodine. 

This  method  yields  only  the  iodine  or  bromine  which  is 
capable  of  replacing  chlorine  in  ammonium  chloride  (MALY, 
loc,  cit.). 

4.  In  compounds  of  organic  bases  with  hydrochloric,  hydro- 
bromic,  or  hydriodic   acid,  the  halogen  may  be  very  easily  de- 
termined by  precipitating  the  aqueous  solution  with  silver  nitrate. 

*  Jahresber.  von  KOPP  und  WILL,  1861,  832. 
t  Zeitschr.  /.  analyt.  Chem.,  iv,  167. 
t  Ibid.,  v,  68. 


§   191. J      COMPOUNDS   CONTAINING    INORGANIC    BODIES.  129 

F.  ANALYSIS  OF  ORGANIC  COMPOUNDS  CONTAINING  INORGANIC 

BODIES. 

§191. 

In  the  analysis  of  organic  compounds  containing  inorganic 
bodies,  it  is,  of  course,  necessary  first  to  ascertain  the  quantity  of 
the  latter  before  proceeding  to  the  determination  of  the  carbon, 
etc.,  as  otherwise  the  amount  of  the  organic  body  whose  constitu- 
ents have  furnished  the  carbonic  acid,  water,  etc.,  not  being  known, 
it  would  be  impossible  to  estimate  the  oxygen  from  the  loss. 

If  the  substances  in  question  are  salts  or  similar  compounds, 
their  basic  radicals  are  determined  by  the  methods  given  in  the 
Fourth  Section;  but  in  cases  where  the  inorganic  bodies  are  of  a 
nature  to  be  regarded  more  or  less  as  impurities  (e.g.,  the  ash  in 
coal),  they  may  usually  be  determined  with  sufficient  accuracy 
by  the  combustion  of  a  weighed  portion  of  the  substance  in  an 
obliquely  placed  platinum  crucible,  or  in  a  platinum  dish  with  the 
aid  of  a  cylinder,  to  promote  a  draught  (see  "Analysis  of  Ashes"). 
If  the  ash  still  contains  carbon,  ignite  repeatedly  with  mercuric 
oxide  until  the  weight  is  constant.  In  the  analysis  of  substances 
containing  fusible  salts,  even  long-continued  ignition  will  often 
fail  to  effect  complete  combustion,  as  the  carbon  is  protected  by 
the  fused  salt  from  the  action  of  the  oxygen.  In  such  cases  the 
best  way  to  effect  the  purpose  is  to  carbonize  the  substance,  treat 
the  mass  with  water,  and  incinerate  the  undissolved  residue;  the 
aqueous  solution  is,  of  course,  likewise  evaporated  to  dryness  and 
the  weight  of  the  residue  added  to  that  of  the  ash. 

The  determination  of  inorganic  substances  in  organic  substances 
is  not  always  as  simple  as  might  appear  at  first  sight,  for  the  ash 
often  does  not  simply  contain  the  sum  of  the  inorganic  substances 
present;  for  instance,  bases  may  have  taken  up  acids  which  were 
formed  during  the  combustion,  or  chlorides  may  have  been  vola- 
tilized during  incineration  (BEHAGHEL  v.  ADLERSKRON  *),  etc 
The  details  will  be  given  under  "Analysis  of  Ashes." 

*  Zeitschr.  f.  analyt.  Chem.,  xii,  390. 


130  ORGANIC   ANALYSIS.  [§   191. 

If  organic  compounds  whose  ash  contains  potassium,  sodium, 
barium,  strontium,  or  calcium  are  burnt  with  cupric  oxide,  part 
of  the  carbonic  acid  evolved  remains  as  carbonate  of  these  metals. 
As  in  many  cases  the  amount  of  carbonic  acid  thus  retained  is  not 
constant,  and  the  results  are,  moreover,  more  accurate  if  the  whole 
amount  of  the  carbon  is  expelled  and  weighed  as  carbonic  acid, 
certain  bodies  are  added  to  the  substance  before  mixing  this  with 
the  cupric  oxide,  which  will  decompose  the  carbonates  at  a  high 
temperature,  e.g.,  antimony  oxide,  cupric  phosphate,  boric  acid 
(FREMY),  etc.,  or  the  combustion  is  effected  with  lead  chromate, 
with  addition  of  TV  of  potassium  dichromate,  according  to  the  di- 
rections given  in  §  176.  Accurate  experiments  have  shown  that  in 
this  case  not  a  trace  of  carbonic  acid  remains  with  the  bases. 

If  the  substance  is  weighed  in  a  porcelain  or  platinum  boat, 
and  the  combustion  is  effected  according  to  §  178,  a,  the  ash,  carbon, 
and  hydrogen  may  be  determined  in  one  portion.  The  amount 
of  carbonic  acid  contained  in  the  ash  is  added  to  that  found  by  the 
process  of  combustion;  if  the  carbonic  acid  in  the  ash  cannot  be 
calculated,  as  in  the  case  of  alkali  carbonates,  it  may  be  deter- 
mined by  means  of  fused  borax,  fusing  with  potassium  dichromate, 
by  PERSOZ'S  method,  or  by  some  other  means  (§  139). 

In  burning  substances  containing  mercury,  the  arrival  of  any  of 
the  metal  at  the  calcium-chloride  tube  may  be  prevented  by  having 
a  layer  of  metallic  copper  (copper  turnings,  a  roll  of  foil,  or  wire 
spiral)  in  the  anterior  part  of  the  combustion  tube,  and  by  not  al- 
lowing the  foremost  portion  to  get  too  hot. 

Substances  with  radicals  containing  metals,  or  such  as  contain 
volatile  metals,  may  be  analyzed  with  the  greatest  ease  by  CARIUS'S 
method  (page  117).  The  metals  are  determined  in  the  nitric- 
acid  solution  obtained  by  means  of  the  usual  methods.  If  the 
substances  also  contain  sulphur,  the  metals  may  be  precipitated 
by  sodium  carbonate  (should  they  be  precipitable  by  this),  and 
the  sulphuric  acid  determined  in  the  nitrate. 

In  the  case  of  substances  which  contain  chlorine,  bromine,  and 
iodine,  the  silver  in  the  nitrate  from  the  precipitated  silver  chloride, 
bromide,  or  iodide  must  first  be  precipitated  by  hydrochloric  acid, 


§   192.]         DIRECT    DETERMINATION    OF   OXYGEN,  ETC.  131 

and  the  metal  in  the  organic  substance  then  determined  in  the 
nitrate. 

If  the  substances  contain  mercury,  this  may  be  determined 
together  with  the  carbon  and  hydrogen  by  a  modification  of  the 
usual  combustion  process  (FRANKLAND  and  DUPPA*).  Substances 
containing  arsenic  may  also  be  analyzed  by  BRUGELMANN'S  phos- 
phorus method,  pages  112  and  120.  f 

SUPPLEMENT  TO  §§  174  TO  191. 

§192. 

In  this  supplement  there  are  detailed  under  A  those  methods 
whereby  oxygen  is  directly  determined,  whether  by  itself  alone 
or  conjointly  with  other  elements;  under  B,  however,  are  given 
several  methods  of  ultimate  organic  analyses  in  which  the  princi- 
ples upon  which  they  are  based  or  the  apparatus  used  differ  ma- 
terially from  the  methods  ordinarily  followed. 

A.  METHODS  FOR  THE  DIRECT  DETERMINATION  OF  OXYGEN. 

As  already  mentioned,  the  oxygen  is  determined,  in  the  ordinary 
methods  of  organic  analysis,  from  the  loss.  Formerly  no  methods 
were  known  for  its  direct  determination ;  such  are  now  known,  but 
they  are  only  exceptionally  used  because  they  are  as  a  rule  incon- 
venient, and  afford  accurate  results  only  when  the  greatest  care 
is  exercised.  It  is  remarkable,  too,  that  of  all  the  methods  here 
detailed  scarcely  any  have  been  tested  except  by  their  authors. 

a.  v.  BAUMHAUER  was  the  first  to  propose  a  method  for  the 
direct  determination  of  oxygen.!  It  consists  in  employing  a  pre- 
viously measured  volume  of  oxygen  in  the  process  usually  followed 
in  determining  the  carbon  and  hydrogen,  in  order  that  the  copper 
may  be  reoxidized.  The  difference  between  the  oxygen  taken 
up  by  the  copper  and  that  present  in  the  carbonic  acid  and  water 
formed  gives  the  oxygen  in  the  substance  analyzed. 

As  in  this  method  the  total  cubic  capacity  of  the  apparatus 
must  be  known  in  order  to  make  the  necessary  correction  for 

*  Annal.  d.  Chem.  u.  Pharm.,  cxxx,  107;  Zeitschr.  f.  analyt.  Chem.,  iv,  138. 

t  Zeitschr.  f.  analyt.  Chem.,  xvi,  1. 

t  Annal.  d.  Chem.  u.  Pharm.,  xc   228. 


132  ORGANIC    ANALYSIS.  [§   192. 

temperature  and  pressure,  and  as  this  requirement  cannot  be  easily 
and  accurately  met,  v.  BAUMHAUER  now  recommends  *  using  a 
weighed  quantity  of  a  substance  which,  on  ignition,  will  yield  a 
given  quantity  of  oxygen;  e.g.,  dry  silver  iodate,  which  answers 
the  purpose  admirably.  The  process  is  thus  adapted  not  only 
for  the  determination  of  carbon,  hydrogen,  and  oxygen,  but,  with 
a  modification  to  be  described  further  on,  also  of  nitrogen,  and 
in  one  and  the  same  portion  of  substance. 

The  combustion  tube  used  is  from  70  to  80  cm.  long  and  open 
at  both  ends.  It  is  charged  as  follows,  beginning  at  the  fore  part 
(which  is  connected  with  the  weighed  absorption  apparatus) :  20 
cm.  copper  turnings,  20  cm.  fragments  of  porcelain  (previously 
washed  with  hydrochloric  acid  and  ignited),  25  cm.  strongly  ig- 
nited, coarsely  granular  cupric  oxide  free  from  powder  and  held 
between  asbestos  plugs,  then  an  unfilled  space  of  5  cm.,  then  the 
weighed  substance  (contained  in  a  boat  if  solid,  or  in  a  small  glass 
bulb  if  liquid)  which,  if  difficultly  combustible,  may  be  mixed  with 
cupric  oxide;  then  another  unfilled  space  of  6  to  7  cm.,  and  lastly 
a  second  boat  containing  a  known  weight  (a  few  grammes)  of  pure 
silver  iodate  dried  at  about  140°. f  A  constant  hydrogen-gas  ap- 
paratus and  a  gasometer  filled  with  pure  nitrogen  are  also  required. 
Both  gases  are  passed  through  the  same  purifying  apparatus  con- 
nected with  the  hinder  end  of  the  combustion  tube.  The  purify- 
ing apparatus  consists  of  a  tube  filled  with  copper  turnings  and 
maintained  at  a  red  heat  during  the  whole  operation,  and  two 
U-tubes,  one  of  which  is  filled  with  fragments  of  pumice-stone 
saturated  with  sulphuric  acid;  the  other  U-tube  is  half  filled  with 
soda-lime,  the  other  half,  which  is  next  the  combustion  tube,  being 
filled  with  calcium  chloride. 

Before  attaching  the  apparatus  for  absorbing  the  water  and 
carbonic  acid,  heat  the  fore  part  of  the  tube  for  a  short  distance 
beyond  the  copper  turnings,  and  pass  a  slow  current  of  hydrogen 
through  the  tube,  in  order  to  make  sure  that  the  copper  is  free 
from  cupric  or  cuprous  oxide.  Now  displace  the  hydrogen  by 

*  Zeitschr.  /.  analyt.  Chem.,  v,  141. 

f  For  its  preparation,  see  loc.  tit.,  p.  143. 


§  192.]          DIRECT    DETERMINATION   OF    OXYGEN,    ETC.  133 

nitrogen,  and,  while  still  maintaining  a  gentle  current  of  the  gas, 
heat  the  part  of  the  tube  containing  the  fragments  of  porcelain 
and  the  cupric  oxide.  Then  attach  the  calcium-chloride  tube 
and  the  potash  bulbs  with  their  potassium-hydroxide  tube  to  the 
combustion  tube.  After  the  nitrogen  gas  has  been  passed  through 
the  apparatus  long  enough  to  completely  fill  it,  and  even  to  saturate 
the  potassa  solution,  weigh  the  cooled  absorption  apparatus  and 
place  it  again  in  position.  Now  heat  with  great  caution  the  sub- 
stance to  be  analyzed,  while  constantly  maintaining  a  slow  current 
of  nitrogen.  As  soon  as  the  substance  has  been  burned,  or  at  least 
completely  carbonized,  very  gradually  heat  the  silver  iodate. 
The  oxygen  evolved  burns  the  carbon  and  oxidizes  the  copper 
resulting  from  the  reduction  of  the  cupric  oxide.  The  excess  of 
oxygen  is  taken  up  by  the  copper  turnings.  After  complete  de- 
composition of  the  silver  iodate,  continue  to  pass  for  some  tune 
a  gentle  current  of  nitrogen  through  the  apparatus  and  then  re- 
move the  absorption  apparatus  to  weigh  it.  Now  close  the  gas 
cocks  one  by  one  until  only  those  that  heat  the  copper  turnings 
remain  lit.  Without  stopping  the  current  of  nitrogen,  wait  until 
the  cupric  oxide  has  become  perfectly  cold  and  then  attach  a  fresh, 
weighed  calcium-chloride  tube.  Now  replace  the  current  of  nitro- 
gen by  one  of  hydrogen  in  order  to  reduce  the  cupric  and  cuprous 
oxides  which  have  formed  on  the  surface  of  the  copper  turnings- 
The  oxygen  contained  in  these  oxides  unites  with  the  hydrogen 
to  form  water;  the  quantity  is  equivalent  to  the  increase  in  weight 
of  the  calcium-chloride  tube.  After  the  boat  has  been  withdrawn 
by  means  of  a  wire  from  the  combustion  tube,  the  latter  is  ready 
for  a  fresh  analysis. 

The  calculation  is  as  follows:  Add  together  the  oxygen  in 
the  carbonic  acid  and  the  water  (collected  in  both  calcium-chloride 
tubes) ,  and  from  this  sum  deduct  the  oxygen  in  the  weighed  silver 
iodate  used  (100  parts  of  the  salt  dried  at  about  140°  yielded 
v.  BAUMHAUER  16-92  parts  of  oxygen*).  The  difference  is  the 
oxygen  contained  in  the  substance. 

*  With  the  atomic  weights  used  in  this  translation  the  theoretical  quantity 
is  16  97  parts — TRANSLATOR. 


134  ORGANIC    ANALYSIS.  [§   192. 

The  test  analyses  of  oxalic  acid  and  of  uric  acid,  supplied  by 
v.  BAUMHAUER,  gave  very  satisfactory  results.* 

If  the  nitrogen  is  to  be  determined  in  the  same  portion  of  sub- 
stance, prepare  the  apparatus  as  before,  but  place  a  screw  pinch- 
cock  on  the  rubber  tube  which  connects  the  hinder  end  of  the  com- 
bustion tube  with  the  U-tubes.  Proceed  just  as  before  up  to  the 
point  where  the  combustion  of  the  substance  is  to  be  commenced. 
While  the  nitrogen  is  still  passing  slowly  through  the  apparatus, 
connect  the  potash  bulbs  with  a  system  of  tubes,  which  serves  to 
measure  the  volume  of  gas  in  the  whole  apparatus  before  and  after 
combustion  of  the  substance.  The  system  consists  of  two  vertical 
tubes  the  lower  ends  of  which  are  connected  by  a  long,  very  stout 
rubber  tube.  One  tube  is  fixed  and  graduated;  the  other  is  sus- 
pended by  a  cord,  and  may  be  raised  or  lowered.  The  system  is 
filled  with  sufficient  mercury  to  completely  fill  the  rubber  tube 
and  about  half  fill  the  vertical  tubes.  Before  connecting  the 
graduated  tube  with  the  potash  bulbs,  it  must  be  completely  filled 
with  mercury  by  raising  the  movable  tube. 

As  soon  as  the  mercury  reaches  the  level  at  which  the  gradua- 
tions on  the  tube  begin,  close  the  screw  pinch-cock  behind  the 
combustion  tube,  allow  to  cool,  and  determine  the  volume  of  gas 
in  the  apparatus  by  taking  two  readings  at  different  pressures, 
the  first  at  diminished  pressure  of  20  mm.,  the  second  with  the 
mercury  at  the  same  height  in  both  tubes.  Now  burn  the  sub- 
stance as  before,  but  without  using  a  current  of  nitrogen,  and  with- 
out heating  the  silver  iodate.  After  the  combustion  is  over,  and 
the  apparatus  has  been  allowed  to  cool  for  several  hours,  take 
two  readings  again  at  different  pressures,  in  order  to  ascertain  the 
volume  of  gas  in  the  entire  apparatus.  The  difference  gives  the 
volume,  and  from  this  the  weight,  of  the  nitrogen  in  the  substance. 

*ALEX.  MITSCHERLICH  (Elementar analyse  vermittelst  Quecksilberoxyds, 
Berlin,  MITTLER  u.  SOHN,  1875;  Zeitschr.  f.  analyt.  Chem.,  xv,  371)  con- 
cludes, from  observations  made  by  him,  that  it  is  very  difficult  to  completely 
reconvert  reduced  copper  into  cupric  oxide  by  heating  in  oxygen,  as  a  kernel 
of  cuprous  oxide  will  remain  if  the  grains  are  of  any  size,  and  particularly 
if  the  substances  are  rich  in  carbon  and  hydrogen ;  v.  BAUMHAUER'S  method 
hence  presents  a  source  of  error  very  difficult  to  obviate. 


§  192.]         DIRECT  DETERMINATION    OF    OXYGEN,    ETC.  135 

Now  disconnect  the  tube  system  from  the  potash  bulbs,  remove 
the  screw  pinch-cock  from  behind  the  combustion  tube,  and  com- 
plete the  combustion  by  heating  the  silver  iodate,  etc.,  as  already 
described. 

The  method  of  simultaneously  determining  nitrogen,  although 
very  well  conceived,  is  nevertheless  imperfect,  so  that,  even  as 
v.  BAUMHAUER  admits,  it  may  be  only  rarely  employed.  As  a  rule 
it  is  preferable  to  determine  the  nitrogen  in  a  separate  portion  of 
the  substance. 

6.  STROMEYER'S  method*  is  based  on  the  determination  of 
the  metallic  copper  or  cuprous  oxide  formed  in  the  combustion. 
The  residue  is  taken  up  with  a  solution  of  ferric  chloride  and  hydro- 
chloric acid,  or  better,  ferric  sulphate  and  sulphuric  acid,  and 
the  ferrous  salt  titrated  with  permanganate  (Cu+Fe2Cl6  =  CuCl2 
+  2FeCl2;  or,Cu2O+Fe2Cl6+2HCl  =  2CuCl2+2FeCl2+H20).  It  is 
thus  evident  that,  no  matter  whether  cupric  oxide  is  reduced  to 
copper  or  to  cuprous  oxide,  for  each  equivalent  of  oxygen  given  up 
2FeCl2  or  2FeO  are  obtained.  On  adding  together  the  oxygen 
contained  hi  the  carbonic  acid  and  water,  and  deducting  from 
this  sum  1  eq.  of  oxygen  for  every  2  eq.  of  FeO  obtained,  the  oxy- 
gen in  the  substance  is  found.  As  the  cupric  oxide  to  be  used 
must  be  free  from  cuprous  oxide,  it  should  be  prepared  from  basic 
cupric  carbonic  by  heating  in  a  glass  flask  (not  in  a  crucible).  The 
oxide  prepared  thus  is  not  so  well  adapted  for  determinations -of 
carbon  and  hydrogen,  because  with  it  the  carbonic  acid  and  water 
are  very  rapidly  evolved.  STROMEYER  hence  recommends  not 
to  determine  the  oxygen  simultaneously  with  the  carbon  and 
hydrogen,  but  to  use  for  this  a  separate  portion  of  the  substance. 
As  the  cupric  oxide  above  mentioned  is  very  reducible,  much  less  of 
it  need  be  employed  than  of  the  coarse  oxide.  Organic  substances 
containing  sufficient  oxygen  to  form  water  with  the  hydrogen 
require  about  three  times  as  much  oxide  as  would  be  required 
theoretically,  and  those  which  contain  an  excess  of  hydrogen  will 
require  four  times  as  much.  For  the  sake  of  certainty,  however, 

*  Annal.  d.  Chem.  u.  Pharm.,  cxvii,  247. 


136  ORGANIC    ANALYSIS.  [§   192. 

more  than  this  is  taken.  The  cupric  oxide  is  mixed  with  half  its 
weight  of  dry  sodium  carbonate.  This  mixture  sinters  on  being 
ignited,  so  that  the  last  particles  of  carbon  are  thereby  burned. 
The  sulphur  in  organic  substances  burns  with  this  mixture  to 
sodium  sulphate,  and  chlorine  yields  sodium  chloride;  and  here 
it  must  not  be  forgotten  that  the  oxygen  of  the  sodium  carbonate 
is  expelled  and  is  utilized  to  form  carbonic  acid  and  water.  For 
nitrogenous  substances,  the  method  is  not  so  well  adapted,  as 
nitro-compounds  yield  too  much  reduced  copper,  because  nitrogen 
oxides  escape;  with  other  nitrogenous  compounds,  however,  the 
results  are  almost  correct. 

Mix  the  substance  with  the  mixture  of  oxide  and  sodium  car- 
bonate in  a  smooth  dish,  using  a  spoon,  introduce  into  the  tube 
through  a  small  funnel,  and  then  add  an  equal  quantity  of  cupric 
oxide.  The  latter  is  granulated  like  gunpowder  by  adding  to  it 
one-tenth  its  weight  of  sodium  carbonate,  moistening  the  mixture 
with  water  and  passing  it  through  a  sieve  made  from  a  metallic 
plate  with  holes  one-twelfth  of  an  inch  in  diameter,  then  drying, 
and  sifting  it  free  from  dust.  The  glass  tube  is  connected  by 
means  of  a  cork  or  rubber  tube  with  a  glass  tube  drawn  out  to  a 
fine  point.  Now  give  the  tube  a  few  taps  and  then  heat  as  usual, 
proceeding  slowly  from  the  fore  part  to  the  rear.  When  the  entire 
tube  is  red-hot  fuse  the  opening  of  the  small  glass  tube  and  allow 
the  combustion  tube  to  cool.  Then  transfer  the  contents  of  the 
tube  (with  the  pieces  of  the  glass  tube,  if  it  cannot  be  done  other- 
wise) to  a  flask,  and  digest  with  a  solution  of  ferric  sulphate  con- 
taining 8  per  cent,  of  ferric  oxide  and  free  from  ferrous  oxide  and 
nitric  acid.  Use  double  the  quantity  of  solution  theoretically 
required,  and  which,  based  upon  the  determination  as  usual  of 
oxygen  from  the  loss  (which  should  be  here  controlled),  is  known, 
and  add  somewhat  more  dilute  sulphuric  acid  (prepared  from  the 
distilled  acid)  than  is  required  to  neutralize  the  sodium  carbonate 
and  dissolve  the  cupric  oxide.  Provide  the  flask  with  a  MOHR 
caoutchouc  valve  (if  it  is  not  preferred  to  pass  in  a  stream  of  car- 
bonic acid),  and  carefully  heat  until  all  the  copper  is  dissolved. 
If  a  few  red  specks  remain  adhering  to  the  glass,  in  consequence 


§   192.]        DIRECT    DETERMINATION    OF   OXYGEN,    ETC.  137 

of  the  application  of  too  high  a  heat,  pour  the  sulphuric-acid  solu- 
tion, when  cold,  into  a  litre  flask,  heat  the  fragments  of  the  glass 
tube  with  a  small  quantity  of  ferric  chloride  and  hydrochloric  acid, 
add  this  solution  to  the  other,  and  dilute  with  water.  Should 
the  solution  so  obtained  not  possess  a  color  like  that  of  copper  sul- 
phate, but  be  yellowish  green,  it  indicates  a  deficiency  of  sul- 
phuric acid,  hence  some  of  this  must  be  added.  Finally  fill  with 
water  up  to  the  mark,  mix,  and  take  250  c.c.  of  the  solution  for 
titration,  first  mixing  it  with  about  250  c.c.  of  water.  In  order 
to  correct  the  error  which  is  introduced  by  reason  of  a  fluid  con- 
taining both  ferric  sulphate  and  cupric  sulphate  requiring  more 
permanganate  to  color  it  than  does  water,  dissolve  one-fourth  of 
the  cupric  oxide  employed  (the  fine  and  the  granulated)  in  dilute 
sulphuric  acid,  add  one-fourth  of  the  above-mentioned  ferric-sul- 
phate solution,  dilute  to  500  c.c.,  and  add  permanganate  solution 
(diluted  for  this  purpose  tenfold,  however)  to  redness.  The  test 
analyses  given  by  the  author  of  the  process  are  satisfactory  *  enough, 
but  as  detailed  even  in  the  experiment,  there  is  always  less  oxygen 
used  than  theory  requires,  hence  the  oxygen  content  of  the  sub- 
stance is  always  too  high.  The  main  cause  of  this  error  is  most 
probably  the  atmospheric  air  in  the  tube,  and  STROMEYER  hence 
suggests  that  in  order  to  obtain  more  accurate  results  it  would  be 
advisable  to  remove  the  air  by  alternately  exhausting  and  filling 
with  carbonic  acid. 

c.  AL.  MITSCHERLICH  has  for  years  been  at  work  trying  to 
find  a  method  by  which  all  the  elements  of  an  organic  substance 

*  For  the  sake  of  greater  clearness,  the  details  of  one  analysis  are  here 
given :  0-  202  grm.  of  cane-sugar  mixed  with  3  grm.  CuO  and  1  •  5  grm.  Na2CO3 
and  3  grm.  granulated  cupric  oxide,  placed  in  front.  Dissolved  in  50  c.c. 
solution  of  ferric  sulphate  containing  8  per  cent,  of  Fe2O3  and  8  c.c.  distilled 
sulphuric  acid  and  diluted  to  1  litre.  250  c.c.  of  this  solution  diluted  to 
500  c.c.  required  in  two  experiments  48-6  c.c.  permanganate  solution,  of 
which  17 -3  c.c.=  l  grm.  ferrous-ammonium  sulphate  or  0-020408  oxygen. 
A  solution  of  0-  75  grm.  fine  and  0-  75  grm.  granulated  CuO  in  dilute  sulphuric 
acid  mixed  with  12-5  c.c.  ferric  oxide  in  solution,  and  water  to  make  half  a 
litre,  required  0-9  c.c.  of  the  permanganate  solution.  This  0-9  c.c.  deducted 
from  the  48-6  c.c.  gives  47-7  c.c.,  which  multiplied  by  4  gives  190-  8= 0-  225078 
oxygen.  For  1  eq.  of  cane-sugar,  C12H22OU,  this  makes  190-5  O  instead  of 
192  (12  at.),  which  are  actually  required. 


138  ORGANIC   ANALYSIS.  [§  192. 

may  be  determined  in  one  and  the  same  analysis.  For  this  pur- 
pose he  first  decomposed  the  organic  substances  by  heating  in  a 
current  of  chlorine,*  whereby  the  hydrogen  was  obtained  in  the 
form  of  hydrochloric  acid,  the  oxygen  in  the  form  of  carbonic  acid 
and  carbonic  oxide,  and  all  thus  determined  (the  numerous  test 
analyses  give  the  hydrogen  and  oxygen  very  satisfactorily).  Later 
onf  he  used  potassium-platinic  chloride  instead  of  chlorine,  in 
order  to  be  able  to  determine  the  carbon  also,  as  well  as  the  oxy- 
gen and  hydrogen,  by  one  combustion,  and  further,  still  more  im- 
proved this  method  by  burning  the  substance  with  a  mixture  of 
potassium-platinic  chloride  and  potassium  chloride.  As,  how- 
ever, in  these  methods  a  portion  of  the  carbon  is  obtained  as  car- 
bon tetrachloride,  whereby  the  carbon  determination  is  rendered 
more  difficult,  he  endeavored  to  attain  the  desired  effect  by  other 
methods,  and  finally  succeeded  in  devising  a  process  whereby  the 
carbon,  hydrogen,  and  especially  oxygen,  as  well  as  nitrogen,  chlo- 
rine, bromine,  iodine,  sulphur,  phosphorus,  and  any  inorganic  sub- 
stances that  might  be  present,  could  be  accurately  determined 
in  one  singl"  analysis.^ 

The  process  consists  in  effecting  the  combustion  of  the  sub- 
stance with  mercuric  oxide.  At  the  temperature  at  which  mer- 
curic oxide  itself  is  decomposed,  there  form,  at  the  expense  of  the 
oxygen  of  a  portion  of  the  mercuric  oxide,  water,  carbonic  acid, 
and  mercury.  On  weighing  the  carbonic  acid  and  water  the  car- 
bon and  hydrogen  are  found;  on  weighing  the  mercury  reduced 
the  oxygen  used  up  in  the  combustion  is  found;  and  on  deducting 
this  latter  from  the  oxygen  present  in  the  combustion  products, 
that  present  in  the  organic  substance  is  found.  In  the  case  of 
nitrogenous  substances,  the  nitrogen  is  obtained  partly  as  such 
and  partly  as  nitric  oxide.  Chlorine,  bromine,  and  iodine,  if  pres- 
ent, combine  with  the  mercury  reduced.  Sulphur  and  phosphorus 
are  obtained  as  mercury  sulphate  and  mercury  metaphosphate 
respectively.  These  salts  as  well  as  almost  all  the  inorganic  sub- 

*  Zeitschr.  /.  analyt.  Chem.,  vi,  136.  f  Ibid->  VII>  272- 

J  Ibid.,  xm,  74;  xv,  371;  also  in  the  brochure,  Elementaranal.  vermitt. 
Queckiilberoxyd,  Berlin,  MITTLER  u.  SOHN,  1875. 


§   192.]          DIRECT   DETERMINATION   OF   OXYGEN,  ETC.  139 

stances  usually  present  remain  with  the  mercuric  oxide  and  must 
later  be  separated  therefrom  and  determined. 

AL.  MITSCHERLICH  has  analyzed  a  large  number  of  various 
substances  according  to  his  method,  and  generally  with  very  satis- 
factory results^  Reports  of  other  chemists  regarding  the  method 
are  not  at  hand. 

The  method  and  the  special  apparatus  required  for  it  have 
been  most  minutely  described  by  MITSCHERLICH.  As,  however, 
serviceable  results  cannot  be  had  without  careful  attention  to  all 
details,  it  would  be  useless  to  give  a  brief  description  of  the  method, 
hence  I  refer  to  the  original  source. 

d.  A.  LADENBURG  *  oxidizes  the  substance  to  be  analyzed  in  a 
sealed  tube  with  silver  iodate  and  sulphuric  acid.    The  substance 
is  weighed  in  a  small  glass  bulb    and  introduced  with  sulphuric 
acid  and  a  known  weight  of  silver  iodate  into  a  tube,  which  is  then 
drawn  out  and  sealed.     After  the  small  glass  bulb  has  been  shat- 
tered by  striking  the  tube  on  the  hand,  heat  the  tube.     When  the 
reaction  is  over  and  the  tube  has  cooled,  weigh  the  latter,  fuse 
the  point  so  as  to  allow  the  gas  to  blow  out  and  escape,  expel  the 
carbonic  acid  absorbed  by  the  sulphuric    acid   by  heating   and 
exhausting,  weigh,  and  repeat  the  operations  until  the  weight  is 
constant.     The  loss  of  weight  is  equal  to  the  carbonic  acid  formed, 
from  which  the  carbon  content  of  the  substance  may  be  calculated. 
Now  cut  the  tube  in  two,  rinse  out  its  contents,  add  potassium 
iodide,  and  determine  the  liberated  iodine  as  under  §146.     The 
iodine  found  gives  the  undecomposed  (as  well  as  the  decomposed) 
silver  iodate,  from  the  quantity  of  which  the  oxygen  necessary 
for  the  oxidation  of  the  substance  may  be  calculated. 

The  test  analyses  supplied  by  LADENBURG  are  on  the  whole 
quite  satisfactory. 

e.  J.  MAUMEN^  f  effects  the  combustion  of  the  substance  with 
litharge  to  which,  in  order  to  prevent  fusion,  one-fourth  its  weight 
of  calcium  phosphate  is  added.     Carbonic  acid  and  water  are  ob- 
tained, as  in  the  ordinary  process,  but  also  metallic  lead.     In  order 

*  Annal.  d.  Chem.  u.  Pharm.,  cxxxv,  1;  Zeitschr.  f.  analyt.  Chem.,  iv,  192. 
t  Compt.  rend.,  LV,  432;  Zeitschr.  f.  analyt.  Chem.,  i,  487. 


140  ORGANIC    ANALYSIS.  [§   192. 

to  obtain  this  as  a  button,  mix  the  contents  of  the  tube,  after  the 
combustion,  with  about  double  their  quantity  of  pure  litharge,  trans- 
fer the  mass  to  a  crucible,  cover  with  a  layer  of  pure  litharge,  and 
heat  to  fusion.  The  button  obtained  is  finally  cleaned  and  weighed. 
The  oxygen  in  the  substance  is  found  by  adding  together  the 
oxygen  in  the  carbonic  acid  and  water  and  subtracting  from  the 
sum  that  corresponding  to  the  lead  obtained.  MAUMENE  does 
not  state  how  the  error  occasioned  by  the  atmospheric  oxygen 
inclosed  in  the  tube  is  avoided. 

/.  CRETIER  *  conducts  the  products  of  the  dry  distillation  of 
the  substance  over  a  known  weight  of  magnesium  heated  in  a 
weighed  combustion  tube,  reduces  thereby  the  water  and  the 
greater  part  also  of  the  carbon  oxides,  weighs  the  tube  again,  sub- 
jects to  special  analysis  the  gaseous  mixture  which  escapes  from 
the  tube  and  which  consists  of  hydrogen,  methyl  hydride,  and 
perhaps  carbonic  oxide.  From  the  data  so  obtained,  the  carbon,, 
hydrogen,  and  oxygen  in  the  substance  are  calculated. 

The  results  are  inaccurate,  however,  and  leave  much  to  be 
desired. 

B.  METHODS  OF  ORGANIC  ANALYSIS  WHICH  DIFFER  MATERIALLY 
FROM  THE  ORDINARY  METHODS  IN  PRINCIPLE  OR  APPA- 
RATUS USED,  AND  WHICH  DO  NOT  EFFECT  A  DIRECT  DETER- 
MINATION OF  THE  OXYGEN. 

a.  CLOEZ  f  has  described  a  process  for  determining  the  car- 
bon and  hydrogen  (and  nitrogen  also)  in  organic  substances,  and 
which  is  adapted  for  solid  or  liquid,  non-volatile  or  volatile  bodies, 
whether  they  consist  only  of  carbon,  hydrogen,  and  oxygen,  or 
whether  they  contain  also  nitrogen,  sulphur,  chlorine,  bromine, 
iodine,  or  inorganic  substances.  In  order  to  be  able  to  present 
the  method  in  a  connected  form,  it  has  been  preferably  given  in 
this  supplement.  The  characteristic  feature  of  the  process,  which 
in  general  is  modeled  after  that  described  in  §  178,  is  that  the  glass 

*  Zeitschr.  /.  analyt.  Chem.,  xm,  1. 

t  Annal.  de  chim.  et  de  Phys.,  Ser.  [Ill]  LXVIII,  394. 


§   192.J  VARIOUS   METHODS    OF    ANALYSIS.  141 

combustion  tube  is  replaced  by  a  tube  of  wrought  iron,  and  that 
instead  of  oxygen,  purified  air  only  is  used.  In  con- 
sequence of  the  first  change  the  apparatus  remains  in 
a  condition  to  be  used  over  and  over  again,  and  is 
hence  especially  adapted  for  extensive  series  of 
scientific  or  technical  experiments.  The  accuracy 
of  the  process  has  been  fully  proved  by  numerous  test 
analyses  of  the  most  varied  kind.  The  majority  of  the 
results  obtained  are  thoroughly  satisfactory.  The  com- 
bustion tube,  Fig.  75,  is  of  wrought  iron  20  to  22  mm. 
diameter  and  115  cm.  long.  Each  end  projects  20  cm. 
from  the  furnace.  The  first  thing  done  is  to  oxidize  the 
inner  surface  by  heating  the  tube  to  redness  and  passing 
steam  through  it.*  As  soon  as  this  is  fully  accomplished,  . 
fill  the  part  between  E  and  F  with  a  layer  of  strongly 
ignited  coarse  cupric  oxide,  keeping  it  well  in  place  by 
means  of  superficially  oxidized  copper-foil  spirals.  The 
unfilled  portions  of  the  tube,  FB  and  AE,  are  destined  jj 
to  contain  the  long,  semi-cylindrical  boats  of  stout  sheet 
iron,  which  may  be  removed  by  means  of  an  iron  wire  ^ 
attached  to  one  end  of  each.  The  boat  inserted  in  the 
fore  part  of  the  tube  at  D  is  20  cm.  long;  in  the  case  of 
substances  composed  only  of  carbon,  hydrogen,  and 
oxygen,  it  is  filled  with  coarse  cupric  oxide,  or,  if  the  sub- 
stance is  readily  combustible,  it  is  omitted  altogether. 
If  the  substance  contains  nitrogen,  the  boat  is  filled  with 
freshly  reduced  copper  turnings;  when  the  substance 
contains  sulphur  or  chlorine,  the  boat  is  filled  with 
minium  or  lead  chromate.  The  boat  inserted  into  the 
hinder  end  of  the  tube  from  C  to  E  is  30  cm.  long.  In 
the  analysis  of  substances  which  consist  only  of  carbon, 
hydrogen,  and  oxygen,  the  boat  is  filled  with  moderately 
ignited  cupric  oxide;  in  the  analysis  of  such  as  contain 
sulphur,  chlorine,  or  bromine,  it  is  filled  with  fused  and 

*  This  procedure  is  of  great  importance,  since  it  appears  to  destroy  the 
very  notable  permeability  of  red-hot  iron  observed  by  SAIXT-CLAIRE  DE- 


142  ORGANIC    ANALYSIS.  [§192 

powdered  lead  chromate.  To  collect  the  water  produced  by  the 
combustion,  CLOEZ  uses  a  U-tube  filled  with  pumice-stone  saturated 
with  sulphuric  acid,  then  the  potash  bulbs,  and  finally  a  U-tube  filled 
with  fragments  of  potassium  hydroxide.  The  air  to  be  passed  through 
the  tube  is  first  passed  through  a  small  flask  containing  dilute  potassa 
solution  into  which  the  air-delivery  tube  just  dips,  then  through  an 
upright  cylinder  contracted  at  its  lower  end  and  filled  with  pumice- 
stone  saturated  with  sulphuric  acid  (Fig.  83,  Vol.  I,  p.  290),  then 
through  two  long,  horizontal  tubes  with  turned-up  ends,  the  first 
being  filled  with  porous  calcium  chloride,  the  second  with  frag- 
ments of  potassium  hydroxide.*  If  a  solid  substance  composed 
only  of  carbon,  hydrogen,  and  oxygen  is  to  be  burned,  fill  both 
boats  with  cupric  oxide,  as  already  stated,  heat  the  tube  along  its 
entire  length  within  the  furnace,  and  for  10  to  15  minutes  conduct 
a  slow  current  of  air  through  it,  while  the  fore  end  is  left  open. 
Allow  part  of  the  tube  containing  the  boat  C  E  to  cool,  seize  the 
tube  with  a  pair  of  tongs,  Fig.  76,  remove  the  stopper  A,  and  with- 
draw the  boat,  leaving  it  to  cool  in  a  closed  iron  tube  kept  for  this 
purpose,  unless  it  is  preferred  to  allow  it  to  cool  in  the  combustion 
tube.  As  soon  as  the  boat  is  sufficiently  cool,  so  that  volatilization 


FIG.  76.  FIG.  77.  FIG.  77a. 

or  decomposition  of  the  substance  is  no  longer  to  be  feared,  with- 
draw it  with  the  tongs,  place  it  on  the  sheet  of  copper  foil,  and  by 
means  of  a  polished  iron  hook,  Fig.  77,  transfer  a  portion  of  the 

VILLB  and  TROOST  (Compt.  rend.,  LVII,  965,  and  Zeitschr.  f.  analyt.  Chem., 
in,  351),  and  CAILLETET  (Compt.  rend.,  LVIII,  327  and  1057;  Zeitschr.  fm 
analyt.  Chem.,  in,  353). 

*  This  arrangement  of  the  drying  apparatus  is  not  correct.  It  allows 
the  entrance  of  air  dried  by  calcium  chloride,  whereas  air  dried  by  sulphuric 
acid  leaves  the  water-absorbing  U-tube.  This  explains  why  CLOEZ  always 
found  a  few  tenths  per  cent,  too  much  hydrogen.  The  construction  of  the 
drying  apparatus  should  hence  be  so  changed  that  the  air,  freed  from  car- 
bonic acid,  should  pass  last  through  the  sulphuric-acid  tube  before  entering 
the  combustion  tube. 


§  192.]  VARIOUS    METHODS    OF   ANALYSIS.  143 

cupric  oxide  to  the  small  brass  shovel,  Fig.  77  a.  Now  quickly  dis- 
tribute the  substance  to  be  burned  over  the  cupric  oxide  remain- 
ing in  the  boat,  cover  rapidly  with  the  cupric  oxide  in  the  shovel, 
reinsert  the  boat  at  once  in  the  combustion  tube,  which  has  previ- 
ously been  connected  with  the  absorption  apparatus,  close  the 
hinder  end  of  the  tube  with  its  stopper,  and  pass  air  slowly  through 
the  apparatus.  The  combustion  is  then  effected,  i.e.,  the  sub- 
stance is  heated  beginning  at  the  fore  end  and  proceeding  gradu- 
ally to  the  hinder  end,  while  the  middle  and  fore  parts  of  the  tube 
are  maintained  at  a  red  heat.  The  progress  of  the  combustion 
as  well  as  the  end  may  be  known  by  comparing  the  air-bubbles 
passing  through  the  potassa  solution  of  the  air-purifying  apparatus 
on  the  one  side  and  those  passing  through  the  weighed  potash 
bulbs  on  the  other.  When  the  operation  is  at  an  end,  remove  the 
weighed  absorption  apparatus  and  continue  heating  the  tube 
while  a  stronger  current  of  air  is  passed  through  it  in  order  to  re- 
oxidize  the  reduced  copper;  the  tube  is  then  ready  for  the  next 
analysis. 

Fluid  non-volatile  substances  are  treated  similarly,  being 
placed  on  the  cupric-oxide  layer  in  the  boat  C  E  by  means  of  a 
drawn-out  tube,  and  their  weight  determined  by  reweighing  the 
tube.  Volatile  hydrocarbons  (amylene,  benzin,  etc.)  are  weighed 
in  a  small,  stoppered  tube  with  drawn-out  end.  After  removing 
the  stopper  place  the  tube  on  the  layer  of  cupric  oxide  in  boat 
C  E,  and  near  the  end  insert  this  into  the  combustion  tube,  and 
pass  a  slow  current  of  air  through  the  tube,  the  foremost  half  of 
which  is  kept  red-hot.  If  the  current  of  air  is  insufficient  to  con- 
vey the  fluid  at  ordinary  temperature  to  the  cupric  oxide,  heat 
that  part  of  the  tube  containing  the  fluid,  proceeding  from  the 
fore  part  to  the  hinder. 

In  the  combustion  of  nitrogeneous  substances  the  boat  D, 
filled  with  cupric  oxide,  is  replaced  by  a  copper  boat  filled  with 
copper  turnings  the  surface  of  which  has  been  first  oxidized,  and 
then  reduced  by  ignition  in  a  current  of  hydrogen.  In  this  case 
the  current  of  air  must  be  particularly  slow,  and  may  be  more 
rapid  only  towards  the  end,  in  order  that  the  fore  part  of  the  tube 


144  ORGANIC    ANALYSIS.  [§    192. 

may  remain  metallic,  and  hence  be  capable  of  reducing  the  nitro- 
gen oxides. 

In  the  analysis  of  compounds  containing  sulphur,  chlorine, 
bromine,  or  iodine,  fill  the  boat  CE  with  lead  chromate,  and  the 
boat  D  with  perfectly  dry  minium  or  lead  chromate,  and  heat  the 
foremost  boat  to  incipient  redness  only,  so  that  its  contents  do 
not  fuse. 

In  the  combustion  of  organic  substances  containing  inorganic 
compounds,  the  substances  are  put  in  a  porcelain  boat  which  is 
placed  on  a  sheet  of  platinum  foil  with  turned-up  ends,  and  by 
means  of  a  wire  attached  to  one  end  of  the  platinum  foil,  pushed  up 
to  the  permanent  layer  of  cupric  oxide  in  the  middle  of  the  tube. 
After  the  products  of  the  dry  distillation  have  been  burned,  finally 
burn  the  residual  carbon  at  the  expense  of  the  oxygen  of  the  cur- 
rent of  air.  In  the  case  of  difficultly  combustible  substances,  e.g., 
graphitic  carbon  deposited  in  gas-resorts,  the  operation  requires 
somewhat  more  time  than  when  oxygen  is  used,  but,  according  to 
CLOEZ,  the  results  are  equally  accurate. 

The  apparatus  above  described  is  equally  applicable  for  the  de- 
termination of  nitrogen  by  volume,  on  DUMAS'  principle  (§  185,  ad). 
The  foremost  boat  in  this  case  is  filled  with  copper  turnings 
which  have  first  been  oxidized  and  then  reduced;  the  hinder 
boat  is  filled  with  cupric  oxide  and  the  substance.  Into  the 
hinder  end  of  the  tube  pass  pure  carbonic-acid  gas  (through  a 
tube  provided  with  a  stopcock)  until  all  the  air  has  been  expelled, 
then  close  the  stopcock,  bring  the  point  of  the  gas-delivery  tube 
attached  to  the  fore  part  of  the  tube  under  the  cylinder  filled  with 
mercury  and  potassa  solution,  and  heat  the  hinder  end  of  the  tube, 
the  middle  and  fore  parts  of  which  have  previously  been  heated 
to  redness;  finally  raise  the  cylinder  as  high  as  practicable,  in  order 
to  diminish  the  mercurial  pressure  as  much  as  possible,  open  the 
stopcock  again,  and  pass  carbon  dioxide  through  the  tube  until  all 
the  nitrogen  has  been  transferred  to  the  cylinder.  The  details 
of  the  process  will  be  found  in  §  185,  aa.  In  the  construction  of 
the  carbon  dioxide  apparatus  care  must  be  taken  that  the  gas  may 
be  given  the  necessary  tension  to  overcome  the  mercurial  pressure. 


§   192.]  DETERMINING    EQUIVALENTS.  145 

b.  C.  M.  WARREN,  whose  methods  of  determining  sulphur 
and  chlorine  in  organic  substances  were  detailed  in  §  188,  5,  a,  and 
§  190,  3,  also  determines  carbon  and  hydrogen  by  burning  the 
substance  altogether  (or  nearly  so)  at  the  expense  of  oxygen.    The 
hinder  part  of  the  combustion  tube  used  by  him  is  bent  upwards 
at  an  obtuse  angle.     The  substance  is  contained  in  the  bent-up 
part,  into  which  air  or  oxygen  is  passed,  according  to  requirements, 
and  which  is  heated  by  a  special  gas-lamp — in  the  case  of  volatile 
substances  a  copper  rod  is  interposed.    The  horizontal  part  of  the 
tube  is  very  uniformly  packed,  next  to  the  bend,  with  a  layer  of 
asbestos  30  to  36  cm.  long,  then  with  6  to  9  cm.  of  strongly  ignited, 
coarse  cupric  oxide,  and  finally  another  asbestos  plug.    The  cupric 
oxide  serves  as  an  indicator  to  show  whether  any  unconsumed 
gases  reach  it,  and  it  also  completes  their  combustion. 

c.  Regarding  WHEELER'S*  method,  in  which  carbon,  hydro- 
gen, and  nitrogen  are  determined  in  one  analysis;  and  FRANZ 
ScHULZE'st  method,  which  is  based  on  gas-measuring,  and  permits 
the  determination  of  the  nitrogen  as  well;   and  also  TH.  SCHLO- 
SING'S{  method,  which  too  serves  for  the  determination  of  carbon, 
hydrogen,  and  oxygen  in  one  operation,  I  must  refer  to  the  original 
sources. 

d.  BRUNNER§  effects  the  oxidation  of  the  substance  in  the 
wet  way  by  treatment  with  potassium  dichromate  and  sulphuric 
acid.    The  process,  modified  by  ULLGREN,  i.e.,  using  chromic  and 
sulphuric  acids,  is  employed  in  determining  carbon  in  iron,  and 
is  given  in  detail  under  "Analysis  of  Cast  Iron"  in  the  Special  Part. 

III.  DETERMINATION  OF  THE  EQUIVALENT  OF  ORGANIC  COMPOUNDS. 

The  methods  of  determining  the  equivalent  of  organic  com- 
pounds differ  materially  according  to  the  properties  of  the  various 
compounds.  There  are  three  general  methods  in  use  which  afford 
the  desired  purpose. 

*  Journ.  f.  prakt.  Chem.,  xcvi,  239;  Zeitschr.  f.  analyt.  Chem.,  v,  217. 

f  Zeitschr.  f.  analyt.  Chem.,  v,  269. 

I  Compt.  rend.,  LXV,  957 ;  Zeitschr.  f.  analyt.  Chem.,  vn,  270. 

§  Poggend.  Annal,  xcv,  379.  Jahresber.  v.  LIEBIG  u.  KOPP,  1855,  773. 


146  ORGANIC  ANALYSIS.  [§  193. 

§193. 

1.  A  determination  is  made  of  the  quantity  of  a  Substance  of 
known  Equivalent,  which  combines  with  the  substance  the  Equivalent 
of  which  is  to  be  determined,  to  form  a  well-characterized  Compound. 
In  this  manner  is  determined  the  equivalent  of  organic  acids, 
organic  bases,  and  many  indifferent  substances  which  possess  the 
property,  of  combining  with  bases  or  acids.  How  the  equivalent  is 
calculated  from  the  results  obtained  will  be  found  under  "The 
Calculation  of  Analyses";  only  the  methods  will  be  given  here. 

a.  The  equivalent  of  organic  acids  is  preferably  determined  from 
the  silver  salt,  because  of  the  almost  positive  certainty  that  no 
basic  or  hydrated  compound  is  produced,  and  because  the  analysis 
is  exceedingly  simple.  Other  salts,  however,  are  also  frequently 
used,  e.g.,  compounds  of  lead,  barium,  and  calcium.  (In  the  case 
of  lead  compounds  especial  care  must  be  exercised  not  to  mistake 
basic  salts  for  neutral;  again,  in  the  case  of  barium  or  calcium 
salts,  hydrated  must  not  be  considered  as  anhydrous  salts.)  The 
method  of  carrying  out  the  determination  is  fully  detailed  in 
Section  4  (Vol.  I). 

6.  The  equivalent  of  organic  bases  which  yield  well-crystallized 
salts  with  sulphuric,  hydrochloric,  or  other  easily  determined  acid, 
may  be  readily  ascertained  by  determining  the  quantity  of  acid 
in  a  weighed  portion  of  the  salt,  by  the  usual  methods. 

If  the  salts  do  not  crystallize,  a  small  weighed  quantity  of  the 
dried  alkaloid  is  introduced,  according  to  LIEBIG,  into  a  drying- 
tube,  Fig.  78,  which  is  then  weighed;  then  a 
stream  of  well-dried  hydrochloric-acid  gas 
passed  slowly  and  for  a  long  time  through 
the  tube ;  finally  the  tube  is  heated  to  100° 
(see  §  29,  Fig.  34)  while  a  current  of  air  is 
passed    through    it.    The    weight    of   the 
FIG.  78.  hydrochloric  acid  taken  up  is  determined 

from  the  increase  in  weight.  To  control  the  results  the  hydro- 
chloride  may  be  dissolved  in  water  and  the  chlorine  precipitated 
with  silver  nitrate.  The  equivalent  of  the  alkaloids  may  also  be 


1       I 


§   194.]  DETERMINING    EQUIVALENTS.  147 

determined  from  the  insoluble  double  salts  obtained  by  precipitat- 
ing the  hydrochlorides  with  platinic  chloride.  The  compounds  are 
cautiously  ignited  ( §  124)  and  the  residual  platinum  weighed. 

c.  In  the  case  of  indifferent  substances  there  is  frequently  no 
other  choice  than  to  determine  the  equivalent  from  the  lead  com- 
pound, because  many  of  these  substances  either  form  no  other 
than  lead  compounds,  or  else  form  such  as  cannot  be  obtained  in  a 
state  of  purity.  Although  the  value  of  the  equivalent  is  thus  left 
in  doubt,  because  lead  oxide  often  combines  with  such  substances 
in  varying  proportions,  the  analysis  of  such  compounds  is  still  of 
interest,  as  it  shows  whether  the  substance  combines  as  such  with 
the  lead  oxide  or  with  elimination  of  water. 

At  times  organic  substances  yielcf  solid  and  crystallizable  salts 
also  with  water,  from  the  analysis  of  which  then  the  equivalent 
may  be  determined. 

§194. 

2.  The  Vapor  Density  of  the  Compound  is  determined. 

Of  the  many  methods  which  have  been  proposed  for  effecting 
this  object,  I  will  describe  in  detail  only  those  two  which  are  most 
easily  applied  and  are  most  frequently  used  in  the  laboratory.  In  all 
vapor-density  determinations  it  is  necessary  that  the  temperature 
at  which  they  are  made  should  be  sufficiently  raised  above  the 
boiling-point  of  the  substances,  so  that  the  vapors  may  have  the 
coefficient  of  expansion  of  a  gas.  The  extreme  importance  of  this 
rule  is  evident  from  the  fact  that  at  temperatures  only  slightly 
above  the  boiling-point  the  vapor  densities  are  too  high,  and 
decrease  with  increasing  temperature,  becoming  constant  only  at 
a  certain  point. 

A.  DUMAS'  PROCESS. 

The  outlines  of  this  method  are  as  follows:  A  glass  globe, 
filled  with  dry  air,  and  the  capacity  of  which  may  be  afterwards 
ascertained,  is  weighed;  the  weight  of  the  air  for  the  temperature 
and  pressure  prevailing  during  the  weighing  is  then  determined 
and  the  weight  subtracted  from  the  weight  of  the  globe  plus  the  air; 
the  difference  gives  the  weight  of  the  globe  when  empty.  The 


148  ORGANIC   ANALYSIS.  [§  194. 

substance,  the  vapor  density  of  which  is  to  be  determined,  is  now 
introduced  in  excess  into  the  globe,  which  is  then  uniformly  heated 
to  a  temperature  sufficiently  above  the  boiling-point  of  the  sub- 
stance, and  until  the  latter  is  completely  converted  into  vapor,  when 
the  excess,  together  with  the  atmospheric  air  originally  present,  is 
then  expelled.  The  globe  is  now  sealed  air-tight  and  weighed,  and 
the  weight  of  the  empty  globe  deducted  from  this.  The  difference 
gives  the  weight  of  the  volume  of  vapor,  and  this  affords  the  data 
necessary  for  determining  the  vapor  density.  It  need  scarcely 
be  mentioned  that  the  result  can  be  accurate  only  when  the  volume 
of  the  air  and  the  vapor  are  first  reduced  to  the  same  temperature 
and  normal  barometric  pressure,  and  that  consequently  the  state 
of  the  barometer  and  thermometer  must  be  taken  at  the  first 
weighing  and  at  the  time  of  sealing  the  globe  with  vapor. 

This  method  is  of  course  only  applicable  in  the  case  of  substances 
which  volatilize  without  decomposition,  and  will  afford  accurate 
results  only  when  the  substance  is  absolutely  pure.  Only  the 
practical  manipulation  of  the  process  is  here  described,  while  the 
necessary  corrections  and  calculations,  as  well  as  the  conclusions 
they  afford  regarding  the  composition  of  the  substances,  will  be 
given  in  "The  Calculation  of  Analyses/'  §  204. 

a.   APPARATUS   AND    REQUISITES. 

1.  THE    SUBSTANCE. — About   8   grammes    are    required.     Its 
boiling-point  must  be  fairly  accurately  known. 

2.  A  GLASS  GLOBE  WITH  DRAWN-OUT  NECK. — Select  an  ordinary 

glass  globe  of  pure  glass  free  from  air-bubbles,  and 
of  a  capacity  of  250  to  500  c.c.;  rinse  it  clean 
with  water,  dry  it  perfectly,  exhaust  it,  allow  dry 
air  to  enter,  and  repeat  the  operation,  using  the 
apparatus    illustrated    in    Fig.    24,    §  174.    The 
neck  of  the  globe  is  then  softened  near  the  body 
and  drawn  out  to  the  shape  shown  in  Fig.  79. 
Cut  off  the  extreme  tip  and  slightly  round  the  edges  by  fusion. 
(As  this  point  must  be  later  on  rapidly  sealed  by  fusion,  it  is  advis- 
able to  ascertain  the  fusibility  of  the  glass  by  trying  to  seal  the 


§  194.] 


DETERMINING    EQUIVALENTS. 


149 


point  on  the  originally  drawn-out  neck.  If  this  is  not  easily 
effected,  the  globe  is  unserviceable.) 

3.  A  SMALL  IRON  OR  COPPER  VESSEL  for  the  reception  of  the 
liquid,  and  in  which  the  globe  is  to  be  heated  (see  Fig.  80).  The 
liquid  to  be  used  for  the  bath  must  admit  of  being  heated  at  least 
30°  to  40°  above  the  boiling-point  of  the  substance.  Almost  all 
determinations  may  be  effected  by  the  use  of  water,  paraffin,  or 
oil.  A  calcium-chloride  bath  is  more  convenient,  however,  than  a 
paraffin-  or  oil-bath,  if  the  temperature  afforded  by  it  (which  may  be 
raised  to  180°  with  a  perfectly  saturated  solution)  is  sufficiently 
high  for  the  purpose,  as  it  permits  the  globe  to  be  more  easily 
cleaned. 

4.  AN  APPARATUS  FOR  HOLDING  THE  GLOBE. — This  may  be 
easily  made  from  a  rod  and  some  iron  wire.  During  the  operation 
it  is  attached  to  a  retort  stand  (see  Fig.  80). 


FIG.  80. 

5.  MERCURY,  in  more  than  sufficient  quantity  to  fill  the  globe. 

6.  A  MEASURING  TUBE,  accurately  graduated,  of  about  100  c.c. 
capacity. 

7.  A  GAS  OR  ALCOHOL  LAMP  and  a  BLOWPIPE. 

8.  An  accurate  BAROMETER. 

9.  An  accurate  THERMOMETER,  with  a  sufficiently  long  scale. 

6.    THE    PROCESS. 

a.  Weigh  the  globe,  placing  a  thermometer  within  the  balance- 
case,  and  leaving  the  globe  on  the  balance  for  ten  minutes  to  ascer- 


150  ORGANIC   ANALYSIS.  [§   194. 

tain  whether  its  weight  remains  constant.  As  soon  as  it  is  so, 
note  the  temperature,  and  the  height  of  the  barometer. 

/?.  Gently  heat  the  globe  and  dip  the  point  into  about  8  grammes 
of  the  fluid  substance;  if  solid,  liquefy  by  gently  heating.  (If  the 
substance  has  a  high  melting-point,  the  neck  and  point  as  well  as 
the  body  of  the  globe  must  be  heated,  in  order  that  solidification 
does  not  take  place  within  the  neck.)  As  soon  as  the  globe  cools 
(which  may  be  accelerated  by  dropping  ether  on  it,  in  the  case  of 
very  volatile  substances),  the  fluid  enters  and  spreads  out  within  it. 
Not  more  than  from  5  to  7  grammes  should  be  allowed  to  enter. 

f.  Heat  the  bath  (a,  3)  to  between  40°  and  60°,  and  in  it  then 
fasten  the  globe  with  a  thermometer,  as  shown  in  Fig.  80.  Raise 
the  temperature  of  the  bath  30°  to  40°  above  the  boiling-point  of 
the  substance,  and  (if  a  calcium-chloride,  paraffin-,  or  oil-bath  is 
used)  maintain  this  temperature  as  uniformly  as  possible,  by 
regulating  the  heat.  As  soon  as  the  temperature  of  the  flask 
rises  somewhat  above  the  boiling-point  of  the  substance,  the 
vapor  of  the  latter  streams  out  through  the  point.  The  volume 
of  the  current  increases  as  the  temperature  of  the  bath  rises; 
gradually,  however,  it  diminishes,  and  finally  (after  about  15 
minutes)  ceases  altogether.  Should  any  vapor  have  condensed 
in  the  point  in  droplets,  a  glowing  piece  of  charcoal  is  passed  be- 
neath the  point  to  and  fro,  whereby  they  are  quickly  volatilized. 
As  soon  as  perfect  equilibrium  is  established  at  the  desired  tem- 
perature, rapidly  fuse  and  seal  the  point  with  the  blowpipe,  and 
immediately  take  note  of  the  temperature.  The  certainty  that 
the  point  is  perfectly  sealed  is  ascertained  by  directing  a  current 
of  air  on  to  the  projecting  point  with  the  blowpipe,  and  thus  cooling 
it;  a  small  quantity  of  the  vapor  will  condense  and  form  a  column 
of  liquid  which  will  be  held  in  the  point  by  capillary  attraction. 
If  the  point  is  not  hermetically  sealed,  this  does  not  take  place.  A 
barometric  reading  is  then  again  taken,  and  a  note  made  of  it 
should  it  have  changed  since  the  first  reading. 

d.  Now  remove  the  sealed  globe  from  the  bath,  clean  it  very 
carefully  after  cooling,  completely  dry,  weigh  it  as  above,  and  thus 
ascertain  the  weight  of  the  inclosed  substance. 


§   194.]  DETERMINING    EQUIVALENTS.  151 

e.  Immerse  the  point  of  the  globe  for  its  entire  length  in  mer- 
cury, make  a  scratch  with  the  file  near  the  end,  and  break  off  the 
point.  The  mercury  at  once  rushes  into  the  globe  because  of  the 
vacuum  caused  by  the  condensation  of  the  vapor.  (The  globe 
should  be  held  in  the  hollow  of  the  hand,  while  this  rests  upon 
the  edge  of  the  trough.)  If  the  globe  contained  no  more  air  at  the 
moment  it  was  sealed,  it  will  become  completely  filled  with  mercury  ; 
otherwise  a  small  air-bubble  will  remain  in  it.  In  either  case 
measure  the  mercury  in  the  globe  by  transferring  it  to  a  graduated 
tube  (a,  6) ;  if  a  bubble  of  air  remained  in  the  globe,  fill  the  latter 
with  water,  and  measure  this  also.  The  difference  between  the 
volumes  of  mercury  and  that  of  the  wrater  gives  the  volume  of  the 
air-bubble. 

The  results  are  very  accurate  if  the  process  has  been  carefully 
carried  out;  for  the  calculation  see  "Calculation  of  Analyses" 
§204. 

B.  PROCESS  BASED  ox  GAY-LUSSAC'S  PRINCIPLE. 

In  the  Dumas  process  the  substance,  the  vapor  of  which  has 
filled  a  known  volume  under  determined  conditions,  is  subsequently 
weighed,  whereas  in  GAY-LUSSAC'S  method  the  volume  which  the 
vapor  of  a  previously  weighed  portion  of  the  substance  occupies 
under  determined  conditions,  is  determined.  The  latter  process 
is  best  carried  out  according  to  the  method  recommended  by 
A.  W.  HOFMANN.* 

For  this  there  is  required  a  calibrated  tube,  closed  at  one  end 
and  about  1  metre  long  and  15  to  20  mm.  wide.  This  tube  is 
carefully  filled  with  mercury  and  inverted  into  a  small  mercurial 
trough,  so  that  a  vacuum  of  from  20  to  30  cm.  forms  in  the  upper 
part  of  the  tube.  Almost  the  entire  length  of  the  tube  is  inclosed 
in  another  glass  tube  80  to  90  cm.  long  and  30  to  40  mm.  wide, 
narrowed  at  its  upper  end — over  the  sealed  end  of  the  calibrated 
tube — to  a  moderately  wide  delivery  tube  which  is  bent  at  a  right 
angle.  The  lower  opening  of  the  tube  is  closed  by  a  stopper  through 

*  Ber.  der  deutsch.  chem.  Gesellsch.,  i,  198;  Zeitschr.  /.  analyt.  Chem.,  vin,  83 


152  ORGANIC   ANALYSIS.  [§  194. 

the  central  wide  perforation  of  which  the  calibrated  tube  passes, 
while  a  narrow  exit  tube  is  fitted  in  a  second  perforation.  The 
external  tube  serves  for  raising  the  calibrated  tube  to  a  definite 
high  temperature  and  maintaining  it  at  the  point  required.  The 
heating  is  effected  by  passing  the  vapor  of  a  liquid  having  a  con- 
stant and  suitable  boiling-point  (water,  aniline,  etc.)  into  the  upper 
tube,  bent  at  right  angles.  When  water  is  employed  the  vapors 
are  permitted  to  ecape  freely  through  the  exit  tube;  if  aniline 
or  other  liquid  is  used,  however,  this  tube  is  connected  with  a 
suitable  condenser.  HOFMANN  has  satisfied  himself  by  direct  ex- 
periment that  with  a  sufficiently  rapid  evolution  of  vapor,  the 
space  between  the  external  tube  and  the  calibrated  tube,  as  well 
as  the  latter  itself,  will  be  constantly  maintained  at  the  temperature 
of  the  boiling-point  of  the  liquid  used,  and  will  render  it  unnecessary 
to  take  the  temperature  during  the  experiment. 

In  carrying  out  the  process,  the  liquid,  the  vapor  density  of 
which  is  to  be  determined,  is  weighed  in  a  very  small  flask,  made 
from  a  piece  of  thin  glass  tubing,  and  closed  with  a  ground-glass 
stopper.  The  size  of  the  flask  must  depend  upon  the  nature  of  the 
liquid;  the  capacity  of  the  smallest  may  be  0-01  grm.,that  of  the 
largest  0-1  grm.,  of  water.  The  weighed  flask  is  now  allowed  to 
rise  in  the  calibrated  tube  filled  with  mercury.  The  stopper 
frequently  springs  out  as  soon  as  the  flask  acquires  the  Torricellian 
vacuum.  No  matter  whether  this  takes  place  or  not,  the  heating 
is  next  begun  by  conducting  into  the  right-angled  tube  the  vapors 
of  water,  aniline,  or  other  liquid  of  constant  boiling-point,  and 
generated  by  boiling  the  liquid  in  a  glass  or  copper  vessel.  After  a 
short  time  the  stopper  of  the  small  flask  will  spring  out  if  it  has 
been  properly  adjusted,  the  liquid  will  run  out  and  be  converted 
into  vapor,  and  the  mercurial  column  will  sink.  When  the  vapor 
has  circulated  long  enough  in  the  space  between  the  two  tubes  to 
insure  a  uniform  temperature,  and  the  height  of  the  mercurial 
column  no  longer  changes,  read  off  the  height  of  the  barometer, 
and  that  of  the  mercury  within  and  without  the  calibrated  tube. 
The  reading-off  of  the  latter  is  rendered  more  convenient  by  having 
the  barometer  tube  graduated  in  millimetres  as  well  as  cubic 


§194.]  DETERMINING    EQUIVALENTS.  153 

centimetres.  The  temperature  of  the  vapor  and  of  the  mercury 
is,  as  above  noted,  that  of  the  boiling-point  of  the  liquid,  the 
vapor  of  which  has  served  for  heating  at  the  observed  barometric 
pressure.  In  making  the  calculations,  which  are  explained  in 
§  204,  the  tension  of  the  mercurial  vapor  and  the  temperature  of 
the  mercury  must  both  be  taken  into  account,  if  a  high  temperature 
has  been  used.  So  far  as  the  temperature  of  the  mercury  is  con- 
cerned a  slight  error  is  unavoidable,  as  the  mean  temperature  of 
the  mercury  at  the  point  where  the  heated  mercury  within  the 
tube  and  that  unheated  below  the  tube  join  cannot  be  ascertained. 
This  slight  error  has  no  appreciable  influence  on  the  results,  however. 

The  advantages  afforded  by  HOFMANN'S  process  are  quite 
important,  since  the  GAY-LUSSAC  principle  may  be  applied  for  the 
determination  of  vapor  densities  at  high  temperatures  without 
the  operator  being  subjected  in  any  way  to  the  poisonous  fumes 
of  mercury;  further,  the  atmosphere  of  vapor  enables  a  constancy 
of  temperature  to  be  maintained  which  it  would  be  difficult  to 
secure  otherwise,  and  the  vapor  volume  may  be  read  off  with 
great  accuracy.  The  greatest  advantage,  however,  is  that  at  so 
low  a  pressure,  which  may  be  reduced  to  20  and  even  10  cm.,  the 
work  may  be  done  at  a  comparatively  low  temperature.  For 
many  substances  which  boil  at  120°  and  even  150°  (according  to 
A.  SCHRODER  even  182°),  the  vapor  of  water  suffices  under  these 
circumstances;  and  the  vapor  of  aniline  (boiling  at  185°)  is  hot 
enough  to  enable  its  own  vapor  density  to  be  accurately  deter- 
mined, as  well  as  that  of  toluidine  boiling  at  198°,  naphtalin  boiling 
at  218°,  and  according  to  A.  SCHRODER  also  of  cumarin,  boiling  at 
270°.*  H.  WICHELHAUS  t  recommends  a  somewhat  modified 
form  of  HOFMAXX'S  apparatus,  shown  in  Fig.  81. 

a  is  a  ground-glass  cup  fitted  to  the  barometer  tube,  and  which 
is  put  on  in  the  mercurial  trough  after  the  substance  has  been  intro- 


*  Regarding  the  clever  manner  in  which  A.  SCHRODER  employs  HOF- 
MAXX'S  apparatus  for  determining  the  water  of  crystallization  in  salts,  etc., 
see  Ber.  d&r  deutsch.  chem.  Gesellsch.,  iv,  471 ;  Zeitschr.  f.  analyt.  Chem.,  Xi,  98. 

t  Ber.  der  deutsch.  chem.  Gesellsch.,  1870,  166;  Zeitschr.  f.  analyt.  Chem., 
IK,  496. 


154 


ORGANIC    ANALYSIS. 


[§    194. 


duced.    The  cup  remains  filled  with  mercury  and  attached  to  the 
tube,  thus  forming  a  siphon,  and  permitting  the  entire  tube  to  be 


FIG.  81. 


surrounded  by  vapor,  and  dispensing  entirely  with  the  mercurial 
trough.    The  consideration  regarding  the  difference  in  tempera- 


§   194.]  DETERMINING    EQUIVALENTS.  155 

ture  between  different  parts  of  the  mercurial  column  is  thus  en- 
tirely obviated. 

The  mercury  displaced  by  the  heat  flows  out  of  the  narrow 
opening  of  the  cup  and  passes  with  the  vapors  through  the  tube  e 
into  the  condenser  and  receiver,  b  denotes  the  zero-point  on  the 
tube,  which  is  graduated  in  cubic  centimetres  and  millimetres,  and 
from  which  the  height  of  the  mercurial  column  is  always  read  off. 
The  outer  tube,  d,  has  the  form  of  a  cylinder,  widened  below,  it  is 
of  such  dimensions  as  to  require  as  little  vapor  to  fill  the  space  be- 
tween the  two  tubes  as  possible.  The  whole  rests  upon  a  large 
cork,  c,  carrying  also  the  tube  e,  which  passes  above  the  surface 
of  the  table.  The  inner  tube  is  secured  near  its  sealed  end  within 
the  outer  tube  by  means  of  a  notched  cork;  this  is  done  because 
were  the  tube  allowed  to  rest  directly  upon  the  glass  cup,  the  latter 
might  be  easily  broken  by  the  weight. 

Other  methods  also  based  on  GAY-LUSSAC'S  principle  have 
been  proposed  by  HUGO  SCHIFF,*  W.  M.  WATTS,!  and  others. 

C.  GRABOWSKI  %  and  LANDOLT  §  have  also  proposed  methods 
founded  on  principles  slightly  different  from  that  of  GAY-LUSSAC. 
In  GRABOWSKI'S  method  two  similar  tubes,  at  first  filled  with  mer- 
cury, are  heated  together  to  the  same  temperature  in  an  air-bath. 
One  of  these  tubes  receives  the  bulb  or  tube  containing  the  weighed 
substance.  As  soon  as  the  vapor  of  the  liquid  has  reached  the 
proper  temperature,  dry  air  is  passed  into  the  other  tube  until  the 
volumes  of  air  and  vapor  are  alike.  This  equality  of  volume 
must  be  maintained,  unless  dissociation  occurs,  with  increasing 
temperature,  as  well  as  on  cooling  to  the  temperature  which  is 
the  lower  limit  of  the  normal  vapor  density  of  the  substance.  After 
completely  cooling,  the  volume  of  air  used  is  measured  in  the  usual 
manner,  and  from  this  the  vapor  density  of  the  substance  is  very 
simply  calculated. 

While  in  GRABOWSKI'S  method  the  quantity  of  normal  sub- 

*  Zeitschr.  f.  analyt.  Chem.,  i,  321. 
f  Ibid.,  vii,  82. 
t  Ibid.,  v,  338. 
§  Ibid.,  xi,  322. 


156  ORGANIC    ANALYSIS.    .  .    .  [§  194. 

stance  (air)  is  adapted  to  that  of  the  substance  to  be  examined, 
LANDOLT,  on  the  contrary,  adapts  the  weight  of  the  substance 
to  be  examined  to  that  of  the  quantity  of  normal  substance  (water 
or  chloroform).  The  direct  comparison  of  volumes  under  the 
same  pressure  and  temperature  is  common  to  both  methods.  L. 
PFAUNDLER  *  has  studied  both  methods,  and  has  recommended  a 
modification  of  GRABOWSKI'S  apparatus,  in  which  steam  is  used 
instead  of  an  air-bath,  and  the  air  is  differently  introduced.  Re- 
garding the  details  I  refer  to  the  original  paper. 

D.  BUNSEN'S  method  f  is  based  upon  the  well-known  principle 
that  the  specific  gravity  of  gases  and  vapors  is  known  when  the 
weight  of  equal  volumes  under  the  same  conditions  is  known. 
The  application  of  the  principle  is,  however,  quite  original.     There 
are  required  three,  sometimes  two,  glass  tubes  having  similar  ca- 
pacities (to  within  0-01  c.c.  of  each  other),  and  equal  in  weight  to 
within  a  fraction  of  a  milligramme.     BUNSEN  employs  an  air-tight 
stopper  of  so  simple  a  construction  that  it  is  possible  to  use  the 
tubes,  the  weight  of  which  has  been  determined  once  and  for  all, 
as  often  as  desired  for  determining  the  specific  gravity  of  gases 
or  vapors.     For  heating  BUNSEN  employs  a  peculiarly  constructed 
large  air-bath  which  permits  an  almost  constant  temperature  to 
be  maintained  for  a  long  time. 

The  method  (the  details  of  which  are  minutely  given  loc.  cit.) 
is  remarkable  in  that  the  density  of  gases  and  vapors  is  obtained 
by  always  using  the  same  tubes  and  simply  determining  two  dif- 
ferent weights,  without  its  being  necessary  to  know  the  volume, 
pressure,  or  temperature  of  the  vapors  or  gases.  The  accuracy  of 
the  results  obtained  by  BUNSEN  is  so  high  that  in  the  case  of  car- 
bonic acid,  as  well  as  ether  vapor,  the  figures  are  identical  to  the 
third  decimal,  but  the  method  requires  a  high  degree  of  skill  in 
the  construction  of  glass  apparatus,  as  well  as  great  dexterity. 

E.  The  determination  of    the  vapor  densities  of    substances 
having  high  boiling-points  is  effected  by  DEVILLE  and  TROOST'S 

*  Ber.  der  deutsch.  diem.  Gesellsch.,  v,  575;  Zeitschr.  f.  analyt.  Chem.,  xu, 
100. 

f  Zeitschr.  f.  analyt.  Chem.,  vi,  1. 


§   195.J  DETERMINING    EQUIVALENTS.  157 

method,*  for  a  description  of  which  I  must  refer  to -the  original 
paper. 

§195. 

3.  A  great  many  indifferent  substances  unfortunately  either 
do  not  combine  with  bases  or  acids,  or  form  compounds  from  which 
the  equivalent  cannot  well  be  determined.  In  such  cases  the 
equivalent  is  determined  by  subjecting  the  compounds  to  the  ac- 
tion of  acids,  bases,  halogens,  etc.,  and  thus  preparing  substitution 
or  decomposition  products  the  equivalents  of  which  are  either 
known  or  may  be  determined,  or  which  may  be  inferred  from  the 
mode  of  formation  of  the  compound  in  question.  In  these  cases 
that  equivalent  is  considered  as  the  correct  one  which  affords  the 
simplest  explanation  of  the  processes  of  formation  and  decompo- 
sition. This  method  of  determining  equivalents  is  ultimately 
connected  with  the  higher  branches  of  organic  chemistry  and  will 
not  be  here  further  considered,  since  methods  which  are  applicable 
in  general  cannot  be  given. 

*  Annal.  d.  Chem.  u.  Pharm.,  cxni,  42. 


DIVISION  II. 

CALCULATION  OF  ANALYSES. 

THE  calculation  of  the  results  obtained  by  an  analysis  presupposes,  as  an 
indispensable  preliminary,  a  knowledge  of  the  general  laws  of  the  combining 
proportions  of  bodies,  on  one  hand,  and  of  the  more  simple  rules  of  arith- 
metic on  the  other.  It  is  a  great  error  to  suppose  that  the  ability  to  make 
chemical  calculations  involves  an  extensive  acquaintance  with  mathematics, 
a  knowledge  of  decimal  fractions  and  simple  equations  being  for  the  most 
part  sufficient.  These  remarks  are  not  intended  to  dissuade  students  of 
chemistry  from  pursuing  the  highly  important  study  of  mathematics,  but 
merely  to  encourage  those  who  have  had  no  opportunity  of  entering  more 
deeply  into  this  science,  and  who,  as  experience  has  shown  me,  are  often  afraid 
to  venture  upon  chemical  calculations.  For  this  reason  I  have  made  the 
whole  of  the  calculations  given  in  the  following  paragraphs  in  the  most  in- 
telligible manner  possible,  and  without  logarithms. 

I.  CALCULATION  OF  THE  CONSTITUENTS  SOUGHT  FROM  THE  COMPOUND 
OBTAINED  IN  THE  ANALYTICAL  PROCESS,  AND  EXHIBITION  OF  THE  RESULT 
IN  PER-CENTS, 

§  196. 

The  bodies  the  weight  of  which  it  is  intended  to  determine  are  separated, 
as  we  have  seen  in  Division  I,  treating  of  the  "  Execution  of  Analysis,"  either 
in  the  free  state  or — and  this  most  frequently — in  combinations  of  known 
composition.  The  results  are  usually  calculated  upon  100  parts  of  the  exam- 
ined substance,  since  this  gives  a  clearer  and  more  intelligible  view  of  the 
composition.  In  cases  where  the  several  constituents  have  been  separated  in 
the  free  state  the  calculation  may  be  made  at  once;  but  if  the  constituents 
have  been  separated  in  combination  with  other  substances,  they  must  first 
be  calculated  from  the  compounds  obtained. 

1.    Calculation  of  the  Results  into  Per-cents  by  Weight,  in  Cases  where  the 

Substance  sought  has  been  separated  in  the  Free  State. 
a.  Solid  Bodies,  Liquids,  and  Gases,  which  have  been  determined  by  Weight. 

§197. 

The  calculation  here  is  exceedingly  simple. 

Suppose  you  have  analyzed  mercurous  chloride,  and  separated  the  mer- 
cury in  the  metallic  state  (§  118, 1)  2-945  grm.  mercurous  chloride  have  given 
say  2 -499  grm.  metallic  mercury. 

2-945  : 2-499  ::  100  :x 
z=84-85 

158 


§   198.]  CALCULATION    OF   ANALYSES.  159 

which  means  that  your  analysis  shows  100  parts  of  mercurous  chloride  to 
contain  84-85  of  mercury,  and  consequently  15-15  of  chlorine. 

Now  as  mercurous  chloride  is  known  to  consist  of  2  at.  mercury  and  2  at. 
chlorine,  and  as  the  atomic  weights  of  both  of  these  elements  are  also  known, 
the  true  percentage  composition  of  the  body  may  be  readily  calculated  from 
these  data.  When  analyzing  substances  of  known  composition  for  practice, 
the  results  theoretically  calculated  and  those  obtained  by  the  analysis  are 
usually  placed  in  juxtaposition,  as  this  enables  the  student  at  once  to  perceive 
the  degree  of  accuracy  with  which  the  analysis  has  been  performed. 
Thus  for  instance — 

Found.  Calculated  (compare  §84,  6). 

Mercury 84-85   84-94 

Chlorine 15-15   15-06 


100-00  100-00 

b.    Gases  which  have  been  determined  by  Measure. 
§198. 

If  a  gas  has  been  determined  by  measure,  it  is,  of  course,  necessary  first  to 
ascertain  the  weight  corresponding  to  the  volume  found  before  the  percent- 
age by  weight  can  be  calculated. 

But  as  the  exact  weights  of  a  definite  volume  of  the  various  gases  have 
been  severally  determined  by  accurate  experiments,  this  calculation  also  is  a 
simple  rule-of-three  question,  if  the  gas  may  be  measured  under  the  same 
circumstances  to  which  the  known  relation  of  weight  to  volume  refers.  The 
circumstances  to  be  taken  into  consideration  here  are : 

Temperature  and  Atmospheric  Pressure. 
Besides  these  the 

Tension  of  the  Aqueous  Vapor 

may  also  claim  consideration  in  cases  where  water  is  used  as  the  confining 
fluid,  or  generally  where  the  gas  has  been  measured  in  the  moist  state. 

The  respective  weights  assigned  in  Table  V*  to  1  litre  of  the  gases  there 
enumerated  refer  to  a  temperature  of  0°  and  an  atmospheric  pressure  of  0  •  76 
metre  of  mercury.  We  have,  therefore,  in  the  first  place,  to  consider  the  man- 
ner in  which  volumes  of  gas  measured  at  another  temperature  and  another 
height  of  the  barometer  are  to  be  reduced  toO°  and  0-76  of  the  barometer. 

a.   Reduction  of  a  Volume  of  Gas  of  any  given  Temperature  to  0°,  or  any 

other  Temperature  between  0°  and  100°. 

The  following  propositions  regarding  the  expansion  of  gases  were  formerly 
universally  adopted : 

1 .  All  gases  expand  alike  for  an  equal  increase  of  temperature. 

2.  The  expansion  of  one  and  the  same  gas  for  each  degree  of  the  ther- 
mometer is  independent  of  its  original  density. 

*  See  Tables  at  the  end  of  the  volume. 


160  ORGANIC   ANALYSIS.  [§  198. 

Although  the  correctness  of  these  propositions  has  not  been  fully  conr 
firmed  by  the  minute  investigations  of  MAGNUS  and  REGNAULT,  yet  they 
may  be  safely  followed  in  reductions  of  the  temperature  of  those  gases  which 
a,re  most  frequently  measured  in  the  course  of  anah'tical  processes,  as  the 
coefficients  of  expansion  of  these  gases  scarcely  differ  from  each  other,  and 
as  there  is  never  any  very  considerable  difference  in  the  atmospheric  pressure 
under  which  the  gases  are  severally  measured. 

The  investigations  just  alluded  to  have  given 

0-3665 

as  the  coefficient  of  the  expansion  of  gases  which  comes  nearest  to  the  truth; 
in  other  words,  as  the  extent  to  which  gases  expand  when  heated  from  the 
freezing-  to  the  boiling-point  of  water.  They  expand,  therefore,  for  every 
degree  of  the  centigrade  thermometer, 

^0.003665.      ,: 

If  we  wish  to  ascertain  how  much  space  1  c.c.  of  gas  at  0°  will  occupy  at 
10°,  we  find 

1X[1  + (10X0- 003665)]=  1-03665. 

If  we  wish  to  ascertain  how  much  space  100  c.c.  at  0°  will  occupy  at 
10°,  we  find 

100X[1  +  (10X0-  003665)] 
=  100  X 1  •  03665=  103  •  665. 

If  we  wish  to  know  how  much  space  1  c.c.  at  10°  will  occupy  at  0°,  we  find 

1  +  (10X0-  003665) = 

How  much  space  do  103-665  c.c.  at  10°  occupy  at  0°? 
103-665 


1  + (10X0 -003665) 


=  100. 


The  general  rule  of  these  calculations  may  be  expressed  as  follows: 
To  calculate  the  volume  of  a  gas  from  a  lower  to  a  higher  temperature,  we 
have  in  the  first  place  to  find  the  expansion  for  the  volume  unit,  which  is  done 
by  adding  to  1  the  product  of  the  multiplication  of  the  thermometrical  differ- 
ence by  0  •  003665,  and  then  to  multiply  this  by  the  number  of  volume  units 
found  in  the  analytical  process.  On  the  other  hand,  to  reduce  the  volume  of 
a  gas  from  a  higher  to  a  lower  temperature,  we  have  to  divide  the  number  of 
volume  units  found  in  the  analytical  process  by  1  -I-  the  product  of  the  multi- 
plication of  the  thermometrical  difference  by  0-003665. 

In  the  case  of  carbonic  acid  the  coefficient  of  expansion  differs  somewhat 
from  that  of  air  and  other  permanent  gases.  According  to  MAGNUS  it  is 
0-00369  for  1°,  and  not  0-003665;  according  to  REGNAULT  it  is  0-00371. 


§  198.]          CALCULATION  OF  ANALYSES.  161 


/?.    Reduction  of  the  Volume  of  a  Gas  of  a  certain   given  Density  to  0-76 

Metre  Barometric  Pressure,  or  any  other  given  pressure. 
According  to  the  law  of  MARIOTTE,  the  volume  of  a  gas  is  inversely  as  the 
pressure  to  which  it  is  exposed;  in  accordance  with  this  a  gas  occupies  the 
greater  space  the  less  the  pressure  upon  it,  and  the  less  space  the  greater  the 
pressure  upon  it. 

Thus,  supposing  a  gas  to  occupy  a  space  of  10  c.c.  at  a  pressure  of  1 
atmosphere,  it  will  occupy  1  c.c.  at  a  pressure  of  10  atmospheres,  and  100 
«.c.  at  a  pressure  of  ^  atmosphere. 

Nothing,  therefore,  can  be  more  easy  than  the  reduction  of  a  gas  of  a 
certain  given  tension  to  760  mm.  bar.  pressure,  or  any  other  given  pressure, 
e.g.,  1000  mm.,  which  is  frequently  used  in  the  analysis  of  gases. 

Supposing  a  gas  to  occupy  100  c.c.  at  780  mm.  bar.,  how  much  space  will 
it  occupy  at  760  mm.? 

760  :  780  ::  100  :  x\  z=102-63. 
How  much  space  will  100  c.c.  at  750  mm.  bar.  occupy  at  760  mm.? 

760:750  ::  100  :  x\  z=98-68. 

How  much  space  will  150  c.c.  at  760  mm.  bar.  occupy  at  1000  mm.? 
1000  :  760  ::  150  :  x\  z=114. 

Condensible  gases  do  not  accurately  follow  MARIOTTE 's  law,  and  those 
most  readily  condensible  deviate  most.  Of  the  condensible  gases  carbonic- 
acid  gas  is  the  one  most  frequently  met  with  in  analyses,  but  no  attention 
need  be  paid  to  the  error  caused  by  the  slight  differences  in  pressure,  except 
in  those  cases  where  the  highest  degree  of  accuracy  is  required.  In  the  case 
of  greater  differences  of  pressure  the  deviation  from  MARIOTTE 's  law  become 
more  marked ;  e.g.,  in  order  to  condense  carbonic-acid  gas  to  half  its  volume 
at  the  same  temperature,  a  pressure  of  1-98292  (according  to  REGNAFLT), 
instead  of  two  atmospheres,  will  be  required. 

7.  Reduction  of  the.  Volume  of  a  Gas  saturated  with  Aqueous  Vapor  to  its 
actual  Volume  in  the  Dry  State. 

It  is  a  well-known  fact  that  water  has  a  tendency,  at  all  temperatures,  to 
assume  the  gaseous  state.  The  degree  of  this  tendency  (the  tension  of  the 
aqueous  vapor) — which  is  dependent  solely  and  exclusively  upon  the  tempera- 
ture, and  not  upon  the  circumstance  of  the  water  being  in  vacua  or  in  any 
gaseous  atmosphere — is  usually  expressed  by  the  height  of  a  column  of  mer- 
cury counterbalancing  it.  The  following  table  indicates  the  amount  of  tension 
for  the  various  temperatures  at  which  analyses  are  likely  to  be  made.* 

Therefore  if  gas  is  confined  over  water,  its  volume  is,  cceteris  paribus, 
always  greater  than  if  it  were  confined  over  mercury;  since  a  quantity  of  aque- 
ous vapor  proportional  to  the  temperature  of  the  water  mixes  with  the  gas, 
and  the  tension  of  this  partly  counterbalances  the  column  of  air  that  presses 

*  Compare  MAGNUS,  Pogg.  Annal.  LXI,  247. 


162 


ORGANIC    ANALYSIS. 


[§  198. 


upon  the  gas,  and  to  that  extent  neutralizes  the  pressure.  To  ascertain  the- 
actual  pressure  upon  the  gas,  we  must  therefore  subtract  from  the  apparent 
pressure  so  much  as  is  neutralized  by  the  tension  of  the  aqueous  vapor. 


TABLE. 


Temperature 
(in  degrees  C.). 

Tension  of  the 
aqueous  vapor 
expressed  in 
millimetres. 

Temperature 
(in  degrees  C.). 

Tension  c.f  the 
aqueous  vapor 
expressed  in 
millimetres. 

0 

4-525 

21 

18-505 

1 

4-867 

22 

19-675 

2 

5-231 

23 

20-909 

3 

5-619 

24 

22-211 

4 

6.032 

25 

23-582 

5 

6-471 

26 

25-026 

6 

6-939 

27 

26-547 

7 

7-436 

28 

28-148 

8 

7-964 

29 

29-832 

9 

8-525 

30 

31-602 

10 

9-126 

31 

33-464 

11      • 

9-751 

32 

35-419 

12 

10-421 

33 

37-473 

13 

11-130 

34 

39-630 

14 

11-882 

35 

41-893 

15 

12-677 

36 

44-2G8 

16 

13-519 

37 

46-758 

17 

14-409 

38 

49-368 

18 

15-351 

39 

52-103 

19 

16-345 

40 

54-969 

20 

17-396 

Suppose  we  had  found  a  gas  to  measure  100  c.c.  at  759  mm.  bar.,  the  tem- 
perature of  the  confining  water  being  15°;  how  much  space  would  this  volume 
of  gas  occupy  in  the  dry  state  and  at  760  mm.  of  the  barometer? 

Our  table  gives  the  tension  of  aqueous  vapor  at  15°=  12 -677;  the  gas  is 
consequently  not  under  the  apparent  pressure  of  759  mm.,  but  under  the 
actual  pressure  of  759-12-677=746-323  mm. 

The  calculation  is  now  very  simple;  it  proceeds  in  the  manner  shown  in 
p;  we  say 

760  :  746-323  ::  100  :  x 
s-98-20. 

When  the  volume  of  a  gas  has  thus  been  adjusted  by  the  calculations  in  a 
and  ,5,  or  7%  to  the  thermometrical  and  barometrical  conditions  to  which  the 
data  of  Table  V  refer,  the  percentage  by  weight  may  now  be  readily  calculated 
by  substituting  the  weight  for  the  volume  and  proceeding  by  simple  rule-of- 
three. 

What  is  the  percentage  by  weight  of  nitrogen  in  an  analyzed  substance  of 
which  0-5  grm.  has  yielded  30  c.c.  of  dry  nitrogen  gas  at  0°,  and  760  mm* 
bar.? 


§   198.]  CALCULATION    OF    ANALYSES.  163 

In  Table  V  we  find  that  1  litre  (1000  c.c.)  of  nitrogen  gas  at  0°,  and  760 
mm.  bar.,  weighs  1-25617  gnu.* 
We  say  accordingly 

1000  :  1-25617  ::  30  :  x 

x= 0-0377. 
And  then 

0-5  :  0-0377  ::  100  :  x 
z=7-54. 

The  analyzed  substance  contains  consequently  7-54  per  cent,  by  weight 
of  nitrogen. 

DR.  GIBBS'  method  of  finding  at  once  the  total  correction  for  temperature,  press- 
ure, and  moisture  in  absolute  determinations  of  nitrogen,  or  other  gases:  f 

' '  I  take  a  graduated  tube,  which  I  fill  with  mercury,  then  displace  about 
two-thirds  of  the  mercury  with  air,  and  invert  the  tube  into  a  cistern  of  mer- 
cury. Then  I  make  four  or  five  determinations  of  the  volume  of  the  included 
(moist)  air  in  the  usual  manner  and  find  the  volume  of  the  air  at  0°  and  760 
mm.  as  a  mean  of  all  the  determinations.  This  tube  I  call  the  companion  tube, 
and  it  always  hangs  in  the  little  room  I  use  for  gas  analyses.  Suppose  the 
volume  of  (dry)  air  at  0°  and  760  mm.  is  132-35  c.c. 

"  Now,  in  making  an  absolute  nitrogen  determination  I  collect  the  nitrogen 
moist  over  mercury  in  a  graduated  tube,  and  then  suspend  the  measuring  tube 
by  the  side  of  the  companion  tube.  I  then  by  a  cord  and  pulley  bring  the  level 
of  the  mercury  in  the  two  tubes  to  correspond  exactly,  and  then  read  off  the 
volume  of  air  in  the  companion  tube  and  the  volume  of  nitrogen  in  the  measur- 
ing tube.  I  ought  to  have  stated  that  the  two  tubes  hang  in  the  same  cistern 
of  mercury.  Suppose  the  volume  of  air  in  the  companion  tube  to  be  143  c.c. ; 
then  the  total  correction  for  temperature,  pressure,  and  moisture  will  be 
143  - 132  •  35=  10  •  65  c.c.  The  correction  for  the  nitrogen  will  then  be  found  by 
rule-of -three.  As  the  observed  volume  of  air  in  the  companion  tube  is  to  the 
observed  volume  of  nitrogen,  so  is  (in  this  case)  10-65  to  the  required  cor- 
rection. In  this  way,  when  the  volume  of  air  in  the  companion  tube  is  once 

*  Taking  MORLEY'S  value,  0-089873,  as  the  most  probable  weight  in  grammes  of  a 
litre  of  hydrogen  at  0°,  760  mm.  bar.,  and  at  45°  latitude,  then  1  litre  of  nitrogen,  using 
the  atomic  weights  employed  in  this  work,  would  weigh  0- 089873 X  13 ••  93  (if  H— 1,  then 
N  =  13  •  93)  =  1  •  25193  grm.  Using  this  value  instead  of  that  of  the  author,  the  proportion 
would  then  be  as  follows: 

1000  :  1-25193  ::  30  :  x,  and  x  =  0-03756, 
and 

0.5:0-03756::  100:  x,  whence  x  =  7 -51, 

the  percentage  weight  of  the  nitrogen  in  the  analyzed  substance.  The  value  1  •  25193  grm. 
for  1  litre  of  nitrogen  also  agrees  more  closely  with  the  value  obtained  for  nitrogen  which 
was  prepared  chemically,  and  which  was  found  to  be  1  -2507  (see  RAYLEIGH,  Chem.  New8, 
Lxvn,  183.  198,  and  211);  while  that  used  by  the  author,  1-25617,  is  most  probably 
based  on  the  value  obtained  for  atmospheric  nitrogen,  which  contained  argon.  In  fact  it 
was  the  difference  between  the  observed  values  of  chemically  prepared  and  atmospheric 
nitrogen  (the  latter  was  found  by  RAYLFIGH  to  be  1-257)  that  led  to  the  discovery  of 
argon  (Proc.  Roy.Soc.,  Iv,  340  [1894J;  Zeitschr.  f.  phys.  Chem.,  xvi,  344  [1895]).— TRANS- 
LATOR. 

t  Private  communication. 


164  ORGANIC   ANALYSIS.  [§  199. 

found,  no  further  observations  of  temperature,  pressure,  or  height  of  mercury  above 
the  mercury  in  the  cistern  are  necessary.  The  companion  tube  lasts  for  an 
indefinite  time.  I  have  even  used  it  filled  with  water,  without  any  appreciable 
change  in  some  weeks,  but  I  prefer  mercury.  As  the  two  tubes  hang  side  by 
side,  there  is  never  an  appreciable  difference  of  temperature.  My  results  are 
most  satisfactory.  Williamson  &  Russell  have,  as  you  know,  used  a  companion 
tube  for  equating  pressures,  but  not  for  finding  the  total  value  of  the  tem- 
perature and  pressure  correction  at  once;  and  I  believe  that  my  process  is 
•wholly  new.  Certainly  it  is  wonderfully  convenient,  and  saves  all  tables  and 
labor  of  computation." 

2.  Calculation  of  the  results  into  Per-cents  by  Weight,  in  Cases  where  the 
Body  sought  has  been  separated  in  Combination,  or  where  a  Compound  has 
to  be  determined  from  one  of  its  Constituents. 

§199. 

If  the  body  to  be  determined  has  not  been  weighed  or  measured  in  its  own 
form,  but  in  some  other  form,  e.g.,  carbonic  acid  as  calcium  carbonate,  sulphur 
.as  barium  sulphate,  ammonia  as  nitrogen,  chlorine  by  a  standard  solution  of 
iodine,  etc.,  its  quantity  must  first  be  reckoned  from  that  of  the  compound 
found  before  the  calculation  described  in  1  can  be  made. 

This  may  be  accomplished  either  by  rule-of-three  or  by  some  abridged 
method. 

Suppose  we  have  weighed  hydrogen  in  the  form  of  water,  and  have  found 
1  grm.  of  water;  how  much  hydrogen  does  this  contain? 

A  molecule  of  water  consists  of 

Hydrogen  ...................   2  at.=   2-016  pts. 

Oxygen  ....................   1  at.  =  16-000    " 

18-016 
We  say  accordingly 

18-016:2-  016::l:rc 


Or,  expressed  in  general  terms, 

Water  X  0  •  1  1  19  =  Hydrogen. 
EXAMPLE.  — 

517  of  water;   how  much  hydrogen? 

517X0-1119=57-8523. 

The  following  equation  results  also  from  the  above  proportion: 

18-016^  1 
2-016      x 

2-016 


18-016  = 


§  199.] 


CALCULATION    OF   ANALYSES. 


165 


Or,  expressed  in  general  terms, 

Water  divided  by  8  -9365= Hydrogen. 
EXAMPLE. — 

517  of  water,  how  much  hydrogen? 


517 
8-9365 


=  57-8523. 


In  this  manner  we  may  find  for  every  compound  constant  numbers  by 
which  to  multiply  or  divide  the  weight  of  the  compound,  in  order  to  find  the 
weight  of  the  constituent  sought  (comp.  Table  III*). 

Thus,  for  instance,  the  nitrogen  contained  in  ammonium  platinic  chloride 
may  be  obtained  by  multiplying  the  weight  of  the  latter  by  0-06328;  thus 
the  carbon  may  be  calculated  from  carbonic  acid  by  multiplying  the  weight 
of  the  latter  by  0-2727,  or  dividing  it  by  3-6667. 

These  numbers  are  by  no  means  simple,  convenient,  and  easy  to  remember. 
It  is  therefore  advisable,  in  the  case  of  carbonic  acid,  for  instance,  to  fix  upon, 
another  general  expression,  viz., 

Carbonic,  acid  X  3      ~    , 

—— = Carbon; 

in  carbonic  acid  being  carbon,  as  may  be  seen  from  tne 

C  12 
2O  32 

44 


12  parts  in  44  (= 
composition 


The  object  in  view  may  also  be  attained  in  a  very  simple  manner,  by  refer- 
ence to  Table  IV,*  which  gives  the  amount  of  the  constituent  sought  for  every 
number  of  the  compound  found,  from  1  to  9;  the  operator  need,  therefore,, 
simply  add  the  several  values  together. 

As  regards  hydrogen,  for  instance,  we  find: 


TABLE. 


Found, 
water 

Sought, 
hydrogen 

1 
0-1119 

2 
0-2238 

3 
0-3357 

4 
0-4476 

5 
0-5595 

6 
0-6714 

7 
0-7833 

8 
0-8952 

9 
1-0071 

From  this  table  it  is  seen  that  1  part  of  water  contains  ()•  1119  of  hydrogen, 
that  5  parts  of  water  contain  0-5595  of  hydrogen;  9  parts,  1-0071,  etc. 

Now,  if  we  wish  to  know,  for  instance,  how  much  hydrogen  5s  contained 
in  5-17  parts  of  water,  we  find  this  by  adding  the  values  for  5  parts,  for  fff 
part,  and  for  jfo  parts,  thus: 

0-5595 

0-01119 

0-007833 


0-578523 


*  See  Tables  at  the  end  of  the  volume. 


166  ORGANIC    ANALYSIS.  [§  200. 

Why  the  numbers  are  to  be  placed  in  this  manner,  and  not  as  follows: 

0-5595 
0-1119 
0-7833 

1-4547 

is  self-evident,  since  arranging  them  in  the  latter  way  would  be  adding  the 
value  for  5,  for  1,  and  for  7  (5  +  1+7=  13),  and  not  for  5-17.  This  reflection 
shows  also  that,  to  find  the  amount  of  hydrogen  contained  in  517  parts  of 
water,  the  points  must  be  transposed  as  follows: 

55-95' 
1-119 
0-7833 

57-8523 

3.  Calculation  of  the  Results  of  Indirect  Analyses  into  Per-cents  by  Weight. 

§200. 

The  import  of  the  term  "indirect  analysis,"  as  denned  in  §151,  p.  596, 
shows  sufficiently  that  110  universally  applicable  rules  can  be  laid  down  for  the 
calculations  which  have  to  be  made  in  indirect  analyses.  The  selection  of  the 
right  way  must  be  left  in  every  special  case  to  the  intelligence  of  the  analyst. 
I  will  here  give  the  mode  of  calculating  the  results  in  the  more  important 
indirect  separations  described  in  Section  V.  They  may  serve  as  examples  for 
other  similar  calculations. 

a.  Indirect  Determination  of  Sodium  and  Potassium. 

This  is  effected  by  determining  the  sum  total  of  the  chlorides  and  the  chlo- 
rine contained  in  them. 

The  calculation  may  be  made  as  follows : 

Suppose  we  have  found  3  grm.  of  sodium  and  potassium  chlorides,  and  in 
these  3  grm.  1-6877  of  chlorine. 

At.  Chlorine.  Mol.  KC1.  Chlorine  found. 

35-45  :  74-56  ::          1-6877  :  x 

x  =         3-5525 

If  all  the  chlorine  present  were  combined  with  potassium,  the  weight  of 
the  chloride  would  amount  to  3-5525.  As  the  chloride  weighs  less,  sodium 
chloride  is  present,  and  this  in  a  quantity  proportional  to  the  difference  (i.e., 
3-5525  —  3=0-5525),  which  is  calculated  as  follows: 

The  difference  between  the  mol.  weight  of  KC1  arid  that  of  NaCl  (16-06) 
is  to  the  mol.  weight  of  NaCl  (58-50)  as  the  difference  found  is  to  the  sodium 
chloride  present: 

16-06  :  58-50  ::  0-5525  :  x 

z=2NaCl 
and  3-2=lKCl. 


§  200.]  CALCULATION    OF    ANALYSES.  167 

From  this  the  following  short  rule  is  derived : 

Multiply  the  quantity  of  chlorine  in  the  mixture  by  2  •  10324,  deduct  from 
the  product  the  sum  of  the  chlorides,  and  multiply  the  remainder  by  3  •  6426 ; 
the  product  expresses  the  quantity  of  sodium  chloride  contained  in  the  mixed 
chloride. 

The  following  formula*  may  also  be  used: 

50n=C  (sum  of  the  chlorides). 
-45rc=c  (sum  of  the  chlorine). 

K  denotes  the  number  of  equivalents  (expressed  in  grammes)  of  potassium 
chloride  contained  in  the  potassium-chloride  mixture,  and  therefore  also  the 
number  of  equivalents  of  potassium  in  the  potassium  present,  or  the  chlorine 
equivalent  of  the  chlorine  combined  with  the  potassium;  n  is  the  equivalent 
-for  sodium  corresponding  to  K. 

.'.     74-5QK=  potassium  chloride  present. 
58-50n  =  sodium 

35-45K=   chlorine  combined  with  potassium. 
35-45n  =         "  "  "     sodium. 

Using  C  and  c,  we  have 

C-74-56#     C-35-45X 


and     /.     K= 


58-50  35-45 

C-l-6502c 


16-06 

The  quantity  of  potassium  chloride  required  is  therefore 
KCl=74-56K=4-6349C-7-647r. 

4 

b.  Indirect  Determination  of  Strontium  and  Calcium. 

This  may  be  effected  by  determining  the  sum  total  of  the  carbonates  and 
the  carbonic  acid  contained  in  them  (§  154,  8).    Suppose  we  have  found  2 
grm.  of  mixed  carbonate,  and  in  these  2  grm.  0-7383  of  carbonic  acid, 
Mol.  CO,  Mol.  SrCOs  CO,  found 

44  :  147-60  ::         0-7383  :  x 

x  =         2-47666. 

If,  therefore,  the  whole  of  the  carbonic  acid  were  combined  with  strontia, 
the  weight  of  the  carbonate  would  amount  to  2-47666  grm.  The  deficiency, 
=  0-47666,  is  proportional  to  the  calcium  carbonate  present,  which  is  calcu- 
lated as  follows: 

The  difference  between  the  molecule  of  SrCO3  and  the  molecule  of  CaC03 
fJ.7-50)  is  to  the  molecule  of  CaCO3  (100-1)  as  the  difference  found  is  to  the 
calcium  carbonate  contained  in  the  mixed  salt: 

.'.   47-5  :   100-1  ::  0-47666  :  x 
9—1. 

*  KRETSCHY,  Zeitschr.  f.  analyt.  Chem.,  xv,  44.  A  clerical  error  in  this  paper  has  been 
here  corrected. 


168  ORGANIC    ANALYSIS.  [§  201, 

The  mixture,  therefore,  consists  of  1  grm.  calcium  carbonate  and  1  grm. 
strontium  carbonate. 

'From  this  the  following  short  rule  is  derived: 

Multiply  the  carbonic  acid  found  by  3-3545,  deduct  from  the  product  the 
sum  of  the  carbonates,  and  multiply  the  difference  by  2  •  10737  ;  the  product 
expresses  the  quantity  of  the  calcium  carbonate. 

c.  Indirect  Determination  of  Chlorine  and  Bromine  (§  169,  1). 

Let  us  suppose  the  mixture  of  silver  chloride  and  bromide  to  have  weighed 
2  grm.,  and  the  diminution  of  weight  consequent  upon  the  transmission  of 
chlorine  to  have  amounted  to  0  •  1  grm.  How  much  chlorine  is  there  in  the 
mixed  salt,  and  how  much  bromine? 

The  decrease  of  weight  here  is  simply  the  difference  between  the  weight  of 
the  silver  bromide  originally  present  and  that  of  the  silver  chloride  which  has 
replaced  it;  if  this  is  borne  in  mind,  it  is  easy  to  understand  the  calculation 
which  follows: 

The  difference  between  the  molecules  of  silver  bromide  and  silver  chloride 
is  to  the  molecule  of  silver  bromide  as  the  ascertained  decrease  of  weight  is 
to  x,  i.e.,  to  the  silver  bromide  originally  present  in  the  mixture: 

/.  44-50  :  187-87  ::  0-1  :  x 
x=  0-42218. 

The  2  grm.  of  the  mixture  therefore  contained  0  •  42218  grm.  silver  bromide, 
and  consequently  2-0-42218  =  1-57782  grm.  silver  chloride. 

It  results  from  the  above  that  we  need  simply  multiply  the  ascertained 
decrease  of  weight  by 


4-2218 


to  find  the  amount  of  silver  bromide  originally  present  in  the  analyzed  mixture. 
And  if  we  know  this,  we  also  know,  of  course,  the  amount  of  the  silver  chloride; 
and  from  these  data  we  next  calculate  the  quantities  of  chlorine  and  bromine 
as  directed  in  §  199,  and  the  percentages  as  directed  in  §  196. 

SUPPLEMENT  TO  I. 

REMARKS  ON  LOSS  AND  EXCESS  IN  ANALYSES,  AND  ON  TAKING  THE  AVERAGE. 

§201. 

If,  in  the  analysis  of  a  substance,  one  of  the  constituents  is  estimated  from 
the  loss,  or,  in  other  words,  by  subtracting  from  the  original  weight  of  the 
analyzed  substance  the  ascertained  united  weight  of  the  other  constituents, 
it  is  evident  that  in  the  subsequent  percentage  calculation  the  sum  total  must 
invariably  be  100.  Every  loss  suffered  or  excess  obtained  in  the  determination 
of  the  several  constituents  will,  of  course,  fall  exclusively  upon  the  one  con- 
stituent which  is  estimated  from  the  loss.  Hence  estimations  of  this  kind 
cannot  be  considered  accurate,  unless  the  other  constituents  have  been  de- 
termined by  good  methods  and  with  the  greatest  care.  The  accuracy  of  the 
results  will,  of  course,  be  the  greater  the  less  the  number  of  constituents 
determined  in  the  direct  way. 


§  201.]          CALCULATION  OF  ANALYSES.  169 

If,  on  the  other  hand,  every  constituent  of  the  analyzed  compound  has 
been  determined  separately,  it  is  obvious  that,  were  the  results  absolutely 
accurate,  the  united  weight  of  the  several  constituents  must  be  exactly  equal 
to  the  original  weight  of  the  analyzed  substance.  Since,  however,  as  we  have 
seen  in  §  96,  certain  inaccuracies  attach  to  every  analysis  without  exception, 
the  sum  total  of  the  results  in  the  percentage  calculation  will  sometimes 
exceed,  and  sometimes  fall  short  of,  100. 

In  all  cases  of  this  description,  the  only  proper  way  is  to  give  the  results 
as  actually  found. 

Thus,  for  instance,  PELOUZE  found,  in  his  analysis  of  potassium  chloro- 
chromate, 

Potassium 21-88 

Chlorine 19-41 

Chromic  acid 58-21 

99-50 
BERZELIUS,  in  his  analysis  of  potassium  uranate, 

Potassa 12-8 

Uranic  oxide 86-8 

99-6 

PLATTNER,  in  his  analysis  of  pyrrhotite, 

Of  Fahlun.  Of  Brasil. 

Iron 59-72  59-64 

Sulphur 40-22  40-43 

99-94  100-07 

It  is  altogether  inadmissable  to  distribute  any  chance  deficiency  or  excess 
proportionately  among  the  several  constituents  of  the  analyzed  compound,  as 
such  deficiency  or  excess  of  course  never  arises  from  the  several  estimations  hi 
the  same  measure;  moreover,  such  "doctoring  "  of  the  analysis  deprives  other 
chemists  of  the  power  of  judging  of  its  accuracy.  No  one  need  be  ashamed  to 
confess  having  obtained  somewhat  too  little  or  somewhat  too  much  hi  an 
analysis,  provided,  of  course,  the  deficiency  or  excess  be  confined  within  cer- 
tain limits,  which  differ  in  different  analyses,  and  which  the  experienced  chem- 
ist always  knows  how  to  fix  properly. 

In  cases  where  an  analysis  has  been  made  twice,  or  several  times,  it  is 
usual  to  take  the  mean  as  the  most  correct  result.  It  is  obvious  that  an  aver- 
age of  the  kind  deserves  the  greater  confidence  the  less  the  results  of  the 
several  analyses  differ.  The  results  of  the  several  analyses  must,  however, 
also  be  given,  or,  at  all  events,  the  maximum  and  minimum. 

Since  the  accuracy  of  an  analysis  is  not  dependent  upon  the  quantity  of 
substance  employed  (provided  always  this  quantity  be  not  altogether  too 
small),  the  average  of  the  results  of  several  analyses  is  to  be  taken  quite  inde- 
pendently of  the  quantities  used ;  in  other  words,  you  must  not  add  together 
the  quantities  used,  on  the  one  hand,  and  the  weights  obtained  in  the  several 
analyses,  on  the  other,  and  deduce  from  these  data  the  percentage  amount; 


170  ORGANIC    ANALYSIS.  [§   202. 

but  you  must  calculate  the  latter  from  the  results  of  each  analysis  separately, 
and  then  take  the  mean  of  the  numbers  so  obtained. 

Suppose  a  substance,  which  we  call  AB,  contains  fifty  per  cent,  of  A, 
and  suppose  two  analyses  of  this  substance  have  given  the  following  results: 

(1)  2  grm.  AB  gave  0-99  grm.  of  A. 

(2)  50     "       "        "    24-00     "       "  " 

From  1,  it  results  that  AB  contains  49-50  per  cent,  of  A. 
H      o    lt       "          ft      tl  (t        48  .  00          "         "   " 

Total  .....................  97-50 

Mean  .....................  48-75 

It  would  be  quite  erroneous  to  say 

2  +  50=52  of  AB  gave  0-99  +  24-00=24-99  of  A, 
therefore  100  of  AB  contain  48-06  of  A; 

for  it  will  be  readily  seen  that  this  way  of  calculating  destroys  nearly  alto- 
gether the  influence  of  the  more  accurate  analysis  (1)  upon  the  average,  on 
account  of  the  proportionally  small  amount  of  substance  used. 


II.     DEDUCTION  OF  EMPIRICAL  FORMULAS. 
§202. 

When  the  percentage  composition  of  a  substance  is  known,  a  so-called 
empirical  formula  may  be  found  for  it,  i.e.,  the  relative  proportion  of  the 
•several  constituents  may  be  expressed  in  a  formula  which,  upon  calculation 
in  percentages,  will  give  figures  corresponding  exactly,  or  nearly  so,  with 
those  obtained  on  analysis.  We  are  confined  to  the  use  of  such  empirical 
formulas  in  the  case  of  all  substances  the  equivalent  of  which  cannot  be  de- 
termined, such  as  wood  fibre,  mixed  substances,  etc. 

The  very  simple  method  of  deducting  the  empirical  formulas  will  be  readily 
understood  from  the  following  considerations  : 

How  should  we  proceed  to  find  the  relative  number  of  equivalents  in 
carbonic  acid? 

We  should  say  :  The  equivalent  of  the  oxygen  is  to  the  quantity  of  oxygen 
in  the  equivalent  of  carbonic  acid  as  1  is  to  x,  i.e. 

16  :  32  ::  1  :  *;  z=2. 

In  a  similar  manner  one  should  find  the  number  of  carbon  equivalents  by  the 
following  equation  : 

12  :  12  ::   1  :  x;  x=l. 

(eq.  of  carbon)  (carbon  in  1  eq.  of 

carbonic  acid) 


§  202.]'  CALCULATION    OF    ANALYSES.  171 

Now  let  us  suppose  we  did  not  know  the  carbonic-acid  equivalent,  but 
only  the  percentage  composition,  thus: 

C  27-273 
O  72-727 


100-000  carbon  dioxide. 

The  relative  proportion  of  the  equivalents  would  still  be  ascertained  even 
though  any  other  given  number,  e.g.,  100,  were  selected.  Supposing  we 
adopted  100  as  the  number,  we  should  then  have  the  following-- 

16          :         72-727  ::  1   :   z;   z=4-5454. 

(eq.  of  oxygen)     (oxygen  in  the  as- 
sumed eq.  100) 

further, 

12          :          27-273  ::  1   :  x\  x=2>ZI27. 

(eq.  of  carbon)    (carbon  in  the  as- 
sumed eq.  100) 

We  see  that,  though  the  numbers  expressing  the  relative  proportions  of 
oxygen  and  carbon  have  changed,  yet  the  relative  proportion  has  not;  since 

2-2727  :  4-5454  ::  1  :  2. 

The  process  may  hence  be  expressed  as  follows : 

Assume  any  number,  most  conveniently  1 00,  as  the  equivalent  of  the  com- 
pound, and  ascertain  how  many  times  the  equivalent  of  each  constituent  of 
the  compound  is  contained  in  the  quantity  of  the  same  constituent  present 
in  100  parts.  When  the  numbers  expressing  the  relative  proportions  have 
been  thus  found,  the  empirical  formula  has,  in  fact,  been  found.  It  is  usual, 
however,  to  reduce  the  number  found  to  the  simplest  expression  possible. 

Suppose  we  take  a  more  complicated  case,  for  example,  the  calculation 
of  the  empirical  formula  of  mannite.  The  percentage  composition  of  mannite 
is 

C  39-536 
H  7-749 
O  52-715 


100-000 
We  obtain  hence  the  following  proportions : 

12  :  39-536  ::  1  :  x;  z=3-295, 

1-008  :    7-749  ::  1  :  x;  z=7-6S8, 

16  :  52-715  ::  1  :  x:  z=3-295. 

We  have  now  the  empirical  formula  for  mannite,  thus: 
C  3-295,  H  7-688,  O  3-295. 

We  see  at  a  glance  that  the  numbers  of  the  equivalents  of  carbon  and 
•oxygen  are  identical ;  and  the  question  arises  whether  the  relative  proportion 


172  ORGANIC   ANALYSIS.  [§  202. 

found  may  not  be  expressed  by  smaller  numbers.  A  simple  calculation  en- 
ables this  question  to  be  answered,  as  follows: 

3-295  :  7-688  ::  60  :  x;  x=UQ. 

(Any  other  number  might  be  substituted  for  60  as  the  third  term  of  the  pro- 
portion, but  the  number  chosen  is  very  suitable  because  it  is  divisible  without 
remainder  by  most  numbers.) 

We  have  now  the  simple  formula 

O60=  C6H14O6. 


The  percentage  composition  of  mannite,  as  given  above,  being  that  calcu- 
lated from  the  formula,  no  doubt,  of  course,  remains  as  to  the  correctness  of 
the  latter.  Let  us  now  take  the  results  of  an  actual  analysis  of  mannite. 

By  the  combustion  of  1  •  593  grm.  of  mannite  with  cupric  oxide,  OPPER- 
MAN  obtained  2-296  CO2  and  1-106  water.  In  per-cents  this  gives 

C  39-31 
H  7-77 
O  52-92 


100-00 
This,  calculated  as  above,  would  give 

^3-270    H7.708   O3.308 

as  the  first  expression  of  the  empirical  formula,  and  by  the  proportion 
3-276  :  7-708  ::  6  :  14-11. 

A  glance  at  these  numbers  will  show  that  14  may  be  readily  taken  for  the 
14-11,  and  that  the  difference  between  3-276  and  3-308  is  so  small  that  both 
may  be  expressed  by  one  number.  From  these  considerations  we  again  come 
to  the  formula 

C6H1406. 

The  proof  as  to  whether  the  formula  is  correct  or  not  is  obtained  by  recal- 
culation in  per-cents.  The  smaller  the  difference  between  the  per-cents  calcu- 
lated and  those  found,  the  more  reason  is  there  to  consider  the  formula  as 
correct.  If  the  difference  is  greater  than  can  be  accounted  for  by  the  defects 
incidental  to  the  methods,  there  is  ground  to  consider  the  formula  as  incorrect, 
and  to  establish  another ;  it  will  be  evident  that  in  the  case  of  substances  the 
equivalent  of  which  is  not  known,  different  formulas  may  be  calculated  from 
the  same  analysis,  or  from  a  number  that  closely  agree,  while  the  numbers 
found  are  never  absolutely  correct,  but  are  always  only  approximately  so. 
For  instance  in  the  case  of  mannite: 

Calculated  Found 

forC6      39-536      f or  C8    39-65  39-31 

H14      7-749            H18     7-49  7-77 

O.  52-715     O3  52-86  52-92 

100-000        100-00      100-00 


§  203.]  CALCULATION    OF  ANALYSES.  173 

III.  DEDUCTION  OP  RATIONAL  FORMULAS. 
§203. 

If  in  addition  to  the  percentage  composition  the  equivalent  of  a  substance 
is  also  known,  it  is  easy  to  deduce  its  rational  formula,  i.e.,  a  formula  expressing 
not  only  the  relative  proportion  of  the  equivalents,  but  also  their  absolute 
number  in  one  equivalent  of  the  substance. 

The  following  examples  will  serve  for  illustration: 

1.    Determining  the  rational  Formula  of  Hyposulphuric  (Dithionic)  Add. 

By  analysis  we  find  first  the  percentage  composition  of  hyposulphuric 
acid,  secondly  that  of  potassium  hyposulphate,  thus : 

Sulphur 44-50        Potassa  (K2O) 39-528 

Oxygen 55-50        Hyposulphuric  acid 60-472 

100-00  100-000 

(equivalent  of  K2O= 94  -  22) 
From  the  equation 

39-528  :  60-472  ::  94-22  :  x\  z=144-14 

it  follows  that  144-14  is  the  sum  of  the  equivalents  of  the  constituents  of  hypo- 
sulphuric  acid,  i.e.,  the  equivalent  of  hyposulphuric  acid. 

We  need  no  longer  assume  any  hypothetical  equivalent  for  our  calculation, 
as  we  did  in  §  202  for  mannite,  since  we  know  now  the  correct  one,  but  can 
at  once  proceed  to  state  the  following: 

100  :  44-50  ::  144-14  :  x;  rr=64-14; 
i.e.,  the  sum  of  the  sulphuric  equivalents;  and  further, 
100  :  55-50  ::  144-14  :  z;  x=80, 

i.e.,  the  sum  of  the  ogygen  equivalents.  Now  the  equivalent  of  sulphur,  32  •  07, 
is  contained  twice  in  64-14;  and  the  equivalent  of  oxygen,  16,  is  contained 
5  times  in  80,  hence  the  rational  formula  for  hyposulphuric  acid  is  SjO6. 

2.   Determining  the  rational  Formula  of  Benzoic  Acid. 

STENHOUSE  obtained  0-9575  CO2  and  0-1698  water  from  0-3807  hydrated 
benzoic  acid  dried  at  100°. 

0-4287  silver  benzoate  dried  at  100°  gave  0-202  silver.  From  these  num- 
bers the  following  percentage  compositions  are  calculated: 

C 68-58        Silver  oxide 54-13 

H 4-99         Benzoic  acid 45-87 

O..  .26-43        Silver  benzoate. ... 


Benzoic  acid 100-00 


100-00 


(equivalent  of  silver  oxide,  123-92) 
64-13  :  45-87  ::  123-92  :  x;  x=  105-01; 


174  ORGANIC    ANALYSIS.  [§   203^ 

i.e.,  the  equivalent  of  the  anhydrous  benzole  acid  would  be  105-01;  hence- 
that  of  the  hydrated  acid  would  be  105.01+18-016=  123-026.  We  now  say 

100  :  68-58  ::  123-026  :  or;  £=84-371, 

100  :    4-99  ::  123-026  :  x\  x=   6-140, 

100  :  26-43  ::  123-026  :  x\  z=32.516. 
12  is  contained  in  84-371     7-03  times. 
1-008  "         "         "      6-140     6.09       " 
16  "         "         "    32-516     2-03       " 

It  will  be  seen  at  a  glance  that  these  quotients  may  be  exchanged  for  whole 
numbers,  7,  6,  and  2  respectively.    The  rational  formula  for  the  benzoic  acid 
would  hence  be  C7H0O2. 
This  gives 

By  calculation.  Found. 

.  ..//  C     68-82  68-58 

H      4-96  4-99 

O     26-22  26-43 

3.    Deduction  of  the  Rational  Formula  of  Theine. 

STENHOUSE  obtained  the  following  figures  on  an  analysis  of  theine  freed 
from  its  water  of  crystallization: 

1.  0-285  grm.  of  substance  gave  0-5125  carbonic  acid  and  0-132  grm.  of 
water. 

2.  On  combustion  with  cupric  oxide  a  mixture  of  gas  was  obtained  consist- 
ing of  CO2  and  N  in  the  proportions  of  4  r  1. 

3.  0-5828  grm.  of  the  double  salt  of  platinum  and  theine  (caffeine)  hydro- 
chlorate  gave  0-142  grm.  platinum.    From  these  data  the  following  percent- 
age composition  is  deduced:       v 

C  49-05 
H  5-18 
N  28-65 
O  17-12 

and  as  the  equivalent  of  theine,  195-15,  since  there  is  every  reason  to  believe 
that  the  formula  for  the  platinum-theine  hydrochlorate  is 

2  (theine +  HCl)+PtCl4. 
The  equivalent  of  the  double  salt  is  found  from  the  equation 

0-142  :  0-5828  ::  194-9  (eq.  of  Pt)  :  x; 
x- 799 -91; 

and  consequently  the  equivalent  of  theine  is  obtained  by  subtracting  from 
799-98  the  sum  of  1  eq.  of  platinum  tetrachloride  (336-7)  and  2  eq.  of  hydro- 
chloric acid  (72-916),  and  dividing  by  2,  thus: 

799-91 -(336-7  +  72-916)  =  390-30;  and 
390-30  +  2=  195 -15 


§  203.]  CALCULATION    pF    ANALYSES.  175 

This  now  gives  the  following  equations: 

100  :  49-05  ::  195-15  •  z;  *=95-721, 
100  :  5-18  ::  195-15  :  x;  z=10-108, 
100  :  28-65  ::  195-15  :  x;  x=55-911, 
100  :  17-12  ::  195-15  :  x;  z=33-409. 

In  the  numbers  found 

12  is  contained  in  95-720     7-98  times, 
1-008  "         "  "  10-108  10-02     " 

14-04  "         "  "  55-911     3-98     " 

16  "         "          "  33-409     2-09     " 

for  which  numbers  we  may  substitute  8,  10,  4,  and  2,  respectively,  when  we 
get  the  following  formula: 


This  gives 

By  calculation.  Found. 

49-42  49-05 

5-19  5-18 

28-91  28-65 

16-48  17-12 


100-00  100-00 

The  platinum-theine  hydrochlorate  yields  in  100  parts, 

Calculated.  Found. 

24-42  24-36 

4.    Special  Method  of  deducing  the  Formulas  of  Oxygen  Salts, 
a.    In  substances  containing  no  Isomorphous  Substances. 
The  rational  formulas  of  oxygen  salts  may  also  be  deduced  by  an  entirely 
different  method,  based  upon  ascertaining  the  ratio  which  the  different  quan- 
tities of  oxygen  bear  to  each  other.    This  method  is  exceedingly  simple. 

In  the  analysis  of  crystallized  sodium-ammonium  sulphate    the  author 
found 

Soda  (Xa2O) 17-93 

Ammonium  oxide  ([NHJjO).  .  '. 15-23 

Sulphuric  anhydride  (SO3>. 46-00 

Water 20-84 

100-00 

1  eq.  of  Na2O       =62-10,  contain   16  O;  hence  17-93  contain    4-62O. 

1"     "    (XH4)2O=52-144,       "        16  O;  "       15-23       "          4-670. 

1  "    "    SO3         =80-07,         "       48  O;  "      46-00       "       27-58  O. 

1"    "    H2O        =18-016,       "       16  O;  "      20-84       "       18-51  O. 

The  proportions  obtained  are  then 

4-62  :  4-67  •:  27-58  :  18-51  =  1  :  1-01  ::  5-97  :  4-01, 


176  ORGANIC    ANALYSIS.  [§  203. 

and  these  may  be  properly  replaced  by  1, 1,  6,  and  4,  respectively,  which  would 
lead  to  the  formula 

Na^O  •  (NH4):O  •  2SO3  •  4H2O,  or 

Na2SO4  +  (NH4)2SO4+4H2O. 

b.  In  substances  containing  Isomorphous  (or  mutually-replacing)  Constituents. 

Isomorphous  constituents  may  replace  each  other  in  all  proportions,  as  is 
well  known,  hence  to  establish  a  formula  for  compounds  containing  isomor- 
phous  constituents,  the  latter  are  taken  collectively,  i.e.,  they  are  expressed  in 
the  formula  as  one  and  the  same  substance.  This  occurs  very  frequently  in 
the  calculation  of  the  formulas  of  minerals  in  particular. 

A.  ERDMANN  found  in  monradite 

Silicic  acid 56-17     29-759 

Magnesia 31-63     12-558 


Ferrous  oxide 8-56       1-905  f 

Water.  .  4-04  3-588 


100-00 

3-588  :  14-463  :  29-759=1  :  4-03  :  8-3,  for  which  1,  4,  and  8  may  be  prop- 
erly taken.  If  now  we  designate  1  eq.  of  metal  by  R,  we  obtain  from  these 
numbers  the  formula 

4(RO.Si02)  +  H20,  or 


Not  only  may  isomorphous  substances  replace  each  other  in  compounds, 
but  all  bodies  generally  of  analogous  compounds  do  so  as  well.  We  find  thus 
that  Na^O,  K2O,  CaO,  MgO,  etc.,  replace  each  other.  These  substances  must 
then  likewise  be  expressed  collectively  in  the  formula. 

ABICH  found  in  andesine 

Silicic  acid  (SiO2) 59-60  31-58 

Alumina  (A12O3)   24-28     H-40) 

Ferric  oxide  (Fe2O3) 1-58       0-48  J 

Lime  (CaO) 5-77 

Magnesia  (MgO) 1-08 

Soda  (Na,O)  6-58 

Potassa  (K26) 1-08 

99-97 

3-91  :  11-88  :  31-58=1:3-04  :  8-07;  and  these  numbers  may  be  properly 
replaced  by  the  numbers  1,  3,  and  8,  respectively. 

Designating  1  eq.  of  metal  by  R,  we  obtain  from  the  numbers  the  formula 
RO,R2Os+4SiO2,  or  we  can  write  it 

Ca 


K2    J 


§  204.]  CALCULATION  OF  ANALYSES.  177 

From  this  it  may  be  seen  that  this  mineral  has  a  composition  similar  to  that 
of  leucite  (K2O-SiO2  +  Al2O3-3SiO2).  The  potassa  in  the  leucite  is,  in  the  case 
of  andesine,  replaced  to  a  great  extent  by  lime,  soda,  and  magnesia;  and  a 
part  of  the  ferric  oxide  is  replaced  by  alumina. 

It  need  scarcely  be  stated  that  what  has  here  been  said  regarding  the 
deduction  of  formulas  of  the  oxygen  salts  applies  equally  as  well  to  the  metallic 
sulphides. 

IV.  CALCULATION  OF  THE  VAPOR  DENSITY  OF  VOLATILE  SUBSTANCES,  AND 
APPLICATION  OF  THE  RESULTS  AS  A  MEANS  OF  CONTROL  OF 
ANALYSES  AND  OF  DETERMINATION  OF  THE  EQUIVALENTS. 

§204. 

It  is  well  known  that  the  specific  gravity  of  a  complex  gas  is  equal  to  the 
sum  of  specific  gravities  of  the  individual  constituents  in  one  volume. 

For  instance,  2  volumes  of  hydrogen  gas  and  1  volume  of  oxygen  gas  give 
2  volumes  of  aqueous  vapor.  If  they  gave  but  1  volume  of  aqueous  vapor, 
the  specific  gravity  of  the  latter  would  be  equal  to  the  sum  of  the  specific 
gravities  of  the  oxygen  and  double  the  specific  gravity  of  the  hydrogen,  thus: 

2X0-06959=0-13918 
+  1-10509 


1 • 24427 

As,  however,  the  gases  yield  2  volumes,  the  specific  gravity  of  1  volume 
would  be  half  of  1-24427,  or  0-62214. 

It  will  be  readily  seen  that  the  knowledge  of  the  vapor  density  of  a  com- 
pound substance  affords  an  excellent  means  of  control  as  to  the  correctness 
of  the  relative  proportions  of  the  equivalents  found,  provided,  however,  that 
the  vapor  density  has  been  properly  determined,  and  at  a  temperature  at  least 
30°  to  40°  above  the  boiling-point  of  the  substance,  because  only  under  these 
conditions  is  the  vapor  density  constant  and  to  be  considered  as  a  true  one. 

For  instance,  the  ultimate  analysis  of  camphor  gives  to  the  latter  the  em- 
pirical formula 

C10H100.      . 

DUMAS  found  the  vapor  density  of  camphor  to  be  5-3136.  How  may  we 
ascertain  whether  the  formula  found  is  correct  with  regard  to  the  relative 
proportion  of  the  equivalents? 

Specific  gravity  of  carbon  vapor 0  •  82882 

"        "   hydrogen  gas 0-06959 

"  "        "   oxygen  gas 1  •  10509 

10  eq.  C    =10  vol.  =10X0-82882=   8-28820 

16  "    H  -16     "    =16x0-06959=    1-11344 

1  "    Q  =   1     "    =    1x1-10509=   1-10509 

10-50673 


178  ORGANIC    ANALYSIS.  [§  204. 

It  will  be  seen  that  this  figure  is  almost  exactly  twice  as  large  as  that  found  for 
the  vapor  density  by  direct  experiment,  a  proof  that  the  relative  proportions 
of  the  equivalent  of  the  empirical  formula  are  correct.  Whether  the  formula 
is  also  correct,  however,  in  regard  to  the  absolute  number  of  equivalents 
cannot  be  determined  with  certainty  from  the  vapor-density,  because  it  cannot 
be  known  how  many  volumes  of  camphor  vapor  correspond  to  1  equivalent  of 
camphor.  Thus  LIEBIG  assumed  1  eq.  of  camphor  to  correspond  to  2  volumes 
of  vapor,  and  assigned  it  the  formula  C10H16O,  while  DUMAS  assumed  1  eq. 
to  correspond  to  4  volumes  of  vapor,  and  accordingly  gave  it  the  formula 
C20H32O2. 

The  knowledge  of  the  vapor  density  hence  affords  simply  a  means  of 
control  as  to  the  correctness  of  the  analysis,  but  not  as  to  that  of  the  rational 
formula,  and  though  notwithstanding  it  is  used  for  the  latter  purpose,  this 
can  be  done  only  in  the  case  of  such  substances  for  which,  by  analogy,  we 
may  infer  a  certain  ratio  of  condensation.  For  instance,  experience  proves 
that  in  the  case  of  the  hydrates  of  the  volatile  organic  acids,  alcohol,  etc., 
1  equivalent  corresponds  to  2  volumes. 

We  found  above  the  rational  formula  of  benzoic  acid  to  be  C7H6O2;  DUMAS 
and  MITSCHERLICH  found  the  vapor  density  to  be  4-26. 

A  number  very  nearly  approximating  this,  however,  is  obtained  by  divid- 
ing by  2  the  sum  of  the  vapor  densities  of  the  constituents  in  1  eq.  of  benzoic 
acid;  e.g., 

7  volumes  C  =5-8017 
6  "  H  =0-4175 
2  "  O=2-2102 


8-4295 
and  8-4302-2=4-2147. 

HERMANN  KOPP  *  has  called  attention  to  the  fact  that  if  the  equivalent  of 
a  substance  referred  to  H=l,  and  the  vapor  density  of  the  same  substance 
referred  to  atmospheric  air=  1,  the  division  of  the  equivalent  by  the  vapor 
density  will  give  the  quotients 

28-944,  14-472,  and  7-236, 

according  as  the  equivalent  corresponds  to  4,  2,  or  1  volume  of  vapor  respec- 
tively. 

28-944  corresponds  to  a  condensation  to  4  volumes. 

14«472  "  "  ft  tl  lt  2         " 

7-236  "•  "  "  "  "  1         " 

KOPP  terms  these  numbers  normal  quotients.  If  the  vapor  density  has  not 
been  accurately  obtained,  but  only  approximately  (by  experiment),  numbers 
differing  from  these  will  be  found,  but  which  should  nevertheless  closely  ap- 
proximate them. 

We  may,  hence,  with  the  greatest  ease  ascertain  whether  a  vapor-density 
determination  has  been  obtained  approximately  correct  or  not,  if  the  equiva- 
alent  of  the  substance  be  known. 

*Compt.  rend.,  XLIV,  1347. 


§  204.]  CALCULATION  OF  ANALYSES.  179 

GAY-LUSSAC  found  the  vapor  density  of  alcohol  to  be  1-6133;  DALTON 
found  it  to  be  2-1.*  Which  number  is  correct?  The  equivalent  of  alcohol  is 
C2H6O=46-048. 


—  3 


We  see  thus  that  GAY-LUSSAC'S  number  is  the  one  more  nearly  approximate, 
as  the  quotient  afforded  by  it  most  nearly  approaches  the  normal  quotient 
28-944. 

Further,  it  is  very  easy  to  calculate  the  theoretical  vapor  density  of  a 
substance,  provided  its  equivalent  is  known  as  well  as  the  number  of  volumes 
of  vapor  corresponding  to  1  equivalent.  For  instance,  the  equivalent  of  ben- 
zoic  acid  is  122-048.  Dividing  this  number  by  28-944  gives  4-216,  i.e.,  the 
number  which  we  obtained  above  as  the  vapor  density  of  benzoic  acid. 

Finally,  by  the  aid  of  these  quotients,  the  equivalent  of  a  substance  may 
be  approximately  ascertained,  provided  we  know  its  vapor  density  approxi- 
mately (by  experiment),  as  well  as  the  ratio  of  condensation. 

For  instance,  the  vapor  density  of  acetic  ether  was  found  by  BOULLAY 
and  DUMAS  to  be  3-06.  On  multiplying  this  number  by  28-944  we  obtain 
as  the  equivalent  of  acetic  ether  the  number  88  •  56,  whereas  the  actual  equiva- 
alent  is  88-064. 

Having  now  found  how  the  knowledge  of  the  vapor  density  of  a  substance 
may  be  applied  as  a  control  in  elementary  analysis,  we  will  proceed  to  show 
how  the  vapor  density  may  be  calculated  from  the  data  given  in  §  194,  A 
and  B. 

A.  Let  us  take  as  an  example  DUMAS'  determination  of  the  vapor  density 
of  camphor. 

The  results  of  the  experiment  were  as  follows  : 

Temperature  of  the  air  .............................  13-5° 

Barometer  .......................................  742  mm. 

Temperature  of  the  bath  when  sealing  the  globe.  .'  ......  244° 

Increase  of  weight  of  globe  .  .  ........................  0  •  708  grm. 

Volume  of  mercury  entering  the  globe  ................  295  c.  c. 

Residual  air.  .  .  .  ...................................  0 

To  find  the  vapor  density  we  must  answer  three  questions: 

1.  What  is  the  weight  of  the  air  held  by  the  globe?     (This  weight  must 
be  known  before  the  second  question  is  answered.) 

2.  What  is  the  weight  of  the  camphor  vapor  held  by  the  globe? 

3.  To  what  volume  at  0°  and  760  mm.  does  the  camphor  vapor  correspond? 
The  answers  to  these  questions  are  quite  simple;  and  if  the  calculations 

appear  to  be  rather  complicated  it  is  only  because  certain  reductions  and  cor- 
rections are  necessary. 

1.    The  weight  of  the  air  in  the  globe. 

The  globe  holds  295  c.c.,  as  we  have  seen  from  the  mercury  required  to 
fill  it.  Now  what  will  be  the  volume  of  295  c.c.  of  air  measured  at  13-5°  and 
742  -mm.  when  measured  at  0°  and  760  mm.? 

*  Gmelin,  Handbuch  der  Chem.,  4.  Aufl.,  550. 


180  ORGANIC    ANALYSIS.  [§  204. 

This  question  is  answered  according  to  §  198,  as  follows: 

760  :  742  ::  295  :  x;  x  =  288  c.c.  (at  13-5°  and  760  mm.); 

Again : 

288  288         0_. 

274  c.c. 


1  + (13 -5X0- 00366)      1-04941 
(at  0°  and  760  mm.) 

As,  however,  1  c.c.  of  air  at  0°  and  760  mm.  weighs  0-0012932  gm.,  274  c.c. 
will  weigh  0  -  0012932  X  274  =  0  -  35434  grm. 

2.  The  weight  of  the  vapor. 

On  beginning  the  experiment  we  first  tared  the  globe  +  the  air  within  it. 
On  afterwards  weighing  we  ascertained  the  weight  of  the  globe  +  the  vapor 
(but  not  the  air).  To  find  the  actual  weight  of  the  vapor,  therefore,  it  is  not 
enough  to  subtract  the  tare  from  the  weight  of  the  globe  +  the  vapor,  because 
(globe  +  vapor)  —  (globe  +  air)  does  not  give  the  weight  of  the  vapor ;  we 
must  either  subtract  the  weight  of  the  air  from  the  tare  or  add  it  to  the  in- 
crease in  weight  of  the  globe.  We  shall  do  the  latter : 

Weight  of  air  in  globe 0-35434  grm. 

Increase  of  weight  of  globe 0  •  70800  grm. 

Weight  of  vapor,  hence 1  •  06234  grm. 

3.   The  volume  to  which  this  1-06234  grm.  of  vapor  corresponds  at  0°  and 

760  mm. 

From  the  above  data  we  know  that  this  weight  corresponds  to  295  c.c. 
at  244°  and  742  mm.  Before  we  can  proceed  to  the  reductions  as  given  under 
§  198,  it  is  necessary  to  first  make  the  following  corrections: 

a.  244°  of  the  mercurial  thermometer  correspond,  according  to  MAGNUS' 
experiments,  to  239°  of  the  air- thermometer  (see  Table  VI). 

b.  According  to  DU!,ONG  and  PETIT  glass  expands,  beginning  at  0°,  Tg£vv 
of  its  volume  for  every  degree  Centigrade.     The  volume  of  the  globe,  at  the 
moment  of  sealing,  must  hence  accordingly  have  been 

295X239 
295+  -35000-  ==297C'C- 

If  we  now  make  the  reductions  for  temperature  and  barometric  pressure, 
we  obtain  by  the  proportion  760  :  742  ::  297  :  x;  x  (i.e.,  the  c.c.  of  vapor  at 

290 
760  mm.  and  2390)  =  290;    and  by  the  equation  1  +  (239xQ .00366)  =  *;    x 

(i.e.,  the  c.c.  of  vapor  at  760  mm.  and  0°)  =  154-6.  154-6  c.c.  of  camphor 
vapor  at  0°  and  760  mm.  hence  weigh  1-06234,  and  consequently  1  litre 
(1000  c.c.)  will  weigh  6-87218  grm.,  since  154-6  :  1-06234  ::  1000  :  6-87154. 
Now,  1  litre  of  air  at  0°  and  760  mm.  .weighs  1-2932  grm.,  consequently  the 
vapor  density  of  camphor  is  5-31245,  since 

1-2932  :  6-87154  ::  1  :  5-31359. 


§  204.]  CALCULATION    OF    ANALYSES.  181 

B.  Determination  of  the  vapor  density  of  ether  by  the  method  of  A,  W. 

H  OFMANN-WlCHELHAUS. 

Weight  of  ether  ..................................  0-0724  grm. 

Heated  to  .......................................  100° 

Volume  read  off  .................................  49-201  c.c. 

Barometer  ......................................  754  mm. 

Temperature  of  air  ...............................  20° 

Murcurial  column  after  heating  to  100°  .............  300  mm. 

Mercurial  tension  at  100°  .........................  0-746  mm. 

The  volume  read  off  at  100°  corresponds  to  a  somewhat  larger  volume, 
because  of  the  expansion  of  the  globe.  For  every  degree  Centigrade  glass 
expands  STS^  of  its  volume,  hence  the  49-201  c.c.  read  off  after  correction 
gave  actually 


This  volume  must  now  be  reduced  from  100°  to  0°.     According  to  §  198, 
49-342  c.c.  at  100°  become 

=  36-108c.c.atO°, 


1+0-003665X100 

and  at  the  pressure  at  which  the  volume  was  read  off.  This  pressure,  however, 
is  equal  to  the  height  of  the  barometer  minus  the  height  of  the  mercurial 
column  at  100°  and  the  mercurial  tension  at  100°. 

As  we  have  read  off  the  barometer  at  20°,  however,  we  must  reduce  this 
to  0°.  The  coefficient  of  expansion  of  mercury  is  0-00018,  therefore  the 
barometric  pressure  of  754  mm.  at  20°  becomes 


=  751-295  mm.  at  0°. 


1+0-00018X20 

The  mercurial  column  of  300  mm.  at  100°  becomes  reduced  to  0°: 
300 


1  +  0-00018X100 


=  294 -695  mm. 


The  tension  of  the  mercurial  vapor  at  100°  =  0-746  mm.  Accordingly,  the 
pressure  =  751  •  295  -  (294  •  695+  0  •  746)  =  455  -  854  mm. 

The  36-108  c.c.  at  455-854  mm.  must  now  be  reduced  to  760  mm.  pres- 
sure, as  follows: 

760  :  455-854  ::  36-108  :  x;  s=  21 -6579. 

1000  c.c.  of  air  at  0°  and  760  mm.  weigh  1-2936  grm.,  therefore  21-6579 
grm.  of  air  will  weigh  0-028  grm.  The  21-6579  c.c.  of  ether  is,  however, 
0-0724  grm.,  hence  the  vapor  density  of  the  ether  is 

0-0724 


PART  II. 

SPECIAL  PART. 


1.  ANALYSIS    OF  WATER. 

A.     ANALYSIS    OF    FRESH     WATER    (SPRING -WATER, 
RIVER -WATER,  ETC.).* 

§205. 

The  analysis  of  the  several  kinds  of  fresh  water  is  usually  re- 
stricted to  the  quantitative  estimation  of  the  following  substances : 

a.  DISSOLVED    SUBSTANCES. 
a.  Inorganic. 

Basic  metals:  Sodium,  calcium,  magnesium. 
Acids:  Sulphric  acid,  nitric  acid,  silicic  acid,   carbonic   acid, 
chlorine. 

/?.  Organic.     Acids  of  humus   and   other  organic   substances. 

6.  MECHANICALLY  SUSPENDED  MATTERS. 
Clay,  etc. 

We  confine  ourselves,  therefore,  here  to  the  estimation  of  these 
bodies.  If  the  examination  is  to  include  other  constituents  also, 
the  methods  described  under  §§  206-213  must  be  resorted  to. 

I.  THE   WATER   IS   CLEAR. 
1.  Determination  of  the  Chlorine. 

This  may  be  effected  either,  a,  in  the  gravimetric  or,  b,  in  the 
volumetric  way. 

a.  Gravimetrically. 

Take  500-1000  grm.  or  c.c.f  Acidify  with  nitric  acid  and 
precipitate  with  silver  nitrate.  Filter  when  the  precipitate  has 

*  Compare  Qualitative  Analysis,  p.  320  et  seq.  See  a  paper  read  before 
the  Chemical  Society  by  DR.  MILLER — the  Society's  Journal  (II),  in,  117  et 
seq.;  also  FRANKLAND,  idem  (II)  iv,  239,  and  vi,  77;  and  WANKLYN,  CHAP- 
MAN, and  SMITH,  idem,  vi.  152. 

f  As  the  specific  gravity  of  fresh  water  differs  but  little  from  that  of  pure 
water,  the  several  quantities  of  water  may  safely  be  measured  instead  of 
weighed  The  calculation  is  facilitated  by  taking  a  round  number  of  c.c. 

185 


186  ANALYSIS    OF   WATER.  [§  205. 

completely  subsided  (§  141 ,  I,  a).  If  the  quantity  of  the  chlorine 
is  so  inconsiderable  that  the  solution  of  silver  nitrate  produces 
only  a  slight  turbidity,  evaporate  a  larger  portion  of  the  water  to 
4>  i;  i>  etc.,  of  its  bulk,  filter,  wash  the  precipitate,  and  treat  the 
filtrate  as  directed. 

b.  Volumetrically. 

Evaporate  1000  grin,  or  c.c.  to  a  small  bulk,  and  determine 
the  chlorine  in  the  residual  fluid,  without  previous  filtration,  by 
solution  of  silver  nitrate,  with  addition  of  potassium  chromate 
(§141,1,  6,  a). 

2.  Determination  of  the  Sulphuric  Add. 

Take  1000  grm.  or  c.c.  Acidify  with  hydrochloric  acid  and 
mix  with  barium  chloride.  Filter  after  the  precipitate  has  com- 
pletely subsided  (§  132,  I,  1).  If  the  quantity  of  the  sulphuric 
acid  is  very  inconsiderable,  evaporate  the  acidified  water,  to  J,  J,  J, 
etc.,  of  the  bulk,  before  adding  the  barium  chloride.  The  filtrate 
may  serve  for  the  direct  determination  of  the  sodium  (§  205,  7). 

3.  Determination  of  Nitric  Acid. 

A.  For  the  exact  determination  of  nitric  acid  in  natural  waters 
only  those  methods  are,  as  a  rule,  suitable  which  give  good  results 
also  in  the  presence  of  organic  matter,  and  which  are  described 
in  §  149.  Of  these,  the  methods  based  upon  the  decomposition 
of  nitric  acid  by  ferrous  chloride,  and  described  by  SCHLOSING 
( §  149,  II,  d,  r)  and  F.  SCHULZE  (Vol.  I,  p.  581),  and  also  §  149,  II,  /, 
are  of  more  particular  service. 

F.  SCHULZE'S  method  as  described  by  H.  WULFERT  *  (Vol.  I, 
p.  581),  in  which  the  nitric  oxide  is  collected  and  measured  over 
mercury,  requires  a  deep  trough  holding  a  comparatively  large 
quantity  of  mercury  and  a  special  tube  provided  with  a  glass  cock 
at  its  upper  end.  The  accuracy  of  the  results  obtainable  by  this 
method  is  perfectly  satisfactory.  TIEMANN,!  without  in  any 
way  diminishing  the  precision,  has  greatly  simplified  the  method 

*  Zeitschr.  f.  analyt.  Chem.,  ix,  400. 

f  Anleitung  zur  Untersuchung  von  Wasser,  von  W.  KUBEL,  2.  Auflage  von 
F.  TIEMANN,  Braunschweig  bei  FR.  VIEWEG  u.  SOHN,  1874,  p.  55. 


§  205.] 


ANALYSIS  OF   FRESH    WATER. 


187 


by  replacing  the  mercury  by  well-boiled  soda-lye.  The  process 
so  modified  is  excellently  adapted  for  accurately  determining  the 
nitric  acid  in  water;  it  requires  the  apparatus  shown  in  Fig.  82. 

In  this  A  is  a  flask  holding  about  150  c.c.    The  tube  c  b  a  is 
drawn  out  at  a,  but  not  too  finely,  and  projects  about  2  cm.  from 


FIG.  82. 

the  lower  surface  of  the  rubber  stopper.  The  orifice  of  tube  e  f  g, 
on  the  other  hand,  is  flush  with  the  lower  surface  of  the  stopper. 
A  piece  of  rubber  tubing  is  slipped  over  the  lower  end  of  the  tube 
g  h  in  order  to  protect  it  from  breakage.  The  trough  B  and  also 
the  tube  C  are  filled  with  well-boiled  10-per  cent,  soda-lye.  The 
tube  C  should  be  as  narrow  as  convenient  and  be  graduated  in 
0-lc.c. 

100  to  300  c.c.  (or  more,  if  necessary)  of  the  water  to  be  ex- 
amined are  evaporated  to  about  50  c.c.  in  a  dish  and  then  trans- 
ferred to  the  flask  A,  the  dish  being  repeatedly  rinsed  with  small 
quantities  of  water.  It  is  immaterial  whether  any  portion  or  all 
of  the  precipitate,  should  such  have  formed  during  evaporation, 


188  ANALYSIS    OF  WATER.  [§  205. 

is  transferred  to  A.  The  tubes  are  left  open  and  the  water  is 
boiled  down  further;  toward  the  end  of  the  operation  the  lower 
end  of  the  tube  e  f  g  h  is  immersed  in  the  soda-lye  so  that  the  vapors 
may  pass  through  the  latter.  After  a  few  minutes  compress  the 
rubber  tube  between  the  fingers  at  g.  .  If  all  the  air  has  been  ex- 
pelled by  the  steam,  the  soda-lye  will  rise  suddenly  in  the  tube 
and  a  slight  shock  will  be  felt  by  the  finger;  when  this  occurs,  put 
on  a  pinch-cock  at  g  and  let  the  steam  pass  off  through  d.  The 
evaporation  is  continued  until  only  about  10  c.c.  of  fluid  remain 
in  A.  Then  remove  the  heat,  close  c  by  means  of  a  pinch-cock, 
and  fill  the  tube  dc  with  water  from  a  wash-bottle.  If  an  air- 
bubble  remains  in  c  it  should  be  removed  by  pressing  between 
the  fingers.  ._ 

Now  place  the  measuring  tube  C  over  the  Orifice;  of  the  tube 
efgh  so  that  about  2  to  3  cm.  of  the  latter  project  into  C.  As 
soon  as  the  rubber  tubes  collapse  at  c  and  g,  owing  to  the  external 
pressure,  pour  a  nearly  saturated  solution  of  ferrous  chloride  acid- 
ulated with  hydrochloric  acid  into  a  small  beaker  on  the  upper 
part  of  which  two  scratches  have  been  made,  the  space  between 
them  indicating  a  volume  o'f  20  c.c.;  fill  a  second  beaker  with  con- 
centrated hydrochloric  acid.  Now  dip  the  tube  d  into  the  ferrous- 
chloride  solution,  open  the  pinch^cock  at  c  long  enough  -to  let  15 
to  20  c.c.  of  the  solution  flow  into  A,  then  dip  d  into  the  hydro- 
chloric acid,  and  let  this  follow  the  iron  solution,  repeating  the 
introduction  of  the  acid  in  small  quantities  to  completely  wash 
all  the  iron  solution  from  the  tube  deb  a.  A  small  bubble  of  hydro- 
chloric-acid gas  frequently  forms  at  b,  but  this  disappears  com- 
pletely, or  nearly  so,  as  soon  as  the  pressure  in  A  increases. 

Now  warm  A,  at  first  gently,  until  the  rubber  tubes  swell 
slightly  at  c  and  g,  then  substitute  the  pressure  of  the  fingers  for 
that  of  the  pinch-cock  at  g,  and,  as  soon  as  the  pressure  of  the  gas 
becomes  stronger,  allow  the  nitric  oxide  evolved  to  pass  into  C. 
Finally  heat  more  strongly,  until  the  volume  of  gas  in  C  ceases  to 
increase,  and  remove  the  delivery  tube  from  the  soda-lye.  The 
operation  must  not  be  hurried  too  much  near  the  end,  in  order 
that  the  hydrochloric-acid  gas  may  be  completely  absorbed.  Ab- 


I  205.]  ANALYSIS    OF   FRESH    WATER.  189 

solutely  tight  india-rubber  joints  are  necessary  in  order  to  assure 
success;  they  can  be  obtained  only  by  binding  them  with  wire. 
(F.  HESS.*) 

Now  close  the  tube  C  with  the  thumb,  shake  it  well,  and  trans- 
fer it  to  a  large  glass  cylinder  filled  with  water  at  15°  to  18°,  im- 
merse it,  and  finally  read  off  the  volume  as  usual  (§  15),  noting 
also  the  temperature  of  the  water  and  the  barometric  pressure. 
After  reducing  the  volume  found  to  0°  and  760  mm.,  allowing  for 
the  tension  of  aqueous  vapor  (§  198),  the  nitric  acid  (as  N2O5)  in 
the  water  is  found  by  multiplying  the  c.c.  of  dry  nitric  oxide  by 
2-413  and  expressing  the  result  in  milligrammes. 

If  the  water  contains  also  nitrous  acid,  this  will  be  included 
in  the  results  obtained;  the  correction  necessary  for  this  is  made 
by  subtracting  from  the  results  1-421  parts  for  every  1  part  of 
nitrous  acid  (as  N2O3)  present,  assuming  that  this  is  present  in 
sufficient  quantity  to  estimate. 

B.  For  approximately  determining  nitric  acid  in  waters,  MARX'S  f 
method,  with  certain  modifications,  is  usually  used.  This  method, 
like  the  older  one  of  BOUSSINGAULT,!  is  based  upon  the  decolori- 
zation  of  indigo  by  nitric  acid.  In  BOUSSINGAULT'S  method  the 
reaction  is  effected  in  hydrochloric-acid  solution  with  the  aid  of 
heat,  whereas  MARX  employs  the  hot  liquid  resulting  from  the 
addition  of  a  large  quantity  concentrated  sulphuric  acid  to  water. 
The  process  has  the  advantage  of  being  very  rapid.  It  has  further 
been  studied  by  H.  TROMMSDORFF,  §  F.  GOPPELSRODER,||  H. 
STRUVE,!  VAN  BEMMELEN,**  R.  WARRiNGTON,ft  KUBEL  and  TIE- 
MANN,;!;  t  SUTTON,§§  and  others. 

Before  describing  the  modifications  of  the  process  which  has 

•     *  Zeitschr.  f.  analyt.  Chem.,  xiii,  260. 
t  Ibid.,  vii,  412. 

J  Agronomic,  Chimie  agricole  et  Physiologic,  n,  244  (1862). 
§  Zeitschr.  f.  analyt.  Chem.,  vin,  364,  and  ix,  171. 
||  Ibid.,  ix,  3,  and  x,  266. 
f  Ibid.,  xi,  25. 
**  Ibid.,  xi,  136. 

ft  Chem.  News,  Feb.  2  and  9,  1877. 
1J  Anl.  zur  Uritersuchung  von  Wasser,  2.  Aufl.,  65. 
§§  Volumetric  Analysis. 


190  ANALYSIS    OF   WATER.  [§  205. 

given  the  best  results  in  my  laboratory,  some  important  observa- 
tions made  in  the  memoirs  cited  will  be  given  here.  These  are 
to  the  effect  that  the  results  obtainable  by  titration  with  indigo 
solution  are  serviceable  only  under  very  definite  conditions,  and 
can  lay  no  claim  to  perfect  accuracy. 

a.  The  quantity  of  the  indigo  which  is  oxidized  by  the  nitric 
acid  is  constant  only  when  the  conditions  under  which  the  reac- 
tion  takes   place    (dilution,   temperature,   quantity   of   sulphuric 
acid,  etc.)  are  identical. 

b.  Even  when  the  conditions  are  identical,  varying  quantities 
of  indigo  are  oxidized,  according  as  the  indigo  solution  is  added 
gradually  to  the  water  mixed  with  the  sulphuric  acid,  or  added  in 
proper  quantity  before  the  sulphuric  acid  is  added.     In  the  former 
case  far  less  indigo  is  oxidized  (VAN  BEMMELEN). 

c.  Like    conditions    must   be    observed   in    standardizing   the 
indigo  solution  against  nitric  acid,  particularly  under  such  whereby 
the  largest  quantity  of  indigo  is  oxidized. 

d.  As  the  reaction  products  resulting  from  the  action  of  nitric 
acid  upon  indigo  are  not  colorless,  but  yellow,  the  liquid  is  colored 
brownish  by  incipient  excess  of  indigo,  in  the  absence  of  chlorides, 
and  acquires  a  greenish  color  only  with  a  somewhat  large  excess; 
of  course  varying  shades  are  obtained  according  to  the  quantity 
of  nitric  acid  present,  i.e.,  according  to  the  quantity  of  the  yellow 
decomposition-product  formed.     The  quantity  of  sulphuric  acid 
and  the  presence  of  chlorides  also  have  an  influence  on  the  color 
of  the  solution  at  the  moment  the  indigo  begins  to  be  in  excess. 
The  end  of  the  reaction  is  hence  not  readily  recognized,  and  must 
be  learned  by  experience. 

e.  The  variation  in  the  results  is  further  increased  when  readily 
oxidizable    substances   are   present,   because   then    the   liberated 
nitric  acid  acts  on  these  as  well  as  on  the  indigo.     If  a  large  quantity 
of  organic  matter  is  present,  approximately  correct  results  will  be 
obtained  only  when  the  organic  matter  is  oxidized  first,  and  before 
the  nitric-acid  estimation.     If  only  a  small  quantity  is  present, 
however,  as  is  usually  the  case  in  spring-water,  the  error  caused  by 
it  is  so  slight  that  it  may  be  disregarded. 


§  205.]  ANALYSIS    OF   FRESH    WATER.  191 

/.  Nitrous  acid,  if  present  in  water,  also  oxidizes  indigo;  if 
present  in  considerable  quantity,  therefore,  a  correction  becomes 
necessary.  Accurate  experiments  showing  the  exact  relative 
action  of  nitric  and  nitrous  acids  on  indigo  are  wanting.  KUBEL. 
and  TIEMANN  (loc.  cit.,  p.  81)  deduct  0-473  parts  of  nitric  acid  for 
every  1  part  of  nitrous  acid. 

g.  Chlorides,  when  present  only  in  the  small  quantities  ubually 
found  in  spring-water,  have  no  appreciable  action  on  the  end 
reaction. 

EXECUTION  OF  THE  METHOD. 

Requisites. 

a.  A  solution  of  pure  potassium  nitrate  in  distilled  water,  1 
litre  to  contain  1-8718  grm.  Each  c.c.  will  then  contain  1  mgrm. 

NA- 

6.  A  solution  of  best  indigo-carmine  in  water.  Its  effective 
value  is  approximately  ascertained  with  the  potassium-nitrate 
solution  a  by  the  process  described  below;  it  is  then  diluted  so  that 
6  to  8  c.c.  will  be  the  equivalent  of  1  mgrm.  nitric  acid. 

c.  Chemically  pure,  concentrated  sulphuric  acid,  sp.  gr.  1  •  842, 
perfectly  free  from  sulphurous  and  arsenous  acids  and  nitrogen 
oxides. 

d.  Several  thin  flasks  of  about  200  c.c.  capacity. 

e.  A  small  cylinder  holding  50  c.c.,  and  graduated  in  c.c. 
/.  A  pinch-cock  burette,  graduated  in  0-1  c.c. 

g.  A  25-c.c.  pipette,  or  another  pinch-cock  burette. 
h.  A  5-c.c.  pipette  graduated  in  c.c.  or  0-5  c.c. 
i.  A  measuring  flask  holding  250  c.c. 

aa.  Preliminary  Test. 

Measure  off  25  c.c.  of  the  water  to  be  examined,  transfer  it  to 
one  of  the  flasks:  fill  the  small  cylinder  with  concentrated  sul- 
phuric acid,  and  the  burette  with  the  indigo  solution.  Pour  the 
sulphuric  acid  all  at  once  into  the  water,  agitate  for  a  moment,  and 
without  delay,  and  as  rapidly  as  possible,  run  in  the  indigo  solution 
until  the  liquid  just  acquires  a  permanent  greenish  tint.  If  not 


192  ANALYSIS    OF    WATER.  [§  205. 

more  than  20  c.c.  of  the  indigo  solution  have  been  required  for  this, 
the  water  may  be  titrated  directly;  otherwise  the  water  must  be 
diluted  suitably,  and  the  preliminary  test  applied  again. 

bb.  The  Titration. 

a.  Measure  off  25  c.c.  of  the  original  water  (or  that  properly 
diluted),  introduce  it  into  one  of  the  flasks,  add  as  much  indigo 
solution  to  it  as  had  been  used  in  the  preliminary  test,  measure 
off  a  volume  of  concentrated  sulphuric  acid  equal  to  that  of  the 
liquid  in  the  flask  and  add  it  all  at  once,  and  then  rapidly  run  in 
from  the  burette  sufficient  indigo  solution  until  the  liquid  just 
becomes  permanently  green. 

/?.  Repeat  the  test,  but  add  to  the  water  at  first  0  •  5  c.c.  less  indigo 
solution  than  the  total  quantity  used  in  a;  then  proceed  as  in  a. 
The  volume  of  indigo  solution  so  found  is  to  be  taken  as  correct, 
and  used  in  the  final  calculations. 

7-.  From  the  approximately  known  effective  value  of  the  indigo 
solution,  calculate  the  quantity  of  potassium-nitrate  solution 
corresponding  with  the  indigo  solution  used  in  /?,  multiply  the 
result  in  c.c.  by  10,  transfer  this  quantity  to  a  250-c.c.  measuring 
flask,  fill  with  distilled  water  up  to  the  mark,  and  then  titrate 
25  c.c.  of  fluid  with  indigo  solution  (as  in  /?).  If  the  quantity  of 
indigo  solution  does  not  quite  correspond  with  that  used  in  /?, 
another  potassium-nitrate  solution  must  be  made  up  in  the  250-c.c. 
flask,  either  more  concentrated  or  dilute,  to  more  nearly  approxi- 
mate the  water,  and  the  titration  repeated.  The  effective  value 
of  the  indigo  solution  so  found  is  used  in  the  final  calculations. 

d.  If  the  water  contains  a  rather  large  quantity  of  organic 
matter,  this  is  first  oxidized  by  potassium  permanganate  (p.  204). 
In  this  case  the  determination  of  the  organic  matter  and  the  nitric 
acid  may  be  conveniently  combined. 

4.  Determination  of  Nitrous  Acid. 

Nitrous  acid  is  never  found  in  good  potable  waters.  It,  how- 
ever, frequently  occurs  in  inferior  potable  waters  and  in  natural 
waters.  As  a  rule  the  quantity  present  is  very  minute,  but  a 


§  205.]  ANALYSIS    OF    FRESH    WATER.  193 

knowledge  of  the  quantity  is  of  great  value  in  forming  an  opinion 
•as  to  the  quality  of  the  water. 

Two  methods  are  in  use  for  determining  the  nitrous  acid  in 
water:  a  colorimetric,  based  on  the  formation  of  starch  iodide, 
^,nd  devised  by  H.  TROMMSDORFF,*  and  the  other  based  on  the 
oxidation  of  nitrous  to  nitric  acid  by  potassium  permanganate, 
and  first  described  by  JEAN  DE  SAINT-GILLES,!  and  later  critically 
tested  by  S.  FELDHAUS,  J  and  finally  improved  and  specially  adapted 
to  water  analysis  by  W.  KUBEL.  §  The  two  methods  complement 
each  other;  the  former  is  excellently  adapted  for  such  waters  as 
contain  but  very  small  quantities  of  nitrous  acid,  while  the  latter 
is  preferable  in  cases  where  the  water  contains  more  than  1  mgrm. 
per  100  c.c.  (TIEMANN-KUBEL,  loc.  cit.,  p.  79). 

a.  Starch-iodide  Method. 

This  method  is  based  upon  the  fact  that  a  water  perfectly 
free  from  nitrous  acid  affords  no  starch-iodide  reaction  on  treating 
it  with  pure,  dilute  sulphuric  acid  and  zinc-iodide-starch  solution,! 
and  setting  it  aside  in  a  dark  place, ^  whereas  if  the  water  contains 
nitrous  acid  it  acquires  a  blue  color  either  at  once  or  after  a  while, 
-the  intensity  depending  on  the  quantity  of  nitrous  acid  present. 

For  this  method  there  are  required  perfectly  pure  water,  free 
particularly  from  nitrous  acid,**  pure  dilute  sulphuric  acid,  zinc- 

*  Zeitschr.  /.  analyt.  Chem.,  vm,  358. 

f  Compt.  rend.,  1858,  XLVI,  624;   Journ.  f.  prakt.  Chem.,  LXXIII,  473. 

J  Zeitschr.  /.  analyt.  Chem.,  i,  426. 

§  Journ.  /.  prakt.  Chem.,  en,  229. 

||  To  prepare  the  solution  boil  5  grm.  starch,  20  grm.  zinc  chloride,  and 
100  grm.  distilled  water  for  several  hours  (replacing  the  water  as  it  evaporates) 
or  until  the  starch  envelopes  are  completely  dissolved,  then  add  2  grm.  dry- 
zinc  iodide,  dilute  to  measure  1  litre,  and  filter.  The  filtration  is  slow,  but 
a  clear  liquid  is  obtained  which,  after  several  months,  deposits  a  few  flocks, 
but  which,  preserved  in  a  dark  place  in  well-stoppered  bottles,  remains  color- 
less (RICHTER,  Zeitschr.  f.  analyt.  Chem.,  viu,  358). 

*"  By  the  action  of  direct  sunlight  a  water  to  which  sulphuric  acid  and  zinc- 
iodide-starch  solution  have  been  added,  but  which  is  free  from  nitrous  acid, 
is  colored  in  about  10  minutes,  but  in  diffused  daylight  only  after  several 
hours  or  days. 

**  If  a  water  free  from  nitrous  acid  is  not  at  hand,  such  may  be  prepared 
t>y  adding  a  few  drops  dilute  sulphuric  acid  to  a  pure  spring  water  and  dis- 


194  ANALYSIS    OF    WATEll.  [§   205. 

iodide-starch  solution,  a  solution  of  potassium  nitrite  1  c.c.  of  which 
should  represent  0-01  mgrm.  of  N203,*  and  four  test  cylinders 
of  equal  width,  and  which  will  hold  50  c.c.  at  a  mark  scratched 
15  to  16  cm.  from  the  bottom. 

a.  Preliminary  Test. 

Add  1  c.c.  of  dilute  sulphuric  acid  and  1  c.c.  of  zinc-iodide-starch 
solution  to  25  c.c.  of  the  water  to  be  examined.  If  a  blue  color 
develops  at  once,  or  after  a  few  minutes,  the  water  contains  too 
much  nitrous  acid,  and  requires  dilution.  In  this  case  introduce 
25, 10,  or  5  c.c.  of  the  water  into  the  test  cylinder,  fill  with  water  up 
to  the  mark,  and  repeat  the  test  with  sulphuric  acid  and  zinc-iodide- 
starch  solution.  If  no  coloration  is  observed  until  at  least  two 
minutes  have  elapsed — the  color  being  best  observed  by  looking 
down  through  the  column  of  liquid  placed  on  a  white  surface— 
the  water  is  adapted  for  further  examination. 

/?.  The  Actual  Test. 

Introduce  into  one  of  the  test  cylinders  50  c.c.  of  the  water 
either  as  on  hand,  or  diluted  as  under  a ;  into  a  second,  third,  and 
fourth  respectively  introduce  0-1,  0-2,  and  0-3  c.c.  of  the  potas- 
sium-nitrite solution,  and  fill  them  up  to  the  mark  with  pure  water. 
Now  add  to  each  of  the  four  cylinders  1  c.c.  of  dilute  sulphuric 
acid  followed  by  1  c.c.  of  zinc-iodide-starch  solution,  and  mix.  If 
the  reaction  in  the  first  cylinder  occurs  simultaneously  with  that 
of  one  of  the  other  cylinders,  and  if  it  proceeds  similarly,  the  two 
liquids  contain  like  quantities  of  nitrous  acid.  If  this  is  not  the 

tilling.  Collect  the  distillate  in  four  fractions  in  separate  receivers,  and  test 
each  with  zinc-iodide-starch  and  sulphuric  acid,  and  use  those  fractions  which 
are  found  to  be  pure. 

*This  is  prepared  by  dissolving  about  2-5  grm.  fused  potassium  nitrite 
in  100  c.c.  water,  diluting  10  c.c.  of  this  solution  to  1  litre,  testing  the  solu- 
tion with  a  solution  of  potassium  permanganate  (0-3162  :  1000)  as  on  p.  195, 
and  then  diluting  so  that  1  litre  will  contain  0-1  grm.  N2O3  (1  c.c.  hence 
should  equal  0-0001  grm.  N2O3).  10  c.c.  of  the  solution  diluted  with  pure 
water  to  100  c.c.  will  be  the  solution  required,  and  of  which  1  c.c.  will  con- 
tain 0-00001  grm.  N2O3.  As  the  potassium-nitrite  solution  does  not  remain 
unaltered  on  keeping,  it  must  be  tested  each  time  before  using,  and,  if  neces- 
sary, prepared  freshly. 


§  205.]  ANALYSIS   OF    FRESH    WATER.  195 

case  repeat  the  tests  with  liquids  of  known  nitrous-acid  content 
until  like  results  are  obtained. 

The  tints  are  at  first  compared  by  looking  down  through  the 
column  of  liquid  in  the  cylinder  placed  on  a  sheet  01  wnite  paper; 
later  on,  when  the  colors  become  more  intense,  the  two  cylinders 
are  held  side  by  side  in  an  inclined  position,  and  the  observations 
made  through  sections  of  similar  thickness  and  against  the  white 
paper  background.  If  so  little  nitrous  acid  is  present  that  the 
color  first  begins  to  develop  in  10  to  20  minutes,  it  is  unnecessary 
to  note  the  increase  in  intensity  of  color,  but  merely  to  observe 
the  moment  when  the  color  appears  in  both  cylinders. 

In  calculating  it  suffices  to  remember  that  the  nitrous  acid  is 
present  in  like  quantity  in  the  two  cylinders  in  which  the  reactions 
were  seen  to  be  alike. 

b.  Permanganate  Method. 

In  the  case  of  dilute  fluids,  and  usually  containing  organic 
matter,  such  as  natural  waters,  the  oxidation,  the  method 
based  on  the  oxidation  of  nitrous  acid  to  nitric  acid  by  potas- 
sium permanganate  cannot  be  applied  as  is  usually  done 
(§  131,  5),  i.e.,  the  permanganate  solution  cannot  be  added 
directly  to  the  acidulated  water  until  the  pale-red  color  persists, 
as  the  time  required  for  the  appearance  of  the  end-reaction  is  so 
long  that  the  permanganate  would  act  on  the  organic  matter, 
and  hence  render  the  nitrous-acid  determination  inaccurate. 
In  the  following  modification  of  KUBEL/S  process  the  object  is 
attained  much  more  rapidly,  so  that  the  influence  of  such  small 
quantities  of  organic  matter  as  is  usual  in  spring  water  does  not 
appreciably  affect  the  accuracy  of  the  results. 

There  are  required  for  the  process  a  solution  of  pure  ferrous- 
ammonium  sulphate  containing  3-92  grm.  of  the  pure,  crystallized, 
dry  salt  in  the  litre  (the  salt  is  dissolved  in  a  litre  flask,  by  the  aid 
of  a  little  dilute  sulphuric  acid,  using  water  which  has  been  freshly 
boiled  and  cooled);  also  a  corresponding  solution  of  potassium 
permanganate,  i.e.,  one  of  which  10  c.c.  suffice  to  oxidize  10  c.c.  of 
the  iron  solution,  leaving  it  faintly  red. 


196  ANALYSIS    OF    WATER.  [§   205. 

In  performing  the  analysis  an  excess  of  potassium  permanganate 
solution  (5,  10,  or  20  c.c.,  according  to  circumstances)  is  added  to 
100  c.c.  of  the  water  to  be  tested;  6  to  8  c.c.  of  pure  dilute  sulphuric 
acid  (1:5)  are  now  added,  followed  immediately  by  sufficient  of  the 
ferrous-ammonium-sulphate  solution  to  effect  decolorization ;  then 
add  again  permanganate  solution  until  the  liquid  is  pale  red,  even 
if  only  transiently. 

In  making  the  calculation,  deduct  the  entire  number  of  c.c.  of 
Iron  solution  taken  from  the  total  c.c.  of  permanganate  solution 
used;  the  remainder  is  the  permanganate  solution  used  up  in 
oxidizing  the  nitrous  acid  present  in  the  water.  Each  c.c.  =0  1902 
mgrm.  N203. 

By  this  method  of  operating,  any  organic  matter  that  may  be 
present  will  not  appreciably  affect  the  results,  as  may  be  seen  by  refer- 
ence to  the  experiments  made  by  TIEMANN-KUBEL  (loc.  cit.,  p.  79). 

5.  Determination  of  the  Silicic  Acid,  Calcium,  and  Magnesium. 
Evaporate  1000  grm.  or  c.c.  to  dryness — after  addition  of 
some  hydrochloric  acid — preferably  in  a  platinum  dish,  treat  the 
residue  with  hydrochloric  acid  and  water,  filter  off  the  separated 
silicic  acid,  and  treat  the  latter  as  directed  §  140,  II,  a.  Determine 
calcium  and  magnesium  in  the  filtrate  as  directed  §  154,  6,  a  (36). 

6.  Determination  of  the  total  Residue  and  of  the  Sodium. 

a.  Evaporate  1000  grm.  or  c.c.  of  the  water,  with  proper  care, 
to  dryness  in  a  weighed  platinum  dish,  first  over  a  lamp,  finally 
on  the  water-bath.  Expose  the  residue,  in  the  air-bath,  to  a 
temperature  of  about  180°,  until  no  further  diminution  of  weight 
takes  place.  This  gives  the  total  amount  of  the  salts  (together  with 
the  organic  matter). 

6.  Treat  the  residue  with  water,  and  add,  cautiously,  pure 
dilute  sulphuric  acid  in  moderate  excess;  cover  the  vessel  during 
this  operation  with  a  dish,  to  avoid  loss  from  spirting;  then  place 
on  the  water-bath,  without  removing  the  cover.  After  ten  minutes, 
rinse  the  cover  by  means  of  a  washing  bottle,  evaporate  the  con- 
tents of  the  dish  to  dryness,  expel  the  free  sulphuric  acid,  ignite 
the  residue,  in  the  last  stage  with  addition  of  some  ammonium  car- 


§  205.]  ANALYSIS  OF  FRESH  WATER.  197 

bonate  (§97,  1),  and  weigh.  The  residue  consists  of  sodium  sul- 
phate, calcium  sulphate,  magnesium  sulphate,  and  some  separated 
silica.  It  must  not  redden  moist  litmus  paper.  The  quantity  of 
the  sodium  sulphate  in  the  residue  is  now  found  by  subtracting 
from  the  weight  of  the  latter  the  known  weight  of  the  silica  and 
the  weight  of  the  calcium  and  magnesium  sulphates  calculated 
from  the  quantities  of  these  earths  found  in  5. 

7.  Direct  Determination  of  the  Sodium. 

If  it  is  desired  to  estimate  the  sodium  directly,  the  filtrate  from 
the  sulphuric-acid  determination  ( §  205,  2)  may  be  employed, 
proceeding  as  in  §  209. 

The  sodium  may  also  be  determined  in  the  direct  way,  with 
comparative  expedition,  by  the  following  method: 

Evaporate  1250  grm.  or  c.c.  of  the  water,  in  a  dish,  to  about  £ 
and  then  add  2  to  3  c.c.  of  thin  pure  milk-of-lime,  so  as  to  impart 
a  strongly  alkaline  reaction  to  the  fluid ;  heat  for  some  time  longer, 
then  wash  the  contents  of  the  dish  into  a  quarter-litre  flask.  (It  is 
not  necessary  to  rinse  every  particle  of  the  precipitate  into  the 
flask;  but  the  whole  of  the  fluid  must  be  transferred  to  it,  and  the 
particles  of  the  precipitate  adhering  to  the  dish  well  washed,  and 
the  washings  also  added  to  the  flask.)  Allow  the  contents  to  cool, 
dilute  to  the  mark,  shake,  allow  to  deposit,  filter  through  a  dry  filter, 
measure  off  200  c.c.  of  the  filtrate,  corresponding  to  1000  grm.  of 
the  water,  transfer  to  a  quarter-litre  flask,  mix  with  ammonium  car- 
bonate and  some  ammonium  oxalate,  add  water  up  to  the  mark, 
shake,  allow  to  deposit,  filter  through  a  dry  filter,  measure  off  200 
c.c.,  corresponding  to  800  grm.  of  the  water,  add  some  ammonium 
chloride,*  evaporate,  ignite,  and  weigh  the  residual  sodium  chloride 
as  directed  §  98,  2.f 

Or  the  following  method  may  be  employed: 

*  To  convert  the  still  remaining  sodium  sulphate,  on  ignition,  into  sodium 
chloride. 

f  This  process,  which  entirely  dispenses  with  washing,  presents  one  source 
of  error — viz.,  the  space  occupied  by  the  precipitates  is  not  taken  into  account. 
The  error  resulting  from  this  is,  however,  so  trifling  that  it  may  safely  be 
disregarded,  as  the  excess  of  weight  amounts  to  5^5  at  the  most. 


198  ANALYSIS    OF    WATER.  [§  205. 

Evaporate  the  filtrate  from  the  barium  sulphate  obtained  in  2 
to  dryness  in  a  platinum  dish  (or  if  nitrates  are  present  in  porcelain) 
to  remove  free  hydrochloric  acid  and  separate  silica.  Digest  the 
residue  with  a  few  c.c.  water,  and  precipitate  magnesium  without 
previous  nitration  by  addition  of  solution  of  barium  hydroxide, 
avoiding  a  large  excess.  Enough  has  been  added  if  a  pellicle  of 
barium  carbonate  forms  upon  the  surface  of  the  liquid  on  exposure 
a  short  time  to  the  air.  Filter  and  wash  the  usually  slight  precipi- 
tate. Heat  the  filtrate,  and  add  ammonium  carbonate  to  precipitate 
the  barium  introduced  and  the  calcium  originally  present,  filter  from 
the  precipitated  carbonates,  evaporate  the  filtrate  to  dryness,  and 
remove  the  ammonium  chloride  completely  by  heating.  Dissolve 
the  sodium  chloride  in  the  residue  with  4  or  5  c.c.  water,  warm,  and 
add  a  few  drops  of  ammonium  carbonate  and  ammonia  to  separate 
possible  remaining  traces  of  barium  and  calcium,  filter  again  into  a 
weighed  platinum  dish,  evaporate  to  dryness,  heat  nearly  to  fusion, 
and  weigh  the  sodium  chloride.  The  sodium  chloride  obtained  by 
either  process  will  contain  the  potassium  (as  chloride)  if  any  is 
present  in  the  water.  If  enough  alkali  chloride  is  obtained  it  may, 
after  weighing,  be  examined  for  potassium  according  to  §  152,  I,. a. 

8.  Calculate  the  numbers  found  in  1-7  to  1000  parts  of  water, 
and  determine  from  the  data  obtained  the  amount  of  carbonic  acid 
in  combination,  as  follows: 

Add  together  the  quantities  of  SO3  corresponding  to  the  basic 
oxides  found,  and  subtract  from  the  sum,  first,  the  amount  of  sul- 
phuric acid  as  SO3  precipitated  from  the  water  by  barium  chloride 
(2),  secondly,  the  amount  equivalent  to  the  nitric  acid  found,  and 
thirdly,  the  amount  equivalent  to  the  chlorine  found;  the  remain- 
der is  equivalent  to  the  carbonic  acid  combined  with  the  bases  in 
the  form  of  normal  carbonates.  80  •  07  parts  of  SO3  remaining  after 
subtracting  the  quantities  just  stated,  correspond  accordingly  to  44 
parts  of  CO2. 

If,  by  way  of  control,  you  wish  to  determine  the  combined  car- 
bonic acid  in  the  direct  way,  evaporate  1000  grm.  or  c.c.  of  the 
water  in  a  flask  to  a  small  bulk;  add  tincture  of  cochineal,  then 
standard  nitric  acid,  and  proceed  as  directed  in  Vol.  I,  p.  483,  bb. 


•§  205.]  ANALYSIS    OF    FRESH    WATER.  199 

9.  Control 

If  the  quantities  of  the  Na2O,  CaO,  MgO,  SO3,  N2O5,  SiO2,  CO2, 
and  Cl  are  added  together,  and  an  amount  of  oxygen  equivalent  to 
the  chlorine  (since  this  latter  is  combined  with  metal  and  not  with 
oxide)  is  subtracted  from  the  sum,  the  remainder  must  nearly 
correspond  to  the  total  amount  of  the  salts  found  in  6,  a.  Perfect 
correspondence  cannot  be  expected,  since,  1,  upon  the  evaporation 
of  the  water  magnesium  chloride  is  partially  decomposed  and  con- 
verted into  a.  basic  salt;  2,  the  silicic  acid  expels  some  carbonic 
acid;  and  3,  it  being  difficult  to  free  magnesium  carbonate  from 
water  without  incurring  loss  of  carbonic  acid,  the  residue  remain- 
ing upon  the  evaporation  of  the  water  contains  the  magnesium 
carbonate  as  a  basic  salt,  whereas,  in  our  calculation,  we  have 
assumed  the  quantity  of  carbonic  acid  corresponding  to  the  normal 
salt.  Nor  do  we  take  into  account  the  organic  matter  present 
(and  the  actual  quantity  of  which  can  scarcely  be  determined), 
as  well  as  the  slight  traces  of  nitrites,  and  the  influence  of  any 
ammonium  salts  present  on  the  weight  of  the  total  residue. 

10.  Determination  of  the  free  Carbonic  Acid. 

In  the  case  of  well-water  this  may  be  conveniently  executed 
by  the  process  described  §  139,  7-  (p.  484).  We  here  obtain  the 
carbonic  acid  which  is  contained  in  the  water  over  and  above  the 
quantity  corresponding  to  the  normal  carbonates,  or  in  other  words, 
the  carbonic  acid  which  is  free  and  which  is  combined  with  the 
carbonates  to  bicarbonates. 

11.  Determination  of  the  Organic  Matter. 

Many  fresh  waters  contain  so  much  organic  matter  as  to  be 
quite  yellow,  others  contain  traces,  and  many  again  may  be  said  to 
be  free  from  such  substances.  The  exact  estimation  of  organic 
matter  is  by  no  means  an  easy  task,  and  the  method  usually  adopted 
— viz.,  ignition  of  the  residue  of  the  water  dried  at  180°,  treatment 
with  ammonium  carbonate,  gentle  ignition  again,  and  calculation 
of  the  organic  matter  from  the  loss  of  weight — yields  merely  an 
approximate  result,  since  we  can  never  be  sure  as  to  the  condition 


200  ANALYSIS   OF   WATER.  [§  205* 

of  the  magnesium  carbonate  in  the  residue  dried  at  180°  and  in 
the  same  after  ignition,  and  since  the  silicic  acid  expels  some  car* 
bonic  acid,  which  is  not  taken  up  again  on  treatment  with  am- 
monium carbonate,  etc.  As  it  is  important,  however,  to  know 
the  quantity  of  organic  matter  present  in  a  water  in  order  to 
judge  of  the  quality  of  the  latter,  many  chemists  have  sought  to 
solve  the  problem,  without  complete  success,  however,  so  far. 
FRANKLAND  and  ARMSTRONG*  boil  a  measured  quantity  (1  litre) 
of  water  with  30  c.c.  of  a  saturated  aqueous  solution  of  sulphurous 
acid,  0-2  grm.  sodium  sulphite,  and  a  few  drops  of  a  solution  of 
ferrous  or  ferric  chloride  for  two  to  three  minutes.  (If  the  water 
contains  much  organic  matter,  the  flask  or  retort  is  connected 
with  a  reflux  condenser.)  The  liquid  is  then  evaporated  to  dryness. 
in  a  glass  dish  while  protecting  it  from  all  dust.  Mix  the  residue 
(which  will  now  be  free  from  carbonic,  nitric,  and  nitrous  acids) 
with  perfectly  pure  lead  chromate,  introduce  the  mixture  into  a, 
combustion  tube  which  is  then  charged  with  cupric  oxide  and 
copper  turnings,  exhaust  the  tube  by  means  of  a  SPRENGEL  mercury 
air-pump,  and  effect  the  combustion  in  the  usual  way,  at  first 
very  slowly.  By  the  aid  of  the  pump  collect  the  combustion 
products  in  a  glass  tube  filled  with  and  standing  in  mercury,  and 
determine  in  the  mixture  the  carbonic  acid,  nitric  oxide,  and 
nitrogen  by  the  usual  methods;  from  the  results  then  calculate 
the  carbon  and  nitrogen  in  the  organic  matter. 

M.  DITTMAR  and  H.  ROBINSON!  have  modified  the  FRANKLAND- 
ARMSTRONG  method,  estimating  the  carbon  and  nitrogen  of  the 
organic  matter  in  two  separate  portions  of  the  water  to  one  of 
which  is  added  sulphurous  acid,  and  to  the  other  sulphurous  acid 
with  a  little  ferrous  or  ferric  chloride.  Both  are  evaporated  first 
partially  in  a  flask  held  in  an  inclined  position,  and  finally  to  dry- 
ness  in  a  dish,  at  times  a  little  potassium  sulphate  being  added 
in  order  to  increase  the  bulk  of  the  residue.  The  carbon  and  nitro- 
gen are  then  determined  in  the  residues  by  combustion.  For 
estimating  the  carbon  there  is  used  a  combustion  tube  charged 

*Journ.  Chem.  Soc.,  vi,  77;  Zeitschr.  f.  analyt.  Chem.,  viu,  488. 
t  Chem.  News,  xx,  July,  1877. 


§  205.]  ANALYSIS    OF    FRESH    WATER.  201 

with  a  spiral  of  silver  foil  and  then  granulated  cupric  oxide.  The 
water  and  sulphurous  acid  are  absorbed  by  an  apparatus  consist- 
ing of  two  tubes,  one  containing  concentrated  sulphuric  acid  and 
a  little  chromic  acid,  the  other  being  filled  with  calcium  chloride. 
The  silver  spiral  and  cupric  oxide  are  first  heated  in  a  current  of 
air  until  the  escaping  air  no  longer  renders  baryta  water  turbid; 
then  the  boat  containing  the  residue  from  the  evaporated  water 
is  inserted  and  the  combustion  effected  in  a  current  of  oxygen. 
The  carbonic  acid  may  be  absorbed  by  a  soda-lime  tube  (Fig.  48). 
The  nitrogen  is  determined  according  to  VARRENTRAPP-WILL'S 
method  (§  186).  The  ammonia  is  determined  colorimetrically 
by  means  of  NESSLER'S  reagent  (p.  208). 

F.  SCHULZE,*  F.  BELLAMY,!  and  others  had  previously  rec- 
ommended the  determination  of  the  carbon  in  the  evaporation 
residues.  Various  objections  have  been  made  against  these 
methods,^  and  more  particularly  that  during  the  evaporation  some 
organic  matter  may  be  lost  through  volatilization  and  decomposi- 
tion. The  data  afforded  by  these  determinations  may  nevertheless 
be  useful  in  forming  an  opinion  on  waters,  particularly  if  the  latter 
be  rather  rich  in  organic  matter. 

Since  these  methods  are  rather  inconvenient  while  they  do  not 
completely  attain  the  object  sought,  it  is  usually  considered  suf- 
ficient to  determine  how  much  permanganate  is  reduced  by  the 
organic  matter  held  in  solution  in  the  water,  i.e.,  to  determine  the 
quantity  of  oxygen  required  to  oxidize  this  matter. 

Comparative  experiments  of  this  kind  are  of  value,  although 
they  do  not  express  numerically  the  quantity  of  organic  matter 
present,  because  different  substances  reduce  differing  quantities 
of  permanganate;  still  less  do  they  permit  any  conclusion  to  be 
drawn  regarding  the  harmlessness  or  otherwise  of  the  organic 
matter  present;  further,  there  can  be  no  doubt  that  putrefying 

*  Landwirthschaftliche  Versuchsstationen,  x,  516;  Zeitschr.  f.  analyt.  Chem., 
viii,  494. 

f  Zeitschr.  f.  analyt.  Chem.,  vm,  495. 

J  Comp.  J.  A.  WANKLYN,  E.  T.  CHAPMAN,  and  M.  H.  SMITH  (Jmirn.  Chem. 
Soc.,  [II],  vi,  152;  and  Zeitschr.  f.  analyt.  Chem.,  vm,  492;  also  KUBEL-TIE- 
MANN  (loc.  cit.,  p.  98). 


202  ANALYSIS    OF   WATER.  [§  205. 

nitrogenous  matter  has  a  more  pernicious  influence  on  health  than 
have  humus  substances. 

In  order  to  differentiate  between  such  organic  substances  as 
are  more  easily  or  more  difficultly  oxidized,  FLECK*  employs  an 
alkaline  silver  solution  instead  of  potassium  permanganate.  Neither 
in  this  case  does  the  quantity  of  reduced  silver  afford  any  conclu- 
sion regarding  the  quantity  of  organic  matter  f  present,  but  like 
potassium  permanganate  it  affords  comparative  values  which 
may  serve  to  characterize  the  water.  The  same,  but  no  more, 
may  be  said  of  the  method  proposed  by  WANKLYN,  CHAPMAN 
and  SMITH,!  in  which,  after  the  ammonia  present  as  such  is  re- 
moved by  boiling,  the  ammonia  formed  by  further  boiling  with 
potassium  permanganate  and  potassium  hydroxide  affords  an 
indication  of  the  quantity  of  certain  (albuminoid)  organic  matter 
present.  A  quantitative  determination  of  the  nitrogen  in  this  is  not 
obtained  in  this  way,  because  by  the  treatment  described  the  nitrogen 
of  only  certain  nitrogenous  substances  is  completely  converted  into 
ammonia,  while  in  other  cases  more  or  less  of  the  nitrogen  is  con- 
verted into  other  nitrogenous  decomposition  products. 

Which  of  these  methods  will  be  of  most  service  in  examining 
water  as  to  its  fitness  for  drinking  purposes  must  still  be  consid- 
ered an  open  question;  it  is  most  advisable  hence  to  describe  these 
methods  in  detail. 

A.  METHODS  BASED  ON  THE  REDUCTION  OF  POTASSIUM 
PERMANGANATE  . 

Potassium  permanganate  was  used  almost  thirty  years  ago  by 
FORCHHAMMER§  for  testing  water  for  organic  matter;  later  it  was 
employed  by  EM.  MONNIER.||  Both  chemists  added  the  per- 
manganate to  the  heated  water  (the  latter  acidulating  the  liquid, 
the  former  not)  until  permanent  redness.  The  method  employed 

*  Journ.  /.  prakt.  Chem.,  N.  F.,  iv,  364. 

f  1  grin,  grape  sugar  precipitates  0  •  9  grm.  silver;  1  grm.  uric  acid,  1  •  285, 
and  1  grm.  gallic  acid,  3-812  grm.  silver. 
J  Journ.  Chem.  Soc.,  N.  S.,  v,  591. 

§  Institut,  1849,  383;   Jahresber.,  Y.  LIEBIQ  u.  KOPP,  1849,  603. 
||  Compt.  rend.,  L,  1084;  Dingier* 's  Polyt.  Journ.,  CLVII,  132. 


§  205.]  ANALYSIS  OF  FRESH  WATER.  203 

at  present  is  different;  the  permanganate  is  first  added  in  excess, 
then  sulphuric  acid  is  adde'd,  then  standard  oxalic  acid  to  decolori- 
zation,  and  finally  again  permanganate  to  incipient  reddening. 
H.  TROMMSDORFF,*  who  improved  SCHULZE'S  earlier  method, 
allows  the  permanganate  to  act  first  in  alkaline  solution,  then  in 
acid  solution,  whereas  KUBEL  f  effects  oxidation  only  in  acid  solu- 
tion. As  the  action  is  more  energetic  in  alkaline  than  in  acid 
solution,  slightly  more  permanganate  is  required  in  the  SCHULZE- 
TROMMSDORF  method,  under  similar  conditions,  than  in  the  KUBEL 
method,  but  the  differences  are,  as  a  rule,  small  (KUBEL-TIEMANN, 
loc.  cit.,  p.  109). 

The  following  is  the  description  of  the  SCHULZE-TROMMSDORFF 
method,  which  is  to  be  preferred  on  the  grounds  above  stated: 

a.  REQUISITES. 

a.  Distilled  Water,  which  should  have  no  (or  scarcely  any) 
reducing  action  on  permanganate.     It  may  be  obtained  by  adding 
some  crystallized  permanganate  and  pure  sodium  hydroxide  to  the 
water,  distilling,  and  rejecting  the  first  quarter  of  the  distillate; 
the  remainder  collected  may  be  used.     No  organic  matter  (luting, 
caoutchouc,  etc.)  should  be  used  at  the  joints  of  the  apparatus. 
TROMMSDORFF  states  that  water  is  serviceable  when  100  c.c.  will 
decolorize  not  more  than  1  c.c.  of  the  permanganate  solution,  e. 

b.  Solution  Sodium  Hydroxide.    This  is  prepared  by  dissolv- 
ing 1  part  of  pure  caustic  soda  prepared  from  sodium,  and  freshly 
fused  in  a  silver  crucible,  in  2  parts  of  distilled  water,  a. 

c.  Dilute  Sulphuric  Acid.    Mix  3  volumes  of  distilled  water 
with  1  volume  pure  concentrated  sulphuric  acid. 

d.  Centinormal  Oxalic-acid  Solution.     Purify  oxalic   acid  by 
rapidly  cooling  a  hot  concentrated  solution  of  the  acid,  and  of 
the  thin  needles  so  obtained  and  dried  at  the  ordinary  tempera- 
ture on  filter  paper  dissolve  0-63024  grm.  in  sufficient  distilled 
water  to  measure  1  litre;  or  dilute  10  c.c.  of  normal  oxalic-acid  solu- 

*  Zeitschr.  /.  analyt.  Chem.,  vin,  344. 

f  Ard.  zur  Untersuchung  von  Wasser,  von  KUBEL  und  TIEMANN,  2.  Aufl., 
p.  104. 


204  ANALYSIS    OF    WATER.  [§   205. 

tion  to  measure  one  litre.  The  0  •  63024  grm.  oxalic  acid  is  capable 
of  reducing  0-31622  grm.  potassium  permanganate.  The  oxalic- 
acid  solution  should  be  preserved  in  glass-stoppered  bottles  in  a 
dark  place. 

e.  Solution  Potassium  Permanganate.  Dissolve  about  0-32 
grm.  crystallized  potassium  permanganate  in  1  litre  distilled  water. 
To  standardize  it,  warm  20  c.c.  of  the  oxalic-acid  solution  d,  after 
the  addition  of  2  c.c.  of  pure  dilute  sulphuric  acid,  to  60°,  and 
then  run  in  the  permanganate  solution  until  a  pale-reddish  per- 
manent coloration  persists  (Vol.  I,  p.  316,  cc);  according  to  the  re- 
sults so  obtained,  dilute  the  solution  so  that  20  c.c.  will  exactly 
decompose  20  c.c.  of  the  oxalic-acid  solution.  1000  c.c.  of  the 
diluted  solution  will  then  contain  exactly  0-31622  grm.  perman- 
ganate. The  solution  should  be  preserved  in  glass-stoppered 
bottles  in  a  dark  place.  For  measuring  it  use  either  a  GAY-LUSSAC 
burette,  or  a  burette  provided  with  a  glass  cock. 

^.   THE    ANALYSIS. 

Introduce  100  c.c.  of  the  water  to  be  examined  in  a  flask  of 
about  300  c.c.  capacity,  add  0-5  c.c.  sodium-hydroxide  solution 
and  10  c.c.  of  the  permanganate  solution,  boil  for  ten  minutes, 
allow  to  cool  to  50°  to  60°,  and  add  5  c.c.  of  the  dilute  sulphuric 
acid  and  10  c.c.  of  the  centinormal  oxalic-acid  solution.  As  soon 
as  the  liquid  has  become  perfectly  colorless  cautiously  add  drop 
by  drop  permanganate  solution,  while  constantly  agitating,  until 
the  liquid  acquires  a  faint  permanent  redness.  The  permanganate 
solution  required  to  effect  this  is  the  quantity  required  for  the 
decomposition  of  the  organic  matter  in  the  100  c.c.  of  water.* 

*  This  result  is  accurate,  however,  only  when  the  water  contains  no  nitrous 
acid,  which  also  exerts  a  reducing  action  on  the  permanganate.  If  such  is 
present,  1  •  6626  parts  of  solid  potassium  permanganate  must  be  deducted  for 
every  1  part  of  N2O3  found,  e.g.,  4  eq.  of  KMnO4  for  every  5  eq.  of  N2O5;  or 

1  •  344  parts  of  permanganate  must  be  deducted  for  every  part  of  HNO2,  e.g., 

2  eq.  of   KMnO4  for  every  5  eq.  of  HNO2.     If  the  water  contains  decided 
traces  of  ammonia,  this  too  occasions  an  error.    In  this  case  boil  off  one-third 
of  the  water,  remove  the  ammonia,  then  make  up  the  volume  again  with  dis- 
tilled water,  and  then  proceed  to  add  permanganate.    Of  course,  small  quan- 
tities of  volatile  organic  matter  may  be  lost  in  this  process. 


§  205.]  ANALYSIS   OF   FRESH   WATER.  205 

The  results  so  obtained  are  expressed  in  terms  of  pure  per- 
manganate, or  of  the  oxygen  contained  in  it  and  used  up  in  oxi- 
dizing the  organic  matter  in  1000  c.c.  of  water.  1  c.c.  of  the 
above-named  solution  contains  0-00031622  grm.  permanganate, 
or  0-00008  grm.  of  available  oxygen. 

If  100  c.c.  of  water  require  more  than  4  c.c.  permanganate 
solution  for  the  oxidation  of  organic  matter,  a  second  experiment 
must  be  made  using  more  permanganate  solution  and  a  corre- 
spondingly larger  quantity  of  sodium-hydroxide  solution,  as  the 
undecomposed  permanganate  remaining  after  boiling  must  be  at 
least  twice  as  great  as  the  quantity  decomposed.  Good  spring- 
waters  never  require  a  larger  addition  than  10  c.c.  of  permanganate 
solution,  as  100  c.c.  of  such  a  water  never  decolorize  more  than 
1  to  2  c.c.  of  the  solution. 

B.  METHOD  BASED  ON  THE  REDUCTION  OF  SILVER. 

H.  FLECK,*  who  first  proposed  using  an  alkaline  solution  of 
silver  nitrate  for  the  comparative  estimation  of  organic  matter  in 
spring- waters,  etc.,  claims  this  method  to  be  preferable  to  the  per- 
manganate method,  because  the  latter  reduces  all  organic  matter 
alike,  whereas  the  alkaline  silver  solution  reduces  only  those  or- 
ganic substances  which  may  be  expected  to  have  an  injurious  effect. 
For  instance,  it  is  not  reduced  by  the  fatty  acids  and  their  salts, 
or  the  salts  of  the  lactic  and  succinic-acid  series,  whereas  it  is  re- 
duced by  biliary  pigments,  and  generally  by  animal  and  vegetable 
coloring  matters,  taurin,  mucus,  uric  acid,  tannin,  gallic  acid,  dis- 
solved proteids,  grape  sugar,  and  particularly  by  all  volatile  de- 
composition products.  It  will  be  seen  that  among  the  substances 
mentioned  many  are  harmful,  while  others  again  are  quite  in- 
nocuous. 

a.   REQUISITES. 

a.  Alkaline  Silver  Solution.  Dissolve  17  grm.  silver  nitrate 
in  about  50  c.c.  water  and  pour  the  solution  into  a  litre  flask  con- 
taining an  aqueous  solution  of  48  grm.  sodium  hydroxide  and  50 
gnu.  crystallized  sodium  thiosulphate.  Shake,  fill  to  the  mark, 

*  Jowrn.  /.  prakt.  Chem.,  N.  F.,  iv,  364. 


206  ANALYSIS    OF   WATER.  [§  205. 

shake  again,  pour  the  mixture  into  a  larger  flask,  and  boil  for  15 
minutes  continuously.  A  little  silver  is  thus  precipitated,  caused 
by  reduction  due  to  organic  matter  present.  After  twenty-four 
hours  decant  from  the  sediment  and  preserve  in  the  dark  in  dark- 
colored  bottles.  In  using  it,  a  GAY-LUSSAC  or  GEISSLER  burette 
is  employed,  or  one  with  a  glass  cock. 

b.  Potassium-iodide  Solution.     Dissolve  8-298  grm.  (^g-  eq.)  of 
chemically  pure  potassium  iodide  (dried  at  180°)  in  water  to  make 
1  litre.    The  solution  thus  made  will  precipitate  exactly  5-396 
grm.  (sV  eq.)  of  silver  from  a  solution  of  silver  nitrate.* 

c.  A  small  quantity  of  freshly  prepared  mixture  of  equal  vol- 
umes of  potassium-dichromate  solutions,  pure  hydrochloric  acid, 
and  starch  paste,  all  of  ordinary  strength. 

/?.    THE    ANALYSIS. 

In  employing  the  silver  solution  three  operations  are  required 
to  ascertain  how  much  silver  is  precipitated  from  the  alkaline 
silver  solution  by  the  organic  matter  present  in  1  litre  of  water: 
a,  determination  of  the  silver  in  the  silver  solution;  b,  treatment 
of  the  water  with  a  known  volume  of  silver  solution;  and  c, 
determination  of  the  silver  remaining  in  solution  after  b  (this  will 
give  hence  the  precipitated  silver  also). 

a.  Introduce  10  c.c.  of  the  silver  solution  into  a  beaker,  add 
100  c.c.  of  distilled  water,  afid  then  run  in  from  a  burette  the 
potassium-iodide  solution  until  a  trace  of  potassium  iodide  is  in 
excess.  This  point  is  found  by  testing — as  soon  as  the  silver  pre- 
cipitation begins  to  decrease — a  drop  of  the  fluid  now  and  then 
on  a  porcelain  dish,  with  a  drop  of  the  chromic-starch  mixture, 
the  excess  of  potassium  iodide  being  indicated  by  the  develop- 
ment of  a  blue  color.  The  slightest  excess  may  be  thus  recog- 
nized, as  silver  iodide  is  decomposed  only  after  very  long  contact 
of  the  two  drops.  If  too  much  potassium  iodide  has  been  added, 
add  a  little  more  silver  solution  and  approach  the  end  reaction 
more  cautiously. 

6.  Introduce  100  c.c.  of  the  water  to  be  examined  into  a  beaker, 

*  Fleck  determined  the  potassium  iodide  in  solution  by  precipitating  the 
iodine  as  silver  iodide  according  to  §  145,  I,  a,  a. 


§  205.]  ANALYSIS    OF    FRESH    WATER.  207 

add  10  c.c.  of  the  silver  solution,*  and  heat  to  boiling,  when  a 
white  precipitate,  consisting  of  calcium  and  magnesium  salts, 
usually  forms;  the  precipitate  gradually  becomes  gray  or  black  if 
organic  substances  are  present.  The  boiling  should  be  continued 
for  about  ten  minutes,  until  the  precipitate  settles  rapidly  on  re- 
moving the  heat.  The  water  lost  by  evaporation  is  then  replaced 
by  distilled  water  and  the  whole  allowed  to  cool. 

c.  In  the  cold  solution  determine  the  dissolved  silver  as  in  a, 
and  without  removing  the  precipitate.  The  difference  in  c.c. 
between  the  potassium-iodide  solution  used  in  a  and  c  corresponds 
to  the  precipitated  silver;  every  c.c.  represents  0-005396  grm.  of 
silver,  and  by  multiplying  the  silver  found  by  10  gives  the  silver 
reduced  by  1  litre  of  water. 

C.  METHOD  BASED  ON  THE  CONVERSION  OF  ALBUMINOID 
NITROGEN  INTO  AMMONIA. 

This  method,  which  was  introduced  by  WANKLYN,  CHAPMAN, 
and  SMITH  f  is  based,  as  already  stated,  on  the  expulsion  of  any 
ammonia  as  such  from  the  water  by  boiling  with  or  without  the 
addition  of  an  alkali,  and  then  decomposing  the  albuminoid  sub- 
stanc.e  by  boiling  with  potassium  permanganate  and  potassium 
hydroxide,  distilling  off  and  determining  the  ammonia:  formed. 
This  method  gives  two  results — the  ammonia  present  as  such  and 
that  formed  from  the  albuminoid  substances. 

a.   REQUISITES. 

a.  Nessler's  Reagent.  This  is  prepared  as  follows:  Boil  to- 
gether 35  grm.  potassium  iodide  and  13  grm.  mercuric  chloride 
with  800  c.c.  water.  When  a  clear  solution  results,  add  drop 
by  drop  a  cold  saturated  solution  of  mercuric  chloride  until  the 
precipitate  just  begins  to  be  permanent.  Now  add  160  grm. 
potassium  hydroxide  (or  120  grm.  sodium  hydroxide),  make  up 

*  Should  a  precipitate  immediately  form,  it  may  be  either  silver  sulphide 
or  metallic  silver ;  the  former  would  indicate  the  presence  of  hydrogen  sulphide 
or  dissolved  sulphides,  the  latter  ferrous  (or  possibly  stannous)  salts. 

t  Jowrn.  Chem.  Soc.,  N.  S.,  v,  591;  also  "Water  Analysis,"  by  J.  A. 
WANKLYN  and  ERN.  TH.  CHAPMAN,  3d  edit.,  London,  TRUBNER  &  Co.,  1874. 


208  ANALYSIS    OF    WATER.  [§  205. 

the  volume  to  1  litre  with  water,  add  a  little  more  mercuric-chlo- 
ride solution,  and  set  the  liquid  aside  to  deposit.  The  clear  solu- 
tion has  a  very  pale-yellowish  color.  2  c.c.  added  to  50  c.c.  of 
water  containing  0-05  mgrm.  ammonia  should  give  an  immediate 
yellowish-brown  coloration.  The  solution  must  be  preserved  in 
well-stoppered  bottles.  In  using  it,  some  is  poured  from  the  stock 
bottle  into  a  small  bottle. 

b.  Standard  Ammonium-chloride  Solutions.     The  stronger  so- 
lution contains  0-001  grm.  NH3  in  every  c.c.,  and  is  prepared  by 
dissolving  3-137  ammonium  chloride  in  sufficient  distilled  water 
to  measure  1  litre;  the  weaker  contains  in  every  c.c.  0-01  mgrm. 
NH3,  and  is  prepared  by  mixing  10  c.c.'  of  the  stronger  solution 
with  sufficient  distilled  water  to  measure  1  litre. 

c.  Alkaline    Potassium-permanganate    Solution.      Dissolve    100 
grm.    potassium   hydroxide    and    4   grm.    crystallized    potassium 
permanganate  in  500  c.c.  water,  boil  for  fifteen  minutes,  introduce 
into  a  500-c.c.  flask,  and  after  cooling,  fill  up  to  the  mark. 

d.  Freshly-ignited  Sodium  Carbonate,  or  a  solution  of  the  salt 
freed  from  all  traces  of  ammonia  by  boiling. 

e.  Ammonia-free   Distilled   Water.     If   the   distilled   water   at 
hand  is  at  all  colored  when  50  c.c.  of  it  are  treated  with  2  c.c.  of 
NESSLER'S  solution,  some  must  be  especially  prepared  by  adding 
a  trace  of  sulphuric  acid  to  the  water  and  redistilling. 

/.  A  tubulated  Retort  (with  glass  stopper)  having  a  capacity 
of  somewhat  more  than  one  litre  when  quite  filled.  This  is  to  be 
clamped  in  a  strong  retort-holder,  and  heated  directly  by  a  large 
gas-burner,  preferably  a  MASTE  burner,  Fig.  47,  p.  82,  Vol.  I. 

g.  A  large  LIEBIG  Condenser.  The  condenser  tube  should  be 
90  cm.  long  and  3  cm.  wide.  The  neck  of  the  retort  is  bound  with 
a  strip  of  writing  paper,  and  inserted  directly  into  the  condenser 
tube. 

h.  Six  Cylinders  of  white  glass,  about  17  cm.  high  and  about 
4  cm.  diameter.  In  use  they  are  placed  on  a  white  porcelain  tile, 
or  on  a  sheet  of  white  paper. 

i.  Measuring  Vessels.  A  half-litre  flask  for  measuring  the 
water;  a  50-c.c.  measuring  cylinder  for  the  alkaline  permanganate 


§  205-]  ANALYSIS  OF  FRESH  WATER.  209 

solution;    a  burette   for  the   ammonium-chloride  solution;    and 
a  2-c.c.  pipette  for  the  NESSLER'S  reagent. 

As  all  the  vessels  kept  in  the  laboratory  usually  have  traces  of 
ammonia  salts  on  their  surfaces,  care  must  always  be  taken  to 
rinse  them  with  pure  distilled  water  just  before  using;  further- 
more the  most  scrupulous  cleanliness  must  be  observed  through 
the  entire  process. 

ft.    THE   ANALYSIS. 

a.  Introduce  500  c.c.  of  the  water  to  be  examined  into  the 
well-washed  retort  properly  supported  and  connected  with  the 
condenser,  and  heat  with  the  naked  flame.*    The  flame  is  moved  at 
first  to  and  fro  beneath  the  retort,  and  the  drops  of  water  which 
condense  on  its  surface  wiped  off  with  a  cloth.     The  water  soon 
boils.     The  distillate  is  collected  in  a  cylinder.     As  soon  as  50  c.c. 
have  been  collected,  replace  the  first  cylinder  (^4.)  by  a  second,  and 
continue  the  distillation  until  150  c.c.  more  have  been  collected. 
In  the  retort  there  will  hence  be  left  500-200  =  300  c.c.     Now 
stop  the  distillation  for  a  moment,  and  introduce  50  c.c.  of  the 
alkaline  permanganate  solution  into  the  retort  through  the  tubulure, 
by  means  of  a  wide-necked  funnel,  then  close  the  retort  again,  and 
continue  the  distillation.     Should  the  liquid  show  signs  of  bumping, 
gently  shake  the  contents  of  the  retort ;  this  will  prevent  it.     When 
50  c.c.  of  the  distillate  have  been  collected  replace  the  cylinder 
( B 1 )  by  another  and  continue  until  two  further  portions  of  50  c.c. 
each   have  been   collected  in   cylinders   marked  respectively  B2 
and  53,  then  stop  the  distillation. 

b.  The  small  quantities  of  ammonia  in  the  four  cylinders  are  now 
determined  colorimetrically  by  means  of  the  NESSLER'S  reagent. t 

For  this  purpose  add  2  c.c.  of  the  NESSLER'S  reagent  by  means 

*  If  the  water  is  acid  add  to  it,  before  applying  heat,  some  freshly-ignited 
sodium  carbonate,  in  order  to  liberate  the  ammonia.  In  the  case  of  waters 
containing,  as  they  usually  do,  carbonates  of  the  alkali  earths,  this  addition 
is  unnecessary. 

f  This  method  of  estimating  ammonia  was  first  employed  by  W.  A.  MILLER 
(Zeitschr.  /.  analyt.  Chem.,  iv,  459). 


210  ANALYSIS    OF   WATER.  [§   205, 

of  the  2-c.c.  pipette  into  the  fluid  in  the  cylinder  A.  If  the  fluid 
contains  ammonia,  it  acquires  on  being  stirred  a  reddish-brown- 
color  which  is  the  deeper  the  greater  the  quantity  of  ammonia 
present.  This  color  has  now  to  be  duplicated  by  adding  a  meas- 
ured quantity  of  ammonium-chloride  solution  of  known  strength 
to  water  in  another  cylinder,  and  adding  to  this  NESSLER'S  reagent.. 
To  effect  this  a  measured  quantity  of  the  weaker  ammonium- 
chloride  solution  is  introduced  into  a  clean  cylinder,  ammonia- 
free  water  added  to  the  mark,  and  then  2  c.c.  of  the  NESSLER'S 
reagent  added.  After  thoroughly  shaking,  the  cylinder  is  placed 
beside  that  marked  A  on  a  white  surface  (a  porcelain  tile  or  sheet 
of  white  paper),  and  after  a  few  minutes,  the  colors  of  the  two 
liquids  compared,  looking  down  through  the  liquid  in  the  tubes. 
If  the  colors  in  both  tubes  are  alike,  the  object  is  attained,  as  it  will 
then  be  known  that  the  cylinder  A  contains  just  as  much  ammonia 
as  the  other  cylinder  the  ammonia  content  of  which  is  known;: 
if  the  colors  are  not  alike,  a  new  trial  must  be  made,  using  more 
or  less  of  the  ammonium-chloride  solution  until  the  colors  in  both 
cylinders  are  alike  in  depth. 

The  ammonium-chloride  solution  should  never  be  added  after 
the  NESSLER'S  reagent,  as  this  causes  turbidity,  and  turbid  solutions 
cannot  be  compared  with  success.  It  must  be  further  remarked 
that  the  conclusion  that  liquids  exhibiting  similar  colors  contain 
like  quantities  of  ammonia  is  true  only  when  the  fluids  have  the 
same  mean  temperature  * ;  and  that  the  colorimetric  comparisons 
according  to  the  process  just  detailed  are  successful  only  when 
the  quantity  of  ammonia  in  50  c.c.  of  the  liquid  lies  between 
0-0025  and  0-05  mgrm. 

The  ammonia  found  in  the  cylinder  A  was  present  in  the  water 
as  such,  i.e.,  in  the  form  of  an  ammonia  salt.  As  the  result  of 
numerous  experiments  by  Messrs.  CHAPMAN,  WANKLYN,  and 
SMITH,  the  authors  find  that  it  is  only  necessary  to  add  one-third 
to  the  ammonia  found  in  the  cylinder  A  in  order  to  obtain  all 
the  ammonia  present  as  such  in  the  500  c.c.  of  water.  In  this 

*  NESSLER,  Zeitschr.  /.  analyt.  Ghent.,  vn,  415. 


§   205.]  ANALYSIS    OF    FRESH    WATER.  211 

manner  the  trouble  of  Nesslerizing  the  first  150  c.c.  of  distillate 
is  saved. 

The  contents  of  cylinders  B\,B2,  and  B  3  are  separately  treated 
like  that  of  cylinder  A ;  the  quantities  of  ammonia  found  are  added 
together,  and  this  represents  the  ammonia  formed  by  the  action 
of  the  alkaline  permanganate  on  the  nitrogenous  albuminoid 
matter.  The  authors  designate  the  ammonia  found  in  the  cylinder 
A  as  free  ammonia;  that  found  in  cylinders  B 1,  2,  and  3,  albu- 
minoid ammonia. 

12.  Determination  of  Ammonia. 

Great  importance  is  justly  placed  on  the  determination  of 
ammoniacal  compounds  in  natural  waters,  since  the  presence  of  any 
considerable  quantity  of  ammoniacal  compounds  generally  in- 
dicates that  the  water  has  been  contaminated  by  the  decomposition- 
products  of  nitrogeneous  substances,  and  that  it  has  not  been 
sufficiently  purified  by  the  action  of  the  air  on  it,  and  by  filtration 
through  earth. 

Various  methods  may  be  employed  for  determining  the  am- 
monia in  waters ;  the  more  important  will  be  here  given. 

a.  Expulsion  of  the  Ammonia  by  Distillation,  and  Conversion 
into  Ammonium-platinic  Chloride.  This  method  is  frequently 
employed  in  the  analysis  of  mineral  waters,  and  is  described  in 
§209. 

6.  Expulsion  of  the  Ammonia  by  Distillation,  and  Colorimetric 
Determination  by  NESSLER'S  Reagent.  This  method  has  been 
already  described  in  detail  on  pages  207-211.  It  is  particularly 
suitable  for  determining  very  small  quantities  of  ammonia. 

c.  Direct  Nesslerizing,  after  Precipitation  of  the  Calcium,  etc. 
This  method,  which  is  exceedingly  simple,  and  suffices  for  most 
cases,  must  be  considered  as  a  decided  improvement  on  the  original 
CHAPMAN  method.*  It  was  devised  by  FRANKLAND  and  STRONG^ 
and  improved  by  HUGO  TROMMSDORFF.}: 

*  Zeitschr.  /.  analyt.  Chem.,  vn,  478. 
f  Ibid.,  vn,  479. 
j  Ibid.,  vin,  356. 


212  ANALYSIS    OF   WATER.  [§  205. 

Place  300  c.c.  of  the  water  to  be  examined  into  a  cylinder,  add 
2  c.c.  of  a  solution  of  sodium  carbonate  (1  part  of  the  salt  to  2  of 
distilled  water),  and  1  c.c.  of  a  sodium-hydroxide  solution  (1  part 
NaOH  to  2  of  distilled  water),  stopper  the  cylinder,  shake,  and 
allow  to  settle.  As  a  rule  the  liquid  settles  sufficiently  to  permit 
100  c.c.  of  clear  liquid  to  be  poured  off;  if  this  is  not  the  case,  how- 
ever, 100  c.c.  must  be  passed  through  a  washed  filter.  To  the 
100  c.c.,  contained  in  a  cylinder  or  test-tube  bearing  a  scratch, 
add  1  c.c.  of  NESSLER'S  reagent  (p.'  207).  If  more  than  a  yellow 
color  develops,  add  1  c.c.  more.  Into  a  second  cylinder  or  test- 
tube  exactly  like  the  first,  introduce  90  c.c.  of  pure,  ammonia- 
free  distilled  water  (p.  208),  0-6  c.c.  of  the  sodium-carbonate  so- 
lution, and  0-3  c.c.  of  the  sodium-hydroxide  solution,  fill  to  the 
mark,  and  from  a  1-c.c.  pipette  graduated  in  0-01  c.c.  run  in  a 
suitable  quantity  of  the  dilute  ammonium-chloride  solution  (p.  208), 
add  1  or  2  c.c.  of  NESSLER'S  reagent  according  to  circumstances, 
and  after  a  few  minutes  compare  the  colors  of  both  cylinders  or 
test-tubes  as  detailed  on  p.  210.  The  general  rules  there  given 
apply  here  naturally  also.  Hence,  should  the  NESSLER'S  reagent 
develop  too  dark  a  color,  a  fresh  portion  of  the  clarified  water 
must  be  taken,  diluted  with  a  suitable  quantity  of  distilled  water 
to  100  c.c.,  and  the  experiment  repeated. 

d.  Precipitation  of  the  Ammonia  by  means  of  Potassium-mer- 
curic Iodide,  and  determination  of  the  Mercury  in  the  Precipitate. 
This  method,  devised  by  FLECK,*  is  especially  adapted  in  cases 
where  the  water  contains  a  relatively  large  quantity  of  ammonia. 
It  hence  supplements  the  methods  b  and  c,  which  are  especially 
suitable  for  waters  containing  very  little  ammonia.  The  method 
is  based  upon  the  precipitation  of  ammonia  by  NESSLER'S  reagent 
as  insoluble  ammonium  iodohydrargyrate  (NHg2I.H20),  a  com- 
pound of  constant  composition. 

In  order  to  be  able  to  filter  this  off  well,  care  must  be  taken  to 
precipitate  it  in  conjunction  with  calcium  carbonate  or  magnesium 
hydroxide;  and  to  be  certain  that  the  precipitation  is  effectual,  a 
little  of  a  solution  of  magnesium  sulphate  is  added  to  the  water. 

*  Journ.  /.  prakt.  Chem.,  N.  F.,  v,  263. 


§    205.]  ANALYSIS   OF   FRESH   WATER.  213 

The  determination  of  the  mercury  is  effected  by  dissolving  the 
ammonium  iodohydrargyrate  in  a  solution  of  sodium  thiosulphate 
and  titrating  with  a  solution  of  potassium-  or  sodium-sulphide. 
2  eq.  of  mercury  found  correspond  to  1  eq.  of  ammonia. 

The  following  reagents  are  required  for  the  process: 

Nessler's  reagent  (p.  207). 

Magnesium-sulphate  solution  (1:8). 

Sodium-thiosulphate  solution  (1:8). 

Standard  potassium-sulphide  solution. 

Lead-acetate  paper,  made  by  immersing  filtering-paper  in  a 
1 : 10-solution  of  lead  acetate,  and  drying.  The  paper  should  be 
preserved  in  well-stoppered  bottles. 

The  sulphide  solution  is  prepared  by  heating  10  grm.  sodium- 
potassium  carbonate  and  4  grm.  sulphur  in  a  covered  porcelain 
crucible  to  calm,  fusion,  dissolving  the  sulphide  when  cold  in  water, 
adding  10  grm.  sodium  hydroxide,  and  making  up  the  whole  to  1 
litre.  The  solution  may  be  preserved  unchanged  for  weeks  in  a 
well-stoppered  flask.  It  is  titrated  with  a  standard  mercuric- 
chloride  solution  100  c.c.  of  which  contain  1  grm.  mercuric  chloride. 
Ammonium  carbonate  is  added  to  10  c.c.  of  the  solution,  the  white 
precipitate  dissolved  in  a  few  drops  of  the  sodium-thiosulphate 
solution,  and  the  sulphide  solution  run  in  from  a  burette  until  the 
liquid,  in  which  a  black  precipitate  of  mercury  sulphide  forms,  floc- 
culent  at  first,  but  granular  later,  begins  to  become  clear,  and 
until  a  drop  placed  on  a  strip  of  the  dry  lead-acetate  paper  de- 
velops a  faint  brown  ring. 

Should  the  sulphide  solution  be  too  concentrated,  it  must  be 
diluted.  Its  titre  is  correct  when  100  c.c.  of  the  solution  precipi- 
tates 0-5  grm.  mercury.  When  everything  is  in  readiness,  add 
to  200  c.c.  of  the  water  to  be  examined  in  a  cylinder  0-5  c.c.  of 
the  magnesium-sulphate  solution,  and  4  c.c.  of  NESSLER'S  reagent, 
close  the  cylinder,  shake,  and  allow  to  settle.  Should  the  result- 
ing precipitate  have  a  yellow  instead  of  a  red  color,  because  so 
little  ammonia  is  present,  employ  a  larger  quantity  of  water,  say 
500  c.c.  at  least.  The  quantities  of  the  magesium-sulphate  solu- 
tion and  NESSLER'S  reagent  are  to  be  increased  proportionately. 


214  ANALYSIS   OF    WATER.  [§  205. 

When  the  precipitate  has  thoroughly  settled,  decant  the  clear 
liquid  so  far  as  possible,  collect  the  precipitate  on  a  small  filter, 
and  wash  it  with  cold  water  until  the  filtrate  is  no  longer  alkaline. 
The  filtering  and  washing  must,  of  course,  be  done  in  an  atmos- 
phere free  from  hydrogen  sulphide  and  ammonia. 

The  filter  containing  the  washed  precipitate  is  now  filled  com- 
pletely with  the  solution  of  sodium  thiosulphate,  whereby  the 
ammonium  iodohydrargyrate  is  dissolved,  after  which  it  is  washed 
with  cold  water,  and  the  mercury  determined  in  the  solution  (which 
may  measure  100  to  150  c.c.)  by  means  of  the  sulphide  solution 
as  above.  In  calculating,  2  eq.  of  mercury  (400)  =  1  eq.  of  am- 
monia (NH3=17-064). 

On  testing  the  methods  b,  c,  and  d,  KUBEL  and  TIEMANN  (loc. 
dt.y  p.  97)  obtained  on  the  whole  satisfactorily  accurate  and  fairly 
concordant  results. 

II.  THE  WATER  IS   NOT  CLEAR. 

1.  Fill  with  the  water  a  large  bottle  of  known  capacity,  close 
it  with  a  glass  stopper,  allow  to  settle  in  the  cold,  siphon  off  the 
clear  liquid  so  far  as  possible,  collect  the  deposit  on  a  filter,  weigh 
it,  then  dry  and  ignite.     The  clear  water  is  treated  as  directed  in  I. 

2.  Fill  a  second    glass-stoppered   bottle  with   the  water  and 
allow  to  settle  in  the  dark.     As  soon  as  it  is  clear,  very  carefully 
siphon  off  the  water  without  disturbing  the  deposit.     Shake  up 
the  latter  with  the  remainder  of  the  water  and  pour  it  into  a  small 
beaker,  which  is  then  covered  and  set  aside  for  the  deposit  to  settle 
again.      The  clear  water  is  again  poured  off  as  closely  as  possible 
and  some  of  the  deposit  drawn  up  in  a  tube  the  end  of  which  is 
drawn  out  to  a  capillary  point.     A  drop  is  now  placed  on  an  object- 
glass,  covered  with  a  cover-glass,  and  microscopically  examined 
for  organized  bodies  (bacteria,  infusoria,  etc.). 

Regarding  the  calculation  of  the  analysis  I  refer  to  §  213;  and 
it  may  be  observed  that  usually  the  principles  here  laid  down  are 
followed  in  stating  the  results  (a  certain  latitude  being,  of  course, 
allowed) : 

Chlorine  is  first  combined  with  sodium;  if  any  remains  (which 


§  205.]          ANALYSIS  OF  FRESH  WATER.  215 

seldom  occurs)  it  is  combined  with  calcium.  Sulphuric  acid  is  next 
combined  with  calcium;  the  nitric  acid  then  with  ammonia,  any 
residual  acid  being  combined  with  sodium  if  such  has  not  been 
entirely  neutralized  by  chlorine,  otherwise  with  magnesium.  Silicic 
acid  is  stated  as  such,  and  the  remainder  of  the  calcium  and  mag- 
nesium as  carbonates,  usually  as  monocarbonates. 

It  must  be  remembered,  of  course,  that  at  times  the  results 
of  the  qualitative  analysis  may  cause  another  arrangement  of  the 
calculation  to  be  adopted.  For  instance,  should  the  evaporated 
water  be  strongly  alkaline,  sodium  carbonate  is  present,  usually 
with  sodium  sulphate,  sodium  chloride,  and  at  times  also  sodium 
nitrate.  In  this  case  the  calcium  and  magnesium  are  then  to  be 
entirely  combined  with  carbonic  acid. 

In  the  report  the  quantities  are  most  convienently  stated  in  parts 
per  1000  by  weight  or  (in  the  case  of  spring-waters  the  specific 
gravity  of  which  differs  but  little  from  that  of  distilled  water)  in 
grammes  per  litre.  I  prefer  this  form  of  statement  to  that  of 
KUBEL-TIEMANN  (who  recommended  reporting  the  results  in 
parts  per  100,000),  because  the. litre  is  now  adopted  generally, 
and  by  moving  the  point  three  decimal  places,  the  results  may  at 
once  be  expressed  in  milligrammes. 


APPENDIX. 

ESTIMATION  OF  THE  HARDNESS. 

FOR  technical  purposes  it  is  at  times  sufficient  to  determine 
the  so-called  hardness  of  water.  By  this  term  is  understood  the 
quality  imparted  to  the  water  by  the  presence  of  a  larger  or  smaller 
quantity  of  calcium  and  magnesium  salts.  A  hard  water  is  one 
rich  in  these  salts;  a  soft  water,  one  containing  but  very  little  of 
them.  By  total  hardness  is  understood  the  hardness  exhibited 
"by  unboiled  water;  the  permanent  hardness  is  that  retained  after 
water  is  boiled  and  made  up  to  its  original  volume  with  distilled 
water;  the  temporary  hardness  is  the  difference  between  the  total 
and  permanent  hardness. 


216  ANALYSIS   OF   WATER.  [§  205* 

The  total  hardness,  both  permanent  and  temporary,  may  be 
obviously  calculated  from  the  results  of  the  analysis.  Since  an 
analysis  of  water  usually  requires  not  inconsiderable  time,  a  more 
rapid  method  has  been  sought  for,  and  was  first  proposed  by  CLARK.* 
His  method  has  been  variously  modified,  but  the  reagent  which  he 
employed,  soap  solution,  is  still  always  used.  The  soap  decom- 
poses all  the  calcium  and  magnesium  salts  present  in  the  water, 
and  a  slight  excess  of  the  soap  is  very  readily  recognized  by  the 
permanent  lather  it  gives  on.  shaking  the  water.  As  this  test,, 
however,  does  not  differentiate  between  the  calcium  or  magnesium 
salts,  the  results  afforded  by  it  are  quite  different  from  those 
obtained  by  actual  analysis,  and  require  some  agreement  regarding 
the  form  of  expressing  the  relationship  of  the  soap  used  to  the 
results  obtained.  Unfortunately  such  an  agreement  does  not 
exist  between  the  various  countries,  the  various  degrees  of  hardness 
having  different  meanings  in  Germany,  France,  and  England,  as 
follows: 

Value  of  Degree  of  Hardness. 

In  Germany:  1  part  CaO  in  100,000  parts  water,  or  0-001  grm. 
CaO  in  100  c.c.f 

In  France:   1  part  CaCO3t  in  100,000  parts  water. 

In  England:  1  part  CaC03  in  70,000  parts  water  or  1  grain 
CaC03  in  an  imperial  gallon. 

The  various  degrees  of  hardness,  therefore,  compare  as  follows: 
German,  0-56;  French,  1;  English,  0-7. 

To  convert  the  German  standard  into  French,  multiply  by 
1-7857;  into  English,  by  1-25.  To  convert  the  English  standard 
into  French  multiply  by  1-4286;  into  German  by  0-8. 

According  to  various  experiments  made  by  KUBEL-TIEMANN, 
the  best  general  method  is  that  of  CLARK  modified  by  A.  FAISZT  and 

*  Jahresber.  /.  Chem.,  1850,  608. 

f  Magnesium  salts,  if  present,  are  calculated  in  equivalent  quantities  of 
lime. 

|  Or  an  equivalent  quantity  of  a  magnesium  salt. 


§  205.J  ANALYSIS    OF    FRESH    WATER.  217 

C.  KNAUSZ.*  It  must  be  stated,  however,  that'  the  methods  of 
BOUTRON  and  BOUDET,!  and  of  WILSON,:}:  have  also  certain  ad- 
vantages. Only  the  first  method  will  be  here  described. 

a.  REQUISITES. 

a.  Standard  Barium-chloride  Solution.  Dissolve  0-5226  grm. 
of  pure,  dry,  crystallized  barium  chloride  (BaCl2+2H20),  i.e., 
the  equivalent  of  0-12  grm.  calcium  oxide  (CaO)  in  sufficient 
distilled  water  to  measure  1  litre.  100  c.c.  will  then  contain 
barium  chloride  equivalent  to  12  milligrammes  of  calcium  oxide 
(CaO)  and  the  solution  will  be  of  12°  hardness  (German). 

6.  A  Glass-stoppered  Bottle,  of  about  200  c.c.  capacity,  with  a 
mark  at  100  c.c. 

c.  Standard  Soap  Solution.  To  prepare  this  heat  150  parts  of 
lead  plaster  on  a  water-bath,  add  40  parts  of  pure  potassium 
carbonate,  and  rub  down  to  a  homogeneous  mass.  Treat  this  with 
strong  alcohol,  allow  to  deposit,  filter,  distil  off  the  alcohol,  and 
dry  the  residual  soap  on  a  water-bath  (Huoo  TROMMSDORFF§). 
Dissolve  20  parts  of  the  soap  so  made  in  1000  parts  of  dilute  alcohol 
(sp.  gr.  0-9213);  introduce  100  c.c.  of  the  barium-chloride  solution 
into  the  stoppered  bottle,  b,  and  from  a  burette  run  in  the  soap 
solution  until,  on  shaking,  there  forms  a  thick  white  foam  which 
remains  for  at  least  fifteen  minutes  on  the  surface  of  the  liquid. 
The  soap  solution  is  added  at  first  in  larger  quantities,  but  towards 
the  last  drop  by  drop,  shaking  after  each  addition.  The  bottle 
should  be  held  upright,  and  shaken  up  and  down. 

If  the  soap  solution  has  been  prepared  as  above,  100  c.c.  of  the 
barium-chloride  solution  will  require  less  than  45  c.c.  of  soap  solu- 
tion. After  the  experiment  is  repeated,  in  order  to  make  sure  of  the 
result,  dilute  the  soap  solution  with  dilute  alcohol  (sp.  gr.  0-9213) 

*  Gewerbeblatt  aus  Wurtemberg,  1852,  193;  also  Chemisch-PharmaceuL 
CentralbL,  1852,  513. 

f  Chem.  CentralbL,  1855,  343. 

J  Annal.  d.  Chem.  und  Pharm.,  cxix,  318;  Zettschr.  f.  analyt.  Chem.,  1, 106. 

§  Zeitschr.  f.  analyt.  Chem.,  vm,  333. 


218 


ANALYSIS   OF    WATER. 


[§  205. 


so  that  45  c.c.  will  exactly  suffice  to  produce  the  foam  in  100  c.c. 
of  the  barium-chloride  solution. 

d.  The  following  table  was  compiled  by  FAISZT  and  KNATJSZ 
from  direct  experiments; 


c.c.  soap 
solution  used. 


Degree  of 


hardness. 


=  to  1  c.c. 
soap  solution. 


3-4 0-5 

£::      :::::::::::::::  1:2  > ••» 

9-4 2-0 

11-3 2-51 

13-2 3-0 

15-1 3-5 

17-0 4-0 

18-9 4-5 

20-8 5-OJ 

22-6 5-5^ 

24-4 6-0 

26-2 6-5  I  n  „ 

28-0 7-0  f *m 

29-8 7-5  I 

31-6 8-Oj 

33-3 8-51 

35-0 :..  9-0 

36-7 9.5! 

38-4 : 10- Of 02W 

40-1 10.5  I 

41-8 11. Oj 

43-4 11.5) 

45-0 12- Of C 

It  will  be  seen  from  this  table  that  the  degrees  of  hardness  are 
not  proportional  to  the  c.c.  of  soap  solution  used.  The  necessity 
for  this  table  is  therefore  evident  for  obtaining  accurate  results. 

[The  soap  solution  may  be  more  conveniently  made  by  dis- 
solving 10  grammes  of  Castile  (Syria)-soap  shavings,  from  a  fresh 
piece  of  soap,  in  1  litre  of  dilute  alcohol  (2  parts  alcohol  and  1  part 
water).  Filter,  if  necessary.  The  solution  may  be  standardized 
against  the  barium-chloride  solution,  or,  as  is  more  commonly 
done,  against  a  solution  prepared  by  dissolving  1  gramme  of  pure 
calcium  carbonate  in  a  little  hydrochloric  acid,  neutralizing  with  a 


§  205.]  ANALYSIS    OF   FRESH   WATER.  219 

slight  excess  of  ammonia  water,  and  diluting  to  1  litre.  Each  c.c. 
of  this  solution  will  contain  a  quantity  of  calcium  salt  equivalent 
to  0-001  gramme  of  CaCO3.  In  standardizing,  10  c.c.  of  this 
solution  are  diluted  with  pure  water  to  100  c.c.,  introduced  into  a 
stoppered  flask,  and  the  soap  solution  run  in  from  a  burette  little 
by  little,  and  shaking  after  each  addition,  until  a  foam,  persisting 
for  10  minutes,  forms.  It  is  well  not  to  add  more  than  0-5  c.c.  of 
soap  solution  at  a  time.  The  experiment  is  now  repeated  with 
100  c.c.  of  pure  water  alone;  the  difference  in  the  soap  solution  used 
will  give  the  soap  solution  required  for  the  calcium  salt  alone  (quite 
an  appreciable  quantity  may  have  been  used  for  the  pure  water). 
The  proper  value  of  1  c.c.  of  the  soap  solution  in  terms  of  CaCO3 
is  thus  ascertained,  and  should  be  noted. — TRANSLATOR.] 

ft.  THE  DETERMINATION. 
aa.  Determining  the  total  hardness. 

Introduce  20  c.c.  of  the  water  into  a  test-tube,  add  about  6  c.c. 
of  the  soap  solution,  shake,  and  note  whether  the  water  becomes 
simply  opalescent,  or  whether  a  more  or  less  pronounced  cloudi- 
ness develops,  or  a  notable  precipitate  forms.  According  to  the 
result  obtained,  the  proper  quantity  of  water  to  be  tested  is  judged, 
i.e.,  if  the  water  is  very  soft,  100  c.c.  are  introduced  into  a  stop- 
pered flask;  if  moderately  soft,  50  c.c.  are  mixed  with  50  c.c.  of 
distilled  water;  in  the  case  of  moderately  hard  waters,  20  c.c.  are 
taken  and  mixed  with  80  c.c.  of  distilled  water;  of  hard  waters, 
10  c.c.  are  mixed  with  90  c.c.  of  distilled  water.  If,  on  shaking 
the  test-tube  in  the  preliminary  test,  a  frothy  pellicle  forms  on  the 
surface  of  the  liquid,  it  indicates  the  presence  of  magnesium  salts 
in  considerable  quantity;  the  water  in  this  case  must  be  largely 
diluted. 

The  soap  solution  is  now  run  from  a  burette  into  the  stoppered 
flask,  shaking  after  each  addition,  until  the  characteristic  per- 
manent froth  forms.  At  the  first  test  the  soap  solution  is  added 
in  larger  quantities  at  first,  and  towards  the  end  in  quantities  of 
only  1  c.c.  each,  in  order  to  expedite  matters;  in  the  second  ex- 


220  ANALYSIS    OF   WATER.  [§  205. 

periment,  nearly  the  entire  quantity  of  soap  solution,  as  ascer- 
tained by  the  first  test,  is  run  in  at  once,  and  then  the  solution 
added  drop  by  drop,  the  end  of  the  experiment  being  thus  rapidly 
reached.  The  concentration  of  the  water  may,  as  a  rule,  be  con- 
sidered correct  when  from  20  to  45  c.c.  soap  solution  have  been 
used.  Not  more  than  45  c.c.  should  ever  be  required. 

After  the  c.c.  of  soap  solution  have  been  read  off,  the  degree  of 
hardness  is  found  from  the  table,  as  follows: 

If  the  c.c.  of  soap  solution  is  a  number  found  in  the  table,  e.g., 
22-6,  the  degree  of  hardness  is  given  directly,  and  in  the  given 
case  would  be  5-5  (assuming  that  100  c.c.  of  the  water  to  be  ex- 
amined had  been  taken).  If  another  number  of  c.c.  of  soap  solu- 
tion has  been  used,  the  degree  of  hardness  is  found  by  first  noting 
the  nearest  lower  number  in  the  table,  and  noting  its  correspond- 
ing degree  of  hardness;  the  difference  between  the  nearest  lower 
number  and  the  c.c.  of  soap  solution  used  is  now  multiplied  by 
the  proper  correction  number  in  the  third  column  of  the  table, 
and  the  product  added  to  the  degree  of  hardness  already  noted. 
An  example  will  make  this  clear. 

Let  us  suppose  we  have  used  for  100  c.c.  of  water  43-6  c.c. 
of  soap  solution.  The  water  will  in  this  case  have  a  degree  of 
hardness  of  11-562,  thus: 

43-4  c.c 11 -5°  hardness 

+  (43-6-43-4)XO-31  =  Q.Q62 
11-562 

If  the  water  has  been  used  diluted,  the  degree  found  must  be 
increased  in  the  proper  proportion. 

bb.  Determination  of  permanent  hardness. 

Boil  500  c.c.  of  the  water  in  a  flask  of  about  1  litre  capacity  for 
one-half  to  one  hour,  replacing  the  water  as  it  evaporates  by  dis- 
tilled water.  After  cooling,  pour  the  water  into  a  500-c.c.  flask, 
rinsing  out  the  larger  flask  with  small  quantities  of  distilled  water, 
then  fill  up  to  the  mark,  shake,  allow  to  settle,  filter  into  a  dry 
flask,  and  determine  the  hardness  as  above  in  100,  50,  or  25  c.c. 


§  206.]  ANALYSIS    OF    MINERAL   WATERS.  221 

B.  ANALYSIS  OF  MINERAL  WATERS.* 

§206. 

In  mineral  waters  a  much  larger  number  of  substances  are  to 
be  determined  by  analysis  than  are  present  in  sweet  waters.  The 
substances  which  may  require  our  attention  are  as  follows: 

a.  Bases:  Ammonia,   oxides    of   potassium,  sodium,    lithium, 
csesium,    rubidium,    calcium,    barium,    strontium,     magnesium, 
aluminium,  iron  (ous),  manganese  (ous),  (zinc,  nickel  [ous],  cobalt 
[ous],  copper  [ic],  lead  [ic],  thallium  [ous],  and  sometimes  also  the 
oxides  of  the  heavy  metals). 

b.  Acids,  etc.:   Sulphuric,  phosphoric,  silicic,  carbonic,  boric, 
nitric,  nitrous,  and  thiosulphuric  acids;  chlorine,  bromine,  iodine, 
fluorine,  hydrogen  sulphide;  crenic,  apocrenic,  formic,  and  pro- 
pionic  acids,  etc.  (arsenous,  arsenic,  and  titanic  acids). 

c.  Uncombined    Elements    and    Indifferent    Gases:    Oxygen, 
nitrogen,  and  light  hydrogen  carbide. 

d.  Indifferent  Organic  Matter.     Many  of  these  substances  are 
found  in  quite  considerable  quantity  in  most  springs;  more  partic- 
ularly soda,  lime,  and  magnesia,  and  at  times  ferrous  iron,  besides 
sulphuric,   carbonic,   and    silicic    acids,  chlorine,  and  sometimes 
hydrogen  sulphide.    The  others  are  nearly  always  found  in  only 
small,  frequently  very  minute  quantities.    The  substances  above 
enumerated  inclosed  in  parenthesis  are  usually  detected  only  in 
the  evaporation  residues  of  large  quantities  of  water,  or  in  the 
muddy  ochreous  deposits  or  solid  sinter-deposits  which  form  in 
most  mineral  springs  in  those  places  where  the  air  acts  on  the 
water  which  runs  out  of  or  is  stored  in  reservoirs.f    The  analysis 
of  these  waters  quite  naturally  falls  under  two  heads:     1.  The 
analytical  process;   2.  The  calculation,  control,  and  arrangement  of 
results. 

*  Compare  Qualitative  Analysis,  §  211. 

f  As  already  mentioned  in  the  Qualitative  Analysis,  if  any  oxides  of  lead, 
copper,  or  tin  are  found,  the  water  must  be  carefully  investigated  in  order  to 
ascertain  whether  these  oxides  are  really  present  in  the  water  itself,  or  are 
derived  from  any  metallic  pipes,  cocks,  etc. 


222  ANALYSIS    OF    WATER.  [§  207. 

I.  THE  ANALYTICAL  PROCESS. 

The  performance  of  the  analytical  process  is  divided  into  two 
parts:     1.  Operations  at  the  well;    2.  Operations  in  the  laboratory. 

A.    OPERATIONS  AT  THE   WELL. 

I.  Apparatus  and  Requisites. 
§207. 

1.  A  common  plunging-siphon  of  from  200  to  250  c.c.  capacity. 

2.  Four  flasks  of  about  300  c.c.  capacity  each.     Each  contains 
about  3  grammes  of  calcium  hydrate  perfectly  free  from  car- 
bonate, or  containing  a  known  quantity  of  carbonate  (Vol.  I,  p.  480) ; 
and,  if  the  mineral  water  contains  sodium  carbonate,  about  1-5 
grm.  dry  calcium  chloride.     Each  flask  is  weighed  with  its  calcium 
hydrate,  stopper,  etc.,  and  the  weight  stated  on  a  label  gummed 
on  the  flask.    The  orifices  of  the  flasks  must  be  nearly  of  the  same 
size  so  that  a  single  stopper  bearing  its  glass  tubes,  as  shown  in 
Fig.  92,  Vol.  I,  will  fit  all  the  flasks;  this  stopper  should  be  pre- 
pared beforehand. 

3.  An  accurate  thermometer  with  very  distinct  scale. 

4.  About  eight  white  bottles  with  well-fitting  glass  stoppers, 
and  of  about  2  to  3  litres  capacity. 

5.  Four  white  bottles  with  well-fitting  glass  stoppers,  and  of 
about  6  to  7  litres  capacity. 

6.  A  perfectly  clean  sulphuric-acid  carboy  in  a  basket,  pro- 
vided with  a  rubber  stopper,  and  rinsed  out  with  distilled  water. 

7.  A  litre-  and  half-litre  flask. 

8.  One  medium-large  and  two  large  funnels. 

9.  Swedish  filtering-paper. 

10.  Flasks,  beakers,  alcohol-lamp,  blast-lamp,  blowpipe,  glass 
rods,  glass  tubes,  rubber  tubing,  files,  scissors,  knife,  rubber  and 
cork  stoppers,  twine,  etc. 

11.  Reagents,  more  especially  the  following:   ammonia,  hydro- 
chloric and  acetic  acids,  silver  nitrate,  barium  chloride,  ammonium 
oxalate,  tannic  and  gallic  acids  (or  infusion  of  galls),  freshly-pre- 
pared litmus  tincture,  and  test  papers. 


§  207.]  ANALYSIS    OF   MINERAL   WATERS.  223 

Besides  these,  the  following  are  also  required  at  times: 

a.  When  the  water  contains  hydrogen  sulphide  or  an  alkaline 
sulphide. 

12.  A  standard  solution  of  iodine  in  potassium-iodide  solution. 
This  must  be  very  dilute,  so  that  1  c.c.  will  contain,  say,  about 
0-001  grm.  iodine.     It  may  be  prepared  by  diluting  one  volume 
of  BUNSEN'S  iodine  solution  ( §  146,  b,  /•)  with  four  volumes  of 
water. 

13.  Powdered  starch. 

14.  A  pinch-cock  burette  and  a  few  pipettes. 

15.  A  solution  of  arsenous  acid  in  hydrochloric  acid,  or  of 
sodium  arsenite,  or  of  cupric  acetate;    also  all  the  reagents  and 
apparatus  detailed  on  pp.  230,  231  of  this  volume. 

b.  When  the  water  contains  much  ferrous  oxide,  and  this  is  to- 
be  determined  directly  (volumetrically)  at  the  well. 

16.  A  solution  of  potassium  permanganate.     For  waters  con- 
taining much  iron,  this  solution  is  to  be  diluted  so  that  100  c.c.  of  it 
will  oxidize  about  0  •  1  grm.  of  iron  from  the  ferrous  to  the  ferric 
state.     For  waters  containing  but  little  iron,  the  solution  must 
be  still  weaker.     If  the  solution  is  to  be  standardized  on  the  spot, 
there  will  be  required  also  weighed  pieces  of  piano  wire  or  a  standard 
oxalic-acid  solution  (Vol.  I,  p.  316),  and  burettes  and  pipettes. 

c.  When  the  total  dissolved  gases  in  the  water  are  to  be  determined. 
According  as  the  water  is  poor  or  rich  in  carbonic-acid  gas,  the 
methods  detailed  under  §  208,  a  or  6,  are  employed. 

17.  The  apparatus  there  described  is  then  required. 

d.  When  the  free  gases  evolved  at  the  spring  are  to  be  determined* 

18.  The  apparatus  described  under  §208,  11,  is  then  required. 

e.  If  the  well  is  deep,  and  specimens  from  various  depths  are 
to  be  examined. 

19.  The  apparatus  figured  and  described  on  pp.  225,  226  is 
then  required. 

/.  //  the  specific  gravity  of  highly  aerated  water  is  to  be  deter- 
mined. 

20.  There  will  be  required  one  or,  better,  several  bottles,  like 
that  figured  and  described  in  §  208,  13. 


224  ANALYSIS    OF   WATER.  [§  208. 

II.  Analytical  Processes. 
§208. 

1.  The  appearance  (color,  clearness,  etc.)  of  the  water  is  noted. 
It  must  be  observed,  here,  that  water  will  frequently  appear  to  be 
clear  at  the  first  glance,  while  on  closer  inspection  in  a  large  white 
bottle  a  few,  or  even  many,  colorless  or  colored  flocks,  etc.,  may 
be  observed.     In  this  case  the  bottle  is  set  aside  in  a  cool  dark 
place,  the  clear  water  then  carefully  siphoned  off,  and  the  de- 
posited matters  then  microscopically  examined.     Infusoria,  plants 
of  the  lowest  order,  etc.,  may  thus  be  often  found.* 

2.  Observe  whether  any  gases  are  evolved  from  the  well,  and 
whether  small  bubbles  of  gas  form  on  the  sides  of  a  dry  bottle  when 
the  latter  is  filled  with  water,  or  whether  any  gas  is  disengaged  on 
shaking  a  bottle  half  filled  with  the  water. 

3.  Note  the  taste  and  odor  of  the  water.     To  detect  very  minute 
quantities  of   odorous  matters  half -fill    a  water-bottle  with    the 
water,  close  with  the  hand,  shake  vigorously,  and  then  observe 
whether  any  odor  is  perceptible. 

4.  Test  the  reaction  of  the  water  with  the  various  test-papers, 
as  well  as  with  blue  and  also  very  slightly  reddened  litmus  tincture, 
and  note  whether  the  colors  imparted  to  blue  litmus  and  curcuma 
papers  change  when  the  latter  are  dried  in  the  air. 

5.  Ascertain   the    temperature   of   the   water.     If   practicable, 
the  best  and  simplest  method  of  ascertaining  this  is  to  sink  the 
thermometer  into  the  well,  and  to  take  the  reading  while  it  is 
immersed;   or  suspend  a  thermometer  in  a  large  bottle  and  im- 
merse this  in  the  well,  allowing  it  to  remain  for  some  time  after 
it  has  been  filled,  then  withdraw  the  bottle  from  the  well  and 
accurately  read  off  the  temperature  from  the  thermometer  in  the 
bottle.     If  the  water  flows  from  a  pipe,  allow  it  to  run  into  a  large 
glass  funnel  the  neck  of  which  is  so  constricted  as  to  let  about  as 
much  water  flow  out  as  runs  in  above.     The   thermometer  is 
then  fixed  in  the  middle  of  the  water  in  the  funnel  and  the  tem- 
perature taken  after  some  time. 

*  Compare   SCHULZ,  Jahrb.  des  Vereins  /.  Naturkunde  im  Herzogthume 
Nassau,  vin,  49. 


208.] 


ANALYSIS    OF    MINERAL    WATERS. 


225 


Besides  the  temperature,  note  must  be  taken  of 

a.  The  date. 

b.  The  temperature  of  the  air. 

c.  The  circumstance  whether  the  temperature  of  the  water 
varies  at  different  periods  of  the  year;  this  may  usually  be  ascer- 
tained at  the  spot. 

6.  Fill  the  bottles  and  carboy  specified  in  §  207,  4,  5,  and  6,  with 
water.  In  doing  this  the  greatest  care  must  be  taken  to  prevent 
the  water  from  becoming  turbid,  which  may  readily  happen  when, 
on  immersing  the  bottles  in  the  well,  the  bottle  grazes  the  bottom 
or  sides.  If  the  water  cannot  be  obtained  perfectly  clear,  it  must 
be  filtered  into  4  of  the  8  smaller  bottles  and  into  the  larger  bottles. 
For  this  purpose  use  large  funnels  with  folded  filters  of  pure,  good 


FIG.  83. 

filtering  paper,  so  that  the  filtration  may  be  very  rapid.  The 
necessity  for  filtration  may  often  be  obviated  by  filling  the  6  or  7 
litre  flasks  and  setting  them  aside  for  an  hour  or  two  in  the  shade, 
and  then,  after  the  flocks  have  completely  subsided,  siphoning 
off  the  clear  water  into  other  bottles,  which  must  be  securely  stop- 
pered and  marked. 

As  impurities  occasionally  float  on  the  surface  of  water  in  springs 
And  wells,  it  is  always  advisable  to  completely  immerse  the  bottles, 
and  to  a  sufficient  depth.  Where  it  its  important  to  avoid  any 


226 


ANALYSIS    OF   WATER. 


[§  208. 


agitation  of  the  water,  the  bottle  or  flask  should  be  provided  with 
the  contrivance  shown  in  Fig.  83.  As  soon  as  the  thumb  is  raised, 
the  water  flows  in,  while  air  escapes  through  the  tube  extending 
above  the  surface  of  the  water. 

If  the  surface  of  the  water  is  deep  down  and  out  of  reach,  tie 
the  flask  or  bottle  to  a  rod,  or  tie  a  weight  to  it  and  lower  it 
with  a  string.  To  keep  the  bottle  or  flask  upright,  use  may 
be  made  of  a  net,  through  a  hole  in  the  middle  of  which  the 
neck  of  the  flask  is  thrust;  the  net  is  then  tied  together  below 
the  bottom  of  the  flask  and  a  weight  attached  to  it,  while  the 
whole  is  suspended  by  a  strong  string  tied 
around  the  neck  of  the  flask. 

If  the  well  is  very  deep,  and  it  is  desired 
to  collect  samples  from  various  depths,  the 
apparatus  shown  in  Fig.  84  may  be  advan- 
tageously used. 

The  strong  flask,  a,  is  provided  with  brass 
cap,  6,  cemented  air-tight  on  it  and  bearing 
two  brass  tubes,  c  and  d.  To  the  tube  c  is 
joined  a  glass  tube,  e,  which  constitutes  the 
lower  continuation  of  c,  and  extends  down 
nearly  to  the  bottom  of  the  flask.  The  tube  d, 
on  the  other  hand,  ends  flush  at  the  interior 
surface  of  the  cap,  and  surrounds  the  glass  tube, 
as  shown  in  Fig.  85.  The  brass  tubes  are  pro- 
vided with  cocks,  /  and  u,  which  when  open 
afford  a  perfectly  free  passage  for  water,  and 
which  are  connected  with  the  arms,  g  and  h, 
whereby  they  may  be  opened  and  shut  with 
ease.  If  the  cocks  are  to  operate  simul- 
taneously, as  is  ususally  the  case, 
the  ends  of  the  arms  are  joined 
by  the  rods  i  and  k.  In  the 
position  shown  by  the  illustra- 
tion, both  cocks  are  closed ;  when 


PIG.  84. 


FIG.  85. 


i  is  raised,  both  are  opened.    In  order  to  prevent  any  mistake 


§  208.]  ANALYSIS   OF   MINERAL   WATERS.  227 

occurring  as  to  whether  the  cocks  are  open  or  shut,  the 
ends  of  the  arms  g  and  h  should  be  suitably  marked.  The 
tubes  ef  and  m  fit  air-tight  on  to  the  taps  and  are  fastened  in 
place  by  the  screws  n  and  o.  The  flask  is  enmeshed  by  a  white 
silk  net  to  which  are  fastened  a  weight,  p,  below,  and  a  knotted 
cord,  q,  above.  This  cord  allows  the  flask  to  be  immersed,  and 
also  serves  to  measure  the  depth  by  the  knots.  The  cord  r  is 
connected  with  the  arm  k,  while  another  cord,  s,  is  connected 
with  i\  the  upper  ends  of  these  cords  are  fastened  to  wooden 
rollers  which  are  marked  to  avoid  confusion. 

To  use  the  apparatus,  which  must  be  empty  and  clean,  close 
the  cocks  and  sink  it  in  the  well  to  the  required  depth.  While 
the  immersion  is  being  effected  by  the  operator,  whom  we  may 
designate  as  Q,  an  assistant,  S,  holds  the  cord  s,  while  a  second 
assistant,  R,  holds  the  cord  r,  loosely,  but  taking  care  that  the 
flask  does  not  rotate  on  its  axis  and  twist  the  cords.  After  the 
apparatus  has  been  immersed  for  some  time  and  the  water  has 
become  perfectly  still  again,  S  pulls  upon  the  cord  s  while  R  loosens 
his  hold  on  r.  The  cocks  are  thus  opened,  and  the  water  enters 
through  e'  e,  while  the  air  escapes  from  the  flask  through  the  cres- 
cent-shaped opening  and  m,  and  ascends  through  the  water  in  the 
form  of  large  bubbles;  when  these  cease  to  appear,  the  flask  is  full. 
R  now  pulls  on  r,  while  S  loosens  his  hold  on  s.  The  cocks  are 
thus  closed,  and  the  apparatus  is  then  drawn  up  by  q,  while  r  and 
s  are  held  loosely.  If  the  flask  has  been  properly  constructed  it 
will  be  found  to  be  completely  full,  and  will  show  no  bubbles  on 
being  inverted.  To  empty  it,  invert  the  apparatus,  place  a  bottle 
under  m,  and  open  the  cocks.* 

7.  To  determine  the  total  carbonic  acidfi  fill  each  of  the  weighed 
flasks  (§  207,  2)  containing  calcium  hydroxide,  or  calcium  hydrox- 

*  The  apparatus  used  by  me  has  the  f ollowing  dimensions :  Capacity  of 
the  flask,  600  c.c.;  internal  diameter  of  the  brass  tubes,  7  mm.;  bore  of  the 
cocks,  5  mm. ;  length  of  the  arms,  90  mm. ;  length  of  the  rods  connecting  the 
arms,  105  mm.;  weight  of  the  sinker,  2-5  kilos. 

f  Regarding  other  methods  of  determining  carbonic  acid  compare  §  139, 
i,  b,  /?.  The  method  here  described  is  exceedingly  simple,  and  is  superior 
to  all  others  in  point  of  exactness.  (Zeitschr.  f.  analyt.  Chem.,  n,  56.) 


228 


ANALYSIS    OF   WATER. 


[§  208. 


FIG 


ide  with  calcium  chloride,  almost  up  to  the  neck,  while  gently 
shaking  round  with  water  just  taken  from  the  well.  If  the  flask 
can  be  immersed  in  the  well,  provide  it  with  a  stopper  carrying 
two  glass  tubes  (Fig.  86)  and  submerge  it  in  such  a  manner  that 

the  water  enters  through  a  6, 
while  the  air  escapes  through 
c  d.  If  the  spring  issues  from  a 
narrow  bore  -  hole,  however,  a 
siphon  is  first  rinsed  out  with  some 
of  the  mineral  water,  and  then 
gradually  inserted,  so  that  it  may 
slowly  fill;  on  withdrawing  it, 
rapidly  dry  its  surface,  and  empty 
into  one  of  the  weighed  flasks. 
If  the  mineral  water  issues  from 
a  tube,  the  weighed  flask  (with 
the  calcium  hydroxide,  etc.)  is 
simply  held  under  the  stream. 

but  not  so  close  that  carbonic  acid,  which  often  (without  being 
absorbed  by  the  water)  flows  out,  can  get  into  the  flask.  When 
the  flasks  have  been  filled  as  described,  it  is  tightly  stoppered  with 
rubber  stoppers,  which  are  then  tied  down  with  parchment  paper. 
If  the  carbonic  acid  is  to  be  determined  in  water  obtained  as 
described  by  aid  of  the  apparatus,  Fig.  84,  from  the  bottom  of  a 
well,  and  which  may  hence  be  supersaturated  with  carbonic  acid, 
it  is  safest  to  use  the  whole  quantity  of  the  water  contained  in  the 
flask  a.  In  this  case  proceed  as  follows:  Introduce  an  excess 
of  carbonate-free  calcium  hydroxide  (or  a  weighed  quantity  of 
calcium  hydroxide  of  known  carbonate  content),  and  also,  if  neces- 
sary, a  quantity  of  calcium  chloride  more  than  sufficient  to  decom- 
pose any  sodium  carbonate  present,  into  a  flask  holding  half  again 
as  much  as  the  flask  a.  After  the  filled  flask  a  has  been  with- 
drawn from  the  well,  unscrew  the  connectors  i  and  k  (so  that  the 
cocks  may  be  operated  separately),  and  also  the  tube-joints  ra  and 
et  and  remove  the  small  quantities  of  water  that  remain  above  the 
-cocks.  Now  invert  the  flask  and  hold  it  obliquely  so  that  the  cock 


§  208.J  ANALYSIS    OF    MINERAL   WATERS.  229 

u  is  lowermost;  next  open  the  cock  u  and  allow  the  water  to  flow 
through  it  into  a  flask,  by  carefully  opening  the  cock  /  for  the  ad- 
mission of  air.  As  soon  as  about  one-fourth  of  the  contents  has 
run  out,  close  the  cocks,  close  the  flask  with  its  rubber  stopper, 
shake  it  gently  to  distribute  the  calcium  hydroxide  through  the 
water  and  to  effect  the  absorption  of  any  carbonic  acid  that  may 
have  been  disengaged  from  the  water  in  pouring  it  in  and  thus 
have  entered  the  flask.  Now  empty  the  remainder  of  the  water 
into  the  flask  as  described  above.  In  order  not  to  lose  any  car- 
bonic  acid  that  may  have  remained  behind  in  a,  introduce  into 
this  50  c.c.  of  lime-water  or  very  dilute  milk-of-lime,  shake  for 
some  time,  and  then  empty  into  the  lime  flask,  into  which  also-- 
empty the  water  with  which  a  is  to  be  rinsed;  the  flask  is  then, 
stoppered,  and  the  stopper  tied  down. 

The  capacity  of  a,  and  consequently  the  quantity  of  water 
employed  in  this  experiment  should  be  accurately  determined  by- 
measuring. 

As  the  quantity  of  free  carbonic  acid  dissolved  by  water  varies 
with  the  pressure,  it  is  hence  necessary  to  note  the  height  of  the 
barometer. 

8.  //  the  water  contains  hydrogen  sulphide,  determine  it  by  means 
of  standard  iodine  solution  ( §  207,  12)  according  to  the  directions- 
given  in  §  148,  I,  a.  If  the  water  contains  an  alkali  thiosulphater 
it  will,  of  course,  be  necessary  to  deduct  the  quantity  of  iodine 
solution  equivalent  to  the  thiosulphuric  acid  present  (and  which  is 
separately  determined),  from  the  total  iodine  solution  used,  in 
order  to  ascertain  how  much  has  been  used  up  by  the  hydrogen 
sulphide.  If  a  gravimetric  control  is  considered  desirable,  use  the 
method  employing  copper  solution  or  arsenous-acid  solution,  and 
described  in  §  148,  I,  c. 

Since  in  the  analysis  of  alkaline  waters  the  question  frequently 
arises  as  to  how  much  of  the  sulphur  compound  should  be  calcu- 
lated as  hydrogen  sulphide,  metallic  sulphide,  or  hydrosulphide 
respectively,  it  is  important  to  know  whether  the  whole  or  a  part 
of  the  sulphur  will  be  removed  from  the  water  on  passing  through 
it  a  current  of  some  indifferent  gas  for  some  time.  To  ascertain. 


230  ANALYSIS    OF   WATER.  [§  208- ' 

this,  pass  a  current  of  hydrogen  gas  which  has  been  passed  first 
through  a  concentrated  alkaline  solution  of  potassium  permanga- 
nate, and  then  through  potassa  solution,  through  a  measured 
volume  of  the  mineral  water  contained  in  a  flask  provided  with  a 
doubly  perforated  cork,  in  one  opening  of  which  is  inserted  a  tube 
reaching  to  the  bottom  of  the  flask  for  admitting  the  gas;  the 
•other  aperture  is  fitted  with  a  tube  bent  at  right  angles  and  ending 
flush  with  the  lower  surface  of  the  stopper.  As  soon  as  the  gas 
Issuing  no  longer  contains  the  least  trace  of  sulphur,  and  hence  no 
longer  decolorizes  a  small  quantity  of  very  weak  starch-iodide 
solution  (and  which  occurs  only  after  the  gas  has  been  passing  for 
some  hours) ,  break  off  the  current  of  hydrogen,  and  again  determine 
the  sulphur  remaining  in  the  mineral  water  thus  treated,  using 
as  before  a  solution  of  iodine,  copper,  or  arsenous  acid.  A  cool 
and  shady  place  should  be  selected  in  which  to  conduct  the  opera- 
tion of  passing  the  hydrogen  gas  through  the  mineral  water.  By 
the  simultaneous  use  of  an  air-pump,  the  removal  of  the  absorbed 
hydrogen  sulphide  is  greatly  facilitated. 

The  sulphur  compound  remaining  in  the  water  after  the  above- 
described  treatment  is,  in  the  case  of  mineral  waters  containing 
also  free  hydrogen  sulphide,  metallic  hydrosulphide.  Although 
this  method  of  deciding  the  question  (as  above  stated),  and  which 
is  also  recommended  by  W.  B.  and  E.  ROGERS,*  is  adapted  for 
use  in  the  case  of  waters  containing  hydrogen  sulphide  alone  or 
almost  exclusively  so,  but  no  thiosulphate,f  it  is  nevertheless 
unserviceable  for  sulphur  waters  containing  chiefly  soluble  metallic 
sulphide  or  hydrosulphides,  and  besides  these,  as  may  frequently 
be  the  case,  thiosulphates. 

In  such  waters  determine  the  sulphur  combined  with  the 
hydrogen  or  metal,  first  jointly,  best  by  means  of  a  cadmium 
solution,  which  is  at  least  as  sensitive  as  any  other  metal  solution 
(Expt.  No.  85),  and  is  not  affected  by  sodium  thiosulphate.  The 
cadmium  sulphide  precipitated  must  not  be  weighed  directly, 

*  Journ.  /.  prakt.  Chem.,  LXIV,  123. 

f  Comp.  FRESENIUS'S  Analysis  of  Weilbach  Mineral  Water,  Journ.  /.  prakt. 
Chem.,  LXX,  8;  also  of  the  Gnndbrunnen  at  Frankfort  a.  M.,  Jahresber.  des 
physikal.  Vereins  zu  Frankfurt  f.  1873  bis  1874,  S.  74. 


§  208.]  ANALYSIS   OF   MINERAL    WATERS.  231 

as  it  is  apt  to  contain  cadmium  chloride  (Expt.  No.  86),  hence  the 
sulphur  in  it  must  be  determined  according  to  §  148,  II,  A,  1  or  2. 
From  a  fresh  quantity  of  water  the  free  hydrogen  sulphide  is  now 
expelled,  and  then  that  combined  with  the  metal  as  hydrosulphide, 
both  being  determined  by  passing  the  gas  expelled  through  am- 
moniacal  silver-nitrate  solution;  the  sulphur  combined  with 
metal  as  a  monosulphide  is  then  determined  from  the  difference 
(if  no  disulphide  is  present). 

For  this  purpose  the  following  method  employed  by  SIMMLER  * 
in  his  exceedingly  careful  analysis  of  the  Stachelberg  mineral 
water  may  be  used :  First  expel  the  free  hydrogen  sulphide  from 
the  water  by  means  of  a  current  of  pure  hydrogen,  with  the  aid 
-of  an  air-pump,  then  pour  into  the  water  through  a  funnel-tube  a 
solution  of  manganous  sulphate,  and  remove  the  liberated  hydro- 
gen sulphide,  which  was  present  as  a  sulpho-a^id  combined  with 
a  metallic  sulphide. 

Filter  off  the  manganese  sulphide,  and  add  to  the  warm  filtrate 
a  solution  of  neutral  silver  nitrate — if  a  thiosulphate  is  present, 
a  precipitate  of  silver  sulphide,  containing  generally  also  silver 
chloride,  forms.  Collect  the  precipitate  on  a  filter,  remove  the 
silver  chloride  with  ammonia,  dissolve  the  washed  silver  sulphide 
in  nitric  acid,  and  determine  the  silver  in  the  solution  as  a  chloride, 
and  from  this  calculate  the  thiosulphuric  acid  (comp.  §  168). 
•Of  course  the  silver  in  the  silver  sulphide  need  not  be  determined 
at  the  well. 

The  precipitate  of  manganese  sulphide  filtered  off  contains  the 
sulphur  which  was  present  in  the  water  as  a  monosulphide.  If 
however,  the  water  contains  a  disulphide  (in  which  case  it  will 
have  a  yellowish  color  in  large  volumes),  the  manganous  sulphide 
is  added  to  the  sulphur  which  was  combined  with  the  monosulphide 
to  disulphide;  on  treating  the  precipitate  with  hydrochloric  acid, 
the  free  sulphur  remains  undissolved. 

For  the  details  of  the  process  and  description  of  the  apparatus 
employed  by  SIMMLER  for  expelling  the  hydrogen  sulphide,  I 
refer  to  the  author's  original  memoir  (loc.  cit.). 

*  Journ.  /.  prakt.  Chem.,  LXXI,  27. 


232  ANALYSIS   OF   WATER.  [§  208, 

9.  //  the  water  contains  a  rather  large  quantity  of  jerrous  carbonate, 
which  is  indicated  by  a  fairly  dark-violet  color  on  adding  gallic 
or  tannic   acid,   an  attempt  should  be  made  to  volumetrically 
determine  the  ferrous  salt  by  means  of   the   dilute  potassium- 
permanganate  solution  (§207,  16  comp.  also  Vol.  I,  p.  317).     For 
this  purpose  500  c.c.  of  the  water  are  used,  and  the  experiment 
performed  in  a  white  bottle  standing  on  a  sheet  of  white  paper. 
Some  dilute  sulphuric  acid  should  first  be  added  to  the  water. 

A  number  of  experiments  should  be  made  until  sufficiently 
constant  results  are  obtained.*  If  the  water  smells  of  hydrogen 
sulphide,  or  if  it  contains  any  notable  quantity  of  organic  matter, 
this  method  cannot  be  employ ed.f  In  the  case  of  waters  rich  in 
chlorides  the  results  will  be  too  high,  and  for  the  reasons  stated 
in  Vol.  I,  p.  319,  unless  the  precautions  there  given  are  observed.^ 

10.  To  determine  the  total  gases  held  in  solution  by  the  water, 
proceed  as  follows,  according  to  a  or  b,  as  the  water  is  poor  or  rich 
in  carbonic  acid: 

a.  For  water  poor  in  carbonic  acid.  Fill  a  globe,  Fig.  87,  with 
the  mineral  water,  and  sink  it,  thus  filled,  by  means  of  a  rod 

*  This  rapid  method  is  of  particularly  great  value,  as  by  means  of  it  the 
chemist  is  enabled  to  quickly  ascertain  the  quantity  of  ferrous  salt  which  the 
spring  loses  in  its  passage  first  to  the  reservoir  and  then  to  the  baths,  or 
how  much  is  lost  when  kept  for  a  shorter  or  longer  time  in  crocks.  The  iron 
determination  which  I  made  by  this  process  in  a  preliminary  examination  of 
the  Schwalbach  springs  corresponded  almost  exactly  with  the  results  obtained 
by  gravimetric  analysis.  This  method  is  also  serviceable  in  prospecting  the 
water  of  chalybeate  springs,  as  by  means  of  it  every  small  contributory  spring 
may  be  examined  at  the  spot  at  once  with  sufficient  accuracy. 

f  If  only  hydrogen  sulphide  is  present  with  the  ferrous  salt,  the  following 
modification,  which  I  have  not  tried,  however,  might  be  adopted :  Determine 
first  the  relation  between  solutions  of  iodine  and  also  potassium  perman- 
ganate with  respect  to  their  action  on  a  very  dilute  pure  hydrogen-sulphide 
water;  then  test  500  c.c.  of  the  mineral  water  with  iodine  solution,  and 
another  500  c.c.  with  the  permanganate  solution;  the  former  process  gives 
the  hydrogen  sulphide  present,  and  the  latter  gives  the  iron  contact  after 
deducting  from  the  c.c.  of  permanganate  solution  used  a  quantity  correspond- 
ing in  its  action  upon  the  hydrogen  sulphide  to  the  iodine  solution  used. 

%  The  characteristic  odor  usually  perceived  when  testing  acidulated  saline 
waters  with  permanganate  is  frequently  due  to  bromine  or  chlorine.  The 
odor  of  bromine  was  most  distinctly  observed  by  me  during  an  examination 
of  the  Elisabethenquelle  at  Homburg  v.  d.  H. 


208.] 


ANALYSIS    OF    MINERAL    WATERS. 


233 


or  attached  weights,  into  the  well;    then  empty  it  by  applying 

suction  to   a  gutta-percha  tube,  a,  reaching  to  the 

bottom  of  the  globe  until  the  mineral  water  in  this 

has  been  completely  replaced  by  fresh  water  from 

the  spring.      In  order  to  prevent  the  return  of  any 

water  in  the  tube  on  discontinuing  suction,  a  cock, 

b,  or  a  small  piece  of  rubber  tubing,  which  may  be 

closed  by  pressing  between  the  fingers,  is  made  use 

of.     Over  the  mouth  of  the  globe  is  tied  a  piece  of 

sheet  rubber,  the  elasticity  of  which  permits  the  tube 

to  be  inserted  laterally,  while  yet  completely  closing 

the  mouth  of  the  globe  when  the  tube  is  withdrawn. 

The  globe  just  filled  in  the  well  is  then  pulled  up 

out  of  the  water,  after  the  suction  tube  has  been 


FIG.  87.  FIG.  88. 

withdrawn,  and  immediately  connected  with  the  flask  of  a  so-called 
rubber  stop-cock,  a,  Fig.  88,*  which  is  filled  with  well-boiled  water, 
and  tightly  stoppered  (R.  BuNSEx).f 

*  Such  a  stop-cock  has  already  been  described  on  page  71,  this  vol. 
f  Gasometrische  Methoden,  2.  Aufl.,  18. 


234  ANALYSIS   OF    WATER.  [§   208. 

If  the  water  flows  from  a  pipe,  connect  this  with  a  rubber  tube, 
conduct  the  water  to  the  bottom  of  the  flask  and  let  it  run  in 
for  some  time,  and  finally  close  the  flask  with  the  rubber  stop- 
cock as  already  described. 

Now  connect  the  other  end  of  the  cock  a  with  the  tube  b, 
and  the  latter  again,  after  pouring  some  water  into  it,  with  the 
graduated  tube  c  by  means  of  another  rubber  stop-cock,  d.  The 
capacity  of  c  must  be  at  least  half  as  much  again  as  the  volume 
of  the  gas  held  in  solution  by  the  water,  and  measured  in  the  cold 
and  at  the  ordinary  pressure.  (Were  this  process  to  be  used  for 
waters  rich  in  carbonic  acid,  either  the  tube  c  would  have  to 
be  greatly  increased  in  size,  or  else  the  volume  of  water  taken 
would  have  to  be  so  small  that  it  would  render  it  imprac- 
ticable to  determine  the  other  gases  dissolved  in  the  water.) 

Incline  the  apparatus  so  that  some  of  the  water  enters  the 
bulb  6,  close  the  cock  a,  open  d,  and  boil  until  all  the  atmos- 
pheric acid  has  been  expelled  and  is  replaced  by  aqueous  vapor ; 
then  close  the  tube  e  by  means  of  a  ligature  or  compression  cock. 
When  the  apparatus  is  cold,  open  the  cock  a;  the  water  in  the 
globe  immediately  begins  to  boil,  while  the  gas  held  by  it  in 
solution  escapes  into  the  vacuum.  Now  warm  for  about  an 
hour  and  a  half  at  a  temperature  not  exceeding  90°  C.;  this 
will  keep  the  water  boiling  and  will  completely  expel  all  the 
gases  from  it.  Heat  the  globe  somewhat  more  strongly  until, 
from  the  greater  expansion  of  the  vapor,  the  boiled  water  just 
reaches  the  ligature  d.  The  instant  this  occurs,  tie  the  ligature, 
remove  the  tube  c  from  6,  and  open  it  under  mercury  by  loosening 
the  ligature  e;  now  note  the  state  of  the  barometer  and  thermome- 
ter, the  height  of  the  mercury  column  in  the  tube,  and  the  volume 
of  the  gas  obtained  (R.  BUNSEN  *).  If  a  graduated  tube,  c,  is  not 
at  hand,  one  not  graduated,  but  of  known  capacity,  may  be  used. 
As  soon  as  the  mercury  within  and  without  the  tube,  after  re- 
moving the  ligature,  stands  at  the  same  level,  the  ligature  is  again 
applied  and  the  mercury  within  the  tube  transferred  to  a  graduated 
cylinder,  where  it  is  measured  and  its  volume  deducted  from  that 

*  Gasometrische  Methoden,  2.  Aufl.,  18. 


§   208.J  ANALYSIS    OF    MINERAL    WATERS.  235 

of  the  known  capacity  of  the  tube;   the  difference  will  give  the 
volume  of  the  gas  expelled  from  the  water. 

As  it  may  be  inconvenient  to  transport  to  the  well  the  entire 
apparatus  necessary  for  the  actual  analysis  of  the  expelled  gases, 
it  is  better  to  take  the  latter  to  the  laboratory  in  sealed  tubes. 
For  this  purpose  replace  the  tubes  c  by  tubes  not  graduated,  but 
of  similar  form  and  drawn  out  at  each  end  near  the  thicker  part 
so  that  they  may  be  readily  sealed.  The  process  is  carried  out  as 
detailed  above,  and  after  the  gases  have  been  expelled  from  the 
water  by  boiling,  and  the  ligature  at  d  has  been  closed,  seal  the 
tubes  at  the  drawn-out  parts  by  means  of  a  blowpipe,  as  in  Fig. 
89,*  or  with  an  eolipile.  It  is  ad- 
visable to  fill  two  or  three  such  tubes 
with  the  gas  in  this  manner.  As  the 
total  volume  of  gas  in  a  definite 
quantity  of  water  has  already  been 
ascertained  by  the  first  experiment; 
it  is  immaterial  whether  the  tubes 
used  for  transporting  the  gas  to  the 
laboratory  contain  all  the  gas  ex- 
pelled from  the  water,  or  whether  a 
small  part  of  it  remains  in  the  globe. 

Instead  of  BUNSEN'S  method  other  ones  may  be  used. 
LOTHAR  MEYER  recommends  LUDWIG'S  apparatus  based  on  the 
principle  of  the  Toricellian  vacuum,f  and  as  described  by  NAW- 
ROCKI.J  He  employed  this  apparatus  in  an  analysis  of  the 
Landeck  thermal  springs. § 

HERBERT  McLEOD  |  heats  the  water  in  the  vacuum  obtained 
by  the  aid  of  a  SPRENGEL  mercury-pump. 

*  a  is  a  small  lamp  holding  about  3  grm.  of  oil,  and  connected  with  the 
blowpipe  by  a  somewhat  flexible  wire,  b,  through  a  loop  in  which  the  blowpipe 
tip  is  passed.  The  flame  may  be  readily  adjusted  by  bending  the  wire.  The 
<;ork  c  serves  as  a  mouthpiece,  so  that  the  whole  contrivance  may  be  held 
and  managed  with  the  teeth  alone. 

f  SETSCHENOW,  Wiener  Sitz.-Ber.,  xxxvi,  293;  SCHOFFER,  ibid.,  XLI,  589. 

t  Zeitschr.  f.  analyt.  Chem.,  n,  120. 

§  Ibid.,  n,  236. 

|  Journ.  Chem.  Soc.,  xxn,  307;  Zeitschr.  f.  analyt.  Chem.,  ix,  364. 


236  ANALYSIS    OF   WATER.  [§  208. 

These  methods  yield  very  good  results,  but  require  complicated 
apparatus  which  are  described  and  figured  in  the  Zeitschrift  fur 
analytische  Chemie  (loc.  cit.). 

b.  For  waters  rich  in  carbonic  acid.  For  such  waters  the  meth- 
ods detailed  under  a  are  not  suitable,  as  already  mentioned.  The 
escape  of  the  other  dissolved  gases  is  in  this  case  facilitated  by  the 
large  volume  of  carbonic-acid  gas  evolved,  hence  the  vacuum  may 
therefore  be  dispensed  with.  In  the  examination  of  such  waters 
I  use  the  following  method :  Fill  a  flask  of  about  500  c.c.  capacity 
with  the  mineral  water  in  the  manner  already  described,  then 
close  it  with  a  perforated  rubber  stopper  which  has  been  well 
kneaded  under  the  surface  of  the  mineral  water;  into 
the  perforation,  which  should  be  filled  with  water,  insert 
the  end  of  a  delivery  tube  which  has  been  entirely  filled 
with  the  water.  This  tube  is  bent  first  at  a  right  angle, 
then  at  an  obtuse;  the  end  of  the  long  downward  limb 
is  turned  upwards.  By  using  the  methods  detailed, 
it  is  an  easy  matter  to  obtain  the  flask  and  tube  com- 
pletely filled  with  water.  Now  place  the  flask  on  a 
wire  gauze  with  the  turned-up  end  of  the  tube  in  a 
dish  containing  a  well-boiled  solution  of  potassa,  sp. 
gr.  1  •  27,  and  with  the  tube  also  filled  with  the  same 
potassa  solution  inverted  over  the  orifice  of  the  tube. 
The  part  a,  Fig.  90,  holds  about  5  c.c. ;  on  the  part  b  is 
gummed  before  use  a  strip  of  paper  with  a  scale  marked 
on  it  showing  the  capacity  of  the  tube  in  c.c.  at  that 
part.  (The  scale  may  be  easily  and  rapidly  made  by 
allowing  water  to  run  from  a  burette  into  the  tube,  held 
inverted  until  it  has  just  reached  the  shoulder,  then  let 
1  c.c.  run  in,  and  make  a  mark;  run  in  a  second  c.c. 
and  make  another  mark,  etc.)  When  the  mouth  of 
the  tube  filled  with  the  potassa  solution  has  been 
brought  over  the  orifice  of  the  delivery  tube,  slowly 
FIG.  90.  nea"k  the  flask.  The  carbonic  acid  is  absorbed  by  the 
potassa  solution,  while  the  unabsorbed  gas  collects  in  a. 
Heat  gradually  to  boiling,  and  continue  until  the  volume  of  gas 


§  208.]  ANALYSIS    OF    MINERAL    WATERS.  237 

no  longer  increases.  Then  remove  the  tube,  allow  to  cool,  read 
off  the  volume  of  gas  on  the  scale,  having  due  regard  to  the 
prevailing  temperature  and  barometric  pressure,  and  fuse  off 
the  part  of  the  tube  a  by  means  of  the  blowpipe,  Fig.  89,  or  an 
eolipile,  for  removal  to  the  laboratory  where  the  gas  may  be 
further  examined.  Should  the  gas  not  reach  as  far  as  the  scale  at 
one  operation,  that  obtained  from  a  second  quantity  of  water 
is  emptied  into  the  same  tube.  It  is  advisable  to  fill  two  tubes 
in  this  manner.  The  error  incident  to  this  method  is  due  to 
two  facts:  First  the  volume  of  water  from  which  the  gas  is  ob- 
tained is  not  accurately  known  (since  on  warming  the  water  a 
portion  of  it  is  driven  into  the  tube  before  its  gas  has  been  expelled, 
and  although  strongly  heated  afterwards  affords  no  certainty  that 
all  its  gas  has  been  expelled);  second,  the  tension  of  the  water 
contained  in  the  potassa  cannot  be  accurately  calculated.  This 
error  is,  however,  far  smaller  than  when  small  quantities  of  highly 
aerated  water  are  treated  as  in  method  a,  and  scarcely  measurable 
quantities  of  unabsorbable  gas  obtained. 

11.  If  it  is  desired  to  accurately  ascertain  the  nature  of  the  gases 
spontaneously  evolved  from  the  spring,  collect  them  in  test-tubes  of 
from  40  to  60  c.c.  capacity,  connected  by  means  of  a  cork  or  rub- 
ber stopper  with  a  funnel,  as  shown  in  Fig.  91.  At  a  the  tubes 
are  to  be  narrowed  to  the  thickness  of  a  thin  straw.  For  col- 
lecting larger  quantities  of  gas,  use  is  made  of  bottles  with  drawn- 
out  necks  as  shown  in  Fig.  92.  After  the  tubes  or  bottles  have 
been  filled  with  the  mineral  water  and  connected  air-tight  with  the 
funnel  by  means-  of  the  cork  or  rubber  stopper,  submerge  the 
whole,  with  the  mouth  of  the  funnel  upwards,  in  the  mineral 
water,  and  by  means  of  a  narrow  tube  reaching  to  the  bottom  of 
the  tube  or  bottle,  suck  out  the  water  of  the  first  filling  (and 
which  had  been  in  contact  with  the  air),  until  certain  that  it 
has  been  replaced  by  a  fresh  quantity  which  has  not  been  ex- 
posed to  air.  Now  invert  the  apparatus  in  the  water  and 
allow  the  gas  spontaneously  disengaged  to  ascend  in  the  funnel. 
If  the  gas  bubbles  are  restrained  from  rising  in  the  neck  of  the 
funnel,  or  at  the  constricted  part  of  the  tube,  they  may  be 


238 


ANALYSIS    OF    WATER. 


[§   208. 


readily  dislodged   by   tapping   the   rim    of  the  funnel  against  a 
hard  body. 

Enough  gas  is  allowed  to  enter  to  fill  the  tube  and  the  neck 
of  the  funnel,  then  a  dish  is  slipped  beneath  the  funnel  and  the 
apparatus  lifted  out  of  the  water ;  the  constricted  part  of  the  tube 


FIG.  91. 


FIG.  92. 


is  then  gently  heated  to  remove  moisture  and  then  sealed.  As 
the  column  of  water  in  the  funnel  above  the  level  of  that  in  the 
dish  diminished  the  pressure  of  the  gas  against  that  of  the  atmos- 
phere, there  need  be  no  fear  that  the  glass  will  blow  out  in  sealing 
(R.  BUNSEN*).  The  warming  and  fusing  are  effected  by  means 
of  an  eolipile  or  blowpipe  (Fig.  89).  It  is  necessary  to  fill  several 
tubes  or  bottles  in  this  manner. 

If  the  nature  of  the  spring  renders  it  impossible  to  fill  the  tubes 
in  the  manner  described,  use  is  made  of  a  funnel  weighted  by  a 
leaden  ring,  c,  Fig.  93,  and  which  is  suspended  by  a  stout  string 
and  lowered  into  the  well  (R.  BUNSEN  f).  The  funnel  tube  is  con- 
nected by  a  rubber  tube  with  a  tin  tube,  a  6,  and  this  in  turn  with 
the  glass  tubes  c  c  c.  After  the  funnel  is  filled  with  water  by  suc- 

*  Gasometrische  Methoden,  2.  Aufl.,  3. 
f  Ibid.,  2.  Aufl.,  5. 


§  208.]  ANALYSIS   OF   MINERAL   WATERS.  239 

tion  up  to  the  cock  6,  allow  the  gas  to  ascend  in  the  funnel  until 
it  is  under  a  pressure  greater  than  that  of  the  atmosphere.  Then 
open  the  cock  b  and  allow  the  gas  to  pass  through  c  c  c  until  cer- 
tain that  all  the  air  has  been  expelled  and  replaced.  The  tubes 
c  c  c  are  of  from  40  to  60  c.c.  capacity,  and  those  parts  near  the 
ends  where  they  are  to  be  sealed  are  somewhat  thickened  and 
constricted;  they  are  connected  by  short  pieces  of  rubber  tubing. 


FIG.  93. 

After  being  filled  with  gas  from  the  spring,  they  are  warmed,  and 
the  two  outside  rubber  connectors  are  closed  air-tight  by  pressure 
between  the  fingers  or  by  a  clamp;  finally,  as  soon  as  the  tem- 
perature has  fallen  so  that  the  external  pressure  is  somewhat  greater 
than  that  within  the  tube,  they  are  fused  off  in  succession. 

Very  often  in  the  case  of  acidulous  waters  the  carbonic  acid 
predominates  to  such  an  extent  in  the  spontaneously  evolved  gas, 
that  a  large  number  of  tubes  must  be  filled  in  order  that  after 
absorption  of  the  carbonic  acid  by  potassa,  a  sufficient  quantity 
of  the  other  gases  (nitrogen,  marsh  gas,  oxygen)  may  be  obtained 
for  analysis.  In  the  case  of  such  wells  I  prefer  to  determine  at 
the  well  the  proportion  between  the  gases  absorbable  and  non- 
absorbable  by  potassa,  and  to  collect  only  the  latter  for  further 
investigation. 

To  effect  the  former,  fill  a  graduated  cylinder.  20  to  30  mm.  wide 
and  of  about  200  to  300  c.c.  capacity,  with  the  mineral  water  by 
sucking  out  with  a  glass  tube  the  water  first  entering,  and  then 
invert  it  in  the  basin  or  spring,  or  in  a  porcelain  dish  filled  with 


240  ANALYSIS    OF   WATER.  [§  208. 

the  mineral  water.  It  must  be  filled  entirely  with  the  gas;  in  the 
first  case  directly  so,  and  in  the  second  by  aid  of  the  above-described 
weighted  funnel  which,  in  this  case,  is  provided  with  a  rubber  tube 
and  gas-evolution  tube  instead  of  the  collecting  tubes.  Now 
remove  the  cylinder  from  the  well  with  the  aid  of  a  porcelain  dish, 
draw  off  almost  all  the  confining  water  in  the  dish  by  means  of  a 
pipette,  and  replace  it  by  well-boiled  potassa  solution;  then  agitate 
the  cylinder  to  favor  the  absorption  of  the  carbonic  acid.  When 
this  has  been  done,  read  off  the  volume  of  unabsorbed  gas,  paying 
due  regard  to  the  prevailing  temperature  and  pressure.  With 
many  wells  the  measurement  of  the  unabsorbed  gases  is  only 
possible,  even  when  large  cylinders  are  used,  when 
the  upper  part  of  these  is  constricted  as  shown 
in  Fig.  94. 

To  collect  the  unabsorbable  gases  alone,  I 
make  use  of  a  large  tin  funnel  (weighted  with 
a  leaden  ring),  the  narrow  stem  of  which  is 
connected  by  means  of  a  rubber  tube  with  a 
narrow  gas-delivery  tube.  This  tube  dips  into 
a  well-boiled  potassa  solution  contained  in  a  dish 
in  which  is  inverted  a  tube  having  the  form 
shown  in  Fig.  95.  The  rubber  tube  should  be 
provided  with  a  screw  pinch-cock,  which  should 
at  first  be  open.  When  certain  that  all  the  gas 
FlG  94  rising  from  the  funnel  is  perfectly  free  from 

atmospheric  air,  bring  the  end  of  the  gas-delivery  pIG.  95. 
tube  '  under  the  inverted  tube,  Fig.  95,  and  by  properly  ad- 
justing the  pinch-cock,  allow  the  gas  to  rise  regularly  in  small 
bubbles.  As  these  will  be  almost  entirely  absorbed,  it  will 
naturally  take  some  time  until  the  tube  is  filled  to  about  the 
point  a,  where  it  is  to  be  sealed  off  as  soon  as  this  has  taken 
place. 

12.  If  hydrogen  sulphide  is  evolved,  it  is  determined  by  filling 
a  large  flask,  with  neck  somewhat  elongated,  with  the  mineral 
water,  and  slipping  over  the  neck  a  wide  rubber  tube  cleaned  with 
soda-lye  and  provided  with  a  strong  pinch-cock.  In  the  other  end 


208.] 


ANALYSIS    OF    MINERAL    WATERS. 


241 


'of  the  tube  insert  a  funnel,  fill  it  also  with  the  water,  invert  the 
whole  under  the  surface  of  the  water,  and  collect  the  gases.  As  soon 
as  the  flask  is  filled,  close  the  pinch-cock,  hi  vert  the  flask  in  a  beaker 
containing  a  solution  of  cupric  chloride  with  ammonia  in  excess, 
open  the  pinch-cock,  allow  a  sufficient  quantity  of  the  solution  to 
enter  the  flask,  shake,  let  stand  for  some  time,  and  finally  deter- 
mine the  sulphur  in  the  copper  sulphide  filtered  off  (from  which 
the  volume  of  hydrogen  sulphide  may  be  calculated),  as  directed 
in  §  148,  II,  A,  2,  a.  On  deducting  the  volume  of  hydrogen  sul- 
phide so  found  from  the  gases  absorbed  by  potassa  solution  (as 
detailed  in  11)  the  volume  of  carbonic  acid  is  found. 

13.  For  determining  the  specific  gravity  of  highly  aerated 
mineral  waters,  a  bottle  as  shown  in  Fig.  96  may  be  used  with 
advantage.  Its  capacity  may  be  from  200  to 
300  c.c.,  and  its  neck,  as  shown  in  the  illustration, 
should  have  a  narrowed  part  about  50  mm. 
long  and  of  as  uniform  a  bore  as  possible,  its 
internal  diameter  to  be  from  5  to  6  mm.;  on 
this  constricted  part  should  be  scratched  or 
etched  a  millimetre  scale.  The  mouth  of  the 
bottle  must  be  perfectly  round,  so  that  it  may 
be  closed  air-tight  by  a  rubber  stopper.  In 
order  to  fill  the  bottle,  it  is  submerged  in  the 
liquid,  first  inserting  a  narrow  tube  in  order  to 
allow  the  air  to  escape;  the  bottle  is  thus  filled 
without  difficulty.  When  nearly  full,  the 
glass  tube,  which  has  meanwhile  been  withdrawn  in  proportion 
as  the  bottle  filled,  is  entirely  removed. 

As  soon  as  the  water  level  stands  at  about  the  middle  of  the 
elongated  neck,  close  the  mouth  under  water  with  the  thumb, 
remove  the  bottle,  and  immediately  insert  and  tie  down  the  stopper. 
Thus  prepared,  the  bottle  is  ready  to  be  transported.  It  is  well  to 
fill  three  or  four  such  bottles.  Each  should  be  separately  packed 
in  cardboard  in  order  to  prevent  breakage  during  transportation. 
In  default  of  such  bottles,  several  ordinary  narrow-necked  and 
ungraduated  prescription  bottles  should  be  filled. 


FIG.  96. 


242  ANALYSIS   OF   WATEB.  [§  209- 

14.  Attention  should  be  paid  to  every  particular  connected 
with  the  spring,  and  every  circumstance  that  may  have  a  bearing 
on  the  investigation;  for  instance,  as  to  how  much  water  and  free 
gas  the  spring  yields;  whether  these  quantities  remain  constant  at 
different  seasons  and  at  the  varying  water-levels  in  neighboring 
streams;  whether  the  level  in  the  spring  is  constant;  whether  a 
muddy  deposit  or  solid  sinter  forms  in  the  delivery  tubes  or  reser- 
voir (in  which  case  a  fairly  large  quantity  should  be  taken  for 
examination);  to  what  geological  formation  the  mountain  belongs 
on  which  the  spring  rises;  the  depth  of  the  spring;  the  character 
of  the  basin;  the  predominant  action  of  the  water,  etc. 

B.   OPERATIONS  IN  THE  LABORATORY. 

I.  Qualitative  Analysis. 

This  is  carried  out  in  the  manner  detailed  in  the  "Qualitative 
Analysis,"  §  211.* 

IL  Quantitative  Analysis. 

§209. 

The  course  to  pursue  in  the  quantitative  analysis  of  mineral 
waters  varies  according  to  the  absence  or  presence  of  alkali  car- 
bonates. As  the  analysis  is  simpler  in  the  case  of  alkaline  waters  (as 
those  containing  alkali  bicarbonates  are  termed),  we  will  first  con- 
sider the  methods  employed  for  these,  starting  with  the  assump- 
tion that  there  are  present  all  the  substances  which  are  usually 
found  in  alkaline  waters.  Thereafter  will  be  detailed  the  modi- 
fications required  in  mramifiing  saline  waters  and  sulphur  waters. 


DETERiaxiXG   THE  SPECIFIC  GRAVITY. 

a.  Water  Poor  in  Gas. 

In  such  a  case,  bring  a  bottle  of  the  mineral  water  and  a  bottle 
of  distilled  water  to  the  same  temperature  and  note  this.  Then 

*  Mineral  waters  which  have  been  kept  for  a  long  time  in  jugs  frequently 
have  an  odor  of  hydrogen  sulphide,  even  though  perfectly  free  from  this  odor 
when  fresh.  This  is  due  to  the  contact  of  the  moist  cork  or  other  organic  mat- 
ters with  the  sulphates,  whereby  a  part  of  these  is  reduced  to  sulphides,  and 
from  which  the  free  carbonic  acid  then  liberates  the  hydrogen  sulphide. 


§  209.J 


ANALYSIS    OF   MINERAL   WATERS. 


243 


fill  an  accurately  tared  bottle  of  at  least  100  grammes  capacity, 
and  provided  with  a  tightly-fitting  ground-glass  stopper,  first  with 
distilled  water,  and  weigh;  then  weigh  again  filled  with  the  min- 
eral water.  The  quotient  obtained  by  dividing 
the  weight  of  the  mineral  water  by  that  of  the 
distilled  water  gives  the  specific  gravity  of  the 
former.  It  is  preferable  to  use  a  pyknometer, 
Fig.  97 — a  bottle  with  a  long,  perforated,  tightly" 
fitting  ground  stopper.  Great  care  must  be  taken 
that  no  gas  bubbles  adhere  to  the  sides  of  the 
filled  bottles,  and  also  that  the  bottle  be  not 
warmed  by  the  hand  when  drying  it.  The  great- 
est certainty  against  any  inequality  of  tempera- 
ture  hi  the  liquids  to  be  weighed  is  afforded  by 
the  use  of  a  pyknometer  with  a  thermometer  pIG  g7 
ground  in. 

b.  Highly  Aerated  Water. 

With  such  waters  the  method  just  described  is  inapplicable, 
unless  a  part  of  the  carbonic  acid  has  first  been  expelled  from  the 
water.  It  is  evident,  however,  that  in  this  case  the  true  specific 
gravity  of  the  mineral  water  as  yielded  by  the  spring  will  not  be 
obtained,  and  that  analysts  will  obtain  varying  results.  The  specific 
gravity  of  such  a  water  is  determined  by  the  aid  of  the  flask  de- 
scribed hi  §  208,  13,  and  filled  as  there  directed. 

The  flask  is  placed  on  a  horizontal  support  in  a  room  of  fairly 
constant  temperature;  by  the  side  of  the  bottle  place  a  somewhat 
larger  bottle  filled  with  distilled  water  and  closed  by  a  perforated 
cork  bearing  a  thermometer  which  dips  into  the  water.  After 
twelve  hours  the  contents  of  both  bottles  will  certainly  have  the 
same  temperature.  Now  read  off  the  thermometer,  and  also  note 
the  height  of  the  mineral  water  on  the  scale,  which  is  best  done 
by  means  of  a  telescope  placed  horizontally,  6  to  8  feet  distant 
and  movable  up  or  down  on  a  vertical  rod. 

Now  weigh  the  bottle  with  its  stopper  on  a  sufficiently  delicate 
balance,  remove  the  stopper  without  wetting  it,  empty  the  bottle, 


244  ANALYSIS    OF    WATER.  [§  209. 

rinse  it  out,  fill  with  distilled  water  to  slightly  above  the  mark  at 
which  the  mineral  water  had  stood,  dry  the  flask  thoroughly,  and 
place  it  for  a  sufficient  length  of  tune  beside  the  other  bottle  con- 
taming  the  thermometer,  and  then  lower  the  level  in  the  neck  un- 
til it  is  at  exactly  the  same  height  as  when  filled  with  the  mineral 
water.  After  making  certain  that  the  temperature  has  remained 
the  same,  insert  the  stopper,  and  weigh.  On  deducting  the  weight 
of  the  empty  dry  bottle  and  its  stopper  (which  must  be  now  ascer- 
tained if  this  was  not  done  before)  from  both  of  the  two  weights 
obtained,  the  data  necessary  for  accurately  calculating  the  analysis 
of  the  mineral  water  are  obtained. 

If,  for  lack  of  bottles  of  the  above  description,  the  determina- 
tion is  to  be  made  with  narrow-necked  prescription  bottles,  mark 
three  fine  points  on  three  narrow  strips  of  paper,  and  gum  these 
on  the  neck  of  the  bottle,  to  take  the  place  of  the  scale.  The  pro- 
cess is  then  carried  out  in  the  manner  described. 

The  several  quantities  of  the  mineral  waters  required  for  the 
estimations  here  described  may  be  determined  directly  by  weight, 
or  by  measure,  in  which  case  multiplying  the  number  of  c.c.  by 
the  sp.  gr.  of  the  water  will  give  the  wreight.  I  prefer  to  weigh 
the  quantities,  as  then  they  are  quite  independent  of  the  tempera- 
ture, and  furthermore,  in  cases  where  it  is  important  the  entire 
contents  of  a  bottle  can  be  used,  or  quantities  of  water  can  be 
taken  weighing  a  round  number  of  grammes. 

1.  DETERMINING  THE  TOTAL  QUANTITY  OF  FIXED  CONSTITUENTS. 

For  this  purpose  carefully  evaporate  the  contents  of  a  small 
or  large  bottle  (say  from  200  to  2000  grm.  according  to  the  con- 
centration of  the  mineral  water)  in  a  weighed  platinum  dish  at  a 
temperature  below  the  boiling-point  of  the  liquid,  and  adding 
the  water  from  time  to  time  as  it  evaporates.  If  the  water  con- 
tains much  gas,  cover  it  with  a  large  watch-glass  when  beginning 
the  evaporation,  and  also  after  adding  each  fresh  portion.  The 
evaporation  is  most  safely  effected  on  a  water-bath,  nevertheless 
it  may  be  accomplished  also  over  the  small  naked  flame  of  a  lamp 


§  209.]  ANALYSIS    OF   MINERAL   WATERS.  245 

if  care  be  taken.  It  is  nevertheless  completed  on  a  water-bath, 
and  the  residue  dried  over  an  air-  or  oil-bath  at  180°  until  the 
weight  is  constant;  this  is  then  noted.  Now  fill  the  dish  half  full 
with  distilled  water,  add  from  time  to  tune  a  drop  of  hydrochloric 
acid,  keeping  the  dish  meanwhile  well  covered  with  a  large  watch- 
glass,  and  when  all  carbonates  have  been  decomposed,  warm  care- 
fully to  expel  the  liberated  carbonic  acid,  rinse  out  the  cover  into 
the  platinum  dish,  and  add  diluted  sulphuric  acid  sufficient  to 
convert  all  the  bases  into  sulphates,  avoiding,  however,  too  large 
an  excess.  Now  evaporate  to  dryness,  and  ignite  gently  for  some 
time,  while  every  now  and  then  adding  ammonium  carbonate  to 
convert  the  acid  sulphates  into  neutral  sulphates  (§  97,  1),  and 
until  the  weight  becomes  constant ;  this  then  note. 

If  there  remained  in  the  bottle  a  small  quantity  of  precipitate 
which  could  not  be  rinsed  out,  dissolve  it  in  a  little  nitric  acid, 
evaporate  the  solution  to  dryness,  and  ignite  and  treat  the  residue 
as  will  be  presently  detailed.  The  weight  so  obtained  must  be 
added  to  that  of  the  principal  residue. 

In  highly  ferruginous  waters  it  is  preferable  to  determine  the 
fixed  residue  in  such  bottles  in  which,  from  prolonged  action  of 
the  air  on  the  iron,  this  has  been  completely  precipitated  as  ferric 
hydroxide.  Filter  off  the  precipitate,  wash  it,  and  treat  the  filtrate 
as  detailed  above.  Dissolve  the  precipitate  in  nitric  acid;  if  any 
silicic  acid  remains  undissolved,  this  is  to  be  determined  and  its 
weight  added.  Evaporate  the  nitric-acid  solution,  ignite  the 
residue,  treat  it  with  water  and  ammonium  carbonate  to  convert 
any  small  quantities  of  caustic  lime  that  may  be  present  into  cal- 
cium carbonate,  heat  moderately  so  as  not  to  decompose  the  cal- 
cium carbonate  formed,  weigh,  and  add  the  weight  so  found  to 
that  of  the  contents  of  the  platinum  dish  dried  at  180°. 

This  mode  of  procedure  avoids  the  difficulty  arising  when, 
on  treating  the  residue  with  sulphuric  acid  and  igniting,  some 
magnesium  sulphate  is  prone  to  be  decomposed  if  the  heat  is  too 
strong;  while  if  insufficiently  heated,  on  the  other  hand,  some  sul- 
phuric acid  remains  behind  combined  with  the  iron. 

How  the  evaporation-residue   and  the  sulphates  into   which. 


246  ANALYSIS   OF   WATER.  [§  209. 

it  is  converted,  etc.,  are  used  to  control  the  analysis  will  be  de- 
scribed further  on. 

2.  DETERMINING  THE  CHLORINE,  BROMINE,  AND  IODINE. 

200  to  2000  grm.  of  the  water  are  taken,  according  to  the  chlo- 
rine content.  If  the  water  contains  relatively  much  chlorine, 
acidulate  it  with  nitric  acid,  precipitate  with  silver  nitrate,  and 
determine  the  precipitate  according  to  §  141,  1,  a,  as  silver  chloride 
containing  some  iodide,  or  convert  it  into  metallic  silver  by  ignition 
in  a  current  of  hydrogen  (§  115,  4,  a). 

Waters  which  contain  but  little  chlorine  should  be  evaporated 
down  to  about  one-fourth  before  adding  the  nitric  acid.  It  is 
then  filtered,  washed,  and  the  filtrate  treated  as  described. 

3.  DETERMINATION  OF  THE  SILICIC  ACID,  IRON,  MANGANESE,  ALU- 
MINIUM, CALCIUM  (TOGETHER  WITH  BARIUM  AND 
STRONTIUM)  AND  MAGNESIUM. 

Use  the  contents  of  one  or  more  bottles  for  this  purpose — say 
2000  to  7000  grm.  The  determinations,  especially  of  the  iron, 
can,  of  course,  be  correct  only  when  the  water  is  clear  and  free 
from  ochreous  flocks  (comp.  §  208,  6).  After  the  bottle  or  bottles 
have  been  weighed  smear  on  the  lip  a  very  thin  layer  of  tallow,  then 
carefully  pour  out  a  portion  of  the  contents  into  a  beaker,  avoid- 
ing the  loss  of  even  a  drop,  and  then  carefully  add  hydrochloric 
acid  in  slight  excess  to  the  contents  of  both  the  bottle  and  the 
beaker.  Now  evaporate  to  dryness  the  whole  of  the  water  in  one 
or  more  large  platinum  dishes,  finishing  on  a  water-bath  *  (§140, 
II,  a),  moisten  the  residue  with  hydrochloric  acid,  add  a  little 
water  after  some  time,  warm,  filter  off  the  undissolved  silicic  acid, 
and  wash  and  weigh  it.  After  the  weighing  treat  it  with  pure 
ammonium  fluoride  or  pure  hydrofluoric  acid  and  sulphuric  acid. 
Any  non-volatile  residue  (small  quantities  of  barium  sulphate  or 
titanic  acid)f  must  be  taken  into  account.  Now  precipitate  the  fil- 

*  If  porcelain  dishes  are  used  for  the  evaporation  the  silicic-acid  determi- 
nation will  be  less  reliable,  while  that  of  the  alumina  will  be  totally  valueless. 
•j-  In  order  to  further  test  a  residue  of  this  kind,  fuse  it  with  a  little  potas- 


I  209.]  ANALYSIS   OF   MINERAL   WATERS.  247 

trate  from  the  silicic  acid  with  ammonia  (best  in  a  large  platinum 
dish),  warm  the  whole,  and  collect  the  precipitate  and  wash  it. 
Dissolve  the  greater  part  of  the  ferric  hydroxide,  of  which  the  pre- 
cipitate consists,  in  hydrochloric  acid,  then  neutralize  with  a  dilute 
ammonium-carbonate  solution  almost  to  the  point  of  turbidity, 
boil,  and  filter  off  from  the  precipitate,  now  free  from  manganese 
and  alkaline  earths.  If  ammonia  produces  traces  of  a  precipitate 
in  the  filtrate,  collect  this  separately  on  a  filter,  dissolve  in  a  very 
little  hydrochloric  acid,  reprecipitate  with  ammonia,  and  collect 
again  by  filtration.  Add  the  filtrate  to  that  first  obtained. 

Now  dissolve  the  larger  precipitate  of  basic  ferric  salt,  as  well 
as  that  subsequently  obtained  with  ammonia,  in  hydrochloric  acid, 
add  to  the  solution  a  little  chemically  pure  potassium  bitartrate 
(the  bitartrate  frequently  contains  alumina),  then  some  ammonia, 
and  precipitate  the  iron  from  the  clear  solution  by  means  of  am- 
monium sulphide  in  a  flask,  which  must  be  nearly  filled  and  kept 
closed,  and  thus  separated  from  alumina  and  phosphoric  acid. 
Dissolve  the  sulphide  in  hydrochloric  acid,  oxidize  the  solution 
with  nitric  acid,  precipitate  with  ammonia,  and  ignite  and  weigh 
the  ferric  oxide  so  obtained.  After  weighing  dissolve  the  oxide 
in  fuming  hydrochloric  acid  to  ascertain  if  there  is  any  residue 
left  other  than  that  due  to  the  filter  ash.  In  case  there  is  (silicic 
acid),  its  weight  must  be  deducted  from  that  of  the  ferric  oxide. 

Evaporate  to  dryness  the  filtrate  from  the  iron  sulphide  in  a 
platinum  dish  with  the  addition  of  some  solution  of  sodium  car- 
bonate perfectly  free  from  alumina  (and  obtained  by  saturating 
with  carbonic  acid  and  filtering  after  standing  for  a  long  time); 
heat  the  residue  with  a  little  pure  potassium  nitrate,  soften  with 
water,  transfer  to  a  beaker,  dissolve  in  hydrochloric  acid,  filter, 
and  precipitate  with  ammonia;  there  are  usually  obtained  a  few 
flocks  of  aluminium  phosphate;  and  that  this  is  the  case  is  shown 
by  the  fact  that  ammonium  molybdate  gives  a  further  precipitate 
with  the  phosphoric  acid  in  the  filtrate,  as  usually  happens.  If 

shim  bisulphate,  treat  the  melt  with  cold  water,  and  filter.  Titanic  acid  goes 
into  solution,  and  precipitates  out  on  prolonged  boiling;  barium  sulphate 
remains  undissolved. 


248  ANALYSIS    OF   WATER.  [§  209- 

this  is  not  the  case,  the  phosphoric  acid  must  be  determined  in. 
the  weighed  alumina  precipitate. 

Slightly  acidulate  the  filtrate  (containing  the  manganese,  cal- 
cium, and  magnesium)  with  hydrochloric  acid,  concentrate,  and 
precipitate  the  manganese  with  ammonium  sulphide.  Allow  the 
nearly  filled  and  stoppered  flask  to  remain  at  rest  for  twenty-four 
hours  in  a  moderately  warm  place,  then  filter  off  the  precipitate, 
wash  it,  dissolve  again  in  hydrochloric  acid,  and  reprecipitate  as 
before  with  ammonium  sulphide.  Finally,  mix  the  manganese  sul- 
phide with  sulphur,  ignite  in  a  current  of  hydrogen,  and  weigh  as 
such;  it  must  be  tested  as  to  its  purity  (§  109,  2). 

Heat  the  filtrate  with  hydrochloric  acid,  evaporate,  filter  off 
from  the  sulphur,  and  precipitate  the  calcium  (together  with  the 
strontium)  with  ammonia  and  ammonium  oxalate.  After  the 
precipitate  has  subsided  collect  it,  wash,  dry,  ignite,  dissolve  the 
residue  in  hydrochloric  acid,  reprecipitate  with  ammonia  and  am- 
monium oxalate,  allow  to  deposit,  collect  again,  and  for  the  pur- 
pose of  weighing  finally  convert  the  calcium  oxalate  into  either 
calcium  carbonate,  calcium  oxide,  or  calcium  sulphate  (§  103.  2, 
b  and  §  154,  6).  As  a  rule  it  contains  strontium,  which,  after  it 
has  been  determined  (as  carbonate,  oxide,  or  sulphate,  as  in  6) 
must  be  deducted  from  the  weight  of  the  calcium  compound  in 
order  to  ascertain  the  true  weight  of  the  calcium  salt. 

Evaporate  the  united  filtrates  to  dryness,  drive  off  the  am- 
monia salts  by  igniting  the  residue  in  a  platinum  dish,  moisten 
with  hydrochloric  acid,  evaporate  to  dryness  on  a  water-bath, 
take  up  with  hydrochloric  acid  and  water,  and  after  ascertaining 
by  testing  a  small  portion  of  the  liquid  that  lime  is  absent  (with 
ammonia  and  ammonium  oxalate),  return  the  small  quantity  of 
liquid  used  in  making  the  test  and  precipitate  the  magnesium 
with  sodium-ammonium  phosphate  and  ammonia,  and  weigh  it 
finally  as  magnesium  pyrophosphate  (§  104,  2). 

If  the  mineral  water  is  so  rich  in  calcium  and  magnesium  that 
2000  to  7000  grm.  would  yield  too  large  a  precipitate,  the  filtrate 
freed  from  the  manganese  and  also  the  sulphur  from  the  excess 
of  ammonium  sulphide,  is  heated,  evaporated,  and  made  up  to 


§  209.]  ANALYSIS    OF    MINERAL    WATERS.  249 

1  litre,  of  which  then  an  aliquot  part,  one-half  or  one-quarter,  is 
used  for  the  determination  of  the  calcium  and  magnesium. 

4.  DETERMINATION  OF  THE  SULPHURIC  ACID,  SODIUM,  AND 
POTASSIUM. 

Acidulate  with  hydrochlroic  acid  2000  to  4000  grm.,  or  the 
contents  of  one  or  two  bottles,  of  the  water,  evaporate,  and  sep- 
arate the  silicic  acid  as  in  3.  The  filtrate,  which  must  not  con- 
tain a  large  excess  of  hydrochloric  acid,  is  then  precipitated  hot 
by  cautiously  adding  barium  chloride.  The  precipitate  of  barium 
sulphate  is  first  weighed  as  it  is,  then  warmed  with  hydrochloric  acid 
and  washed.  Add  a  few  drops  of  barium-chloride  solution  to  the 
acid  washings,  evaporate  almost  to  dryness,  add  some  water,  filter, 
collect  the  slight  quantity  of  barium  sulphate  so  obtained,  and  add 
it  to  the  main  bulk,  and  again  weigh  (§132,  1).  The  weight  so 
obtained  is  to  be  considered  as  correct,  and  from  it  the  sulphuric 
add  should  be  calculated.  If  a  weighable  quantity  of  barium  sul- 
phate is  found  with  the  silicic  acid  it  must  be  added  to  the  main  bulk. 

Evaporate  the  filtrate  from  the  barium  sulphate  to  dryness 
on  a  water-bath,  take  up  the  residue  with  water,  and  boil  the  solu- 
tion with  a  slight  excess  of  milk-of-lime  (§  153,  4,  a,  /?).  Filter , 
precipitate  the  filtrate  with  ammonium  carbonate  and  ammonia, 
and  finally  add  a  little  ammonium  oxalate.  Evaporate  to  dryness 
the  filtrate  from  the  precipitate  so  obtained,  drive  off  the  am- 
monia salts  by  ignition  in  a  platinum  dish,  and  repeat  the  opera- 
tion to  effect  the  separation  of  the  magnesium  (which  is  still  pres- 
ent in  slight  quantities),  using,  however,  carefully  measured  quan- 
tities of  the  reagents.  After  expelling  the  ammonia  salts  by  gen- 
tly igniting,  the  alkali  chlorides  are  finally  weighed  in  a  covered 
platinum  dish. 

In  order  to  separate  the  potassium  chloride  from  the  sodium 
chloride  and  the  small  quantity  of  lithium  chloride  present,  con- 
vert them  all  into  double  platinum  salts  by  adding  platinic  chlo- 
ride, treat  with  80-per  cent,  alcohol,  filter,  wash  with  alcohol 
( §  152,  1,  a),  and  dry  on  the  filter.  Transfer  the  potassium-platinum 
chloride  to  a  small  weighed  platinum  dish;  dissolve  the  remainder 


250  ANALYSIS    OF    WATER.  [§  209. 

on  the  filter  with  boiling  water,  evaporate  the  whole  to  dryness, 
dry  at  130°,  and  weigh  as  potassium-platinum  chloride.  In  order 
to  ascertain  if  this  is  pure,  treat  it  repeatedly  with  small  quantities 
of  cold  water,  pour  the  solution  into  a  porcelain  dish,  add  some 
platinic  chloride,  evaporate  almost  to  dryness  on  a  water-bath, 
treat  with  alcohol,  filter,  dissolve  the  small  quantity  of  residual 
potassium-platinum  chloride  on  the  filter  in  some  boiling  water 
(after  first  washing  it  with  alcohol  and  drying  the  filter),  and  evap- 
orate together  with  the  main  quantity  of  potassium-platinum 
chloride,  dry  at  130°,  and  weigh.  If  the  weight  is  not  the  same 
as  that  at  first  obtained,  it  shows  that  the  potassium-platinum 
chloride  first  obtained  contained  some  lithium-  or  sodium-platinum 
chloride.  The  last  weighing  is  taken  as  the  correct  one,  and  the 
potassium  calculated  from  it.  The  quantity  of  sodium  chloride, 
and  consequently  that  of  the  sodium,  is  found  by  subtracting  the 
weight  of  the  potassium  chloride  from  the  total  weights  of  the 
alkali  chloride  after  deducting  that  of  the  lithium  chloride  (the 
method  of  estimating  which  will  be  given  further  on). 

In  order  to  be  quite  certain  that  the  alkali  chlorides  contain 
no  traces  of  alkaline  earths,  evaporate  the  solution  of  the  sodium- 
lithium-platinum  chloride  to  dryness,  heat  the  residue  in  a  cur- 
rent of  hydrogen,  treat  with  hydrochloric  acid  and  water,  filter 
off  the  liquid  from  the  metallic  platinum,  and  test  it  first  witn 
sulphuric  acid  for  barium,  then  with  ammonium  and  ammonium 
oxalate  for  calcium,  and  finally  with  sodium-ammonium  phos- 
phate for  magnesium.  If  traces  of  the  alkaline  earths  are  still 
found,  they  are  to  be  determined  and  their  weight  m  the  form  of 
chlorides  deducted  from  that  of  the  total  alkali  chlorides. 

The  amount  of  the  alkalies  combined  with  carbonic  acid  is  de- 
termined indirectly  with  perfect  accuracy  by  calculation  of  the 
results  of  the  analysis,  provided,  of  course,  that  this  has  been  care- 
fully made.  Of  the  direct  methods  which  may  be  advantageously 
used  in  a  preliminary  examination  of  alkaline  waters,  I  recom- 
mend the  following: 

Boil  600  to  800  grm.  of  the  water  for  a  long  time,  filter,  and 
wash  the  precipitate  with  hot  water.  Divide  the  filtrate  mixed 


§  209.]  ANALYSIS    OF    MINERAL    WATERS.  251 

with  the  washings  into  two  equal  portions  (or  at  least  into  aliquot 
parts),  concentrate  one  portion,  and  in  it  volumetrically  determine 
the  alkali  carbonate  (together  with  the  trace  of  calcium  and  the 
small  quantity  of  magnesium  present  in  it)  according  to  §  220; 
the  other  portion  is  used  to  determine  the  calcium  and  magnesium, 
in  order  to  correct  the  result  obtained  with  the  first  portion,  as 
calcium  carbonate  and  magnesium  carbonate  neutralize  acids  in 
the  same  way  as  the  equivalent  quantity  of  sodium  carbonate. 

5.  DETERMINATION  OF  THE  TOTAL  CARBONIC  ACID.* 
The  flasks  previously  prepared  at  the  spring  (§  208,  7)  serve 
for  this  purpose.  Weigh  them,  and,  if  but  a  short  time  has  elapsed 
between  the  filling  and  the  analysis,  heat  them  for  some  time  in  a 
water-bath  (§  139,  I,  6,  a);  if,  however,  they  have  already  stood 
for  a  long  time  filled,  the  heating  is  unnecessary.  Filter  as  much 
as  possible  of  the  clear  liquid  through  a  small  folded  filter  t  with- 
out disturbing  the  precipitate,  and,  without  washing  the  filter, 
introduce  it  into  the  flask  containing  the  precipitate  and  the  re- 
mainder of  the  liquid;  then  determine  the  carbonic  acid  according 
to  §  139,  II,  e.  In  the  case  of  waters  rich  in  carbonic  acid,  and 
particularly  if  many  determinations  have  to  be  made,  the  carbonic 
acid  may  be  collected  hi  weighed  GEISSLER'S  potash  bulbs  (Fig. 
46),  with  a  soda-lime  tube  placed  behind  them.  The  frequent 
filling  of  the  soda-lime  tubes  is  avoided  by  renewing  the  potassa 
solution  after  every  second  operation.  The  results  obtained  leave 
nothing  to  be  desired  (Expl.  No.  87).  If  the  water  from  which 
the  calcium-containing  precipitate  is  obtained  has  been  measured, 
multiply  the  number  of  c.c.  taken  by  the  specific  gravity  to  obtain 
the  weight  in  grammes  of  the  water  corresponding  to  the  carbonic 
acid  found. 

If  the  carbonic  acid  is  to  be  determined  hi  mineral  waters 
contained  in  bottles  or  jugs,  a  loss  of  carbonic  acid  will  be  una- 

*  See  also  the  exhaustive  paper  on  The  Estimation  of  Carbonic  Acid  in 
Water,  by  Jos.  W.  ELLMS  and  JAY  C.  BENEKER,  Jour.  Amer.  Chem.  Soc., 
xxiii.  No.  6.— Translator. 

f  The  liquid  must  be  strongly  alkaline,  and  must  remain  clear  on  adding 
calcium  chloride. 


252 


ANALYSIS    OF    WATER. 


[§  209. 


voidable  on  drawing  the  corks,  and  particularly  if  the  water  i& 
highly  charged  with  the  gas.  In  such  cases  it  is  first  necessary 
to  determine  the  carbonic  acid  which  escapes  on  drawing  the  cork, 
and  then  to  determine  that  remaining  dissolved  in  the  water.  Of 
the  many  methods  of  boring  the  stopper  without  loss  of  gas,  that 
of  FR.  ROCHLEDER*  is  the  simplest  (Fig.  98).  a  is  a  cork-borer 
with  a  hole,  b,  in  the  side;  the  upper  aperture 
of  the  borer  is  closed  by  a  stopper  in  which  is 
inserted,  air-tight,  a  tube  c.  On  introducing 
the  borer  into  the  cork,  a  short  section  projects 
below  the  lower  side  of  the  cork  without  allow- 
ing any  gas  to  escape.  Now  connect  the  tube 
c  with  an  apparatus  for  drying  and  collecting 
carbonic  acid  (described  in  Vol.  I.,  p.  493,  e), 
by  means  of  a  short  rubber  tube  provided  with 
a  screw  pinch-cock,  then  slowly  turn  the  borer 
downwards.  As  soon  as  the  opening,  b,  passes 
the  cork,  the  gas  begins  to  issue  from  the  bottle, 
the  stream  being  regulated  by  the  pinch-cock. 
When  no  more  gas  issues,  remove  the  bottle  or 
jug,  and  draw  air,  freed  from  carbonic  acid, 
through  the  tubes.  The  increase  in  weight  of 
the  absorption  apparatus  gives,  together  with 
the  weight  of  the  gas  in  the  upper  part  of  the 
bottle,  the  carbonic  acid  lost  by  the  water  on  removal  of  the 
pressure.  Immediately  after  disconnecting  the  bottle  from  the 
apparatus,  siphon  off  the  water  from  it,  and  determine  the  carbonic 
acid  in  the  water  according  to  §  139,  I,  6,  a. 

6.  DETERMINATION  OF  THE  IODINE,  BROMINE,  LITHIUM,  BARIUM, 

AND  STRONTIUM.! 

Evaporate  the  contents  of  a  carboy  (about  60  litres)  in  a  tinned 
copper  or  polished  iron  vessel  to  about  4  or  5  litres,  filter  off  the 

*  Zeitschr.  f.  analyt.  Chem.,  i,  20. 

f  If  the  quantities  of  manganese  or  aluminium  present  are  so  small  that 
they  could  not  be  determined  in  the  water  used  in  3,  they  must  be  determined 
in  this  larger  quantity;  and  so  must  also  bases  and  acids  (oxides  of  cassium,. 


§  209.]  ANALYSIS   OF   MINERAL  WATERS.  253 

alkaline  liquid,  and  wash  the  residue  with  boiling  water  until  the 
washings  cease  to  have  an  alkaline  reaction.  For  the  sake  of 
safety,  the  residue  is  examined  spectroscopically  to  see  that  it  no 
longer  gives  the  lithium  lines. 

The  solution  A  serves  for  the  determination  of  the  iodine,  bro- 
mine, and  lithium;  the  residue  B  for  the  determination  of  the 
aluminium,  manganese,  barium,  and  strontium. 

A.  The  Aqueous  Solution. 

Evaporate  it  until  only  a  moist  saLne  mass  remains,  and  while 
triturating  with  a  pestle,  add  a  considerable  quantity  96-per  cent, 
alcohol.  Filter,  and  boil  the  residue  thrice  with  alcohol  of  the 
same  strength.  Add  two  drops  of  strong  potassa  solution  to  the 
alcoholic  solution  and  distil  off  the  alcohol.  Dissolve  the  residue 
so  obtained  in  a  little  water,  evaporate  again  until  only  a  moist 
saline  mass  is  obtained,  and  repeat  the  treatment  with  96-per 
cent,  alcohol  as  above.  Again  distil  off  the  alcohol,  and  repeat 
the  treatment  of  the  residue  once  more  as  before. 

By  this  treatment  there  is  finally  obtained  an  alcoholic  solution 
containing  all  the  iodine  and  bromine  and  but  a  smah1  quantity 
of  alkali  chlorides.  Add  to  the  solution  two  drops  of  potassa  solu- 
tion, evaporate  to  dryness  in  a  platinum  dish,  gently  ignite  the 
residue,*  and  completely  extract  with  boiling  water.  If  the  solu- 
tion still  has  a  brownish  color,  again  add  two  drops  of  potassa 
solution  and  a  very  small  quantity  of  potassium  nitrate,  evaporate, 
and  again  gently  ignite  the  residue.  On  now  extracting,  a  clear, 
colorless  solution  will  be  obtained. 

To  this  solution  add  carbon  disulphide,  acidulate  with  diluted 
sulphuric  acid,  cautiously  add  a  small  quantity  of  a  sulphuric- 
rubidium,  zinc,  nickel,  cobalt,  copper,  lead,  thallium,  and  antimony,  and  boric, 
arsenous,  arsenic,  and  titanic  acids),  if  such  are  present  in  quantity  sufficient 
to  render  their  determination  possible,  and  if  sufficiently  large  supplies  of 
water  are  not  available. 

*  If  the  residue  is  very  strongly  ignited,  considerable  iodine  may  be  lost 
in  consequence  of  the  decomposing  action  of  the  chlorides  on  potassium 
iodide  (UBALDINI,  Compt.  rend.,  XLIX,  306;  Journ.  f.  prakt.  Chem.,  LXXXIV, 
191),  whereas  by  gentty  igniting  in  the  presence  of  potassium  hydroxide  there 
is  no  loss  of  iodine.  Compare  FRESENIUS,  Zeitschr.  /.  analyt.  Chem.,  v,  318. 


254  ANALYSIS   OF   WATER.  [§  209. 

acid  solution  of  nitrous  acid,  and  shake;  the  carbon  disulphide 
will  take  up  the  iodine  and  become  violet-colored.  It  is  separated 
from  the  aqueous  liquid,  washed,  and  the  iodine  determined  in  it 
by  means  of  a  very  dilute  sodium-thiosulphate  solution  of  known 
strength  (§  145,  I,  b,  /?).  From  the  liquid  separated  from  carbon 
disulphide  precipitate  the  bromine  and  chlorine  as  silver  salts, 
and  determine  the  bromine  from  the  loss  in  weight  on  heating  a 
weighed  portion  of  the  mixed  silver  bromide  and  chloride  in  a  cur- 
rent of  chlorine  (§  169,  I,  a). 

Precipitate  the  excess  of  silver  in  the  filtrate  from  the  mixed 
silver  bromide  and  chloride  by  means  of  hydrochloric  acid,  and 
reserve  the  filtrate. 

To  determine  the  lithium  (and  some  other  substances  present 
in  small  quantities  in  the  aqueous  solution  A)  there  are  used:  a, 
the  three  saline  residues  insoluble  in  alcohol;  /?,  both  filters  (these 
must  be  incinerated)  through  which  the  solutions  freed  from  organic 
matter  and  containing  the  iodides,  bromides,  and  chlorides  had 
been  filtered;  and  f,  the  solution  from  which  the  excess  of  silver 
had  been  precipitated  by  hydrochloric  acid. 

These  are  all  mixed,  some  water  added,  then  hydrochloric  acid 
in  slight  excess,  filtered  (if  necessary)  into  a  flask  of  one  or  two 
litres  capacity,  filled  up  to  the  mark  and  shaken  (the  silicic  acid 
filtered  off  may  contain  some  titanic  acid). 

To  determine  the  lithium,  an  aliquot  part  of  the  solution  is 
used;  the  quantity  taken  depends  upon  the  quantity  of  lithium 
present,  this  being  approximately  ascertained  by  evaporating 
a  small  quantity  of  the  original  water  and  examining  spectro- 
scopically.  As  a  rule  one-fourth  of  the  solution  is  sufficient, 
corresponding  to  about  15  litres  of  water.  In  this  portion  the 
caesium,  rubidium,  and  thallium  may  also  be  tested  for.  The 
remainder  of  the  liquid  is  reserved  for  the  detection  or  estima- 
tion of  boric  acid,  and  also  for  the  detection  of  arsenic. 

a.  Evaporate  almost  to  dryness  the  measured  portion  of  the 
solution  for  determining  the  lithium.  Triturate  the  residue  with 
a  sufficient  quantity  of  strong  alcohol,  filter,  and  repeatedly  boil 
the  residue  with  small  quantities  of  strong  alcohol  until  neither 


§  209.]  ANALYSIS   OF   MINERAL   WATERS.  255 

the  residue  of  sodium  chloride  nor  the  residue  from  the  last  alco- 
holic extract  gives  the  lithium  spectrum.  Distil  off  the  alcohol 
from  the  alcoholic  solution,  add  two  drops  of  hydrochloric  acid 
to  the  residue,  dissolve  it  in  water,  and  evaporate  to  a  moist  saline 
mass;  repeat  the  treatment  with  strong  alcohol,  distil  off  again, 
and  treat  this  residue  exactly  like  the  original  one.  The  last  time 
add  to  the  alcohol  half  its  volume  of  ether.  The  residue  should 
always  be  examined  spectroscopically  to  see  that  it  is  free  from 
lithium.  If  any  is  still  found,  the  treatment  with  boiling  alcohol 
must  be  continued. 

Distil  off  the  ether-alcoholic  solution,  moisten  the  residue  with 
a  little  water,  add  a  little  hydrochloric  acid,  evaporate  to  dryness 
in  a  porcelain  dish  on  a  water-bath,  take  up  with  water,  and,  hi 
order  to  remove  any  phosphoric  acid  that  may  have  been  taken  up 
by  the  water,  add  two  drops  ferric-chloride  solution,  then  milk- 
of-lime  in  slight  excess,  boil,  filter  off  the  precipitate  (consisting 
chiefly  of  magnesium  hydroxide),  and  wash  it  with  boiling  water 
until  it  no  longer  gives  a  lithium  reaction.  To  the  filtrate  add 
ammonium  oxalate,  wash  and  ignite  the  precipitate,  dissolve  it  in 
hydrochloric  acid,  evaporate,  and  test  a  small  portion  of  the  resi- 
due spectroscopically  for  lithium.  If  this  is  still  found  to  be  pres- 
ent, dissolve  the  residue  hi  water,  and  again  precipitate  with  am- 
monia and  ammonium  oxalate. 

Evaporate  to  dryness  the  filtrate  (or  both  filtrates)  from  the 
calcium  oxalate,  drive  off  the  ammonia  salts,  moisten  the  residue 
with  hydrochloric  acid,  add  a  little  water,  evaporate  to  dryness 
on  a  water-bath,  and  repeat  the  treatment  with  milk-of-lime,  etc., 
using  small,  very  carefully  measured  quantities  of  reagents,  and 
frequently  testing  the  precipitates  for  lithium.  After  repeatedly 
driving  off  the  ammonia  salts,  moistening  with  hydrochloric  acid, 
and  evaporating  on  the  water-bath,  precipitate  the  lithium  finally 
as  lithium  phosphate  (§  100),  weigh  it,  and  test  it  to  see  if  it  dis- 
solves in  hydrochloric  acid  without  leaving  a  residue,  and  whether 
the  solution,  somewhat  diluted,  yields  a  slight  precipitate  on 
supersaturating  with  ammonia  in  the  cold.  If  a  precipitate  forms, 
dissolve  it  in  hydrochloric  acid,  precipitate  again  with  ammonia, 


256  ANALYSIS    OF    WATER.  [§  209. 

collect  the  precipitate,  weigh,  and  deduct  its  weight,  together  with 
that  of  the  small  residue  insoluble  in  hydrochloric  acid,  from  the 
weight  of  the  lithium  phosphate.  Of  course  the  precipitates  must 
be  previously  tested  spectroscopicaUy  to  see  that  they  are  free  from 
lithium. 

The  filtrate  from  the  lithium  phosphate  may  serve  for  testing 
for  ccesium,  rubidium,  and  thallium,  and  even  for  their  determina- 
tion, when  the  evaporation  residues  of  larger  quantities  of  the 
water  are  not  available.  For  this  purpose,  heat  the  liquid  to  drive 
off  any  ammonia  that  may  be  present,  add  some  ferric  chloride 
to  precipitate  any  phosphoric  acid  present,  then  cautiously  neu- 
tralize with  ammonia.  Filter  off  the  precipitate,  which  must  be 
yellowish  brown  and  not  white,  evaporate  to  dryness  the  filtrate, 
drive  off  the  ammonia  salts  by  gently  igniting,  dissolve  the  residue 
in  a  little  hot  water,  precipitate  with  concentrated  platinic-chloride 
solution,  and  boil  the  precipitate  repeatedly  with  small  quantities 
of  water  to  free  it  from  the  greater  part  of  the  potassium-platinum 
chloride;  reduce  in  a  current  of  hydrogen  at  a  low  red  heat,  ex 
haust  with  boiling  alcohol,  and  test  the  residue  left  on  evaporating 
the  alcoholic  solution  spectroscopically  for  caesium  and  rubidium; 
the  undissolved  part  test  for  thallium.* 

In  60  litres  of  a  mineral  water  there  will  scarcely  ever  be  suffi- 
cient of  these  metals  present  to  separate  them  and  determine  them 
quantitatively.  Should  this,  however,  happen,  the  mixture  of 
potassium,  rubidium,  and  caesium  chloride,  obtained  by  decom- 
posing the  precipitate  yielded  by  platinic  chloride  may  be  best 
separated  by  adding  stannic-chloride  solution  to  the  concentrated 
hot  solution  to  which  quite  a  considerable  quantity  of  hydrochloric 
acid  has  been  added.  The  caesium  is  thus  thrown  down  as  csesium- 


*  R.  BOTTGER  in  this  manner  found  thallium  in  the  saline  residue  obtained 
on  evaporating  the  Nauheim  mother  liquors.  If  insufficient  platinic  chloride 
is  used  to  precipitate  the  extract  of  the  saline  mass  made  with  80-per-cent. 
alcohol,  the  potassium-platinum  chloride  obtained  contains  caesium  and 
rubidium;  an  aqueous  extract  treated  similarly  yields  potassium-platinum 
chloride  containing  thallium  (Begluckwunschungsschrift  des  Frankf.  physik. 
Vereins  zur  Jubelfeier  des  hundertjahrigen  Bestehens  der  Senkenberg' schen 
Stiftung,  1863).  :"* 


§  209.]  ANALYSIS    OF    MINERAL   WATERS.  257 

stannic  chloride,  in  the  form  of  a  crystalline  precipitate  (STOLBA*), 
whereas  potassium  and  rubidium  remain  in  solution.  The  tin 
may  be  thrown  down  from  the  solution  by  means  of  hydrogen 
sulphide,  and  the  potassium  and  rubidium  in  the  filtrate  converted 
into  chlorides,  and  these  metals  indirectly  determined  by  esti- 
mating the  chlorine  in  the  weighed  mixture  of  chlorides  (§  200). 

6.  The  remainder  of  the  solution,  in  an  aliquot  part  of  which 
the  lithium  was  determined,  may  be  used  for  testing  for  arsenic, 
and  for  determining  the  boric  acid. 

Treat  the  solution,  warmed  to  70°,  with  hydrogen  sulphide 
for  some  time,  and  if  any  precipitate  forms,  test  it  for  arsenic  (and 
also  antimony).  Free  the  filtrate  from  hydrogen  sulphide  by  a 
prolonged  gentle  heat  (not  boiling,  however),  add  a  slight  excess 
of  potassium  carbonate,  evaporate  to  dryness,  extract  the  residue 
with  alcohol  and  a  little  hydrochloric  acid  (the  insoluble  residue 
may  contain  titanic  acid),  make  the  filtrate  strongly  alkaline  with 
potassa  solution,  distil  off  the  alcohol,  heat  the  residue  wifh  water 
and  a  little  potassium  carbonate  (to  precipitate  the  last  trace  of 
calcium),  boil,  filter,  acidulate  the  nitrate  with  hydrochloric  acid, 
separate  the  phosphoric  and  boric  acids  according  to  §  166,  3,  c 
(231),  and  determine  the  latter  according  to  §  136,  I,  1,  d  (Vol. 
I,  p.  466). 

B.   The  Residue  Insoluble  in  Water. 

Cover  the  residue  with  water  in  a  large  porcelain  dish,  add 
hydrochloric  acid  in  considerable  excess,  and  also  five  drops  diluted 
sulphuric  acid.  If  any  residue  remains  adhering  to  the  vessel, 
remove  it  by  means  of  a  little  diluted  acetic  acid,  add  the  solution 
to  the  main  bulk  of  the  liquid,  and  evaporate  to  dryness.  Treat 
the  residue  with  hydrochloric  acid  and  water,  filter  off  the  silicic 
acid,  etc.,  boil  the  precipitate  with  a  solution  of  sodium  carbonate 
until  the  silicic  acid  appears  to  be  dissolved,  filter  the  solution 
(using  a  hot-water  funnel),  and  wash  the  residue.  (The  silicic 
acid  may  be  precipitated  from  the  solution  and  tested  for  titanic 
acid.)  Incinerate  the  filter  with  the  residue,  fuse  with  sodium 
*  Zeitschr.  f.  analyt.  Chem.,  xn,  440. 


258  ANALYSIS    OF   WATER,  [§  209. 

carbonate,  boil  the  melt  with  water,  and  filter  off  the  small  residue 
of  barium  carbonate,  etc.  (Here,  too,  the  silicic  acid  may  be  pre- 
cipitated from  the  solution  and  tested  for  titanic  acid.)  Wash 
the  precipitate,  dissolve  in  diluted  hydrochloric  acid,  remove  any 
traces  of  lead  with  hydrogen  sulphide,  evaporate  the  fluid  (filtered 
off  from  the  lead  sulphide,  if  necessary)  on  the  water-bath,  take 
up  the  residue  with  water  and  several  drops  hydrochloric  acid, 
and  precipitate  by  adding  a  few  drops  diluted  sulphuric  acid. 
After  allowing  to  settle  for  some  time,  filter,  and  mix  the  filtrate 
with  three  volumes  of  alcohol.  If  a  precipitate  forms,  it  is  barium 
sulphate,  or  possibly  calcium  sulphate,  and  it  must  be  kept.  We 
will  designate  it  as  x. 

After  collecting  and  washing  the  barium  sulphate,  allow  it  to 
remain  in  contact  with  a  concentrated  solution  of  ammonium 
carbonate  for  twelve  hours  in  a  funnel  the  stem  of  which  has  been 
closed  by  a  stopper,  or  in  a  separatory  funnel.  Then  remove 
the  stopper,  allow  the  liquid  to  run  off,  wash  the  precipitate,  treat 
it  with  very  dilute  nitric  acid  (to  remove  any  strontium  that  may 
be  present  now  as  carbonate),  wash  with  water,  dry,  ignite,  and 
weigh  the  now  pure  barium  sulphate.  The  solution,  containing 
nitric  acid,  and  possibly  also  strontium,  is  kept.  We  will  designate 
it  as  y. 

Largely  dilute  the  filtrate  from  the  silicic  acid,  treat  it  warm 
with  hydrogen  sulphide  in  order  to  precipitate  any  metals  of  the 
fifth  and  sixth  groups  that  may  be  present,*  filter,  boil  the  filtrate 
with  nitric  acid,  precipitate  ferric  oxide  (§  160,  B,  3,  a),  and  slightly 
supersaturate  the  filtrate  with  ammonia.  If  a  further  small 
quantity  of  precipitate  is  thus  obtained,  free  it  from  manganese 
by  repeatedly  dissolving  in  hydrochloric  acid  and  precipitating 
with  ammonia.  Precipitate  the  manganese  from  the  concentrated 
filtrate  with  ammonium  sulphide  as  usual  f  (see  3,  p.  248);  and  pre- 

*  If  a  precipitate  occurs,  and  if  any  of  the  metals  of  the  fifth  or  sixth  group 
are  found,  care  must  be  taken  to  ascertain  whether  they  may  not  have  been 
derived  from  the  vessel  in  which  the  water  was  evaporated. 

t  If  the  ammonium-sulphide  precipitate  is  dark-colored,  it  may  contain 
nickel  or  cobalt,  and  even  zinc  also;  the  separation  may  be  effected  according 
to  §  160,  B,  6. 


§  209.]  ANALYSIS    OF    MINEKAL   WATERS.  259 

cipitate  the  calcium,  etc.,  in  the  filtrate  with  ammonium  carbonate 
and  ammonia.  If  the  aluminium  in  3  has  not  yet  been  determined, 
unite  the  larger  precipitate  obtained  by  basic  precipitation  with 
the  smaller  precipitate  obtained  by  ammonia  (and  consisting 
chiefly  of  ferric  hydroxide,  but  which  contains  the  aluminium, 
and  the  residual  silicic  acid  as  well  as  titanic  acid,  if  present), 
dissolve  them,  and  in  the  solution  determine  the  aluminium  ac- 
cording to  3,  p.  247. 

Collect  the  precipitate,  consisting  chiefly  of  calcium  carbonate, 
wash,  dissolve  in  nitric  acid,  add  to  the  solution  the  above-men- 
tioned solution  y,  which  may  contain  strontium,  and  evaporate 
to  dryness,  this  operation  being  finally  accomplished  in  a  flask 
heated  on  a  sand-bath  and  freed  from  its  moist  air  by  means  of  a 
water  air-pump.  Then  treat  the  residue  with  ether-alcohol,  in 
not  too  large  a  quantity,  however,  to  dissolve  the  calcium  nitrate. 

Dissolve  the  residue  insoluble  in  ether-alcohol  in  water  (any 
residual  matter  should  be  incinerated  and  examined  spectroscopic- 
ally),  evaporate  to  a  small  bulk,  add  a  concentrated  (1:4)  solution 
of  ammonium  sulphate  in  excess,  and  set  aside  for  twelve  hours. 

Next  collect  the  above-mentioned  precipitate  x,  if  any,  on  a 
small  filter;  then  collect  that  produced  by  the  ammonium  sulphate, 
in  doing  which  it  is  advisable  to  at  first  close  the  funnel  at  the 
bottom,  so  that  the  ammonium-sulphate  solution  may  dissolve 
any  calcium  sulphate  there  may  be  in  x.  After  the  precipitate 
has  been  washed  with  ammonium-sulphate  solution  until  the 
filtrate  is  no  longer  rendered  cloudy  by  ammonium  oxalate,  dry 
and  ignite  the  strontium  sulphate.  After  being  weighed,  it  must 
be  examined  spectroscopically. 

7.  DETERMINATION  OF  THE  PHOSPHORIC  ACID. 

The  determination  of  the  phosphoric  acid  may  be  combined 
with  that  of  the  ferric  oxide,  alumina,  etc.,  in  3,  and,  if  necessary, 
in  the  portion  6;  it  is  far  better,  however,  and  safer  to  use  for  the 
determination  the  contents  of  a  separate  bottle  (about  6  litres). 
Add  hydrochloric  acid,  evaporate,  separate  the  silicic  acid,  evap- 
orate the  filtrate  repeatedly  with  nitric  acid  almost  to  dryness, 


260  ANALYSIS    OF   WATER.  [§  209. 

dissolve  the  residue  in  nitric  acid  and  water,  precipitate  with  a 
solution  of  ammonium  molybdate  in  nitric  acid,  and  finally  de- 
termine the  phosphoric  add  as  magnesium  pyrophosphate  (§  134, 
I,  6, -ft- 

8.  DETERMINATION  OF  THE  AMMONIA. 

For  determining  the  ammonia  I,  as  a  rule,  use  the  following 
method:  Add  a  small  measured  quantity  of  diluted  hydrochloric 
acid  to  about  2000  grammes  of  the  water,  and  evaporate  with 
the  greatest  care  to  a  small  bulk  in  a  tubulated  retort.  Now  add 
through  a  funnel  a  sufficient  quantity  of  a  freshly  prepared  sodium- 
hydroxide  solution,*  the  neck  of  the  resort  being  inclined  upwards, 
and  prolong  the  boiling  until  the  liquid  has  almost  entirely  evap- 
orated. Conduct  the  whole  of  the  vapors  passing  off  through  a 
LJEBIG  condenser  and  collect  the  distillate  in  a  tubulated  receiver 
containing  a  small  quantity  of  water  acidulated  with  hydrochloric 
acid,  the  tubulure  being  connected  with  a  U-tube  containing  some 
water.  Convert  the  ammonium  chloride  in  the  water  in  the 
receivers  into  ammonium-platinic  chloride  by  evaporation  with  a 
measured  quantity  of  platinic-chloride  solution  (§99,  2).  Make 
a  control  test,  using  like  quantities  of  hydrochloric  acid,  platinic 
chloride,  and  alcohol,  and  deduct  the  platinic-chloride  salt  so  ob- 
tained from  that  found  in  the  first  experiment;  the  difference  gives 
that  afforded  by  the  water,  and  with  great  exactness. 

Instead  of  this  method  the  simpler  one  proposed  by  BOUSSIN- 
GAULT  f  may  also  be  satisfactorily  used.  It  is  carried  out  as  follows : 

Heat  about  10  litres  of  the  water  in  a  retort  until  about  two- 
fifths  have  distilled  off  (in  the  case  of  saline  waters  a  little  soda 
solution  or  milk-of-lime  must  be  added  in  order  to  insure  all  the 
ammonia  passing  over  in  the  distillate).  Now  transfer  this  dis- 
tillate to  a  flask  connected  with  a  LIEBIG  condenser,  and  distil 
off  one-fifth;  in  this  distillate  determine  the  ammonia  by  adding 

*  Should  the  water  contain  any  notable  quantity  of  organic  matter,  it  is 
advisable  to  replace  the  sodium  hydroxide  by  freshly  ignited  magnesia  sus- 
pended in  water,  for  the  expulsion  of  the  ammonia. 

f  Compt.  rend.,  xxxvi,  814;  Pharm.  Centralbl,  1853,  369. 


§  209.]  ANALYSIS    OF    MINERAL    WATERS.  261 

5  to  10  c.c.  of  very  dilute  sulphuric  acid,  and  neutralizing  the  excess 
with  soda-lye  of  which  5  c.c.  should  neutralize  1  c.c.  of  the  sulphuric 
acid  (comp.  §  99,  3).  Now  distil  off  another  one-fifth,  and  in  this 
determine  the  ammonia  (if  any)  similarly.  As  a  rule  the  first 
portion  will  contain  all  the  ammonia. 

Regarding  the  determination  of  ammonia  with  NESSLER'S 
reagent  see  §205,  12  (p.  211). 

9.  DETERMINING  THE  NITRIC  ACID. 

The  determination  of  nitric  acid  in  mineral  waters  is  effected 
in  precisely  the  same  way  as  hi  spring  waters,  comp.  §  205,  3  (p.  1 86). 

10.   DETECTION  AND  DETERMINATION  OF  THE  CRENIC  AND 
APOCRENIC  ACIDS. 

Boil  a  fairly  large  quantity  of  the  precipitate  obtained  on 
evaporating  the  water,  for  about  one  hour  with  potassa-lye,  filter, 
acidulate  the  filtrate  with  acetic  acid,  and  add  ammonia;  after 
twelve  hours  collect  the  precipitate  of  silica  and  alumina,  which 
as  a  rule  forms,  again  acidulate  with  acetic  acid,  and  then  add 
neutral  cupric  acetate.  If  a  brownish  precipitate  forms,  it  is 
cupric  apocrenate  (which,  according  to  MULDER,  contains  variable 
quantities  of  ammonia,  and  which,  dried  at  140°,  gave  42-8  per 
cent,  cupric  oxide).  Filter,  and  to  the  filtrate  add  ammonium 
carbonate  until  the  greenish  color  has  changed  to  blue,  and  then 
warm  gently.  If  a  bluish-green  precipitate  forms,  it  is  mercuric 
crenate,  which,  dried  at  140°,  gave  MULDER*  74-12  per  cent, 
cupric  oxide. 

11.  DETECTION  AND  DETERMINATION  OF  VOLATILE 
ORGANIC  ACIDS. 

ScHERERf  in  his  analysis  of  the  Briickenau  (Bavaria)  mineral 
spring  found  also  butyric,  propionic,  acetic,  and  formic  acids — 

*  Further  details  regarding  crenic  and  apocrenic  acids  are  afforded  by 
BERZELIUS  (Lehrbuch  der  Chem.,  4  Aufl.,  vin,  393  and  405),  and  also  MULDEB 
(Journ.  f.  pract.  Chem.,  xxxn,  321). 

t  Annal.  d.  Chem.  u.  Pharm.,  xcix,  257. 


262  ANALYSIS   OF   WATER.  [§   209. 

substances  which  had  not  been  observed  before  in  mineral  waters. 
Soon  thereafter  I  found  these  acids,  although  present  in  traces,  in  the 
Weilbach  sulphur  water.*  If  a  mineral  water  is  to  be  tested  for 
the  presence  of  these  acids,  it  must  be  used  quite  fresh,  otherwise 
these  acids  may  result  from  decomposition  subsequent  to  collection 
of  the  water.  The  process  employed  by  SCHERER  for  their  de- 
termination was  as  follows: 

Evaporate  a  rather  large  quantity  of  the  water  (if  no  bicar- 
bonate is  present,  add  first  some  sodium  carbonate  to  alkaline 
reaction),  and  filter  off  the  liquid  from  the  precipitate.  Cautiously 
acidulate  the  concentrated  mother-liquor  with  sulphuric  acid, 
and  precipitate  the  chlorine  with  silver  sulphate,  taking  care  to 
leave  a  trace  of  chlorine  present  rather  than  an  excess  of  silver. 
Distil  the  filtrate  so  long  as  the  distillate  has  an  acid  reaction, 
saturate  the  distillate  with  baryta  water,  remove  any  excess  of 
baryta  with  carbonic  acid,  boil,  concentrate,  filter,  evaporate  in 
a  weighed  dish  to  dryness,  dry  at  100°,  and  weigh  the  barium  salts 
of  the  volatile  acids.  Now  extract  the  residue  with  warm  alcohol; 
barium  formate  remains  undissolved,  and  after  it  has  been  dried 
and  weighed  test  it  with  silver  solution  and  mercuric  chloride. f 
Evaporate  the  alcoholic  solution  of  the  other  barium  compounds 
at  a  gentle  heat,  take  up  the  greater  part  of  the  residue  with  a  large 
quantity  of  water,  and  cautiously  precipitate  the  barium  with 
silver  sulphate.  Filter,  and  allow  the  filtrate  to  evaporate  in  the 
desiccator.  As  soon  as  a  sufficient  quantity  of  the  silver  salt  has 
crystallized  out,  remove  it  from  the  liquid,  dry  it  over  sulphuric 
acid,  and  employ  it  for  the  determination  of  the  equivalent.  Fin- 
ally, allow  the  remainder  of  the  silver  solution  to  evaporate  over 
sulphuric  acid,  press  between  blotting-paper,  dry  over  sulphuric 
acid,  and  analyze. 

As  a  control  test  determine  with  sulphuric  acid  the  barium  in 
another  portion  of  the  barium  salts  yielded  by  the  alcoholic  solution. 
In  this  experiment  the  characteristic  odor  of  the  volatile  fatty  acid 

*  Journ.  f.  prakt.  Chem.,  LXX,  15. 

t  Attention  is  called  to  the  fact  that  the  barium  formate  may  contain 
barium  nitrate. 


§  209.]  ANALYSIS    OF   MINERAL   WATERS.  263 

(propionic  acid,  butyric  acid,  etc.)  may  be  recognized;  and  if  the 
liquid  has  been  sufficiently  concentrated,  and  allowed  to  remain 
at  rest  for  some  time,  the  microscope  will  occasionally  distinctly 
show  minute  fatty  drops  on  the  surface  of  the  liquid. 

If  only  very  small  traces  of  the  volatile  acids  are  present,  while 
the  quantity  of  chlorides  present  is  large,  the  precipitation  of  the 
chlorine  with  silver  sulphate,  as  in  SCHERER'S  method,  cannot  be 
carried  out  at  all,  or  is  effected  only  with  great  difficulty.  This 
occurred  to  me  hi  an  examination  of  the  Grindbrunnen,  Frankfurt. 
A  modification  of  SCHERER'S  method  was  hence  employed,*  and 
this  I  would  recommend  for  similar  cases.  Evaporate  a  rather 
large  quantity  of  water  (if  necessary  adding  some  sodium  carbon- 
ate) to  a  small  bulk,  filter  the  strongly  alkaline  fluid,  gradually  add 
diluted  sulphuric  acid  first  to  neutrality,  and  then  until  the  liquid 
is  slightly  acid.  Now  distil  the  acidulous  liquid  until  only  a  small 
quantity  remains  in  the  retort.  Neutralize  the  slightly  acid  dis- 
tillate with  baryta  water,  evaporate  to  dryness,  and  heat  the  resi- 
due with  absolute  alcohol.  Evaporate  the  solution,  and  repeat 
the  treatment  with  the  hot  absolute  alcohol.  On  the  evaporation 
of  the  alcohol,  there  are  obtained  the  barium  compounds  of  pro- 
pionic, butyric,  etc.,  acids,  which  are  readily  soluble  in  alcohol, 
while  the  barium  formate,  difficultly  soluble  in  alcohol,  can  be 
extracted  from  the  residue  with  water,  f 

12.  DETERMINATION  OF  OTHER  ORGANIC  MATTERS  (RESINS, 
EXTRACTIVES). 

Besides  the  substances  mentioned  in  10  and  11,  mineral  waters 
may  contain  other  organic  matters.  Those  which  may  be  ex- 
tracted by  alcohol  from  the  evaporation-residue  of  a  mineral  water 
are,  as  a  rule,  of  a  resinous  nature,  and  are  so  put  down ;  others  are 
insoluble  in  alcohol,  but  are  dissolved  out  from  the  residue  by 
water,  and  these  are  usually  designated  as  extractive  matters, 

*  Zeitschr.  f.  analyL  Chem.,  xiv,  323.    - 

f  100  grammes  of  boiling  absolute  alcohol  dissolve  0-0055  grm.  barium 
formate;  0-0284  grm.  barium  acetate;  0-261  grm.  barium  propionate,  and 
1  •  1717  grm.  barium  butyrate  (E.  LUCK,  Zeitschr.  /.  analyt.  Chem.,  x,  185). 


264  ANALYSIS   OF    WATER.  [§  209. 

for  lack  of  more  accurate  knowledge  regarding  their  nature.  Some- 
times also  small  quantities  of  organic  matters  remain  in  the  residue 
after  extraction  with  water  and  with  alcohol;  these  are  decom- 
position products  which  have  formed  during  evaporation. 

To  accurately  detect  or  determine  any  resinous  or  extractive 
matter  it  is  absolutely  necessary  that  the  water,  during  trans- 
portation, does  not  come  into  contact  with  the  cork  or  rubber 
stopper;  that  during  evaporation  all  contamination  from  dust  be 
prevented;  and  that  there  be  used  perfectly  pure  alcohol,  which, 
on  evaporation,  should  not  leave  the  slightest  residue.  //  these  pre- 
cautions are  not  observed  resinous  or  extractive  matters  may  be  found 
which  may  not  owe  their  origin  to  the  mineral  water. 

For  the  determination  of  these  organic  matters  in  the  Grind- 
brunnen  waters  at  Frankfurt  the  following  method  *  was  em- 
ployed, and  it  is  recommended  in  similar  cases : 

Evaporate  to  dryness  a  large  volume  of  the  water  (10  to  20 
litres)  with  the  most  scrupulous  regard  to  cleanliness,  the  final 
stage  being  conducted  with  the  greatest  care,  and  then  extract 
the  residue,  reduced  to  powder,  with  perfectly  pure  alcohol.  There 
are  thus  obtained  a  solution,  a,  and  a  residue,  b.  Distil  off  the 
solution  a,  treat  the  resulting  residue  with  water  (in  which  the 
greater  part  dissolves),  and  pass  through  a  small  asbestos  filter. 
If  this  retains  a  trace  of  resin,  wash  it  with  water,  dry,  dissolve 
in  absolute  alcohol,  evaporate  the  solvent  in  a  weighed  platinum 
dish,  weigh  the  residue,  heat,  and  note  the  odor;  weigh  any  in- 
combustible residue,  and  enter  the  difference  in  weight  between 
the  two  as  resin.  Add  the  aqueous  liquid  filtered  off  from  the 
resin  to  the  residue  b,  exhaust  the  whole  with  water,  acidulate 
the  solution  with  diluted  sulphuric  acid,  and  gently  heat  for  some 
time  to  drive  out  all  the  carbonic  acid.  Now  add  some  freshly 
ignited  lead  oxide  perfectly  free  from  carbonate,  evaporate  to  dry- 
ness,  then  add  an  excess  of  lead  chromate  to  the  residue,  and  sub- 
ject it  to  analysis  by  combustion  (§  176).  The  humus-like  sub- 
stance may  be  calculated  from  the  carbon  with  approximate  ac- 

*  Zeitschr.  /.  analyt.  Chem.,  xiv,  323. 


§  210.]  ANALYSIS  OF    MINERAL   WATERS.  265 

curacy  by  taking  the  figures  given  by  FR.  SCHULZE  *  for  100  parts 
of  humus-like  substance,  viz.  :    58  parts-  carbon. 

Treat  the  residue,  insoluble  in  alcohol  and  water,  with  diluted 
hydrochloric  acid,  Should  the  residue  left  contain  organic  matter, 
collect  it  on  an  asbestos  filter,  wash,  ignite  it  with  lead  chromate 
(§  176),  and  calculate  the  insoluble  humus-like  substance  from 
the  carbon. 

13.  EXAMINATION  OF  THE  GASES. 
§210. 

To  examine  the  gases  collected  at  the  spring  and  transported 
to  the  laboratory  in  sealed  tubes,  whether  expelled  from  the  water 
by  boiling  (§  208,  10,  a  or  b)  or  whether  spontaneously  disengaged 
at  the  spring  (§  208,  11),  proceed  as  follows:  Fill  with  mercury  f 
a  graduated  tube  of  the  kind  described  in  Vol.  I,  p.  29,  Fig.  4, 
after  first  moistening  the  inside  with  a  drop  of  water,  then  im- 
merse tne  tube  containing  the  gas  hi  the  mercurial  trough,  break 
off  the  point,  and  by  properly  inclining  the  tube  allow  the  gas  to 
ascend  into  the  graduated  tube.  After  the  volume  of  the  gas  has 
been  carefully  read  off,  the  temperature  and  barometric  pressure 
being  duly  noted,  push  up  into  the  tube  a  ball  of  potassium  hydrox- 
ide fused  on  the  end  of  a  platinum  wire  and  moistened  with 
water. J  The  potassium  hydroxide  must  contain  water  of  crys- 
tallization in  addition  to  its  water  of  hydration;  and  care  must 
be  also  taken  that  the  end  of  the  wire  does  not  project  above  the 
surface  of  the  mercury,  otherwise  diffusion  of  the  combined  gas 
with  the  air  will  take  place  along  the  wire  not  in  contact  with  the 
mercury.  When  the  volume  of  gas  no  longer  diminishes  replace 
the  moist  ball  of  potassium  hydroxide  by  another,  and  when  ab- 
sorption finally  ceases  replace  it  again  by  a  dry  one,  and  remove 

*  Jcmrn.  f.  prakt.  Chem.,  XLVII,  241. 

t  See  footnote  page  59. 

t  Such  balls  are  made  by  pouring  fused  crystallized  potassium  hydroxide 
into  a  bullet  mold  of  about  6  mm.  inner  diameter,  while  the  end  of  a  platinum 
wire  is  inserted  to  about  the  middle.  After  cooling,  the  potassium  hydroxide 
adheres  fast  to  the  wire.  The  neck  which  forms  on  the  wire  may  be  removed 
with  a  knife. 


266  ANALYSIS    OF   WATER.  [§  210. 

this  after  an  hour,  and  read  off  the  volume  of  gas.  The  gas  ab- 
sorbed is  carbonic  acid;  and  in  cases  where  it  is  present  hydrogen 
sulphide  also  (which  has  already  been  determined,  or  may  be  de- 
termined from  the  potassium  sulphide  in  the  potassa  ball,  accord- 
ing to  Vol.  I,  p.  569,  B,  a). 

The  residual  gas  consists,  as  a  rule,  only  of  oxygen  and  nitrogen, 
and  may  be  examined  exactly  as  directed  in  the  chapter  on  the 
Analysis  of  Atmospheric  Air.  If  the  presence  of  marsh  gas  is  sus- 
pected the  oxygen  is  removed. 

This  is  best  effected  by  means  of  a  ball  of  papier-mache  fixed 
on  a  platinum  wire  and  impregnated  with  a  concentrated  alkaline 
solution  of  potassium  pyrogallate;  if  necessary  the  ball  may  be 
replaced  after  some  time  by  a  second  one.  After  this  operation 
also  dry  the  gas  by  means  of  a  potassium-hydroxide  ball  (BUNSEN). 
Now  ascertain  the  composition  of  the  residual  gas,*  which  consists 
generally  of  either  nitrogen  alone,  or  of  a  mixture  of  nitrogen  and 
marsh  gas,  by  transferring  it,  wholly  or  in  part,  to  a  eudiometer 
(Vol.  I,  p.  29,  Fig.  3),  mixing  it  with  8  to  12  volumes  of  air  and 
2  volumes  of  oxygen  (to  guard  against  the  formation  of  nitric 
acid),  and  trying  to  explode  the  mixture.  If  the  attempt  is  unsuc- 
cessful add  detonating  gas,  electrolytically  prepared  from  water, 
to  the  mixture  until  this  becomes  explosive ;  finally  absorb  the  car- 
bonic acid  generated,  calculate  from  it  the  marsh  gas,  and  deter- 
mine the  nitrogen  from  the  difference.  The  details  of  the  process 
will  not  be  here  given,  as  they  are  minutely  described  in  BUNSEN'S 
"Gasometry,"  which  should  be  in  the  possession  of  every  one  en- 
gaged in  gas  analysis. 

To  determine  whether  any  carburetted  hydrogen  is  present  in 
the  residual  gas  left  after  the  carbonic  acid  has  been  absorbed,  and 
to  estimate  its  quantity,  I  have  frequently  made  use  of  the  following 

*  Should  the  gas  have  contained  but  little  oxygen  there  need  be  no  fear 
that  any  appreciable  trace  of  carbonic  may  be  formed  by  the  action  of  the 
oxygen  on  the  potassium  pyrogallate;  if,  however,  considerable  oxygen  has 
been  found,  it  is  necessary,  in  order  to  avoid  any  error,  to  test  for  hydrocar- 
bons another  portion  of  the  original  gas,  from  which  the  carbonic  acid,  but 
not  the  oxygen,  has  been  removed  (BOUSSINGAULT,  CALVERT,  CLOEZ,  POLECK, 
Zeitschr.  /.  analyt.  Chem.,  in,  347,  and  vin,  451. 


§  210.]  ANALYSIS    OF   MINERAL   WATERS.  267 

method  with  good  results:  Bend  a  narrow  glass  tube  to  an  angle 
of  45°,  and  introduce  one  limb  into  the  cylinder  containing  the  re- 
sidual gas  confined  over  water;  to  the  other  limb  fasten  a  rubber 
tube  provided  with  a  pinch-cock. 

An  apparatus  is  now  arranged  as  follows:  Introduce  a  little 
potassa  solution  into  a  small  U-tube,  the  outer  limb  of  which  carries 
a  small  tube  bent  at  right  angles  and  closed  by  a  bit  of  rubber  tubing 
provided  with  a  screw  pinch-cock.  The  other  limb  of  the  U-tube 
connect  with  a  small  U-tube  filled  with  soda-lime;  to  this  is  now 
connected  a  thin  piece  of  combustion  tubing  about  2  decimeters 
long,  the  middle  part  of  which  is  filled  with  fine  copper  turnings 
strongly  oxidized  by  ignition  in  oxygen,  and  rather  tightly  packed  in 
a  layer  about  8  cm.  long.  Connect  the  tube  in  turn  with  a  somewhat 
larger  U-tube  containing  baryta  water,  and  this  again  connect  with 
a  potassium-hydroxide  tube,  and  finally  with  an  aspirator.  After 
the  cock  of  the  latter  has  been  opened,  to  ascertain  whether  the 
joints  are  all  air-tight,  heat  the  copper  turnings  to  redness  with  two 
gas-lamps,  cautiously  open  the  screw  pinch-cock,  and  allow  a  current 
of  air  to  pass  slowly  for  five  minutes  through  the  apparatus.  The 
baryta  water  must  not  be  rendered  turbid  in  the  slightest  degree  by 
this  operation;  if  this  should  happen,  renew  the  baryta  water 
after  the  first  ignition,  and  repeat  the  experiment.  When  the  baryta 
water  remains  clear  connect  the  rubber  tube,  which  is  closed  by  a 
plain  pinch-cock,  with  the  small  glass  tube  provided  with  the  screw 
pinch-cock.  As  the  former,  which  closes  the  U-tube  leading  to  the 
cylinder,  remains  closed,  no  more  air-bubbles  can  pass  through  the 
apparatus.  Now  slightly  open  the  pinch-cock,  and  allow  the  gas 
to  very  slowly  enter  the  cylinder.  The  quantity  of  gas  is  usually 
so  small  that  it  remains  entirely  in  the  first  U-tube.  After  the 
gas  has  been  entirely  drawn  in  allow  also  some  water  to  enter,  and 
finally  close  the  pinch-cock  when  the  water  just  makes  its  appear- 
ance in  the  little  tube  behind  it.  Now  close  the  screw  pinch-cock, 
remove  the  rubber  tube  with  the  plain  pinch-cock,  then  slightly 
open  the  screw  pinch-cock,  and  allow  a  very  slow  current  of  pure  air 
(taken  from  the  open  and  filtered  through  cotton)  to  pass  for  a 
sufficient  length  of  time  over  the  red-hot  cupric  oxide.  The 


268  ANALYSIS    OF    WATER.  [§  211. 

current  of  air  carries  with  it  the  gas  which  has  previously  entered. 
If  the  latter  contains  carburetted  hydrogen  the  baryta  water  is 
rendered  turbid  from  the  formation  of  barium  carbonate.  If  the 
turbidity  is  sufficiently  marked,  the  barium  carbonate  may  be 
determined,  and  from  this  the  quantity  of  marsh  gas  may  be 
calculated.  If  the  carbonic  acid  formed  is  to  be  collected  in  a 
weighed  soda-lime  tube,  the  apparatus  described  by  me  in  the 
Zeitschr.  f.  analyt.  Chem.,  Ill,  340,  should  be  used. 

MODIFICATIONS    REQUIRED    WITH    SALINE    WATERS, 

I.E.,  WITH   SUCH   AS  CONTAIN   NO  ALKALI 

BICARBONATE. 

§   211. 
1.  DETERMINATION  OF  THE  TOTAL  FIXED  CONSTITUENTS. 

If  the  total  quantity  of  the  fixed  constituents  is  determined  by 
the  method  detailed  in  §  209,  1,  there  is  a  slight  loss  of  magnesium 
chloride,  as  a  small  portion  is  decomposed  by  the  water  during 
evaporation,  hydrochloric  acid  being  evolved,  and  magnesia 
remaining.  The  error  is,  however,  as  a  rule,  scarcely  appreciable, 
and  may  hence  be  usually  disregarded,  especially  as  the  total  salts 
found  by  direct  evaporation  never  agrees  accurately  with  the  total 
constituents  determined  directly,  and  from  causes  already  stated 
in  §  205,  I,  9.  To  avoid  the  source  of  error  noted  we  may  adopt 
FR.  MOHR'S  suggestion  to  evaporate  the  water  with  the  addition 
of  a  weighed  quantity  of  ignited  sodium  carbonate,  or,  according 
to  TILLMANN'S  *  method,  to  add  a  known  quantity  of  potassium 
sulphate  before  evaporation.  In  the  latter  case  the  MgCl2  and 
2K2S04  form  the  double  salt  MgSO4-K2SO4,  and  also  2KC1. 

2.  DETERMINATION  OF  THE  CALCIUM  AND  MAGNESIUM. 

If  a  mineral  water  contains  alkali  carbonate  no  soluble  cal- 
cium or  magnesium  salt  can  be  present,  but  all  the  calcium  and 
magnesium  found  must  be  considered  as  carbonates  dissolved  by 

*  Annal  der  Chem.  u.  Pharm.,  LXXXI,  369. 


§  211.]   MODIFICATIONS  REQUIRED  WITH  SALINE  WATERS.      269 

carbonic  acid,  even  though  only  a  part  of  the  calcium,  and  still  less 
of  the  magnesium  is  precipitated  on  boiling  the  water.  With 
saline  waters,  however,  the  case  is  different.  These  contain  almost 
always  calcium  and  magnesium  carbonates,  together  with  soluble 
calcium  and  magnesium  salts.  In  order  to  determine  in  saline 
waters  just  in  what  proportions  both  bases  are  combined  with  car- 
bonic acid  and  other  acids,  it  is  necessary,  in  addition  to  the  de- 
termination of  the  total  calcium  according  to  §  209,  3,  to  separately 
determine  the  calcium  remaining  in  solution  on  boiling  the  water; 
the  portions  of  magnesium  combined  with  carbonic  and  other  acids 
may  then  be  calculated  (see  §  213).* 

Tare  or  weigh  a  flask  of  about  1500  c.c.,  introduce  into  it  1000 
grm.  of  the  mineral  water,  and  boil  for  an  hour,  replacing  the 
evaporated  water  from  time  to  time  by  distilled  water.  When 
perfectly  cold  weight  the  flask  and  its  contents,  deduct  the  weight 
of  the  empty  flask,  and  thus  ascertain  the  weight  of  the  boiled 
liquid.  Now~  pass  through  a  dry  filter,  without  washing  the  pre- 

*  The  earlier  method  of  determining  the  calcium  precipitated  and  remain- 
ing dissolved  or  boiling,  and  which  consisted  in  filtering  the  boiled  water, 
thoroughly  washing  the  precipitate  with  water,  and  determining  the  calcium 
in  the  precipitate  and  filtrate,  I  have  discarded  and  replaced  by  the  process 
above  described.  It  will  be  readily  understood  that  in  both  processes  the 
calcium  in  the  solution  must  be  too  high,  while  that  in  the  precipitate  must 
be  too  low,  because  the  small  quantity  of  ammonium  chloride  usually  present 
in  saline  waters  reacts  with  calcium  carbonate  on  boiling,  and  also  because 
calcium  carbonate  is  not  absolutely  insoluble  in  water.  The  error  caused  by 
the  latter  becomes  naturally  the  greater  when  the  precipitated  calcium  car- 
bonate is  washed.  Under  these  circumstances  the  correction  given  in  the 
method  described  may  be  neglected,  as  the  water,  after  boiling,  contains  some 
calcium  carbonate  in  suspension,  so  that  its  influence  on  the  result  is  scarcely 
appreciable,  it  being  so  small,  in  fact,  as  to  lie  well  within  the  limits  of  un- 
avoidable error.  The  determination  of  what  portions  of  the  magnesium  are 
combined  with  carbonic  acid,  hydrochloric  acid,  sulphuric  acid,  etc.,  cannot  be 
accurately  effected  by  boiling  the  water  and  determining  the  magnesium  in 
the  precipitate  and  filtrate ;  moreover,  it  is  unnecessary,  because  the  desired 
result  is  obtained  on  the  calculation  of  the  analysis.  With  waters  containing 
calcium  sulphate,  however,  this  is  not  the  case  with  certainty,  because,  as  E. 
BOHLIG  (Pharm.  Centralb.,  xvm,  430)  has  shown,  magnesium  bicarbonate 
and  calcium  sulphate  are  decomposed  on  boiling  into  magnesium  sulphate, 
calcium  carbonate,  and  carbonic  acid.  According  to  my  investigations,  how- 
ever, this  decomposition  does  not  occur  in  waters  rich  in  magnesium  sulphate. 


270  ANALYSIS   OF   WATER.  [§  211. 

cipitate,  weigh  the  filtrate,  and  in  it  determine  the  calcium  by 
precipitation  with  ammonium  oxalate  as  in  §  209,  3,  and  calculate 
the  quantity  remaining  dissolved  in  1000  grm.  from  the  following 
consideration :  Knowing  the  weight  of  calcium  given  by  the  weighed 
quantity  of  filtrate  filtered  off  from  the  precipitate,  how  much 
calcium  will  the  1000  grm.  of  water  retain  in  solution  after  boiling? 

If  this  determination  is  performed  twice,  perfectly  concordant 
results  will  be  obtained.  That  thcee  are  too  high,  because  of  the 
solubility  of  the  calcium  carbonate  in  water,  is  an  error  that  cannot 
be  well  avoided.  A  correction  can  be  made  for  this  it  is  true, 
as  we  know  that  1  part  of  calcium  carbonate  is  soluble  in  28,500 
parts  of  water  (Vol.  I,  p.  174),  and  I  would  recommend  such  a 
correction  to  be  made,  though  it  can  make  no  claim  to  great  ac- 
curacy, as  the  various  soluble  salts  present  in  the  mineral  have 
an  appreciable  influence  on  the  solubility  of  the  calcium  carbonate, 
but  which  it  is  difficult  to  estimate. 

In  the  calcium  found  in  the  boiled  water  the  greater  part  of 
the  strontium  and  barium  present  are,  as  a  rule,  found  also,  while 
smaller  quantities  will  have  been  precipitated  as  carbonates  on 
boiling,  in  consequence  of  the  double  decomposition  (which  may 
be  considered  as  very  probable)  between  calcium  bicarbonate 
(in  water  containing  sodium  chloride)  and  the  barium  and  strontium 
sulphates,  with  the  formation  of  barium  and  strontium  carbonates, 
calcium  sulphate,  and  carbonic  acid.  The  quantity  of  calcium 
remaining  in  solution  appears  on  this  account  to  be  slightly  larger 
than  it  actually  is.  If  all  the  barium  and  strontium  originally 
present  in  the  water  is  deducted,  as  is  usually  done,  from  the 
calcium  found  in  the  water  after  boiling  (and  containing  the  stron- 
tium and  barium),  a  slight  error  is  evidently  introduced  because 
of  the  inequality  of  the  atomic  weights,  for,  properly  speaking, 
only  so  much  of  the  strontium  and  barium  contained  in  the  boiled 
water  should  be  deducted  from  or  added  to  the  calcium  as  is  equiv- 
alent to  the  strontium  or  barium  separated  by  boiling. 

To  avoid  this  small  error,  there  but  remains  to  determine  the 
strontium  and  barium  in  the  calcium  (containing  the  strontium 
and  barium)  obtained  from  the  boiled  water,  and  to  deduct  the 


§  211.]   MODIFICATIONS  REQUIRED  WITH  SALINE   WATERS.      271 

weight  found  from  that  of  the  calcium  +  strontium  +  barium 
obtained  from  the  boiled  water,  while,  on  the  other  hand,  the 
weight  of  the  calcium  equivalent  to  the  small  quantities  of  stron- 
tium and  barium  separated  as  carbonates  with  calcium  carbonate 
on  boiling  is  added  to  the  weight  of  the  calcium  thus  found.  These 
quantities  are  determined  by  subtracting  the  strontium  and  barium 
found  hi  the  boiled  water  from  the  total  weights  originally  found. 

These  slight  corrections  are  scarcely  worth  considering,  how- 
ever, because  magnesium  bicarbonate  is  decomposed  by  calcium 
sulphate  on  boiling  (see  foot-note,  p.  269). 

3.  DETERMINATION  OF  THE  IODINE  AND  BROMINE. 

In  the  case  of  alkaline  waters,  the  evaporation  of  large  volumes 
of  the  mineral  water,  as  described  in  §  209,  6,  may  be  effected 
without  any  addition  and  without  fear  of  any  loss  of  bromine 
or  iodine.  The  like  certainty  is  not  afforded,  however,  in  the  case 
of  non-alkaline  waters,  because  portions  of  these  halogens  may  be 
volatilized  by  the  decomposition  of  magnesium  bromide  and  iodide. 
It  becomes  necessary,  hence,  to  add  to  the  non-alkaline  water 
sufficient  perfectly  pure  sodium  carbonate  (it  is  best  to  use  such 
as  has  been  repeatedly  boiled  with  alcohol)  until  the  liquid  is 
strongly  alkaline  before  evaporating.  The  determination  of  the 
iodine,  bromine,  etc.,  is  then  carried  out  as  detailed  in  §  209,  6. 

4.  DETERMINATION  OF  THE  BARIUM  AND  STRONTIUM. 

The  behavior  of  the  mineral  water  on  boiling  affords  no  suffi- 
ciently satisfactory  conclusion  regarding  the  forms  of  the  com- 
pounds in  which  the  barium  and  strontium  are  present  in  saline 
waters.  As  a  rule,  portions  of  the  barium  and  strontium  are 
found  in  the  precipitate,  whereas  other  portions  remain  dissolved, 
and  according  as  one  or  the  other  appears  to  be  larger  in  quantity 
(a  spectroscopic  examination  will  afford  an  approximate  idea),  it  is 
usual  to  calculate  the  two  bases  either  as  sulphates  or  carbonates. 
On  account  of  the  different  methods  of  arranging  the  results,  the 
analyses  of  mineral  waters  are  not  comparable;  I  consider  it  would 
be  best  to  calculate  the  barium  and  strontium  in  saline  waters  as 


272  ANALYSIS    OF    WATER.  [§  212- 

sulphates.  These  are  more  soluble  in  water  containing  sodium 
chloride  than  in  pure  water,  hence  their  occurrence  (especially  that 
of  the  barium  sulphate)  in  solution  is  not  at  all  astonishing,  and 
their  partial  separation  as  carbonates  on  boiling  the  water  is  ex- 
plained by  the  double  decomposition  between  the  calcium  bicar- 
bonate and  the  sulphates,  to  form  calcium  sulphate,  and  barium 
jind  strontium  carbonates,  as  already  noticed,  §  211/2. 

5.  DETERMINATION  OF  THE  AMMONIA,  AND  DETECTION  AND 
DETERMINATION  OF  THE  VOLATILE  ORGANIC  ACIDS. 

Attention  has  already  been  drawn  ( §  209,  8  and  11)  to  the  slight 
modifications  in  BOUSSINGAULT'S  method,  to  be  employed  in  de- 
termining the  ammonia,  and  in  evaporating  the  mineral  water  for 
the  detection  and  determination  of  the  volatile  organic  acids,  when 
the  water  contains  no  sodium  bicarbonate. 

REMARKS  ON  THE  ANALYSIS  OF  SULPHUR  WATER. 

§  212. 

It  has  already  been  noted  (§  208,  8)  in  what  forms  sulphur 
may  be  found  in  sulphur  waters;  also  the  methods  best  adapted  for 
determining  the  free  hydrogen  sulphide  as  well  as  that  combined 
with  a  metallic  sulphide  in  the  form  of  a  sulpho  salt;  also  the 
sulphur  present  as  mono-  and  disulphide,  and  that  present  as 
thiosulphate. 

The  few  additional  observations  made  by  others  as  well  as  by 
myself  may  be  here  added. 

1.  The  determination  of  the  sulphuric  acid  cannot  be  effected 
in  the  usual  manner,  as  the  hydrogen  sulphide  is  constantly  under- 
going oxidation  by  the  atmospheric  air,  which  hence  introduces 
serious  errors.     The  determination  is  made  as  in  §  167  (247). 

2.  The  total  quantity  of  the  sulphur,  whether  combined  with 
oxygen,  hydrogen,  or  metal,  is  determined,  by  way  of  control,  by 
conducting  air-free  chlorine  gas  into  a  measured  volume  of  water, 
which  is  then  acidulated   with  hydrochloric   acid,   concentrated, 
and  the  sulphuric  acid  formed  precipitated  with  barium  chloride. 


§  212.]    REMARKS    ON   THE    ANALYSIS    OF    SULPHUR    WATER.    273 

3.  The  behavior  of  waters  containing  free  hydrogen  sulphide 
differs  of  course  from  that  of  waters  containing  metallic  sulphides, 
or  sulpho  salts  (hepatic  waters).  As  an  example  of  the  former 
kind  may  be  mentioned  the  Weilbach  water,  which  contains  in 
the  form  of  hydrogen  sulphide  all  the  sulphur  not  combined  with 
oxygen.  The  water  smells  strongly  of  hydrogen  sulphide,  and 
on  being  shaken  in  a  half-filled  bottle  disengages  hydrogen  sul- 
phide and  carbonic  acid ;  on  passing  a  current  of  hydrogen  through 
it,  it  almost  completely  loses  its  hydrogen  sulphide.  When  kept 
in  a  bottle  containing  also  air,  it  soon  deposits  sulphur,  the  liquid 
becoming  turbid,  while  the  odor  of  hydrogen  sulphide  constantly 
diminishes ;  by  the  further  action  of  the  air,  the  precipitated  sul- 
phur is  oxidized  (to  sulphuric  acid)  and  as  a  rule  dissolves,  leaving 
the  water  as  clear  as  at  first. 

The  Stachelberg  water,  analyzed  by  SIMMLER,*  will  serve  as 
an  example  of  the  latter  kind  of  water.  It  has  but  a  slight  odor 
(in  winter  almost  none  at  all)  of  hydrogen  sulphide,  renders  red 
litmus  paper  perfectly  blue  in  the  course  of  one  minute,  but  has 
no  effect  on  turmeric  paper;  manganous  chloride  causes  in  it  a 
flesh-colored  precipitate,  ferrous  sulphate  a  black  one,  while  sodium 
nitroprussiate  develops  a  reddish-violet  color.  If  a  bottle  be  filled 
with  the  water,  this  soon  becomes  slightly  cloudy;  but  within  five 
minutes  the  water  becomes  clear  again,  and  then  has  a  distinctly 
yellowish  tinge;  by  the  further  action  of  air,  and  after  repeated  tur- 
bidity and  clearing,  the  water  becomes  deep  yellow  in  color,  due 
to  the  formation  of  disulphate.  With  full  access  of  air,  a  copious 
deposit  of  sulphur  forms,  with  the  simultaneous  formation  of  sodium 
thiosulphate. 

The  cause  of  the  different  behavior  of  the  two  kinds  of  water 
becomes  at  once  apparent  when  we  consider  the  different  pro- 
portion in  which  the  sulphur,  in  combination  with  hydrogen  or 
metals,  bears  to  the  free  carbonic  acid  in  the  two  waters.  In  the 
case  of  the  Weilbach  water  this  proportion  is  1:24,  while  in  the 
Stachelberg  water  it  is  1:2.  Were  a  current  of  carbonic  acid 
passed  into  the  latter,  it  would  convert  the  hepatic  water  into  one 

*  Journ.  f.  prakt.  Chem.,  LXXI,  1. 


274  ANALYSIS    OF    WATER.  [§  213. 

containing  free  hydrogen  sulphide,  because  carbonic  acid  expels 
hydrogen  sulphide  from  sodium  sulphide  or  sodium  sulphydrate, 
as,  on  the  other  hand,  hydrogen  sulphide  expels  carbonic  acid 
from  sodium  bicarbonate. 

Owing  to  the  slight  difference  of  affinity,  the  action  depends 
upon  the  amount  of  either  of  the  compounds  present;  the  greater 
the  quantity  of  free  carbonic  acid  present  in  a  water  containing 
sodium  carbonate,  the  smaller  will  be  the  quantity  of  combined 
hydrogen  sulphide  and  the  greater  that  of  free  hydrogen  sulphide. 
The  temperature  also  has  some  influence  on  this  point;  for  instance 
in  the  cold  sodium  bicarbonate  may  be  present  beside  sodium 
sulphide,  whereas  at  a  higher  temperature  sodium  monocarbonate 
will  be  formed  with  evolution  of  hydrogen  sulphide.  Sulphur 
waters  which  contain  no  alkali  bicarbonate,  and  which  hence  ac- 
quire no  alkaline  reaction  on  being  boiled,  are  to  be  considered 
as  simple  solutions  of  hydrogen  sulphide,  like,  for  instance,  the 
sulphur  water  analyzed  by  A.  and  H.  STRECKER.* 

2.  CALCULATION,  CONTROL,  AND  ARRANGEMENT   OF  THE  RE- 
SULTS OF  ANALYSES  OF  MINERAL  WATERS. 

§213. 

The  results  of  the  analyses  performed  as  described  in  1  are  ob- 
tained by  direct  experiment,  and  are  altogether  independent  of 
any  theoretical  considerations  regarding  the  manner  in  which  the 
various  constituents  are  combined  or  associated  with  each  other 
As  the  theoretical  views  may  change  according  as  chemical  science 
develops,  it  becomes  absolutely  necessary,  in  reporting  the  analyses 
of  waters,  to  give  the  direct  results  and  also  the  methods  by  which 
they  were  obtained.  The  analysis  is  then  of  service  for  all  time, 
as  it  at  least  gives  the  data  for  determining  whether  the  composi- 
tion of  the  water  is  constant  or  not. 

So  far  as  the  principles  are  concerned,  according  to  which  the 
acids  and  bases  are  as  a  rule  associated  hypothetically  to  form 
salts,  it  is  assumed  that  the  bases  and  acids  are  combined  accord- 

*  Annal.  d.  Chem.  u.  Pharm.,  xcv,  175. 


§  213.]      RESULTS   OF   ANALYSES   OF  MINERAL   WATERS.  275 

ing  to  their  respective  affinities,  i.e.,  the  strongest  base  is  assumed 
to  be  combined  with  the  strongest  acid,  etc.,  due  attention  being 
also  paid,  however,  to  the  greater  or  less  solubility  of  the  salts, 
which,  as  is  well  known,  exercise  a  considerable  influence  on  the 
manifestations  of  the  force  of  affinity.  For  instance,  it  is  assumed 
that,  when  calcium,  potassium,  and  sulphuric  acid  are  found  in 
water  that  has  been  boiled,  the  sulphuric  acid  is  combined  with 
the  calcium,  etc.  It  cannot  be  denied,  however,  that  there  is 
thus  introduced  the  possible  variation  due  to  the  personal  views 
of  the  analyst,  and  that  consequently  different  reports  may  be 
calculated  from  the  results  of  the  same  direct  experiments. 

It  would  be  very  advantageous  to  have  a  general  understand- 
ing regarding  the  arrangement  of  the  results  of  analyses,  because 
otherwise  the  comparison  of  two  mineral  waters  is  effected  with 
the  greatest  difficulty;  it  cannot  be  expected,  however,  that  such 
an  understanding  will  be  soon  arrived  at,  but  so  long  as  it  is  want- 
ing, the  comparison  of  two  mineral  waters  can  only  be  made  with 
regard  to  the  immediate  and  direct  results  of  the  analyses. 

On  one  point,  however,  an  agreement  should  at  once  be  arrived 
at,  and  that  is  to  put  down  all  the  salts  in  the  anhydrous  condition. 

In  order  to  more  clearly  show  the  principles  which  serve  as  a 
basis  of  the  most  correct  arrangement  of  the  results  of  analyses, 
as  also  the  method  whereby  the  results  may  be  controlled,  I  cite 
as  an  example  the  Elisabethenquelle  at  Homburg  v.  d.  Hohe, 
which  was  analyzed  by  me.  This  water  is  saline;  it  has  been  se- 
lected because  its  calculation  is  somewhat  complicated.  In  the 
case  of  alkaline  waters  the  calculation  is  simpler,  as  in  these  the 
alkaline  earths  are  usually  calculated  as  carbonates  or  bicarbonates. 

ANALYSIS  OF  THE  WATER  OF  THE  ELISABETHENQUELLE  AT  HOMBURG, 

v.  D.  HOHE. 

a.    Direct  Results  of  the  Analysis. 

The  numbers  express  the  mean  of  two  or  three  concordant  experiments 
and  give  the  weight  in  grammes  of  substance  in  1000  grammes  of  the  water! 

1.  Silver  chloride,  bromide  and  iodide  together 28-97763 

2.  Bromide  and  iodine — 

a.  Bromine 0-002486 

Corresponding  with  silver  bromide 0  •  00584 


276  ANALYSIS    OF    WATER.  [§  213. 

b.  Iodine 0-0000285 

Corresponding  with  silver  iodide 0-000053 

3.  Chlorine — 

Silver  chloride,  bromide  and  iodide 28-97763 

Deduct— 

Silver  bromide 0-00584 

Silver  iodide  ..  .  0-00005 0-00589 


Remainder,  silver  chloride  28-97174 

Corresponding  with  chlorine 7  •  16264 

4.  Sulphuric  acid 0-01796 

5.  Carbonic  acid  (total) 3-32925 

6.  Silicic  acid 0-02635 

7.  Ferrous  oxide 0-01438 

8.  Lime  and  strontia  together,  expressed  as  carbonates 2- 15835 

9.  Magnesia  (total) 0-32129 

10.  Lime  and  strontia  *  retained  in  solution  after  boiling  the 

water,  expressed  as  carbonates 0  •  64633 

11.  Lime  precipitated  on  boiling — 

Total  lime  +  strontia,  expressed  as  carbonates 2-15885 

Lime  and  strontia  retained  in  solution  on  boiling,  ex- 

3  carbonates. .  0-64633 


The  remainder=  1  •  51252 

Gives  in  form  of  carbonate  the  amount  of  lime  precipi- 
tated on  boiling ;  this  corresponds  with  lime 0  •  84701 

12.  Lime  retained  in  solution  after  boiling — 

Sum  of  the  lime  and  strontia  retained  in  solution,  ex- 
pressed as  carbonates 0  •  64633 

Deduct  the  strontia  (see  13),  which  calculated  into  car- 
bonate   =  0-01428 

Remainder=  0-63205 

Which  corresponds  with  lime  0-35395 

13.  Baryta,  strontia,  and  manganous  oxide — 

a.  Baryta 0-00066 

6.  Strontia 0-01002 

c.  Manganous  oxide 0  •  00094 

14.  Phosphoric  acid 0-00043 

15.  Lithia  . 0-00764 

Corresponding  with  lithium  chloride 0-02163 

16.  Sodium  chloride  +  potassium  chloride  +  lithium  chloride.  10-22880 

17.  Potash 0-21876 

Corresponding  with  potassium  chloride 0  •  34627 


*  All  the  strontia  was  retained  in  solution ,  the  trace  of  baryta  which  was  within  the 
limits  of  the  experimental  error  in  the  lime  determination  was  neglected  in  Miscalculation. 


§  213-]     RESULTS   OF   ANALYSES   OF   MINERAL   WATERS,  277 

18.  Soda- 

Sum  of  the  chlorides  of  sodium,  potassium  and  lithium .   10  •  22880 

Deduct— 

Potassium  chloride 0-34627 

Lithium  chloride 0-02163 0-36790 

Remainder,  sodium  chloride  9-86090 

Which  corresponds  with  soda  5-22899 

19.  Ammonium  oxide 0-010655 

20.  Total  of  fixed  constituents 13-18438 

21.  Specific  gravity 1-01140  at  19-5° 

The  following  substances  were  present  in  unweighable  amounts,  viz., 
caesia,  rubidia,  alumina,  nickelous  oxide,  cobaltous  oxide,  oxide  of  copper, 
teroxide  of  antimony,  arsenic  acid,  boric  acid,  fluorine,  nitric  acid,  volatile 
organic  acids,  non-volatile  organic  matter,  nitrogen,  light  carburetted  hy- 
drogen, hydrogen  sulphide. 

b.  Calculation. 

a.  Barium  sulphate — 

Baryta  present  (13) 0-00066 

Combines  with  sulphuric  acid 0  •  00034 


To  form  barium  sulphate  0-00100 
6.  Strontium  sulphate — 

Strontia  present  (13) 0-01002 

Combines  with  sulphuric  acid 0-00774 

To  form  strontium  sulphate     0-01776 
c.  Calcium  sulphate — 

Sulphuric  acid  present  (4)   0-01796 

Of  this  is  combined — 

With  barium 0-00034 

With  strontium .  .  .  0-00774. .  0-00808 


The  remainder  0-00988 

Combines  with  calcium 0  •  00692 

To  form  calcium  sulphate  0-01680 
d.  Magnesium  bromide — 

Bromine  present  (2) 0-002486 

Combines  with  magnesium 0  •  000373 


To  form  magnesium  bromide  0-002859 
e.  Magnesium  iodide — 

Iodide  present 0-0000285 

Combines  with  magnesium 0-OOC0027 

To  form  magnesium  iodide  0-0000312 


278  ANALYSIS    OF    WATER.  [§  213. 

/.  Calcium  chloride — 

Lime  present  in  boiled  water  (12) 0-35395 

Of  this  is  combined  with  sulphuric  acid  (c) 0  •  00692 


The   remainder     0-34703 

Corresponds  with  calcium     0-24788 

Which  combines  with  chlorine     0-43949 


To  form  calcium  chloride  0-68737 
g.  Potassium  chloride — 

Potassa  present  (17) 0-21876 

Corresponds  with  potassium 0- 18161 

Which  combines  with  chlorine 0-16466 

To  form  potassium  chloride  0  •  34627 

h.  Lithium  chloride 0  •  00764 

Lithia  present  (15) 0  •  00356 

Corresponds  with  lithium 0-01807 


Which  combines  with  lithium  0-02163 
i.  Ammonium  chloride — 

Ammonium  oxide  present  (19) 0-01065 

Corresponds  with  ammonium 0 . 00737 

Which  combines  with  chlorine  .  .  0-01452 


To  form  ammonium  chloride  0-02189 
k.  Sodium  chloride — 

Soda  present  (18) 5-22899 

Corresponds  with  sodium 3  •  87957 

Which  combines  with  chlorine  .  .  5-98133 


To  form  sodium  chloride     9  •  86090 
1.  Magnesium  chloride — 

Chlorine  present  (3) 7-16264 

Of  this  is  combined — 

With  calcium 0-43949 

With  potassium 0-16466 

With  lithium 0-01807 

With  ammonium 0-01452 

With  sodium.,  .5-98133..  6-61807 


Remainder  0 . 54457 

Which  combines  with  magnesium  0-18429 

•    To  form  magnesium  chloride  0-72886 
m.  Calcium  phosphate — 

Phosphoric  acid  present  (14). . 0 . 00043 

Combines  with  lime  (3  eq.) 0-00051 

To  form  basic  calcium  phosphate  0-00094 


§  213.]     RESULTS    OF   ANALYSES   OF   MINERAL   WATERS.  279 

n.  Calcium  carbonate — 

Calcium  present  in  precipitate  obtained  by  boil- 
ing (11) 0-84701 

Of  this  is  combined  with  phosphoric  acid  (ra) . . .     0-00051 

The  remainder    0-84650 
Combines  with  carbonic  acid     0-66511 

To  form  calcium  monocarbonate     1-51161 
o.  Magnesium  carbonate — 

Total  magnesia  (9) 0-32129 

Corresponds  with  magnesium 0-19277 

Of  which  is  combined — 

With  bromine  (d) 0-000373 

With  iodine  (e) 0-000003 

With  chlorine  (0 0-184290 0-18467 


The  remainder     0.00810 

Corresponds  to  magnesium     0-01350 

Which  combines  with  carbonic  acid     0  •  01485 


To  form  magnesium  monocarbonate  0-02835 
p.  Ferrous  carbonate — 

Ferrous  oxide  present  (7) 0-01438 

Combines  with  carbonic  acid 0*  00879 

To  form  ferrous  carbonate  0-02317 
q.  Manganous  carbonate — 

Manganous  oxide  present  (13) 0-00094 

Combines  with  carbonic  acid  .  0-00058 


To  form  manganous  carbonate  0  •  00152 
r.  Silicic  acid — 

Silicic  acid  present  (6) 0-02635 

s.  Free  carbonic  acid — 

Total  carbonic  acid  (5) 3-32925 

Of  this  is  combined  to  form  neutral  salts — 

With  lime  (n) 0-66511 

With  magnesia  (o) 0-01485 

With  ferrous  oxide  (p) 0-00879 

With  manganous  oxide  (q) 0-00058 0-68933 


Remainder  2-63992 
Of  this  is  combined  with  monocarbonates  forming 

bicarbonates 0-68933 

Remainder,  free  carbonic  acid  1-95059 


280  ANALYSIS    OF   WATER.  [§  213. 

c.  Comparison  of  the  Total  Quantity  of  Fixed  Constituents  Found 

Directly  with  the  Sum  of  the  Several  Constituents. 
The  several  determinations  have  given — 

Barium  sulphate 0-00100 

Strontium  sulphate 0-01776 

Calcium  sulphate 0-01680 

Magnesium  bromide 0-00286 

Magnesium  iodide 0-00003 

Calcium  chloride 0-68737 

Potassium  chloride 0-34627 

Lithium  chloride 0-02163 

Ammonium  chloride 0-02189 

Sodium  chloride 9-86090 

Magnesium  chloride 0  •  72886 

Calcium  phosphate 0-00094 

Calcium  carbonate 1  •  51161 

Magnesium  carbonate 0-02835 

Ferric  oxide  * 0.01598 

Manganese  protosesquioxide  * 0-00101 

Silicic  acid..  .  0-02635 


13-28961 
The  residue  dried  at  180°  13-18438 

An  accurate  agreement  between  these  figures  cannot  be  ex- 
pected, particularly  in  the  case  of  a  water  like  the  above;  in  fact, 
were  they  to  agree,  we  could  conclude  that  the  analysis  was  in- 
correct. The  causes  of  the  difference  are  manifest,  although  they 
can  scarcely  be  expressed  numerically.  In  the  first  place  the 
ammonium  chloride  and  calcium  carbonate  decompose  each 
other  during  the  evaporation,  calcium  chloride  and  ammonium 
carbonate  being  formed,  the  latter  escaping;  then  the  magnesium 
chloride,  bromide,  and  iodide  become  basic  with  loss  of  a  portion 
of  their  respective  hydrogen  acids;  furthermore,  silicic  acid  expels 
carbonic  acid  from  carbonates  during  evaporation.  It  will  be 
seen  that  all  these  causes  tend  in  one  direction,  'i.e.,  to  cause  the 
sum  of  the  severally  determined  constituents  to  be  higher  than  that 
of  the  residue  obtained  on  evaporation. 

A  more  accurate  control  is  obtained  by  treating  the  evapora- 
tion-residue with  sulphuric  acid  (p.  245),  and  comparing  the  resi- 
due of  the  sulphates  (the  iron  is  present  as  ferric  oxide)  with  the 

*  These  compounds  are  here  put  down  in  the  condition  in  which  they  are  present  in  the 
residue  dried  at  180°. 


§  213.J      RESULTS    OF    ANALYSES    OF    MINERAL    WATERS.  281 

sum  of  the  fixed  alkalies,  alkaline  earths,  and  manganese  calculated 
as  sulphates,  plus  the  ferric  oxide  and  silicic  acid,  also  any  alumina 
or  aluminium  phosphate,  should  such  be  present,  as  well  as — in 
the  case  of  alkaline  waters — any  additional  phosphoric  acid  as 
sodium  pyrophosphate  (in  saline  waters  as  calcium  phosphate), 
and  subtracting  from  the  sum  the  quantity  of  sodium  sulphate 
(as  calcium  sulphate)  corresponding  with  sodium  pyrophosphate 
(or  calcium  phosphate). 

As  an  example  I  give  here  the  control  relating  to  my  analysis 
of  the  Kranchen  water  at  Ems.* 

The  residue  obtained  on  evaporating  with  sulphuric  acid  and 
gently  igniting  is  compared  with  the  sum  of  the  several  constitu- 
ents calculated  as  sulphates,  or  oxides,  both  results  being  expressed 
in  parts  per  thousand. 

Found  soda  1  •  355391,  calculated  as  sodium  sulphate 3  •  102042 

Found  potassa  0-019891,  calculated  as  potassium  sulphate  0-036773 

Found  lithia  0-001029,  calculated  as  lithium  sulphate 0-003769 

Found  lime  0-084068,  calculated  as  calcium  sulphate 0-204165 

Found  strontia  0  •  001266,  calculated  as  strontium  sulphate  0  •  002245 
Found  baryta  0-0006513,  calculated  as  barium  sulphate.   0-000992 
Found  magnesia  0-064683,  calculated  as  magnesium  sul- 
phate     0-194050 

Found  ferrous  oxide  0-000895,  calculated  as  ferric  oxide.  0-000994 
Found  manganous  oxide  0-0000773,  calculated  as  man- 

ganous  sulphate 0-000164 

Found  silicic  acid  and  calculated  as  such 0-049741 

Found  aluminium  phosphate 0-000116 

Found  residual  phosphoric  acid  0-000637,  calculated  as 

sodium  pyrophosphate .   0 . 001367 


Total 3-596418 

Deduct  sodium  sulphate  for  sodium  phosphate 0-001459 

Residual  sulphates,  etc 3  •  594959 

Found  directly 3 . 594699 

d.  Arrangement  of  Results. 

The  results  are  best  arranged  in  a  manner  to  show  the  number 
of  parts  of  the  constituents  .per  thousand  (or  1,000,000)  parts  of 
water  (or  grains  per  gallon,  see  pp.  215,  216). 

*  Jahrbucher  des  nassauischen  Sereins  fur  Naturkunde,  Jahrgang  27  and 
28,  pp.  114  et  seq. 


ANALYSIS    OF    WATER.  [§  213. 

The  following  are  the  heads  under  which  the  several  constituents 
are  best  classified : 

a.  Present  in  weighable  quantity. 

b.  Present  in  unweighable  quantity. 

Regarding  carbonates,  it  is  a  question  whether  they  should  be 
put  down  as  neutral  salts,  calculating  the  excess  of  carbonic  acid 
partly  as  bicarbonates  and  partly  as  free  acid,  or  calculating  the 
whole  as  bicarbonates,  the  excess  of  carbonic  acid  being  then  con- 
sidered as  being  present  in  the  free  state.  Sometimes  one  way; 
sometimes  the  other,  is  adopted.  I  usually  report  analyses  in 
both  ways,  in  order  to  facilitate  the  comparison  of  the  results  with 
those  of  the  analysis  of  other  similar  springs. 

It  is  usual  to  give  the  volume  of  the  carbonic  acid  (and  of  gases 
generally)  in  c.c.  per  litre  (or  cubic  inches  per  gallon),  calculated 
to  the  temperature  of  the  spring  and  the  normal  pressure  (760  mm.). 

As  further  examples  of  the  methods  of  calculating,  controlling, 
and  reporting  the  results  of  analyses  of  mineral  waters  the  follow- 
ing memoirs  are  cited : 

1.  Analysis  of  the  Kochbrunnen  of  Wiesbaden  (saline  thermal  spring). 

2.  Analysis  of  the  mineral  springs  of  Ems  (thermal  alkaline  springs). 

3.  Analysis  of  the  springs  of  Schlangenbad  (thermal  springs  holding  only 
an  extremely  small  quantity  of  solid  constituents  in  solution). 

4.  Analysis  of  the  mineral  springs  of  Langenschwalbach  (alkaline  chaly- 
beate springs,  abounding  in  carbonic  acid). 

5.  Analysis    of    the  Weilbach   sulphuretted    spring    (cold    sulphuretted 
spring). 

6.  Analysis  of  the  mineral  spring  of  Geilnau  (alkaline  chalybeate  spring, 
abounding  in  carbonic  acid). 

7.  Analysis  of  the  new  soda  spring  of  Weilbach  (alkaline  spring  contain- 
ing much  lithia). 

8.  Analysis  of  the  mineral  spring  at  Niederselters  (alkaline  spring  abound- 
ing in  carbonic  acid). 

9.  Analysis  of  the  mineral  spring  at  Fachingen  (very  rich  in  bicarbonate 
of  soda). 

All  these  papers  are  comprised  in  one  work,  entitled  "Chemische 
Untersuchung  der  wichtigsten  Mineralwasser  des  Herzogthums 
Nassau,  von  Professor  Dr.  R.  FRESENIUS"  (C.  W.  KREIDEL,  Wies- 
baden). They  will  also  be  found  in  the  "  Jahrbiichern  des  Nassau- 
ischen  Naturhistorischen  Vereins." 


§  213.]      RESULTS    OF   ANALYSES   OF    MINERAL   WATERS.  283 

Nos.  1  and  2  contain  a  detailed  description  of  the  methods  em- 
ployed in  the  examination  of  the  muddy  ochreous  deposits  and 
solid  sinter  deposits  of  the  springs  in  question.  Nos.  4,  5,  and  6  are 
also  published  in  the  "Journal  fiir  praktische  Chemie,"  Band  64,  70, 
72. 

The  student  may  also  consult  the  author's  "Analyses  of  the 
Homburg  Mineral  Springs"  (KREIDEL,  Wiesbaden) — these  springs 
abound  in  carbonic  acid,  contain  iron,  and  are  very  saline — and 
1 '  Analysis  of  the  Mineral  Springs  at  Wildungen "  (MITTLER,  Arol- 
sen) — this  water  abounds  in  carbonic  acid,  is  more  or  less  alkaline 
and  chalybeate,  and  contains  much  alkaline  earthy  bicarbonate. 

The  following  are  examples  of  analyses  of  mineral  waters  more 
recently  made  by  the  author: 

Trinkquelle,  Badequelle,  and  Helenenquelle  at  Pyrmont 1  (chalybeate 
springs  containing  much  sulphate  of  lime). 

Trinkquelle  at  Driburg  (chalybeate  spring  containing  much  sulphate  of 
lime),  Herster  mineral  spring  (earthy  mineral  spring),  also  Satzer  sulphuretted 
mud  spring.2 

Tonnissteiner  Heilbrunnen  (containing  alkaline  salts  and  very  rich  in 
carbonate  of  magnesia),  and  Tonnissteiner  Stahlbrunnen.3 

Lamscheider  mineral  spring  4  (alkaline  salts). 

Augustaquelle,  Victoriaquelle,  Romerquelle,  fresh  examination  of  the 
Kranchen,  Fiirstenbrunnen,  Kesselbrunnen,  and  the  new  Badequelle  at  Ems,5 

Stahlbrunnen  at  Homburg,  v.  d.  H.' 

Carlsquelle  at  Bad  Helmstedt  7  (chalybeate  spring). 

Deutsch-Kreutzer  Sauerbrunnen  at  Oedenburg  8  (alkaline  salts). 

New  Selser  springs  at  Grosskarben  9  (earthy  salts). 

Grindbrunnen  at  Frankfort-on-the-Maine 10  (containing  alkaline  sul- 
phides). 

Mineral  spring  at  Birresborn  n  (alkaline  salts). 

Mineral  spring  at  Neudorf  in  Bohemia  12  (alkaline  and  iron  salts). 

Thermal  spring  at  Assmannshausen  13  (alkaline  salts,  rich  in  lithia). 

Mineral  spring  at  Biskirchen  14  (alkaline  salts). 

Wappenquelle  at  Ems  15  (alkaline  thermal  spring). 

Thermal  brine  spring  at  Werne.16 

1  A.  SPEYER,  Arolsen,  1865. 

2  C.  W.  KREIDEL,  Wiesbaden,  1866.  3  Ibid.,  1869.  4  Ibid.,  1869. 
6  Ibid.,  1865,  1869,  1870,  1872.  6  Ibid.,  1872.             7  Ibid.,  1873. 
*Ibid.,  1874.  »Ibid.,  1874. 

10  C.  NAUMANN,  Frankfort-on-the-Maine,  1874. 

11  C.  W.  KREIDEL,  Wiesbaden,  1876.  12  Ibid.,  1876.  13  Ibid.,  1876. 
u  Ibid.,  1876.                                                              15  Ibid.,  1876.  16  Ibid.,  1877. 


284:  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  214, 


II.  ANALYSES  OF  SUCH  PRODUCTS  AS  ARE  FRE- 
QUENTLY THE  OBJECT  OF  CHEMICAL  IN- 
VESTIGATION, WITH  PROCESSES  FOR  DETER- 
MINING THEIR  COMMERCIAL  VALUE. 

1.  DETERMINATION  OF  FREE  ACID  (ACIDIMETRY). 

A.  DETERMINATION  BY  SPECIFIC  GRAVITY. 
§214. 

As  the  relation  between  the  specific  gravity  of  an  aqueous 
liquid  or  acid  and  the  quantity  of  real  acid  present  in  the  liquid  is 
known,  as  the  result  of  exact  experiments  which  have  been  tabu- 
lated, it  is  frequently  only  necessary  to  ascertain  the  specific 
gravity  of  a  liquid  in  order  to  ascertain  its  acid  strength.  Care 
must,  however,  be  taken  that  the  acids  be  free  or  almost  free  from 
other  soluble  substances.  In  the  case  of  volatile  acids  (and  most 
of  the  common  ones  are  volatile — sulphuric,  hydrochloric,  nitric, 
acetic),  any  non-volatile  substances  may  be  usually  readily  de- 
tected by  evaporating  a  small  sample  of  the  acid  in  a  small  plati- 
num or  porcelain  dish  and  observing  whether  it  leaves  a  fixed 
residue. 

The  determination  of  the  specific  gravity  is  effected  either  by 
weighing  equal  volumes  of  acid  and  water  and  comparing  the 
weights  (pp.  208  and  209),*  or  by  means  of  a  good  hydrometer. 
Care  must  be  taken  to  make  the  determination  at  the  temperature 
to  which  the  tables  are  calculated. 

The  following  tables  give  the  relationship  between  the  specific 
gravity  and  acid  content  of  sulphuric  acid,  hydrochloric  acid,  nitric 
acid,  phosphoric  acid,  acetic  acid,  tartaric  acid,  and  citric  acid: 

*  Zeitschr.  /.  analyt.  Ghent.,  ix,  233  and  344. 


§  214.] 


ACIDIMETRY. 


285 


TABLE  la. 

Showing  the  percentages  of  Acid  (H,SO4)  and  Anhydride  (SO3)  corresponding  to 
various  specific  gravities  of  aqueous  Sulphuric  Acid  by  BINEAU;  calculated 
for  15°  by  OTTO. 


Specific  ' 
gravity. 

Percentage 
of  H^SO4. 

Percentage 
of  SO3. 

Specific 
gravity. 

Percentage 
of  H2S04. 

Percentage 
of  S03. 

1-8426 

100 

81-63 

•398 

50 

40-81 

1-842 

99 

80-81 

•3886 

49 

40-00 

1-8406 

98 

80-00 

•379 

48 

39-18 

1-840 

97 

79-18 

•370 

47 

38-36 

1-8384 

96 

78-36 

-361 

46 

37-55 

1-8376 

95 

77-55 

-351 

45 

36-73 

1-8356 

94 

76-73 

-342 

44 

35-82 

1-834 

93 

75-91 

•333 

43 

35-10 

1-831 

92 

75-10 

•324 

42 

34-28 

1-827 

91 

74-28 

•315 

41 

33-47 

1-822 

90 

73-47 

•306 

40 

32-65 

1-816 

89 

72-65 

-2976 

39 

31-83 

1-809 

88 

71-83 

•289 

38 

31-02 

1-802 

87 

71-02 

1-281 

37 

30-20 

-794 

86 

70-10 

1-272 

36 

29-38 

•786 

85 

69-38 

1-264 

35 

28-57 

'      -777 

84 

68-57 

1-256 

34 

27-75 

•767 

83 

67-75 

1-2476 

33 

26-94 

.756 

82 

66-94 

1-239 

32 

26-12 

•745 

81 

66-12 

1-231 

31 

25-30 

•734 

80 

65-30 

1-223 

30 

*    24-49 

•  722 

79 

64-48 

1-215 

29 

23-67 

•710 

78 

63-67 

1-2066 

28 

22-85 

•698 

77 

62-85 

1-198 

27 

22-03 

•686 

76 

62-04 

1-190 

26 

21-22 

1-675 

75 

61-22 

1-182 

25 

20-40 

1-663 

74 

60-40 

1-174 

24 

19-58 

1-651 

73 

59-59 

1-167 

23 

18-77 

1-639 

72 

58-77 

1-159 

22 

17-95 

1-627 

71 

57-95 

1-1516 

21 

17-14 

1-615 

70 

57-14 

1-144 

20 

16-32 

1-604 

69 

56-32 

1-136 

19 

15-51 

1-592 

68 

55-59 

1-129 

18 

14-69 

1-580 

67 

54-69 

1-121 

17 

13-87 

1-568 

66 

53-87 

1-1136 

16 

13-06 

1-557 

65 

53-05 

1-106 

15 

12-24 

•545 

64 

52-24 

1-098 

14 

11-42 

•534 

63 

51-42 

•091 

13 

10-61 

•523 

62 

50-61 

•083 

12 

9-79 

•512 

61 

49-79 

•0756 

11 

8-98 

•501 

60 

48-98 

•068 

10 

8-16 

•490 

59 

48-16 

•061 

9 

7-34 

•480 

58 

47-34 

•0536 

8 

6-53 

•469 

57 

46-53 

•0464 

7 

5-71 

•4586 

56 

45-71 

1-039 

6 

4-89 

1-448 

55 

44-89 

.     1-032 

5 

4-08 

1-438 

54 

44-07 

1-0256 

4 

3-26 

1-428 

53 

43-26 

1-190 

3 

2-445 

1-418 

52 

42-45 

1-013 

2 

1-63 

1-408 

51 

41-63 

1-0064 

1 

0-816 

286 


DETERMINATION   OF   COMMERCIAL  VALUES.         [§  214. 


TABLE  16. 

Showing  the  quantity  of  add  in  mixtures  of  sulphuric  acid  and  water  at  each 
degree  BATJME  from  0  to  66,  with  the  corresponding  specific  gravities  at  15°, 
by  J.  KOLB.* 


Degree 
BAUME, 

Sp.gr. 

80s. 

H2S04. 

Degree 
BAUME. 

Sp.gr. 

S04. 

HaSO,. 

0 

1-000 

0-7 

0-9 

34 

1-308 

32-8 

40-2 

1 

1-007 

1-5 

1-9 

35 

1-320 

33-9 

41-6 

2 

1-014 

2-3 

2-8 

36 

1-332 

35-1 

43-0 

3 

1-022 

3-1 

3-8 

37 

1-345 

36-2 

44-4 

4 

-029 

3-9 

4-8 

38 

1-357 

37-2 

45-5 

5 

-037 

4-7 

5-8 

39 

1-370 

38-3 

46-9 

6 

•045 

5-6 

6-8 

40 

1-383 

39-5 

48-3 

7 

.    -052 

6-4 

7-8 

41 

1-397 

40-7 

49-8 

8 

•060 

7-2 

8-8 

42 

1-410 

41-8 

51-2 

9 

-067 

8-0 

9-8 

43 

1-424 

42-9 

52-8 

10 

-075 

8-8 

10-8 

44 

1-438 

44-1 

54-0 

11 

•083 

9-7 

11-9 

45 

1-453 

45-2 

55-4 

12 

-091 

10-6 

13-0 

46 

1-468 

46-4 

56-9 

13 

-100 

11-5 

14-1 

47 

1-483 

47-6 

58-3 

14 

-108 

12-4 

15  -.2 

48 

1-498 

48-7 

59-6 

15 

-116 

13-2 

16-2 

49 

1-514 

49-8 

61-0 

16 

•125 

14-1 

17-3 

50 

1-530 

51-0 

62-5 

17 

-134 

15-1 

18-5 

51 

-540 

52-2 

64-0 

18 

•142 

16-0 

19-6 

52 

•563 

53-5 

65-5 

19 

•152 

17-0 

20-8 

53 

•580 

54-9 

67-0 

20 

-162 

18-0 

22-2 

54 

•597 

56-0 

68-6 

21 

-171 

19-0 

23-3 

55 

•615 

57-1 

70-0 

22 

-180 

20-0 

24-5 

56 

•634 

58-4 

71-6 

23 

-190 

21-1 

25-8 

57 

-652 

59-7 

73-2 

24 

-200 

22-1 

27-1 

58 

-671 

61-0 

74-7 

25 

-210 

23-2 

28-4 

59 

-691 

62-4 

76-4 

26 

-220 

24-2 

29-6 

60 

•711 

63-8 

78-1 

27 

-231 

25-3 

31-0 

61 

•732 

65-2 

79-9 

28 

-241 

26-3 

32-2 

62 

•753 

66-7 

81-7 

29 

•252 

27-3 

33-4 

63 

•774 

68-7 

84-1 

30 

•  263 

28-3 

34-7 

64 

•796 

70-6 

86-5 

31 

1-274 

29-4 

36-0 

65 

•819 

73-2 

89-7 

32 

1-285 

30-5 

37-4 

66 

•842 

81  -G 

100-0 

33 

1-297 

31-7 

38-8 

*Politechn.  CentralbL,  1873,  826;  DINGLER'S  Polyt.  Journ.,  ccrx,  268; 
Zeitschr.  /.  analyt.  Chem.,  xn,  333.  KOLB'S  results  agree  with  BINEAU'S 
(Table  la)  very  closely,  although  not  absolutely.  With  reference  to  BAUME'S 
degrees  it  should  be  observed  that  the  zero  is  determined  in  pure  water  at 
15°,  and  the  degree  66°  B.  in  pure  hydrated  sulphuric  acid  of  1-842  specific 
gravity. 


§  214.] 


ACIDIMETRY. 


287 


TABLE  Ha. 

Showing  the  percentages  of  Anhydrous  Add  (HC1)  corresponding  to  various  specific 
gravities  of  aqueous  solutions  of  Hydrochloric  Acid,  by  URE.  Tempera- 
ture 15°. 


Specific  gravity. 

Percentage  of 
hydrochloric-acid  gas 
(HC1). 

Specific  gravity. 

Percentage  of 
hydrochloric-acid  gas 
(HC1). 

1-2000 

40-777 

1-1000 

20-388 

I  -  1982 

40-369 

1-0980 

i9-980 

1-1964 

39-961 

1-0960 

19-572 

1  -  1946 

39-554 

1-0939 

19-165 

1  •  1928 

39-146 

1-0919 

18-757 

1-1910 

38-738 

1-0899 

18-349 

1  •  1893 

38-330 

1-0879 

17-941 

1  •  1875 

37-923 

1-0859 

17-534 

1  •  1857 

37-516 

1-0838 

17-126 

1  -  1846 

37-108 

1-0818 

16-718 

1  -  1822 

36-700 

1-0798 

16-310 

1-1802 

36-292 

1-0778 

15-902 

1-1782 

35-884 

-0758 

15-494 

1-1762 

35-476 

-0738 

15-087 

1-1741 

35-068 

•0718 

14-679 

1-1721 

34-660 

•0697 

14-271 

1-1701 

34-252 

•0677 

13-863 

1-1681 

33-845 

1-0657 

13-456 

1-1661 

33-437 

1-0637 

13-049 

1-1641 

33-029 

1-0617 

12^641 

1-1620 

32-621 

1-0597 

12-233 

1-1599 

32-213 

1-0577 

11-825 

1-1578 

31-805 

1-0557 

11-418 

1-1557 

31-398 

•0537 

11-010 

1-1537 

30-990 

•0517 

10-602 

1-1515 

30-582 

-0497 

10-194 

1  •  1494 

30-174 

•0477 

9-786 

1  •  1473 

29-767 

•0457 

9-379 

•  1452 

29-359 

•0437 

8-971 

•1431 

28-951 

•0417 

8-563 

•1410 

28-544 

•0397 

8-155 

-1389 

28-136 

1-0377 

7-747 

-1369 

27-728 

1-0357 

7-340 

-1349 

27-321 

1-0337 

6-932 

-1328 

26-913 

1-0318 

6-524 

•1308 

26-505 

1-0298 

6-116 

•1287 

26-098 

1-0279 

5-709 

1  •  1267 

25-690 

-0259 

5-301 

1-1247 

25-282 

1-0239 

4-893 

1-1226 

24-874 

-0220 

4-486 

1-1205 

24-466 

-0200 

4-078 

1-1185 

24-058 

•0180 

3-670 

1-1164 

23-650 

•0160 

3-262 

1-1143 

23-242 

-0140 

2-854 

1-1123 

22-834 

1-0120 

2-447 

1-1102 

22-426 

1-0100 

2-039 

1-1082 

22-019 

1-0080 

1-631 

1-1061 

21-611 

1-0060 

1-124 

1-1041 

21-203 

1-0040 

0-816 

1-1020 

20-796 

1-0020 

0-408 

288 


DETERMINATION    OF    COMMERCIAL  VALUES. 


[§  214. 


TABLE  116. 

Showing  the  amount  of  acid  in  aqueous  Hydrochloric  Acid  at  each  degree 
BAUMK,  from  0  to  25-5,  with  the  corresponding  specific  gravity  at  15°  C., 
by  J.  KOLB.* 


100  parts  contain: 

100  parts  contain: 

Degree 
BAUME. 

Specific 
gravity. 

Hydro- 
chloric- 

Hydro- 
chloric- 

Degree 
BAUMK. 

Specific 
gravity. 

Hydro- 
chloric- 

Hydro- 
chloric- 

acid  gas 

acid  gas 

acid  gas 

acid  gas 

at  0°  C. 

at  15°  C. 

at  0°  C. 

at  15°  C. 

0 

1-000 

0-0 

0-1 

17 

1-134 

25-2 

26-6 

1 

1-007 

1-4 

1-5 

18 

1-143 

27-0 

28-4 

2 

•014 

2-7 

2-9 

19 

1-152 

28-7 

30-2 

3 

•022 

4-2 

4-5 

19-5 

1-157 

29-7 

31-2 

4 

•029 

5-5 

5-8 

20 

1-161 

30-4 

32-0 

5 

•036 

6-9 

7-3 

20-5 

1-166 

31-4 

33-0 

6 

•044 

8-4 

8-9 

21 

1-171 

32-3 

33-9 

7 

•052 

9-9 

10-4 

21-5 

1-175 

33-0 

34-7 

8 

•060 

11-4 

12-0 

22 

1-180 

34-1 

35-7 

9 

•067 

12-7 

13-4 

22-5 

1-185 

35-1 

36-8 

10 

•075 

14-2 

15-0 

23 

1-190 

36-1 

37-9 

11 

•083 

15-7 

16-5 

23-5 

1-195 

37-1 

39-0 

12 

•091 

17-2 

18-1 

24 

1-199 

38-0 

39-8 

13 

1-100 

18-9 

19-9 

24-5 

1-205 

39-1 

41-2 

14 

1-108 

20-4 

21-5 

25 

1-210 

40-2 

42-4 

15 

1-116 

21-9 

23-1 

25-5 

1-212 

41-7 

42-9 

16 

1-125 

23-6 

24-8 

*  Compt.  rend.,  LXXIV,  337;  Zeitschr.  /. 


.  Chem.,  xi,  339. 


§  214.] 


ACIDIMETRY. 
TABLE  III. 


289 


Showing  the  percentages  corresponding  with  various  specific  gravities  of  aqueous 
Nitric  Acid,  both  hydrated  and  anhydrous,  by  J.  KOLB.* 


100  parts  contain: 

Sp.  gr. 

100  parts  contain: 

Sp.  gr. 

HNOg 

N203 

at  0° 

at  15° 

HNO3 

N^Os 

at  0° 

at  15° 

100-00 

85-71 

•559 

1-530 

58-88 

50-47 

1-387 

1-368 

99-84 

85-57 

-559 

1-530 

58-00 

49-71 

1-382 

•363 

99-72 

85-47 

•558 

1-530 

57-00 

48-86 

1-376 

•358 

99-52 

85-30 

•557 

1-529 

56-10 

48-08 

1-371 

•353 

97-89 

83-90 

•551 

1-523 

55-00 

47-14 

1-365 

•346 

97-00 

83-14 

•548 

1-520 

54-00 

46-29 

1-359 

•341 

96-00 

82-28 

1-544 

1-516 

53-81 

46-12 

1-358 

•339 

95-27 

81-66 

1-542 

1-514 

53-00 

45-40 

1-353 

•335 

94-00 

80-57 

1-537 

1-509 

52-33 

44-85 

1-349 

•331 

93-01 

79-72 

1-533 

1-506 

50-99 

43-70 

1-341 

•323 

92-00 

78-85 

-529 

•503 

49-97 

42-83 

1-334 

•317 

91-00 

78-00 

-526 

•499 

49-00 

42-00 

1-328 

•312 

90-00 

77-15 

-522 

•495 

48-00 

41-14 

1-321 

•304 

89-56 

76-77 

•521 

•494 

47-18 

40-44 

1-315 

•298 

88-00 

75-43 

•514 

•488 

46-64 

39-97 

1-312 

•295 

87-45 

74-95 

•513 

1-486 

45-00 

38-57 

1-300 

•284 

86-17 

73-86 

1-507 

1-482 

43-53 

37-31 

1-291 

•274 

85-00 

72-86 

1-503 

1-478 

42-00 

36-00 

1-280 

-264 

84-00 

72-00 

1-499 

1-474 

41-00 

35-14 

1-274 

•257 

83-00 

71-14 

1-495 

1-470 

40-00 

34-28 

1-267 

•251 

82-00    '    70-28 

1-492 

1-467 

39-00 

33-43 

1-260 

•244 

80-96    !    69-39 

1-488 

1-463 

37-95 

32-53 

1-253 

•237 

80-00       68-57 

1-484 

1-460 

36-00 

30-86 

1-240 

•225 

79-00    !    67-71 

1-481 

1-456 

35-00 

29-29 

1-234 

•218 

77-66       66-56 

1-476 

1-451 

33-86 

29-02 

1-226 

•211 

76-00 

65-14 

1-469 

1-445 

32-00 

27-43 

1-214 

•198 

75-00 

64-28 

1-465 

1-442 

31-00 

26-57 

1-207 

•192 

74-01 

63-44 

1-462 

1-438 

30-00 

25-71 

1-200 

•185 

73-00 

62-57 

1-457 

•435 

29-00 

24-85 

-194 

•179 

72-39 

62-05 

1-455 

•432 

28-00 

24-00 

•187 

•172 

71-24 

61-06 

•450 

•429 

27-00 

23-14 

•180 

•166 

69-96 

60-00 

•444 

•423 

25-71 

22-04 

•171 

•157 

69-20 

59-31 

•441 

•419 

23-00 

19-71 

•153 

•138 

68-00 

58-29 

•435 

•414 

20-00 

17-14 

•132 

•120 

67-00 

57-43 

•430 

•410 

17-47 

14-97 

•115 

•105 

66-00 

56-57 

1-425 

•405 

15-00 

12-85 

•099 

•089 

65-07 

55-77 

1-420 

•400 

13-00 

11-14 

•085 

•077 

64-00 

54-85 

1-415 

1-395 

11-41 

9-77 

•075 

•067 

63-59 

54-50 

1-413 

1-393 

7-22 

6-62 

.050 

•045 

62-00 

53-14 

1-404 

1-386 

4-00 

3-42 

•026 

•022 

61-21 

52.46 

1-400 

1-381 

2-00 

1-71 

•013 

•010 

60-00 

51-43 

1-393 

1-374 

0-00 

0-00 

1-000 

0-999 

59-59 

51-08 

1-391 

1-372 

i 

*  Ann.  chim.  phys.  [4]  x,  140;  Zeitschr.  /.  analyt.  Chem.,  v,  449. 


290 


DETERMINATION    OF    COMMERCIAL    VALUES.         [§  214. 


TABLE  IV. 

Showing  the  percentages  of  Anhydrous  Acid  corresponding  with  various  specific 
gravities  of  aqueous  Phosphoric  Acid,  by  J.  WATTS.* 


Sp.  gr. 
at  15-5°  C. 

Percentage 
of  P2OS. 

Sp.  gr. 
at  15-5°  C. 

Percentage 
of  P206. 

Sp.  gr. 
at  15-5°  C. 

Percentage 
of  P206. 

•508 

49-60 

1-328 

36-15 

-144 

17-89 

•492 

48-41 

1-315 

34-82 

-136 

16-95 

•476 

47-10 

1-302 

33-49 

•124 

15-64 

-464 

45-63 

1-293 

32-71 

-113 

14-33 

•453 

45-38 

•285 

31-94 

•109 

13  25 

•442 

44-13 

•276 

31-03 

•095 

12-18 

•434 

43-95 

•268 

30-13 

1-081 

10-44 

1-426 

43-28 

•257 

29-16 

1-073 

9-53 

1-418 

42-61 

•247 

28-24 

1-066 

8-62 

1-408 

41-60 

•236 

27-30 

1-056 

7-39 

1-392 

40-86 

•226 

26-36 

1-047 

6-17 

1-384 

40-12 

•211 

24-79 

1-031 

4-15 

1-376 

39-66 

1-197 

23-23 

1-022 

3-03 

1-369 

39-21 

1-185 

22-07 

1-014 

1-91 

1-356 

38-00 

1-173 

20-91 

1-006 

0-79 

1-347 

37-37 

1-162 

19-73 

1-339 

36-74 

1-153 

18-81 

*  Journ.   Chem.  Soc.,  xix,   499;  Journ.  f.  prakt.  Chem.,  ci,  59;   Zeitschr.  /.  analyt. 
Chem.,  vii,  357. 


§  214.] 


ACIDIMETRY. 


291 


TABLE  V. 

Showing  the  percentages  of  Hydrated  Acetic  Acid  corresponding  with  various 
specific  gravities  of  aqueous  Acetic  Acid,  by  A.  C.  OUDEMANS.* 


Percent- 
age of 
hydrated 
acetic 
acid. 

Specific 
gravity 
at  15°  C. 

Specific 
gravity 
at  20°  C. 

Percentage 
of  hydrated 
acetic  acid. 

Specific 
gravity 
at  15°  C. 

Specific 
gravity 
at  20°  C. 

0 

0-9992 

0-9983 

51 

1-0623 

1-0583 

1 

•0007 

0-9997 

52 

1-0631 

1-0590 

2 

•0022 

1-0012 

53 

1-0638 

1-0597 

3 

•0037 

1-0026 

54 

1-0646 

1-0604 

4 

•0052 

1-0041 

55 

1-0653 

1-0611 

5 

•0067 

1-0055 

56 

1-0660 

1-0618 

6 

•0083 

1-0069 

57 

1-0666 

•0624 

7 

1-0098 

1-0084 

58 

1-0673 

•0630 

8 

1-0113 

1-0098 

59 

•0679 

•0636 

9 

1-0127 

1-0112 

60 

•0685 

•0642 

10 

1-0142 

1-0126 

61 

•0691 

-0648 

11 

1-0157 

1-0140 

62 

•0697 

•0653 

12 

1-0171 

1-0154 

63 

•0702 

•0658 

13 

1-0185 

-0168 

64 

•0707 

•0663 

14 

1-0200 

•0181 

65 

•0712 

1-0667 

15 

1-0214 

•0195 

66 

•0717 

1-0671 

16 

1-0228 

•0208 

67 

-0721 

1-0675 

17 

-0242 

-0222 

68 

1-0725 

1-0679 

18 

•0256 

•0235 

69 

1-0729 

1-06S3 

19 

•0270 

•0248 

70 

1-0733 

1-0686 

20 

•0284 

•0261 

71 

1-0737 

1-0689 

21 

-0298 

•0274 

72 

1-0740 

1-0691 

22 

•0311 

•0287 

73 

1-0742 

1-0693 

23 

•0324 

•0299 

74 

1-0744 

1-0695 

24 

•0337 

-0312 

75 

1-0746 

1-0697 

25 

•0350 

•0324 

76 

1-0747 

1-0699 

26 

•0363 

•0336 

77 

1-0748 

1-0700' 

27 

•0375 

1-0348 

78 

1-0748 

1-0700 

28 

•0388 

1-0360 

79 

1-0748 

1-0700 

29 

•0400 

1-0372 

80 

1-0748 

1-0699 

30 

-0412 

1-0383 

81 

1-0747 

1-0698 

31 

•0424 

1-0394 

82 

1-0746 

1-0696 

32 

1-0436 

1-0405 

83 

1-0744 

1-0694 

33 

1-0447 

1-0416 

84 

1-0742 

1-0691 

34 

1-0459 

1-0426 

85 

1-0739 

1-0688     • 

35 

1-0470 

1-0437 

86 

1-0736 

•0684     , 

36 

1-0481 

1-0448 

87 

1-0731 

1-0679 

37 

1-0492 

1-0458 

88 

1-0726 

•0674 

38 

1-0502 

1-0468 

89 

1-0720 

•0668 

39 

1-0513 

1-0478 

90 

•0713 

•0660 

40 

1-0523 

1-0488 

91 

•0705 

•0652 

41 

1-0533 

1-0498 

92 

-0696 

•0643 

42 

1-0543 

1-0507 

93 

-0686 

-0632 

43 

•0552 

1-0516 

94 

-0674 

-0620 

44 

•0562 

1-0525 

95 

•0660 

•0606 

45 

•0571 

•0534 

96 

•0644 

•0589 

46 

•0580 

•0543 

97 

•0625 

•0570 

47 

•0589 

•0551 

98 

•0604 

•0549 

48 

•0598 

•0559 

99 

•0580 

•0525 

49 

•0607 

•0567 

100 

•0553 

•0497 

50 

-0615 

•0575 

*  "The  Specific  Gravity  of  Acetic  Acid  and  Mixtures  of  the  Acid  with  Water.1 
COHEN  &  SON,  Bonn,  1866;  Zeitschr.  f.  analyt.  Chem.,  v,  453. 


M, 


292 


DETERMINATION    OF    COMMERCIAL    VALUES.          [§  214. 


TABLE  VI. 

Showing  the  percentages  of  crystallized  Tartaric  and  Citric  Acids  corresponding 
with  various  specific  gravities  of  aqueous  solutions  of  the  acids,  by  GERLACH.* 


Percent- 
age by 
weight 
in  the 
solution. 

Crystallized 
tartaric  acid, 
specific 

TI^ 

Crystallized 
citric  acid, 
specific 
gravity 
at  15°. 

Percent- 
age by 
weight 
in  the 
solution.  . 

Crystallized 
tartaric  acid, 
specific 
gravity 
at  15°. 

Crystallized 
citric  acid, 
specific 
gravity 
at  15°. 

1 

•0045 

1-0037 

34 

1-1726 

1-1422 

2 

•0090 

1-0074 

35 

1-1781 

1-1467 

3 

•0136 

1-0111 

36 

1-1840 

1-1515 

4 

•0179 

1-0149 

37 

1-1900 

1-1564 

5 

•0224 

1-0186 

38 

1-1959 

1-1612 

6 

•0273 

1-0227 

39 

1-2019 

1-1661 

7 

•  0322 

1-0268 

40 

1-2078 

1-1709 

8 

•0371 

1-0309 

41 

1-2138 

1-1756 

9 

•0420 

1-0350 

42 

1-2198 

1-1814 

10 

1-0469 

1-0392 

43 

1-2259 

1-1851 

11 

1-0517 

1-0431 

44 

1-2317 

1-1899 

12 

1-0565 

1-0470 

45 

1-2377 

1  •  1947 

13 

1-0613 

1-0509 

46 

1-2441 

1-1998 

14 

1-0661 

1-0549 

47 

•2504 

1-2050 

15 

1-0709 

1-0588 

48 

•2568 

1-2103 

16 

1-0761 

1-0632 

49 

•2632 

1-2153 

17 

1-0813 

1-0675 

50 

-2696 

1-2204 

18 

1-0865 

1-0718 

51 

-2762 

1-2257 

19 

1-0917 

1-0762 

52 

-2828 

1-2307 

20 

1-0969 

1-0805 

53 

•2894 

1-2359 

21 

1  -  1020 

1-0848 

54 

-2961 

1-2410 

22 

1-1072 

1-0889 

55 

-3027 

1-2462 

23 

1-1124 

1-0930 

56 

-3093 

1-2514 

24 

1-1175 

1.0972 

57 

•3159 

1-2572 

25 

•1227 

1-1014 

58 

1-2627 

26 

•1282 

1  -  1060 

59 

1-2683 

27 

•1338 

1-1106 

60 

1-2738 

28 

•1393 

1-1152 

61 

1-2794 

29 

•1449 

1-1198 

62 

1-2849 

30 

•1505 

1  -  1244 

63 

1-2904 

31 

-1560 

1-1288 

64 

1-2960 

32 

•1615 

1  •  1333 

65 

1-3015 

33 

-1670 

1-1378 

66 

1-3071 

Zeitschr.  /.  analyt.  Chem.,  viu,  295. 


In  all  cases  in  which  the  determination  of  the  specific  gravity 
fails  to  attain  the  end  in  view,  or  which  demand  particular  accuracy, 
the  volumetric  method  described  under  B  is  employed. 


§  215.]  ACIDIMETRY.  293 


B.  ESTIMATION  BY  SATURATION  WITH  AN  ALKALINE  FLUID    OP 
KNOWN  STRENGTH.* 

§215. 

This  method  requires — 

1.  A  dilute  acid  of  known  strength.     Sulphuric  or  hydrochloric 
acid  may  be  used.     Nitric  and  oxalic  acids  are  less  frequently 
employed. 

2.  An  alkaline  fluid  of  known  strength. 

I.  PREPARATION  OF  THE  SOLUTIONS. 

1.  The  acid  should  be  of  such  strength  that  1000  c.c.  at  17-5° 
(  =  14°  R.)  will  contain  the  exact  equivalent  number  (H=  1-008) 
of  grammes  of  the  acid,  e.g.,  49-043  of  sulphuric  acid,  36-458 
hydrochloric  acid,  63-024  oxalic  acid,  etc.  Acids  of  this  strength 
we  term  normal  acids;  equal  volumes  of  them  have  equal  power 
to  saturate  alkalies.  As  a  rule  normal  sulphuric  or  hydrochloric 
acid  is  used,  or,  as  recommended  by  MOHR,  normal  oxalic  acid. 

2.  For  the  alkali  solution  a  caustic-soda  lye  is  used  of  such 
strength  that  one  volume  will  suffice  to  neutralize  one  volume  of 
normal  acid,  so  that  on  mixing  the  two  last  drops  the  soda  solu- 
tion imparts  a  blue  color  to  the  acid  solution  faintly  reddened  by 
litmus.  A  soda  solution  of  such  strength  is  termed  a  normal  soda 
solution,  and  1000  c.c.  saturate  one  equivalent  of  any  monobasic 
acid  expressed  in  grammes. 

Various  methods  may  be  used  for  preparing  normal  acids;  of 
these  the  most  serviceable  (a),  in  which  pure  anhydrous  sodium 
carbonate  is  used  for  standardizing,  is  available  for  all  acids,  while 
the  others  (6)  can  be  employed  only  for  the  valuation  of  individual 
normal  acids.  The  manner  of  preparing  the  normal  soda  solution 
will  be  described  under  both  a  and  b. 

*  According  to  NICHOLSON  and  PRICE  (Chem.  Gaz.,  1856,  p.  30)  the  com- 
mon method  of  acidimetry  is  not  suited  for  determining  free  acetic  acid,  on 
account  of  the  alkaline  reaction  of  neutral  sodium  acetate;  however,  OTTO 
(Annal.  d.  Chem.  u.  Pharm.,  en,  69)  has  clearly  demonstrated  that  the  error 
arising  from  this  is  so  inconsiderable  that  it  may  safely  be  disregarded. 


294  DETERMINATION    OF   COMMERCIAL    VALUES.         [§  215. 

a.    GENERAL   METHODS    (BY   NEUTRALIZATION). 

1.  Requisites. 

a.  Pure  sodium  carbonate,  to  be  used  as  a  standard.  This  is 
most  easily  prepared  from  the  purest  commercial  sodium  bicarbon- 
ate. Powder  it,  pack  it  firmly  in  a  funnel  in  which  a  small  filter 
has  been  placed,  level  the  surface  and  place  on  it  several  layers  of 
filter  paper,  and  pour  on  small  quantities  of  cold,  distilled  water, 
continuing  the  washing  until  the  liquid  passing  through  no  longer 
shows  traces  of  sulphuric  acid  or  chlorine.  Then  dry  the  washed 
salt  and  heat  it  (best  in  a  platinum  dish)  to  convert  the  bicarbonate 
into  anhydrous  carbonate.  This  is  then  powdered  and  preserved 
for  use.  Before  weighing  off,  moderately  heat  a  suitable  quantity 
in  a  platinum  crucible  for  a  long  time  and  introduce  the  still  hot 
powder  into  a  dry,  well-closed  tube,  which  is  to  be  preserved  under 
a  desiccator. 

/?.  The  alkali  solution.  Caustic-soda  solution  is  used  for  this 
purpose.  It  is  sufficient  for  the  purpose  if  it  has  a  specific  gravity 
of  from  1  •  046  to  1  •  048,  as  determined  by  the  hydrometer,  when 
the  litre  will  contain  somewhat  more  than  one  equivalent  of  Na2O, 
i.e.,  from  32  to  34  grammes.  The  use  of  the  hydrometer  can  be 
avoided  if  a  soda  solution  of  approximately  correct  strength  is  at 
hand,  by  making  a  rough  determination  and  then  diluting  the  so- 
lution so  that  from  19  to  19  -5  c.c.  will  be  required  to  saturate  20  c.c. 
normal  acid.  If  it  is  desired  to  expel  carbonic  acid  from  a  con- 
centrated soda  solution  containing  some  sodium  carbonate,  dilute 
the  solution  suitably,  heat  to  boiling,  add  milk-of-lime,  boil,  cool 
somewhat,  and  fill  into  flasks,  in  which  allow  to  settle.  Close  the 
flask  with  a  perforated  stopper  bearing  a  bulb-tube  containing  soda- 
lime  (Fig.  99,  p.  298).  When  perfectly  clear  siphon  off  the  solu- 
tion into  another  flask. 

7-.  A  dilute  acid,  each  litre  of  which  contains  somewhat  more 
than  one  combining  equivalent  of  the  acid  (H  =  1-008)  expressed 
in  grammes;  e.g.,  each  litre  will  contain  41  to  42  grammes  of 
anhydrous  sulphuric  acid,  37  to  39  grammes  of  hydrochloric  acid, 
etc.  It  is  sufficient  to  determine  the  strength  of  the  acid  by  means. 


§  215.]  ACIDIMLTRY.  295 

of  the  hydrometer;  and  the  following  may  be  taken  as  the  limits 
of  the  specific  gravities  at  15°: 

Dilute  sulphuric  acid 1  •  032  to  1  •  033 

1 '       hydrochloric  acid 1  •  018  to  1  •  019 

"       nitric  acid 1-037  to  1-038 

d.  As  tincture  of  litmus  is  frequently  so  alkaline  as  to  require 
a  notable  quantity  of  acid  to  redden  it,  the  excess  of  acid  must  be 
neutralized,  so  that  on  dilution  with  water  the  tincture  will  be 
violet-colored,  and  will  be  reddened  by  a  trace  of  acid  and  rendered 
blue  by  a  minimum  of  alkali  ( §  65,  2).  Regarding  the  special  kinds 
of  tincture  of  litmus  and  other  indicators*  used  for  ascertaining 
the  neutrality-point  of  liquid,  see  §  215,  6. 

The  requisites  being  at  hand,  we  proceed — 

1 .  To  accurately  determine  the  acid  content  of  the  dilute  acid. 

2.  To  dilute  the  acid  to  normal  strength. 

3.  To  dilute  the  soda  solution  to  normal  strength. 

2.  Accurate  Determination  of  the  Acid  Content. 

a.  Fill  one  pinch-cock  burette  with  the  dilute  acid  (1,70,  an^  a 
second  one  with  the  alkali  (1,  /?),  both  to  the  zero-point.  Then  run 
20  c.c.  of  the  acid  into  a  beaker  containing  about  100  c.c.  water, 
color  it  slightly  red  with  litmus  tincture,  and  run  in  the  soda  solu- 
tion until  the  liquid  becomes  just  distinctly  blue.  If  the  point  has 
not  been  exactly  hit,  add  more  acid,  and  then  soda  solution,  until 
the  point  is  accurately  reached.  After  a  few  minutes  read  off  the 
height  in  both  burettes,  and  thus  ascertain  the  relation  of  the 
soda  solution  to  the  acid.  Let  us  assume  we  had  used  19-5  c.c. 
of  the  soda  solution  to  20  c.c.  of  the  acid. 

We  refill  both  burettes  up  to  the  zero-point. 

ft.  Weigh  off  two  portions  of  the  pure,  anhydrous  sodium 
carbonate,  weighing  from  1  to  1-5  grammes  each,  introduce  them 
into  flasks  of  about  300  c.c.  capacity  each,  and  dissolve  them  in  100 
to  150  c.c.  of  water  each. 

f.  Heat  one  of  the  solutions  of  sodium  carbonate,  color  it 

*  For  a  complete  treatise  on  indicators,  see  "  Indicators  and  Test  Papers," 
by  ALFRED  I.  COHN.  JOHN  WILEY  &  SONS,  New  York,  2d  edition,  1902. 


296  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  215. 

faintly  blue  with  litmus  tincture,  and  run  in  from  the  burette 
acid  in  small  portions  at  a  time  with  constant  agitation,  until  the 
liquid  has  become  reddish  violet.  Now  heat  and  maintain  at  a 
gentle  boil  for  some  time.  The  liquid  becomes  blue  again,  as  the 
carbonic  acid  is  expelled.  Now  run  in  more  acid  until  the  color 
becomes  distinctly  yellowish-red,  boil  for  a  few  minutes,  and 
then  cautiously  add  from  the  burette  soda  solution  until  the 
liquid  just  appears  blue.  If  this  point  has  not  been  accurately  hit, 
add  some  more  acid  and  then  soda  solution  until  the  right  point 
is  reached.  After  a  few  minutes,  read  off  the  height  in  both  burettes 
and  from  the  quantities  of  alkali  solution  used  calculate,  according 
to  the  proportion  found  in  2,  a,  the  excess  of  the  dilute  acid  em- 
ployed above  that  necessary  to  neutralize  the  sodium  carbonate; 
deduct  this  excess  from  the  total  acid  used,  and  thus  obtain  the 
acid  required  to  saturate  the  weighed  quantity  of  sodium  car- 
bonate, and  consequently  the  exact  quantity  of  absolute  acid  con- 
tained in  the  dilute  acid,  since  1  mol.  of  sodium  carbonate,  or 
106-1  grm.,  corresponds  with  98-086  grm.  sulphuric  acid  (H2S04), 
or  80-07  grm.  sulphuric  anhydride  (SO3),  72-916  grm.  (2  mol.) 
hydrochloric  acid  (HC1),  or  126-096  grm.  (2  mol.)  nitric  acid 
(HNO3),  or  108-08  grm.  nitric  anhydride  (N205). 

An  example  will  illustrate  this:  weight  of  sodium  carbonate, 
1-2  grm.;  total  hydrochloric  acid  used,  22  c.c.;  total  soda  solution 
used,  1-2;  hence  20  c.c.  of  the  dilute  acid  corresponds  to  19-5  c.c. 
soda  solution. 

Since  19  •  5  c.c.  of  soda  solution  corresponds  to  20  c.c.  of  the  dilute 
hydrochloric  acid,  1-2  c.c.  soda  solution  will  correspond  to  1-23  c.c. 
of  dilute  acid.  Therefore  the  quantity  of  acid  required  to  saturate 
the  sodium  carbonate  was  22  —  1  •  23  =  20  •  77  c.c. ;  and  this  contains 
the  hydrochloric  acid  equivalent  to  1-2  grm.  sodium  carbonate, 
according  to  the  proportion  106-1  :  72-916  ::  1-2  :  x;  z  =  0-8247 
grm.  hydrochloric  acid.  But  as  20-77  c.c.  of  the  dilute  acid  con- 
tains 0-8247  grm.  hydrochloric  acid,  1000  c.c.  will  contain  39-71 
grammes.  .!' 

The  second  portion  of  sodium  carbonate  is  treated  in  exactly 
the  same  way,  and  a  comparison  made  as  to  whether  the  results 


§  215.]  ACIDIMETRY.  297 

obtained  are  just  or  nearly  like  those  obtained  with  the  first  portion. 
The  comparison  is  best  made  by  calculating  the  results  of  both 
experiments  to  1  grm.  sodium  carbonate.  A  closer  agreement 
than  0-1  grm.  of  acid  content  in  1000  c.c.  cannot  be  expected,  as 
under  the  conditions  of  the  experiment,  this  corresponds  to  only 
0-05  c.c.  of  the  acid  employed.  For  instance,  if  the  first  experi- 
ment gave  39-71  grm.  and  the  second  gave  39-8  grm.  of  hydro- 
chloric acid  in  1000  c.c.,  there  would  be  no  cause  for  making  a 
third  experiment.  If  the  difference,  however,  is  considerably 
greater,  i.e.,  if  much  more  than  0-05  c.c.  of  the  dilute  acid  per  1 
grm.  of  sodium  carbonate  has  been  required,  the  experiment  must 
be  repeated  with  a  fresh  weighed  portion  of  sodium  carbonate. 

3.  Dilution  of  the  Acid  to  Normal  Strength. 

When  the  quantity  of  anhydrous  acid  in  the  dilute  acid  has  been 
determined  according  to  2,  the  liquid  must  be  dilute  so  that  1000  c.c. 
at  17-5°  will  contain  the  equivalent  of  the  acid  (H  =  1-008)  in 
grammes,  and  thus  becomes  a  normal  acid.  Let  us  suppose  that 
we  found  the  1000  c.c.  to  contain  39-71  grammes  of  hydrochloric 
acid  in  our  first  experiment  and  39-8  grammes  in  our  second,  or  a 
mean  of  39  •  76  grammes.  According  to  the  equation  36  •  458  : 1000 
::39-76  :  x;  z=  1090 -57,  we  should  have  to  dilute  each  1000  c.c. 
of  the  hydrochloric  acid  with  distilled  water  to  measure  1090-57 
c.c.  This  is  simply  and  accurately  done  by  filling  a  one-litre  flask 
to  the  mark  with  the  acid  at  a  temperature  of  17-5°,  carefully 
emptying  it  into  a  larger,  dry  flask  in  which  the  acid  is  to  be 
preserved  later,  then  measuring  66-3  c.c.  of  distilled  water  from  a 
burette  or  pipette  into  the  litre  flask,  shaking  well,  and  pouring 
into  the  larger  flask;  after  again  shaking  well,  pour  back  half  of  the 
liquid  into  the  litre  flask,  shake  once  more,  and  again  pour  back 
into  the  larger  flask,  and  preserve  for  use  after  finally  shaking 
again.  Each  time  before  use  the  flask  should  be  shaken,  because 
water  evaporates  in  the  half-filled  flask  and  condenses  in  the  upper 
part,  mixing  with  the  liquid  when  this  is  poured  out,  whereby  this  is 
rendered  weaker  in  acid,  while  that  remaining  in  the  flask  becomes 
so  much  the  stronger. 


298  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  215. 

4.  Diluting  the  Soda  Solution  to  Normal  Strength. 

By  normal  soda  solution  is  understood  a  solution  of  sodium 
hydroxide  of  which  one  volume  suffices  to  neutralize  one  volume 
of  normal  acid,  so  that  on  mixing  the  two  the  last  drop  of  the  soda 
solution  will  render  blue  the  normal  acid  reddened  by  litmus. 
1000  c.c.  of  such  a  soda  solution,  measured  at  17-5°,  will  saturate 
1  equivalent  of  a  monobasic  acid,  expressed  in  grammes. 

Though  the  proportion  in  which  the  soda  solution  must  be 
diluted  may  be  readily  determined  from  the  relation  already  de- 
termined (2,  a)  between  the  original  acid  solution  (2, 7-,  the  strength 
of  which  has  now  been  accurately  determined)  and  the  soda  solu- 
tion, the  proportion  may  be  more  simply  found  by  directly  ascer- 
taining the  relation  between  the  soda  solution  and  the  recently 
prepared  normal  acid;  i.e.,  to  find  out  how  much  soda  solution 
must  be  added  to  render  distinctly  blue  20  or  30  c.c.  of  the  normal 
acid  diluted  with  100  c.c.  water  and  faintly  reddened  with  litmus 
tincture.  Suppose  we  found  that  27-4  c.c.  of  soda  solution  were 
required  for  30  c.c.  of  normal  acid;  we  should  have  to  add  to  each 

27-4  c.c.  of  soda  solution  30-27-4=2-6 
c.c. ,  and  to  each  1000  c.c.  hence  94-9 
c.c.,  distilled  water. 

The  addition  of  the  water  is  made  in 
exactly  the  same  manner  as  described 
in  preparing  the  normal  acid  (in  3). 

The  bottle  in  which  the  normal 
soda  solution  is  to  be  preserved  should 
be  closed,  as  recommended  by  MOHR, 
with  a  cork  bearing  a  small  bulb-tube 
of  the  form  of  a  calcium-chloride  tube. 
This  tube  is  to  be  filled  with  soda-lime, 
and  is  provided  with  a  narrow  open 
tube  (Fig.  99). 

Besides    the   normal   soda   solution, 
FIG.  99.  other   solutions    five    or    ten    times    as 

dilute   may  also   be   prepared   if   desired.     These   solutions   are 


§  215.]  ACIDIMETRY.  299 

best  prepared  by  introducing  50  c.c.  of  the  normal  solution  (for 
example  in  the  case  of  the  more  dilute  solution)  into  a  500-c.c. 
measuring  flask,  and  filling  up  to  the  mark  with  distilled  water, 
shaking  well  occasionally. 


b.    SPECIAL   METHODS   FOR   PREPARING   NORMAL  ACID  AND  ALKALI 

SOLUTIONS. 

1.  Preparing  Normal  Sulphuric  Add. 

To  prepare  this  there  is  used  a  dilute  sulphuric  acid  of  specific 
gravity  1-032  to  1-033.  Measure  off  accurately  two  portions  of 
20  c.c.  each  (best  by  means  of  a  pinch-cock  burette)  of  the  acid, 
and  determine  the  sulphuric  acid  hi  both  with  barium  chloride 
(§132  I,  1).  If  the  results  of  the  two  determinations  are  quite 
concordant,  take  the  mean,  and  then  dilute  the  sulphuric  acid 
so  that  each  1000  c.c.  will  contain  exactly  40-035  grm.  anhydrous 
sulphuric  acid  (SO3).  Suppose  we  found  that  20  c.c.  of  our  liquid 
contained  0-840  sulphuric  acid;  then  1000  c.c.  will  contain  42 
grammes.  According  to  the  proportion  40-035 : 1000  ::42:x;  x= 
1049-1,  each  1000  c.c.  of  the  acid  must  hence  be  diluted  with  dis- 
tilled water  to  measure  1049-1  c.c.  The  best  method  of  diluting 
has  already  been  described  (p.  297). 

2.  Preparation  of  Normal  Hydrochloric  Add. 

To  prepare  this  there  is  used  a  hydrochloric  acid  of  specific 
gravity  1-018  to  1-019  (and  which  must  leave  no  residue  on  evap- 
oration in  a  platinum  or  porcelain  dish).  Measure  off  accurately 
two  portions  of  20  c.c.  each,  and  determine  the  hydrochloric  acid 
in  each  by  acidulating  with  nitric  acid,  precipitating  with  silver 
nitrate,  and  weighing  the  silver  chloride  precipitated  (§  141,  I,  a). 
If  the  results  of  both  experiments  are  quite  concordant,  take  the 
mean,  and  calculate  how  much  water  to  add  to  reduce  the  acid 
to  normal  strength.  Supposing  we  had  found  0-78  grm.  hydro- 
chloric acid  in  the  20  c.c.,  then  1000  grm.  would  contain  39  grm.; 
hence,  according  to  the  equation  36-458:1000  :: 39: x;  x  =1069 -7, 
each  1000  c.c.  would  have  to  be  diluted  with  distilled  water  to 


300  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  215. 

measure  1069-7  c.c.     The  method  of  diluting  and  preserving  the 
solution  has  already  been  detailed  (p.  297). 

3.  Preparation  of  Normal  Oxalic  Acid. 

An  essential  requirement  for  the  preparation  of  this  solution 
is  perfectly  pure  oxalic  acid  free  from  potassium  binoxalate,  cal- 
cium oxalate,  sulphuric  acid,  sulphates,  etc.  The  method  of  pre- 
paring such  an  acid,  as  recommended  by  MOHR,  is  detailed  in  Vol. 
I,  p.  144).  REISCHAUER,*  who,  using  MOHR'S  method,  did  not 
obtain  a  perfectly  pure  oxalic  acid,  but  one  containing  somewhat 
less  potassium,  recommends  the  analyst  to  prepare  the  oxalic  acid 
himself  by  the  action  of  nitric  acid  on  starch.  HABEDANKf 
dissolves  commercial  oxalic  acid  in  the  smallest  possible  quantity 
of  hot  absolute  alcohol.  After  several  hours  the  crystals  which 
form  in  the  liquid  filtered  off  from  the  residual  calcium  oxalate 
and  potassium  binoxalate  (the  mother  liquor  may  be  used  for 
dissolving  a  fresh  quantity  of  oxalic  acid)  are  collected,  drained 
well,  and  recrystallized  from  boiling  distilled  water.  F.  STOLBA  £ 
dissolves  commercial  oxalic  acid  in  a  10-  to  15-per  cent,  boiling 
hydrochloric  acid,  filters,  cools  the  liquid  rapidly  under  constant 
stirring,  siphons  off  the  mother  liquor  from  the  crystalline  powder, 
and  washes  the  latter  with  small  quantities  of  cold  water  until 
the  washings  contain  only  very  slight  traces  of  hydrochloric  acid; 
the  oxalic  acid  is  then  recrystallized  from  boiling  water. 

The  method  by  which  the  oxalic  acid  is  tested  as  to  its  purity 
and  properly  dried  in  order  to  give  it  the  formula  H2C2O4  +  2H2O, 
and  hence  the  equivalent  126-048,  is  detailed  in  §  65,  1.  It  is  to 
be  noted  that  the  solution  must  be  tested  for  free  sulphuric  acid 
and  sulphates  (by  observing  whether  the  acid  remains  clear  on 
adding  hydrochloric  acid  and  barium  chloride  §). 

As  a  rule  the  crystalline  oxalic  acid  is  used,  i.e.,  H2C2O4  +  2H2O. 
According  to  0.  L.  ERDMANN'S  recommendation,  however,  the 

*  DINGLER'S  polyt.  Joum.,  CLXVII,  47;  Zeitschr.  f.  analyt.  Chem.,  11,  426. 

f  Zeitschr.  f.  analyt.  Chem.,  xi,  282. 

%  Ibid.,  XIIT,  50. 

§  Comp.  O.  BINDER,  Ibid.,  xvi,  334. 


§  215.J  ACIDIMETRY.  301 

acid  may  be  dried  to  constant  weight  at  100°,  and  freed  from  its 
water  of  crystallization,  and  thus  converted  into  the  anhydrous 
salt,  H2C2O4.  When  the  hydrated  acid  is  used  63  •  024  grammes, 
or  when  the  anhydrous  salt  is  used,  45-008  grammes,  are  accurately 
weighed  off,  transferred  to  a  litre  flask  and  dissolved  hi  water  by 
shaking,  then  diluted  to  the  mark  at  17-5°,  shaken  again,  and 
preserved  where  it  is  not  exposed  to  direct  sunlight.* 

The  flask  should  be  shaken  each  time  before  using,  and  for  the 
reasons  already  stated. 

It  must  be  remarked  that  only  concentrated,  hence  also  normal, 
oxalic-acid  solutions  can  be  preserved  in  the  manner  stated  with- 
out suffering  decomposition.  More  dilute  solutions,  e.g.,  deci- 
normal  solutions,  undergo  a  change,  the  oxalic  acid  being  gradually 
decomposed  (G.  Biziof).  According  to  NEUBAUER|  the  decom- 
position is  accompanied  by  a  moldy  growth;  this,  however,  can 
be  entirely  prevented  by  heating  the  decinormal  solution  in  se- 
curely closed  vessels  for  half  an  hour  on  a  water-bath  at  60°  to  70°. 

4.  Preparation  of  Normal  Alkali. 

To  use  the  normal  acid  solution  prepared  according  to  6,  we 
must  have  also  a  normal  alkali  solution.  This  is  made  from  a 
carbonic-acid-free  sodium-hydroxide  solution  of  specific  gravity 
1-046  to  1-048.  Its  relation  to  the  normal  acid,  and  its  dilution, 
to  correspond  accurately  with  this,  are  described  on  p.  298. 

II.  VERIFICATION  OF  THE  STANDARD  ACID  AND  ALKALI. 

Although  the  standard  solutions  prepared  as  above  must  of 
course  be  correct,  if  the  operations  have  been  carefully  performed, 
there  is  a  greater  sense  of  certainty  if  we  ascertain  their  accuracy 
before  using  them.  This  is  done  by  beginning  a  fresh  experiment 
the  object  of  which  is  to  show  whether  equal  volumes  when  mixed 
perfectly  neutralize  each  other;  we  proceed  thus: 

Weigh  off  two  portions  of  1  to  1  •  5  grammes  each  of  chemically 
pure  sodium  carbonate  perfectly  dehydrated  by  gentle  ignition 

*  WITTSTEIX,  Zeitschr.  f.  analyt.  Chem.,  i,  496. 
f  Ibid.,  ix,  392. 
J  Ibid.,  ix,  392. 


302  DETERMINATION   OF   COMMERCIAL    VALUES.         [§  215. 

and  proceed  as  detailed  on  p.  295,  f.  The  sodium  carbonate  theo- 
retically corresponding  with  the  acid  used  is  then  calculated  thus: 
1000  : 106-08  (eq.  of  Na2CO3)  : :  the  c.c.  of  acid  used  :  x. 

The  result  should  correspond  with  the  known  weight  of  the 
sodium  carbonate  taken.  Differences  of  from  0-001  to  0-003 
grammes  may  be  neglected,  as  they  are  within  the  limits  of  experi- 
mental error.  It  is  usually  advisable  to  repeat  the  experiment 
once  more. 

Instead  of  using  sodium  carbonate  for  testing  the  normal  hydro- 
chloric (or  nitric)  acid,  pure  Iceland  spar  may  also  be  used.  Pow- 
der the  spar,  dry  it  at  100°,  and  weigh  off  two  portions  of  1  or  1  •  5 
grammes  each.  Introduce  one  of  the  portions  into  a  flask,  and 
from  a  burette  filled  with  hydrochloric  acid  to  the  zero-point,  allow 
sufficient  acid  to  gradually  run  in  to  dissolve  the  spar.  Solution 
may  be  facilitated  by  gently  heating,  but  a  strong  heat  should  be 
avoided  as  yet,  as  the  liquid  may  contain  more  than  a  slight  trace 
of  hydrochloric  acid,  and  in  such  a  case  some  hydrochloric  acid 
may  be  lost  if  a  strong  heat  is  applied.  After  solution  is  effected, 
add  sufficient  litmus  tincture  to  just  color  the  liquid  faintly  red, 
and  from  a  burette  filled  to  the  zero-point  run  in  soda  solution 
until  the  liquid  contains  but  a  trace  of  free  acid.  Now  expel  the 
carbonic  acid  by  gently  boiling  the  liquid  for  several  minutes,  and 
finally  add  soda  solution  until  the  liquid  just  becomes  blue.  After 
deducting  the  soda  used  from  the  acid,  proceed  to  calculate  as  above 
detailed. 

III.  DETERMINATION  OF  FREE  ACIDS. 

a.    ORDINARY  METHOD. 

As  1000  c.c.  of  normal  soda  solution  correspond  with  the  equiva- 
lent number  of  each  monobasic  acid  expressed  in  grammes;  1000 
c.c.  of  the  one-fifth  normal  solution  with  one-fifth  gramme-equiva- 
lent; 1000  c.c.  of  decinormal  solution  with  one-tenth  gramme-equiva- 
lent: there  remains  but  little  to  be  said  regarding  the  process,  as 
it  is  evident  that  according  to  the  quantity  of  free  acid  to  be  neu- 
tralized one  or  other  of  the  three  alkali  solutions  is  chosen,  the  se- 
lection being  so  made  as  to  require  about  15  to  30  c.c.  of  the  soda 


§  215.]  ACIDIMETRY.  303 

solution,  the  last  portions  of  which  must  be  very  cautiously  added 
until  the  liquid  faintly  reddened  by  litmus  tincture  is  just  rendered 
blue. 

In  scientific  investigations  I  recommend  the  weighing  off  of 
indeterminate  quantities  of  the  acids,  as  this  can  be  far  more  easily 
done  on  a  chemical  balance,  and  the  trifling  calculation  gives  but 
little  or  no  trouble.  For  instance,  suppose  we  had  weighed  off  4-5 
grammes  of  a  dilute  acetic  acid,  and  25  c.c.  of  normal  soda  solution 
had  been  required  to  neutralize  this;  the  equation 

1000  :  60 - 032  (eq.  of  C2H4O2)  : :  25  :  x\  x=l- 5008 

shows  that  the  4 . 5  grammes  of  dilute  acetic  acid  weighed  off  con- 
tained 1-5008  grammes  of  hydrated  acetic  acid;  and  the  further 
equation 

4-5  : 1-5008  ::  100  :  z;  z  =  33-35 

gives  the  percentage  of  hydrated  acetic  acid  in  the  liquid  used. 
Or  the  calculations  may  also  be  made  as  follows: 

4-5  grammes  of  acetic  acid  having  required  25 c.c. normal  alkali 
solution,  for  neutralization  how  much  would  be  required  had  we 
weighed  off  6-0032  grammes  (one-tenth  the  gramme-equivalent 
of  hydrated  acetic  acid)  ? 

4-5  :  6-0032  ::  25  :x;  z  =  33.55. 

It  will  be  seen  that  in  this  case  the  number  of  c.c.  found  as  x  ex- 
presses at  once  the  percentage  of  hydrated  acetic  acid,  since  100  c.c. 
of  normal  alkali  solution  corresponds  with  one-tenth  gramme- 
equivalent  of  pure  hydrated  acid,  i.e.,  acetic  acid  of  100  per  cent, 
strength. 

In  technical  analysis  it  is  mare  convenient  if  the  number  of  c.c. 
or  half  c.c.  of  the  normal  soda  solution  used  directly  expresses,  and 
without  need  of  any  further  calculation,  the  percentage  of  the  acid 
being  tested.  In  order  to  accomplish  this,  the  one-tenth  or  one- 
twentieth  equivalent  in  grammes  of  the  hydrated  or  anhydrous 
acid  is  weighed  out,  according  as  the  number  of  c.c.  or  half  c.c. 
of  normal  alkali  used  is  to  express  the  percentage  of  hydrated  or 
anhydrous  acid  in  the  liquid  examined. 


304  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  215. 

The  following  are  the  quantities  for  the  more  common  acids: 

T*j5  eq.  number    5^  eq.  number 
of  grammes.        of  grammes. 

Sulphuric  anhydride  (SO8) 4  •  0035  2-0018 

Sulphuric  acid  (H2SO4) 4-9043  2-4521 

Nitric  anhydride  (N2O5) 5-404  2-702 

Nitric  acid  (HNO3) 6-3048  3-1524 

Hydrochloric  acid  (HC1) 3-6458  1  •  8229 

Oxalic  acid,  anhydrous  (H2C2O4) 4 - 5008  2-2504 

Oxalic  acid,  crystallized  (H2C2O4-2H2O). .  6-3024  3-1512 

Acetic  anhydride  (C4H6O3) 5-1024  2-5512 

Acetic  acid  (C2H4O2) 6-0032  3-0016 

Tartaric  acid  (C4H6O6) 7-5024  3-7512 

As  the  weighing  of  small  definite  quantities,  however,  is  far 
less  accurate,  it  is  better  to  weigh  the  half -equivalent  in  grammes 
(e.g.,  20-018  grammes  of  sulphuric  anhydride,  or  24-521  grammec 
of  the  monohydrated  sulphuric;  18-229  hydrochloric  acid,  etc.) 
in  a  500-c.c.  flask,  to  dilute  with  water  (in  the  case  of  sulphuric  acid 
the  acid  should  be  cautiously  poured  into  half  the  water  already 
contained  in  the  flask),  allowed  to  cool,  if  necessary,  then  accu- 
rately filled  with  water  to  the  mark,  shaken,  and  then  100  c.c.  or 
50  c.c.  withdrawn  with  a  pipette  according  as  one-tenth  or  one- 
twentieth  gramme-equivalent  of  acid  is  to  be  used. 

b.    DEVIATIONS   FROM   THE  PRECEDING   METHOD. 

1.  At  times  it  is  preferred  to  use  a  soda  solution  of  approxi- 
mately correct  strength,  rather  than  to  prepare  &  normal  soda 
solution,  in  which  case  its  effective  strength  is  ascertained  by  means 
of  accurately  measured  quantities  of  normal  acid.  Of  course  a 
short  rule-of-three  calculation  then  becomes  necessary.  Suppose 
18-5  c.c.  of  soda  solution  had  been  found  to  correspond  to  10  c.c. 
normal  sulphuric  acid  (i.e.,  y^-g-  gramme-equivalent,  or  0-40035 
gramme  of  sulphuric  anhydride),  they  will  correspond  equally 
with  Y-J--0-  gramme-equivalent  of  all  other  acids,  and  consequently 
with  0-60032  gramme  acetic  acid.  For  instance,  had  12  e.c.  of 
the  soda  solution  been  required  to  neutralize  10  grammes  of  vin- 
egar, the  acetic  acid  contained  in  this  would  be  found  as  follows: 

18-5: 0-60032::  12:  x;  z=0-3894; 


§  215.]  ACIDIMETRY.  305 

and  expressed  in  per  cent. : 

10:0-3894  :  :  100  :  x;   z=3-894. 

2.  At  times  it  is  preferable  to  have  the  soda  solution  of  such  a 
strength  that  the  number  of  c.c.  or  half-c.c.  used  to  neutralize  a 
definite  quantity  of  acid  should  directly  express  the  percentage  of 
acid  present.     For  instance,  if  we  add  20  c.c.  of  water  to  1000  c.c. 
of  normal  alkali  solution,  these  1020  c.c.  will  neutralize  51-024 
grammes  of  anhydrous  acetic  acid,  1000  grammes  will  consequently 
neutralize  50  grammes  of   acetic   anhydride.     If,  hence,  we   add 
to  10  grammes  of  vinegar  (10  c.c.  will  do  as  well,  as  the  sp.  gr.  of 
vinegar  scarcely  differs  from  that  of  water)  sufficient  of  the  soda 
solution  diluted  as  just  described,  i.e.,  until  the  liquid  colored  with 
litmus  tincture  is  just  rendered  blue,  the  c.c.  of  soda  solution  used, 
divided  by  2,  will  express  directly  the   percentage  of  acetic  an- 
hydride in  the  vinegar  tested.* 

3.  If  the  color  of  a  liquid  prevents  the  distinct  recognition  of 
the  color  change  afforded  by  the  litmus  tincture  added,  red  litmus 
paper  or  turmeric  paper  is  used  to  indicate  the  neutrality  point; 
i.e.,  the  soda   solution  is   added   until   a   strip  of  the   paper  im- 
mersed in  the  liquid  gives  a  faint  alkaline  reaction.     As,  however, 
in  this  process  somewhat  more  alkali  is  used  than  when  litmus 
tincture  is  employed,  it  is  necessary,  when  making  exact  deter- 
mination, to  make  a  correction  for  the  excess.     This  is  done  by 
very  cautiously  adding  to  a  volume  of  distilled  water   equal  to 
that  used  in  the  experiment,  just  sufficient  soda  solution  to  give 
an   alkaline   reaction   equal  in  intensity  to  that  afforded  in  the 
experiment.     The  quantity  of  soda  solution  required  to  effect  this 
is  then  deducted  from  that  used  hi  the  first  experiment. 

This  method  is  used  in  testing  crude  argol  for  its  content 
of  potassium  bitartrate.  If  one-tenth  equivalent-grammes,  or 
18-815  grammes,  are  weighed  out,  the  c.c.  of  soda-lye  used  will 
directly  express  in  per-cents.  the  potassium  bitartrate  present;  as 
this  quantity  is  too  large,  however,  one-fourth  of  it  may  be  taken, 
i.e.,  4-7038  grammes,  and  the  number  of  c.c.  of  soda  solution  used 

*  Zeitschr.  f.  analyt  Chem.,  i,  253. 


306  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  215. 

then  multiplied  by  4.  In  the  analysis  of  crude  tartar,  it  must  be 
remembered  that,  on  account  of  its  high  equivalent,  a  small  dif- 
ference in  the  quantity  of  soda  solution  used  will  have  a  serious 
effect  on  the  result.  For  instance,  suppose  21  •  6  c.c.  of  soda  solution 
were  used  in  one  case  for  4-7038  grammes  of  tartar,  while  in  a 
second  21-7  c.c.  were  used;  the  former  would  give  a  percentage 
of  21-6x4=86-4,  while  the  latter  would  give  21-7x4  =  86-8. 

The  argol  should  be  in  very  fine  powder;  it  should  be  heated 
with  the  water  under  constant  stirring,  and  the  soda  solution 
added  under  constant  heating  until  a  drop  of  the  liquid  just  gives 
a  brownish  spot  on  turmeric  paper,  or  a  blue  one  on  red  litmus 
paper.  In  a  second  experiment,  almost  the  entire  quantity  of 
soda  solution  may  be  added  at  once,  and  then,  after  heating  for  a 
sufficiently  long  time,  adding  the  soda  solution  drop  by  drop  until 
the  end  reaction  is  reached.  According  to  my  investigations  it  is 
not  proper  to  add  an  excess  of  soda  solution,  heat,  add  normal 
acid,  and  again  add  alkali  until  neutral,  as  this  method  gives,  after 
subtracting  the  normal  acid  from  the  soda  solution,  too  high  a 
number  for  the  soda  solution,  and  consequently  too  high  a  result 
because  the  coloring  matter  combines  with  the  soda.  In  accurate 
analyses  the  correction  made  as  above  described  must  not  be 
omitted.  That  this  method  of  analyzing  tartar  is  suitable  only 
when  no  other  substances  which  afford  an  acid  reaction  (except 
potassium  bitartrate)  are  present  is  of  course  readily  understood.* 

4.  The  titration  of  free  (tribasic)  phosphoric  acid  with  normal 
alkali  is  not  successful,  because  the  so-called  neutral  salt,  Na2HP04, 
which  has  an  alkaline  reaction,  and  the  acid  salt,  NaH2P04, 
which  has  an  acid  reaction,  do  not  neutralize  each  other,  so  that 
the  acid  reaction  of  one  is  observed  along  with  the  alkaline  re- 
action of  the  other.  When  phosphoric  acid  is  saturated  with  soda 
solution,  it  will  be  found  that  at  a  certain  stage  the  liquid  turns 
red  litmus  paper  blue  or  blue  litmus  paper  red.  This  point, 
which  was  observed  already  long  ago  in  many  urines,  was  termed 
by  BAMBERGERf  amphoter.  Milk,  too,  shows  a  similar  reaction 

*  Comp.  A.  SCHEURER-KESTNER,  Compt.  rend.,  LXXXVI,  1024;  Chem. 
Centralbl,  1878,  423. 

f  Wurzburger  medicin.  Zeitschr.,  1861,  93. 


§  215-j  ACIDIMETRY.  307 

(SOXHLET*).  Hence,  if  it  is  desired  to  titrate  free  phosphoric  acid, 
or  to  determine  how  much  base  is  still  required  to  form  the  basic 
salt,  NagPO4,  the  formation  of  a  soluble  alkaline  phosphate  must 
be  prevented;  i.e.,  the  phosphoric  acid  must  be  removed  from 
the  liquid,  and  in  the  form  of  a  compound  of  known  composition. 
MALY|  has  based  on  this  principle  an  acidimetric  method  of 
determining  phosphoric  acid,  whether  free  or  combined,  and 
which  gives  satisfactory  results.  The  phosphoric  acid  is  precipi- 
tated as  barium  phosphate,  Ba3(PO4)2.  The  process  is  as  follows: 

Measure  the  not  too  concentrated  solution  of  the  free  phos- 
phoric acid,  or  of  the  neutral  or  acid  alkali  phosphate,  into  a  flask, 
run  in  a  measured  quantity  of  semi-  or  one-fourth  normal  soda 
solution,  more  than  sufficient  to  convert  all  the  phosphoric  acid 
into  basic  phosphate,  then  color  with  the  indicator,  add  a  suf- 
ficient quantity  of  barium  chloride,  heat,  and  titrate  with  semi- 
or  one-fourth  normal  acid  to  just  acid  reaction.  The  liquid  must 
be  kept  hot  during  the  experiment. 

The  barium  phosphate  floating  in  the  liquid  does  not  interfere 
with  the  tit-ration.  Corallin  (see  below,  6,  cc)  is  particularly  recom- 
mended as  the  indicator  to  be  used;  one  drop  of  a  moderately 
concentrated  solution  suffices  to  color  the  liquid,  and  the  precipitate 
also,  a  deep  rose-red. 

Add  the  acid  until  the  whole  is  milk-white,  boil,  and  dissipate 
the  pink  .color,  which  again  appears,  by  adding  a  drop  or  two  of 
acid.  The  neutrality  point  is  reached  when,  after  boiling  for  a  few- 
minutes,  the  mixture  remains  milk-white  or  has  at  most  a  yellowish 
tint.  Deduct  the  c.c.  of  acid  used  from  the  c.c.  of  soda  solution;  the 
difference  represents  the  quantity  of  alkali  which  was  required  by 
the  phosphoric  acid  or  phosphate  to  form  the  basic  salt,  NasPO4. 

5.  For  all  ordinary  analyses  by  saturation,  litmus  tincture 
prepared  from  good  litmus  (Vol.  I,  p.  145)  answers  perfectly. 
For  especially  accurate  investigations,  a  litmus  tincture  prepared 
from  purified  litmus,  or  made  in  a  different  manner,  is  recommended 


*  Journ.  f.  prakt.  Chem.,  N.  F.,  vi,  16. 
f  Zeitschr.  f.  analyt.  Chem.,  xv,  417. 


308  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  215. 

by  different  persons.  BERTHELOT  and  A.  DE  FLEURIEU  *  add  pure 
diluted  sulphuric  acid  to  concentrated,  aqueous  litmus  tincture 
to  acidity,  expel  the  carbonic  acid  by  boiling,  add  baryta  water 
to  alkalinity,  pass  in  a  little  carbonic  acid,  boil  once  more,  filter, 
and  add  to  the  filtrate  one-tenth  its  volume  of  alcohol.  WARTHA,| 
who  pointed  out  that  litmus  frequently  contains  indigo,  recom- 
mends the  following  process  for  preparing  litmus  tincture :  Shake 
the  commercial  litmus  with  ordinary  alcohol,  and  reject  the  cloudy, 
bluish-violet  liquid.  Then  treat  the  residual  litmus  with  distilled 
water  for  twenty-four  to  forty-eight  hours,  pour  off  the  deeply 
colored  liquid  and  evaporate  it  on  the  water-bath;  treat  the 
residue  repeatedly  with  absolute  alcohol  acidulated  with  acetic 
acid,  and  evaporate  this  also.  By  this  treatment,  the  residue 
becomes  dehydrated  and  brittle.  Powder  it,  exhaust  the  brown 
powder  with  absolute  alcohol  acidulated  with  acetic  acid,  and  by 
this  treatment  remove  a  scarlet-red  coloring  matter  which  gives 
a  purple-red,  not  blue,  color  with  alkalies.  Dissolve  the  brown 
coloring  matter,  insoluble  in  absolute  alcohol,  in  water;  filter 
the  solution,  evaporate  to  dryness  on  a  water-bath,  and  repeatedly 
moisten  with  alcohol,  and  evaporate  to  drive  off  all  the  acetic 
acid.  The  residue  dissolved  in  water  affords  a  very  sensitive 
litmus  tincture.  FR.  MOHR|  exhausts  the  litmus  with  hot  dis- 
tilled water,  evaporates  the  filtered  solution,  supersaturates  with 
acetic  acid  (which  causes  evolution  of  carbonic  acid),  evaporates 
further  to  the  consistency  of  a  thick  extract,  introduces  the  mass 
into  a  flask,  and  treats  it  with  a  large  quantity  of  90-per-cent. 
alcohol.  The  blue  coloring  matter  is  thus  precipitated,  while 
a  red  coloring  matter  and  potassium  acetate  dissolve.  Filter, 
wash  the  precipitate  with  alcohol,  dissolve  the  residual  coloring 
matter  in  warm  water,  and  filter. 

6.  Instead  of  litmus  tincture,  various  other  coloring  matters 
may  be  used  to  detect  the  first  excess  of  alkali  when  neutralizing 


*  Zeitschr.  /.  analyt.  Chem.,  v,  100. 

f  Ber.  der  deutsch.  chem.  Gesellsch.,  ix,  217;    Zeitschr.   /.  analyt.  Chem. 
xv,  322. 

t  Lehrbuch  der  Titrirmethode,  5.  Aufl.,  724. 


§  215.]  ACIDIMETRY.  309 

an  acid.  As  a  whole,  I  prefer  litmus  tincture  to  all  other  indicators, 
although  in  certain  cases  other  indicators  possess  advantages  over 
it.  In  selecting  these,  it  must  be  remembered  that  the  power  of 
distinguishing  colors  varies  in  different  individuals,  and  that  some 
eyes  are  better  adapted  for  recognizing  one  tint,  some  another. 
Furthermore,  the  illumination  has  some  influence,  and  indicators 
which  cannot  be  advantageously  used  by  daylight,  may  be  well 
adapted  for  use  by  gaslight.  When  we  further  consider  that  every 
discoverer  of  a  new  indicator  has  his  own  particular  liking  for  it, 
and  that  habituation  to  its  use  has  a  great  influence,  it  may  be 
readily  understood  how  the  literature  of  indicators  may  gradually 
become  very  extensive.  In  the  following  only  the  most  essential 
of  the  indicators  proposed  are  described.* 

aa.  Cochineal  Tincture.^  This  was  recommended  by  C.  LucKowJ 
for  acidimetric  and  alkalimetric  purposes.  It  has  a  deep  ruby- 
red  color,  which,  on  gradually  diluting  the  tincture  with  the 
purest  distilled  water,  becomes  orange,  then  yellowish  orange. 
By  gaslight  the  color  appears  almost  colorless.  On  adding  the 
slightest  trace  of  caustic  alkali  or  alkali  carbonate,  or  caustic  alka- 
line earth,  or  of  dissolved  alkaline-earth  carbonate,  the  liquid  ac- 
quires a  violet-carmine  color.  Cochineal  tincture  may  be  ad- 
vantageously used  whenever,  in  the  determination  of  free  acid, 
free  carbonic  acid  is  naturally  present  or  evolved  during  the  de- 
termination. While  carbonic  acid  interferes  with  the  detection 
of  the  first  trace  of  alkali  when  litmus  tincture  is  used,  and  thus 
renders  it  necessary  to  expel  the  carbonic  acid  by  heating  the 
liquid,  this  is  not  the  case  to  the  same  extent  with  cochineal  tinc- 
ture, as  the  coloring  matter  of  this  is  an  acid — carminic  acid.  Car- 
bonic acid  is  not,  however,  altogether  without  influence,  as  the 


*  For  a  complete  treatise  on  indicators,  see  "Indicators  and  Test  Papers  ", 
by  ALFRED  I.  COHN.  JOHN  WILEY  &  SONS,  New  York. 

f  The  tincture  is  prepared  as  follows :  Digest  about  3  grammes  of  good 
cochineal  in  powder  with  250  c.c.  of  a  mixture  of  3  to  4  volumes  of  distilled 
water  and  1  volume  alcohol  at  the  ordinary  temperature,  and  with  frequent 
shaking,  and  then  filter  through  Swedish  filter  paper.  The  tincture  may  be 
preserved  well  in  closed  bottles. 

J  Journ,  f.  prakt.  Chem.,  LXXXIV,  424;  Zeitschr.  f.  analyt.  Chem.,  i,  386. 


310  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  215. 

first  drop  of  normal  alkali  imparts  a  violet  color  to  distilled  water 
to  which  some  cochineal  tincture  has  been  added;  but  this  is  not 
the  case  if  carbonic-acid  water  is  first  added.  Salts  of  ammonia 
have  no  prejudicial  influence  on  the  results.  If  acetates  are  pres- 
ent, or  salts  of  iron  or  aluminium,  cochineal  tincture  cannot  be 
used.  In  alkaline  solution  the  carminic  acid  is  decomposed  by 
the  atmospheric  oxygen,  so  that  an  alkaline  solution  colored  violet 
by  cochineal  becomes  first  discolored,  then  colorless. 

bb.  Extract  and  Tincture  of  Logwood.  These  were  recom- 
mended by  POHL*  and  WILDENSTEIN.!  The  former  used  the 
commercial  liquid  extract  of  about  1-036  sp.  gr.  The  latter 
prepares  the  tincture  by  splitting  a  sound  piece  of  logwood  free 
from  splits  or  cracks,  removes  from  the  inner  surfaces  fine 
shavings  by  means  of  a  plane,  boils  the  shavings  with  distilled 
water,  and  mixes  one  volume  of  the  concentrated  decoction  with 
one  or  two  volumes  of  alcohol.  The  tincture  must  be  protected 
from  the  action  of  light.  The  commercial  ground  logwood 
(Hcematoxylum  campechianum)  cannot  be  employed  for  the 
preparation  of  the  tincture,  as  the  desired  red  color  is  already 
imparted  to  it  during  the  grinding  by  moistening  with  cal- 
careous spring-water. 

On  adding  extract  or  tincture  of  logwood  to  neutral  liquids, 
these  acquire  a  yellow  color  which,  on  adding  an  acid,  remains 
yellow  or  becomes  only  slightly  paler.  On  now  neutralizing  with 
an  alkali,  the  slightest  trace  in  excess  of  the  latter  causes  a  hand- 
some deep-red  to  purple-violet  color  to  develop.  The  transition 
is  very  characteristic,  and  is  very  sharply  observed  even  by  lamp- 
light. POHL  recommends  extract  of  logwood  particularly  for  the 
determination  of  free  acid  in  wine  (even  in  red  wine,  if  sufficiently 
diluted)  and  in  must.  The  logwood  tincture  cannot  be  used  if 
even  the  slightest  traces  of  oxides  of  the  heavy  metals  (iron,  copper, 
lead,  tin,  antimony,  etc.)  are  present. 

It  should  be  especially  remarked  that  the  coloring  matter  is 


*  Journ.  f.  jyrakt.  Chem.,  LXXXI,  59. 
f  Zeitschr.  /.  analyt.  Chem.,  n,  9. 


§  115.]  ACIDIMETRY.  311 

very  rapidly  oxidized  in  alkaline  solution  under  the  influence  of 
atmospheric  oxygen. 

cc.  Rosolic  Add  (Corallin).  This  is  prepared  by  heating  a  mix- 
ture of  1  part  of  crystallized  oxalic  acid,  1J  parts  crystallized  color- 
less phenol,  and  2  parts  concentrated  sulphuric  acid  (all  by  weight) 
for  five  to  six  hours  in  a  flask  provided  with  an  upright  reflux 
condenser,  and  on  an  oil-bath  heated  to  140°  to  150°.  The  re- 
sulting dark,  semi-fluid  mass  is  poured  into  a  large  volume  of  water, 
when  the  rosolic  acid  separates  in  the  form  of  a  resinous  mass, 
which  is  then  boiled  with  water  until  free  from  the  odor  of  phenol, 
and  washed  thoroughly  with  cold  wTater.  The  product  so  ob- 
tained, although  not  perfectly  pure  rosolic  acid,  is  nevertheless 
perfectly  well  adapted  for  use  as  an  indicator.  It  is  dissolved  in 
alcohol  and  the  solution  filtered.  The  deep-reddish-violet  fluid 
colors  water  a  reddish  yellow;  with  a  drop  of  normal  acid  the 
liquid  becomes  colorless,  or  very  pale  yellow,  and  with  the  slightest 
excess  of  alkali,  a  handsome  reddish  violet.  A  liquid  so  colored 
becomes  pale  yellow  on  the  addition  of  also  carbonic-acid  water. 
Corallin  is  very  well  adapted  for  use  as  an  indicator  when  free 
acids  are  to  be  neutralized  by  caustic  alkalies.  Carbonic  acid, 
however,  exerts  a  disturbing  action  if  present.  Neutral  ammo- 
nium salts  do  not  interfere  with  the  reaction. 

dd.  Phenolphtalein.  This  coloring  matter,  discovered  by 
BAEYER,*  was  recommended  by  E.  LUCK  f  as  an  indicator  in  vol- 
umetric analysis.  It  is  prepared  by  heating  a  mixture  of  10  parts 
phenol,  5  parts  phtalic  anhydride,  and  4  parts  concentrated  sul- 
phuric acid  for  several  hours  at  120°  to  130°.  The  reddish  mass 
so  obtained  is  first  boiled  with  water,  and  the  resinous  residue 
then  boiled  with  benzene,  whereby  it  is  converted  into  a  yellowish- 
white  powder.  The  indicator  is  prepared  by  dissolving  1  part  of 
phenolphtalein  in  30  parts  of  90-per-cent.  alcohol.  1,  or  at  most  2, 
drops  of  this  solution  are  added  to  80  to  100  c.c.  of  the  liquid  to  be 
titrated.  If  the  liquid  is  acid,  it  becomes  at  first  opalescent,  but 
becomes  perfectly  clear  on  stirring.  Water  or  a  dilute  acid  is  not 

*  Ber.  d.deutsch.  chem.  Ges.  zu  Berlin,  iv,  658  (1871). 
f  Zeitschr.  f.  analyt.  Chem.,  xvi,  332. 


312  DETERMINATION    OF    COMMERCIAL    VALUES.         [§   215. 

colored  by  the  indicator,  but  if  an  alkali  is  added,  the  slightest 
trace  in  excess  develops  an  intensely  purple-red  color.  On  adding 
a  drop  of  acid,  the  liquid  again  becomes  colorless.  The  liquid 
reddened  by  an  alkali  is  decolorized  by  carbonic  acid;  hence  the 
presence  of  carbonic  acid  must  be  avoided,  as  it  disturbs  the  re- 
action. The  indicator  cannot  be  used  if  ammonia  salts  are  present. 

ee.  Tropceolin.  Under  this  name  various  dyes,  discovered  by 
Dr.  O.  WITT  (Star  Works,  Brentford,  near  London),  are  found  on 
the  market.  Two  of  them,  bearing  the  numbers  00  and  OOO, 
have  been  recommended  as  indicators  by  W.  v.  MILLER.*  A  0  •  05- 
per-cent.  aqueous  solution,  or  a  cold  saturated  alcoholic  solution 
of  the  tropseolin  OO  is  prepared;  if  2  c.c.  of  the  aqueous  or  several 
drops  of  the  alcoholic  solution  are  added  to  50  c.c.  water,  a  bright- 
yellow  solution  is  obtained  which  is  unchanged  by  free  carbonic 
acid  or  bicarbonates,  but  which,  on  the  addition  of  a  dilute  min- 
eral acid  (as  well  as  certain  organic  acids,  particularly  oxalic  acid), 
becomes  colored  yellowish  red,  and  with  a  large  excess  of  acid,  red. 
On  adding  an  alkali  the  red  color  again  changes  to  yellow.  MILLER 
recommends  this  indicator  especially  because  carbonic  acid  has 
no  influence  on  the  color  change,  and  because  with  tropseolin  solu- 
tion (best  the  alcoholic)  free  acid  may  be  recognized  and  deter- 
mined in  the  presence  of  metallic  salts.  Ammonia  salts  have  no 
disturbing  effect  on  the  reaction  when  tropseolin  OO  is  used. 

Tropseolin  OOO  may  be  used  just  like  tropseolin  OO  for  the 
detection  of  free  alkalies.  One  drop  of  a  cold  saturated  aqueous 
solution  of  tropseolin  000  is  added  to  the  acid  solution  to  be 
titrated;  this  develops  a  scarcely  noticeable  yellow  color  which,  on 
adding  an  alkali,  becomes  red  as  soon  as  the  alkali  is  present  in 
excess.  The  color  change  is  distinct  and  sharp.  Ammonia  salts 
have  no  disturbing  effect  on  the  reaction.  If  carbonic  acid  is 
present,  tropseolin  OOO  cannot  be  used. 

The  fact  that  the  methods  of  preparing  these  two  tropjeolins 
are  not  yet  known  is  likely  to  stand  in  the  way  of  the  more  general 
employment  of  these  two  indicators. 

*  Ber.  d.  deutsch.  chem.  Gesellsch.,  xi,  460;  Zeitschr.  f.  analyt.  Chem., 
xvn,  474. 


§  215.]  .        ACIDIMETRY.  313 


IV.  APPLICATION  OF  THE  ACIDIMETRIC  PRINCIPLE  TO  THE  DETER- 
MINATION OF  COMBINED  ACIDS. 

a.  The  acidimetric  principle  may  be  frequently  employed  also 
for  the  determination  of  combined  acids,  particularly  when  the 
base  is  completely  precipitated,  and  in  a  state  of  purity,  by  soda 
solution  (or  also  sodium  carbonate).  For  instance,  acetic  acid  in 
iron  mordant,  or  in  verdigris,  may  be  thus  estimated:  Precipitate 
the  solution  with  a  measured  excess  of  normal  soda  solution  (a 
solution  of  sodium  carbonate  of  known  strength),  boil,  filter,  wash, 
concentrate  the  filtrate,  add  normal  acid  just  to  acidity,  boil  to 
expel  the  carbonic  acid  taken  up  by  the  soda  during  evaporation, 
and  then  titrate  the  liquid  with  soda  solution,  using  litmus  as  the 
indicator,  until  a  blue  color  develops.  On  deducting  the  acid  used 
from  the  total  soda  solution  used,  the  difference  gives  the  soda 
solution  neutralized  by  the  acid  contained  in  the  substance  (both 
combined  and  free).  Of  course  trustworthy  results  can  be  ex- 
pected only  when  no  basic  salt  is  precipitated  by  the  soda  solution 

6.  If  the  salt  contains  a  base  precipitable  by  hydrogen  sulphide, 
and  a  non-volatile  acid  having  no  action  on  hydrogen  sulphide, 
conduct  into  the  boiling  solution  hydrogen  sulphide  (according  to 
WALCOTT  GIBBS*)  until  decomposition  is  complete,  filter,  wash 
with  hot  water,  allow  to  cool,  dilute  to  a  litre  or  half  litre,  and  in 
an  aliquot  portion  determine  the  free  acid.  If  the  acid  is  nitric 
or  hydrochloric  acid,  add  some  sodium-potassium  tartrate;  this 
prevents  the  decomposing  action  of  the  nitric  acid  on  the  hy- 
drogen sulphide,  and  the  volatilization  of  the  acid.  Salts  of  the 
alkalies  and  alkaline  earths  are  without  influence,  if  present;  iron 
or  aluminium  salts  must,  however,  be  absent.  This  method  can, 
of  course,  give  accurate  results  only  when  the  precipitated  metallic 
sulphides  are  pure,  i.e.,  free  from  any  of  the  acids  present. 

c.  If  the  sulphuric  acid  in  alum  is  to  be  titrimetrically  deter- 
mined, it  cannot  be  done  by  the  direct  addition  of  normal  soda 
solution  to  saturation,  because  then  basic  aluminium  sulphate  is 

*  Sillim.  American  Journ.  [n],  XLIV,  207;  Zeitschr.  f.  analyt.  Chem.,  vii,  94. 


314  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  215. 

precipitated,  and  the  soda  solution  used  up  does  not  correspond  to 
the  sulphuric  acid  present.  If,  however,  before  adding  the  soda 
solution,  an  excess  of  barium  chloride  is  added,  as  recommended 
by  E.  ERLENMEYER  and  LEWINSTEIN,  this  difficulty  is  avoided, 
as  then  pure  aluminium  hydrate  is  prepitated  from  the  aluminium- 
chloride  solution  thus  formed. 

If  the  aluminium  salt — as  is  the  case  with  pure  alum — is  a 
neutral  salt,  and  if  no  free  acid  is  present,  the  quantity  of  acid 
found  gives  also  the  quantity  of  alumina  present,  by  calculating  1 
equivalent  of  alumina  for  every  3  equivalents  of  acid.  The  easiest 
method  of  ascertaining  whether  an  aluminium  salt  contains  free 
acid,  is,  according  to  W.  STEIN*  by  means  of  ultramarine  paperf 
which  is  decolorized  by  free  acid.  Reliable  results  are  also  afforded 
by  the  use  of  freshly  precipitated,  carefully  washed  ammonium- 
magnesium  phosphate,  which  was  recommended  for  a  similar  pur- 
pose by  ERLENMEYER  and  LEWINSTEIN.  On  adding  an  excess  of 
the  phosphate  this  is  decomposed  by  neutral  aluminium  salts  in 
such  a  manner  as  to  afford  a  neutral  liquid.  The  most  convenient 
method,  however,  is  to  test  with  an  alcoholic  solution  of  tropseolin 
OO  (see  p.  312). 

d.  The  method  in  which,  in  many  cases,  a  slight  excess  of  a 
particular  acid  can  be  determined  acidimetrically  in  conjunction 
with  the  gravimetric  method,  will  be  later  on  detailed  under  the 
analysis  of  calcium  and  lead  acetates. 


*  Zeitschr.  f.  analyt.  Chem.,  v,  289. 

f  STEIN  (Zeitschr.  f.  analyt.  Chem.,  vm,  450)  prepares  this  paper  by  stir- 
ring ultramarine  of  suitable  quality  with  carragheen  (Iceland  moss)  jelly  (1 
part  of  the  moss  boiled  with  30  to  40  parts  of  water),  and  spreading  it  evenly 
on  unsized  paper  with  a  broad  brush.  It  is  advisable  to  prepare  both  a  light- 
colored  and  dark-colored  paper.  The  ultramarine  may  be  considered  to  be 
suitable  when  the  paper  prepared  from  it  is  readily  decolorized  by  diluted 
sulphuric  acid,  but  is  not  affected  by  a  neutral  solution  of  alum  which  has 
been  prepared  by  repeated  precipitation  with  alcohol. 


§  216.]  ACIDIMETRY.  315 


C.  DETERMINATION  BY  SATURATING  THE  FREE  ACID  WITH  AN 
ALKALINE  LIQUID  WITHOUT  USING  A  COLORING  MATTER 
AS  AN  INDICATOR. 

§216. 

Instead  of  titrating  free  acid  with  soda  solution  of  known 
strength  and  determining  the  neutrality-point  with  litmus  tincture, 
an  ammoniacal  copper  solution  may  be  used  for  this  purpose, 
as  recommended  byKiEFER*;  the  neutrality-point  is  hi  this  case 
known  by  the  turbidity  which  occurs  the  moment  all  the  free  acid 
is  neutralized.  The  copper  solution  used  for  this  purpose  is  pre- 
pared by  adding  ammonia  to  an  aqueous  cupric-sulphate  solution 
until  the  precipitate  of  basic  salt  just  redissolves.  After  the 
effective  value  of  this  solution  has  been  determined  by  means  of 
normal  sulphuric  or  hydrochloric  (not  oxalic)  acid,  the  copper 
solution  can  be  used  for  the  determination  of  all  the  stronger 
acids  (excepting  oxalic  acid),  provided  the  fluids  are  clear.  As  the 
precipitate  of  basic  salt  which  characterizes  the  end  reaction  is  not 
insoluble  in  the  ammonia  salt  formed,  but  can  hence  form  only 
when  the  solution  is  saturated  with  it,  and  as  its  solubility  depends 
upon  the  degree  of  concentration  and  upon  the  presence  of  other 
salts,  particularly  ammonia  salts  (CAREY  LEA  f),  the  method  lacks 
scientific  accuracy.  As  the  variations  occasioned  by  the  causes 
mentioned  are  inconsiderable,!  the  method  still  remains  applicable 
for  technical  purposes,  for  which,  in  fact,  it  was  originally  proposed. 
KIEFER'S  method  is  of  particular  use  in  cases  in  which  free  acid 
is  to  be  determined  in  the  presence  of  a  neutral  mineral  salt  with 
acid  reaction,  e.g.,  free  sulphuric  in  the  mother  liquors  of  cupric 
sulphate,  zinc  sulphate,  etc.  It  is  advisable  to  determine  the 
effective  value  of  the  ammoniacal  copper  solution  before  every 
fresh  series  of  experiments. 

*  Annal.  d.  Chem.  u.  Pharm.,  xcm,  386. 
t  Chem.  Neics,  1861,  195. 

J  Compare  my  experiments  on  the  subject  in  the  Zeitschr.  /.  analyt.  Chem., 
i,  108. 


316 


DETERMINATION    OF    COMMERCIAL    VALUES.          [§  217. 


D.  DETERMINATION  BY  WEIGHING  THE  CARBONIC  ACID  EXPELLED 
FROM  SODIUM  BICARBONATE. 

§217. 

Weigh  a  portion  of  the  acid  to  be  tested  in  the  flask  A  (Fig.  100), 
and  if  too  concentrated,  add  sufficient  water  to  have  the  liquid 

occupy  about  one-third  the  space 
in  the  flask.  Next  fill  a  small  glass 
tube  with  sodium  (or  potassium) 
bicarbonate,  and  suspend  it  by  a 
thread  in  the  flask  A,  by  pressing  the 
thread  between  the  stopper  and  the 
neck  of  the  flask,  the  apparatus 
being  arranged  exactly  as  described  in 
§  139,  d,  Vol.  I,  p.  488.  (The  sodium 
or  potassium  bicarbonate  used  may 
contain  sodium  chloride,  sulphate, 
etc.,  but  must  be  free  from  carbonate, 
and  the  quantity  used  must  be  more  than  sufficient  to  saturate  the 
acid  in  the  flask.)  Tare  the  flask  on  the  balance,  then  raise  the 
stopper  slightly,  allow  the  tube  together  with  the  thread  to  fall  into 
the  flask,  and  immediately  reinsert  the  stopper  air-tight.  When 
this  has  been  done,  place  the  flask  A  in  hot  water  (50°  to  55°) ;  as 
soon  as  the  renewed  evolution  of  carbonic  acid  thus  produced  has 
again  ceased,  slightly  open  the  wax  stopper  b  on  the  tube  a,  re- 
move the  flask  from  the  water-bath,  and  apply  suction  to  d  by 
means  of  a  rubber  tube,  until  all  the  carbonic  acid  still  in  the 
apparatus  is  replaced  by  air.  Suction  is  best  applied  by  means 
of  an  aspirator  or  hydraulic  air-pump.  After  cooling,  again  place 
the  apparatus  on  the  balance  and  restore  the  equilibrium  with  the 
proper  weights.  The  sum  of  these  gives  the  quantity  of  carbonic 
acid  expelled.  For  every  equivalent  of  acid  used,  one  equivalent 
of  carbon  dioxide  is  obtained,  thus: 


FIG.  100. 


§  217-1 


ACIDIMETRY. 


317 


NaHC03+HN03=NaN03+C02+H2O.  The  results  are  sat- 
isfactory.* If  possible,  the  quantity  of  acid  taken  should  be  so 
adjusted  as  to  yield  1  to  2  grms.  carbon  dioxide.  This  method 
is  preferable  to  that  described  under  B  only  when  the  liquid  is  so 
colored  that  the  litmus  reaction  cannot  be  distinctly  observed. 
Instead  of  determining  the  carbonic  acid  from  the  loss  of  weight, 
the  method  described  in  Vol.  I,  p.  493,  may  be  used. 

E.  METHODS  USED  FOR  PARTICULAR  ACIDS. 

Determining   the  Strength    of   Acetic   Acid    from    its    Solidifying 

point. 

FR.  RUDORFF  f  recommends  the  determination  of  the  solidifying- 
point  for  the  valuation  of  highly  concentrated  acetic  acid.  The 
following  table,  based  on  his  results,  shows  the  relation  of  the 
temperature  of  solidification  to  the  quantity  of  hydrated  acetic 
acid: 


100  parts  of  hydrated 
acetic  acid 
are  mixed  with  — 

100  parts  of  the  mixture 
contain  — 

Solidifying  temperature. 

0-0  water 

0-0      water 

+  16-70° 

0-5      " 

0-497      " 

15-65 

1-0       " 

0-990      " 

14-80 

1-5       " 

1-477      " 

14-00 

2-0       " 

1-961      " 

13-25 

3-0       " 

2-912      " 

11-95 

4-0       " 

3-846      " 

10-50 

5-0      " 

4-761      " 

9-40 

6-0      " 

5-660      " 

8-20 

7-0      " 

6-542      ' 

7-10 

8-0       " 

7-407      ' 

6-25 

9-0       " 

8-257      ' 

5-30 

10-0       ' 

9-090      ' 

4-30 

11-0      ' 

9-910      ' 

3-60 

12-0      ' 

10-774      ' 

2-70 

15-0       ' 

13-043      ' 

-0-20 

18-0       ' 

15-324      ' 

2-60 

21-0       ' 

17-355      ' 

5-10 

24.0 

19.354      ' 

7.40 

*  Compare  "New  Methods  of  Testing  Potash  and  Soda,  and  of  Determin- 
ing the  Commercial  Value  of  Acids  and  Manganese, ' '  by  Drs.  R.  FRESENIUS 
and  WILL.  Edited  by  J.  L.  BULLOCK.  TAYLOR  &  WALTON,  1843. 

f  Bericht  d.  deutsch.  chem.  Gesellsch.,  in,  390;  Zeitschr.  /.  analyt.  Chem., 
X,  106. 


318 


DETERMINATION    OF    COMMERCIAL   VALUES. 


[§  217. 


Table  showing  the  percentages  of  Acetic  Acid  (HC2H3O2)  corresponding  to  vari* 
ous  specific  gravities  of  aqueous  solutions  of  Acetic  Acid,  by  MOHR. 


Specific 
gravity. 

Percentage  of 
acetic  acid 
(HC2H302). 

Specific 
gravity. 

Percentage  of 
acetic  acid 
(HC2H3O2). 

Specific 
gravity. 

Percentage  of 
acetic  acid 
(HC2H302). 

Specific 
gravity. 

Percentage  of 
acetic  acid 
(HC2H302). 

Specific 
gravity. 

Percentage  of 
acetic  acid 
(HC2H302). 

•0635 

100 

1-0735 

80 

1-067 

60 

1-051 

40 

1-027 

20 

•0555 

99 

1-0735 

79 

1-066 

59 

1-050 

39 

1-026 

19 

•0670 

98 

1-0732 

78 

1-066 

58 

1-049 

38 

1-025 

18 

•0680 

97 

1-0732 

77 

1-065 

57 

1-048 

37 

1-024 

17 

•0690 

96 

1-0730 

76 

1-064 

56 

•047 

36 

•023 

16 

•0700 

95 

•0720 

75 

1-064 

55 

•046 

35 

•022 

15 

•0706 

94 

,     -0720 

74 

1-063 

54 

•045 

34 

•020 

14 

•0708 

93 

-0720 

73 

1-063 

53 

•044 

33 

•018 

13 

•0716 

92 

-0710 

72 

1-062 

52 

•042 

32 

•017 

12. 

•0721 

91 

•0710 

71 

1-061 

51 

•041 

31 

•016 

11 

•0730 

90 

•0700 

70 

1-060 

50 

1-040 

30 

•015 

10 

•0730 

89 

•0700 

69 

1-059 

49 

1-039 

29 

•013 

9 

•0730 

88 

•0700 

68 

1-058 

48 

1-038 

28 

1-012 

8 

•0730 

87 

•0690 

67 

1-056 

47 

1-036 

27 

1-010 

7 

-0730 

86 

•0690 

66 

1-055 

46 

1-035 

26 

1-008 

6 

•0730 

85 

•0680 

65 

1-055 

45 

1-034 

25 

1-007 

5 

1-0730 

84 

•0680 

64 

1-054 

44 

1-033 

24 

1-005 

4 

1-0730 

83 

•0680 

63 

1-053 

43 

1-032 

23 

1-004 

3 

1-0730 

82 

•0670 

62 

1-052 

•  42- 

1-031 

22 

1-002 

2 

1-0732 

81 

•0670 

61 

1-051 

41 

1-029 

21 

1-001 

1 

In  determining  the  solidifying-point  it  is  necessary  to  take  care 
that  only  a  little  of  the  acid  separates.  This  is  accomplished  with 
the  most  certainty  by  cooling  the  fluid  to  about  1°  below  the 
approximately  determined  solidifying-point,  and  then  throwing 
in -a  small  fragment  of  solid  hydrated  acetic  acid  and  stirring,  and 
thus  causing  the  separation  of  the  hydrated  acetic  acid.  The 
temperature  is  thus  caused  to  rise  to  the  solidifying-point  of  the 
mixture.  Small  quantities  of  solid  acetic  acid  are  readily  pro- 
cured by  introducing  a  small  quantity  of  glacial  acetic  acid  into 
a  small  test-tube,  and  with  it  stirring  a  mixture  of  cold  water  with 
ammonium  chloride,  ammonium  nitrate,  or  potassium  sulpho- 
cyanide. 


§  218.] 


ALKALIMETRY. 


319 


2.  DETERMINATION  OF  CAUSTIC  ALKALI  AND  ALKALI 
CARBONATE  (ALKALIMETRY.) 

A.  ESTIMATION  OF  POTASSA,  SODA,  POTASSIUM  AND  SODIUM  CAR- 
BONATES, OR  AMMONIA,  FROM  THE  SPECIFIC  GRAVITY 
OF  THEIR  SOLUTIONS. 

§218. 

In  pure  or  nearly  pure  solutions  of  hydrated  soda  or  potassa,  or 
of  ammonia,  the  percentage  of  alkali  may  be  estimated  from  the 
specific  gravity  of  the  solution. 

TABLE  I. 

Potassa   and  Potassium  Hydroxide  in  Potassa  Solution  at   various  specific 
gravities,  by  SCHIFF  and  TUNNERMANN,  calculated  by  GERLACH.* 


Amount 
in  100 
parts  by 
weight  of 
solution. 

Potassa, 
(K20), 
sp.  gr. 
at  15°. 

Potassium 
hydrate, 
(KOH) 
sp.  gr.  at  15°. 

Amount 
in  100 
parts  by 
weight  of 
solution. 

Potassa 
(K20), 
sp.  gr. 
at  15°. 

Potassium 
hydrate, 
(KOH), 
sp.  gr. 
at  15°. 

1 

•010 

•009 

36 

1-455 

1-361 

2 

•020 

•017 

37 

1-460 

1-374 

3 

•030 

•025 

38 

1-475 

1-387 

4 

•039 

•033 

39 

1-490 

•400 

5 

•048 

•041 

40 

1-504 

-411 

6 

•058 

•049 

41 

1-522 

•425 

7 

•068 

•058 

42 

1-539 

•438 

8 

•078 

•065 

43 

1-564 

•450 

9 

•089 

•074 

44 

1-570 

•462 

10 

1-099 

•083 

45 

1-584 

•475 

11 

1-110 

•092 

46 

1-600 

•488 

12 

1-121 

•110 

47 

1-615 

•499 

13 

1-132 

•111 

48 

1-630 

•511 

14 

1-143 

•119 

49 

1-645 

•527 

15 

1-154 

•128 

50 

1-660 

-539  . 

16 

1-166 

•137 

51 

1-676 

•552 

17 

•178 

•146 

52 

1-690 

•565 

18 

1-190 

•155 

53 

1-705 

•578 

19 

1-202 

•166 

54 

1-720 

1-590 

20 

1-215 

•177 

55 

1-733 

1-604 

21 

1-230 

•188 

56 

1-746 

1-618 

22 

1-242 

•198 

57 

1-762 

1-630 

23 

1-256 

•209 

58 

1-780 

1-641 

24 

1-270 

•220 

59 

1-795 

1-655 

25 

1-285 

1-230 

60 

1-810 

1-667 

26 

1-300 

1-241 

61 

1-682 

27 

1-312 

1-252 

62 

1-695 

28 

•326 

1-264 

63 

1-705 

29 

•340 

1-278 

64 

•718 

30 

•355 

1-288 

65 

•729 

31 

•370 

1-300 

66 

•740 

32 

•385 

1-311 

67 

•751 

33 

•403 

1-324 

68 

.768 

34 

•418 

1-336 

69 

•7«0 

35 

•431 

1-319 

70 

1-790 

Zcitachr.  f.  analyt.  Chem.,  vm,  279. 


320 


DETERMINATION    OF    COMMERCIAL    VALUES. 


[§  218. 


TABLE  Ha. 

Soda,  (Na2O),  and  Sodium  Hydroxide,  (NaOH),  in  soda  solutions  at  various 
specific  gravities,  by  SCHIFF.     Calculated  by  GERLACH.* 


Quantity 
in  100 
parts  by 
weight  of 
solution. 

Soda,  (Na20), 
sp.  gr.  at  15°. 

Sodium 
hydroxide, 
(NaOH),  sp.  gr. 
at  15°. 

Quantity 
in  100 
parts  by 
weight  of 
solution. 

Soda,  (Na20), 
sp.  gr.  at  15°. 

Sodium 
hydroxide, 
(NaOH),  sp.  gr. 
at  15°. 

1 

1-015 

1-012 

36 

1-500 

-395 

2 

1-020 

1-023 

37 

1-515 

-405 

3 

•043 

1-035 

38 

1-530 

-415 

4 

•058 

1-046 

39 

1-543 

•426 

5 

•074 

1-059 

40 

1-558 

•437 

6 

•089 

1-070 

41 

1-570 

•447 

7 

•104 

1-081 

42 

1-583 

•456 

8 

•119 

1-092 

43 

1-597 

-468 

9 

•132 

•103 

44 

1-610 

•478 

10 

•145 

•115 

45 

1-623 

•488 

11 

•160 

•126 

46 

1-637 

1-499 

12 

•175 

•137 

47 

•650 

1-508 

13 

1-190 

•148 

48 

•663 

1-519 

14 

1-203 

•159 

49 

-678 

1-529 

15 

1-219 

•170 

50 

-690 

1-540 

16 

1-233 

1-181 

51 

-705 

1-550 

17 

1-245 

1-192 

52 

1-719 

1-560 

18 

1-258 

1-202 

53 

1-731 

1-570 

19 

1-270 

1-213 

54 

1-745 

1-580 

20 

1-285 

1-225 

55 

1-760 

1-591 

21 

1-300 

1-236 

56 

1-770 

1-601 

22 

1-315 

1-247 

57 

1-785 

1-611 

23 

1-329 

1-258 

58 

1-800 

1-622 

24 

1-341 

1-269 

59 

1-815 

1-633 

25 

1-355 

1-279 

60 

1-830 

1-643 

26 

1-369 

1-290 

61 

1-654 

27 

1-381 

1-300 

62 

1-664 

28 

1-395 

1-310 

63 

•674 

29 

1-410 

1-321 

64 

•684 

30 

1-422 

1-332 

65 

•695 

31 

1-438 

1-343 

66 

•705 

32 

1-450 

1-351 

67 

•715 

33 

1-462 

1-363 

68 

•726 

34 

1-475 

1-374 

69 

1-737 

35 

1-488 

1-384 

70 

1-748 

*  Zeitschr.  f.  analyt.  Chem.,  viu,  279. 


I  218.] 


ALKALIMETRY. 


321 


TABLE  116. 

Percentages  of  Anhydrous  Potassa,  (K2O),  corresponding  to  different  specific 
gravities  of  solution  of  potassa. 


DALTON. 

TUNNERMANN  (at   15°). 

Specific 
gravity. 

Percentage 
of  anhydrous 
potassa. 

Specific 
gravity. 

Percentage 
of  anhydrous 
potassa. 

Specific 
gravity. 

Percentage 
of  anhydrous 
potassa. 

1-60 

46-7 

1-3300 

28-290 

1  •  1437 

14-145 

1-52 

42-9 

1-3131 

27-158 

1  •  1308 

13-013 

1.47 

39-6 

1-2966 

26-027 

1-1182 

11-882 

1-44 

36-8 

1-2803 

24-895 

1  •  1059 

10-750 

1-42 

34-4 

1-2648 

23-764 

1-0938 

9-619 

1-39 

32-4 

1-2493 

22-632 

1-0819 

8-487 

1-36 

29-4 

1-2342 

21-500 

1-0703 

7-355 

1-33 

26-3 

1-2268 

20-935 

•0589 

6-224 

1-28 

23-4 

1-2122 

19-803 

•0478 

5-002 

1-23 

19-5 

1  •  1979 

18-671 

•0369 

3-961 

1-19 

16-2 

1  •  1839 

17-540 

•0260 

2-829 

1-15 

13-0 

1-1702 

16-408 

•0153 

1-697 

1-11 

9-5 

1-1568 

15-277 

•0050 

0-5658 

1-06 

4-7 

TABLE  He. 


Percentages  of  Anhydrous  Soda,  (Na^jO),  corresponding  to  different  specific  grav- 
ities of  solution  of  soda. 


DALTON. 


TUNNERMANN  (at  15). 


Specific 
gravity. 

Percent- 
age of 
anhydrous 
soda. 

Specific 
gravity. 

Percent- 
age of 
anhydrous 
soda. 

Specific 
gravity. 

Percent- 
age of 
anhydrous 
soda. 

Specific 
gravity. 

Percent- 
age of 
anhydrous 
soda. 

1-56 

41-2 

1-4285 

30-220 

-2982 

20-550 

1-1528 

10-275 

1-50 

36-8 

1-4193 

29-616 

-2912 

19-945 

1-1428 

9-670 

1-47 

34-0 

1-4101 

29-011 

-2843 

19-341 

1-1330 

9-066 

1-44 

31-0 

1-4011 

28-407 

•2775 

18-730 

1-1233 

8-462 

1-40 

29-0 

1-3923 

27-802 

•2708 

18-132 

1-1137 

7-857 

1-36 

26-0 

1-3836 

27-200 

•2642 

17-528 

1-1042 

7-253 

1-32 

23-0 

1-3751 

26-594 

•2578 

16-923 

1-0948 

6-648 

1-29 

19-0 

1-3668 

25-989 

•2515 

16-319 

1-0855 

6-044 

1-23 

16-0 

1-3586 

25-385 

1-2453 

15-714 

•0764 

5-440 

1-18 

13-0 

1-3505 

24-780 

1-2392 

15-110 

•0675 

4-835 

1-12 

9-0 

1-3426 

24-176 

1-2280 

14-506 

•0587 

4-231 

1-06 

4-7 

•3349 

23-572 

1-2178 

13-901 

-0500 

3-626 

•3273 

22-967 

1-2058 

13-297 

•0414 

3-022 

•3198 

22-363 

1  -  1948 

12-692 

•0330 

2-418 

•3143 

21-894 

1-1841 

12-088 

•0246 

1-813 

•3125 

21-758 

1-1734 

11-484 

1-0163 

1-209 

•3053 

21-154 

1  •  1630 

10-879 

1-0081 

0-604 

322 


DETERMINATION    OF   COMMERCIAL    VALUES.          [§  2l8~ 


TABLE  III. 

Anhydrous  Potassium  and  Sodium  Carbonates  in  aqueous  solutions  at  various? 
specific  gravities,  by  GERLACH.* 


Amount  in 
100  parts 
by  weight 
of  the 
solution. 

Potassium 
carbonate, 
sp.  gr.  at  15°. 

Sodium 
carbonate, 
sp.  gr.  at  15°. 

Amount  in 
100  parts 
by  weight 
of  the 
solution. 

Potassium 
carbonate, 
sp.  gr.  at  15°. 

Sodium 
carbonate, 
sp.  gr.  at  15°.. 

1 

1-00914 

•01050 

27 

1-26787 

2 

1-01829 

•02101 

28 

1-27893 

3 

1-02743 

•03151 

29 

1-28999 

4 

1-03658 

•04201 

30 

1-30105 

5 

1-04572 

-05255 

31 

1-31261 

6 

1-05513 

1-06309 

32 

1-32417 

7 

1-06454 

1-07369 

33 

1-33573 

8 

1-07396 

1-08430 

34 

1-34729 

9 

1-08337 

1-09500 

35 

1-35885 

10 

1-09278 

1-10571 

36 

1-37082 

* 

11 

1  •  10258 

1-11655 

37 

1-38279 

12 

1-11238 

1  -  12740 

38 

1-39476 

13 

1-12219 

1  -  13845 

39 

1-40673 

14 

1-13199 

1  -  14950 

40 

1-41870 

15 

1-14179 

41 

1-43104 

16 

1-15200 

42 

1-44338 

17 

1  •  16222 

43 

1-44573 

18 

•17243 

44 

1-46807 

19 

1  -  18265 

45 

1-48041 

20 

1  -  19286 

46 

1-49314 

21 

•20344 

47 

1-50588 

22 

1-21402 

48 

1-51861 

23 

•22459 

49 

1-53135 

24 

1-23517 

50 

1-54408 

25 

1-24575 

51 

1-55728 

26 

1-25681 

52 

1-57048 

TABLE  IVa. 

Ammonia,  (NH3),  in  Solutions  of  Ammonia  of  various  specific  gravities,  by 
CARIUS,  calculated  by  GERLACH.* 


Amount 

Amount 

Amount 

Amount 

in  100 
parts  by 
weight 
of  solu- 

Ammonia, 
sp.  gr.  at 
16°. 

in  100 
parts  by 
weight 
of  solu- 

Ammonia, 
sp.  gr.  at 
16°. 

in  100 
parts  by 
weight 
of  solu- 

Ammonia, 
sp.  gr.  at 
16°. 

in  100 
parts  by 
weight 
of  solu- 

Ammonia* 
sp.gr.  at 

tion. 

tion. 

tion. 

tion. 

1 

0-9959 

10 

0-9593 

19 

0-9283 

28 

0-9026 

2 

0-9915 

11 

1-9556 

20 

0-9251 

29 

0-9001 

3 

0-9873 

12 

0-9520 

21 

0-9221 

30 

0-8976 

4 

0-9831 

13 

0-9484 

22 

0-9191 

31 

0-8953 

5 

0-9790 

14 

0-9449 

23 

0-9162 

32 

0-8929 

6 

0-9749 

15 

0-9414 

24 

0-9133 

33 

0-8907 

7 

0-9709 

16 

0-9380 

25 

0-9106 

34 

0-8885 

8 

0-9570 

17 

0-9347 

26 

0-9078 

35 

0-8864 

9 

0-9631 

18 

0-9314 

27 

0-9052 

36 

0-8844 

*  Zeitschr  ./.  analyt.  Chem  ,  vin,  279. 


§  219.] 


ALKALIMETRY. 
TABLE  IVb. 


323 


Percentages  of  Ammonia,  (NH3),  corresponding  to  different  specific  gravities  of 
solution  of  ammonia  at  16°  (J.  OTTO). 


Specific 
gravity. 

Percentage 
of  ammonia. 

Specific 
gravity. 

Percentage 
of  ammonia. 

Specific 
gravity. 

Percentage 
of  ammonia. 

0-9517 

12-000 

0-9607 

9-625 

0-9697 

7-250 

0-9521 

11-875 

0-9612 

9-500 

0-9702 

7-125 

0-9526 

11-750 

0-9616 

9-375 

0-9707 

7-000 

0-9531 

11-625 

0-9621 

9-250 

0-9711 

6-875 

0-9536 

11-500 

0-9626 

9-125 

0-9716 

6-750 

0-9540 

11-375 

0-9631 

9-000 

0-9721 

6-625 

0-9545 

11-250 

0-9636 

8-875 

0-9726 

6-500 

0-9550 

11-125 

0-9641 

8-750 

0-9730 

6-375 

0-9555 

11-000 

0-9645 

8-625 

0-9735 

6-250 

0-9556 

10-950 

0-9650 

8-500 

0-9740 

6-125 

0-9559 

10-875 

0-9654 

8-375 

0-9745 

6-000 

0-9564 

10-750 

0-9659 

8-250 

0-9749 

5-875 

0-9569 

10-625 

0-9664 

8-125 

0-9754 

5-750 

0-9574 

10-500 

0-9669 

8-000 

0-9759 

5-625 

0-9578 

10-375 

0-9673 

7-875 

0-9764 

5-500 

0-9583 

10-250 

0-9678 

7-750 

0-9768 

5-375 

0-9588 

10-125 

0-9683 

7-625 

0-9773 

5-250 

0-9593 

10-000 

0-9688 

7-500 

0-9778 

5-125 

0-9597 

9-875 

0-9692 

7-375 

0-9783 

5-000 

0-9602 

9-750 

B.  DETERMINATION  OP  THE  TOTAL  CAUSTIC  ALKALI  AND  ALKALI 
CARBONATE  IN  A  SUBSTANCE. 

I.   VOLUMETRIC   METHODS. 

a.  Method  of  DESCROIZILLES  and  GAY-LUSSAC,  slightly  nidified. 

§219. 

The  principle  of  this  method  is  the  converse  of  that  on  which 
the  acidimetrie  method  described  §  215  is  based,  i.e.,  if  we  know 
the  quantity  of  an  acid  of  known  strength  required  to  saturate  an 
unknown  quantity  of  caustic  potassa  or  soda,  or  of  potassium  car- 
bonate or  sodium  carbonate,  we  may  readily  calculate  from  this 
the  amount  of  alkali  present. 

This  method  requires  but  one  solution  of  known  strength- 
standard  sulphuric  acid.  This  is  now  almost  generally  made  of 
such  a  strength  that  50  c.c.  of  it  will  saturate  5  grm.  of  pure,  anhy- 
drous sodium  carbonate. 


324  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  219. 

The  method  of  preparing  and  using  it  is  as  follows: 

a.  Mix  about  60  grm.   of    concentrated  sulphuric    acid  with 
500  c.c.  of  water,  or  120  grm.  with  1000  c.c.  water,  and  allow  to 
cool. 

b.  Accurately  weigh  off  5  grm.  of  pure,  anhydrous  sodium  car- 
bonate, introduce  it  into  a  flask,  dissolve  it  in  about  200  c.c. 
of  water,  and  color  the  solution  distinctly  blue  with  a  measured 
quantity  (about  1  c.c.)  of  violet  litmus  tincture*  (see  p.  295,  d). 

N.B.  This  method  is  intended  for  the  use  of  those  who 
are  not  accustomed  to  weigh  on  fine  analytical  balances.  Where 
chemical  balances  are  used,  as  is  generally  the  case  in  chemical 
laboratories,  it  is  far  better  to  gently  ignite  4-5  to  5  grm.  of 
the  sodium  carbonate  in  a  platinum  crucible,  then  to  dry  under 
an  exsiccator,  and  to  finally  weigh  the  crucible  accurately.  The 
contents  of  the  crucible  are  now  introduced  into  the  flask,  the 
crucible  weighed  once  more,  and  the  quantity  of  sodium  car- 
bonate transferred  to  the  flask  accurately  ascertained  from  the 
difference  in  the  two  weighings.  This  process  is  far  more  easily 
performed  by  the  skilled  chemist  than  the  other,  and  yields 
much  more  trustworthy  results,  since  the  weighing  is  effected  with 
covered  crucibles.  If  several  portions  are  to  be  consecutively 
weighed,  the  ignited  salt  is  transferred  while  still  hot  to  a  test- 
tube  provided  with  a  stopper,  weighed,  a  suitable  quantity 
shaken  out,  the  tube  weighed  again,  etc.  The  potash  or  soda 
to  be  subsequently  examined  is  to  be  treated  in  the  same  man- 
ner as  the  pure  sodium  carbonate. 

c.  Fill  a  burette  (preferably  one  holding  50  c.c.)  .to  the  zero- 
point  with  the    cooled   acid,  and  allow  enough  of  it  to  flow  into 
the  soda  solution  until  saturation  is  complete  (see  below).     This' 
experiment  it  is  better  to  repeat.     If  less  than  exactly  5  grm.  of 
sodium  carbonate  were  taken,  it   is  necessary  to   calculate   from 
the  results  obtained  just  how  much  acid  would  have  been  required 
for  5  grm.  of  sodium  carbonate. 

*  Regarding  the  use  of  other  indicators,  see  page  309 ;  also  "  Indicators 
and  Test  Papers  ",  by  ALFRED  I.  COHN.     JOHN  WILEY  &  SONS,  New  York. 


§  219.]  ALKALIMETRY.  325 

d.  Dilute  the  remainder  of  the  acid  with  water  so  that  50  c.c. 
of  it  will  exactly  neutralize  5  grm.  of  sodium  carbonate.     Had 
45  c.c.  of  the  acid,  for  instance,  been  required  to  saturate  5  grm. 
of  sodium  carbonate,  then  5  volumes  water  would  have  to  be  added 
for  every  45  volumes  of  the  acid.     The  dilution  is  effected  in  the 
manner  described  on  p.  297.     I  urgently  recommend  that  the  acid, 
after  dilution,  be  once  more  tested  in  the  manner  described  above. 

e.  The  standard  acid  thus   prepared  should  be  preserved  in 
well-stoppered  vessels,  and  should  be  well  shaken  before  every 
fresh  series  of  experiments  (p.  297).     It  serves  for  the  examination 
of  soda,  potash,  and  caustic  alkalies;  the  number  of  half-c.c.  used 
gives  directly  the  percentage  of  alkali  carbonate  or  caustic  alkali 
provided  the  experiment  be  made  with  a  weighed  quantity  of  the 
substance  equivalent  to  5  grm.  of  sodium  carbonate. 

The  following  table  gives  the  equivalent  quantities: 

50  c.c.  of  the  standard  acid  saturates  5          grm.  Na^CO, 

"     "  "     "         "  "         "          2-926     "     NajO 

"    "  "     "        "  "         "          6-515     "     K2CO3 

"    "  "     "         "  "         "  4-441     "     K2O 

Accordingly,  if  6*515  grm.  potassium  carbonate  mixed  with 
potassium  salts  having  a  neutral  reaction  be  taken,  the  number 
of  half-c.c.  used  gives  directly  the  percentage  of  alkali  expressed 
as  potassium  carbonate;  if  4'441  grm.  be  taken,  the  number  of 
half-c.c.  of  the  standard  acid  gives  the  percentage  of  alkali  ex- 
pressed as  anhydrous  caustic  potassa,  K2O,  etc. 

When  examining  substances  poor  in  caustic  alkali  or  alkali 
carbonate,  a  multiple,  i.e.,  twice,  thrice,  ten  times,  etc.,  of  the 
quantities  above  stated  should  be  taken,  and  the  number  of 
half-cc.  of  acid  used  divided  by  the  corresponding  number. 

/.  Regarding  the  determination  of  the  saturation -point,  this 
is  easily  done  in  the  case  of  caustic  alkalies;  but  with  alkali  car- 
bonates the  carbonic  acid  liberated  changes  the  color  of  the  liquid 
to  a  wine-red  and  causes  some  difficulty.  This  may  be  overcome 
in  two  ways. 

a.  When  sufficient  of  the  standard  acid  has  been  added  to  im 
part  a  wine-red  color  to  the  cold,  or  even  previously  heated  solu- 


326  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  219. 

tion  of  alkali  carbonate  contained  in  a  flask,  heat  the  liquid  to 
boiling,  with  frequent  shaking,  when  the  color  will  change  again 
to  blue  as  the  carbonic  acid  escapes.  Now  add  more  of  the  stand- 
ard acid  to  the  almost  boiling  liquid,  heating  occasionally;  the 
point  of  saturation,  or  more  properly  incipient  supersaturation, 
is  thus  very  easily  and  accurately  observed  by  the  color  of  the 
liquid  becoming  red  with  a  yellowish  tint. 

ft.  The  saturation  point  may  also  be  ascertained  without  heat- 
ing the  liquid,  but  not  with  equal  accuracy.  The  flask  in  this 
case  must  not  be  too  small.  After  every  addition  of  the  acid,  the 
flask  must  be  carefully  but  vigorously  shaken,  the  acid  being  con- 
stantly added  so  long  as  the  red  color  of  the  liquid  continues  to 
have  a  violet  tint.  When  the  saturation-point  is  nearly  reached, 
the  acid  is  added  two  drops  at  a  time,  and  after  every  fresh  ad- 
dition, a  glass  rod  is  dipped  into  the  solution,  and  one,  or  better, 
two  spots  made  with  it  on  a  strip  of  good  blue  litmus  paper,  the 
volume  read  off  each  time,  and  the  reading  marked  down  between 
the  spots.  This  procedure  is  continued  until  the  spots  appear 
decidedly  red.  The  litmus  paper  is  now  allowed  to  dry,  and  the 
lowest  reading  taken  as  correct  where  the  spots  between  which 
it  is  marked  just  remain  red. 

It  must  be  remembered  as  a  rule  that  the  standard  acid  must  be 
tested  by  the  same  method  which  is  to  be  used  in  the  actual  analysis. 
On  this  account  a  normal  sulphuric,  hydrochloric  or  oxalic  acid, 
prepared  according  to  §  215,  cannot  be  employed  for  the  direct 
and  immediate  titration  of  alkalies. 


For  the  analysis  we  may  also  conveniently  weigh  off  such  a 
quantity  of  the  substance  that  the  number  of  c.c.  of  normal  acid 
required  to  neutralize  it  shall  directly  express  its  percentage  of 
the  alkali  or  carbonate  sought. 

Since  100  c.c.  of  the  normal  solution  contain  ^  of  98*086  grm. 
H2SO4,  the  proper  quantities  of  the  sodium  and  potassium  com- 
pounds to  employ  are  ^  of  the  weight  of  the  compound  required 
to  neutralize  98*086  grm.  H2S04,  viz. : 


§  219.]  ALKALIMETRY.  327 

Potassa,  K2O 4-711  grm. 

Potassium  hydroxide,  KOH 5-612  " 

Potassium  carbonate,  K2CO3 6-911  " 

Hydrogen  potassium  Carbonate,  KHCO3 10-012  " 

Soda,  Na/) 3-105  " 

Sodium  hydroxide,  NaOH 4-006  " 

Sodium  carbonate  (dry),  NaaCOj 5-305  " 

Sodium  carbonate  crystallized,  Na2CO3-10H20 14-313  " 

Hydrogen  sodium  carbonate,  NaHCO3 8-406  " 

With  regard  to  the  examination  of  pearlash  by  this  method,  the 
following  points  deserve  attention: — 

The  various  sorts  of  potash  of  commerce  contain,  besides  potas- 
sium carbonate  (and  caustic  potassa): 

a.  Normal  salts  (e.g.,  potassium  sulphate,  potassium  chloride). 

b.  Salts  with  alkaline  reaction  (e.g.,  potassium  silicate,  potas- 
sium phosphate). 

c.  Admixtures  insoluble  in  water,  more  especially  calcium  car- 
bonate, phosphate,  and  silicate. 

The  salts  named  in  a  exercise  no  influence  upon  the  results, 
but  not  so  those  named  in  b  and  c.  Those  in  c  may  be  removed 
by  filtration;  but  the  admixture  of  the  salts  named  in  b  constitutes 
an  irremediable  though  slight  source  of  error;  that  is  to  say,  if  it 
is  desired  to  confine  the  determination  to  the  caustic  and  carbon- 
ated alkali.  But  as  regards  the  estimation  of  the  value  of  pearl- 
ash  for  many  purposes,  the  term  error  cannot  be  applied;  as,  for 
instance,  in  the  preparation  of  caustic  potassa,  by  boiling  the  solu- 
tion with  lime,  the  alkali  combined  with  silicic  acid  and  with  phos- 
phoric acid  is  converted,  like  the  carbonate,  into  the  caustic  state. 

If  you  are  not  satisfied  with  finding  the  percentage  of  available 
alkali,  but  desire  also  to  know  whether  the  remainder  consists 
simply  of  foreign  salts,  or  whether  water  is  also  present,  the  de- 
termination of  the  latter  substance  must  precede  the  alkalimetric 
examination.  The  same  remark  applies  also  to  soda. 

With  regard  to  the  examination  of  soda  by  this  method,  the  fol- 
lowing points  deserve  attention: 

The  soda  of  commerce,  prepared  by  LEBLANC'S  method,  con- 
tains, besides  sodium  carbonate,  always,  or  at  least  generally, 


328  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  219. 

sodium  hydroxide,  sodium  sulphate,  sodium  chloride,  sodium 
silicate  and  aluminate,  and  not  seldom  also  sodium  sulphide, 
sodium  thiosulphate  and  sulphite.* 

The  three  last-named  substances  impede  the  process,  and  inter- 
fere more  or  less  with  the  accuracy  of  the  results.  Their  presence 
is  ascertained  in  the  following  way: 

a.  Mix  with  sulphuric  acid;  a  smell  of  hydrogen  sulphide  re- 
veals the  presence  of  sodium  sulphide,  with  which  sodium  thio- 
sulphate is  also  invariably  associated. 

6.  Color  dilute  sulphuric  acid  with  a  drop  of  solution  of  potas- 
sium permanganate  or  chromate,  and  add  some  of  the  soda  under 
examination,  but  not  sufficient  to  neutralize  the  acid.  If  the  solu- 
tion retains  its  color,  this  proves  the  absence  of  both  sodium  sul- 
phite and  thiosulphate;  but  if  the  fluid  loses  its  color,  or  turns 
green,  as  the  case  may  be,  one  of  these  salts  is  present. 

c.  Whether  the  reaction  described  in  b  proceeds  from  sodium 
sulphite  or  thiosulphate  is  ascertained  by  supersaturating  a  clear 
solution  of  the  sample  under  examination  with  hydrochloric  acid. 
If  the  solution,  after  the  lapse  of  some  time,  becomes  turbid,  owing 
to  the  separation  of  sulphur  (emitting  at  the  same  time  the  odor 
of  sulphurous  acid),  this  may  be  regarded  as  a  proof  of  the  presence 
of  sodium  thiosulphate;  however,  the  solution  may,  besides  the 
thiosulphate,  also  contain  sodium  sulphite.  With  respect  to  the 
detection  of  sodium  sulphite  in  the  presence  of  thiosulphate,  comp. 
"Qual.  Anal.,"  p.  204. 

The  defects  arising  from  the  presence  of  the  three  compounds 
in  question  may  be  remedied  in  a  measure  by  igniting  the  weighed 
sample  of  the  soda  with  potassium  chlorate  before  proceeding  to 
saturate  it.  This  operation  converts  the  sodium  sulphide,  thiosul- 
phate, and  sulphite  into  sodium  sulphate.  But  if  sodium  thiosul- 
phate is  present,  the  process  serves  to  introduce  another  source  of 
error,  as  that  salt,  upon  its  conversion  into  sulphate,  decomposes  a 
molecule  of  sodium  carbonate  and  expels  the  carbonic  acid  of  the 
latter.  [Na2S2O3+40  (from  the  potassium  chlorate) +  Na2CO3= 
2(Na2S04)+C02.] * 

*  Traces  of  sodium  cyanide  are  also  occasionally  found. 


§  220.]  ALKALIMETRY.  329 

The  presence  of  sodium  silicate  and  of  sodium  aluminate  may 
be  generally  recognized  by  the  separation  of  a  precipitate  as  soon 
as  the  solution  is  saturated  with  acid.  If  you  intend  the  result  to 
express  the  quantity  of  carbonated  and  caustic  alkali  only,  the 
presence  of  these  two  bodies  becomes  a  slight  source  of  error;  but 
if  you  wish  to  estimate  the  value  of  the  soda  for  many  purposes, 
no  error  will  be  caused. 

b.  Method  of  FR.  MOHR,  modified. 
§  220. 

Instead  of  estimating  the  alkalies  in  the  direct  way  by  means 
of  an  acid  of  known  strength,  we  may  estimate  them  also,  as  pro- 
posed first  by  FR.  MOHR,*  by  supersaturating  with  standard  acid, 
expelling  the  carbonic  acid  by  boiling,  and  finally  by  determining 
by  standard  alkali  solution  the  excess  of  standard  acid  added. 

This  process  gives  very  good  results,  and  is  therefore  particu- 
larly suited  for  scientific  investigations.  It  requires  the  standard 
fluids  mentioned  in  §  215,  viz.,  a  standard  acid  and  standard  solu- 
tion of  potassium  or  sodium  hydroxide.  Each  of  these  fluids  is 
filled  into  a  MOHR  burette. 

The  process  is  as  follows: 

Dissolve  the  alkali  carbonate  or  caustic  alkali  hi  water,  and 
color  a  pale  blue  with  a  measured  quantity  of  litmus  tincture  ;f 
run  hi  now  as  much  of  the  standard  acid  as  will  suffice  to  impart  a 
violet  tint  to  the  fluid;  then  boil,  run  in  more  acid  until  the  color 
is  decidedly  yellowish  red,  then  a  further  quantity  to  the  next 
c.c.  mark.  The  alkali  will  now  be  decidedly  supersaturated;  then 
remove  the  last  traces  of  carbonic  acid  by  boiling,  shaking,  blowing 
into  the  flask,  and  finally  sucking  out  the  air. 

Now  add  standard  solution  of  potassa,  drop  by  drop,  until  the 
color  just  appears  light  blue.  This  point  is  easily  determined 
if  the  liquid  is  free  from  carbonic  acid,  and  only  slightly  colored  by 
litmus;  if,  however,  the  reverse  is  the  case,  the  end-point  cannot 

*  Annal.  d.  Chem.  u.  Pharm.,  LXXXVI,  129. 
t  For  other  indicators  see  page  309. 


330  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  220. 

be  accurately  determined,  as  the  blue  color  imparted  to  the  liquid 
continues  to  change  to  a  violet  for  some  time. 

If  the  standard  solutions  of  soda  and  acid  are  of  correspond- 
ing strength,  the  number  of  c.c.  of  the  soda  solution  used  is 
simply  deducted  from  the  number  of  c.c.  of  the  acid  used.  The 
remainder  expresses  the  volume  of  the  acid  solution  neutralized  by 
the  alkali  in  the  examined  sample.  If  the  two  standard  fluids  are 
not  of  corresponding  strength,  the  excess  of  acid  added,  and  sub- 
sequently neutralized  by  the  soda  solution,  is  calculated  from  the 
known  relation  the  one  bears  to  the  other. 

If  one-tenth  equivalent  number  (H  =  1-008)  in  grammes  of 
the  alkali  to  be  tested  had  been  weighed  out,  e.g.,  anhydrous 
sodium  carbonate  5-305  grm.,  or  potassium  carbonate  (pearlash) 
6-911  grm.,  the  number  of  c.c.  of  normal  acid  used  expresses 
directly  the  percentage  of  anhydrous  sodium  carbonate  or  of 
potassium  carbonate  in  the  samples  examined,  since  100  c.c.  of 
normal  acid  containing  one-tenth  gramme  equivalent  of  acid  will 
just  suffice  to  neutralize  one-tenth  gramme-equivalent  of  pure 
sodium  or  potassium  carbonate.  If  any  other  suitable  quantity 
of  alkali  has  been  weighed  out,  a  simple  calculation  will  give  the 
proper  result. 

To  make  this  simple  calculation  quite  clear,  a  most  complicated 
one  is  selected,  assuming  that  the  soda  solution  and  the  normal 
acid  do  not  correspond  in  strength,  but  that  1-1  c.c.  of  the  soda 
solution  neutralize  1  c.c.  of  the  normal  acid;  and  also  that  instead 
of  one-tenth  gramme-equivalent,  2  •  12  grm.  of  impure  potassium 
carbonate  had  been  weighed  out. 

The  quantity  of  normal  acid  added  was  26  c.c.;  the  excess 
required  2-1  c.c.  of  soda  solution  for  neutralization.  The  equation 

1-1  :1  ::2-l  :x;  z=l-91 

shows  that  an  excess  of  1-91  c.c.  of  acid  was  present.  26  — 1  -91  = 
24-09  c.c.  of  the  acid  were  accordingly  neutralized  by  the  potas- 
sium carbonate.  The  equation 

2-1  :  24-09  ::  6-911(TV  eq.  K2CO3):x;  z  =  79-28 


I  221.]  ALKALIMETRY.  331 

shows  that  the  impure  potassium  carbonate  contains  79-28  per 
cent,  of  pure  carbonate. 

II.    GRAVIMETRIC   METHOD   OP   FRESENIUS   AND   WlLL.* 
§221. 

In  this  method  the  quantity  of  alkali  carbonate  is  calculated 
from  the  quantity  of  carbonic  acid  disengaged  by  it.  It  is  accord- 
ingly necessary  that  all  the  alkali  to  be  determined  is  present  in  the 
form  of  a  neutral  carbonate,  and  also  that  the  substance  should 
contain  no  other  carbonate.  If  these  conditions  are  not  fulfilled, 
it  is  necessary  to  treat  the  substance  in  order  to  bring  them  about. 

If  the  substance  to  be  tested  contains  alkali  bicarbonate  (yielding 
carbonic  acid  on  ignition),  it  must  be  first  ignited  before  proceeding 
to  the  carbonic-acid  determination;  if,  on  the  other  hand,  it  con- 
tains caustic  alkali  (which  gives  an  alkaline  filtrate  after  adding  an 
excess  of  barium  chloride),  heat  the  quantity  weighed  off  with 
about  its  own  weight  of  quartz  sand,  about  one-third  its  weight  of 
powdered  ammonium  carbonate,  and  as  much  water  as  the  mixture 
will  absorb  until  all  the  water  has  been  driven  off;  then  proceed  to 
determine  the  carbonic  acid  in  the  residue  thus  abtained. 

The  determination  of  the  carbonic  acid  is  effected  in  the  manner 
described  in  Vol.  I,  p.  488,  da.  Other  methods  may,  however,  be 
also  employed ;  for  instance  that  detailed  in  Vol.  I,  p.  493,  e.  The 
former  method  is  more  suitable  for  technical  purposes;  the  latter 
for  scientific  investigations. 

If  6  •  2827  grm.  of  a  substance  containing  potassium  carbonate, 
or  4-822  grm.  of  one  containing  sodium  carbonate,  are  weighed 
out,  it  is  only  necessary  to  divide  the  number  of  centigrammes 
of  carbonic  acid  found  by  2,  in  order  to  obtain  without  further 
calculation  the  percentage  content  of  anhydrous  potassium-  or 
sodium  carbonate  in  the  substance  examined. 

It  is  of  course  evident  that  neither  this  nor  the  volumetric 
method  will  enable  a  determination  to  be  made  of  potassium  car- 
bonate in  the  presence  of  sodium  carbonate;  the  results  are  accurate 

*  Compare  the  pamphlet  mentioned  in  the  foot-note,  p.  317. 


332  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  222. 

only  when  either  potassium  or  sodium  carbonate  alone  is  present 
(besides  other  neutral  salts). 

The  special  points  to  be  noted  in  the  analysis  of  pearlash  or 
soda-ash  will  be  detailed  later  on  (§224  and  §  229). 

C.  DETERMINATION  OF  CAUSTIC  ALKALI  PRESENT  WITH  ALKALI 

CARBONATE. 

§222. 

a.  When  it  is  desired  to  determine  both  the  caustic  alkali  and 
alkali  carbonate  in  mixtures  of  sodium   carbonate   and  sodium 
hydroxide,  the  methods  described  in  §§  219  or  220  may  be  com- 
bined with  that  detailed  in  §  221,  i.e.,  the  total  caustic  alkali  and 
carbonate  expressed  in  per-cents.  of  sodium-  or  potassium  carbon- 
ate may  be  estimated  by  one  of  the  former  methods,  while  by  the 
latter — of  course  without  previous  treatment  with  ammonium  car- 
bonate— the  quantity  of  carbonic  acid,  and  hence  that  of  the  alkali 
carbonate  present,  is  determined.     The  difference  between  both 
determinations  gives  the  quantity  of  alkali  carbonate  correspond- 
ing  with   the    caustic    alkali    present.     To    calculate   anhydrous 
sodium  carbonate  into  anhydrous  caustic  soda  (Na2O),  multiply  it 
by  0-5853;  to  calculate  it  into  sodium  hydroxide  (NaOH),  multiply 
it  by  0-7551.    To  calculate  potassium  carbonate  into  anhydrous 
caustic  potassa  (K20),  multiply  by  0-68167;  to  calculate  it  into 
potassium  hydroxide  (KOH),  multiply  it  by  0-812. 

b.  It  will  be  readily  seen  that  the  object  may  also  be  attained 
by  the  method  described  in  §  221,  by  directly  determining  the 
carbonic  acid  in  one  weighed  sample,  while  in  another  it  is  deter- 
mined after  previous  treatment  with  ammonium  carbonate. 

c.  The  purpose  may  also  be  accomplished  by  purely  volumetric 
methods,  and  by  the  aid  of  the  same  principle  which  has  already 
been  made  use  of  when  testing  alkali  carbonate  for  caustic  alkali. 

Weigh  out  three-tenths  gramme-equivalents  of  the  carbon- 
ate to  be  tested  for  caustic  alkali,  i.e.,  20-733  grammes  of  potas- 
sium carbonate,  or  15-915  grammes  of  sodium  carbonate,  dissolve  it 
in  water  in  a  300-c.c.  flask,  fill  to  the  mark,  shake,  allow  the  liquid 


§  222.]  ALKALIMETRY.  333 

to  settle  out  of  contact  with  the  air,  and  then  remove  two  por- 
tions of  100  c.c.  each  for  analysis.  In  one  portion  determine  the 
total  caustic  alkali  and  carbonate  according  to  §  220;  the  number 
of  c.c.  of  normal  acid  used  up  will  give  the  caustic  alkali  and  alkali 
carbonate  expressed  in  per  cents,  of  the  latter.  Introduce  the 
other  portion  into  a  500-c.c.  flask,  add  200  c.c.  of  water,  then  barium- 
chloride  solution  until  no  further  precipitate  is  given  by  it,  fill 
up  with  water  to  the  mark,  shake,  allow  to  settle  out  of  contact 
with  the  air,*  measure  off  250  c.c.  of  the  clear,  supernatant 
liquid  (containing  now  caustic  baryta  equivalent  to  the  caustic 
alkali  present  in  the  sample),  add  litmus  tincture,  and  then  normal 
hydrochloric  acid  to  acid  reaction.  Now  titrate  the  excess  of 
acid  with  normal  soda  solution,  and  thus  ascertain  from  the  num- 
ber of  c.c.  of  normal  acid  used  the  equivalent  quantity  of  caustic 
baryta.  On  now  multiplying  by  2  (since  only  one-half  of  the  sec- 
ond portion  had  been  taken  in  the  experiment),  the  result  will 
give  the  percentage  of  caustic  alkali  expressed  as  anhydrous 
sodium-  or  potassium  carbonate.  On  deducting  this  number  from 
that  obtained  in  the  first  experiment  the  difference  will  give  the 
potassium-  or  sodium  carbonate  present  as  such.  In  order  to 
calculate  the  caustic  alkali  into  the  anhydrous  or  hydrated  forms, 
it  is  only  necessary  to  multiply  by  the  numbers  stated  in  a. 

D.  ESTIMATION    OF   SODIUM   CARBONATE   IN   THE    PRESENCE   OF 
POTASSIUM  CARBONATE. 

Soda,  being  much  cheaper  than  potash,  is  occasionally  used  to 
adulterate  the  latter.  The  common  alkalimetric  methods  not 
only  fail  to  detect  this  adulteration,  but  they  give  the  admixed 
sodium  carbonate  as  potassium  carbonate.  Many  processes  f 
have  been  proposed  for  estimating  in  a  simple  way  the  soda  con- 
tained in  potash,  but  not  one  of  them  can  be  said  to  satisfy  the 
requirements  of  the  case. 

*  By  filtering  through  a  dry  filter,  somewhat  too  low  a  yield  of  caustic 
alkali  is  obtained,  as  the  paper  retains  caustic  baryta  (A.  MULLER,  Journ.  f. 
prakt.  Chem.,  LXXXIII,  384;  Zeitschr.  /.  analyt.  Chem.,  i,  84). 

f  Comp.  Handworterbuch  der  Chemie,  2  Aufl.,  i,  443. 


334  DETERMINATION    OF    COMMERCIAL   VALUES.         [§   223. 

The  following  tolerably  expeditious  process,  however,  gives 
accurate  results:  Dissolve  6-25  grm.  of  the  gently-ignited  pearlash 
in  water,  filter  the  solution  into  a  quarter-litre  flask,  add  acetic 
acid  in  slight  excess,  apply  a  gentle  heat  until  the  carbonic  acid  is 
expelled,  then  add  to  the  fluid,  while  still  hot,  lead  acetate,  drop 
by  drop,  until  the  formation  of  a  precipitate  of  lead  sulphate  just 
ceases;  allow  the  mixture  to  cool,  add  water  up  to  the  mark,  shake, 
allow  to  deposit,  filter  through  a  dry  filter,  and  transfer  200  c.c. 
of  the  filtrate,  corresponding  to  5  grm.  of  pearlash,  to  a  J-litre 
flask.  Add  hydrogen-sulphide  water  up  to  the  mark,  and  shake. 
If  the  lead  acetate  has  been  carefully  added,  the  fluid  will  now 
smell  of  hydrogen  sulphide,  and  no  longer  contain  lead;  in  the  con- 
trary case,  hydrogen-sulphide  gas  must  be  conducted  into  it. 
After  the  lead  sulphide  has  subsided  filter  through  a  dry  filter. 
Evaporate  50  c.c.  of  the  filtrate  (corresponding  to  1  grm.  of  pearl- 
ash) with  addition  of  10  c.c.  hydrochloric  acid,  of  1-10  sp.  gr.,  in  a 
weighed  platinum  dish,  to  dry  ness,  then  cover  the  dish,  heat,  and 
weigh;  the  weight  found  expresses  the  total  quantity  of  potassium 
and  sodium  chlorides  given  by  1  grm.  of  the  pearlash.  Estimate 
the  potassium  and  sodium  now  severally  in  the  indirect  way,  by 
determining  the  chlorine  volumetrically  (§  141,  I,  6). 

3.    ESTIMATION    OF   ALKALI-EARTH    METALS   BY  THE 
ALKALIMETRIC  METHOD. 

§223. 

The  alkali-earth  metals,  when  in  the  form  of  oxides,  hydrox- 
ides, or  carbonates,  may  also  be  determined  volumetrically  by 
means  of  standard  acid  and  alkali  solutions.  Standard  sulphuric 
acid  may  be  used  for  magnesium;  standard  hydrochloric  or  nitric 
acid  for  barium,  strontium,  and  calcium.  The  only  advantage 
which  these  acids  possess  over  hydrochloric  is  that  there  is  less 
liability  of  loss  on  heating  solutions  containing  them  in  the  free 
state,  which  is  necessary  when  carbonic  is  present.  Hydrochloric 
acid  can,  however,  be  used  with  safety  if  precaution  be  taken  to 
avoid  the  presence  of  an  unnecessary  quantity  when  the  solution 
is  heated. 


§  223.]  ALKALIMETRY.  335 

If  an  oxide  or  hydroxide  free  from  carbonic  acid  is  to  be  exam- 
ined, add  some  water  to  a  weighed  quantity,  and  allow  the  stand- 
ard hydrochloric  or  nitric  acid  to  flow  in  from  a  burette  until  solu- 
tion is  effected  and  the  solution  colored  with  litmus  gives  an  acid 
reaction.  Then  determine  the  excess  of  acid  used  by  means  of 
the  standard  soda  solution. 

Deduct  the  soda  solution  used  from  the  acid,  and  calculate 
the  result  from  the  equation  as  follows: 

1000  c.c.  :  number  of  c.c.  acid  used  : :  76-7  (i  eq.)  BaO,  or  51-8 
(i  eq.)  SrO,  or  28-05  (i  eq.)  CaO,  or  20-15  (£  eq.)  of  MgO  :  x  (  = 
grammes  of  BaO,  SrO,  CaO,  or  MgO).  Should  the  exact  neutrality 
point  not  have  been  hit  the  first  time,  add  another  c.c.  of  acid,  and 
then  again  soda  solution  to  neutrality. 

In  case  of  a  carbonate,  dissolve  a  weighed  quantity  in  a  flask 
by  heating  with  water,  then  add  standard  hydrochloric  or  nitric 
acid  from  a  burette  in  small  successive  portions,  until  solution  is 
complete  and  a  slight  excess  of  acid  is  present;  next  add  the  indi- 
cator (litmus  or  cochineal)  and  allow  the  standard  alkali  solution 
to  run  in  from  a  burette  until  the  free  acid  is  nearly  neutralized 
and  only  0-5  or  1  c.c.  of  acid  is  in  excess.  Now  remove  the  car- 
bonic acid  by  boiling  a  few  minutes  and  shaking,  and  complete 
the  neutralization  with  the  standard  alkali. 

1000  c.c.  of  normal  acid  correspond  to  98-7  grm.  BaCO3,  73-8 
grm.  SrCO3,  50-05  grm.  CaCO3,  or  42-15  grm.  MgCO3. 

If  it  is  desired  to  avoid  all  calculation  whatever,  ^  or  -^  gramme- 
equivalent  of  the  pure  caustic  alkaline  earth,  or  carbonate  of  the 
alkaline  earth,  may  be  weighed  off;  in  the  former  case  the  number 
of  c.c.,  in  the  latter  half  the  number  of  c.c.  of  the  normal  acid  used 
expresses  the  percentage. 

To  determine  the  alkaline  earths  in  soluble  neutral  salts  of  the 
latter,  precipitate  the  barium,  strontium,  or  calcium  solution  with 
ammonia  and  ammonium  carbonate,  warm,  filter,  wash  with  pure 
water,  and  then  treat  the  precipitate  as  above  described.  Mag- 
nesium salts  may  be  precipitated  with  potassa  or  soda-lye,  and 
the  washed  magnesium  hydrate  treated  similarly,  but  the  de- 
termination made  thus  is  apt  to  give  too  low  a  result  because  of 
the  solubility  of  magnesium  hydrate. 


336  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  224. 


4.   THE   TECHNICALLY    MOST    IMPORTANT   POTASSIUM 

COMPOUNDS. 

A.  POTASH  (PEARLASH). 

§224. 

Potash,  which  was  formerly  almost  exclusively  obtained  from 
wood  ashes  or  the  ashes  of  other  portions  of  plants,  is  now  manu- 
factured in  large  quantities  in  the  same  manner  as  sodium  car- 
bonate by  the  LEBLANC  process,  which  consists  in  fusing  potassium 
sulphate  with  carbon  (coal)  and  calcium  carbonate.  Potash  is 
also  obtained  from  the  residues  of  beet-root  molasses  by  evaporat- 
ing, calcining,  lixiviating,  and  concentrating  the  lye.  In  con- 
sequence of  this  the  substances  which  potashes  may  contain  besides 
potassium  carbonate,  may  be  exceedingly  various.  Those  soluble 
in  water  may  be  specially  noted  as  follows:  Potassium  sulphate, 
potassium  chloride  (present  in  potash  from  plant-ashes  in  only 
small  quantity  usually,  but  present  in  considerable  quantity  in 
potash  made  by  the  LEBLANC  process  or  from  beet-root  molasses). 
In  smaller  quantity  there  are  or  may  be  found  caustic  alkalies, 
silicates,  phosphoric  acid,  alkali  manganates-,  alkali  sulphides 
(and  from  the  action  of  the  air  on  these  also  alkali  thiosulphates), 
besides  alkali  cyanides  and  sulphocyanates,  and  under  certain 
circumstances  also  alkali  iodides  and  bromides  and  organic  matter. 

Of  the  constituents  insoluble  in  water,  the  following  may  be 
especially  noted:  Silicic  acid,  calcium  silicate,  carbonate  and 
phosphate,  magnesium  phosphate  and  carbonate,  ferric  oxide, 
manganese  oxides,  cupric  oxide,  alumina,  sand,  and  carbon  (coal). 

Besides  these,  potashes  as  a  rule  contain  also  water. 

The  substances  insoluble  in  water  may,  of  course,  be  removed 
by  treatment  with  water  and  filtration;  the  frequent  occurrence 
of  sodium  carbonate  in  the  potashes,  now  often  found  in  commerce, 
however,  renders  it  very  difficult  to  analyze  and  determine  the 
constituents  soluble  in  water,  as  the  sodium  carbonate  interferes 
with  the  analysis  which  is  directed  to  the  determination  of  the 


§   224.]  POTASSIUM   COMPOUNDS.  337 

content  of  potassium  carbonate  (and  caustic  potassa).  It  is 
therefore  necessary,  before  beginning  an  analysis  of  a  potash,  to 
first  ascertain  whether  it  contains  an  appreciable  quantity  of  sodium 
carbonate. 

As  potash  attracts  water  very  rapidly,  correct  and,  on  repeating 
the  analysis,  concordant  results  are  only  possible  when  all  the 
determinations  of  potash  are  based  upon  or  referred  to  the  original 
water  content.  Before  opening  the  bottle  containing  the  potash 
to  be  examined,  the  operator  should  provide  himself  with  two  or 
three  perfectly  dry  test-tubes  with  well-fitting  stoppers;  these 
tubes  are  to  be  rapidly  filled  after  the  bottle  is  opened,  then  stop- 
pered, and  kept  in  the  desiccator. 

I.  Determination  of  Moisture. 

Weigh  off  about  2  grm.  of  potash  from  one  of  the  test-tubes 
into  a  platinum  crucible,  heat  to  dull  redness,  and  determine  the 
Joss  of  weight.  This  is  considered  as  water.  The  determination  is 
not  quite  accurate  if  the  potash  contains  free  silicic  acid,  because 
this,  on  heating,  expels  carbonic  acid  from  the  potassium  carbonate. 
If  in  such  a  case  the  water  is  to  be  accurately  determined,  proceed 
according  to  §  36.  If  the  potash  contains  potassium  hydroxide, 
the  water  of  hydration  of  the  latter  is  not  driven  off  by  ignition. 

II.  Determination  of  all  other  Constituents. 

a.  Weigh  off  about  10  grm.  of  the  potash  from  one  of  the  test- 
tubes  and  treat  with  water   in  a  beaker,  at  a  gentle  heat,  until  all 
the  soluble  portion  is  dissolved,  then  filter  through  a  small  filter 
paper  and  wash  the  insoluble  portion  with  hot  water  until  the 
washings  are  no  longer  alkaline.     Collect  the  filtrate  and  washings 
in  a  500-c.c.  measuring  flask  and  fill  with  water  to  the  mark.     Dry 
the  filter  with  the  insoluble  residue,  incinerate,  treat  with  a  little 
ammonium  carbonate,  evaporate,  gently  ignite,   and  weigh.     In 
almost 'all  cases  it  suffices  to  enter  the  weight  as  "portion  insoluble 
in  water" 

b.  Treat  100  c.c.  of  the  solution  according  to  §  220  or  §  219. 
The  acid  required  for  neutralization  corresponds  with  the  potas- 


338  DETERMINATION    OF    COMMERCIAL    VALUES.          [§   224. 

slum  carbonate,  and  also  the  potassium  hydroxide,  sodium  car- 
bonate, and  sodium  hydroxide,  if  these  are  present.  First  calculate 
the  acid  as  used  up  for  potassium  carbonate.  If  an  alkali  s.licate  is 
present  in  any  appreciable  quantity,  a  correction  must  be  made  for 
it.  Alkali  phosphates,  sulphides,  and  cyanides  also  use  up  a 
small  quantity  of  acid;  the  quantity  of  these  present  is  as  a  rule 
so  small,  however,  that  no  correction  need  be  made  for  them. 

c.  Carefully  supersaturate  50  c.c.  with  hydrochloric  acid  in  a 
flask  or  covered  beaker,  heat  to  drive  off  all  the  carbonic  acid,, 
evaporate  in  a  porcelain  or  platinum  dish  to  dryness,  moisten  the 
residue  with  hydrochloric  acid,  take  up  with  water,  filter  off  the 
silicic  acid,  and  determine  this  according  to  §  140,  II,  a.     Heat  the 
filtrate  to  boiling,  and  very  cautiously  add  barium-chloride  solution 
until  a  precipitate  no  longer  forms.     From  the  weight  of  the  barium 
sulphate  filtered  off  that  of  the  sulphuric  acid  present  may  be 
calculated  (§132,  1). 

d.  If  the  potash  contains  a  determinable  quantity  of  sodium 
carbonate,  the  solution  filtered  off  from  the  barium  sulphate  in  c- 
may  be  used  for  the  preparation  of  pure  alkali  chlorides,  and  for 
the  determination  of  the  potassium  chloride  contained  in  them.    In 
this  case  evaporate  to  dryness,  take  up  the  residue  with  water, 
precipitate  the  excess  of  barium  salt  which  had  been  added  with 
ammonium  carbonate  (§101,  2),  evaporate  the  filtrate  to  dryness, 
expel  the  ammonium  salt  by  gently  igniting,  take  up  with  water,, 
remove  the  last  traces  of  dissolved  barium  by  a  little  ammonia 
and  ammonium  carbonate,  filter,  evaporate  in  a  weighed  platinum 
dish,   weigh   the   alkali   chlorides,   and   determine   the   potassium 
chloride    present    as    potassium-platinic    chloride    (p.   345);     the 
difference  gives  the  sodium  chloride,  and  from  this  the  sodium 
present  hi  the  potash  is  obtained.      Of  course  the  quantity  of 
potassium   chloride   and   sodium   chloride   in   the   weighed   alkali 
chlorides  may  also  be  indirectly  determined  (§152,  3),  but  this 
method  is  to  be  recommended  only  when  the  quantity  of  sodium 
salt  present  is  not  too  small. 

e.  In  50  c.c.  of  the  solution  determine  the  chlorine  according 
to  §  141,  I,  a  or  6. 


§  224.]  POTASSIUM   COMPOUNDS.  339 

/.  If  the  potash  contains  caustic  alkali  (i.e.,  if  its  solution 
affords  a  filtrate  of  alkaline  reaction  on  being  treated  with  an 
excess  of  barium  chloride),  add  an  excess  of  barium-chloride 
solution  to  200  c.c.  of  the  solution  contained  in  a  500-c.c.  flask,  nil 
with  water  to  the  mark,  stopper,  shake,  allow  to  settle,  and  in  250 
c.c.  of  the  clear  fluid  determine  the  alkalinity  with  normal  acid 
(§  222).  The  acid  used  corresponds  to  the  caustic  alkali  contained 
in  100  c.c.  of  the  potash  solution. 

g.  Finally  smaller  quantities  of  the  potash  solution  are  em- 
ployed for  qualitative  tests  for  phosphoric  acid,  etc.  If  a  large 
quantity  of  phosphoric  acid  is  found  to  be  present,  as  now  and 
then  happens,  it  must,  of  course,  be  determined;  and  since  in  that 
case  the  potassium-carbonate  content  cannot  be  accurately  de- 
duced from  the  determination  of  the  alkalinity  (according  to  II,  6), 
a  determination  of  the  carbonic  acid  in  the  potash  solution  be- 
omes  necessary.  For  this  purpose  the  last  50  c.c.  of  the  solution, 
may  be  used,  and  the  determination  made  according  to  §  139,  II* 
d  or  e. 

Calculation  and  Statement  of  Results. 

Although  a  potash  neither  loses  nor  gains  in  value  if  the  bases 
and  acids  contained  in  it  are  combined  in  one  way  or  another  to 
form  salts,  still  it  is  very  desirable  that  certain  principles  should 
be  agreed  upon  regarding  the  arrangement  in  stating  the  results, 
otherwise  different  chemists,  using  exactly  the  same  analytical 
results,  would  calculate  very  different  constituents  of  the  potash. 
I  consider  it  best  to  combine  any  soda  present — if  caustic  potassa 
is  present — first  with  water  to  form  sodium  hydroxide,  then  with 
silicic  acid  as  sodium  silicate,  then  with  carbonic  acid  as  sodium 
carbonate.  Potassa,  on  the  other  hand,  is  first  combined  with 
sulphuric  acid,  then  (as  potassium)  with  chlorine,  then  with  car- 
bonic acid,  silicic  acid,  and  finally  with  water  as  potassium  hy- 
droxide. 

In  order  to  arrive  at  the  correct  quantity  of  potassium  carbonate 
—in  the  absence  of  determinable  quantities  of  phosphoric  acid — 


340  DETERMINATION    OP    COMMERCIAL    VALUES.          [§  224. 

the  following  are  to  be  deduced,  according  to  circumstances,  from 
the  number  found  in  II,  6,  for  potassium  carbonate: 

1  eq.  potassium  carbonate  for  2  eq.  sodium  or  potassium  hy- 
droxide. 

1  eq.  potassium  carbonate  for  1  eq.  sodium  or  potassium  silicate 
(Na2SiO3  or  K2SiO3). 

1  eq.  potassium  carbonate  for  1  eq.  sodium  carbonate. 

If  determinable  quantities  of  phosphoric  acid  are  present,  the 
content  of  alkali  carbonates  must  be  calculated  from  the  carbonic 
acid  found. 

III.   Determination  of  the  Potash  Alone. 

Under  "  potash  content "  is  properly  understood  the  quantity 
<of  potassium  carbonate,  or  mixture  of  carbonate  with  hydroxide, 
present,  the  hydroxide  being  expressed  in  terms  of  carbonate. 

//  a  potash  contains  no  sodium  salt,  the  following  methods  are 
adopted  for  determining  its  composition;  if,  however,  a  sodium 
salt  is  present,  one  of  the  methods  of  analysis  described  under 
II  will  have  to  be  used,  in  which,  according  to  circumstances,  the 
determination  of  chlorine,  sulphuric  acid,  and  caustic  alkali  may 
be  omitted: 

1.  Weigh  off  about  10  grm.  of  potash,  dissolve  in  warm  water, 
filter,  wash  the  residue,  make  up  the  filtrate  and  washings  to  500  c.c., 
and  in  100  c.c.  determine  the  alkalinity  according  to  §  220,  or  in 
200  c.c.  according  to  §  219.     From  the  quantity  of  acid  required 
for  neutralization  calculate  the  potassium-carbonate  content.     It 
will  be  readily  seen  that  in  this  process  the  silicic  acid  and  potassium 
phosphate,  as  well  as  any  potassium  sulphide  present,  is  calculated 
as  carbonate  together  with  the  caustic  alkali  and  carbonate  present, 
and  that  hence  a  small  error  is  caused  in  the  "content"  as  defined 
above.     For  many  applications  of  potash,  the  term  error  cannot  be 
said  to  apply,  as,  for  instance,  in  the  preparation  of  caustic  lye 
from  potash  by  boiling  the  solution  of  this  with  calcium  hydroxide ; 
the  potassium  combined  with  silicic  and  phosphoric  acids  is  also 
converted  into  caustic  potassa. 

2.  Determine  the  carbonic  acid  in  about  5  giro,  of  potash 


§  225.]  POTASSIUM  COMPOUNDS.  341 

according  to  §  221,  and  from  the  result  calculate  the  potassium- 
carbonate  content.  If  the  potash  contains  carbonates  of  the 
alkaline  earths,  dissolve  it  in  water,  filter,  concentrate  the  filtrate, 
and  proceed  as  directed.  If  caustic  potassa  and  potassium  sulphide 
are  present,  proceed  as  with  soda  under  similar  circumstances 
(§  229). 

It  is  obvious,  from  what  has  been  stated  under  III,  1,  that 
in  the  case  of  potash  containing  also  potassium  silicate,  phosphate, 
and  sulphide,  the  results  obtained  according  to  III,  1  and  2  cannot 
k  agree  accurately. 

If  it  is  desired  to  learn  not  only  the  total  content,  but  also  to 
obtain  a  more  complete  knowledge  as  to  whether  the  content  is 
lowered  by  the  presence  in  the  potash  either  of  foreign  salts 
mixed  with  the  carbonate  or  of  water,  the  alkalimetric  determina- 
tion must  be  supplemented  by  a  water  estimation.  Guaranteed 
contents  are  always  referred  to  anhydrous  potash. 

B.    POTASSIUM  CHLORIDE;   AND 
C.    POTASSIUM  SULPHATE. 

§225. 

From  the  residual  salts  obtained  from  the  Stassfurt  and  other 
salt  beds,  large  quantities  of  potassium  salts,  particularly  potas- 
sium chloride  and  sulphate,  are  prepared  in  various  degrees  of 
purity  for  different  industrial  or  agricultural  purposes. 

The  portion  of  these  salts  soluble  in  water  contains,  as  a  rule, 
the  following  bases:  Potassium,  sodium,  magnesium,  and  calcium; 
and  the  acids,  sulphuric  and  hydrochloric  (i.e.,  chlorine  in  the  form 
of  metallic  chlorides).  The  residue  insoluble  in  water  consists 
usually  of  sand,  alumina,  ferric  hydroxide,  and  magnesia.  Lastly,, 
the  salts  always  contain  water.  If  magnesium  chloride  is  also 
present,  the  salts  are  hygroscopic.  The  samples  employed  for 
these  are  secured  exactly  as  in  the  case  of  potash  (p.  337). 

I.  Determination  of  Moisture. 

The  method  by  which  the  water  is  to  be  estimated  should  be 
determined  by  a  preliminary  experiment;  this  consists  in  igniting 


342  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  225. 

a  sample  of  the  salt  in  a  glass  tube  and  testing  whether  the  steam 
and  the  condensed  water  have  an  acid  reaction  or  not.  The  former 
is  the  case  particularly  when  the  salt  contains  magnesium  chloride. 
If  the  steam  is  not  acid,  the  water  determination  is  effected  simply 
by  gently  igniting  1  or  2  grm.  of  the  salt  in  a  platinum  crucible; 
if  it  is  acid,  however,  this  method  will  yield  too  high  a  result.  In 
this  case  weigh  off  1  or  1  •  5  grm.  of  the  salt  in  a  small  boat,  mix  it 
with  finely  triturated,  perfectly  anhydrous  sodium  carbonate, 
cover  the  mixture  with  a  layer  of  the  latter,  insert  the  boat  in  a 
glass  tube  about  20  cm.  long,  heat  in  a  current  of  dry  air,  and 
collect  the  water  given  off  in  a  weighed  calcium-chloride  tube  ( §  36) . 

II.  Determination  of  all  the  Constituents. 

a.  Weigh  off  about  10  grm.  of  the  substance,  treat  with  warm 
water,  filter  off  from  any  insoluble  residue,  and  wash  the  latter 
until  the  filtrate  together  with  the  washings  measure  500  c.c. 
Dry  the  residue,   ignite,   weigh,   and   determine  its   composition 
later  on;  it  must  be  remembered,  however,  that  it  may  still  con- 
tain undissolved  calcium  sulphate. 

b.  In  50  c.c.  of  the  solution  determine  the  sulphuric  acid  ac- 
cording to  §  132,  I,  1,  or  2,  e. 

c.  In  50  c.c.  determine  the  chlorine  according  to  §  141,  I,  a, 
or  b,  a. 

d.  Determine  the  calcium  by  adding  to  100  c.c.  of  the  solution 
ammonium   chloride,   ammonia,    and   ammonium   oxalate;    from 
the   filtrate   precipitate   the   magnesium    as    ammonio-phosphate 
(§154,  6,  a). 

e.  Boil  50  c.c.  of  the  solution  with  some  milk-of-lime  to  pre- 
cipitate  the  magnesium,  filter  and  wash.     Treat  the  filtrate  hot 
with  barium  chloride  until  all  the  sulphuric  acid  has  been  precipi- 
tated, allow  to  cool,  add  ammonia  and  ammonium  carbonate  to 
precipitate  calcium   and  barium,  filter,  evaporate,   drive  off  the 
ammonia  salts  by  gently  igniting,  treat  with  a  little  water,  and 
precipitate  the  last  traces  of  barium  and  calcium  by  adding  am- 
monia   and    ammonium    carbonate.     Weigh    the    pure    metallic 
chlorides  and  determine  the  potash  in  them  (§  224,  II,  d). 


§  225.]  POTASSIUM   COMPOUNDS.  343 

Calculation. 

From  the  manner  in  which  the  salts  in  solutions  containing 
potassium,  sodium,  calcium,  magnesium,  and  sulphuric  and  hy- 
drochloric acids  are  deposited  *  on  evaporation,  the  inference  has 
been  drawn  that  the  sulphuric  acid  must  be  first  combined  with 
calcium,  then  with  magnesium.  The  metals  not  present  as  sul- 
phides then  appear  in  the  total  as  metallic  chlorides.  After  the 
potassium  chloride,  the  principal  salts  present  are  arranged  in  the 
following  order:  CaSO4,  MgSO4,  MgCl2,  NaCl,  KC1.  This  arrange- 
ment is  at  all  events  convenient,  because  it  states  all  the  potassium 
as  potassium  chloride,  consequently  in  the  form  of  the  salt  which 
gives  the  substance  its  name  and  value.  A  different  method 
of  arrangement  is  employed,  as  a  rule,  when  potassium  sulphate 
is  the  chief  salt  present.  In  this  case  the  sulphuric  acid  is  com- 
bined first  with  the  calcium,  then  with  the  potassium,  and  finally 
with  the  magnesium,  so  that  the  following  salts  are  obtained: 
CaSO4,  K2SO4,  MgSO<,  MgCl2,  and  NaCl.f  In  regards  to  this  method 
of  arranging,  it  may  be  urged  that  kieserite  and  potassium  chloride 
decompose  each  other  to  form  potassium-magnesium  sulphate 
and  magnesium  chloride.  At  all  events  this  method  of  arrange- 
ment is  also  convenient  in  that  it  gives  the  potassium  in  the  form 
of  one  salt  in  the  statement  of  the  results. 

III.  Determination  of  the  Total  Potassium  Present. 

Frequently  only  one  determination  is  desired  for  potassium 
salts,  i.e.,  one  estimation  of  the  potassium,  which,  according  to 
circumstances,  is  then  usually  calculated  either  as  potassium 
chloride  or  sulphate.  As  such  determinations  very  frequently 
occur  in  works  which  make  or  use  potassium  salts,  attempts  have 
been  made  to  precipitate  the  potassium  as  a  bitartrate  or  per- 
chlbrate,  or  to  separate  it  as  alum,  etc.,  but  all  these  methods 
riave  failed  because  they  yield  insufficiently  accurate  results. 

*  Comp.  AD.  FRANK,  in  WAGNER'S  Jahresber.  d.  chem.  Technolog.  fur 
1875,  480. 

f  Comp.  loc.  cit.,  p.  495. 


344  DETERMINATION    OF    COMMERCIAL   VALUES.          [§   225. 

The  potassium  is  now  always  determined,  at  least  for  seller's 
analyses,  in  the  form  of  potassium-platinic  chloride.*  On  this 
account  I  shall  not  describe  the  other  methods  here,  but  give 
references  as  to  where  they  may  be  found. \ 

In  the  employment  of  the  platinum-chloride  method  the  follow- 
ing questions  must  be  considered: 

1.  Must  the  sulphuric  acid  be  precipitated?  2.  Must  the  cal- 
cium and  magnesium  be  removed,  and  subsequently  also  the 
excess  of  baryta  added,  before  separating  the  potassium  as  potas- 
sium-platinic  chloride?  Lastly,  3.  Which  method  of  treating  the 
potassium-platinic  chloride  is  to  be  most  recommended? 

The  first  question  is  answered  in  the  negative  by  TESCHE- 
MACHER  and  SMITH  J  if,  as  in  saltpetre,  but  little  sulphuric  acid  is 
present,  and  that  is  combined  with  alkalies  or  magnesium;  but 
in  the  analysis  of  potassium  chloride  and  sulphate,  in  which  atten- 
tion must  always  be  paid  to  the  presence  of  calcium  sulphate  and 
sometimes  to  that  of  large  quantities  of  other  sulphates,  it  must 
be  decidedly  answered  in  the  affirmative,  as  has  also  been  affirmed 
by  STOHMANN,§  and,  when  somewhat  large  quantities  of  sulphates 
are  present,  also  by  G.  KRAUSE.|| 

To  the  second  question  it  may  be  replied  that  a  separation  of 
the  alkaline  earths  (according  to  §  225,  II,  or  by  precipitation 
with  ammonium  carbonate  at  the  boiling-point  [STOHMANN]) 
is  not  necessary  (STOHMANN,  KRAUSE,  R.  FRESENIUS,  and  A. 
SOUCHAY!"),  because  the  double  salts  which  calcium  chloride, 
magnesium  chloride,  and  barium  chloride  form  with  platinic 
chloride  are  soluble  in  alcohol,  but  that,  if  the  alkaline  earths 
have  not  been  removed,  it  is  particularly  necessary  to  be  careful 
that  only  perfectly  pure  potassium-platinic  chloride  is  weighed. 

*  Compare  AD..  FRANK,  loc.  cit.,  p.  484. 

f  MOHR,  Zeitschr.  /.  analyt.  Chem.,  i,  59. — ESSELENS,  ibid.,  iv,  215. — 
TH.  BECKER,  method  of  AD.  FRANK,  ibid.,  vi.  257, — BOLLEY,  ibid.,  vm, 
505. — FLEISCHER,  ibid.,  ix,  331. — E.  SALKOWSKI,  ibid.,  xi,  474. — SHLOSING,, 
ibid.,  xi,  193. — KRAUT,  ibid.,  xiv,  152. 

J  Zeitschr.  f.  analyt.  Chem.,  vm,  90. 

§  Ibid.,  v,  306. 

\\IUd.,  xrv,  184. 

H  Ibid.,  xvi,  63. 


§  225.]  POTASSIUM  COMPOUNDS.  345 

In  answer  to  the  third  question  it  may  be  stated  that  the 
potassium-platinic  chloride  is  best  weighed  in  the  manner  recom- 
mended by  me,*  and  not  on  a  weighed  filter,  but  in  a  small  dish. 

The  operation  is  conducted  as  follows :  Weigh  off  about  2  grm. 
of  the  potassium  salt  to  be  examined,  add  about  300  c.c.  of  water, 
heat  until  all  the  soluble  portion  is  dissolved,  filter,  add  1  c.c. 
hydrochloric  acid,  heat  almost  to  boiling,  and  very  cautiously  add 
barium  chloride  until  all  the  sulphuric  acid  is  just  precipitated; 
a  notable  excess  of  barium  chloride  must  be  avoided.  After 
settling,  filter  into  a  litre  flask,  cool,  add  distilled  water  up  to 
the  mark  and  shake;  remove  50  c.c.  of  the  liquid  with  a  pipette, 
evaporate  in  a  porcelain  dish  to  a  volume  of  about  15  c.c.,  and 
add  sufficient  of  a  platinic-chloride  solution,  as  neutral  as  possible, 
to  make  certain  that  all  the  metallic  chlorides  present  have  been 
converted  into  platinum  double  salts,  and  to  leave  a  slight  excess 
of  platinic  chloride.  This  is  by  far  the  most  easily  effected  by 
employing  a  platinic-chloride  solution  of  known  strength,  and, 
if  the  above-mentioned  quantities  have  been  employed,  adding 
a  volume  containing  1  grm.  of  platinic  chloride. 

Stir  the  fluid  with  a  small  glass  rod,  evaporate  to  a  syrupy 
consistency  f  on  a  water-bath  the  water  in  which  is  not  allowed 
to  quite  reach  the  boiling-point;  cover  the  residue,  when  cold, 
with  80-per  cent,  alcohol,  mix  carefully,  allow  to  stand  for  some 
time  with  frequent  stirring;  next  pass  the  deep  brownish-yellow 
alcoholic  solution  through  an  unweighed  filter-paper,  which  must 
not  be  too  large,  and  treat  the  residue  in  the  dish  several  times 
with  small  quantities  of  alcohol  until  the  potassium-platinic  chlo- 
ride appears  to  be  pure;  then  collect  the  latter  on  a  filter  and 
wash  it  thoroughly  with  small  quantities  of  alcohol  repeatedly 
sprinkled  on.  Now  dry  the  filter  in  the  funnel  at  a  gentle  heat, 
to  drive  off  all  the  alcohol,  carefully  transfer  the  contents  of  the 
filter  to  a  watch-glass,  place  the  filter,  to  which  small  particles 

*  Zeitschr.  f.  analyt.  Chem.,  xn,  63. 

t  ULEX  (Zeitschr.  f.  analyt.  Chem.,  xvn,  175)  finds  it  advantageous,  after 
adding  the  platinic  chloride,  to  add  1  to  5  c.c.  of  a  20  per  cent,  solution  of 
glycerin,  in  order  to  prevent  the  sodium-platinic  chloride  from  becoming 
too  dry,  otherwise  it  might  not  completely  dissolve. 


346  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  226. 

of  the  double  salt  still  adhere,  in  the  funnel  again,  and  dissolve 
these  in  a  small  quantity  of  boiling  water.  Evaporate  to  dryness 
the  yellow  solution  thus  obtained  in  a  small  tared  platinum  dish 
on  the  water-bath,  add  to  the  residue  the  main  bulk  of  the  pre- 
cipitate from  the  watch-glass,  dry  at  130°  to  constant  weight, 
and  weigh.  If  it  is  desired  to  make  perfectly  certain  that  the 
weighed  potassium-platinic  chloride  is  pure,  the  method  described 
on  p.  250  affords  an  easy  and  certain  means  of  doing  so. 

If  there  is  any  reason  to  believe  that  the  double  salt  first  pre- 
cipitated is  not  perfectly  pure,  the  first  weighing  may,  of  course, 
be  omitted,  and  the  purification  detailed  in  the  method  just  re- 
ferred to  is  at  once  adopted. 

The  weighed  potassium-platinic  chloride  must  be  completely 
soluble  in  boiling  water,  and  samples  of  the  dilute  solution  must 
give  no  precipitates  on  treatment  with  sulphuric  acid,  nor — after 
precipitating  the  platinum  with  hydrogen  sulphide — with  am- 
monium oxalate  or  with  ammonia  and  sodium  phosphate. 

D.  POTASSIUM  NITRATE. 
§226. 

In  the  analysis  of  commercial  potassium  nitrate  as  it  occurs 
in  the  market,  it  is  necessary  to  consider  whether  we  have  to  deal 
with  crude  saltpetre  or  with  the  very  pure  saltpetre  employed 
in  the  manufacture  of  gunpowder.  In  the  case  of  crude  saltpetre 
determinations  of  the  chlorine,  sulphuric  acid,  nitric  acid,  calcium, 
magnesium,  potassium,  sodium,  insoluble  residue,  and  water  are 
required.  The  analysis  presents  no  special  difficulties,  and  can, 
as  a  rule,  be  performed  according  to  the  method  detailed  in  §  225. 
The  determination  of  the  nitric  acid  is  most  easily  effected  ac- 
cording to  REICH'S  method  (Vol.  I,  p.  572,  a,  /?).  The  watef 
is  determined  by  the  loss  of  weight  which  the  saltpetre  undergoes 
when  it  is  heated  just  to  the  point  of  fusion.  Should  in  this  case 
acid  vapors  be  evolved,  mix  a  little  dry  neutral  potassium  chromate 
with  the  sample.  Of  course  this  method  of  determining  the 
water  is  applicable  only  when  the  saltpetre  contains  no  organic 


§  226.]  POTASSIUM  COMPOUNDS.  347 

matter.     If  the  saltpetre  contains  a  weighable  quantity  of  a  ni- 
trite, determine  the  nitrous  acid  according  to  §  131,  5. 

The  analysis  of  nearly  pure  saltpetre  is  more  difficult,  because 
it  involves  the  determination  of  very  small  quantities  of  calcium, 
magnesium,  sodium,  and  chlorine,  which  are  nevertheless  of  con- 
siderable importance  in  determining  the  quality  of  the  saltpetre.! 
The  following  methods  are  recommended  for  the  determination 
of  such  almost  pure  saltpetres.* 

1.  Determination  of  Moisture. 

This  is  effected  as  usual  by  moderately  heating  a  weighed 
sample  in  a  platinum  crucible.  The  heat  should  be  gradually 
increased  until  the  saltpetre  just  begins  to  melt.  The  water 
content  is  found  from  the  loss  in  weight.  The  error  resulting  from 
the  decomposition  of  the  exceedingly  small  traces  of  calcium  and 
magnesium  nitrates  and  the  organic  substances,  which  saltpetre 
fit  for  gunpowder  contains,  is  without  appreciable  influence  on 
the  result. 

2.  Determination  of  the  Water-insoluble  Residue,  and  the  Chlorine. 

Dissolve  100  grm.  of  the  saltpetre  in  hot  water,  collect  the 
residue  on  a  filter  dried  at  100°,  and  weigh.  If  the  residue  is 
considerable,  the  residue  and  the  filter  are  best  dried  at  120°. 

Acidulate  the  filtrate  with  pure  nitric  acid,  add  a  little  silver 
nitrate,  and  gently  warm  the  solution  for  a  long  time  with  ex- 
clusion of  light.  Collect  the  precipitate  of  silver  chloride  on  a 
small  filter  and  determine  it,  in  the  usual  manner,  as  either  silver 
chloride  or  as  metallic  silver. 

MOHR'S  volumetric  method  does  not  afford  satisfactory  results 
in  the  case  of  such  small  quantities  of  chlorine,  as  it  is  necessary  to 
use  about  400  c.c.  of  a  concentrated  solution  of  saltpetre. 

3.   Determination  of  the  Calcium,  Magnesium,  and  Sodium. 

Dissolve  in  a  platinum  or  porcelain  dish  100  grm.  of  the  salt- 
petre in  about  100  c.c.  of  water,  with  the  addition  of  about  1-5 

*  R.  FRESENIUS,  Zeitschr.  f.  analyt.  Chem.,  xv,  65. 


348  DETERMINATION    OF   COMMERCIAL  VALUES.         [§•  226. 

grm.  calcium  chloride  (which  serves  for  decomposing  the  sodium 
nitrate),  and  with  the  aid  of  heat;  then  pour  the  solution  with 
constant  stirring  into  about  500  c.c.  of  pure  96-per  cent,  alcohol. 
After  settling,  collect  the  crystalline  precipitate  on  a  well-washed 
vacuum  filter  and  wash  it  with  alcohol,  while  maintaining  the 
vacuum  constantly  during  the  washing. 

Free  the  filtrate  of  its  alcohol  by  distillation,  dissolve  the  residue 
in  a  little  water,  and  once  more  pour  the  solution  into  alcohol. 
After  again  collecting  and  washing  the  precipitate  with  alcohol, 
again  distil  off  the  alcohol,  and  once  more  dissolve  and  repeat 
the  precipitation  by  pouring  into  alcohol.  On  now  washing  the 
residue  with  alcohol,  we  have  an  alcoholic  solution  containing 
all  the  calcium,  magnesium,  and  sodium,  with  so  little  potassium 
that  a  separation  of  the  potassium  and  sodium  appears  practi- 
cable. It  will  be  observed  that  this  conclusion  is  accurate  only 
when  the  saltpetre  contains  no  sulphates,  because  these  when 
present,  will  give  a  precipitate  of  calcium  sulphate  on  adding  the 
alcohol. 

As  a  rule,  however,  the  solutions  of  such  saltpetre  remain 
perfectly  clear  on  adding  barium  chloride,  and  hence  contain  no 
appreciable  quantities  of  sulphates. 

After  the  alcohol  has  been  evaporated  off  from  the  solution 
last  obtained,  evaporate  the  saline  residue  repeatedly  with  hydro- 
chloric acid  to  convert  it  into  pure  chlorides  free  from  nitrates, 
and  from  the  filtered  solution  of  the  chlorides  precipitate  the 
calcium  by  adding  a  few  drops  of  ammonium-oxalate  solution; 
filter,  and  in  the  filtrate  precipitate  the  magnesia  by  a  small  quan- 
tity of  pure  ammonium  phosphate.  Heat  the  filtrate  in  a  plat- 
inum dish  to  expel  the  ammonia,  add  one  or  two  drops  ferric- 
chloride  solution,  neutralize  with  ammonia  or  ammonium  carbo- 
nate so  that  the  liquid  will  be  very  slightly  alkaline,  heat,  and 
filter  off  the  precipitated  basic  ferric  phosphate.  Evaporate  the 
filtrate  to  dryness,  drive  off  the  ammonium  salts,  and  separate  the 
potassium  chloride  as  potassium-platinic  chloride;  then  evaporate 
the  alcoholic  filtrate  to  dryness  and  decompose  the  sodium-platinic 
chloride  together  with  any  excess  of  platinic  chloride  present  by 


§  227.]  POTASSIUM    COMPOUNDS.  349 

cautiously  heating  in  a  current  of  hydrogen.  Now  extract  the 
sodium  chloride  with  water,  evaporate  the  solution  to  dryness, 
and  from  the  weighed  residue  calculate  the  sodium,  after  having 
tested  it  to  see  that  it  is  free  from  potassium,  calcium,  and  magne- 
sium. A  determination  of  the  sodium  chloride  from  the  differ- 
ence between  the  alkali  chlorides  and  the  potassium  chloride 
corresponding  with  the  potassium-platinic  chloride  would  be  less 
accurate.  It  will  be  seen,  of  course,  that  in  such  an  investigation 
unusual  care  must  be  exercised  to  ascertain  that  all  the  reagents 
employed  are  perfectly  pure. 

As  it  is  of  interest  to  know  how  small  the  impurities  in  salt- 
petres intended  for  making  gunpowder  is,  I  append  the  results 
of  an  analysis  made  by  me: 

Potassium  nitrate 99-8124 

Sodium  nitrate 0-0207 

Magnesium  nitrate 0  •  0093 

Calcium  nitrate 0.0006 

Sodium  chloride 0.0134 

Insoluble  residue . .  0-0210 

Moisture.,  0-1226 


100-0600 

APPENDIX  TO  POTASSIUM  NITRATE. 

E.  ANALYSIS  OF  GUNPOWDER.* 

§227. 

Gunpowder  consists,  as  is  well  known,  of  saltpetre,  sulphur, 
and  carbon  (charcoal),  and  in  the  ordinary  condition  always  con- 
tains a  small  quantity  of  moisture.  The  analysis  is  frequently 
confined  to  the  determination  of  the  three  substances  above  men- 

*  Details  regarding  the  determination  of  the  specific  gravity  of  gun- 
powder have  been  given  by  HEEREN  (Mittheilung  des  Gewerbevereins  fur  Han- 
over, 1856,  168  to  l7S.—Polyt.  Centralbl,  1856,  1118).  This  method  has 
been  criticised  by  E.  LUCK  (Zeitschr.  f.  analyt.  Chem.,  xn,  183).  Regarding 
the  determination  of  the  density  of  prismatic  powders  compare  also  BOTHE 
(Zeitschr.  /.  analyt.  Chem.  xiv,  99). 


350  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  227. 

tioned  together  with  the  moisture,  but  the  investigation  is  not 
infrequently  also  directed  to  the  nature  of  the  charcoal,  and  to  a 
determination  of  the  carbon,  hydrogen,  oxygen,  and  ash  con- 
tained. 

In  the  following  there,  will  be  given  (1)  a  process  by  which  the 
various  constituents  in  different  portions  of  the  substance  may 
be  determined,  and  also  a  choice  of  methods  for  determining  in- 
dividual constituents. 

(2)  LINK'S  method,  in  which  all  the  constituents  are  deter- 
mined in  one  and  the  same  portion  of  powder. 

It  appears  to  me  impossible  to  say  which  of  these  methods 
is  undoubtedly  the  best  under  all  circumstances;  it  is  hence  left 
to  the  analyst  to  choose  the  methods  which  will  best  suit  his  special 
purpose. 

I.    METHOD    IN    WHICH     INDIVIDUAL     CONSTITUENTS     ARE     DETER- 
MINED  IN   SEPARATE    PORTIONS   OF   THE   POWDER. 

a.  Determination  of  the  Moisture. 

Weigh  off  2  or  3  grm.  of  the  powder  (not  reduced  to  powder) 
between  two  well-fitting  watch-glasses,  and  dry  to  constant  weight 
in  the  exsiccator,  or  at  a  gentle  heat,  not  exceeding  60°.  If  the 
powder  is  weighed  in  a  glass  tube  drawn  out  at  one  end  and  pro- 
vided with  an  ignited  asbestos  plug,  the  drying  may  be  facilitated 
by  employing  a  current  of  dry  air  (comp.  p.  353). 

b.  Determination  of  the  Saltpetre. 

Place  an  accurately  weighed  quantity  of  the  powder  (about 
5  grm.)  into  filter  previously  moistened  with  water,  moisten  the 
powder  with  as  much  water  as  it  will  absorb,  and  after  some  time 
completely  wash  out  all  the  saltpetre  by  pouring  on  repeatedly 
small  quantities  of  hot  water.  The  first  portion  of  the  saltpetre 
solution  running  through,  collect  in  a  small  weighed  platinum 
dish;  the  washings  collect  in  a  beaker  or  small  flask.  Evaporate 
the  saltpetre  solution,  adding  the  washings  from  time  to  time, 


§  227.]  POTASSIUM  COMPOUNDS.  351 

heat  the  residue  carefully  to  incipient  fusion,  and  weigh.*  If 
the  charcoal  and  sulphur  are  thoroughly  washed  on  a  weighed 
filter  dried  at  100°,  the  filter  and  its  contents  then  dried  at  100°, 
weighed,  and  the  increase  of  weight  together  with  the  moisture 
determined  in  a  (and  calculated  with  reference  to  the  quantity 
of  substance  here  taken)  is  deducted  from  the  powder  taken, 
the  difference  will  give  the  saltpetre  by  way  of  control.  As, 
however,  this  method  is  quite  troublesome,  while  accurately 
concordant  results  cannot  be  expected,  since  a  small  loss  of  sul- 
phur occurs  on  drying  this  at  100°,  this  method  of  control  cannot 
be  recommended. 

c.  Determination  of  the  Sulphur, 
a.  By  Conversion  into  Sulphuric  Acid  in  the  Wet  Way. 

aa.  Oxidize  2  or  3  grm.  of  the  powder  with  concentrated, 
pure  nitric  acid  and  potassium  chlorate,  this  last  being  added  in 
small  quantities,  while  the  liquid  is  kept  boiling  gently.  As, 
if  the  operation  is  continued  long  enough,  both  the  sulphur  and 
the  charcoal  become,  as  a  rule,  completely  oxidized,  a  clear  solu- 
tion is  finally  obtained.  Evaporate  this  to  dryness  on  a  water- 
bath  with  an  excess  of  pure  hydrochloric  acid,  moisten  the  residue 
again  with  hydrochloric  acid,  evaporate,  filter  if  any  undissolved 
charcoal  should  render  this  necessary,  and  determine  the  sul- 
phuric acid  according  to  §  132,  I,  1.  Regarding  the  purification 
of  the  barium  sulphate  see  p.  249,  4. 

66.  Boil  about  1  grm.  of  the  powder  in  a  small  glass  flask  with 
a  concentrated  solution  of  pure  potassium  permanganate,  and 

*The  accuracy  of  the  saltpetre  determination  is  affected  by  the  fact 
that  the  large  quantity  of  water  necessary  for  extraction  also  dissolves  out 
appreciable  quantities  of  organic  matter  from  the  charcoal  (compare  LINK'S 
method,  p.  353).  To  rapidly  determine  the  saltpetre  and  with  sufficient 
accuracy  for  technical  purposes  a  hydrometer  may  be  employed  which  is 
constructed  so  as  to  show  the  percentage  of  saltpetre  present  when  the  in- 
strument is  floated  in  water  in  which  a  definite  quantity  of  gunpowder  is 
dissolved.  A  method  based  upon  the  same  principle,  and  proposed  by 
UCHATTUS,  is  described  in  the  Wiener  akad.  Ber.,  x,  748;  also  in  Annal.  d. 
Chem.  u.  Pharm.,  LXXXVTII,  395. 


352  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  227. 

add  more  of  the  solution  from  time  to  time  until  the  fluid  is  colored 
permanently  violet.  The  whole  of  the  sulphur  and  the  charcoal 
will  now  have  been  oxidized  to  sulphuric  acid  and  carbon  dioxide, 
respectively.  Now  add  pure  hydrochloric  acid,  heat  until  the 
precipitated  manganese  dioxide  is  dissolved  and  the  chlorine  has 
been  expelled,  dilute,  and  determine  the  sulphuric  acid  by  precipi- 
tation with  barium  chloride  as  in  aa  (CLOEZ  and  GUIGNET*). 

/?.  By  Conversion  with  Sulphuric  Acid  in  the  Wet  Way. 

Mix  1  part  (about  1  to  1  •  5  grm.)  of  the  finely  powdered  powder 
with  an  equal  quantity  of  anhydrous,  pure  sodium  carbonate 
(free  from  sulphuric  acid),  then  add  1  part  pure  saltpetre  and 
6  parts  pure,  dry  sodium  chloride;  the  substances  must  be  mixed 
very  intimately  and  the  mixture  heated  in  a  platinum  crucible 
until  the  combustion  is  complete  and  the  mass  has  become  white. 
Then  dissolve  the  saline  mass  in  water,  acidulate  with  hydro- 
chloric acid,  evaporate  repeatedly  with  hydrochloric  acid  until 
all  the  nitric  acid  has  been  expelled,  and  finally  determine  the 
sulphuric  acid  (resulting  from  the  oxidation  of  the  sulphur)  by 
precipitation  with  barium  chloride,  as  above:  c,  a,  aa  (GAY-LussAc). 

f  By   Extraction  with  Carbon  D  sulphide  and  Weighing  the  Sulphur. 
See  LINK'S  PROCESS,  under  II. 

d.  Determination  of  the  Charcoal. 

Digest  a  weighed  quantity  of  the  powder  repeatedly  with 
ammonium  sulphide  until  all  the  sulphur  is  dissolved  out,  collect 
the  charcoal  on  a  filter  dried  at  100°,  wash  it  first  with  water  con- 
taining ammonium  sulphide,  then  with  pure  water,  then  dry  at 
100°  and  weigh. 

The  charcoal  thus  obtained  must,  under  all  circumstances, 
be  tested  for  sulphur  by  one  of  the  methods  given  under  c,  a,  or 
/?,  and,  if  necessary,  the  sulphur  remaining  in  it  must  be  determined 
in  an  aliquot  part.  The  charcoal  may  also  be  tested  regarding 

*  Compt.  rend.,  XLVI,  1110. — Journ.  /.  prakt.  Chem.,  LXXV,  175. 


§  227.]  POTASSIUM  COMPOUNDS.  353 

its  behavior  toward  potassa  lye  (in  which  "red  charcoal"*  is 
partially  soluble),  or  an  aliquot  part  may  be  subjected  to  elemen- 
tary analysis  according  to  §  188.  For  this  purpose  dry  at  190° 
(WELTZIEN)  a  sample  of  powder  previously  dried  at  100°.  If 
the  charcoal  suffers  any  loss  of  weight  hereby,  the  loss  must  be 
calculated  into  per  cents,  of  the  powder,  deducted  from  the  char- 
coal, and  added  to  the  moisture. 

The  carbon  disulphide,  too,  does  not  completely  extract  the 
sulphur  (see  LINK'S  process).  If  it  is  desired  to  make  an  analysis 
of  the  charcoal  itself,  LINK'S  process  is  to  be  particularly  recom- 
mended, as  in  this  method  the  charcoal  is  much  less  likely  to 
be  subjected  to  change  than  when  it  is  digested  with  ammonium 
sulphide  during  the  extraction  of  the  sulphur. 

II.   PROCESS     IN     WHICH    ALL    THE    CONSTITUENTS    OF    GUNPOWDEK 
ARE    DETERMINED    IN    ONE    PORTION   (LlNK's    PROCESS  f). 

In  this  process  there  is  used  a  glass  tube  of  9  mm.  bore  and 
about  14  cm.  long;  at  one-third  of  its  length  it  is  drawn  out  to 
2  mm.  bore,  and  at  the  point  where  the  tube  begins  to  narrow, 
a  loose  plug  of  ignited  asbestos,  about  15  mm.  long,  is  placed. 
After  being  thoroughly  dried,  the  tube  is  first  weighed,  then  filled 
with  the  powdered  gunpowder  (about  3  grm.),  and  weighed  again. 
The  quantity  of  gunpowder  is  ascertained  exactly.  Now  pass 
through  the  tube  a  current  of  perfectly  dry  air  at  the  ordinary 
temperature,  until  it  ceases  to  lose  weight  (requiring  about  ten 
hours);  the  difference  gives  the  moisture  in  the  powdered  gun- 
powder. J 

Now  connect  the  tube  a,  Fig.  101,  by  means  of  a  perforated 
cork,  6,  with  the  flask,  c,  which  should  have  a  capacity  of  about 
24  c.c.,  and  carefully  pour  onto  the  powder  rectified  carbon 
disulphide  which  rapidly  runs  through  clear  into  c.  As  soon 

*  Incompletely  carbonized  wood. 

f  Annal.  d.  Chem.  u.  Pharm.,  cix,  53. 

t  This  quantity  is  frequently  somewhat  greater  than  that  contained 
in  the  granular  gunpowder,  as  the  powder  may  attract  a  little  moisture 
during  trituration.  On  this  account  a  correction  becomes  necessary  (see 
p.  356). 


354 


DETERMINATION    OF    COMMERCIAL    VALUES.          [§  227. 


as   the  flask   becomes 


FIG.  101. 


about  one-third  filled,  from  the  repe- 
tition of  the  washing,  heat  it 
in  a  water-bath  at  a  tempera- 
ture of  70°  to  80°,  and  distill 
off  the  carbon  disulphide  into 
the  dry  receiver,  d.  The  dis- 
tillate serves  for  repeating  the 
extraction.  After  six  por- 
tions of  8  c.c.  each  of  carbon 
disulphide  have  been  poured 
on  the  powder,  all  the  sulphur 
that  can  be  extracted  will  have 
been  removed  from  the  pow- 
der. The  sulphur  remaining 
in  c  is  cautiously  heated  just 
to  the  point  of  fusion,  the 
flask  cooled,  and  any  vapor  of 
carbon  disulphide  that  may 
remain,  removed  by  a  current 
of  dry  air;  the  flask  is  then 
weighed. 

The   tube    containing    the 
exhausted    powder    is    again 
connected  with  the  aspirator, 
100°    drawn    through    it   until 
The    difference    between    this 


and  a  current  of  dry  air  at 
the  weight  remains  constant, 
weight  and  that  of  the  tube  plus  the  dry  unexhausted  powder 
represents  the  quantity  of  sulphur  extracted,  together  with  the 
very  small  quantity  of  water  which  the  powder  loses  when  heated 
at  100°.  This  small  quantity  of  moisture  is  found  by  deducting 
from  the  difference  just  found  the  quantity  of  the  sulphur  found 
directly;  it  must  be  added  to  the  moisture  found  first. 

In  order  to  next  determine  the  small  quantity  of  sulphur  still 
contained  in  the  exhausted  powder,  shake  out  an  aliquot  portion 
of  the  latter  (0-$  to  0-7  grm.),  weigh  the  tube  again,  and  thus 
ascertain  the  weight  of  the  quantity  shaken  out,  as  well  as  that 


§  227.] 


POTASSIUM    COMPOUNDS. 


355 


which  remains.  Oxidize  the  portion  removed  with  aqua  regia, 
evaporate  with  hydrochloric  acid,  and  determine  the  small  quan- 
tity of  sulphuric  acid  formed  by  precipitating  with  barium  chloride 
(see  I,  c,  a,  aa);  calculate  the  barium  sulphate  into  sulphur,  and 
from  this  the  quantity  present  in  the  whole  of  the  exhausted 
powder.  The  quantity  thus  obtained  (which  amounts  to  about 
0  •  1  per  cent,  according  to  LINK)  is  added  to  the  sulphur  directly 
weighed. 

The  saltpetre  in  the  portion  of  exhausted  powder  remaining 
in  the  tube  is  next  determined.  For  this  purpose  connect  the 
tube  a,  Fig.  102,  together  with 
the  vessel  dt  airtight  to  the 
air-pump  receiver,  6,  by  means 
of  rubber  connector,  e;  then 
treat  the  contents  of  a  with 
cold  water,  and  operate  the 
pump  very  slowly  so  as  to 
cause  the  liquid  to  pass,  drop 
by  drop,  into  the  flask  c.  In 
order  to  prevent  the  crystal- 
lization of  the  saltpetre  in  the 
point  of  the  tube  a,  the 
operation  is  repeated  with 
warmer  and  warmer  portions 
of  water,  the  last  water  used 
being  as  hot  as  possible;  the 
vessel  d  should  be  filled  during 
the  process  with  water  of 
same  temperature  as  that  used 
for  the  exhaustion.  In  this  FIG.  102. 

manner  the  saltpetre  may  be  completely  removed  from  2  grms. 
of  powder  with  18  to  24  c.c.  of  water;  thus  is  avoided  the 
error  introduced  when  using  large  quantities  of  water,  and  which 
is  due  to  the  extraction  of  an  appreciable  quantity  of  organic 
matter  from  the  charcoal. 

Evaporate  the  saltpetre  solution  in  a  platinum  crucible,  dry 


356  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  227. 

the  residue  at  120°,  weigh,  and  calculate  with  reference  to  the 
total  weight  of  powder. 

Now  raise  the  asbestos  plug  a  little  so  as  to  loosen  it,  by  push- 
ing it  upwards  with  a  platinum  wire,  and  dry  the  residual  char- 
coal at  100°  in  a  current  of  dry  air.  If  the  weight  of  the  charcoal 
is  slightly  greater  than  the  difference  between  the  weight  of  the 
saltpetre  together  with  the  charcoal  minus  the  saltpetre  directly 
found,  the  difference  is  due  to  the  fact  that  pure  charcoal  retains 
water  more  firmly  than  when  mixed  with  saltpetre.  This  small 
difference  (of  1  to  1-5  mgm.)  is  hence  to  be  considered  as  water 
adhering  to  the  charcoal,  and  is  to  be  deducted  from  the  water 
obtained  in  the  elementary  analysis. 

For  the  purpose  of  combustion,  mix  the  charcoal  in  the  tube 
with  some  lead  chromate,  cut  off  the  drawn-out  portion  of  the 
tube,  mix  the  asbestos  plug  with  the  contents  until  an  air-current 
can  freely  pass  over  the  mixture,  insert  the  whole  into  a  combus- 
tion-tube filled  as  usual  with  oxidized  copper  turnings,  and  con- 
duct the  combustion  in  the  customary  manner,  and  in  a  current 
of  oxygen  (§  178).  The  quantities  of  carbon,  hydrogen,  and 
oxygen  obtained  (together  with  the  small  quantity  of  ash)  are 
also,  like  the  saltpetre,  to  be  calculated  with  reference  to  the 
whole  quantity  of  powder  originally  taken. 

If  it  is  desired  to  correct  the  very  small  error  caused  by  the 
powder  attracting  a  small  quantity  of  moisture  during  trituration, 
dry  a  fresh  portion  of  the  untriturated  powder  in  the  manner 
described  above,  and  using  the  figure  so  obtained  calculate  the 
weight  of  the  original  gunpowder  contained  in  the  triturated 
powder.  For  instance,  if  the  original  granulated  powder  yielded 
0-5  water,  and  hence  contained  99-5  of  dry  powder,  the  weight 
of  the  dried  triturated  powder  will  have  to  be  increased  in  the 
proportion  of  99  •  5 :100,  in  order  to  ascertain  the  quantity  of  gran- 
ulated powder  equivalent  to  it;  and  on  the  true  weight  thus  found 
all  the  results  of  the  analysis  should  be  calculated. 


228.]  POTASSIUM    COMPOUNDS.  357 

F.  POTASSIUM  BITARTRATE  (TARTAR). 
§228. 

Crude  tartar,  which  is  taken  partly  from  wine  vats,  and  partly 
obtained  from  wine  lees,  and  which  serves  as  the  source  of  tartaric 
acid  and  pure  tartrates,  almost  always  contains,  besides  potassium 
bitartrate,  also  neutral  calcium  tartrate,  CaC4H4Ott+4H2O,  both 
in  varying  quantities,  together  with  coloring  matter,  lees,  etc. 
If  gypsum  has  been  used  in  the  manufacture  of  the  wine,  as  has 
been  the  practice  for  a  long  tune  in  France,  the  crude  tartar  will 
also  always  contain  calcium  sulphate. 

In  the  examination  of  crude  tartars,  it  is  desired  to  ascertain 
the  total  quantity  of  tartaric  acid  they  contain,  or  how  much  of 
the  tartaric  acid  is  present  in  the  form  of  potassium  bitartrate 
and  how  much  as  calcium  tartrate. 

I.  DETERMINATION  OF  THE  TOTAL  TARTARIC  ACID. 

For  this  purpose  M.  LEONARD'S  method,  as  briefly  described 
by  SCHEURER-KESTNER,*  is  the  most  convenient.  It  affords 
correct  results,  whether  the  tartar  contains  calcium  sulphate  or 
not. 

Dissolve  about  5  grm.  of  the  tartar  in  hydrochloric  acid, 
filter,  neutralize  with  carbonic-acid  free  soda  lye,  add  an  excess 
of  calcium  chloride,  and  after  allowing  to  stand  a  long  time, 
collect  the  precipitated  calcium  tartrate  on  a  filter.  After  wash- 
ing the  precipitate,  dry,  ignite,  and  titrate  with  normal  hydro- 
chloric or  nitric  acid  (see  §  223).  Every  100  c.c.  of  the  normal 
acid  required  to  neutralize  the  caustic  lime  or  calcium  carbonate 
resulting  from  the  ignition  represents  7  •  5024  grm.  of  tartaric  acid, 


*  Remarques  sur  1'essais  des  tartres  bruts  pr£sent£es  &  la  soci£t£  indus- 
trielle  de  Mulhouse  dans  la  stance  du  Avril  1878.  —  Compt.  rend.,  LXXXVI, 
lQ24.—Zetischr.  f.  analyt.  Chem.,  xvin,  111. 


358  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  228. 

II.    DETERMINATION   OF   THE    POTASSIUM    BITARTRATE. 

a.  The   determination  of  the  potassium  bitartrate  in   crude 
tartar  is  as  a  rule  effected  by  neutralization  with  normal  soda 
solution,  exactly  as  described  on  p.  305,  3.     This  determination, 
of  course,  is  correct  only  when  no  other  substances  having  an 
acid  reaction  (tannic  acid,  etc.)  are  present  in  the  tartar. 

b.  If  the  method  of  determination  described  under  a  is  not 
practicable,  or  if  it  is  to  be  controlled,  the  following  is  recom- 
mended:  Carbonize   about  10  grm.  of  the   tartar,  and  heat  for  a 
sufficient  length  of  time  with  access  of  air,  but  not  too  strongly, 
until  all  the  organic  substances  have  been  completely  decom- 
posed.    Boil   the   residue  with   water,   filter,   wash   with  boiling 
water  until  the  washings  cease  to  have  an  alkaline  reaction,  and 
make  up  the  cooled  liquid  to  500  c.c.     In  200  c.c.  of  this  deter- 
mine the   caustic  potassa  and   potassium  carbonate  with  normal 
acid  (§  220).     Acidulate  another  100  c.c.  with  hydrochloric  acid, 
add  barium  chloride,  and  if  a  precipitate  of  barium  sulphate  forms, 
determine  its  weight.     By  calculating  the  ratio  of  the  solution 
employed  to  the  whole  solution,  the  following  considerations  lead 
to  the  desired  result :  If  there  is  no  sulphuric  acid,  the  normal  acid 
used  up  is  directly  proportional  to  the  potassium  carbonate  formed 
from  the  potassium  bitartrate,  hence  100  c.c.  normal  acid  will 
represent  18-815  grm.  potassium  bitartrate,  representing  15-0048 
grm.  of   tartaric    acid,  H2C4H406.      If,  however,    sulphuric    acid 
is  present  as  potassium    sulphate,  this   has  been  formed  by  the 
action  of  calcium  sulphate  on  potassium  carbonate,  and  conse- 
quently the   quantity  of  potassium  bitartrate   cannot  be  directly 
deduced  from  the  potassium  carbonate  found  (SCHEURER-KESTNER, 
loc.  cit.);   it  will,  however,  be   correct   if  for  every  40-035  mgm. 
of  SO3  present  in  the  500  c.c.  of  the  alkaline  solution,  1  c.c.  of 
normal   acid  is   added   to   the   quantity  which  was   required  to 
neutralize   the    caustic    potassa    and   potassium   carbonate   con- 
tained in  500  c.c.,  and  from   the   total  c.c.  of   normal  acid  thus 
obtained  calculating  the  potassium  bitartrate  from  the  proportion 
100:18-815. 


§  228.]  POTASSIUM   COMPOUNDS.  359 

III.    DETERMINATION    OF    THE    CALCIUM   TARTRATE. 

If  the  determination  of  this  is  attempted  in  the  neutralized 
tartar  solution  obtained  in  III,  a,  by  filtering  off  the  solution  of 
the  neutral  alkali  tartrate,  in  order  to  determine  the  calcium  tar- 
trate  in  the  insoluble  residue,  an  incorrect  result  would  be  ob- 
tained even  in  the  case  of  a  tartar  free  from  gypsum,  because 
solutions  of  neutral  alkali  tartrates  dissolve  appreciable  quantities 
of  calcium  tartrate;  the  results  would,  however,  be  far  more  out 
of  the  way  in  case  of  tartar  containing  gypsum,  because  neutral 
alkali  tartrates  immediately  decompose  gypsum,  to  form  alkali 
sulphates  and  calcium  tartrate,  the  latter  precipitating  (SCHEURER- 
KESTNER,  loc.  cii.). 

The  calcium  tartrate  must  hence  be  determined  either  by 
subtracting  the  tartaric  acid  present  in  the  form  of  tartar 
found  by  II)  from  the  total  tartaric  acid  as  determined  in  §  228,  1, 
and  calculating  the  calcium  tartrate  from  the  difference,  or  by 
igniting  the  water-insoluble  residue  of  chiefly  carbon  and  cal- 
cium carbonate  (§  228,  II,  6),  until  the  carbon  is  burnt  off,  and 
then  determining  the  calcium  or  calcium  carbonate  in  the  residue 
with  normal  acid  (§  223).  If  no  sulphuric  acid  was  found  in 
§  228,  II,  b,  the  acid  employed  in  the  neutralization  gives  at  once 
the  quantity  of  calcium  artrate  (100  c.c.  of  normal  acid  corre- 
spond with  13-01  grm.  of  crystallized  calcium  tartrate,  CaC4H4O6+ 
4H20,  or  with  9-4066  grm.  of  the  anhydrous  salt,  CaC4H4O6,  or 
with  7-5024  grm.  of  tartaric  acid,  H2-C4H4O6).  If,  on  the  other 
hand,  the  alkaline  solution  contains  sulphuric  acid,  the  quantity 
of  normal  acid  corresponding  to  it  (1  c.c.  of  normal  acid  for  every 
40-035  mgm.  of  SO-)  must  first  be  deducted  from  the  normal 
acid  used  in  neutralizing  the  calcium,  before  the  calcium  tartrate 
can  be  calculatd,  since  for  every  equivalent  of  potassium  sulphate 
formed  from  the  mutual  decomposition  of  calcium  sulphate  and 
potassium  carbonate,  one  equivalent  of  calcium  carbonate  would 
be  precipitated. 


360  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  22Q. 

5.  SODIUM  COMPOUNDS. 

A.  SODIUM  CARBONATE  (SODA). 
§229. 

Soda,  by  which  name  is  known  the  sodium  carbonate  manu- 
factured on  the  large  scale,  and  containing  other  salts  in  smaller 
or  larger  quantities,  occurs  in  the  market  in  the  calcined  as  well  as 
the  crystallized  form.  Up  to  a  few  years  ago  soda  was  almost 
exclusively  made  by  the  LEBLANC  process  (fusion  of  sodium  sul- 
phate, coal,  and  calcium  carbonate,  then  lixiviating,  etc.) ;  latterly, 
however,  large  quantities  are  also  obtained  by  heating  sodium 
bicarbonate  obtained  by  the  action  of  carbon  dioxide  on  a  solu- 
tion of  sodium  chloride  saturated  with  ammonia  gas  (so-called 
" ammonia  soda").  The  soda  prepared  according  to  the  latter 
process  is  for  the  most  part  very  pure,  and  as  a  rule  contains  only 
a  little  sodium  chloride. 

The  commercial  LEBLANC  soda,  however,  and  particularly  the 
inferior  grades,  contains  a  far  greater  number  of  foreign  salts,  etc., 
particularly  sodium  sulphate,  sodium  chloride,  sodium  silicate, 
sodium  aluminate,  sodium  hydroxide,  and  not  infrequently 
sodium  sulphide,  sodium  sulphite,  and  sodium  thiosulphate. 
Sodium  cyanide  is  also  frequently  found,  although  usually  only 
in  traces;  sodium  ferrocyanide  and  suphocyanate  are  also  at 
times  found  in  slight  quantities.  To  these  must  be  added,  in 
many  kinds  of  soda,  substances  insoluble  in  water,  such  as  alumina, 
sand,  coal,  ferric  oxide,  calcium  carbonate,  etc.  Finally  the 
black  ash  obtained  by  the  LEBLANC  process  contains  not  only 
all  the  above-mentioned  substances  soluble  in  water,  but  also,  in 
the  portion  insoluble  in  water,  large  quantities  of  calcium  sul- 
phide, calcium  carbonate,  and  caustic  lime,  besides  magnesia, 
iron  sulphide,  silica,  alumina,  sand,  and  coal.  Its  examination 
hence  presents  considerable  difficulty,  as  the  analysis  can  afford 
but  little  information  as  to  the  character  of  the  melt,  if,  without 
taking  into  account  the  solubility  of  the  individual  substances, 
the  proportions  of  the  different  ingredients  were  alone  deter- 


§  229.]  SODIUM   COMPOUNDS.  361 

mined  in  the  mass.  For  the  analysis  to  be  of  use  to  the  soda 
manufacturer,  a  determination  must  be  made  of  those  constitu- 
ents which  go  into  solution  on  lixiviating  with  water,  and  those 
remaining  undissolved. 

In  the  following  the  analysis  of  black  ash  is  first  considered; 
then  that  of  commercial  soda. 

I.     ANALYSIS    OF  BLACK   ASH. 

1.  //  only  the  substances  passing  into  solution  are  to  be  examined, 
introduce  53-05  grm.  of  the  finely  powered  black  ash  (and  cor- 
responding with  one-half  equivalent  of  sodium  carbonate)  into 
a  litre  flask  fill  up  to  the  neck  with  water  at  45°  to  50°,*  stopper 
well,  and  shake  vigorously  and  frequently.  After  several  hours, 
when  the  liquid  has  cooled  to  the  mean  temperature,  fill  with  cold 
water  up  to  the  mark,  add  15  c.c.  of  water  (to  allow  for  the  bulk 
of  the  insoluble  residue),  stopper,  shake,  and  let  settle. 

The  solution  generally  contains,  besides  sodium  carbonate, 
the  following  substances  in  determinable  quantities:  Sodium 
hydroxide,  sodium  sulphide,  odium  sulphite,  sodium  sulphate, 
sodium  chloride,  sodium  silicate,  and  sodium  aluminate. 

It  is  frequently  considered  sufficient  to  determine,  on  the  one 
hand,  the  sum  of  the  soda  compounds  which  neutralize  acid  (ex- 
pressed in  the  equivalent  of  sodium  carbonate);  and,  on  the 
other  hand,  the  sum  of  the  sulphur  compounds  which  convert 
iodine  into  hydriodic  acid.  In  this  case  the  following  determina- 
tions will  suffice: 

a.  Remove  50  c.c.  of  the  clear  liquid  (corresponding  to  2-6525 
of  black  ash)  with  a  pipette,  and  subject  it  to  the  alkalimetric 
test  (§220).     Now,  as  2-6525=-^  equivalent  of  sodium  carbonate 
(compared  with  normal  acid),  it  is  only  necessary  to  double  the 
number  of  c.c.  of  acid  used  in  order  to  obtain  the  soda  neutralized 
by  the  acid  expressed  in  per  cents,  of  sodium  carbonate. 

b.  Dilute  50  c.c.  of  the  solution  with  about  200  c.c.  water  in 

*  The  lixiviation  is  usually  conducted  at  this  temperature  also  at  the 
alkali  works.  • 


362  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  229. 

a  flask,  and  from  a  burette  run  in  cautiously  and  with  constant 
stirring,  perfectly  pure  dilute  acetic  acid  (best  prepared  from 
glacial  acetic  acid)  until  the  liquid  no  longer  colors  turmeric  paper 
brown.  When  the  e.c.  of  dilute  acetic  acid  required  to  effect 
this  has  been  ascertained,  measure  off  a  fresh  50  c.c.  of  the 
soda  solution,  dilute  it  in  a  large  flask  with  about  200  c.c.  water, 
and  very  slowly  add,  with  gentle  shaking,  a  volume  of  dilute 
acetic  acid  equal  to  that  used  up  in  the  preliminary  experiment; 
the  acid  should  be  introduced  by  means  of  a  funnel  the  stem  of 
which  reaches  to  the  bottom  of  the  flask.  The  liquid  now  con- 
tains sodium  acetate  and  bicarbonate.  Add  now  some  thin  starch 
paste  and  then  titrate  with  standard  iodine  solution  (§  146)  until 
just  blue.  The  iodine  used  gives  the  sodium  sulphide  and  sodium 
sulphite  together. 

If  the  nature  of  the  compounds  which  neutralize  the  acid, 
and  the  sulphur  compounds  which  decolorize  iodine,  are  both  to 
be  determined,  and  if  the  other  substances  present  in  the  solu- 
tion have  to  be  estimated,  the  following  additional  determina- 
tions must  be  made: 

c.  Add  barium-chloride  solution  to  100  c.c.  of  the  liquid  con- 
tained in  a  500-c.c.  flask  so  long  as  a  precipitate  forms;   then  fill 
with  water  to  the  mark,  stopper,  allow  to  settle,  draw  off  250  c.c. 
of  the    clear  liquid  (corresponding    to  2-6525  grm.  of  soda  ash) 
and  titrate  (§  220).     The  c.c.  of  normal  acid  used,  multiplied  by  2 
will  give  the  caustic  soda  present,  expressed  in  per  cents,  of  so- 
dium   carbonate;     this  number  multiplied   by  0-7551    gives    the 
percentage  of  sodium  hydroxide. 

d.  Mix  100  c.c.  of  the  solution  in  a  500-c.c.  flask  with  zinc- 
sulphate  solution  to  which  potassa  solution  has  been  added  until 
the  precipitate  first  formed  is  redissolved.     Add  the  zinc-sulphate 
solution  until  it  causes  no  further  precipitation,  and  all  the  sul- 
phur present  as  sodium  sulphide  has  hence  been  precipitated  as 
hydrated  zinc  sulphide.     Now  fill  the  flask  with  water  up  to  the 
mark,  stopper,  shake,  and  allow  to  settle;   then  draw  off  250  c.c. 
of  the  clear  liquid   (corresponding  with  2-6525  grm.  of  the  soda 
ash),  acidulate  with  pure  acetic  acid  (best  prepared  from  glacial 


§  229.]  SODIUM  COMPOUNDS.  363 

acetic  acid),  and  titrate  with  iodine  solution  to  incipient  blueness. 
From  the  quantity  of  iodine  used  the  quantity  of  sodium  sulphite 
(2  eq.  of  iodine  =  253 -70  corresponds  with  1  eq.  of  Na2SO3=126-17) 
can  be  calculated,  and  from  the  difference  between  the  iodine 
used  here  and  in  b,  the  quantity  of  sodium  sulphide  (2  eq.  iodine  = 
253-70  corresponds  with  1  eq.  ^8  =  78-17)  may  be  ascertained.* 

Instead  of  the  alkaline  zinc-oxide  solution  an  alkaline  lead- 
oxide  solution  may  be  used  for  precipitating  the  sulphur  com- 
bined with  sodium;  the  lead  solution  is  easily  made  by  adding 
soda  lye  to  solution  of  lead  acetate  until  the  precipitate  formed 
redissolves.  Great  care  must,  however,  be  taken  that  the  lead 
solution  is  added  in  slight  excess  only.  The  determination  of 
the  sulphur  combined  with  sodium  may  be  finally  controlled  by 
filtering  off  the  zinc  sulphide,  or  lead  sulphide,  and  analyzing  it 
gravimetrically  (§§  108  and  116). 

e.  Add  a  little  pure  potassium  nitrate  to  100  c.c.  of  the  solution, 
evaporate  to  dry  ness,  heat  just  to  fusion  in  order  to  convert  so- 
dium sulphide  and  sulphite  into  sodium  sulphate,  dissolve  the 
fused  mass  in  water,  filter  into  a  100-c.c.  flask  or  cylinder,  and 
in  50  c.c.  of  the  liquid  (corresponding  to  2-6525  grm.  of  black 
ash),  determine  the  chlorine  according  to  §  141  b,  a;  in  the  re- 
maining 50  c.c.  determine  the  sulphuric  acid  according  to  §  132. 
From  the  quantity  of  the  latter  deduct  the  quantity  correspond- 
ing with  the  sulphur  of  the  sodium  sulphide  and  sulphite. 

/.  Acidulate  100  c.c.  of  the  solution  with  hydrochloric  acid, 
evaporate  to  dryness,  separate  the  silici  acid  according  to  §  140, 
II,  a,  and  in  the  filtrate  determine  the  alumina  according  to 
§  105,  a. 

In  the  calculation  and  arrangement  of  the  results,  combine  the 
silicic  acid  and  alumina  with  sodium  to  form  Na.jSiO3  and 

*  Sodium  thiosulphate  in  the  presence  of  sodium  sulphite  may  be  de- 
termined in  precisely  the  same  manner.  The  analysis  of  lyes  obtained  as 
by-products  in  alkali  manufacture  is  more  difficult,  as  they  contain  sodium 
sulphite  and  sodium  thiosulphate  besides  sodium  sulphate,  and  generally 
also  sodium  sulphide.  The  determination  of  these  various  sulphur-oxygen 
compounds  is  best  accomplished  by  indirect  analysis.  See  J.  GROSSMAN, 
Zeitschr.  f.  analyt.  Chem.,  xvm,  79. 


364  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  229. 

Na2O-Al2O3,  respectively.  The  sodium  of  these  compounds,  and 
also  that  of  the  sodium  hydroxide  and  sodium  sulphide,  must  be 
calculated  into  equivalent  quantities  of  sodium  carbonate,  and 
their  sum  deducted  from  the  percentage  obtained  in  a,  the 
remainder  thus  giving  the  sodium  carbonate  actually  present. 

If  it  is  desired  to  determine  the  sodium  sulphide  alone  in  soda 
lyes,  the  following  expeditious  method  proposed  by  LESTELLE  * 
may  be  employed:  Add  ammonia  to  the  lye  to  be  tested,  heat 
to  boiling,  and  run  in  an  ammoniacal  silver  solution  drop  by  drop 
until  the  whole  of  the  sulphur  is  just  precipitated.  When  this 
point  approaches  filter  off  a  portion  and  test  it,  repeating  this 
until  the  further  addition  of  the  silver  solution  causes  only  a  slight 
turbidity.  If  the  silver  solution  is  made  to  contain  2-761  grm. 
of  pure  silver,  or  4-3485  grm.  of  pure  silver  nitrate  in  the  litre, 
each  c.c.  will  correspond  with  1  mgrm.  of  sodium  sulphide.  VER- 
STRAET  t  uses  an  ammoniacal  copper  solution  instead  of  an  am- 
moniacal silver  solution.  r 

2.  //  the  residue  insoluble  in  water  is  to  be  examined,  the  follow- 
ing will  be  the  easiest  and  most  certain  course  to  pursue: 

a.  Pour  some  water  over  about  10  grm.  of  the  finely  powdered 
black  ash  contained  in  a  flask,  heat  almost  to  boiling,  and,  while 
constantly  heating,  add  gradually  hydrochloric  acid  until  it  is 
present  in  considerable  excess,  and  all  the  soluble  substances 
present  have  gone  into  solution.  After  the  heating  has  been 
continued  further  for  some  time  until  all  carbon  dioxide  and  hy- 
drogen sulphide  have  been  expelled,  filter  the  solution  into 
a  500-c.c.  flask  through  a  filter  dried  at  100°  and  weighed,  wash 
the  residue,  dry  it  at  100°,  and  thus  ascertain  the  sand  and  coal; 
after  ignition  the  sand  alone  will  be  found,  and  the  difference 
will  give  the  carbon. 

Make  up  the  solution  to  500  c.c.,  and  mix. 

6.  Add  a  little  nitric  acid  to  200  c.c.  of  the  solution,  and  evapo- 
rate to  dryness  on  the  water-bath;  the  silicic  acid  is  separated 
as  usual,  and  then  the  ferric  oxide  and  alumina  are  precipitated 

*  Zeitschr.  /.  analyt.  Chem. ,  11,  94. 
.,  iv,  216. 


§  229.] 


SODIUM    COMPOUNDS. 


365 


by  ammonia  (§  161,  4).  After  weighing,  fuse  them  with  potas- 
sium bisulphate,  dissolve  the  melt,  and  in  the  solution  determine 
the  iron  volumetrically  or  gravimetrically  (§  160,  A,  2);  the 
alumina  is  found  by  the  difference.  In  the  filtrate  from  the  am- 
monia precipitate  determine  the  calcium,  and  also  any  magnesium, 
if  it  is  present  (§154,  6). 

c.  In  200  c.c.  of  the  solution  determine  the  sodium,  according 
to  the  method  described  on  p.  249,  4. 

d.  A  fresh  portion  of  about  0-7  to  0-8  grm.  of  the  powdered 
black  ash  is  used  for  the  determination  of  the  carbonic  acid,  and 
of  the  sulphur  present  in  the  form  of  calcium  sulphide,  sodium 
sulphide,  and  iron  sulph  de;  i.e.,  that  which  is  expelled  as  hydro- 
gen sulphide  by  the  action  of  hydrochloric  acid.     For  this  purpose 
the  method  proposed  by  me  some  years  ago'*  is  employed,  with 
the    apparatus  .shown  in  Fig.  103,  and  which   has   already  been 
referred  to  in  Vol.  I,  p.  561,  d,  and  p.  742,  7  [253]. 


FIG.  103. 

The  flask  a,  which  receives  the  weighed  substance,  has  a  capacity 
of  about  200  c.c.  The  tube  u,  which  must  not  be  too  narrow, 
leads  to  the  small  reflux  condenser,  6,  the  object  of  which  is  to 

*  Zeitschr.  f.  analyt.  Chem.,  x,  75. 


366  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  229. 

condense  the  steam  containing  hydrochloric  acid  driven  off  dur- 
ing the  latter  portion  of  the  heating.  As  the  heating  must  be 
continued  for  a  long  time  in  order  to  completely  expel  all  the 
hydrogen  sulphide,  the  small  condenser  is  quite  essential.  The 
condenser-tube,  which  must  also  not  be  too  narrow,  is  expanded 
to  a  bulb  near  the  top,  and  is  connected  with  a  U-tube,  e,  contain- 
ing only  a  small  quantity  of  calcium  chloride  in  the  lower  part  of  the 
tube,  while  the  upper  part  is  empty.  Of  the  tubes  which  follow, 
/,  g,  and  h  contain  calcium  chloride  dried  at  200°,  i  and  k  contain 
copper-sulphate  pumice  and  calcium  chloride  (comp.  Vol.  I,  p.  562), 
and  /  and  m  soda-lime  and  calcium  chloride;  i,  k,  I,  and  m  are 
accurately  weighed;  the  bulb  of  n  contains  soda-lime  while  the 
tube  contains  calcium  chloride,  the  whole  serving  as  a  protecting 
tube ;  o  is  half  fillecf  with  water,  and  serves  as  an  indicator  of  the 
progress  of  the  operation;  p  is  the  cock  connecting  with  the  suc- 
tion-tube of  the  water  air-pump.  Of  course  the  air-pump  may  be 
replaced  by  any  other  aspirator. 

On  closing  the  screw  pinch-cock  s  on  the  funnel-tube  t,  lead- 
ing into  the  flask  a,  and  opening  the  cock  p,  the  operator  may 
ascertain  if  the  apparatus  is  tight  in  all  its  parts;  if  this  is  so, 
the  passage  of  the  air-bubbles  through  the  water  in  o  gradually 
ceases. 

If  this  is  the  case,  fill  the  funnel  over  the  pinch-cock  s  repeat- 
edly with  water,  and  allow  this  to  flow  into  a  by  opening  s,  then 
introduce  into  the  flask  in  a  similar  manner  small  portions  of  hy- 
drochloric acid  of  sp.  gr.  1  •  12,  until  the  acid  is  present  in  decided 
excess.  The  liquid  should  one-third  fill  the  flask. 

After  the  more  rapid  disengagement  of  gas  has  ceased  re- 
move the  funnel  over  s,  and  replace  it  by  a  small  glass  tube  v, 
which  insert  into  the  rubber  tube  over  s;  then  open  the  screw 
pinch-cock  slightly,  so  that  a  gentle  current  of  air  may  pass  un- 
interruptedly through  the  fluid  in  a,  and  through  the  entire  appa- 
ratus, and  then  heat  the  flask  a  so  that  its  contents  are  kept  con- 
stantly yet  gently  boiling.  As  soon  as  the  water  in  the  condenser 
begins  to  get  warm,  sufficiently  open  the  cock  c  connecting  with  the 
water-supply,  so  as  to  properly  cool  the  condenser.  The  action  of 


§  229.]  SODIUM    COMPOUNDS.  367 

the  hydrogen  sulphide  on  the  copper-sulphate  pumice  is  indicated 
by  a  progressive  blackening;  and  that  of  the  carbonic  acid  on  the 
soda-lime  by  a  progressive  heating  of  the  contents  of  the  tubes. 
After  the  contents  of  a  have  been  kept  gently  boiling  for  about 
five  minutes,  open  the  screw  pinch-cock  slightly  more,  so  that  a 
somewhat  stronger  air-current  may  pass  through  and  completely 
remove  the  hydrogen  sulphide  and  the  carbonic  acid  and  bring 
them  into  the  absorption  tubes.  In  order  that  the  air  entering 
the  apparatus  may  be  perfectly  free  from  carbonic  acid,  pass  it 
first  through  the  potassa  solution  contained  in  q,  and  then  through 
the  soda-lime  tube  r.  An  indication  as  to  whether  the  quantity 
of  copper-sulphate  pumice  and  soda-lime  are  sufficient  for  the 
gases  evolved  is  afforded  by  observing  whether  the  copper-sul- 
phate pumice  in  the  second  absorption-tube,  k,  is  but  little  black- 
ened, and  the  soda-lime  in  the  second  tube,  ra,  is  but  slightly 
warmed. 

After  the  stronger  current  of  air  has  passed  for  fifteen  minutes 
through  the  boiling  liquid,  remove  the  heat  from  below  a,  but 
allow  the  current  of  air  to  pass  through  a  for  ten  minutes  longer. 
The  absorption-tubes  will  now  have  become  cold,  and  the  opera- 
tion is  finished.  Remove  the  tube  from  n,  close  p,  and  remove 
the  absorption-tubes  and  weigh  them.  The  increase  in  weight 
of  the  copper-sulphate  tubes  gives  the  quantity  of  hydrogen  sul- 
phide, and  that  of  the  soda  lime  tubes  gives  the  carbon  dioxide. 
If  the  directions  here  given  have  been  followed,  the  air  in  a,  e, 
etc.,  will  no  longer  have  the  odor  of  hydrogen  sulphide. 

Calculation. 

On  deducting  from  the  quantities  of  silica,  alumina,  sodium, 
carbon  dioxide,  and  sulphur  which  were  found  in  2  (i.e.,  the  total 
quantities  in  the  black  ash),  those  quantities  found  in  1  (i.e.,m  the 
solution),  the  results  will  give  the  quantities  of  these  substances 
remaining  in  the  residue.  In  the  arrangement  of  the  results 
combine  the  iron  first  with  sulphur  as  FeS;  then  combine  the 
balance  of  the  sulphur  in  the  insoluble  residue  with  calcium  as 
CaS;  the  carbonic  acid  in  the  residue  also  combine  with  calcium, 


368  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  229. 

the  remainder  of  the  calcium  being  reckoned  as  lime;  the  silica, 
alumina,  and  the  soda  in  the  residue  are  also  put  down  as  such 
as  it  is  difficult  to  determine  in  what  combinations  these  sub- 
stances exist  in  the  residue. 

The  following  ingredients  are  hence  determined  in  the  solution 
and  in  the  residue : 

Solution:  Na2C03,  NaOH,  Na2SiO3,  Na20-Al2O3,  Na2S,  Na2SO4, 
Na,S08,  and  NaCl. 

Residue:  CaS,  CaC03;  CaO,  MgO,  FeS,  Si02  A^Og,  Na20,  Carbon, 
and  Sand. 

II.    COMMERCIAL   SODA. 

Most  of  the  soda  comes  into  the  market  in  the  calcined  con- 
dition, as  "  soda-ash,"  the  far  smaller  quantity  in  the  crystallized 
form.  Regarding  the  analysis  of  soda,  particularly  soda-ash, 
the  following  points  must  be  considered: 

1.  The  collection  of  the  sample  to  be  analyzed  and  the  de- 
termination of  the  water  are  performed  precisely  as  in  the  case 
of  potash  (§  224). 

2.  The    determination   of    all    other   weighable   quantities    of 
constituents  is  effected  by  the  same  methods  recommended  for 
the  analysis  of  the  substances  in  crude  black  ash  which  go  into  so- 
lution (§  229,  I   1). 

3.  If  an  insoluble  residue  remains  on  dissolving  soda  in  water, 
it  is  collected   on  a  filter,  washed,  ignited,  weighed,  and  finally 
submitted  to  further  analysis. 

4.  If  only  the  soda  is  to  be  determined,  proceed  as  in  the  de- 
termination of  potash,   the  method   §  224,  III,   1,  usually  being 
adopted,  and  occasionally  §  224,  III,  2. 

In  the  forme-  case  the  following  must  be  noted: 
If  the  soda  contains  sodium  sulphide  the  errors  resulting  from 
its  presence  may  be  avoided  by  igniting  the  weighed  sample  of 
soda  with  potassium  chlorate,  before  neutralizing  it.  By  this 
treatment  the  sodium  sulphide,  and  also  sodium  sulphite  and 
thiosulphate,  are  converted  into  sodium  sulphate.  If  sodium 


§  229.]  SODIUM  COMPOUNDS.  369 

thiosulphate  is  present  in  considerable  quantity  this  process  is 
not  applicable  because  this  salt,  on  being  converted  into  sodium 
sulphate,  decomposes  one  equivalent  of  sodium  carbonate,  and 
expels  carbon  dioxide,  thus:  Na2S2O3  +  4O  (from  potassium  chlo- 
rate) +  Na2CO3  =  2Na2SO4  +  CO2. 

If  the  soda  is  to  be  determined  according  to  §  224,  III,  2,  the 
following  points  must  be  carefully  noted: 

If  a  soda  contains  sodium  sulphide,  sulphite,  or  thiosulphate, 
or  sodium  chloride  in  considerable  quantity,  the  injurious  influ- 
ence exerted  by  these  compounds  may  be  averted  by  proceeding 
according  to  Vol.  I,  p.  489. 

If  the  soda  contains  caustic  soda  (known  by  the  alkaline  fil- 
trate obtained  on  adding  an  excess  of  barium  chloride  to  its  solu- 
tion), the  carbon-dioxide  determination  will  give  no  indication 
as  to  the  alkali  present,  unless  the  caustic  soda  has  been  first 
converted  into  sodium  carbonate.  To  effect  this  triturate  about 
5  grm.  of  the  soda  (either  dried  or  not  dried)  with  3  to  4  parts 
of  clean  quartz  sand,  and  about  one-third  part  of  powdered  am- 
monium carbonate,  transfer  the  mixture  to  a  small  iron  dish, 
rinse  out  the  mortar  with  some  sand,  moisten  the  mass  with  as 
much  water  as  it  will  absorb,  and  allow  to  stand  for  a  short  time; 
then  heat  gently  until  all  the  water  has  been  driven  off.  The 
residue  will  now  be  free  from  any  trace  of  ammonium  carbonate. 
If  the  soda  contains  sodium  sulphide  in  addition  to  the  caustic 
soda,  moisten  the  mass  with  ammonia  water  instead  of  with  water, 
in  order  to  convert  the  ammonium  sesquicarbonate  into  neutral 
carbonate;  otherwise  ammonium  sulphide  would  be  formed, 
and  a  portion  of  the  sodium  sulphide  would  be  converted  into 
sodium  carbonate. 

When  cold,  transfer  the  mass  from  the  dish  to  the  flask  A, 
Fig.  93,  Vol.  I  (and  which  may  be  readily  done  with  the  aid  of  a 
spatula),  rinse  the  dish  with  a  little  water,  and  then  proceed  as 
usual.  The  sand  added  serves  to  prevent  the  caking  of  the  mass, 
as  well  as  the  spurting  which  would  otherwise  occur  during  the 
drying;  if  it  were  omitted,  the  drying  would  have  to  be  most 
cautiously  conducted,  and  it  would  be  exceedingly  difficult  to 


370  DETERMINATION    OF   COMMERCIAL    VALUES.          [§   229. 

completely  remove  the  dried  mass  from  the  dish  and  transfer  it 
to  the  flask.  This  transfer  is  most  easily  accomplished  by  coating 
the  inside  of  the  iron  dish  with  fine  sand  before  introducing  the 
mixture;  and  this  is  effected  by  moistening  the  inner  side  of  the 
dish  placing  some  sand  in  it,  and  shaking  out  the  excess. 

If  the  soda  contains  sodium  silicate  and  sodium  aluminate. 
they  too  are  converted  into  sodium  carbonate  by  the  treatment, 
with  ammonium  carbonate. 

Calculation  and  Arrangement  of  the  Results. 

Since  there  is  no  other  base  but  sodium  in  the  aqueous  solu- 
tion of  soda,  there  is  no  difficulty  regarding  its  calculation.  At- 
tention must,  however,  be  called  to  one  point.  All  soda  is  packed 
at  the  factories  in  the  anhydrous  condition.  Its  composition, 
as  guaranteed  by  the  manufacturers,  is  hence  based  on  its  anhy- 
drous condition.  When  the  soda  barrels  are  kept  for  a  long  time 
in  stock,  the  soda  not  infrequently  attracts  moisture,  and  the 
barrels  become  heavier,  but  the  soda,  when  sampled  and  tested, 
shows  a  lower  soda  content. 

It  is  advisable,  therefore,  in  analyses  of  soda  to  always  cal- 
culate the  soda  in  its  anhydrous  condition,  and  to  state  in  ad- 
dition the  water  content.  If  the  quantity  of  anhydrous  soda 
correspond  with  the  guaranteed  contents,  and  if  the  average 
quantity  of  moisture  (not  that  from  a  samp  e  taken  from  the 
top  of  .the  barrel)  is  in  correct  proportion  to  the  increase  in  weight 
of  the  barrel,  the  soda  may  be  considered  as  unobjectionable. 

In  the  soda  trade  the  content  is  stated  in  degrees.  As,  how- 
ever, these  degrees  represent  different  values  in  different  coun- 
tries, the  determination  of  the  price  of  soda  in  various  countries 
is,  on  this  account,  rendered  quite  difficult. 

In  Germany  a  degree  is  the  equivalent  of  1  per  cent,  of  so- 
dium carbonate,  Na2CO  =106-1;  in  France  the  GAY-LTJSSAC 
degree  represents  the  percentage  of  caustic  soda,  Na/)  =  62-l: 
the  English  degree  represents  the  percentage  of  caustic  soda  cal- 
culated from  the  equivalent  of  caustic  soda,  Na2O  =  64  (the  ratio 
between  sodium  carbonate  and  caustic  soda  is  106  •  1  :  62  •  86) 


§  230.]  SODIUM  COMPOUNDS.  371 

was  formerly  considered  as  correct,  and  is  still  retained,  although 
now  known  to  be  incorrect  Lastly,  the  DESCROIZILLES'  degree 
indicates  how  many  parts  by  weight  of  hydrated  sulphuric  acid 
(H^SO4=98-086)  are  neutralized  by  100  parts  of  soda. 

The  various  degrees  bear  the  following  relations  to  each  other: 
106  •  1  German  are  equal  to  62  •  1  of  GAY-LUSSAC'S,  or  62  •  86  Eng- 
lish, or  49-043  DESCROIZILLES'. 

Whichever  degrees  are  therefore  used  in  stating  the  soda  con- 
tent it  is  certain  that  in  every  case  all  the  soda  compounds  that 
neutralize  acids  are  calculated,  according  to  circumstance, 
as  sodium  carbonate,  caustic  soda,  or  soda  capable  of  neutraliz- 
ing sulphuric  acid ;  .e  ,  not  only  the  sodium  carbonate  and  caus- 
tic soda,  but  also  the  sodium  silicate  and  sodium  aluminate. 

B.  SODIUM  CHLORIDE  (COMMON  SALT). 
§230. 

In  commercial  alt  there  are  found,  as  a  rule,  appreciable 
quantitie  of  the  following  constituents:  In  the  portion  soluble 
in  water:  Sodium,  magnesium,  calcium,  chlorine,  and  sulphuric 
acid.  In  the  portion  insoluble  in  water:  Calcium  carbonate,  silica, 
alumina,  and  ferric  oxide. 

There  are  also  found  in  small  quantities  potassium,  ammo- 
nium, bromine,  organic  matter,  etc. 

Regarding  the  taking  of  the  sample,  what  has  been  stated 
under  potash  applies  here  equally  (p.  337). 

Reduce  the  salt  by  trituration  to  a  uniform  powder,  and  put 
this  into  a  ctoppered  bottle. 

a.  Wei^h  off  10  grm.  of  the  powder,  and  dissolve  in  a  beaker 
by  digestion  with  water;  filter  the  solution  into  a  >litre  flask, 
and  thoroughly  wash  the  small  residue  which  generally  remains. 
Finally,  fill  the  flask  with  water  up  to  the  mark,  and  shake  the 
fluid. 

If  small  white  grains  of  calcium  sulphate  are  left  on  dissolving 
the  salt,  reduce  them  to  powder  in  a  mortar,  add  water,  let  the 


372  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  230. 

mixture  digest  for  some  time,  decant  the  clear  supernatant  fluid 
on  to  a  filter,  triturate  the  undissolved  deposit  again,  add  water, 
etc.,  and  repeat  the  operation  until  complete  solution  is  effected. 

b.  Ignite  and  weigh  the  dried  insoluble  residue  of  a,  and  sub- 
ject it  to  a  qualitative  examination,  more  especially  with  a  view 
to  ascertain  whether  it  is  perfectly  free  from  calcium  sulphate. 

c.  Of  the  solution  a  measure    off  successively  the  following 
quantities  : 

For  d.    50  c.c.  corresponding  to  1  grm.  of  common  salt. 
"    e.  150  c.c.  "  "  3     "      "         "          " 

"    f.  150  c.c.  "  "  3     "      "        "         " 

"    g.    50  c.c.  "  "  1 


"      "         "          " 


d.  Determine,  in  the  50  c.c.  measured  off,  the  chlorine  as  directed 
in  §  141,  I,  a  or  6. 

e.  Determine,  in  the  150  c.c.  measured  off,,  sulphuric  acid  as 
directed  in  §  132,  I,  1. 

/.  Determine,  in  the  150  c.c.  measured  off,  the  calcium  and 
magnesium  as  directed  in  §  154,  B,  6,  [36]. 

g.  Mix  the  50  c.c.  measured  off  in  a  platinum  dish  with  about 
0-5  c.c.  of  pure  concentrated  sulphuric  acid,  and  proceed  as  di- 
rected in  §  98,  1.  The  neutral  residue  contains  the  sulphates  of 
sodium,  calcium,  and  magnesium.  Deduct  from  this  the  quantity 
of  the  two  latter  substances  resulting  from  /;  the  remainder  is 
sodium  sulphate. 

h.  Determine,  in  another  weighed  portion  of  the  salt,  the  water 
as  directed  in  §  35,  a,  a  (at  the  end). 

i.  Bromine,  potassium,  and  other  bodies,  of  which  only  very 
minute  traces  are  found  in  common  salt,  are  determined  by  the 
methods  described  in  the  analysis  of  mineral  waters. 

Calculation. 

The  sulphuric  acid  is  first  combined  with  the  calcium,  then 
with  the  magnesium.  If  there  is  any  remainder  of  sulphuric 
acid,  it  is  combined  with  potassium,  if  this  has  been  determined, 
and  then  with  sodium.  If,  on  the  other  hand,  there  is  a  balance 


§  231.J  SODIUM  COMPOUNDS.  373 

of  magnesium,  it  is  calculated  as  magnesium  chloride.  This 
mode  of  arrangement  is  in  agreement  with  that  adopted  in  the 
case  of  potassium  chloride  (p.  343),  and  is  based  upon  the  fact 
that  when  magnesium  chloride  and  sodium  sulphate  are  dis- 
solved in  water  and  the  solution  is  evaporated,  sodium  chloride 
separates  out.  I  would  mention,  however,  that  in  the  published 
analyses  of  salt  there  is  an  entire  lack  of  agreement  as  to  the 
manner  in  which  the  various  bases  and  acids  have  been  com- 
bined. 

C.  SODIUM  SULPHATE  (SALT-CAKE). 
§  231. 

The  impure  sodium  sulphate  which  formed  in  the  salt-cake 
furnaces  by  the  action  of  sulphuric  acid  on  common  salt  is  found 
in  the  market  under  the  name  of  "salt-cake."  It  is  used  not 
only  for  the  manufacture  of  soda,  but  is  sent  into  the  market 
as  such,  and  in  large  quantities,  as  it  is  used  particularly  in  the 
manufacture  of  glass.  Smaller  quantities  serve  for  the  prepara- 
tion of  crystallized  GLAUBER'S  salt. 

Salt-cake  contains  as  a  rule  the  following  constituents  in 
weighable  quantities : 

Neutral  sodium  sulphate,  frequently  also  some  sodium  bisul- 
phate,  ferric  sulphate,  aluminium  sulphate,  calcium  sulphate, 
magnesium  sulphate,  sodium  chloride,  and  a  residue  insoluble 
in  water. 

The  sampling  is  done  as  in  the  case  of  potash  (p.  337). 

1.  Determination  of  Moisture.  If  the  sample  yields  acid  vapors 
when  heated  in  a  glass  tube,  the  quantity  of  water  cannot  be 
ascertained  from  the  loss  in  weight  on  ignition,  but  if  must  be 
determined  as  described  in  §  225,  I. 

2.  Treat  about  10  grm.  of  the  sample  with  100  c.c.  of  cold 
water  until  the  greater  part  is  dissolved,  then  filter  into  a  500-c.c. 
flask,  and  thoroughly  wash  the  residue  with  cold  water.     Should 
the  filtrate  be  cloudy,  add  first   a  little  hydrochloric  acid,  then 
fill  up  with  water  to  the  mark,  and  mix. 


374  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  231. 

3.  Ignite  the  undissolved  residue,  weigh,  and  examine  further 
according  to  circumstances. 

4.  In  50  c.c.  of  the  solution  determine  the  sulphuric  acid  ac- 
cording to  §  132,  I,  1,  or  2,  e. 

5.  Add  some  ammonium  chloride  to  100  c.c.  of  the  liquid, 
heat  with  addition  of  ammonia,  and  determine  the  ferric  oxide 
alumina,  calcium,  and  magnesium  according  to  §  229, 1,  2,  b  (p.  364) . 

6.  Add  two  drops  of  pure  concentrated  sulphuric  acid  to  50  c.e, 
of  the  solution  in  a  weighed  platinum  dish,  evaporate  to  dryness, 
ignite  (finally  in  an  atmosphere  of  ammonium  carbonate,  §  97,  1), 
and  weigh.     After  deducting  the  calcium  and  magnesium  (cal- 
culated as  sulphates),  and  iron  and  aluminium  (as  oxides),  the 
residue  gives  the  caust  c  soda  from  the  weight  of  -the  sodium  sul- 
phate.     (This  determination  is  not  absolutely  necessary  if  the 
determination  given  in  8  is  adopted,  because  the  caustic-soda 
content  may  be  calculated  from  the  chlorine  and  sulphuric  acid; 
it  furnishes,  however,  a  good  control). 

7.  Determine  the  chlorine  in  100  c.c.  of  the  liquid  (§  141,  I,  a 
or  6,  a),  provided  hydrochloric  acid  has  not  been  added  in  2.     If 
this  has  been  done,  the  chlorine  must  be  determined  by  treating 
a  fresh  quantity  of    the  substance  with  water  and  adding  nitric 
acid  to  the  filtrate  instead  of  hydrochloric  acid. 

8.  Although    the    sodium  bisulphate  present  is  already  given 
by  the  calculation— presupposing  the  determination  of  the  caustic 
soda— it  is  nevertheless  advisable  to  make  a  direct  determina- 
tion.    For  this  purpose  dissolve  about  5  grm.  of  the  salt-cake 
in   the  least  possible  quantity  of  cold  water,  and  without  filtering 
add  about  9  grm.  crystallized  barium  chloride,  then  a  little  litmus 
tincture,  .and  finally  from  a  burette,   decinormal  soda  solution 
just  to  incipient  alkalinity.     On  deducting  from  the  soda  solu- 
tion   used  up  the  equivalent  quantity  of   sulphuric  acid,  corre- 
sponding; with  the  ferric  .and   aluminium  sulphates  (FeSO4  and 
AUS04]3),  the  acid  which  is  combined  as  hydrate  with  neutral 
sodium  sulnhate  to  form  sodium  bisulnhate    (Na-jSCX  +  NaHSOj, 
is    obtained.    Regarding   the   addition  of   barium    chloride,    see 
p.  313,  c. 


§  232.]  BARIUM  COMPOUNDS.  375 

6.  BARIUM  COMPOUNDS. 

HEAVY  SPAR. 
§232. 

Heavy  spar  is  employed  partly  as  an  adulterant  of  white  lead, 
etc.,  and  partly  for  the  preparation  of  barium  chloride  and  other 
barium  compounds.  If  it  is  not  perfectly  pure  white  when 
ground,  it  is  useless  for  the  former  purpose,  and  its  purity  must 
be  unquestioned,  if  it  is  to  be  used  for  the  latter  purpose. 

Heavy  spar  must,  therefore,  frequently  be  examined  analytic- 
ally. As  a  rule,  it  contains,  besides  barium  sulphate,  the  folow- 
ing  constituents  in  weighable  quantities:  Calcium  sulphate, 
strontium  sulphate,  ferric  oxide,  alumina,  silica,  and  moisture 

1.  The  moisture  is  determined  most  simply  by  gently  igniting 
a  sample  of  about  2  grm.  in  a  platinum  crucible. 

2.  Mix  the  ignition-residue  from  1  with  four  times  its  quan- 
tity of  potassium  and  sodium  carbonates,  fuse,   and  treat  the 
melt  with  water  (§  132,  II,  6,  a). 

3.  Cautiously  neutralize  the  solution  obtained  in  2  with    hy- 
drochloric acid,  heat  to  drive  off  the  carbon  dioxide,  evaporate 
to  dryness,  separate  the  silica  (§  140,  II,  a),  and  in  the  filtrate 
determine  the  sulphuric  acid  (§  132). 

4.  Dissolve  the  residue  remaining  in  2  in  diluted  hydrochloric 
acid,  evaporate  to  dryness,  treat   the   residue  with  hydrochloric 
acid,  separate  the  remainder  of  the  silica  (§  140.  II,  a),  and  in 
the  nitrate  precipitate  the  ferric  oxide  and  alumina  by  adding 
ammonia    (§  161,  4).     After    moderately   washing,  dissolve    the 
residue  again  in  hydrochloric  acid,  heat,  again  precipitate  with 
ammonia,  filter,  dry,  ignite,  and  determine  the  ferric  oxide  and 
alumina  according  to  §  160,  B,  12. 

5.  Neutralize    with    hydrochloric  '  acid    the    filtrate    obtained 
in  4,  and  containing  the  alkaline  earths,  heat,  and  add  diluted 
hydrochloric    acid   in   slight   excess.     After   the   precipitate   has 
settled  completely,  pour  the  supernatant  liquid  through  a  filter 


376  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  233. 

(Filtrate  I).  As  soon  as  this  has  been  done,  treat  the  bulk  of  the 
precipitate  which  has  remained  in  the  beaker  as  well  as  that  which 
has  gone  on  the  filter,  and  without  previously  washing,  with  am- 
monium carbonate  (§  154,  B,  3).  To  effect  this,  close  the  stem 
of  the  funnel  containing  the  filter.  After  twelve  hours  remove 
the  stopper,  allow  the  liquid  to  run  off,  and  transfer  the  contents 
of  the  beaker  (Filtrate  II)  together  with  the  precipitate  to  the 
filter,  wash  the  precipitate,  and  treat  it  with  very  dilute  hy- 
drochloric acid.  The  liquid  which  passes  through  now  mix  with 
Filtrates  I  and  II ;  dry  the  precipitate,  however,  which  is  now  pure 
barium  sulphate,  weigh,  and  calculate  the  barium. 

6.  Concentrate  the  united  filtrates  from  5,  taking  care  that 
the  liquid  is  just  acid,  add  4  volumes  of  alcohol,  allow  to  stand 
for  12  hours,  filter,  wash  with  alcohol,  and  finally  separate  the 
calcium  and  strontium  in  the  precipitate  by  ammonium  sulphate 
(§  154,  B,  5). 

7.  CALCIUM  COMPOUNDS. 

A.  CALCIUM  PHOSPHATE  (PHOSPHORITE,  ETC.). 

(See  V.    Analysis  of  Manures.) 

B.  CHLORINATED  LIME. 

§233. 

The  "chloride  of  lime,"  or  "bleaching  powder"  of  commerce, 
contains  calcium  hypochlorite,  calcium  chloride,  and  calcium 
hydroxide.  The  two  latter  ingredients  are  for  the  most  part 
combined  with  one  another  as  calcium  oxy chloride.  In  freshly 
prepared  and  perfectly  normal  chlorinated  lime,  the  quantities  of 
calcium  hypochlorite  and  calcium  chloride  present  stand  to  each 
other  in  the  proportion  of  their  mol.  weights.  When  such  chlo- 
rinated lime  is  brought  into  contact  with  dilute  sulphuric  acid, 
the  whole  of  the  chlorine  it  contains  is  liberated  in  the  elemen- 
tary form,  in  accordance  with  the  following  equation: 

(CaCl202  +  CaCl2)  +  2H2SO4  =  2CaSO4 + 2H20 + 4C1. 
On  keeping  chlorinated  lime,  however,  the  proportion  between 
calcium  hypochlorite  and   calcium  chloride  gradually  changes — 


§  233.J  CALCIUM    COMPOUNDS.  377 

the  former  decreases,  the  latter  increases.  Hence,  from  this  cause 
alone,  to  say  nothing  of  original  difference,  the  commercial  article 
is  not  of  uniform  quality,  and  on  treatment  with  acid  gives  some- 
times more  and  sometimes  less  chlorine. 

As  the  value  of  this  article  depends  entirely  upon  the  amount 
of  chlorine  set  free  on  treatment  with  acid,  chemists  have  devised 
various  simple  methods  of  determining  the  available  quantity  of 
chlorine  in  any  given  sample.  These  methods  have  collectively 
received  the  name  of  Chlorimetry. 

The  number  of  chlorimetric  methods  proposed  is  so  great 
that  I  cannot  give  them  all  here,  hence  only  those  will  be  described 
which  are  characterized  either  by  the  ease  with  which  they  may 
be  carried  out  or  by  the  accuracy  of  the  results  afforded  by  them. 

GAY-LUSSAC'S  method,  which  depends  upon  the  conversion 
of  arsenous  acid  into  arsenic  acid  in  hydrochloric-acid  solution, 
and  in  which  indigo  solution  is  used  as  an  indicator,  was  dropped 
from  the  Sixth  Edition  because  it  is  surpassed  by  PENOT'S  method 
both  in  convenience  and  in  accuracy. 

Before  proceeding  to  a  description  of  the  method,  I  would 
point  out  that  the  results  obtained  in  testing  chlorinated  lime 
are  expressed  in  various  ways.  While  it  is  usual  scientifically 
to  characterize  a  chlorinated  lime  according  to  its  percentage 
content  of  available  chlorine,  in  practice  it  is  usual  to  quote  and 
sell  it  by  chlorimetric  degrees.  This  mode  of  expression,  origi- 
nating with  GAY-LUSSAC,  denotes  how  many  litres  of  chlorine 
gas  at  0°  and  760  mm.  pressure  are  contained  in  1000  grm.  of 
chlorinated  lime. 

Both  modes  of  expression  may  be  easily  compared  with  each 
other,  since  we  know  that  1  litre  of  chlorine  at  0°  and  760  mm. 
weighs  3-16636  grm.  For  instance,  a  chlorinated  lime  of  90° 
contains  3-16636X90  =  284-97  grm.  chlorine  in  1000  grm.,  hence 
28-5  per  cent.;  and  a  chlorinated  lime  containing  34-2  per  cent, 
of  chlorine  is  108-01°;  for,  since  100  grm.  contain  34-2  chlorine, 

342 
1000  grm.  will  contain  342.    These,  however,  =3<16636;  *•*•»  = 

108-01  litres. 


378  DETERMINATION   OF   COMMERCIAL  VALUES.          [§  233. 


Preparation  of  the  Solution  of  Chlorinated  Lime. 

The  solution  is  prepared  alike  for  all  methods,  and  best  in 
the  following  manner: 

Weigh  off  10  grm.,  triturate  finely  with  a  little  water,  add 
gradually  more  water,  pour  the  liquid  into  a  litre  flask,  triturate 
the  residue  again  with  water,  and  rinse  the  contents  of  the  mortar 
carefully  into  the  flask;  fill  the  latter  to  the  mark,  shake  the 
milky  fluid,  and  examine  it  at  once  in  that  state,  i.e.,  without 
allowing  it  to  deposit;  and  every  time,  before  measuring  off  a 
fresh  portion,  shake  again.  The  results  obtained  with  this  turbid 
solution  are  much  more  constant  and  correct  than  when,  as  is1 
usually  recommended,  the  fluid  is  allowed  to  deposit,  and  the 
experiment  is  made  with  the  supernatant  clear  portion  alone. 
The  truth  of  this  may  readily  be  proved  by  making  two  separate 
experiments,  one  with  the  decanted  clear  fluid  and  the  other 
with  the  residuary  turbid  mixture.  Thus,  for  instance,  in  an 
experiment  made  in  my  own  laboratory,  the  decanted  clear  fluid 
gave  22-6  of  chlorine,  the  residuary  mixture  25-0,  the  uniformly 
mixed  turbid  solution  24-5. 

One  c.c.  of  the  solution  of  chlorinated  lime  so  prepared  corre- 
sponds to  0-01  grm.  chlorinated  lime. 

RUD.  WAGNER*  recommends  preparing  the  chlorinated-lime 
solution  by  shaking.  He  shakes  together  10  grm.  of  the  chlori- 
nated lime  with  coarsely  powdered  glass  (pieces  of  broken-up 
glass  rods  about  5  to  10  mm.  long)  and  water  in  a  strong  flask, 
until  the  chlorinated  lime  is  completely  divided.  The  volume 
occupied  by  the  pieces  of  glass  must  be  previously  determined  in 
a  glass  measuring  cylinder  by  pouring  over  them  a  measured 
quantity  of  water.  The  milky  liquid,  together  with  the  glass, 
is  rinsed  into  a  litre  flask  and  diluted  to  measure  1  litre  at  17-5°; 
a  volume  of  water  equal  to  that  occupied  by  the  glass  is  then 
added  and  the  whole  shaken.  One  c.c.  of  this  solution,  there- 
fore, corresponds  also  with  0-01  grm.  chlorinated  lime. 

*  Zeitschr.  /.  analyt.  Chem.,  iv,  223. 


§  233.]  CALCIUM   COMPOUNDS.  379 

A.  PENOT'S  METHOD.* 

This  method,  like  that  of  the  older  one  of  GAY-LUSSAC,  is 
based  upon  the  conversion  of  arsenous  acid  into  arsenic  acid,  or, 
more  strictly,  an  arsenite  into  an  arsenate,  since  the  conversion 
is  effected  in  an  alkaline  solution.  Potassium  iodide-starch  paper 
is  employed  to  ascertain  the  exact  point  when  the  reaction  is 
completed. 

a.  Preparation  of  the  Potassium  Iodide-Starch  Paper. 

The  following  method  is  preferable  to  the  original  one  given 
by  PENOT: 

Stir  3  grm.  of  potato  starch  in  250  c.c.  of  cold  water,  boij  with 
stirring,  add  a  solution  of  1  grm.  potassium  iodide  and  1  grm. 
crystallized  sodium  carbonate,  and  dilute  to  500  c.c.  Moisten 
strips  of  fine  white  unsized  paper  with  this  fluid  and  dry.  Keep 
in  a  closed  bottle. 

b.  Preparation  of  the  Solution  of  Arsenous  Add. 

Dissolve  4-4213  grm.  of  pure  arsenous  oxide,  (A^O,,),  and  13 
grm.  pure  crystallized  sodium  carbonate  in  600-700  c.c.  water, 
with  the  aid  of  heat,  let  the  solution  cool,  and  then  dilute  to  1 
litre.  Each  c.c.  of  this  solution  contains  an  amount  of  sodium 
arsenite  equivalent  to  0-0044213  grm.  arsenous  oxide,  (As2Og), 
which  corresponds  to  1  c.c.  chlorine  gas  of  0°  and  760  mm.  at- 
mospheric pressure.f 

*  Bulletin  de  la  Sodete  Industriette  de  Mulhcwse,  1852,  No.  118. — DINO 
LER'S  Polytech.  Journal,  cxxvn,  134. 

f  PENOT  gives  the  quantity  of  arsenous  oxide  as  4  •  44 ;  but  this  number 
has  been  corrected  to  4-4213,  in  accordance  with  the  atomic  weights  of 
the  substances  used  in  this  book  and  specific  gravity  of  chlorine  gas — after 
the  following  proportion: 

141-8  (4  at.  Cl):  198  (1  mol.  AsA)::  3-16636  (weight  of  1  litre  of  chlorine 
gas) :  x ;  x= 4  -  4213,  i.e. ,  the  quantity  of  arsenous  oxide  which  1  litre  of  chlorine 
gas  converts  into  arsenic  acid. 

This  solution  is  arranged  to  suit  the  foreign  method  of  designating  the 
strength  of  chlorinated  lime,  viz.,  in  chlorimetrical  degrees  (each  degree 
represents  1  litre  of  chlorine  gas  at  0°  and  760  mm.  pressure  in  a  kilogramme 


380  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  233. 

As  sodium  arsenite  in  alkaline  solution  is  liable,  when  exposed 
to  access  of  air,  to  be  gradually  converted  into  sodium  arsenate, 
PENOT'S  solution  should  be  kept  in  small  bottles  with  glass  stoppers, 
filled  to  the  top,  and  a  fresh  bottle  used  for  every  new  series  of 
experiments.  According  to  FR.  MOHR  *  the  solution  keeps  un- 
changed if  the  arsenous  oxide  and  the  sodium  carbonate  are 
both  absolutely  free  from  oxidizable  matters  (arsenous  sulphide, 
sodium  sulphide,  and  sodium  sulphite). 

c.  The  Process. 

Measure  off  with  a  pipette  50  c.c.  of  the  solution  of  chlo- 
rinated lime  prepared  according  to  the  directions  in  §  233,  transfer 
to  a  beaker,  and  from  a  50-c.c.  burette  add  slowly,  and  at  last 
drop  by  drop,  the  solution  of  arsenous  acid,  with  constant 
stirring,  until  a  drop  of  the  mixture  produces  no  longer  a 
blue-colored  spot  on  the  iodized  paper;  it  is  very  easy  to  hit 
the  point  exactly,  as  the  gradually  increasing  faintness  of  the  blue 
spots  made  on  the  paper  by  the  fluid  dropped  on  it  indicates  the 
approaching  termination  of  the  reaction,  and  warns  the  operator 
to  confine  the  further  addition  of  the  solution  of  arsenous  acid 
to  a  single  drop  at  a  time..  The  number  of  J  c.c.  used  indicates 
directly  the  number  of  chlorimetrical  degrees  (see  note),  as  the 
following  calculation  shows:  If  you  have  used  40  c.c.  of  solu- 
tion of  arsenous  acid,  then  the  quantity  of  chlorinated  lime 
used  in  the  experiment  contains  40  c.c.  of  chlorine  gas.  Now 
the  50  c.c.  of  solution  employed  correspond  to  0-5  grm.  of  chlo- 
rinated lime;  therefore  0-5  grm.  of  chlorinated  lime  contain 

of  the  substance).  This  method  was  proposed  by  GAY-LUSSAC.  The  de- 
grees may  readily  be  converted  into  per  cents.,  and  vice  versa,  thus:  A  sample 
of  chlorinated  lime  of  90°  contains  90X3-16636=284-97  grm.  chlorine 
in  1000  grm.  or  28  •  50  in  100 ;  and  a  sample  containing  34  •  2  per  cent,  chlorine 
is  of  108-01°,  for  100  grm.  of  the  substance  contain  34-2  grm.  chlorine;  .  . 
1000  grm.  of  the  substance  contain  342  grm.  chlorine,  but  342  grm.  chlorine 

342 

=  ;r-—— litres  =108 -01   litres;   .'.    1000  grm.    of    the    substance    contain 
3-16636 

108-01  litres  chlorine. 

*  Lehrbuch  der  Titrirmethode,  5.  Aufl.,  S.  325. 


§  233.]  CALCIUM  COMPOUNDS.  381 

40  c.c.  chlorine  gas,  therefore  1000  grm.  contain  80,000  c.c.  =  80 
litres.  This  method  gives  very  constant  and  accurate  results,  and 
appears  to  be  particularly  well  suited  for  use  in  manufacturing 
establishments  where  there  is  no  objection  on  the  score  of  dan- 
ger in  the  employment  of  arsenous  acid. 

B.    MOHR'S    MODIFICATION  OF   PENOl's   METHOD.* 

The  principle  of  this  modification  is  as  follows:  Measure  off 
a  definite  quantity  of  the  chlorinated-lime  solution,  add  a  meas- 
ured quantity  of  a  standardized  solution  of  potassium  arsenite 
in  excess,  and  then  determine  the  excess  of  potassium  arsenite 
with  iodine  (§  127,  5). 

MOHR  employs  a  decinormal  potassium-arsenite  solution,  and 
a  corresponding  decinormal  iodine  solution.  The  former  is  pre- 
pared by  digesting  4-95  grm.  (one-fourth  of  the  one-tenth  equiv- 
alent, because  1  eq.  of  As2O3  is  converted  into  As-jOg  by  4  eq. 
of  iodine)  of  pure  powdered  arsenous  acid  in  about  200  c.c.  of 
water  and  5  to  10  grm.  of  potassium  bicarbonate  and  shaking 
until  the  greater  part  of  the  arsenous  acid  is  dissolved.  Then 
pour  off  the  liquid  into  a  litre  flask  and  dissolve  the  residual 
arsenous  acid  in  water  with  the  addition  of  a  small  quantity  of 
potassium  bicarbonate,  add  20  to  25  grm.  more  of  potassium 
bicarbonate,  and  make  up  the  whole  to  measure  1  litre  and  shake. 
One  c.c.  corresponds  to  0-003545  grm.  chlorine,  i.e.,  the  arsenous 
acid  contained  in  1  c.c.  will  be  converted  into  arsenic  acid  by 
0.003545  grm.  chlorine. 

The  iodine  solution  is  prepared  by  dissolving  6-4  grm.  of 
iodine  by  means  of  about  9  grm.  of  potassium  iodide  in  sufficient 
water  to  measure  500  c.c. ;  the  solution  is  then  standardized  against 
the  arsenous-acid  solution  (§  127,  5),  and  diluted  to  agree  with  it. 

In  the  valuation  of  chlorinated  lime  it  is  convenient  to  use 
50  c.c.  of  the  chlorinated-lime  solution  prepared  as  above.  To 
this  add  potassium-arsenite  solution  until  a  drop  of  the  liquid 
no  longer  causes  a  blue  spot  on  potassium  iodide-starch  paper, 

*  Lehrbuch  der  Titrirmethode,  5th  edit.,  p.  321. 


382  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  233. 

then  dilute  with  150  to  200  c.c.  water,  add  some  ammonium- 
bicarbonate  solution  prepared  in  the  cold,  then  some  starch  solu- 
tion, and  lastly  some  iodine  solution  until  the  blue  color  of  starch 
iodide  develops,  and  remains  even  on  adding  a  small  quantity 
of  ammonium  carbonate.  Deduct  the  c.c.  of  iodine  solution 
used  from  those  of  the  potassium-arsenite  solution,  and  thus 
ascertain  how  many  c.c.  of  the  latter  solution  have  been  oxidized 
by  the  chlorinated  lime.  These  c.c.  multiplied  by  0-003545  give 
the  chlorine  content  of  0-5  grm.  of  the  chlorinated  lime. 

This  method  gives  good  results,  but  certainly  will  not  super- 
sede PENOT'S  method,  which  is  simpler  and  equally  as  accurate. 

C.   IODOMETRIC   METHODS. 

In  his  treatise  on  "A  Volumetric  Method  of  Very  General 
Applicability,*  BUNSEN  remarked  that  hypochlorites,  and  par- 
ticularly chlorinated  lime,  could  very  well  be  analyzed  by  adding 
an  excess  of  potassium-iodide  solution  to  the  solution  of  the  salt, 
then  adding  hydrochloric  acid  to  slightly  acid  reaction,  and  then 
determining  the  iodine  volumetrically.  For  this  purpose  BUN- 
SEN  employed,  as  is  well  known,  an  aqueous  solution  of  sulphurous 
acid. 

Later  on  most  chemists  preferred  to  use  sodium  thiosulphate, 
as  first  proposed  by  H.  ScHWARZ,f  instead  of  the  aqueous  solu- 
tion of  sulphurous  acid  for  the  iodine  determination;  and  it  is 
thus  that  the  iodometric  method  described  in  §  146  originated. 
This  "combined  method"  of  iodine  determination,  which  is  de- 
scribed elsewhere,  has  also  been  specially  recommended  for  chlo- 
rinated-lime determinations  by  R.  WAGNER. J  FR.  MOHR  §  de- 
clared WAGNER'S  method  to  be  inaccurate,  but  CL.  WINKLER  || 

*  Annal.  d.  Chem.  u.  Pharm.,  LXXXVI,  277. 

f  Anleiten  zu  Maasanalysen,  Supplement,  Brunswig,  FR.  VIEWEG  &  SOHN, 
1853,  p.  21. 

t  DINGL.  polyt.  Journ.,  CLTV,  p.  146,  and  CLXXVI,  p.  131. 

§  Lehrbuch  der  Titrirmethode,  2.  Aufl.  i,  254;  also  Z&itschr.  /.  analyt. 
Chem.,  vui,  311 

!!  DINGL.  volyt.  Journ.,  CXLIII,  198. 


§  233.]  CALCIUM    COMPOUNDS.  383 

pointed  out  why  MOHR  had  obtained  varying  results,  and  proved, 
as  WAGNER  had  already  done,  that  when  the  iodometric  method 
is  correctly  carried  out,  it  also  gives  exceedingly  good  results 
when  sodium  thiosulphate  is  used.  This  opinion  I  must  con- 
firm and  would  advise  the  following  procedure: 

To  10  c.c.  of  the  chlorinated-lime  solution  containing  0-1 
grm.  chlorinated  lime  prepared  as  above  and  contained  in  a  beaker, 
add  first  about  100  c.c.  of  water,  then  about  6  c.c.  of  potassium- 
iodide  solution  (containing  0-6  grm.  KI  and  prepared  accord- 
ing to  Vol.  I,  p.  544,  7-)  acidulated  with  hydrochloric  acid,  and 
determine  the  liberated  iodine  according  to  §  146.  Since  1  eq. 
of  iodine  corresponds  to  1  eq.  of  chlorine,  the  calculation  is  quite 
easy. 

R.  WAGNER  recommends  using  2  •  5  grm.  of  potassium  iodide 
to  1  grm.  chlorinated  lime  dissolved  in  100  c.c.  of  water,  and  to 
add  hydrochloric  acid  only  to  faintly  acid  reaction.  Although 
an  unnecessarily  large  excess  of  acid  is  not  to  be  recommended, 
yet  there  is  no  need  to  be  so  very  careful  in  acidulating.  WINKLER 
(loc.  cit.)  obtained  equally  good  results  whether  he  added  1,  5,  10, 
or  20  c.c.  of  hydrochloric  acid  to  10  c.c.  of  the  chlorinated-lime 
solution. 


D.  OTTO'S  METHOD. 

The  principle  of  this  method  is  as  follows: 

Two  molecules  of  ferrous  sulphate  when  brought  into  contact 
with  chlorine  in  presence  of  water  and  free  sulphuric  acid  give  1 
mol.  ferric  sulphate  and  2  mol.  HC1,  the  process  consuming  2  at. 
chlorine: 

Fe2(S04)3+2HCl. 


One  mol.  crystallized  ferrous  sulphate,  (FeSO4-7H2O)=278-082, 
corresponds  to  35-45  of  chlorine,  or,  in  other  terms,  0-7844  gnu. 
crystallized  ferrous  sulphate  corresponds  to  0-1  grm.  chlorine. 

The  ferrous  sulphate  required  for  these  experiments  is  best 
prepared  as  follows: 


384  DETERMINATION    OF    COMMERCIAL    VALUES.          [§   .233 

Take  iron  nails  free  from  rust  and  dissolve  in  dilute  sulphuric 
acid,  applying  heat  in  the  last  stage  of  the  operation;  filter  the 
solution,  still  hot,  into  about  twice  its  volume  of  common  alcohol. 
The  precipitate  consists  of  FeSO4  +  7H2O. 

Collect  upon  a  filter,  wash  with  common  alcohol,  spread  upon  a 
sheet  of  blotting-paper,  and  dry  in  the  air.  When  the  mass  smells 
no  longer  of  alcohol,  transfer  to  a  bottle  and  keep  this  well 
corked.  Instead  of  ferrous  sulphate,  ammonium  ferrous  sulphate, 
FeS04(NH4)2SO4  +  6H2O,  may  be  used.  0  •  1  grm.  of  chlorine  reacts 
with  1-1066  grm.  of  this  double  sulphate. 

The  Process.  Dissolve  3-1376  grm.  (4x0-7844  grm.)  of  the 
precipitated  ferrous  sulphate,  or  4-4264  grm.  (4x1-1066  grm.)  of 
ammonium  ferrous  sulphate,  with  addition  of  a  few  drops  of  dilute 
sulphuric  acid,  in  water,  to  200  c.c. ;  take  out  with  a  pipette  50  c.c., 
corresponding  to  0-7844  grm.  ferrous  sulphate,  or  1-1066  grm. 
ammonium  ferrous  sulphate,  dilute  with  150-200  c.c.  water,  add  a 
sufficiency  of  pure  hydrochloric  acid,  and  run  in  from  a  50-c.c. 
burette  the  freshly  shaken  solution  of  chlorinated  lime,  prepared 
according  to  §  225,  until  the  ferrous  sulphate  is  completely  con- 
verted into  ferric  sulphate.  To  know  the  exact  point  when  the 
reaction  is  completed,  place  a  number  of  drops  of  a  solution  of 
potassium  ferricyanide  on  a  plate,  and  when  the  operation  is 
drawing  to  an  end  apply  some  of  the  mixture  with  a  stirring-rod 
to  one  of  the  drops  on  the  plate,  and  observe  whether  it  produces 
a  blue  precipitate;  repeat  the  experiment  after  every  fresh  addi- 
tion of  two  drops  of  the  solution  of  chlorinated  lime.  When  the 
mixture  no  longer  produces  a  blue  precipitate  in  the  solution  of 
potassium  ferricyanide  on  the  plate,  read  off  the  number  of  volumes 
used  of  the  solution  of  chlorinated  lime. 

The  quantity  of  solution  of  chlorinated  lime  used  contained  0  •  1 
grm.  of  chlorine.  Suppose  40  c.c.  have  been  used;  as  every  c.c. 
corresponds  to  0-1  grm.  of  chlorinated  lime,  the  percentage  by 
weight  of  available  chlorine  in  the  chlorinated  lime  is  found  by  the 
following  proportion: 

0-40:0-1  ::100  :x;  x  =  25; 


§  233.]  CALCIUM   COMPOUNDS.  385 

or  by  dividing  1000  by  the  number  of  c.c.  used  of  the  solution  of 
chlorinated  lime. 

This  method  also  gives  very  satisfactory  results,  provided 
always  that  the  ferrous  salt  is  perfectly  dry  and  free  from  ferric 
salt. 

Modifications  of  the  preceding  Method. 

1.  Instead  of  the  solution  of  ferrous  sulphate,  a  solution  of 
ferrous  chloride,  prepared  by  dissolving  pianoforte  wire  in  hy- 
drochloric acid  (according  to  Vol.  I,  p.  318, /?),  may  be  used  with 
the  best  results.     If  0-6307  of  pure  metallic  iron,  i.e.,  0-6326  of 
fine  pianoforte  wire  (which  may  be  assumed  to  contain  99-7  per 
cent,  of  iron),  are  dissolved  to  200  c.c.,  the  solution  so  prepared 
contains  exactly  the  same  amount  of  iron  as  the  solution  of  fer- 
rous sulphate  above  mentioned — that  is  to  say,  50  c.c.  of  it  corre- 
sponds to  0- 1  grm.  chlorine.      But  as  it  is  inconvenient  to  weigh  off 
a  definite  quantity  of  iron  wire,  the  following  course  may  be  pur- 
sued in  preference:    Weigh  off  about  0-15  grm.,  dissolve,  dilute 
the  solution  to  about  200  c.c.,  convert  the   ferrous  into  ferric 
chloride  with  the  solution  of  chlorinated  lime,  prepared  according 
to    the   directions  of  §  225,  and  calculate  the  chlorine  by  the 
proportion   55-9  :  35-45  ::  the   quantity  of   iron   used  :  x;    the  x 
found  corresponds  to  the  chlorine  contained  in  the  volume  of 
the  solution  of  chlorinated  lime  used.     This  calculation  may  be 
dispensed  with  by  the  application  of  the  following  formula,  in 
which  the  carbon  in  the  pianoforte  wire  is  taken  into  account: 

Multiply  the  weight  of  the  pianoforte  wire  by  6307,  and  divide 
the  product  by  the  number  of  c.c.  of  the  solution  of  chlorinated 
lime  used;  the  result  expresses  the  percentage  of  chlorine  by 
weight. 

This  method  gives  very  good  results.  I  have  described  it  here 
principally  because  it  dispenses  altogether  with  the  use  of  standard 
fluids.  It  is  therefore  particularly  well  adapted  for  occasional 
examinations  of  samples  of  chlorinated  lime,  and  also  by  way  of 
control. 

2.  Instead  of  directly  oxidizing  ferrous  oxide  or  chloride  by 


386  DETERMINATION    OF    COMMERCIAL  VALUES.  [§  233. 

the  chlorinated  lime,  the  following  may  also  be  employed  with 
good  results: 

Weigh  off  accurately  0-3  grm.  of  fine  iron  wire,  dissolve  it  to 
ferrous  chloride  in  a  current  of  carbon  dioxide,  dilute  the  still 
acid  solution  with  water  to  200  or  300  c.c.,  and  from  a  burette 
run  in  50  c.c.  of  the  chlorinated-lime  solution  (prepared  as  above) 
slowly  and  while  stirring;  then  determine  the  quantity  of  ircn 
remaining  still  unoxidized  (or  raised  from  ferrous  to  ferric  chloride) 
by  means  of  a  solution  of  potassium  dichromate  (Vol.  I,  p.  319,  6). 
If  permanganate  solution  is  used  instead  of  dichromate,  the  re- 
marks in  Vol.  I,  p.  318,  j,  must  be  borne  in  mind,  as  the  solution 
contains  hydrochloric  acid.  By  this  means  the  quantity  of  iron 
oxidized  by  the  chlorinated  lime  is  ascertained,  and  from  this 
the  chlorine  content,  according  to  the  proportion  stated  above 
in  1. 

These  by  no  means  exhaust  the  number  of  excellent  chlo- 
rometric  methods.  For  instance,  a  standard  solution  of  potassium 
ferrocyanide  may  be  used  with  good  results  instead  of  the  ferrous 
salt,  as  recommended  by  E.  DAVY.*  After  adding  an  excess  of 
solution  of  potassium  ferrocyanide  to  the  chlorinated-lime  solu- 
tion, acidulate  with  hydrochloric  acid  and  determine  the  residual 
ferrocyanide  by  means  of  potassium  dichromate.  The  end  of  the 
reaction  is  reached  when  a  drop  taken  out  and  brought  into  con- 
tact with  dilute  ferric-chloride  solution  on  a  porcelain  plate  no 
longer  affords  a  blue  or  green  color.  The  determination  of  the 
residual  potassium  ferrocyanide  may  be  just  as  accurately  and 
more  conveniently  ac  omplished  by  means  of  potassium-per- 
manganate solution,  Vol.  I,  p.  554,  g. 

Again,  an  acid  ferrous- chloride  solution  may  be  added  in 
excess  to  the  chlorinated-lime  solution,  and  the  ferric  chloride 
formed  titrated  with  stannous  chloride  (Vol.  I,  p.  327,  6,  a).  Each 
equivalent  of  ferric  chloride,  Fe2Cl0,  corresponds  with  2  eq.  of  CL, 
(2FeCl2  +  2Cl  =  Fe2Cle).  The  solution  of  iron  employed  must,  of 
course,  be  free  from  ferric  chloride;  or  if  it  contains  any,  the 
quantity  must  be  determined  (Vol.  I,  p.  578). 

*  Phil.  Mag.  (4),  xxi,  214. 


§  234.]  CALCIUM   COMPOUNDS.  387 

C.  CALCIUM  ACETATE. 
§234. 

The  calcium  acetates  which  are  obtained  by  neutralizing 
rectified  or  crude  wood  vinegar  with  calcium  hydroxide  and  evap- 
orating the  solution,  and  which,  as  is  well  known,  are  intermediate 
products  between  wood  vinegar  and  pure  acetic  acid  or  pure 
acetates,  come  into  the  market  in  bulk;  as  their  composition  is 
variable,  they  must  be  tested  as  to  their  acetic-acid  content  in 
order  to  determine  their  value. 

The  products  consist  of  calcium  acetate  containing  small 
quantities  of  calcium  propionate  and  butyrate,  etc.,  empyreu- 
matic  substances  which  remain  undissolved  on  treatment  with 
water,  and  usually  a  little  calcium  carbonate,  alumina,  etc.  They 
also  contain  varying  quantities  of  water. 

In  testing  calcium  acetate,  the  small  quantities  of  propionic 
and  butyric  acids,  etc.,  are  determined  with  the  acetic  acid,  and 
calculated  as  such.  Should  it  be  particularly  desired  to  deter- 
mine the  quantities  of  these  acids,  the  method  proposed  by  E. 
LUCK  may  be  used.* 

Of  the  methods  which  are  here  described,  the  first  is  suitable 
for  every  kind  of  calcium  acetate;  the  other  two  only  for  the 
purer  sorts. 

I.    DISTILLATION  METHOD .f 

a.  Introduce  a  weighed  average  sample  (about  5  grm.)  of 
the  calcium  acetate  into  a  small  tubulated  retort,  add  50  c.c. 
of  water  and  50  c.c.  of  ordinary  phosphoric  acid  (free  from  nitric 
acid)  of  about  1-2  sp.  gr.,  and  place  the  retort  on  a  small  sand- 
bath  with  the  neck  inclined  slightly  upwards;  connect  the  retort 
with  a  condenser  by  means  of  a  glass  tube  bent  into  an  obtuse  angle, 
and  distill  off  the  contents  at  a  gentle  heat  almost  to  dryness, 
taking  care  that  all  the  distillate  is  collected  without  loss.  A 

*  Zeitschr.  f.  analyt.  Chem.,  x,  184. 
f  R.  FUESENIUS,  Ibid.,  v,  315. 


388  DETERMINATION    OF   COMMERCIAL    VALUES.          [§  234. 

250-c.c.  flask  serves  as  the  receiver.  It  is  advisable  to  surround 
the  upwardly  inclined  neck  of  the  retort  with  a  paper  covering. 
After  cooling,  dilute  the  contents  of  the  retort  with  50  c.c.  of 
water,  distill  again  almost  to  dryness,  and  repeat  the  operation 
a  third  time.  Now  dilute  the  distillate  to  250  c.c.,  shake,  and 
in  50  or  100  c.c.  determine  the  free  acid  by  means  of  normal  soda 
solution  (§215).  Before  calculating  the  quantity  of  acetic  acid 
from  the  soda  solution  used,  test  a  small  portion  of  the  distillate 
with  silver  nitrate.  If  only  a  faint  opalescence  develops,  which 
is  as  a  rule  the  case,  the  above  calculation  may  be  proceeded  with, 
i.e.,  after  calculating  the  relation  of  the  portion  taken  to  the  whole: 
6-0032  grm.  of  acetic  acid,  (C2H402),  or  7-9074  grm.  of  calcium 
acetate,  (Ca[C2H3O2]2),  correspond  with  every  100  c.c.  of  normal 
soda  solution  used.  If,  however,  silver  nitrate  causes  any  con- 
siderable precipitate  insoluble  in  diluted  nitric  acid,  the  hydro- 
chloric acid  in  the  distillate  must  be  determined  in  an  aliquot 
portion  and  allowed  for  in  the  calculation. 

6.  If  there  is  frequent  necessity  for  testing  calcium  acetates 
by  the  distillation  method,  it  is  advisable  to  employ  the  steam- 
distillation  method  *  proposed  by  me.  The  small  tubulated 
retort  is  arranged  as  detailed  under  a,  but  the  condenser  had  better 
be  larger.  A  500-c.c.  flask  is  used  as  a  receiver.  Into  the  tubu- 
lure  of  the  retort  there  is  inserted  a  glass  tube,  bent  at  an  obtuse 
angle  and  its  end  slightly  drawn  out  inside  the  retort;  the  other 
end  of  the  tube  bears  a  piece  of  rubber  tubing  provided  with  a 
screw  pinch-cock.  Through  this  tube  steam  is  passed  in  as  re- 
quired. 

For  the  supply  of  an  easily  regulated  current  of  steam,  a  small 
iron  or  copper  steam-boiler  with  a  safety-valve  is  most  suitable; 
if  this  is  not  available,  a  flask  fitted  with  a  doubly  perforated 
rubber  stopper  will  answer.  In  one  perforation  insert  a  tube 
bent  at  right  angles  and  connected  with  the  steam-inlet  tube  of 
the  retort  by  means  of  a  piece  of  rubber  tubing;  in  the  other 
aperture  fit  a  tube  bent  twice  at  right  angles,  and  the  outer  limb 

*  Zeitschr.  /.  analyt.  Chem.,  xiv.,  172. 


§  234.]  CALCIUM  COMPOUNDS.  389 

of  which,  about  25  cm.  long,  dips  into  a  strong  test-tube  about 
6  cm.  high  and  filled  with  mercury.  This  test-tube,  securely 
fixed  in  a  large  cork,  stands  in  a  beaker  of  cold  water.  It  will 
be  seen  that  this  contrivance  serves  to  supply  steam  at  a  certain 
tension,  and  at  the  same  time  acts  as  a  safety-valve,  and  allows 
the  current  of  steam  to  be  regulated  as  desired. 

Distillation  is  carried  on  with  the  screw  pinch-cock  closed 
until  only  a  very  small  quantity  of  rather  thick  liquid  remains, 
taking  care,  by  cautiously  heating,  that  the  liquid,  inclined  to  froth, 
does  not  come  over.  As  soon  as  the  contents  of  the  retort  again 
begin  to  froth,  lower  the  heat  applied  to  the  sand-bath,  and  by 
cautiously  opening  the  screw  pinch-cock  admit  steam,  which,  of 
course,  must  already  have  the  required  tension.  The  distilla- 
tion is  proceeded  with  in  this  manner  until  the  last  drops  of  dis- 
tillate cease  to  have  an  acid  reaction.  By  more  or  less  strongly 
heating  the  sand-bath,  and  by  opening  the  pinch-cock  more  or 
less,  the  operation  may  be  regulated  at  will,  and  completed  in  a 
shorter  time  than  is  possible  when  no  steam  is  used. 

c.  The  distillation  carried  out  according  to  a  may  also  be  ac- 
celerated by  using  an  air-current.  In  this  case  there  are  used  a 
distilling  flask  and  a  receiver  of  strong  glass.  The  latter  is  fitted 
airtight  to  the  condenser,  and  through  its  tubulure  air  is  pumped 
out — most  conveniently  with  a  water  air-pump — until  the  pres- 
sure on  the  liquid  is  only  about  one-half  an  atmosphere.  The 
distillation  flask  may  be  heated  in  a  water-bath  filled  with  a  satu- 
rated solution  of  common  salt;  the  air  pumped  out  is  passed  through 
a  U-tube  containing  a  little  water  (comp.  L.  WEIGERT,  "On  the 
Determination  of  Acetic  Acid  in  Wine"  *). 

II.   ALKALIMETRIC   METHOD. 

Boil  5  grm.  of  the  calcium  acetate  to  be  examined  with  water, 
filter  into  a  500-c.c.  flask,  wash,  make  up  the  filtrate  when  cold 
to  250  c.c.,  and  shake;  measure  off  100  c.c.  and  evaporate  in  a 
platinum  dish,  ignite  the  residue  with  access  of  air  until  the  car- 

*  Zeitschr.  f.  analyt.  Chem.,  xviu,  207. 


390  DETERMINATION    OF   COMMERCIAL    VALUES.          [§  234. 

bon  is  consumed,  and  in  the  residue  determine  the  calcium  alkali- 
metrically  (§  223),  calculating  2  eq.  of  acetic  acid  for  every  equiv- 
alent of  calcium  found. 

In  the  case  of  a  salt  considerably  contaminated  with  empy- 
reumatic  substances,  this  simple  method,  as  already  mentioned 
above,  gives  an  incorrect  (too  high)  result,  because  the  compounds 
of  the  empyreumatic  substances  with  calcium  dissolve  in  water 
in  appreciable  quantities,  and  on  evaporation  and  ignition  also 
yield  calcium  carbonate  or  caustic  lime. 

III.    COMBINED   ACIDIMETRIC   METHOD. 

This  method  published  by  me  *  a  few  years  ago  is  based  on 
the  following  reaction :  If  an  excess  of  oxalic  acid  is  added  to 
the  solution  of  all  the  soluble  substances  dissolved  out  from  cal- 
cium acetate  by  water,  all  the  calcium  will  be  obtained  in  the 
precipitate  as  an  oxalate,  together  with  a  portion  of  the  empy- 
reumatic substances,  and  also  alumina,  silica,  sand,  etc.,  while 
the  solution  will  contain  the  acid  substances,  i.e.,  acetic  acid 
together  with  small  quantities  of  its  homologues  and  the  excess 
of  oxalic  acid  (that  portion  not  neutralized  by  the  calcium);  in 
addition  to  these,  there  are  also  present  in  the  solution  empyreu- 
matic substances  which  have  no  acid  reaction,  and  which  impart 
a  more  or  less  yellow  to  brown  color  to  the  solution. 

If  in  the  solution,  on  the  one  hand,  we  determine  the  acidity, 
i.e.,  the  sum  of  the  acetic  acid  (together  with  propionic  and  butyric 
acids)  and  oxalic  acid  by  means  of  normal  alkali,  and  on  the  other 
hand  the  quantity  of  oxalic  acid,  we  have  but  to  subtract  the 
normal  alkali  solution  corresponding  with  the  latter  from  the 
total  quantity  employed,  in  order  to  be  able  to  calculate  from 
the  difference  the  acetic  acid  (together  with  propionic  and  butyric 
acids,  etc.)  present. 

This  conclusion  is,  of  course,  correct  only  if  the  solution  con- 
tains no  other  neutral  acetates  the  bases  of  which  are  incompletely 
or  not  at  all  precipitated  by  oxalic  acid,  e.g.  magnesium  acetate. 

*  Zeitschr.  f.  analyt.  Chem.,  xiu,  153. 


§  234.]  CALCIUM   COMPOUNDS.  391 

As,  however,  every  manufacturer  of  calcium  acetate  knows  that 
the  employment  of  lime  for  the  saturation  of  wood  vinegar  is 
disadvantageous,  calcium  acetates  strongly  contaminated  with 
magnesium  are  but  seldom  met  with  in  commerce;  and  the  pos- 
sible error  caused  by  the  presence  of  magnesium  in  the  calcium 
acetate  is  rarely  of  any  importance,  and  is  due  to  subtraction  of 
too  large  a  quantity  of  oxalic  acid,  i.e.,  the  sum  of  the  free  and 
of  the  combined  oxalic  acid  remaining  in  the  solution,  from  the 
total  free  acids  found,  thus  causing  the  quantity  of  acetic  acid  found 
to  be  too  low. 

The  Process:  Accurately  weigh  off  5  grm.  of  the  calcium  acetate 
to  be  examined,  introduce  it  into  a  250-c.c.  flask  (which  has  also 
a  mark  at  which  it  holds  252-1  c.c.),  and  dissolve  in  150  c.c.  of 
water;  then  add,  without  filtering,  70  c.c.  of  normal  oxalic-acid 
solution,  fill  to  the  252-1-c.c.  mark,*  close  the  flask  with  a  rubber 
stopper,  shake  well,  allow  to  settle,  and  filter  off  at  least  200  c.c. 
of  liquid  through  a  dry,  plaited  filter,  using  a  covered  funnel, 
into  a  dry  flask. 

1.  To  100  c.c.  of   the   clear,  frequently  yellow  filtrate  add  a 
little  litmus  tincture,  and  then  normal  soda  solution  until  per- 
fectly neutral.     As  the  color  of  the  liquid  renders  it  difficult  to 
observe  the  change  from  red  to  blue,  litmus  and  turmeric  papers 
must  be  also  employed  to  ascertain  the  neutrality  point;    it  is 
also  advisable  to  determine  it  several  times  by  adding,  after  one 
experiment  is  finished,  a  small  quantity  of  normal  hydrochloric 
acid,  and  then  again  normal  soda  solution  to  neutralization.    The 
titration  may  be  considered  as  completed  only  when  concordant 
results  are  thus  obtained.     By  multiplying  the  number  of  c.c. 
of  soda  solution  used  by  2-5,  the  quantity  corresponding  with 
250  c.c.  of  solution,  i.e.,  with  the  5  grm.  of  substance  taken,  is 
found. 

2.  To  another  100  c.c  of  the  solution  add  a  solution  of  pure 

*  The  2-1  c.c.  (i.e.,  the  difference  between  250  and  252-1  c.c.)  represent, 
as  nearly  as  possible  without  accurately  knowing  the  composition  of  the 
calcium  acetate,  the  volume  which  the  precipitated  calcium  oxalate  (sp.  gr. 
2-2202)  occupies. 


392  DETERMINATION   OF   COMMERCIAL    VALUES.  [§   234. 

calcium  acetate,  allow  to  settle  in  a  moderately  warm  place,  filter 
off  the  calcium  oxalate,  wash  it,  and  convert  it  as  usual  (by  gently 
igniting  and  treating  the  residue  with  ammonium  carbonate,  etc.) 
into  calcium  carbonate;  multiply  the  number  obtained  by  49-95 
(see  below),  and  thus  find  the  number  of  c.c.  of  normal  soda  solu- 
tion which  the  free  oxalic  acid  (as  H2C2O4)  in  the  solution  required 
for  saturation.  Deduct  this  number  from  the  number  of  c.c.  of 
soda  solution  found  in  1,  and  from  the  remainder  calculate  the 
acetic  acid  (together  with  the  small  quantities  of  propionic  and 
butyric  acids,  etc.)  contained  in  the  5  grm.  of  substance  taken.* 

If  it  is  desired  to  avoid  weighing  the  calcium  carbonate  ob- 
tained by  gently  igniting  the  calcium  oxalate,  the  calcium  oxa- 
late obtained  by  precipitating  100  c.c.  of  the  acid  liquid  with 
calcium  acetate  may  be  strongly  ignited,  and  the  calcium  in  the 
residue,  whether  as  calcium  oxide  or  carbonate,  titrated  with 
normal,  hydrochloric  acid,  the  excess  of  hydrochloric  acid  being 
titrated  back  with  normal  soda  solution  (§  223).  The  calculation 
is  then  simply  effected  by  subtracting  the  c.c.  of  normal  hydro- 
chloric acid  required  for  neutralizing  the  calcium  obtained  from 
the  calcium  oxalate,  from  the  c.c.  of  normal  soda  solution  required 
for  neutralizing  the  free  acid  in  100  c.c.  of  the  filtrate.  The  re- 
mainder, multiplied  by  2-5,  directly  gives  the  quantity  of  soda 
solution  corresponding  to  the  acetic  acid  (together  with  the  pro- 
pionic and  butyric  acids,  etc.  in  the  250  c.c.  of  filtrate,  and  hence 
in  the  5  grm.  of  substance  weighed  out. 

*The  abbreviation  of  the  calculation  as  detailed  here,  i.e.,  the  fact  that 
it  is  only  necessary  to  multiply  by  49-95  the  calcium  carbonate  obtained 
by  gently  igniting  the  calcium  oxalate  obtained  from  100  c.c.  of  the  nitrate, 
in  order  to  find  the  number  of  c.c.  of  soda  solution  corresponding  with  the 
free  oxalic  acid  (as  H202O4=90-016)  present  in  the  250  c.c.,  is  based  on  the 
following  proportions,  from  which  the  free  oxalic  acid  contained  in  the  250 
c.c.  is  calculated  from  the  calcium  carbonate  (=y)  obtained  from  the  calcium 
oxalate  precipitated  from  100  c.c.  :  100  :250  ::y:x.  The  calcium  carbonate 
=  100-1  (=yf)  thus  found  for  the  250  c.c.  is  calculated  into  oxalic  acid  thus: 
100-1  : 90 -01 6  ::?/,  \x,  and  the  oxalic  acid  thus  found  is  calculated  into  nor- 

,         2000       ,  .,  2-5X90-016X2000 

mal  soda  solution  by  multiplying  by  ^Q^\   but  y  X      iOQ.ix90-016    ' 

=  y  X  49-95. 


§  235.]  CALCIUM    COMPOUNDS.  393 

The  results  obtained  by  me  when  using  this  method  corre- 
sponded very  satisfactorily  with  those  afforded  by  the  distillation 
method  in  the  case  of  calcium  acetate  prepared  from  rectified 
wood  vinegar. 

D.  ANALYSIS  OF  LIMESTONES,  DOLOMITES,  MARLS, 
CEMENTS,  ETC. 

§235. 

As  the  minerals  containing  calcium  and  magnesium  carbonates 
play  a  very  important  part  in  manufactures  and  agriculture,  the 
chemist,  is  often  called  upon  to  analyze  them.  The  analytical 
process  varies  according  to  the  object  in  view.  For  technical 
purposes,  it  is  sufficient  to  determine  the  principal  constituents; 
the  geologist  takes  an  interest  also  in  the  substances  present 
in  smaller  proportions,  whilst  the  agricultural  chemist  seeks  a 
knowledge  not  only  of  the  constituen  s  but  also  of  the  state  of 
solubility,  in  different  menstrua,  in  which  they  are  severally  present. 

I  will  give,  in  the  first  place,  a  process  for  effecting  a  complete 
and  accurate  analysis ;  in  the  second  place,  the  volumetric  methods 
by  which  the  calcium  and  magnesium  carbonates  may  be  deter- 
mined; and  lastly,  the  analysis  of  the  products  formed  by  heating 
these  minerals,  i.e.,  quicklime  and  cements.  An  accurate  qual- 
itative examination  should  always  precede  the  quantitative  an- 
alysis. 

I.    METHOD    OF   EFFECTING  THE   COMPLETE   ANALYSTS. 

a.  Reduce  a  large  piece  of  the  mineral  to  powder,  mix  this 
uniformly,  and  preserve  in  a  well-stoppered  bottle. 

b.  Weigh  off  about  2  grm.  of  the  powdered  mineral  between 
two  watch-glasses,  and  dry  to  constant  weight  at  100°  (the  loss 
in  weight  gives  the  moisture);   then  introduce  the  powder  into  a 
beaker,  add  water,  warm,  cover  the  beaker  with  a  large  watch- 
glass,  and  gradually  add  hydrochloric  acid  until  all  the  carbonates 
are  just  dissolved.     Too  large  an  excess  of  hydrochloric  acid  and 
too  strong  a  heat  must  be  avoided,  in  order  that  any  clay  present 
may  be  decomposed  as  little  as  possible.     After  gently  warming 


394  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  235. 

for  quite  some  time,  collect  the  residue  on  a  filter  paper  previously 
dried  at  100°,  wash  it,  and  weigh.  It  generally  consists  of  sep- 
arated silica,  day,  and  sand;  but  it  often  contains  also  humus-like 
matter.  Opportunity  will  be  afforded  in  g  for  examining  this 
residue. 

c.  Mix  the  hydrochloric-acid  solution  with  chlorine  water  (or 
aqueous  solution  of  bromine),  then  with  ammonia  in  slight  excess, 
and  let  the  mixture  stand  at  rest  for  some  time,  in  a  covered  vessel, 
at  a  gentle  heat.     Filter  off  the  precipitate,  which  contains — be- 
sides the  hydrate  of  sesquioxide  of  manganese,  ferric  and  aluminium 
hydroxides — the  phosphoric  acid  which  the  analyzed  compound 
may  contain,  the  silicic  acid  which  may  have  gone  into  solution, 
and,    moreover,    invariably    traces    of    calcium    and   magnesium; 
wash  slightly,  and  redissolve  in  hydrochlo  ic  acid;  heat  the  solu- 
tion, add  chlorine  (or  bromine)  water,  and  then  precipitate  again 
with  ammonia;    filter  off  the  precipitate,  wash,  dry,  ignite,  and 
weigh. 

If  a  pure  white  precipitate  of  magnesium  hydrate  is  obtained 
on  adding  the  ammonia,  in  the  case  of  dolomites,  instead  of  a 
small  quantity  of  a  yellowish  one,  it  is  an  evidence  that  the  solu- 
tion does  not  contain  sufficient  ammonium  chloride.  In  this 
case  dissolve  the  precipitate,  without  filtering,  by  means  of  hy- 
drochloric acid,  add  chlorine  water,  and  then  precipitate  with 
ammonia. 

For  the  estimation  of  the  several  components  of  the  precipitate, 
viz.,  Von,  manganess,  aluminium,  and  phosphoric  acid,  opportunity 
will  be  afforded  in  g. 

d.  Unite  the  fluids  filtered  from  the  first  and  second  precipi- 
tates produced  by  ammonia,  and  determine  the  calcium  and  mag- 
nesium as  directed  in  §  154,  6  [36]. 

e.  As   a   rule   the   minerals   here   considered   contain,   besides 
moisture,  a  small  quantity  of  water  which  is  not  driven  off  at  100°. 
To  determine  this  heat  a  fresh  sample  of  the  undried  mineral 
(or  even  if   it  has  been    dried  at  100°)  in  a  small  boat,  inserted 
into  a  glass  tube  about  25  cm.  long,  while  passing  a  current  of 
dry  air,  and  collect  the  water  in  a  weighed  calcium-chloride  tube 


§  235.J  CALCIUM   COMPOUNDS.  395 

(§36).  As  certain  minerals  give  off  dust  when  thus  treated, 
the  glass  tube  is  constricted  in  front  of  the  boat,  and  a  loose  as- 
bestos plug  is  placed  there  to  retain  the  powder.  Before  inserting 
the  boat  with  the  powdered  mineral,  the  tube,  asbestos  plug,  and 
corks  must  be  thoroughly  dried  by  heating  in  a  current  of  air. 
If  the  substance  dried  at  100°  has  been  used,  the  increase  in  weight 
of  the  calcium-chloride  tube  gives  directly  the  combined  water. 
When  an  undried  mineral  is  used,  the  moisture  determined  in  a 
must  be  subtracted  from  the  total  water  contained  in  it,  in  order 
to  find  the  combined  water. 

/.  If  the  mineral  contains  no  volatile  substances  other  than 
water  and  carbon  dioxide,  the  latter  may  be  determined  by  igni- 
tion with  vitreous  borax  (Vol.  I,  p.  487,  c).  If  the  mineral  has 
been  dried  at  100°,  the  water  found  in  e  is  subtracted  from  the 
loss  of  weight  it  undergoes,  in  order  to  find  the  carbonic  acid  from 
the  difference;  if,  however,  the  undried  mineral  has  been  taken, 
both  the  combined  water,  e,  and  the  moisture  must  be  subtracted. 
If  it  is  not  desired  to  use  this  method,  or  if  it  is  inapplicable,  the 
carbon  dioxide  may  be  determined  according  to  Vol.  I,  p.  490,  66; 
or,  more  accurately,  Vol.  I,  p.  493. 

g.  To  effect  the  estimation  of  the  constituents  present  in 
smaller  proportion,  as  well  as  the  analysis  of  the  residue  insoluble 
in  hydrochloric  acid,  and  of  the  precipitate  produced  by  ammonia, 
dissolve  10  to  50  grm.  of  the  undried  mineral  in  diluted  hydrochloric 
acid  in  the  manner  described  in  6.  As  the  evaporation  to  dryness 
of  large  quantities  of  fluid  is  always  a  tedious  operation,  gently 
heat  the  solution  for  some  time,  to  expel  the  carbonic  acid;  then 
filter  through  a  weighed  filter  into  a  litre  flask,  wash  the  residue, 
dry  it  at  100°,  and  weigh  it.  (The  weight  will  not  quite  agree  with 
that  of  the  residue  in  6,  as  the  latter  contains  also  that  part  of  the 
silicic  acid  which  here  still  remains  in  solution.) 

a.  Analysis  of  the  Insoluble  Residue. 

aa.  Treat  a  portion  with  boiling  solution  of  pure  sodium  car- 
bonate (§  235,  6),  and  separate  the  silicic  acid  from  the  solution 
(§  140,  II,  a);  this  process  gives  the  quantity  of  that  portion  of 


396  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  235. 

the  silicic  acid  contained  in  the  residue,  which  is  soluble  in 
alkalies. 

bb.  Ignite  a  portion  with  access  of  air;  the  loss  of  weight  cor- 
responds with  the  content  of  water  together  with  organic  matter. 
In  the  ignition  residue  determine  the  silicic  acid  and  the  bases 
(§  140,  II,  6).  On  deducting  the  silicic  acid  found  in  aa  from  the 
quantity  found  here,  the  silicic  acid  present  in  the  form  of  sand 
and  clay  is  ascertained.  If  it  is  required,  as  in  the  determination 
of  hydraulic  limes,  to  estimate  each  separately,  a  separate  portion 
of  the  residue  must  be  heated  with  sulphuric  or  phosphoric  acid 
(comp.  Analysis  of  Clay). 

cc.  If  the  residue  contains  organic  matter  (humus),  determine,  in 
a  portion,  the  carbon  by  the  method  of  ultimate  analysis  (§  178,  a). 
PETZHOLDT,*  who  determined  the  coloring  organic  matter  of  sev- 
eral dolomites  by  this  method,  assumes  that  58  parts  of  carbon 
correspond  to  100  parts  of  organic  substance  (humic  acid).  Of 
the  hydrogen  found,  4-5  parts  for  every  58  of  carbon  must  be 
calculated  as  belonging  to  organic  matter,  the  remainder  being 
calculated  as  derived  from  the  water  contained  in  the  residue. 

dd.  If  the  residue  contains  pyrites,^  fuse  another  portion  of  it 
with  sodium  carbonate  and  potassium  nitrate;  macerate  in  water, 
add  hydrochloric  acid,  evaporate  to  dryness,  moisten  with  hydro- 
chloric acid,  gently  heat  with  water,  filter,  determine  the  sulphuric 
acid  in  the  filtrate,  and  calculate  from  the  result  the  amount  of 
pyrites  present.  % 

/?.  Analysis  of  the  Hydrochloric- Acid  Solution. 
Make  the  solution  up  to  1  litre. 

aa.  For  the  determination  of  the  silicic  acid  that  has  passed 
into  solution,  and  of  the  barium,  strontium,  aluminium,  manga- 

*  Journ.  f.  prakt.  Chem.,  LXIII,  194. 

f  Compare  PETZHOLDT,  loc.  cit.;  EBELMEN  (Compt.  rend.,  33,  681); 
DEVTLLE  (Compt.  rend.,  xxxvn,  1001;  Journ.  /.  prakt.  Chem.,  LXII,  81); 
ROTH  (Journ.  f.  prakt.  Chem.,  LVIII,  84). 

J  If  the  residue  contains  barium  or  strontium  sulphate,  these  compounds 
are  formed  again  upon  evaporating  the  soaked  mass  with  hydrochloric 
acid;  they  remain  accordingly  on  the  filter,  while  the  sulphuric  acid  formed 
by  the  sulphur  of  the  pyrites  passes  into  the  filtrate. 


§  235.]  CALCIUM   COMPOUNDS.  397 

nese,  iron,  phosphoric  acid,  as  well  as  traces  of  cupric  oxide  and 
other  metals  precipitable  by  hydrogen  sulphide  in  acid  solution, 
evaporate  500  c.c.,  and  proceed  as  on  p.  257,  B,  this  vol. 

bb.  Determine  the  phosphoric  acid  in  250  c.c.  of  the  hydro- 
chloric-acid solution,  according  to  p.  259,  this  vol. 

cc.  The  remaining  quarter  of  the  dilute  hydrochloric-acid  solu- 
tion is  used  for  the  estimation  of  the  alkalies*  Mix  with  chlo- 
rine water,  then  with  ammonia  and  ammonium  carbonate;  after 
allowing  the  mixture  to  stand  for  some  time,  filter  off  the  precipi- 
tate, evaporate  the  filtrate  to  dryness,  ignite  the  residue  in  a 
platinum  dish  to  remove  the  ammonium  salts,  and  finally  separate 
the  magnesium  from  the  alkalies  as  directed  (Vol.  I,  p.  610,  ft  [16]). 
The  reagents  must  be  most  carefully  tested  for  fixed  alkalies,  and 
the  use  of  glass  and  porcelain  vessels  avoided  so  far  as  practicable 
in  order  to  obtain  trustworthy  results. 

Should  the  limestone  contain  a  sulphate  soluble  in  hydrochloric 
acid,  precipitate  the  sulphuric  acid  by  adding  a  small  excess  of 
barium  chloride,  allow  to  settle,  and  filter  off  the  barium  sulphate 
(which  is  to  be  determined  in  the  usual  manner)  before  proceed- 
ing as  above  to  the  estimation  of  the  alkalies. 

h.  The  iron  found  in  g  may  be  present  in  the  mineral  as  ferric 
or  ferrous  oxide,  or  as  compounds  of  both  oxides.  To  decide 
this  question,  dissolve  about  10  grm.  of  the  undried  mineral  in  a 
250-c.c.  flask  by  warming  with  diluted  hydrochloric  acid  (Fig. 
84,  Vol.  I).  When  cold,  dilute  the  solution  to  250  c.c.,  shake, 
allow  to  settle;  draw  off  100  c.c.  of  the  liquid  with  a  pipette,  and 
in  it  determine  the  ferrous  oxide  according  to  PENNY'S  method 
(Vol.  I,  p.  319).  Any  ferric  oxide  is  finally  determined  from  the 
difference. 

*  The  simplest  way  of  ascertaining  whether  and  what  alkalies  are  present 
in  a  limestone  is  the  process  given  by  ENGELBACH  (Annal.  d.  Chem.  u.  Pharm., 
cxxm,  260) — viz.,  ignite  a  portion  of  the  triturated  mineral  strongly  in  a 
platinum  crucible  over  the  blast,  boil  with  a  little  water,  filter,  neutralize 
with  hydrocholoric  acid,  precipitate  with  ammonia  and  ammonium  car- 
bonate, filter,  evaporate  the  filtrate  to  dryness  and  examine  with  the  spec- 
t-o^oone.  The  ammonium-carbonate  precipitate  may  be  evaporated  with 
hydrochloric  acid  to  dryness,  and  examined  in  like  manner  for  barium  and 
strontium. 


398  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  235. 

i.  As  calcite  and  aragonite  may  contain  -fluorides  (JENZSCH*), 
the  possible  presence  of  fluorine  must  not  be  disregarded  in  accu- 
rate analyses  of  limestones.  Treat,  therefore,  a  larger  sample  of 
the  mineral  with  acetic  acid  until  the  calcium  and  magnesium  car- 
bonates are  decomposed;  evaporate  to  dryness  until  the  excess  of 
acetic  acid  is  completely  expelled,  and  extract  the  residue  with 
water  (§  138,  I).  We  have  the  fluorine  in  the  residue.  If  it  can 
be  distinctly  detected  in  a  portion  of  the  latter,  f  the  determination 
may  be  attempted  as  in  §  166,  4,  b. 

k.  If  the  limestone  under  examination  contains  chlorides,  treat 
a  large  sample  with  water  and  nitric  acid,  at  a  very  gentle  heat; 
filter,  and  precipitate  the  chlorine  from  the  filtrate  by  solution  of 
silver  nitrate. 

/.  It  is  often  interesting  for  agriculturists  to  know  the  degree 
of  solubility  of  a  sample  of  limestone  or  marl  in  the  weaker  solv- 
ents. This  may  be  ascertained  by  treating  the  sample  first  with 
water,  then  with  acetic  acid,  finally  with  hydrochloric  acid,  and 
examining  each  solution  and  the  residue.  The  analysis  of  marls 
made  by  C.  STRUCKMANN  J  were  done  in  this  manner. 

m.  To  effect  the  separation  of  the  caustic  or  carbonated  lime,  in 
hydraulic  limes,  from,  the  silicates,  DEVILLE  §  proposed  to  boil  with 
solution  of  ammonium  nitrate,  which  he  stated  would  dissolve  the 
caustic  lime  and  carbonate  of  lime,  without  exercising  a  decom- 
posing action  on  the  silicates.  GUNNING  ||  found,  however,  that 
by  this  process  the  double  silicates  of  aluminium  and  calcium  are 
more  or  less  decomposed,  with  separation  of  silicic  acid.  As  yet 
no  method  is  known  by  which  the  object  here  stated  can  be  accom- 
plished with  absolute  accuracy.  Even  though  at  times  treatment 
with  diluted  acetic  acid  gives  good  results ,  yet  as  a  general  rule, 
careful  treatment  with  diluted  hydrochloric  acid  gives  best  results. 
C.  KNAUSZ  If  also  recommends  hydrochloric  acid. 

*  Pogg.  AnnaL,  xcvi,  145. 

f  See  Qual  Anal,  §  146,  6. 

j  AnnaL  d.  Chem  u.  Pharm..,  LXXIV,  170. 

§  Compt.  rend.,  xxxvn,  1001;  Journ.  /.  prakt.  Chem.,  LXII,  81. 

||  Journ.  f.  prakt.  Chem.,  LXII,  318. 

IT  Gewerbeblatt  aus  Wurtemberg,  1855,  Nr.  4;   Chem.  Centralbl,  1855,  244. 


§  235.]  CALCIUM  COMPOUNDS.  399 

II.  VOLUMETRIC  DETERMINATION  OF  CALCIUM  CARBONATE  AND 
MAGNESIUM  CARBONATE  (FOR  TECHNICAL  PURPOSES). 

a.  If  a  mineral  contains  only  calcium  carbonate,  the  amount  of 
the  latter  may  be  estimated  from  the  quantity  of  acid  required  to 
effect  its  decomposition,  the  method  described  in  §  223  being 
employed  for  the  purpose.*  Or  the  carbonic  acid  in  the  mineral 
may  be  determined,  say  by  the  method  detailed  in  Vol.  I,  p.  490,  66, 
and  1  mol.  calcium  carbonate  =  100  •  1  calculated  for  each  mol. 
carbon  dioxide  =  44. 

6.  But  if  the  mineral  contains,  besides  calcium  carbonate,  also 
magnesium  carbonate,  the  results  obtained  by  either  process  give 
the  quantity  of  calcium  carbonate  +  magnesium  carbonate,  the 
latter  being  expressed  by  its  equivalent  quantity  of  calcium  car- 
bonate (i.e.,  100-1  of  calcium  carbonate  for  84-3  of  magnesium 
carbonate).  If,  therefore,  you  desire  to  know  the  actual  amount 
of  each,  you  must,  in  addition  to  the  above  determination,  de- 
termine one  of  the  alkali-earth  metals  separately.  For  this  pur- 
pose one  of  the  two  following  methods  may  be  employed: 

1.  Mix  the  dilute  solution  of  2  to  5  grm.  of  the  mineral  with 
ammonia  and  ammonium  oxalate  in  excess,  allow  to  stand  for 
twelve  hours  and  then  filter.     Ignite  the  precipitate  of  calcium 
oxalate,  together  with  the  filter,  and  treat  the  calcium  carbonate 
produced  as  directed  §  223.    This  process  gives  the  amount  of 
calcium  contained  in  the  analyzed  mineral  the  difference  between- 
this  and  the  former  result  gives  the  calcium  carbonate  which  is 
equivalent  to  the  amount  of  magnesium  carbonate  present.     To 
obtain  perfectly  accurate  results  by  this  method,  repeated  precip- 
itation is  indispensable  (see  §  154,  6,  a). 

2.  Dissolve  2  to  5  grm.  of  the  mineral  in  the  least  possible 
excess  of  hydrochloric  acid,  and  add  a  solution  of  lime  in  sugar 
water  so  long  as  a  precipitate  forms.     By  this  operation  the  mag- 
nesia only  is  precipitated.     Filter,  wash,  and  treat  the  precipitate 
as  directed  in  §  223 ;  the  result  represents  the  quantity  of  the  mag- 
nesium.    Deduct   the  quantity  of   calcium    carbonate  equivalent 

*  This  method,  somewhat  modified,  was  first  proposed  by  BINEAU. 


400  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  235. 

thereto  from  the  result  of  the  total  determination;  the  remainder 
is  the  amount  of  calcium  carbonate  present. 

The  method  2  is  only  suitable  when  the  proportion  of  magne- 
sium is  small. 

III.   ANALYSIS    OF   QUICK-LIME   AND  CEMENTS. 

Ordinary  limestones  when  properly  ignited  yield  quick-lime, 
which  is  used  in  the  preparation  of  mortar,  and  for  many  other  pur- 
poses; limestones  which  contain  25  per  cent,  of  clay,  or  —  ex- 
pressed in  general  terms— silicates  which  are  decomposable  on 
ignition  with  lime,  yield  cements  on  suitably  igniting.  Such 
cements  are  also  obtained,  as  is  well  known,  when,  instead  of 
limestones  containing  clay  in  their  natural  condition,  an  artifi- 
cially prepared  mixture  of  clay  with  lime  or  calcium  carbonate 
is  heated. 

The  changes  which  occur  on  ' '  burning  "  the  ordinary  lime- 
stone, as  well  as  that  containing  clay,  are  as  follows: 

Water  and  carbon  dioxide  are  expelled,  ferrous  carbonate 
and  manganous  carbonate  are  converted  into  ferric  and  manganic 
oxides  respectively,  and  organic  matters  are  burnt  or  at  least  decom- 
posed, leaving  a  small  residue  of  carbon ;  but  above  all,  any  silicates 
present  are  decomposed  so  that  their  bases  become  soluble  in 
hydrochloric  acid,  while  their  silicic  acid  is  partially  dissolved  on 
treatment  with  hydrochloric  acid,  and  partly  separates  as  a  hydrate. 
Any  admixed  quartz,  on  the  other  hand,  scarcely  undergoes 
change  by  heating.  If  the  burned  limestones  or  cements  are 
exposed  to  the  action  of  the  air,  they  gradually  absorb  water 
and  carbon  dioxide. 

Of  course  no  mention  is  here  made  of  technical  tests,  by  which 
the  suitability  of  the  burned  limes  and  cements  for  building  pur- 
poses is  determined;*  regarding  the  most  suitable  methods  for 
their  analysis,  however,  the  following  remarks  may  be  made : 

1.  Ignite    several    grm.    in    a    platinum    crucible    over    the 

*  Excellent  advice  on  this  point  is  given  by  Dr.  W.  MICHAELIS  in  his  work 
"Zur  Beurtheilung  des  Cementes,"  Berlin,  polytechnische  Buchhandlung 
(A.  SEIDEL),  1876. 


^  235.]  CALCIUM  COMPOUNDS.  401 

gas  blowpipe.     The  loss  in  weight  gives  the  water  and  carbon  dioxide. 

2.  In  a  larger  sample  (about  10  grm.  determine  the  carbon 
dioxide  according  to  Vol.  I,  p.  493.     The  water  is  found  from  the 
difference,  or  it  may  be  directly  determined  according  to  §  235, 
I,  e. 

3.  Treat  about  5  grm.  with  an  excess  of  diluted  hydrochloric 
acid,  evaporate  to  dryness  in  a  platinum  or  porcelain  dish,  moisten 
the  residue  with  hydrochloric  acid,  warm,  add  water,  filter,  and 
wash  the  undissolved  portion  (§  140,  II.  a). 

4.  Wash  the  contents  of  the  filter  in  3  into  a  dish  without 
damaging  the  filter,  boil  with  successive  quantities  of  a  concen- 
trated solution  of  sodium  carbonate,  pass  through  the  same  filter 
placed  in  a  hot- water  funnel,  until  all  the  hydrated  silica  is  dis- 
solved (i.e.,  until  a  few  drops  remain  clear  when  heated  with 
ammonium-chloride  solution),  and  wash  the  residue.     From  the 
alkaline  solution  separate  the  silicic  odd  according  to  §  140,  II, 
a,   ab.     The   residue  insoluble   in  sodium   carbonate   consists   of 
quartz  sand  and  residual  undecomposed  silicate.     Wash  this  into 
a  platinum  dish,  add  the  filter  ash  to  it,  evaporate  w'th  water  to 
a  small  bulk,  when  cold  add  sulphuric  acid,  and  then  heat  for  some 
time.    The  bases  are  dissolved  by  this  treatment,  and  the  silica 
separated    from  them  may  now  be  separated  from  the  quartz 
sand  by  treating  the  insoluble  washed  residue  with  sodium-car- 
bonate  solution.     In   the   sulphuric  acid   solution   any   alumina, 
ferric   oxide,   etc.,   are  determined.     Should  the  treatment  with 
sulphuric    acid   in  open  vessels  not  be  successful,  heat  with  sul- 
phuric acid  in  sealed  tubes  (Vol.  I.  p.  521). 

5.  Make   up  the  hydrochloric-acid  solution    obtained  in  3  to 
500  c.c.,  and  in  250  c.c.  determine  the  sulphuric  add,  *  potassium, 
and  sodium    (§  209,  4) ;    in    the   other  250  c.c.  separate  the  ferric 
oxide  (manganic  oxide}   and  alumina  by  repeatedly  precipitating 
with  ammonia  (§  235,  I,  c).     Make  up  the  filtrate  to  500  c.c.,  and 
in  250  c.c.  of  it  determine  the  calcium  and  magnesium. 

*  Cements  generally  contain  this.  See  Dr.  W.  MICHAELIS,  Die  hydrau- 
lischen  Mortel,  insbesondere  der  Portland-Cement,"  Leipzig,  QUANDT  u. 
HANDEL,  1869,  p.  89. 


402  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  235. 

[6.  It  is  often  desirable  in  cement  analysis  to  estimate  only 
CaO.  The  usual  method  of  procedure  is  to  disolve  the  cement 
in  dilute  HC1,  add  excess  of  ammonia  to  precipitate  silica,  A1203, 
and  Fe2O3,  precipitate  the  calcium  as  oxalate,  and  ignite  to  CaO. 

According  to  R.  F.  YOUNG  and  B.  F.  BAKER,*  this  method 
gives  an  entirely  erroneous  result,  which  may  be  as  much  as 
1.5  per  cent  too  high  or  too  low,  and  the  reason  of  which  is  that 
when  cement  is  dissolved  in  dilute  hydrochloric  acid,  part  of  the 
calcium  silicate  is  not  decomposed,  but  merely  dissolves  and  is 
precipitated  on  neutralizing  the  acid  with  ammonia.  This  causes 
a  low  result;  but,  on  the  other  hand,  the  ignited  CaO  will  invariably 
contain  very  appreciable  quantities  of  SiO2,  A12O3,  and  Fe2O3,  which 
will  cause  a  high  result. 

The  two  following  methods  have  been  found  to  give  very  satis- 
factory results: 

1.  One  grm.  of  the  cement  is  treated  in  a  conical  beaker  with 
a  small  quantity   of    concentrated   hydrochloric    acid.     A   little 
nitric  acid  is  added,  and  the  contents  evaporated  to  dryness  on  a 
sand-bath,  and  heated  till  the  contents  are  distinctly  red;    then 
treated  with   dilute  hydrochloric   acid,   and   excess   of   ammonia 
added.    The  SiO2,  A12(OH)6,  and  Fe2(OH)6  are  filtered  off,  and 
the  calcium  precipitated  as  oxalate  and  ignited  to  CaO  in  the  usual 
way. 

2.  One  grm.  of  cement  is  dissolved  in  dilute  hydrochloric  acid, 
ammonia  added,  and  the  precipitate  of  iron,  alumina,  and  silica 
filtered  off.     This  precipitate  is  re-dissolved  in  concentrated  hydro- 
chloric acid  and  re-precipitated  by  ammonia.     The  two  filtrates 
and  washings  are  collected,  and  the  calcium  estimated  as  above. 

In  accurate  estimations,  it  is  advisable  in  both  methods  to 
dissolve  the  ignited  CaO  after  weighing  in  hydrochloric  acid,  and 
estimate  the  Si02,  A12O,,  and  Fe203  it  may  contain. 

The  volumetric  estimation  of  calcium  by  titrating  the  excess 
of  a  known  quantity  of  standard  oxalic  acid  left  after  precipitating 
in  ammoniacal  solution,  was  found  to  invariably  give  low  results. 

*  Chem.  News,  LXXXVI,  p.  146. 


§  236.]  ALUMINIUM    COMPOUNDS.  403 

This  seems  to  point  to  the  fact  that  all  the  calcium  is  not  precipi- 
tated as  oxalate. — TRANSLATOR.] 


8.  ALUMINIUM  COMPOUNDS. 

A.  CLAYS. 
(See  Silicon  Compounds,  §  238.) 

B.  ALUMINIUM  SULPHATE. 
§236. 

Of  the  aluminium  compounds,  aluminium  sulphate  will  be 
first  considered.  It  is  manufactured  on  a  large  scale  according 
to  various  methods  (more  recently  by  treating  with  sulphuric 
acid  the  aluminium  hydroxide  obtained  from  cryolite  or  bauxite), 
and  occurs  in  the  market  usually  in  the  form  of  crystalline  cakes 
containing  variable  quantities  of  water;  it  exhibits  varying  de- 
grees of  purity  and  is  hence  frequently  the  subject  of  chemical 
analysis. 

1.  The  quantity  of  water,  which  amounts  to  from  40  to  50  per 
cent.,  cannot  be  accurately  ascertained  by  direct  heating,  because 
the  water  driven  off  has  an  acid  reaction.     To  determine  it  from 
the  loss  of  weight,  therefore,  ignite  about  0-5  grm.  of  the  aluminium 
sulphate  with  pure  lead  oxide    §  35,  /?).     The  water  may  be  de- 
termined directly  by  igniting  the  aluminium  sulphate  with  anhy- 
drous   sodium  carbonate  (§  225.  I).     It  must  be  observed  that 
both  of  these  methods  of  water  determination  give,  besides  the 
water  of  crystallization,  also  the  water  in  any  acid  alkali  sulphate 
or  sul  hate  that  may  be  present 

2.  Dissolv^  about  12  grm.  in  water.     If  an  insoluble  residue 
remains,  collect  it  on  a  filter,  ignite,  and  weigh.     Make  up  the 
solution  to  500  c.c. 

3.  Dilute  150  c.c.  of  the  solution,  add  a  little  hydrochloric 
acid,  and  precipitate  hot  with  barium  chloride,  but  in  slight  excess 
only   (§  132,  1).     The   total   sulphuric   acid   is    determined   from 
the  barium  sulphate  so  obtained. 

4.  Precipitate  the  aluminium  and  the  excess  of  barium  from 


404  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  236. 

the  filtrate,  obtained  in  3  by  adding  ammonia  and  ammonium 
carbonate;  from  the  filtrate  separate  the  alkali  chlorides  (§  225, 
II,  e),  and  in  these  finally  determine  the  potassium.  As  a  rule 
the  preparations  found  in  the  market  contain  cnly  sodium. 

5.  To  100  c.c.  of  the  solution  obtained  in  2  add  ammonium 
chloride,    precipitate   with   ammonia    (§  105,   a),    wash   the   pre- 
cipitate moderately  and  dissolve  it  in  hot  hydrochloric  acid,  and 
reprecipitate    the   diluted   solution   with   ammonia.     The   weight 
of  the  thoroughly  washed  and  ignited  precipitate  gives  the  quan- 
tity of  alumina  together  with  any  ferric  oxide  that  may  be  present. 

6.  Gradually  add  200  c.c.  of  the  solution  obtained  in  3  to  a 
hot,   moderately   concentrated   potassa   or   soda  solution,   finally 
.adding  a  larger  quantity,  so  as  to  redissolve  the   alumina  pre- 
cipitated.    After  prolonged  heating,  there  still  remains,  as  a  rule, 
.a   small   quantity   of   residue   undissolved.     Dilute,   filter,   wash, 
dissolve  the  precipitate  in  hot  hydrochloric  acid,  heat,  precipitate 
with  ammonia,  heat  again  until  the  fluid  is  but  just  faintly  alkaline, 
filter,  and  in  the  filtrate  determine  the  small  quantities  of  calcium 
and   magnesium,   should   these   be   present.     In   the   precipitate, 
which  usually  contains  a  little  alumina,  determine  the  ferric  oxide 
according  to  §  160,  A,  2. 

7.  If  all  the  bases  are  calculated  as  neutral  sulphates,  (A12[SO4]3; 
Fe?  [SO4]3;  Na2SO4,  etc.),  and  the  sulphuric  acid  contained  in  them 
is  subtracted  from  that  found  in  3,  there  is  generally  obtained  a 
small  remainder  which,  so  far  as  the  quantity  of  alkaline  sulphates 
is  concerned,  is  considered  to  be  combined  with  a  corresponding 
quantity  of  these  to  form  alkali  disulphates;    in  the  other  case 
the  excess  of  sulphuric  anhydride  would  be  expressed  as  hydrated 
sulphuric  acid.     If  it  is  desired  to  determine  the  sulphuric  acid 
which  will  neutralize  alkali  (such  as  that  combined  with  aluminium 
and   iron,  as  well  as   that  combined  with  neutral  alkali  sulphate 
to  form  disulphate,  or  present  in  the  free  state)  as  an  acidimetric 
control,  the  method  detailed  on  p.  314,  c,  this  vol.,  must  be  used. 


237.]  SILICON  COMPOUNDS.  405 


9.  SILICON  COMPOUNDS. 

A.  ANALYSIS  OF  NATIVE,  AND   MORE   PARTICULARLY  OF  MIXED, 

SILICATES.* 

§237. 

As  the  analysis  of  silicates  completely  decomposable  by  acids 
has  been  described  in  §  140/  II,  a;  and  that  of  silicates  not  de- 
composable by  acids  in  §  140,  II,  b,  there  but  remains  to  add 
here  a  few  remarks  particularly  regarding  the  examination  of 
mixed  silicates,  i.e.,  such  as  are  composed  of  silicates  of  both 
classes  (phonolites,  clay  slates,  basalts,  etc.). 

1.  Prepare  a  homogeneous,  air-dried,  finely  powdered  sample 
and  in  it  determine  the  moisture   by  drying  1  or  2  grm.  at  120° 
to  constant  weight. 

2.  It  is  customary  to    treat  a  second  portion  of  the  air-dried 
substance  with  moderately  concentrated  hydrochloric  acid  for  a 
long  time  at  a  gentle  heat,  evaporate  to  dryness  on  a  water-bath, 
moisten  the  residue  with  hydrochloric  acid,  add  water,  and  then 
filter;    it  is  often  preferable,  however,  to  digest  the  powder  with 
diluted  hydrochloric  acid  (of  about  15  per  cent.)  for  several  days 
at  a  gentle  heat,  and  then  to  at  once  filter.     Which  of  the  two 
methods  is  to  be  resorted  to,  or  whether  the  method  here  described, 
and  which  was  first  employed  by  CHR.  GMELIN  in  the  analysis 
of  phonolites,  is   at  all  eligible  for  use,  depends  upon  the  nature 
of  the  mixed  minerals.     The  more  easily  decomposable  one  of 
the  constituents  of  the  mixture  is,  and  the  more  undecomposable 
the  remainder,  the  more  constant  will  be  the  proportion  between 
the  undissolved  and  the  dissolved  portions  in  different  experiments ; 
and  the  less  the  undissolved  part  is  attacked  by  further  treatment 
with  hydrochloric  acid  the  more  safely  may  this  method  of   de- 
composition be  employed. 

*  Comp.  Qual.  Anal.,  §§  205  to  208.  It  is  absolutely  essential  to  make 
a  minute  and  comprehensive  qualitative  analysis  before  proceeding  to  the 
quantitative  analysis. 


406  DETERMINATION   OF    COMMERCIAL    VALUES.         [§  237. 

This  process  gives: 

a.  A   hydrochloric-acid   solution,    containing,   besides   more   or 
less    quantities    of   silicic    acid    according   to    circumstances,  the 
bases  of  the  decomposed  silicate  in  the  form  of  metallic  chlorides; 
these,  after  the  removal  of  the  silicic  acid  (§  140,  II,  a),  are  separated 
and  determined  according  to  the  methods  detailed  in  the  fifth 
section. 

b.  An   insoluble   residue,   which    contains,    besides    the   unde- 
composed  silicate,  the  silica  separated  from  the  decomposed  silicate. 

After  the  latter  has  been  thoroughly  washed  with  water  to 
which  a  few  drops  of  hydrochloric  acid  have  been  added,  it  is 
transferred,  while  still  moist,  and  in  small  portions  at  a  time,  to  a 
boiling  solution  of  silica-free  sodium  carbonate  contained  in  a 
platinum  dish;  maintain  the  boiling  for  some  time,  and  filter 
each  time,  while  very  hot  (most  conveniently  by  the  aid  of  a  hot- 
water  funnel),  through  a  weighed  filter.  Finally,  rinse  the  last 
portions  of  the  residue  adhering  to  the  filter  completely  into  the 
dish.  If  this  cannot  be  successfully  done,  incinerate  the  dried 
filter,  transfer  the  ash  to  the  platinum  dish,  and  again  boil  with 
sodium-carbonate  solution  until  a  few  drops  of  the  liquid  finally 
passing  through  remains  clear  on  being  warmed  with  an  excess 
of  ammonium-chloride  solution.  Wash  the  undissolved  residue 
first  with  hot  water,  then — in  order  to  insure  the  removal  of  every 
trace  of  adhering  sodium  carbonate — with  water  faintly  acidu- 
lated with  hydrochloric  acid,  and  finally  again  with  pure,  water. 

Acidulate  the  alkaline  fluid  with  hydrochloric  acid  and  in 
it  determine  the  silicic  acid  which  resulted  from  the  silicate  de- 
composed by  the  acid,  according  to  §  140,  II,  a.  Dry  the  undis- 
solved silicate  at  120°  and  weigh.  Deduct  its  weight  together 
with  that  of  the  moisture  from  the  weight  of  the  substance  origi- 
nally taken;  the  difference  gives  the  quantity  of  the  dissolved 
silicate  in  the  dry  state.  Treat  the  undissolved  silicate  exactly 
as  directed  in  §  140,  IT,  b. 

3.  Water.  Silicates  dried  at  120°  occasionally  contain  water. 
This  is  determined  by  taking  a  weighed  portion  dried  at  120° 
(see  1)  and  igniting  in  a  platinum  crucible,  or — in  presence  of 


§  237.]  SILICON    COMPOUNDS.  407 

carbon,  carbonates,  or  ferrous  iron — in  a  tube,  through  which 
a  stream  of  dry  air  is  drawn,  the  moisture  expelled  from  the  sub- 
stance being  retained  by  a  weighed  calcium-chloride  tube. 

To  ascertain  whether  the  water  expelled  proceeds  from  the  silicate 
decomposable  by  hydrochloric  acid,  or  from  that  not  decomposable, 
ignite  in  a  similar  manner  a  sample  of  the  silicate  dried  at  120°. 
For  instance,  suppose  the  mixed  silicate  consisted  of  50  per  cent, 
decomposable  and  50  per  cent,  undecomposable  silicate;  and  that 
the  latter  contains  47  parts  of  anhydrous  substance  and  3  parts 
water;  the  water  determination  would  give  for  the  mixed  silicate 
3  per  cent.,  and  for  the  undecomposable  portion  6  per  cent.  Now 
as  3:6  as  the  undecomposed  silicate  (50  per  cent.):  the  mixed 
silicates  (100  per  cent.),  it  is  evident  that  the  decomposable  sili- 
cate gives  no  water  on  ignition. 

If  the  escaping  aqueous  vapors  manifest  an  acid  reaction, 
owing  to  the  disengagement  of  hydrofluoric  acid  or  silicon  fluoride, 
mix  the  finely  powdered  substance  with  anhydrous  sodium  car- 
bonate, ignite  in  a  current  of  dry  air,  and  collect  the  water  in  a 
weighed  calcium-chloride  tube  (§  36).  The  best  method  of  con- 
ducting this  water  determination  in  silicates  has  been  thoroughly 
studied  by  E.  LUDWIG  *  and  L.  Sipocz.f  The  former  ignites  the 
mixture  in  an  expanded  platinum  tube;  the  latter  in  a  platinum 
boat.  SIPOCZ  recommends  the  following  method: 

Ignite  4  parts  sodium  carbonate  in  a  platinum  crucible  till 
water  is  completely  expelled,  allow  to  cool  to  50°  or  60°,  mix  in- 
timately with  a  platinum  wire  with  1  part  of  the  pulverized  dried 
silicate,  and  introduce  the  mixture  into  a  capacious  platinum 
boat,  rinsing  out  the  last  adhering  portions  with  sodium  carbonate. 
The  boat,  provided  with  a  cover,  is  now  placed  in  the  middle  of 
a  porcelain  tube  (glazed  inside)  40  cm.  long  and  17  mm.  inner 
diameter,  and  heated  in  an  air-bath  for  an  hour  to  120°  or  130°. 
During  this  time  every  trace  of  moisture  should  be  removed  from 

*  Untersuchungen  vber  die  chemisette  Zusammensetzung  des  Pyrosmaliths, 
mineralog.  Mittheilungen  von  G.  TSCHERMAK,  1875,  211  (Zeitschr.  J.  analyt. 
Chem.  xvii,  206). 

t  Zeitschr.  f.  analyt.  Chem.,  xvii,  207. 


408  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  237. 

the  mixture  by  passing  dried  air  through  the  tube  by  means  of  a 
gasometer.  The  end  of  the  tube  through  which  the  current  of  air 
makes  its  exit  is  provided  with  a  calcium-chloride  tube,  which  at 
the  end  of  the  drying  process  is  replaced  by  a  weighed  U-tube 
containing  glass  beads  moistened  with  pure  strong  sulphuric  acid. 
The  other  end,  connected  with  the  gasometer,  is  provided  with 
intermediate  soda-lime  and  sulphuric-acid  tubes.  The  substance 
is  now  gradually  brought  to  a  red  heat  in  a  combustion  furnace, 
and  a  regulated  current  of  air  (dried  by  sulphuric  acid)  is  passed 
over  it  for  about  half  an  hour  to  carry  the  expelled  water  vapor 
into  the  absorbing  apparatus.  (It  is  obvious  that  this  method 
can  be  used  in  any  case  instead  of  ignition  with  lead  oxide.) 

According  to  SAINTE-CLAIRE  DEVILLE  and  FOUQUE  *  the 
water  in  silicates  containing  fluorine  compounds  may  as  a  rule 
be  expelled  free  from  the  latter  by  properly  igniting,  since  the 
fluorine  compounds  require  far  higher  temperatures  for  their 
expulsion  than  does  water.  After  the  water  has  been  driven  off 
the  fluorine  is  expelled,  if  the  substance  is  ignited,  either  as  an 
alkali  fluoride  or  silicofluoride. 

4.  Occasionally   the  portion   of  silicates   undecomposable   by 
hydrochloric  acid  contains  carbonaceous  organic  matter.     In  this 
case  it  is  safest  to  treat  an  aliquot  part  in  a  current  of  oxygen, 
and  to  weigh  the  resulting  carbon  dioxide   (§  178).     According 
to  DELESSE  traces  of  nitrogen  are  always,  or  nearly  always  present 
in  the  organic  matter  contained  in  silicates. 

5.  Silicates    quite    frequently    contain    admixtures    of    other 
minerals    (magnetite,   pyrites,   apatite,    calcium   carbonate,    etc.) 
which  may  sometimes  be  detected  with  the  naked  eye  or  with  the 
aid  of    a  magnifying-glass.     It  is  scarcely  possible   to  devise  a 
process  which  would  be  applicable  to  all  such  cases;   it  may  be 
noted,  however,  that  it  is  occasionally  advantageous  to  first  treat 
the  substance  with  acetic  acid  before  acting  on  it  with  hydro- 
chloric acid.     In  this  way  the  separation  of  the  carbonates  of 
the   alkaline  earths  in  particular  is   effected   without   difficulty. 

*  Compt.  rend.,  xxxviu,  317;  Journ.  f.  prakt.  Chem.,  LXII,  78. 


§   237.]  SILICON    COMPOUNDS.  409 

The  analyses  by  DOLLFUSS  and  NEUBAUER,*  which  were  carried 
out  in  our  laboratory,  may  be  adduced  as  examples  of  complete 
examinations  of  this  kind. 

6.  If  the  silicates   contain   sulphides,   determine   the  sulphur 
content  according  to  one  of  the  methods  described  in  §  148,  11,^4, 
by  the  dry  way;  or,  which  is  as  a  rule  preferable,  in  the  wet  way,  or 
according  to  CARIUS'  method  (§  190,  p.  126).     When  operating  in 
the  wet  way,  it  must  be   remembered  that  if  barium,  strontium, 
or  lead  is  present,  a  part  of  the  resulting  sulphuric  acid  is  found 
in  the  insoluble  residue:  this,  however,  is  not  the  case  if  the  min- 
eral is  fused  with  an  alkali  carbonate  and  nitrate.     If  a  sulphate 
is  present  besides  sulphide,  determine  the  sulphuric  acid  by  boiling 
a  separate  portion  of  the  silicate  with  a  potassium-  or  sodium- 
carbonate  solution  for  a  long  time,  filtering,  and  precipitating  the 
acidulated  filtrate  with  barium  chloride.     The  quantity  of  sul- 
phuric acid  thus  found  is  subtracted  from  that  obtained  by  treat- 
ment with  oxidizers;   the  difference  gives  the  sulphur  in  the  sul- 
phide.    In  many  cases  it  is  preferable  to  extract  the  substance 
with  hydrochloric  acid  rather  than  to  boil  with  sodium  carbonate, 
in  order  to  determine  the  sul  huric  acid  in  sulphates. 

7.  The  iron,  which  is  almost  always  found  in  silicates,  may  be 
present  in  either  the  ferric  or  ferrous  state,  or  in  both.     As  the 
knowledge  as  to  whether  ferric  or  ferrous  iron  is  present  (or  both) 
is  of  great  importance  in  forming  a  judgment  regarding  a  min- 
eral,  and  the  accurate  determination  of  the  ferrous  iron  is  beset 
with  many  difficulties,  the  subject  is  one  that  has  been  the  object 
of  frequent  and  much  research.     The  following  methods   are  of 
importance  : 

a.  HERMANN'S  method:  Decomposition  of  the  mineral  by 
fusing  with  borax  in  a  current  of  carbon  dioxide;  this  gives  too 
high  a  ferrous-oxide  content,  and  is  to  be  rejected  (RAMMELSBERG  ;  f 


b.  In  many  cases  the  object  may  be  effected  by  heating  a 

*  Journ.  f.  prakt.  Chem.,  LXV,  199. 

f  Zeitschr.  der  deutsch.  geologischen  Gesellsch.,  1872,  69. 

t  Zeitschr.  f.  analyt.  Chem.,  xvn,  212, 


410  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  237. 

portion  of  the  substance  with  hydrochloric  or  sulphuric  acid  in  a 
sealed  glass  tube  (Vol.  I,  p.  521,  e)  and  determining  the  ferrous 
iron  in  the  solution  so  obtained  by  means  of  potassium  chromate 
or  permanganate,  or  the  ferric  iron  volumetrically  with  stannous 
chloride. 

c.  In  those  cases  where  6  does  not  give  the  desired  results, 
and  in  all  cases  generally,  a  solution  in  which  the  ferrous  or  ferric 
iron  may  be  titrated  can  be  obtained  by  decomposing  the  sub- 
stance with  hydrofluoric  and  sulphuric  acids,  or  hydrofluoric  and 
hydrochloric  acids.  Quite  frequently  it  suffices  to  carry  out  the 
treatment  in  open  vessels  with  exclusion  of  air  (comp.  Vol.  I,  p. 
310*).  If  the  hydrofluoric  acid  contains  reducing  substances 
(arsenous  acid  [C.  JEHN  f],  hydrogen  sulphide,  sulphurous  acid, 
etc.),  it  must  be  distilled  with  potassium  permanganate  from  a 
platinum  retort  (E.  LUDWIG).  In  order  to  avoid  this  operation 
DOLTER  (loc.  tit.)  recommends  evaporating  the  solution  obtained 
by  decomposing  the  substance  with  hydrofluoric  and  sulphuric 
acids,  in  an  atmosphere  of  carbon  dioxide,  in  order  to  expel  the 
excess  of  the  hydrofluoric  acid  and  with  it  the  reducing  sulphur 
compounds  contained  in  it,  before  titrating.  This  does  not, 
however,  exclude  those  errors  which  arise  from  the  reduction 
of  the  ferric  iron  during  solution  by  the  reducing  substances  present 
in  the  hydrofluoric  acid. 

In  the  case  of  silicates  which  are  decomposed  with  great  diffi- 
culty, heat  the  very  finely  powdered  substance  with  pure  hydro- 
fluoric acid  and  moderately  dilute  sulphuric  acid  in  sealed  tubes 
of  Bohemian  potash  glass.  In  order  to  obtain  perfectly  accurate 
results  SUIDA  J  recommends  treating  in  precisely  the  same  manner 
like  quantities  of  the  same  hydrofluoric  and  sulphuric  acids  in 
a  piece  of  the  same  glass  tubing  by  the  side  of  that  containing 
the  substance  to  be  decomposed,  and  subtracting  the  quantity 

*  Regarding  other  apparatus  used  for  this  purpose,  see  COOKE,  Zeitschr. 
f.  analyt.  Chem.,  vii,  98. — WILBUR  and  WHITTLESEY,  ibid.,  x,  98. — A.  R. 
LEEDS,  ibid.,  xvi,  323. — DOLTER,  ibid.,  xviu,  53. 

f  Zeitschr.  f.  analyt.  Chem.,  xni,  176 

I  Ibid.,  xvn,  213. 


§  237.]  SILICON    COMPOUNDS.  411 

of  potassium  permanganate  required  to  color  the  liquid  from 
that  used  for  the  decomposed  substance. 

8.  If  the  silicates  contain  a  small  quantity  of  titanic  acid,  which 
is  frequently  the  case,  special  care  must  be  exercised  not  to  over- 
look it.  When  the  silicic  acid  has  been  separated  by  evaporation 
with  hydrochloric  acid,  whether  the  decomposition  of  the  silicate 
has  been  effected  by  hydrochloric  acid  or  whether  the  silicate 
has  been  previously  submitted  to  the  action  of  alkali  carbonate, 
the  titanic  acid  is  as  a  rule  found  partly  with  the  silicic  acid,  partly 
in  the  hydrochloric-acid  solution. 

In  order  to  ascertain  whether  the  silicic  acid  separated  contains 
titanic  acid,  treat  it  in  a  platinum  dish  with  hydrofluoric  acid 
and  a  little  sulphuric  acid,  evaporate,  fuse  any  residue  with  potas- 
sium disulphate,  dissolve  in  cold  water,  filter  if  necessary,  and 
separate  the  titanic  acid  from  the  sulphuric-acid  solution  according 
to  the  method  detailed  in  §  107,  2. 

The  greater  portion  of  the  titanic  acid  is  frequently  found  in 
the  hydrochloric-acid  solution  filtered  off  from  the  silicic  acid. 
It  is  precipitated  with  ferric  oxide  and  alumina  on  the  addition 
of  ammonia  (§  161,  4),  and  is  determined  in  the  precipitate  either 
by  igniting  this  in  a  current  of  hydrogen,  extracting  the  reduced 
iron  by  digestion  with  diluted  nitric  acid  (Vol.  I,  p.  652,  7,  a), 
fusing  the  residue  with  potassium  disulphate,  taking  up  the  melt 
with  cold  water,  and  precipitating  the  titanic  acid  by  boiling 
(§  107) ;  or  by  at  once  fusing  the  precipitate  (consisting  of  ferric 
oxide,  alumina,  and  titanic  acid)  with  potassium  disulphate,  dis- 
solving the  melt  in  cold  water,  neutralizing  the  solution  as  nearly 
as  possible  with  sodium  carbonate,  and  diluting  with  water  so 
that  50  c.c.  of  the  liquid  will  contain  not  more  than  0-1  grm. 
of  the  oxides.  Now  add  to  the  cold  solution  a  slight  excess  of 
sodium  thiosulphate,  wait  until  the  liquid,  at  first  violet,  has  be- 
come colorless,  and  the  ferric  iron  has  consequently  been  reduced 
to  a  ferrous  state,  heat,  and  maintain  boiling  until  no  more  sul- 
phurous acid  is  evolved;  then  filter,  wash  the  precipitate  with 
boiling  water,  dry,  and  gently  ignite  in  a  covered  porcelain  cruci- 
ble to  expel  the  sulphur,  then  remove  the  lid,  and  ignite  strongly 


412  DETERMINATION    OF    COMMERCIAL    VALUES.          [§237. 

with  access  of  air.  In  this  manner  the  alumina  (CHANCEL*) 
and  the  titanic  acid  (A.  STROMEYER  f)  are  obtained  free  from 
iron,  and  may  be  separated  by  the  method  given  above.  When 
separating  the  titanic  acid  by  boiling  the  sulphuric-acid  solution, 
the  operation  must  be  conducted  very  carefully  (comp.  §  107), 
otherwise  the  titanic  acid  will  not  be  completely  precipitated 
(see  RILEY  I).  In  order  to  with  certainty  precipitate  pure  titanic 
acid  by  boiling  from  solutions  containing  iron,  G.  STREIT  and 
B.  FRANZ  §  recommended  adding  about  an  equal  volume  of  acetic 
acid. 

9.  If  the  silicates  contain  boric  acid,  the  method  proposed 
by  A.  DITTE  ||  may  be  employed  instead  of  that  described  in  Vol. 
I,  p.  738,  6;   the  method  is  based  upon  the  separation  of  boric 
acid  in  the  form  of  calcium  borate,  which  is  allowed  to  crystallize 
from  a  fused  mixture  of  calcium,  sodium,  and  potassium  chlorides. 
See  Appendix. 

10.  The    determination  of    chlorine,   fluorine,   and    phosphoric 
acid  in  silicates  has  already  been  minutely  described  in  §§  166  and 
167. 

11.  Among  the  most  complicated  analyses  of  silicates  is  that 
of  meteorites,  in  which,  besides  the  silicates,  there  are  found  present 
also  uncombined  metals,  sulphides,  phosphides,  and  carbides,  as 
well  as  chrome  iron  ore.     Regarding  the  examination  of  meteor- 
ites, which  occurs  but  seldom,  I  would   refer   to  the  treatise  on 
the  analysis  of  Zsadanyer  meteorites  by  W.  PILLITZ,^[  in  which 
the  method  considered  most  advantageous  is  accurately  detailed. 

12.  The  analysis  of    ultramarines  also  presents  unusual  dif- 
ficulties.   Regarding  the  most  suitable  methods  for  their  analysis 
I  refer  to  REINHOLD  HOFFMANN'S  comprehensive  work  on  ultra- 
marine.** 

*  Compt.  rend.,  XLVI,  987;  Ann.  d.  Chem.  u.  Pharm.,  cvm,  237. 
•\Annal.  d.  Chem.  u.  Pharm.,  xcui,  127. 
\Journ.  Chem.  Soc.,  xv,  311;  Zeitschr.  f.  analyt.  Chem.,  u,  70. 
§Journ.  f.  prakt.  Chem.,  cvin,  65;   Zeitschr.  /.  analyt.  Chem.,  ix,  388. 
\\Annal.  Chim.  Phys.  (5  ser.),  iv,  549;  Zeitschr.  f.  analyt.  Chem.,  xiv,  360. 
^Zeitschr.  f.  analyt.  Chem.,  xvm,  58. 

**  "  Ueber  Ultramarin,"  1873.     Frankfort,  R.  BAIST. — WAGNER'S  Jahres- 
ber.,  1873,  378  et  seg. 


§  238.]  SILICON   COMPOUNDS.  413 

13.  If  a  silicate  undecomposable  by  acids  contains  #n  ad- 
mixture of  quartz,  and  if  the  quantity  of  this  is  to  be  separately 
determined,  proceed  according  to  one  of  the  methods  described 
in  §  238,  II,  /. 


The  analysis  of  clay,  about  to  be  described,  may  be  effected 
according  to  processes  differing  slightly  from  those  employed  in 
the  analysis  of  silicates. 

B.  ANALYSIS  OF  CLAYS. 
§238. 

The  various  clays,  resulting  from  the  disintegration,  i.e.,  mechan- 
ical reduction  and  chemical  decomposition,  of  rocks  containing 
aluminium  silicates  (such  as  felspar  and  clay  shale),  consist  com- 
monly of  a  mixture  of  true  clay  with  quartz-sand  or  felspar-sand, 
etc.,  and  frequently  contain  also  separated  silicic  acid,  which 
may  be  extracted  by  means  of  a  boiling  solution  of  sodium  car- 
bonate. If  the  clays  are  no  longer  in  the  locality  where  they 
were  found,  they  are  usually  less  pure,  and  contain  admixtures  of 
various  minerals  and,  as  a  rule,  also  organic  matter. 

As  it  is  important  to  know  not  only  the  chemical  composition, 
but  also  the  constituents  into  which  it  may  be  mechanically  sep- 
arated, in  order  to  judge  of  the  fitness  of  the  clays  for  technical 
purposes,  it  is  best  to  make  a  mechanical  analysis  before  pro- 
ceeding to  the  chemical  analysis.* 

I.   MECHANICAL   ANALYSTS. 

By  the  aid  of  mechanical  analysis  the  quantities  of  coarse  and 
very  fine  sand,  and  of  the  finest  portions  removable  by  elutriation 
(clay)  which  form  the  constituent  parts  of  the  natural  clays  are 
ascertained. 

The  mechanical  analysis  of  clays  has  of  late  been  repeatedly 
the  object  of  investigation.  The  elutriation  apparatus  with 
which  the  analysis  is  effected,  have  been  improved,  and  the  me- 

*  Compare  FRESENIUS'  "  Untersuchung  d?r  vnchtigsten  Nassauischen 
Thone,"  Journ.  fur  prakt.  Chem.,  LVII,  65. 


414  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  238. 

chanioally  separable  constituents  of  the  clay  more  sharply  de- 
fined. The  best  apparatus  for  elutriating  is  that  of  SCHONE,* 
which  has  been  slightly  modified  by  W.  SCHUTZE  f  for  washing 
clay;  the  component  parts  of  the  clay  mechanically  separable 
have  also  been  more  accurately  defined  by  SEGER  J  as  follows: 
Coarse  sand — all  the  grains  of  which  are  over  0-2  mm.  large; 
medium  sand — all  the  grains  of  which  are  from  0-04  to  0-02  mm. 
in  size;  fine  sand — all  the  grains  of  which  are  from  0-02  to  0-04 
mm.  in  size;  marly  clay — all  the  grains  of  which  are  from  0-01 
to  0-02  mm.  in  size;  clay — everything  smaller. 

In  spite  of  these  improvements  the  mechanical  analysis  of 
clays  is  still  incomplete.  For  instance  the  fine  sand  obtained 
by  SEGER  §  with  the  SCHONE  washing  machine  from  the  SEFTEN- 
BERG  clay  still  contained  9-3  per  cent,  alumina;  and  that  ob- 
tained similarly  from  the  ARDENNES  clay  contained  as  much  as 
25-32  per  cent. 

I  would  therefore  refer  those  who  are  specially  engaged  in 
the  mechanical  analysis  of  clay  to  the  treatises  above  quoted,  and 
particularly  to  Dr.  CARL  BISCHOF'S  comprehensive  and  excellent 
work  "  Die  feuerfesten  Thone,  etc./'  Leipzig,  QUANDT  u.  HANDEL, 
1876,  in  which  pages  74  to  86  treat  of  the  analysis  of  clay  by  elu- 
triation. 

For  the  ordinary  valuation  of  a  clay,  the  simple  elutriation 
of  the  clay  as  effected  by  the  author  in  the  case  of  the  Nassau 
clay  above  quoted,  and  as  will  be  described  below,  is,  as  a  rule, 
sufficient. 

For  this  purpose  there  is  used  the  elutriating  apparatus  recom- 
mended by  FR.  SCHULZE  ||  for  the  mechanical  analysis  of  soils, 
and  which,  while  not  perfect,  is  n  vertheless  very  convenient, 
and  particularly  simple.  The  more  complete,  but  at  the  same 
time  more  complicated  elutriation  apparatus  devised  by  SCHONE, 

*  Zeitschr.  /.  analyt.  Chem.r  vn,  29. 
t  Notizblatt  f.  Fabrikation  von  Ziegeln  u.  s.  w.%  1872,  188 
%  Ibid.,  1873,.  109. 
§  Zeitschr.  /.  analyt.  Chem.,  ix,  397. 
.  /.  prakt.  Chem.,  XLVII,  241. 


§  238.]  SILICON   COMPOUNDS.  415 

and  above  alluded  to,  will  be  described  when  treating  of  the  analysis 
of  soils. 

For  the  analysis  by  elutriation  FR.  SCHULZE  employs: 
a  A  glass  of  the  form  of  a  large  champagne  glass,  on  the  rim 
of  which  is  cemented  a  brass  ring  15  mm.  wide,  and  with  an  exit 
tube  directed  slightly  downward  proceeding  from  its  side.  The 
body  of  the  glass  is  20  cm.  deep,  and  the  diameter  at  the  mouth 
7  cm. 

6.  A  funnel-tube,  the  funnel  of  which  is  5  cm.  and  the  tube 
40  cm.  long  and  about  7  m.m.  in  diameter.  The  tube  is  drawn 
out  at  the  point  so  that  the  aperture  is  only  1-5  mm.  wide. 

c.  A  vessel  of  at  least   10-litres  capacity  filled  with  water, 
provided  at  the  top  with  an  aperture  for  filling,  and  at  the  side 
near  the  bottom  with  a  stop-cock.     The  vessel  is  best  made  of  sheet 
zinc,  and  should  be  placed  upon  a  support  which  may  be  raised 
or  lowered.     The  funnel-tube  is  suspended  from  the  stop-cock  by 
a  small  cord;  and  the  aperture  of  the  stop-cock  should  be  within 
or  directly  above  the  funnel. 

d.  A  dish  or  large  beaker  to  receive  the  liquid  running  from 
the  discharge  tube. 

For  the  elutriation,  crush  30  grm.  of  the  air-dried  clay  and 
boil  the  substance  for  an  hour  in  a  porcelain  dish  with  twice  or 
thrice  its  volume  of  water,  gently  stirring  with  a  pestle,  in  order 
to  effect  as  complete  a  separation  as  possible  of  the  component 
parts.  After  cooling,  wash  the  contents  of  the  dish  completely 
into  the  elutriating  glass,  open  the  stop-cock  of  the  water  reser- 
voir slightly,  and  insert  the  funnel-tube,  while  the  water  is  flowing 
from  it,  into  the  elutriating  glass.  Care  must  be  taken  to  have 
the  point  of  the  funnel-tube  a  few  millimetres  above  the  deepest 
part  of  the  elutriating  glass,  and  this  may  be  accomplished  by 
lowering  the  water  reservoir,  or  raising  the  elutriating  glass.  The 
stop-cock  must  be  so  regulated  that  the  funnel  should  always  be 
about  half  filled  with  water.  Under  these  conditions  the  pressure 
of  water  (i.e.,  the  difference  in  levels  in  the  elutriating  glass  and 
the  funnel-tube)  will  be  about  20  cm. 

By  the  force  of  the  stream  of  water  the  particles  of  clay  are 


416  DETERMINATION    OF    COMMERCIAL  VALUES.          [§  238. 

violently  stirred  up,  but  only  the  finer  and  finest  are  thrown  up 
sufficiently  high  to  be  carried  off  with  the  stream  of  water  flowing 
through  the  side-tube,  while  the  coarser  sand  remains  in  the  elu- 
triating glass.  When  the  water  flows  off  almost  clear,  close  the 
stop-cock,  remove  the  elutriating  glass,  and  rapidly  decant  the 
slightly  turbid  liquid  from  the  coarse  sand  in  the  dish;  then  wash 
the  residual  sand  into  a  small  dish  by  the  aid  of  a  wash-bottle 
with  upwardly  directed  jet,  and  dry,  ignite,  and  weigh  it. 

Allow  the  dish  or  beaker  containing  the  turbid  liquid  to  settle 
for  at  least  six  hours,  and  decant  the  clear  or  slightly  turbid  super- 
natant liquid  from  the  deposit;  the  deposit,  however,  which  is 
now  sure  to  contain  all  the  fine  sand,  wash  into  an  elutriating 
glass,  and  repeat  the  operation  of  elutriation,  with  the  difference 
that  the  flow  of  water  is  restricted  only  to  a  mere  dropping  on 
to  the  side  of  the  funnel,  and  so  that  the  level  of  water  in  the 
funnel-tube  is  only  about  3  cm.  higher  than  that  in  the  elutriat- 
ing glass.  This  operation  is  repeated  until  the  water  runs  off 
clear,  which  usually  is  the  case  in  from  three  to  four  hours.  The 
residual  fine  sand  is  then  treated  in  the  same  manner  as  the  coarse 
sand  was  treated  above. 

The  water .  content  is  now  determined  by  igniting  a  separate 
weighed  portion  of  the  air-dried  clay,  and  the  quantity  of  the 
finest  particles  (the  clay  proper)  separable  by  elutriation  ascer- 
tained from  the  difference.  The  following  analysis  of  the  poor 
clay  of  Hillscheid  and  the  far  fatter  clay  from  Ebernhahn,  made 
by  me,  gave  the  following  results: 

Hillscheid  Clay.     Ebernhahn  Clay. 

Coarse  sand 24-68  6-66 

Finesand 11-29  9-66 

Ciay 57-82  74-82 

Water.,  6-21  8-86 


100-00  100-00 

II.   CHEMICAL   ANALYSIS. 

The  quantitative  analysis  should  be  preceded  by  a  qualitative 
examination  which  should  be  sufficiently  extended  to  show  what 


§  238.J  SILICON    COMPOUNDS,  417 

substances  are  dissolved  on  prolonged  boiling  of  the  clay  with 
water  and  allowing  to  stand  for  some  time  to  settle  (sodium  and 
ammonium  chlorides,  calcium  sulphate,  ferrous  sulphate,  or- 
ganic substances,  etc.);  and  also  what  substances  are  dissolved  by 
treatment  with  very  dilute  hydrochloric  acid  at  a  gentle  heat 
(calcium  and  magnesium  carbonates,  ferric  oxide,  phosphoric 
acid,  etc.).  The  clay  is  quantitatively  examined  either  as  it  is,  or, 
according  to  circumstances,  after  previous  treatment  with  weak 
acids  (acetic  or  very  dilute  hydrochloric  acid)  to  free  it  from  ad- 
mixed alkaline-earth  carbonates;  or,  after  the  coarser  sand  has 
been  separated  by  elutriation. 

First  Method. 

a.  Triturate  the  air-dried  clay  as  fine  as  possible,  and  transfer 
it  to  a  stoppered  test-tube. 

6.  Dry  about  2  grm.  in  a  platinum  crucible  or  dish  at  120° 
to  constant  weight.  The  loss  of  weight  gives  the  moisture.  Then 
ignite,  at  first  gently,  then  strongly,  and  for  quite  some  time; 
the  loss  in  weight  represents  the  combined  water  (together  with 
the  organic  and  volatile  constituents  of  the  clay,  if  such  are  present). 

c.  Decompose  1  or  2  grm.  of  the  air-dried  clay  with  potassium 
and  sodium  carbonates,  proceeding  exactly  as  detailed  in  §  140, 
II,  b.    The  silicic  acid  obtained  is  weighed,  and  then  volatilized 
by  treatment  with  ammonium  fluoride  and  sulphuric  acid.     If 
any  non- volatile  residue  remains,  its  weight  must  be  subtracted 
from  that  of  the  impure  silicic  acid.     Fuse  this  residue  with  potas^- 
sium  disulphate,  and  in  the  solution  determine  any  titanic  acid 
that  may  be  present  (§  237,  8),  and  also  the  small  quantity  of 
alumina  that  is  sometimes  present. 

d.  Evaporate   the  hydrochloric-acid   solution   separated  from 
the  silicic  acid,  with  the  addition  of  a  few  drops  of  nitric  acid, 
until  the  greater  part,  of  the  free  acid  has  been  driven  off,  then 
dilute  with  water,  add  an  excess  of  pure  barium  carbonate,  and 
digest  in  the  cold  for  twenty-four  hours  with  frequent  stirring; 
filter  off   the   precipitate   of   aluminium   hydroxide  containing  a 
little  ferric   hydroxide  and   barium   carbonate,   then  wash,   first 


418  DETERMINATION    OF   COMMERCIAL    VALUES.          [§  238. 

by  decantation,  then  on  the  filter.  Now  dissolve  the  precipitate 
in  hydrochloric  acid,  precipitate  the  barium  with  sulphuric  acid, 
collect  the  precipitate,  wash,  add  the  washings  to  the  filtrate,  and 
divide  the  latter  into  two  equal  portions,  a  and  /?,  either  by  measur- 
ing or  weighing: 

a.  Precipitate  with  ammonia,  decant,  and  filter  after  standing 
some  time  in  a  warm  place;  wash  thoroughly,  dry,  ignite  (finally 
with  a  gas  blast-lamp),  weigh,  multiply  by  2,  and  thus  ascertain 
the  alumina  and  ferric  oxide.* 

/?.  Concentrate,  and  determine  the  iron  present  with  stannous 
chloride  (Vol.  I,  p.  328),  or  add  potassium  tartrate,  ammonia, 
and  ammonium  sulphide,  and  determine  the  iron  as  ferric  oxide 
(Vol.  I,  p.  642  [77]).  Multiply  the  ferric  oxide  obtained  by  2. 

The  alumina  =  the  result  of  a  minus  the  result  of  ft,  and  minus 
the  small  quantities  of  titanic  and  silicic  acids  (if  these  have  been 
found)  obtained  in  a,  and  which,  of  course,  must  be  first  multiplied 
by  2. 

To  the  filtrate  from  the  precipitate  caused  by  the  barium  car- 
bonate, and  without  previous  concentration,  carefully  add  sulphuric 
acid  (§  132,  1),  filter  off  the  barium  sulphate  and  wash  it  until  the 
washings  no  longer  react  for  sulphuric  acid;  collect  and  unite  the 
washings  and  filtrate,  concentrate  somewhat  (yet  not  sufficiently 
to  precipitate  calcium  sulphate),  and  separate  the  calcium  and 
magnesium  according  to  §  154,  6  [36]. 

e.  Add  a  little  sulphuric  acid  to  2  grm.  of  the  air-dried  clay 
with  strong  aqueous  hydrofluoric  acid  (Vol.  I,  p.  513),  gaseous  hydro- 
fluoric acid  (Vol.  I,  p.  515),  or  ammonium  fluoride  (Vol.  I,  p.  516). 
Treat  the  sulphates  obtained  by  any  one  of  these  methods  with 
hydrochloric  acid.  If  there  is  any  residue,  allow  it  to  settle,  decant 
the  liquid  so  far  as  possible,  and  treat  the  residue  again  with  hy- 

*  In  this  precipitate  is  usually  found  the  greater  part  of  any  titanic  acid 
that  may  be  present,  if  the  precipitate  is  treated  according  to  the  method 
described  in  the  preceding  paragraphs,  p.  411.  If  an  insoluble  residue 
remains  on  fusing  with  potassium  disulphate  and  treating  the  melt  with 
water,  it  consists  of  silicic  acid.  This  must  be  flocculent  in  appearance, 
otherwise  the  residue  must  be  fused  again  with  potassium  disulphate,  or 
decomposed  with  sodium  carbonate  (§  140,  II,  6). 


§  238.]  SILICON    COMPOUNDS.  419 

drofluoric  acid  or  ammonium  fluoride.  To  the  diluted  hydro- 
chloric-acid solution  cautiously  add  barium  chloride  so  long  as  a 
precipitate  forms;  then,  without  i.ltering,  add  ammonium  carbon- 
ate and  some  ammonia.  Allow  to  settle  in  the  cold,  filter,  wash, 
evaporate  the  solution,  and  ignite  the  residue  to  drive  off  the 
ammonium  salts ;  take  up  the  residue  with  water,  boil  with  a  little 
pure  milk-of-lime  to  remove  magnesium,  filter,  and  in  the  filtrate 
precipitate  any  calcium  and  barium  present  by  adding  ammonium 
carbonate  and  ammonia,  etc.;  determine  the  alkalies  present 
according  to  p.  249  this  volume. 

The  general  composition  of  the  clay  is  ascertained  by  these 
methods.  If,  however,  it  is  desired  to  ascertain  also  (A)  how 
much  of  the  silicic  acid  found  is  chemically  combined  with  the 
bases  of  the  clay;  (B)  how  much  as  hydrated  acid;  (C)  and  how 
much  as  quartzr-sand.  or  as  silicate  present  in  the  form  of  sand 
(e.  g.  felspar  sand),  the  following  additional  processes  are  required: 

/.  Heat  a  third  portion  of  the  air-dried  clay  (1  to  2  grms.) 
with  an  excess  of  pure  sulphuric  acid  to  which  a  little  water  has 
been  added,  for  ten  to  twelve  hours,  until  near  the  end  the  excess 
of  acid  has  been  nearly  but  not  altogether  driven  off.  Allow  to 
cool,  add  a  considerable  quantity  of  water,  wash  the  undissolved 
residue  A  +  5-hsand),  and  while  still  moist,  transfer  it  to  a  plati- 
num or  porcelain  dish,  and  treat  it  with  a  boiling  solution  of  so- 
dium carbonate,  as  detailed  in  §  237,  2,  b.  By  determining  the 
silicic  acid  dissolved  by  the  alkaline  solution  we  ascertain  A+B. 
The  sand  is  washed,  ignited,  and  weighed. 

If  the  weight  of  the  sand + A  +B  is  equal  to  the  total  weight  of 
the  silicic  acid  found  in  c,  the  sand  is  pure  quartz  sand;  if,  on  the 
contrary,  it  is  higher,  the  sand  is  not  pure  quartz  sand,  but  is  the 
more  or  less  sandy  powder  of  a  silicate,  e.g.,  felspar  sand;  in  this 
case  C  is  then  found  by  subtracting  A  +  B  from  the  total  silicic  acid 
found  in  c.  If  the  composition  of  the  sand  is  to  be  more  minutely 
ascertained,  the  separated  sand  must  be  subjected  to  a  special 
analysis. 

The  quartz  sand  may  be  separated  from  the  admixed  silicates 
by  heating  with  a  little  dilute  sulphuric  acid  in  sealed  glass  tubes 


420  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  238. 

(Vol.  I,  p.  521,  e),  or,  by  cautiously  heating  with  phosphoric  acid 
which,  on  gradually  raising  the  temperature,  decomposes  first  the 
silicates  with  the  separation  of  gelatinous  silicic  acid,  and  then 
attacks  the  quartz  (AL.  MULLER*).  The  heat  must  be  very 
.cautiously  regulated  and  maintained  at  from  190°  to  200°.  A. 
MULLER  has  devised  a  suitable  furnace  for  this  purpose.f  E. 
LAUFER'S  communication  J  shows  this,  and  also  to  what  extent 
fquartz  sand  is  attacked  by  heating  with  phosphoric  acid. 

g.  To  ascertain  the  quantity  of  silicic  acid  which  will  be  dissolved 
out  from  clay  by  a  boiling  solution  of  sodium  carbonate  (B),  and 
which  may  be  assumed  to  be  present  as  hydrated  silicic  acid, 
repeatedly  boil  a  somewhat  larger  portion  of  the  air-dried  clay 
-with  the  sodium-carbonate  solution,  and  in  the  filtrate  determine 
the  silicic  acid  by  evaporating  with  hydrochloric  acid.  Finally 
4  =  (A  +  B)  -B. 

h.  If  clays  contain  weighable  quantities  of  organic  substances 
or  sulphides,  determine  the  former  according  to  §  237,  4;  and  the 
latter  according  to  §  237,  6. 

Second  Method. 

If  the  clays  to  be  analyzed  are  composed  of  quartz  sand, 
the  clayey  part  of  which  is  readily  decomposed  by  sulphuric 
acid,  the  analysis  may  be  greatly  simplified  by  employing  the 
following  process: 

a.  Preparation    for    analysis,    drying,    and    determination    of 
water,  just  as  in  the  first  method. 

b.  Decompose  about  2  grm.  of  the  clay  with  sulphuric  acid  as 
In  /  in  the  first  method,  remove  the  greater  portion  of  the  sulphuric 
acid  by  evaporating,  dilute  with  water,  filter  off  the  silicic  acid 
and  sand,  separate  these  by  boiling  with  a  solution  of  sodium 
carbonate,  and  determine  both  as  in  §  237,  1,  b. 

c.  To  the  filtrate  from  6  cautiously  add  a  solution  of  lead 
nitrate,  taking  care  to  avoid  any  considerable  excess,  filter  off  the 

*  Zeitschr.  /.  analyt.  Chem.,  v,  431. 
f  Ibid.,  vii,  465. 
I  Ibid,  xvn,  368. 


§  239.]  CHROMIUM   COMPOUNDS.  421 

lead  sulphate  after  several  hours,  wash,  add  the  washings  to  the 
filtrate,  and  from  the  united  liquids  remove  the  last  trace  of  lead 
with  hydrogen  sulphide;  then  filter,  evaporate  the  filtrate  (finally 
in  a  small  dish),  and  treat  the  residue  according  to  §  161,  5  [118]. 
As  clay  rarely  contains  weighable  traces  of  manganese,  this  method 
is  reduced  to  a  very  simple  form. 

10.  CHROMIUM  COMPOUNDS. 
ANALYSIS  OF  CHROME  IRON  ORE. 

§  239. 

Chrome  iron  ore  is  essentially  a  compound  of  chromic  oxide 
and  ferrous  oxide;  occasionally  a  part  of  the  chromic  oxide  is 
replaced  by  ferric  oxide  and  alumina,  while  a  part  of  the  ferrous 
OAide  is  replaced  by  magnesia.  The  mineral  frequently  contains, 
in  addition,  silicic  acid  or  silicates,  small  quantities  of  calcium,, 
manganese  oxides,  titanic  acid,  etc.  On  account  of  its  very  vary- 
ing chromium  content,  the  mineral  is  frequently  the  object  of 
chemical  analysis.  As  chrome  iron  ore  is  not  as  easily  decomposed 
as  most  other  minerals,  many  chemists  have  made  investigations 
with  a  view  to  finding  the  best  methods  of  decomposing  it.  As 
a  knowledge  of  these  is  instructive,  I  give  in  the  foot-note  *  a  list 
of  the  most  important  papers  that  have  been  published  lately, 
and  give  a  detailed  description  only  of  the  best  and  simplest 

*P.  HART  (Journ.  f.  prakt.  Chem.,  LXVII,  320).— CALVERT  (Dingl.  polyL 
Journ.,  cxxv,  466.)— CH.  O'NEILL  (Chem.  News,  1862,  No.  123,  199;  Zeitschr. 
/.  analyt.  Chem.,  i,  497).— OUDESLUYS  (Chem.  News,  1862,  No.  127,  254; 
Zeitschr.  f.  analyt.  Chem.,  i.  498).—  T.  S.  HUNT  (Sill.  Am.  Journ.  [2],  v,  418). 
— F.  A.  GENTH  (Chem.  News,  1862,  No.  137,  32;  Zeitschr.  f.  analyt.  Chem., 
L  498)._GIBBS  and  P.  C.  DUBOIS  (Zeitschr.  f.  analyt.  Chem.,  in,  401).— F.  W. 
CLARKE  (Zeitschr.  f.  analyt.  Chem.,  vn,  463).— J.  BLODGET  BRITTON  (Chem, 
News,  xxi,  266;  Zeitschr.  f.  analyt.  Chem.,  ix,  487).— FR.  C.  PHILLIPS  (Zeit- 
schr. f.  analyt,  Chem.,  xn,  189).— F.  H.  STORER  (Zeitschr.  f.  analyt.  Chem.,  ix, 
71,  and  comp.  F.  E.  STODDART,  ibid  ,  xm,  86).— R.  KAYSER  (Zeitschr.  /. 
analyt.  Chem.  xv,  187). — H.  HAGER  (Untersuchungen,  i,  163).— A.  CHRIS- 
TOMANOS  (Zeitschr.  f.  analyt.  Chem.,  xvii,  249).— E.  F.  SMITH  (ibid.,  514).— 
W.  DITTMAR  (ibid.,  xvm,  126).— F.  FELS  (ibid.,  xvm,  498).— W.  J.  SELL 
(Jaurn.  Chem.  Soc.,  1879,  293). 


422  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  239. 

methods.  These  include  both  the  determination  of  the  chromium 
and  the  accurate  determination  of  all  the  substances  present. 

In  all  the  methods  it  is  required  that  the  chrome  iron  ore  be 
reduced  to  the  form  of  very  finest,  impalpable  powder.  This  oper- 
ation must  be  patiently  and  conscientiously  performed,  as  upon  it 
depends  the  success  of  the  analysis. 

CHRISTOMANOS  recommends  to  strongly  ignite  the  coarse 
powder  on  a  platinum  cover  for  a  short  time,  in  order  to  facilitate 
the  subsequent  trituration  in  the  agate  mortar.  The  powder  must 
finally  be  separated  from  the  coarser  portions  by  sifting,  and  these 
again  powdered  and  mixed  in.  Elutriation  is  inadmissible,  as 
this  renders  the  sample  uneven.  If  CHRISTOMANOS'  method  of 
powdering  is  adopted,  the  sifted  powder  is  heated  again  before 
weighing.  The  analysis  is  then  performed  on  the  anhydrous 
substance. 

I.   METHOD    OF   DECOMPOSITION. 

a.  J.  BLODGET  BRITTON'S  Method.    Mix  as  intimately  as  possible 
0-5  grm.  of  the  very  finely  powdered  mineral  with  4  grm.  of  a 
mixture  of  1  part  potassium   chlorate  and  3  parts  soda-lime,  and 
heat  for  at  least  an  hour  and  a  half  to  bright  redness  in  a  covered 
platinum  crucible.     The  unfused  mass  may  be  readily  removed 
from  the  crucible  and  powdered.     The  decomposition  is  complete. 
If  the  temperature  be  raised  by  employing  a  gas  blast-lamp,  the 
total  decomposition  may  be  effected  in  20  minutes  (FELS).     The 
melt  contains  all  the  chromium  as  alkali  chromate.    The  operation, 
a  modification  of  CALVERT'S  process  (in  which  potassium  nitrate 
is  used  instead  of  potassium  chlorate),  is  simple,  certain,  and,  as 
it  may  be  performed  in  a  platinum  crucible,  is  strongly  to  be 
recommended. 

b.  KAYSER'S   Method.     Mix   1   part   (about  0-5  grm.)   of  the 
very  finely  powdered  chrome  iron  ore  with  2  parts  of  anhydrous 
sodium  carbonate  and  3  parts  of  calcium  hydroxide,  and  maintain 
the  mixture  at  a  bright-red  heat  for  about  an  hour  with  the  aid 
of  a  gas  blast-lamp,  in  an  open  platinum  crucible,  and  with  fre- 
quent stirring.      The  result  is  a  sintered  mass,  from  which  the 


§  239.]  CHROMIUM  COMPOUNDS.  423 

sodium  chromate  formed  may  be  easily  extracted  with  hot  water. 
If  the  operation  has  been  properly  conducted,  the  residue  will 
contain  no  chromium. 

c.  DITTMAR'S  Method.     Fuse  2  parts   of  borax  glass  with  3 
parts  of  sodium-potassium  carbonate,  and  preserve  the  flux  in 
closed  vessels.     For  the  decomposition,  fuse  0-5  grm.  of  the  very 
finely  powdered  ore  with  5  to  6  grm.  of  the  flux  in  a  platinum 
crucible,  over  a  BUXSEX  burner.     At  first  heat  to  redness  for  about 
five  minutes  with  the    crucible    covered,  then  remove  the  cover, 
place  it  obliquely  over  the  flame,  heat  as  strongly  as  possible,  and 
stir  the  mixture  with  a  platinum  wire  until  the  ore  is  completely 
dissolved,   maintaining   the   mixture   at  fusion  for  about  three- 
quarters  of  an  hour  with  access  of  air.     All  the  chromium  in  the 
melt  may  be  extracted  from  the  mass,  and  in  the  form  of  alkali 
chromate,  by  means  of  hot  water.     Should  the  BUNSEN  burner 
be  insufficient  to  heat  the  mixture  to  bright  redness,  the  gas  blow- 
pipe must  be  employed  if  the  decomposition  is  to  be  effected  with 
certainty  (FELS). 

d.  CHRTSTOMANOS'    Method.     Where   chromite   is   to   be   com- 
pletely analyzed,  CHR-STOMAXOS  recommends  the  method  of  PE- 
LIGOT   and  CLOUET,  somewhat   modified.     Mix  0-3   to   0-5   grm. 
of  the  very  finely  powdered  chrome  iron  ore  intimately  with  3 
to  3-5  grm.  of  pure,  anhydrous  sodium  carbonate,  and  heat  the 
mixture  in  a  platinum  dish,  provided  with  a  cover,  for  two  hours 
by  means  of  a  gas   blowpipe,  so  that  it  is  kept  in  a  fused  state. 
'By  adding   about   0-5  grm.   saltpetre,   the  decomposition  may 
be  greatly  hastened,  but  then  the  dish  will  be  strongly  attacked. 
Hence  it  is  inadvisable  to  add  any  saltpetre).     The  decomposi- 
tion is  complete,  but  the  continued  heating  for  two  hours  is  rather 
inconvenient.     The  melt  contains  all  the  chromium  as  alkali  chro  - 
mate. 

e.  To  just  simply  determine  the  quantity  of  chromium  present, 
CHRISTOMAXOS  intimately  mixes  0-3  to  0-5  grm.  of  the  chrome 
iron  ore  with  4  grm.  of  thoroughly  dried  and  still  warm  caustic 
soda  and  1-7  to  2  grm.  calcined  magnesia  in  a  mortar,  and  heats 
the  mixture  in  a  platinum  (or,  better,  gold)  crucible  for  an  hour 


424  DETERMINATION    OF    COMMERCIAL   VALUES.         [§    239. 

by  means  of  an  ordinary  BUNSEN  burner,  frequently  stirring  the 
mixture  with  a  platinum  wire.  On  boiling  the  sintered  mass 
with  water,  all  the  chromium  is  readily  obtained  in  solution  in 
the  form  of  sodium  chromate. 

/.  Method  of  T.  S.  HUNT  and  F.  A.  GENTH.  Fuse  about  0-5 
grm.  of  the  powdered  ore  in  a  capacious  platinum  crucible  with 
6  grm.  of  potassium  disulphate  for  fifteen  minutes  at  a  tempera- 
ture but  slightly  above  the  melting-point  of  the  latter,  then  in- 
crease the  heat  somewhat  so  that  the  bottom  of  the  crucible  ap- 
pears just  red-hot,  and  maintain  at  this  temperature  for  from 
fifteen  to  twenty  minutes.  The  melt  must  never  more  than  half  fill 
the  crucible.  During  this  period  the  mass  begins  to  flow  quietly, 
and  vapors  of  sulphuric  acid  are  copiously  evolved.  After  twenty 
minutes,  increase  the  heat  so  that  the  second  equivalent  of  sul- 
phuric acid  is  driven  off,  and  even  the  iron  and  chromium  sul- 
phates are  partially  decomposed.  To  the  fused  mass  now  add 
3  grm.  pure  sodium  carbonate,  heat  to  fusion,  and  gradually  add 
3  grm.  saltpetre  during  the  course  of  an  hour  while  maintaining 
the  whole  at  a  gentle  red  heat;  then  heat  for  fifteen  minutes  to 
bright  redness.  The  melt  contains  the  chromium  as  alkali  chro- 
mate. The  operation  is  rather  inconvenient,  and  the  platinum 
crucible  is  attacked,  but  the  results  obtained  are  good. 

II.   ANALYTICAL   METHODS. 

a.  Determination  of  all  the  Constituents. 

If  all  the  constituents  of  the  chrome  iron  ore  are  to  be  de- 
termined, it  is  best  to  employ  one  of  the  methods  in  which  only 
salts  of  the  alkalies  are  used,  preferably — in  order  to  avoid  the 
presence  also  of  boric  acid — the  method  d  01  /.  Treat  the  cooled 
melt  with  boiling  water,  filter  hot,  and  wash  the  undissolved  por- 
tion with  boiling  water.  Digest  the  residue  with  warm  hydro- 
chloric acid.  If  any  ore  remains  undecomposed,  this  must  not  be 
weighed  and  deducted,  but  subjected  to  the  decomposition 
process  until  decomposed.  In  the  alkaline  filtrate,  containing  all 
the  chromium  as  alkali  chromate,  are  occasionally  found  small 


§  239.]  CHROMIUM  COMPOUNDS.  425 

quantities  cf  manganic  and  silicic  acids,  alumina,  and  more  rarely 
titanic  acid.  To  separate  these  evaporate  the  solution  with  an 
excess  of  ammonium  nitrate  on  the  water-bath  almost  to  dryness, 
and  until  all  the  ammonia  liberated  is  expelled.  After  adding 
water,  there  remain  undissolved  silicic  and  titanic  acids,  alumina, 
and  manganic  oxide.  Filter,  add  an  excess  of  sulphurous  acid 
to  the  filtrate  to  reduce  the  chromic  acid  to  chromic  oxide, 
cautiously  heat  to  boiling,  and  add  pure  ammonia  free  from  silicic 
acid  in  slight  excess,  best  in  a  platinum  dish;  a  porcelain  dish 
may  be  used  if  this  is  not  at  hand,  but  a  glass  dish  must  not  be 
used.  Boil  for  several  minutes,  and  wash  the  separated  chromium 
hydroxide  by  repeatedly  boiling  and  decanting  on  a  filter  until 
the  washings  are  free  from  sulphuric  acid.  Afte  the  precipitate 
has  been  dried  and  ignited,  it  will  contain  alkali  chromate,  in 
consequence  of  the  presence  of  a  small  quantity  of  alkali  not  re- 
moved by  the  washing.  Before  weighing  the  precipitate,  hence 
boil  it  with  a  little  water,  add  first  a  few  drops  sulphurous  acid, 
then  ammonia,  filter  again,  wash,  dry,  ignite,  and  weigh  the  now 
perfectly  pure  chromic  oxide  (F.  A.  GENTH  *). 

The  constituents  of  the  hydrochloric-acid  solution,  as  well 
as  those  separated  by  evaporation  with  ammonium  nitrate,  sepa- 
rate by  the  methods  detailed  in  the  General  Part. 

CHRISTOMANOS  f  has  also  thoroughly  investigated  the  com- 
plete analysis  of  chrome  iron  ore.  He  advises  the  following 
method:  Prepare  the  melt  according  to  I,  d.  Just  before  it  has 
become  cold,  place  the  crucible  with  its  contents  and  cover  in  a 
deep  porcelain  dish  containing  300  to  400  c.c.  boiling  water.  The 
melt  rapidly  disintegrates.  After  about  five  minutes  remove  the 
crucible  and  cover,  rub  off  the  adhering  particles,  and  carefully 
wash  with  hot  water.  Then  introduce,  a  small  quantity  of  hydro- 
chloric acid  into  the  crucible  and  set  the  latter  aside  for  a  time. 

Now  boil  the  contents  of  the  porcelain  dish  for  five  or  ten 
minutes  until  the  color  of  the  liquid,  which  is  at  first  rusty  brown, 
green,  or  bluish-green  from  the  presence  of  sodium  manganate 
and  ferrate,  has  changed  to  a  pure  deep  yellow.  As  soon  as  this 

*  Zeitschr.  /.  analyt.  Chem.,  i,  498.  t  *&*&»  XVII>  249- 


426  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  239. 

occurs,  filter  the  liquid  by  means  of  a  vacuum  filter,  thoroughly 
wash  the  precipitate  with  hot  water,  and  dry  it  by  drawing 
through  it  a  rather  strong  current  of  air,  so  that  it  may  be  readily 
removed  from  the  filter.  Then  treat  it,  together  with  the  filter 
ash,  with  hydrochloric  acid,  add  the  hydrochloric  acid  from  the 
crucible  which  was  set  aside,  and  evaporate  on  the  water-bath  to 
dryness  with  the  addition  of  a  few  drops  nitric  acid,  moisten  the 
residue  with  hydrochloric  acid,  and  once  more  evaporate  to  dry- 
ness;  treat  with  hydrochloric  acidr  then  with  water  remove  the 
silicic  acid,  and  then  separate  the  iron,  calcium,  and  magnesium 
according  to  the  methods  detailed  in  Vol.  I.  Should  the  silicic 
acid  removed  not  completely  dissolve  in  a  boiling  solution  of 
sodium  carbonate,  the  residue  of  undecomposed  chrome  iron  ore 
must  again  be  treated  and  decomposed. 

In  the  yellow  solution  obtained  by  boiling  the  molt  with  water, 
all  the  aluminium  is  found  as  sodium  aluminate,  and  the  chromium 
as  sodium  chromate;  the  solution  may  also  contain  a  little  sodium 
silicate,  and  in  certain  cases  a  little  titanic  acid.  These  are  sep- 
arated by  the  methods  already  described. 

[The  silica  in  chrome  ore,  as  well  as  the  silicon  in  ferro-chromium, 
may  also  be  determined  according  to  GEO.  TATE  *  as  follows: 
One  to  two  grm.  of  ferro-chromium  or  of  ore  are  fused  with  about 
five  times  their  weight  of  sodium  peroxide  in  a  nickel  crucible. 
The  crucible  and  contents,  after  cooling,  are  brought  into  water 
contained  in  a  capacious  nickel  dish.  The  alkaline  liquid  so 
obtained,  containing  chromate  and  silicate,  together  with  oxides  of 
iron  and  nickel  in  suspension,  is  treated  with  hydrochloric  acid  in 
quantity  insufficient  to  neutralize  the  alkali,  and  then  evaporated 
to  dryness  in  a  nickel  dish.  The  residue  is  scraped,  so  far  as  is 
practicable,  from  the  sides  to  the  bottom  of  the  dish,  and  40  c.c. 
of  strong  pure  sulphuric  acid  rapidly  poured  on.  Fumes  of  hydro- 
chloric and  chlorochromic  acids  are  evolved,  and  completely  ex- 
pelled by  applying  heat.  The  temperature  is  raised  until  the 
sulphuric  acid  begins  to  fume,  thereby  ensuring  the  dehydration 

*  Chem.  News,  LXXX,  p.  235 


§  239.]  CHROMIUM   COMPOUNDS.  427 

of  the  silicic  acid.  After  removal  of  the  flame  and  cooling  for  a  few 
minutes,  water  is  cautiously  added.  To  prevent  undue  corrosion 
of  the  nickel  vessel,  the  turbid  liquid  is  transferred  to  a  porcelain 
dish,  and,  after  making  the  bulk  about  250  c.c.,  boiled  for  fifteen 
to  thirty  minutes,  or  until  the  sulphates  have  completely  dissolved 
The  silica  is  filtered  off,  washed  thoroughly,  ignited  in  a  platinum 
crucible,  and  weighed.  The  silica  so  obtained  should  be  white,  but, 
as  a  few  mgrm.  of  metallic  oxides  usually  accompany  it,  the  real 
weight  of  SiO2  (from  which  the  silicon  is  reduced)  is  obtained  by 
determining  the  loss  in  weight  occasioned  by  evaporation  with 
hydrofluoric  acid  and  one  drop  of  sulphuric  acid,  followed  by 
strong  ignition. 

It  is  advisable  to  test  the  purity  of  the  reagents  by  conducting 
a  blank  test. 

The  results  are  very  concordant  and  apparently  exact.  Ex- 
periments have  shown  that  90  to  95  per  cent,  of  the  chromium 
can  be  volatilized  by  the  action  of  the  sulphuric  acid ;  the  removal 
of  the  chromium  prevents  the  contamination  of  the  silica  by 
basic  salts  of  that  metal. 

Test  experiments,  wherein  known  weights  of  silica  were  fused 
with  bichromate  of  sodium  peroxide,  and  the  products  submitted 
to  the  above  treatment,  have  shown  that  the  process  brings  prac- 
tically the  whole  of  the  silicon  into  a  weighable  form. — TRANSLATOR.] 
In  the  calculation  and  arrangement  of  the  results,  the  chro- 
mium is  to  be  put  down  as  chromic  oxide;  with  iron,  however, 
the  question  is  mo*re  difficult.  As  a  rule,  it  is  all  present  as  fer- 
rous iron,  but  in  certain  chromites  ferric  oxide  replaces  part  of 
the  chromic  oxide.  In  this  case  the  information  desired  can 
only  be  gained  from  the  loss  of  weight  which  the  anhydrous  mineral 
sustains  on  prolonged  ignition  in  a  current  of  hydrogen.  Chro- 
mites containing  ferric  oxide  in  the  admixed  gangue  give  it  up 
on  prolonged  heating  of  the  finely  powdered  mineral  with  hydro- 
chloric acid.  If  calcium  is  present  (usually  as  carbonate),  a 
carbon-dioxide  determination  is  as  a  rule  required.  The  chromite 
to  be  used  for  this  determination  must,  of  course,  not  be  ignited. 


428  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  24Q. 

b.  Simple  Chromium  Determination  in  Chrome  Iron  Ore. 

As  the  value  of  chrome  iron  ore  depends  only  upon  the 
chromium  content,  it  is  frequently  sufficient  to  simply  determine 
the  chromium  only.  For  this  purpose  a  volumetric  method  is  as 
a  rule  chosen,  one  of  the  following  being;  adopted: 

a.  Thoroughly  extract  the  melt  (best  prepared  according  to 
I,  a,  b,  or  e)  by  boiling  with  water,  warm  with  an  excess  of  sul- 
phuric acid  to  redissolve  the  precipitated  aluminium  hydroxide, 
cool  the  solution,  and  in  it,  or  in  an  aliquot  portion  of  it,  determine 
the  chromic  acid  according  to  §  130,  I,  e,  a.  If  the  solution  con- 
tains no  chloride  (melt  I,  b  or  e),  determine  the  excess  of  ferrous 
sulphate  with  (most  conveniently)  potassium  permanganate 
(§  112;  2,  a) ;  if,  however,  a  chloride  is  present  (melt  I,- a),  PENNY'S 
method  is  preferable  (§  112,  2,  b). 

/?.  Heat  melt  I  a  with  a  small  quantity  (about  20  c.c.)  of  water, 
and  after  cooling,  add  15  c.c.  of  hydrochloric  acid,  sp.  gr.  1-12. 
Everything  but  the  separated  silica  should  go  into  solution.  Now 
add  (according  to  §  130,  I,  'e,  a)  a  known  quantity  of  ferrous 
sulphate  in  excess  and  determine  the  excess  (J.  BLODGET  BRITTON). 
The  determination  of  the  excess  of  ferrous  sulphate  by  means  of 
potassium  permanganate  as  recommended  by  BRITTON,  is  inad- 
missible (comp.Vol.  I,  p.  319,  f) ;  for  this  purpose  PENNY'S  method 
(§  112,  2,  6,  p.  319)  must  be  employed. 

Melts  prepared  with  the  addition  of  an  alkali  nitrate  cannot 
be  examined  by  these  methods,  as  alkali  nitrates  are  present,  the 
acid  of  which  would  partially  reduce  the  chromic  acid  on  acidulat- 
ing the  aqueous  solution  of  the  melt. 

11.  ZINC  COMPOUNDS. 

A.  CALAMINE;   B.  ELECTRIC  CALAMINE. 

§240. 

Calamine  consists  of  zinc  carbonate  with  more  or  less  admixed 
ferrous,  manganous,  lead,  cadmium,  calcium,  and  magnesium 
oxides,  and  silicic  acid,  and  sometimes  also  cupric  oxide.  Electric 


§  240.]  ZINC    COMPOUNDS.  429 

calamine  consists  of  a  hydrated  basic  zinc  silicate,  frequently  con- 
taining admixed  zinc  carbonate,  and  which  besides  usually  contains 
ferric  and  ferrous  oxides,  and  occasionally  also  manganous,  lead, 
aluminium,  calcium,  and  magnesium  oxides. 

The  minerals  are  finely  powdered,  and  analyzed  in  an  air- 
dried  condition,  or  after  drying  at  100°.  In  the  former  case,  the 
moisture  is  determined  by  drying  a  sample  at  100°.  If  the  degree 
of  oxidation  of  the  iron  is  to  be  accurately  determined,  the  analysis 
should  be  carried  out  with  the  air-dried  powder. 

Determination  of  all  the  Constituents. 

a.  Treat  a  sample  according  to  §  140,  II,  a;  i.e.,  separate  the 
silicic  acid  in  the  usual  manner.    As  the  acid  generally  contains 
sand  or  undecomposed  gangue,  it  must  be  separated  from  these  by 
boiling  with  a  solution  of  sodium  carbonate  (§  237,  2,  6).     When 
treating  the  residue  with  hydrochloric  acid  and  water,  care  must 
be  taken  to  use  about  100  parts  of  water  for  every  4  parts  of  hydro- 
chloric acid  of  sp.  gr.  1-1  (§  162,  A,  /?). 

b.  Precipitate  the  solution  so  obtained  with  hydrogen  sulphide, 
and  separate  any  metals  of  the  fifth  and  sixth  groups  that  may  be 
thrown  down,  according  to  the  methods  described  in  Section  V. 
A  too  long-continued  passing-in  of  hydrogen  sulphide  should  be 
avoided,  otherwise  zinc  sulphide  may  also  be  precipitated.     In  any 
case  it  is  advisable  to  dissolve  the  precipitated  sulphides  in  hot 
hydrochloric  acid  with  the  addition  of  a  little  brominized  hydro- 
chloric acid,  and  after  driving  off  the  excess  of  bromine,  to  repeat 
the  precipitation  with  hydrogen  sulphide.      In  this  second  pre- 
cipitation, too,  care  must  be  taken  to  add  4  parts  of  hydrochloric 
acid  to  every  100  parts  of  water  (§  162,  A,  /?*). 

c.  Neutralize  the  filtrate  or  filtrates  with  ammonia,  precipitate 

*  According  to  GERH.  LARSEN  (Zeitschr.  f.  analyt.  Chem.,  xvii,  312)  the 
double  precipitation  may  be  avoided  if  during  the  first  prec:p;tation  with 
hydrogen  sulphide  30  c.c.  of  hydrochloric  acid  of  sp.  gr.  1-1  are  present 
in  250  c.c.  of  the  solution  (a  proportion  of  acid  which  is  suitable  for  the 
separation  of  zinc  from  copoer,  but  not  from  cadmium),  and  the  precipitate 
H  f  rst  washed  with  hydrochloric  acid  of  sp.  gr.  1-05  saturated  with  hydrogen 
sulphide,  and  then  with  aqueous  solution  of  hydrogen  sulphide. 


430  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  241. 

with  ammonium  sulphide,  treat  the  precipitate  exactly  as  described 
in  §  108,  b,  boil  the  ignited  zinc  oxide  (containing  ferric  and  man- 
ganic oxides  and  some  silicic  acid)  with  water,  weigh,  then  volu- 
metrically  determine  the  manganese  present  (Vol.  I,  p.  665  [109]); 
filter  the  solution  from  the  un dissolved  silicic  acid  which  is  then 
to  be  determined,  and  finally  determine  in  the  hydrochloric-acid 
solution  obtained  the  ferric  oxide  by  means  of  stannous-chloride 
solution  (Vol.  I,  p.  327).  The  quantity  of  zinc  oxide  is  ascertained 
from  the  difference.  Of  course  any  other  of  the  methods  described 
in  §  160  may  be  employed  for  the  separation  or  determination  of 
the  zinc,  manganese,  and  iron  in  ammonium-sulphide  precipi- 
tates, but  in  none  other  are  accuracy  and  rapidity  so  equally  com- 
bined as  in  the  one  described.  If,  however,  too  large  a  ferric-  or 
ferrous-oxide  content  is  present,  it  is  preferable  to  make  a  direct 
determination  of  the  zinc  by  the  second  method  given  in  §  241. 

d.  Acidulate  the  filtrate  from  the  zinc  sulphide  with  hydro- 
chloric acid,  boil  for  some  time,  filter  off  the  separated  sulphur, 
and  determine  the  calcium  and  magnesium  according  to  §  154,  6  [36]. 

e.  Ignite  a  separate  sample  in  a  bulb-tube  of  the  apparatus 
described  in  Vol.  I,  p.  76.     The  loss  of  weight  of  the  bulb-tube  gives 
the  water  +  the  carbon  dioxide     the  increase  of  weight  of  the 
calcium-chloride  tube  gives  the  water  alone;   the  difference  gives 
the  carbon  dioxide.     In  cases  where  the  presence  of  a  considerable 
proportion  of  ferrous  oxide  or  lime  impairs  the  accuracy  of  the 
indirect  determination  of  the  carbon   dioxide,   or  if  the  carbon 
dioxide  is  present  in  but  very  small  quantity,  one  of  the  methods 
described  in  §  139,  II,  e}  should  be  employed. 

/.  If  the  ore  contains  ferrous  and  ferric  oxides,  determine  them 
by  means  of  potassium  chromate  in  a  hydrochloric-acid  solution 
prepared  in  a  current  of  carbon  dioxide  (Vol.  I,  p.  319,  b). 

C.  ZINC  BLENDE. 
§241. 

Zinc  blende  consists  of  zinc  sulphide,  frequently  containing 
other  admixed  sulphides,  more  especially  those  of  lead,  cadmium, 


§  241.]  ZINC    COMPOUNDS.  431 

copper,  iron,  and  manganese.  Occasionally  there  are  also  found  in 
blende  small  quantities  of  arsenic,  antimony,  nickel,  and  cobalt. 
Besides  these,  due  regard  must  be  had  in  the  analysis  to  admixed 
gangue. 

The  blende  must  be  very  finely  powdered,  and  dried  at  100°. 

DETERMINATION    OF   ALL   THE   CONSTITUENTS. 

First  Method. 

a.  Determine  the  sulphur  in  one  portion,  best  according  to  the 
process  detailed  in  Vol.  I,  p.  562, 1,  a;  it  must  be  remembered  that 
blende  frequently  contains  lead. 

b.  The  metals  are  determined  in  a  fresh  portion.     For  this 
purpose  heat  1  or  2  grm.  of  the  ore  with  fuming  hydrochloric  acid 
until  no  more  hydrogen  sulphide  is  evolved,  then  add  a  little  nitric 
acid  and  about  5  to  6  c.c.  pure  sulphuric  acid  previously  diluted 
with  a  little  water,  and  evaporate  until  the  hydrochloric  and  nitric 
acids  have  been  driven  off.    Then  dilute  with  20  to  30  c.c.  water, 
and  filter  off  the  residue  from  the  solution.     If  the  residue  con- 
tains (as  it  frequently  does)  lead  sulphate,  wash  it  first  with  water 
acidulated  with  sulphuric  acid,  then  with  alcohol  (the  alcoholic 
washings  must  be  collected  separately).     Boil  the  washed  residue 
repeatedly  with  a  solution  of  ammonium  acetate  until  all  the  lead 
sulphate  is  dissolved,  and  ignite  and  weigh  the  small  quantity  of 
residual  gangue.     Precipitate  the  lead  in  the  ammonium-acetate 
solution  with  hydrogen  sulphide  and  determine  it  as  lead  sulphide 

§  H6?  3). 

To  the  sulphuric-acid  solution  add  hydrochloric  acid  of  sp.  gr. 
1  •  1  in  the  proportion  of  4  parts  of  acid  to  100  parts  of  solution, 
and  proceed  according  to  §  240,  b.  In  the  case  of  blende  rich  in 
iron,  it  is  better  to  proceed  according  to  the  second  or  third  method, 
or  to  separate  the  zinc  as  a  sulphide  in  the  presence  of  ammonium 
sulphocyanate,  according  to  a  method  recently  proposed  by  ZIM- 

MERMANN.* 

For  this  purpose  evaporate  on  the  water-bath,  almost  to  dry- 
*  Ann.  der  Chem.,  cxcix,  1. 


432  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  241. 

ness,  the  filtrate  from  the  precipitate  caused  by  hydrogen  sulphide, 
dilute,  and  cautiously  add  sodium  carbonate  (towards  the  last 
in  dilute  solution)  until  a  permanent,  slight  turbidity  ensues,  and 
the  solution  is  as  nearly  neutral  as  possible;  this  is  an  essential 
condition  for  the  success  of  ZIMMERMAN'S  method.  Now  add  an 
excess  of  a  not  too  dilute  ammonium-sulphocyanate  solution, 
rinse  down  the  walls  of  the  vessel  (best  by  means  of  an  ERLENMEYER 
flask)  with  water,  warm  to  60°  or  70°,  and  pass  a  very  moderate 
current  of  hydrogen  sulphide  through  the  liquid  several  times,  but 
for  not  too  long  a  time,  until  the  odor  of  the  gas  no  longer  disappears 
on  exposing  the  solution  to  the  air.  The  liquid  at  first  acquires 
a  nearly  milk-white  turbidity,  but  later  on  the  zinc  sulphide  sepa- 
rates completely,  while  the  iron  and  manganese  (also  nickel  and 
cobalt)  remain  dissolved.  Allow  to  deposit  in  a  moderately  warm 
place,  filter,  wash  the  perfectly  white  precipitate  with  water  con- 
taining hydrogen  sulphide  and  ammonium  sulphocyanate,  dry, 
and  ignite  the  zinc  sulphide  according  to  Vol.  I,  p.  289,  2).  Instead 
of  this  jnethod  of  determination,  the  method  proposed  by  VOLHARD  * 
may  be  employed.  This  method  consists  in  dissolving  the  zinc 
sulphide  in  hydrochloric  acid,  evaporating  the  solution  to  dryness 
in  a  weighed  platinum  dish,  adding  an  excess  of  pure,  alkali- free 
mercuric  oxide  suspended  in  water,  again  evaporating,  and  igniting ; 
'the  zinc  oxide  thus  obtained  is  then  weighed. 

In  the  liquid  filtered  off  from  the  zinc  sulphide  the  sulpho- 
cyanates  are  next  decomposed  by  cautiously  heating  with  nitric 
acid  added  gradually  in  small  quantities,  conducting  the  opera- 
tion in  a  capacious  flask;  then,  if  necessary,  after  filtering,  pre- 
cipitate the  iron  as  a  basic  ferric  salt  (Vol.  I,  p.  644,  3,  a),  and  in 
the  filtrate  precipitate  the  manganese  with  ammonium  sulphide. 

Second  Method  (HAMPE'S  f). 

a.  Boil  about  1  grm.  of  the  finely  powdered  ore  dried  at  100° 
with  nitric  acid  in  a  long-necked  flask.  After  all  the  nitrous 
acid  has  been  expelled,  and  the  liquid  has  been  highly  concen- 

*  Loc.  cit.,  p.  6.  f  Zeitschr.  /.  analyt.  Chem.,  xvn,  362. 


§  241.]  ZINC    COMPOUNDS.  433 

trated,  add  30  c.c.  nitric  acid  of  sp,  gr.  1-2,  and  about  200  c.c. 
water. 

b.  Precipitate  the  solution,  without  previous  filtration,  with 
hydrogen  sulphide  and  without  warming,  filter  off  the  precipitate 
(when  this  is  completely  deposited)  together  with  the  undissolved 
gangue,  wash,  and  treat  the  precipitate  on  the  filter  with  hot  but 
not  too   concentrated   nitric   acid;    then  perforate  the  point  of 
the  filter,  wash  all  the  undissolved  substance  into  a  flask,  wash 
the  filter,  concentrate  the  liquid  by  evaporation,  add  about  200  c.c. 
water  and  30  c.c.  nitric  acid  of  sp.  gr.  1-2,  again  precipitate  with 
hydrogen  sulphide,  and  add  the  filtrate  to  that  first  obtained. 

c.  Concentrate  the  filtrate  almost  to  dryness  by  boiling  in  a 
long-necked  flask,  supersaturate  with  ammonia  the  solution  now 
free  from  hydrogen  sulphide  but  containing  all  the  iron  as  a  ferric 
salt,  filter,  wash,  dissolve  the  precipitate  on  the  filter  with  hot, 
moderately  strong   nitric  acid,  and  when  cold   precipitate  again 
with  an  excess  of  ammonia;  filter  through  the  same  filter,  and 
repeat  the  operation  of  dissolving  with  nitric  acid  and  precipitating 
with   ammonia    once   or   twice    more.     The    precipitate    consists 
chiefly  of  ferric  oxide,  but  it  may  also  contain  alumina  and  man- 
ganese sesquioxide,  hence  effect  the  separation  according  to  §  161. 

d.  Acidulate  with  acetic  acid  the  ammoniacal  liquids  obtained 
in  c,  dilute  to  at  least  two  litres,  and  pass  in  hydrogen  sulphide, 
Allow  to  stand  for  at  least  twelve  (better  twenty-four)   hours, 
pour  off  the  clear  fluid  through  the  filter,  and  then  transfer  also 
the  perfectly  white  zinc  sulphide  to  the  filter.     On  account  of 
the  extreme  dilution,  and  because  in  the  analysis  neither  hydro- 
chloric acid  nor  other  non-volatile  substances  have  been  added, 
it  suffices  to  wash  but  for  a  short  time  with   hydrogen-sulphide 
water  to  which  a  small  quantity  of  ammonium  acetate  has  been 
added.     Fuse  the  dried  zinc  sulphide  in  a  ROSE  crucible  together 
with  the  filter  ash  and  a  little  pure  sulphur,  and  then  proceed  ac- 
cording to  §  108,  2. 

e.  To  the  fluid  separated  from  the  zinc  sulphide,   and  con- 
tained in  a  large  flask,  add  ammonia  to  alkaline  reaction,  then 
add  ammonium  sulphide,  and  allow  to  stand  for  at  least  twenty- 


434  DETERMINATION    OF   COMMERCIAL    VALUES.         [§  241. 

four  hours  in  a  warm  place.  If  a  precipitate  deposits,  examine 
it  to  see  if  it  contains  anv  zinc ;  if  the  operation  has  been  properly 
performed  it  will  contain  none.  As  a  rule  the  precipitate  thus 
formed  is  manganese  sulphide. 

/.  The  filter-contents  obtained  in  b  treat  with  hydrochloric 
acid  containing  a  little  bromine;  the  gangue  remains  undissolved, 
and  is  to  be  dried  and  weighed.  As  a  precaution,  heat  it  with 
ammonium-acetate  solution  to  see  whether  it  yields  up  to  this 
solution  any  lead  sulphate. 

g.  Heat  with  ammonia  the  brominized  hydrochloric  acid 
obtained  in  /,  in  order  to  remove  the  excess  of  bromine,  and  in 
the  solution  then  determine  the  metals  present  (lead,  copper, 
cadmium,  arsenic,  and  antimony)  according  to  the  methods  de- 
tailed in  §§  163  and  164. 

h.  Determine  the  sulphur  by  the  first  method. 

Third  Method  (CLASSEN'S*). 

Heat  the  blende  with  concentrated  hydrochloric  acid,  add 
towards  the  end  a  little  nitric  acid,  evaporate  the  excess  of  the 
acids,  take  up  the  residue  with  hydrochloric  acid  and  water, 
filter  off  the  gangue,  and  precipitate  the  metals  of  the  fifth  and 
sixth  groups  with  hydrogen  sulphide  (comp.  §  240,  a  and  6).  Con- 
centrate the  filtrate  and  washings  by  evaporation,  adding  towards 
the  end  some  nitric  acid  or  bromine  water  in  order  to  insure  all 
the  iron  being  present  as  ferric  'oxide  or  chloride.  Expel  the 
excess  of  acids  by  evaporating  on  the  water-bath,  and  after  cooling 
add  10  c.c.  bromine  water  and  digest  for  some  time  on  the  water- 
bath. 

Now  add  a  1  : 3  potassium-oxalate  solution  equal  to  about 
seven  times  the  quantity  of  the  oxides  present,  warm  for  about 
fifteen  minutes  on  the  water-bath,  and  dissolve  any  slight  residue 
of  basic  ferric  salt  by  adding  acetic  acid  drop  by  drop.  Tf  suf- 
ficient potassium  oxalate  has  been  employed,  there  is  obtained  a 
perfectly  clear  more  or  less  green  solution;  if,  however,  insufficient 
*  has  been  used  to  form  potassio-ferric  oxalate  and  potassio-zinc 

*Zeitschr.  f.  analyt.  Chem.,  xvi,  471;  xvin,  190,  381,  397. 


§  242.]  ZINC  COMPOUNDS.  435 

oxalate,  the  liquid  will  be  turbid  from  the  presence  of  zinc  oxalate ; 
if  the  latter  is  the  case  potassium  oxalate  must  be  added  until 
the  liquid  is  clear.  Now  heat  the  solution  to  boiling,  and  add 
concentrated  (80-per  cent.)  acetic  acid,  with  constant  stirring. 
The  quantity  of  acetic  acid  added  must  be  at  least  equal  in  volume 
to  that  of  the  liquid  to  be  precipitated.  By  this  treatment  all 
the  zinc  is  precipitated  as  heavy,  crystalline  zinc  oxalate,  while 
the  iron  remains  in  solution.  Heat  the  well-covered  beaker  for 
about  six  hours  at  about  50°,  filter  while  hot,  thoroughly  wash 
with  a  mixture  of  equal  volumes  of  concentrated  acetic  acid, 
alcohol,  and  water,  and  dry  the  precipitate;  burn  the  filter  first 
on  a  platinum  wire,  then  heat  the  precipitate  in  a  covered  crucible, 
at  first  gently,  then  with  increased  heat,  finally  igniting  with  access 
of  air,  and  then  weigh.  Now  heat  the  ignition-residue  with  a 
little  water  and  test  its  reaction;  if  alkaline,  remove  the  potas- 
sium carbonate  still  present  by  washing  with  water,  and  weigh 
again. 

If  the  ore  contains  manganese,  the  zinc  oxide  may  contain 
the  whole  of  it  as  manganese  oxide.  If  the  quantity  is  weighable, 
determine  the  manganese  according  to  Vol.  I,  p.  665,  d.  The  quan- 
tity of  zinc  oxide  is  then  ascertained  from  the  difference. 

The  iron  in  the  liquid  filtered  off  from  the  zinc  oxalate  may 
be  precipitated  by  ammonia.  The  sulphur  is  determined  as  in 
the  first  method. 

The  test  analyses  communicated  by  CLASSEN  are  very  sat- 
isfactory. I  am  not  personally,  sufficiently  familiar  with  the 
method,  however,  to  give  a  decided  opinion  regarding  it. 

D.  Zixc  ORES  GENERALLY. 

I.  VOLUMETRIC    ZINC  DETERMINATION. 

§242. 

As  the  gravimetric  methods  of  determining  zinc  take  much 
time,  volumetric  methods  are  almost  exclusively  employed  in 
zinc  work,  as  the  results  afforded  are  sufficiently  accurate  for  most 
purposes,  and  may  be  much  more  rapidly  obtained. 


436  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  242. 

a.  Sodium-Sulphide  Method. 

This  method,  first  proposed  by  SCHAFFNER,*  has  been  modified 
in  many  ways,  in  the  course  of  time.  These  are  described  in  the 
foot-note  here  given,  f  The  following  methods  have  been  found 
to  be  the  best: 

a.  Method  with  SCHAFFNER'S  Modified  End  Reaction. 

REQUISITES. 

Sodium-Sulphide  Solution.  Prepare  this  either  by  dissolving 
crystallized  sodium  sulphide  in  water  (about  100  grm.  to  1000 
or  1200  c.c.  water),  or  by  supersaturating  a  carbonate-free  caus- 
tic-soda solution  with  hydrogen  sulphide  and  then  heating  the 
solution  in  a  flask  to  expel  the  excess  of  hydrogen  sulphide.  Then 
dilute  the  solution,  prepared  by  either  process,  so  that  1  c.c.  will 
precipitate  about  0-01  grm.  of  zinc  (see  below). 

Zinc  Solution.  To  prepare  a  solution  of  accurately  known 
zinc  content,  dissolve  10  grm.  of  chemically  pure  zinc,  or  12-4465 
grm.  of  pure  zinc  oxide,  in  hydrochloric  acid,  or  43-973  dry,  crys- 
tallized zinc  sulphate  (ZnSO4-7H2O)  or  62-358  grm.  of  dry,  crys- 
tallized zinc  and  potassium  sulphate  (ZnK2  [SO4]2-4H2O)  in  water, 
and  dilute  the  solution  with  water  to  measure  1  litre.  Each  c.c. 
will  then  contain  0-01  grm.  zinc. 

Ferric  Hydroxide.  Dissolve  3  grm.  of  iron  wire  in  hydrochloric 
acid  with  the  aid  of  heat,  add  a  little  nitric  acid,  and  boil  to  con- 
vert the  ferrous  into  ferric  chloride,  and  dilute  the  solution  to 
100  c.c.  Just  before  using,  add  1  or  2  drops  (always  taking  the 
same  number  of  drops)  to  1  c.c.  of  undiluted  aqueous  ammonia/ 
each  drop  producing  a  ring  of  ferric  hydroxide,  which  requires 
but  a  few  moments  to  impart  the  desired  opacity  to  the  liquid. 

*  Journ.  f.  prakt.  Chem.,  LXXIII,  410. 

f  C.  KITNZEL  (Jour.  f.  prakt.  Chem.,  LXXXVIII,  486). — C.  GROLL  (Zeitschr. 
f.  analyt.  Chem.,  i,  21). — STABLER  (ibid.,  iv,  213  and  468).— DEUS  (ibid., 
ix,  465). — SCHOTT  (ibid.,  x,  209). — LAUR  (Berg-  und  Hiittenmann.  Ztg., 
xxxv,  148,  173). — THUM  (ibid.,  xxxv,  225). — TOBLER  (ibid.,  xxxv,  304, 
Zeitschr.  f.  analyt.  Chem.,  xvn,  357). — W.  HAMPE  und  FRAATZ  (Ibid.,  xvn; 
359). 


§  242.]  ZINC  COMPOUNDS.  437 

In  about  one  minute  the  ferric  hydroxide  suspended  in  the  liquid 
is  ready  for  use  (THUM). 

The  Method. 

SOLUTION    OF    THE    ORE    AND    PREPARATION    OF    THE    AMMONIACAL 
ZINC    SOLUTIONS. 

Introduce  into  a  small  flask  about  1  gnn.  of  rich  ore,  or  2 
grm.  of  poor  ore,*  finely  powdered  and  either  air-dried  or  dried  at 
100°,  dissolve  with  the  aid  of  heat  in  hydrochloric  acid  with  a 
little  nitric  acid  added,  and  expel  the  excess  of  acid  by  evaporation. 
If  lead  is  present,  separate  it  by  evaporating  with  sulphuric  acid, 
take  up  the  residue  with  water,  and  filter.  If  other  metals  of 
the  fifth  and  sixth  groups  are  present,  precipitate  these  with  hy- 
drogen sulphide  (comp.  §  240,  a  and  6), 

Boil  the  solution,  free  from  or  no  longer  containing  metals  of 
the  fifth  or  sixth  groups,  with  nitric  acid  if  necessary  in  order  to 
convert  all  the  iron  into  ferric  oxide  or  chloride,  add  (if  manganese 
is  present)  brominized  hydrochloric  acid,  and  dilute  with  water; 
then  add  to  the  cold  liquid  an  excess  of  ammonia,  and  filter  off 
the  precipitate  consisting  chiefly  of  ferric  hydroxide.  If  the 
quantity  of  the  precipitate  is  small,  wash  it  with  luke-warm  water 
and  aqueous  ammonia  until  the  washings  no  longer  give  a  white 
turbidity  (zinc  sulphide)  with  ammonium-  or  sodium  sulphide;  for 
in  this  case  the  quantity  of  zinc  which  is  contained  in,  and  cannot 
be  washed  out  from,  the  ferric  hydroxide  (which,  according  to 
HAMPE  and  FRAATZ  is  approximately  one-fifth  of  the  weight  of 
the  iron  present) ,  may,  as  a  rule,  be  disregarded.  If,  however,  the 
quantity  of  ferric  hydroxide  precipitated  is  considerable,  wash 
it  moderately,  dissolve  it  in  hydrochloric  acid,  and  precipitate  the 
iron  again  as  a  basic  ferric  salt,  best  according  to  §  160,  3,  a,  or  by 
method  4.  The  solution  filtered  off  from  it  concentrate  by  evap- 
oration, then  add  an  excess  of  ammonia,  filter  if  necessary,  add 
to  the  principal  solution,  and  make  up  to  1  litre.  If  the  zinc  ore 
contains  an  appreciable  quantity  of  manganese,  add  brominized 

*  If  the  ore  contains  organic  matter,  destroy  this  by  gentle  ignition. 


438  DETERMINATION    OF   COMMERCIAL    VALUES.         [§  242. 

hydrochloric  acid  to  the  filtrate  separated  from  the  basic  ferric 
salt  and  concentrated  by  evaporation,  before  adding  the  excess 
of  ammonia;  then,  after  standing  for  quite  some  time,  filter  off 
from  the  precipitated  hydrated  manganese  peroxide,*  and  make 
up  the  liquid  to  1  litre. 

TITRATION   OF  THE   SOLUTION. 

To  500  c.c.  of  the  ammoniacal  zinc  solution  add  ferric  hydroxide 
suspended  in  ammonia  (see  above),  and  then  from  a  burette  run 
in  sodium-sulphide  solution  until  the  greater  part  of  the  ferric 
hydroxide  collected  on  the  sides  and  bottom  of  the  beaker  just 
acquires  a  brown  or  black  tint  (it  is  necessary  to  select  one  of 
these  tints  once  and  for  all),  and  read  off.  Now  measure  off  a 
quantity  of  zinc  solution  of  known  strength  approximately  cor- 
responding to  the  sodium-sulphide  solution  used,  add  excess  of 
ammonia,  dilute  with  water  so  that  the  volume  will  be  as  nearly 
equal  as  possible  to  that  of  the  solution  first  titrated,  add  an  equal 
quantity  of  ferric  hydroxide  suspended  in  ammonia  water,  and 
then  run  in  sodium-sulphide  solution  until  the  ferric  hydroxide, 
after  an  equal  interval  of  time,  exhibits  the  same  shade  of  brown 
or  black  as  was  obtained  in  the  first  titration.  If  it  is  believed 
that  the  end  point  of  the  reaction  has  not  been  sharply  hit,  the 
other  half  litre  may  be  used  with  which  to  repeat  the  experiment. 

The  relation  of  the  sodium-sulphide  solution  to  the  zinc  solu- 
tion of  known  content  is  thus  accurately  ascertained,  as  was  pre- 
viously done  with  that  of  unknown  strength,  hence  the  zinc  con- 
tained in  the  solution  of  the  ore  may  be  readily  calculated.  It  is 
unnecessary  to  make  any  correction  for  the  quantity  of  sodium 
sulphide  required  to  blacken  the  ferric  hydroxide,  because  the 
titration  is  effected  under  similar  conditions  in  both  cases,  and 
with  solutions  containing  almost  identical  quantities  of  zinc  (THUM; 
HAMPE).  But  even  when  all  these  precautions  are  taken,  this 
method  is  accurate  only  up  to  within  0-5  per  cent.  (HAMPE). 

*A11  these  precipitates  of  hydrated  manganese  peroxide,  or  those  ob- 
tained in  a  similar  manner,  retain  a  little  zinc. 


§  242.]  ZINC    COMPOUNDS.  439 

BARRESWIL,*  instead  of  using  flocks  of  ferric  hydroxide,  em- 
ploys small  fragments  of  ignited  porcelain  saturated  with  ferric- 
chloride  solution  and  then  thrown  into  an  ammoniacal  zinc  solu- 
tion. 

ft.  The  KUNZEL-GROLL  End  Reaction. 

There  are  required  solutions  of  sodium  sulphide  and  of  zinc 
of  known  strength,  as  in  a,  and  also  a  pure,  dilute  nickelous- 
chloride  solution. 

The  Method. 

The  ore  is  dissolved,  and  the  zinc  is  made  up  to  one  litre  of 
ammoniacal  solution  free  from  any  of  the  other  heavy  metals, 
as  detailed  in  a. 

To  500  c.c.  of  this  solution  now  run  in  from  a  burette  sodium- 
sulphide  solution  so  long  as  a  distinct  precipitate  still  forms,  then 
stir  thoroughly,  transfer  a  few  drops  of  the  liquid  with  a  glass  rod 
to  a  porcelain  plate,  spread  them  on  the  plate,  and  in  the  centre 
place  1  drop  of  pure  dilute  nickelous-chloride  solution.  If  all 
the  zinc  is  not  yet  precipitated  by  the  sodium-sulphide  solution, 
the  margin  of  the  drop  of  nickelous-chloride  solution  remains 
•colored  blue  or  green;  in  this  case  continue  to  add  sodium  sulphide, 
and  until,  on  testing,  the  margin  of  the  nickelous-chloride  solution 
exhibits  a  grayish-black  color;  the  reaction  is  then  complete,  all  the. 
zinc  having  been  precipitated,  and  a  little  sodium  sulphide  being 
present  in  excess.  The  depth  of  the  color  exhibited  by  the  drop 
of  nickelous-chloride  solution  must  be  carefully  noted,  as  it  must 
serve  as  a  standard  in  the  succeeding  experiments.  To  make 
certain  that  all  the  zinc  has  been  precipitated,  a  few  tenths  of  a 
c.c.  of  sodium-sulphide  solution  may  be  added,  when  the  color  of 
the  drop  of  nickelous-chloride  solution  must  become  darker.  Note 
the  number  of  c.c.  of  sodium-sulphide  solution  used,  and  repeat  the 
experiment  with  the  remaining  500  c.c.  of  solution,  adding  at  once 
all  but  a  few  c.c.  of  the  sodium-sulphide  solution,  and  then 

*Journ  de  pharm.,  1857,  431;   Polytechn.  Centralbl,  1858,  285. 


440  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  242. 

adding  only  0-2  c.c.  at  a  time  until  the  end  reaction  is  reached. 
This  experiment  is  considered  as  giving  the  correct  result. 

Now  measure  off  as  much  of  the  zinc  solution  of  known  strength 
as  will  correspond  with  the  sodium-sulphide  solution  used  in  the 
last  experiment,  add  an  excess  of  ammonia,  and  then  add  water 
until  the  volume  is  about  equal  to  that  of  the  solution  first  titrated ; 
then  run  in  sodium-sulphide  solution  until  the  end  reaction  is 
reached.  In  this  manner  the  relation  of  the  sodium  sulphide 
solution  to  the  zinc  solution  of  unknown  strength  is  once  more 
determined;  and  from  this  the  zinc  content  of  the  ore  may  be 
easily  calculated. 

According  to  C.  KUNZEL,  the  error,  when  carefully  operating 
with  this  method,  does  not  exceed  0-5  per  cent. 

[J.  E.  CLENNELL  *  describes  a  method  in  which  the  zinc  is  pre- 
cipitated by  means  of  a  solution  of  sodium  sulphide  of  known 
strength,  added  in  slight  excess,  the  excess  in  sulphide  being  then 
determined  by  making  use  of  the  reaction 

Na2S +2KAgCy2= Ag2S +2NaCy +2KCy. 

Requisites. 

The  solutions  required  are: 

Sodium  Sulphide. — A  convenient  strength  being  about  0.2 
per  cent.  Na2S. 

Silver  Double  Cyanide. — Prepared  by  adding  silver  nitrate  to  a 
solution  of  potassium  cyanide  (say  2  or  3  per  cent.  KCy)  till  a 
slight  permanent  precipitate  of  AgCy  is  produced,  allowing  to  stand, 
and  filtering. 

Silver  Nitrate. — Any  dilute  solution  of  known  strength.  A 
convenient  standard  is  one  containing  5.165  grms.  AgNO3  per  litre, 
1  c.c.  being  equivalent  to  0.001  grm.  zinc. 

Potassium  Iodide. — 1-per  cent,  solution. 

It  is  perhaps  advisable  also  to  have  a  standard  zinc  solution 
prepared  from  pure  metallic  zinc  or  re-crystallized  zinc  sulphate, 
and  containing  (say)  0  •  5  per  cent,  to  1  per  cent.  Zn. 

*  Chem.  Neivs,  LXXXVII,  121. 


§   242.]  ZINC   COMPOUNDS.  441 

Method. 

The  zinc  in  ores  or  similar  substances  is  brought  into  solution 
in  the  ordinary  way,  and  the  liquid  made  strongly  alkaline  with 
caustic  soda  or  ammonia,  boiled,  diluted,  and  filtered  if  necessary. 
In  cyanide  solutions,  the  sulphide  may  in  general  be  applied  direct; 
in  some  cases,  however,  it  may  be  necessary  to  remove  the  cyano- 
gen by  a  preliminary  operation. 

The  liquid  to  be  tested  is  mixed  with  a  measured  volume  of 
sodium  sulphide,  slightly  in  excess  of  that  required  to  precipitate 
the  whole  of  the  zinc.  The  liquid  is  well  shaken  in  a  stoppered 
flask;  a  little  lime  may  be  added  to  promote  settling.  The 
whole,  or  an  aliquot  part,  is  then  filtered,  and  an  excess  of  the 
double  silver  cyanide  added.  The  precipitate  of  Ag2S  generally 
settles  rapidly,  and  is  easily  filtered  and  washed  (occasionally  it 
may  be  necessary  to  add  a  little  more  lime).  About  5  c.c.  of  the 
1  per  cent.  KI  solution  are  added  to  the  filtrate,  and  the  liquid 
titrated  with  AgNO3  till  a  slight  yellowish  turbidity  remains  per- 
manent. 

1  grm.  KCy=0-3  grm.  Na^O-25  grm.  7n. 

In  the  presence  .of  ferrocyanide  and  thiocyanate,  it  appears  to 
be  necessary  to  make  the  solution  strongly  alkaline  to  ensure  com- 
plete precipitation  of  the  zinc  sulphide. — TRANSLATOR.] 

Regarding  other  reactions  by  means  of  which  small  quantities 
of  sodium  sulphides  may  be  detected  in  the  precipitated  zinc 
solution,  the  following  may  be  briefly  noted: 

DEUS,  in  his  criticism  of  the  end  reactions,  arrives  at  the  con- 
clusion that  the  most  certain  indicator  is  afforded  by  filter-paper 
impregnated  with  cobaltous-chloride  solution  (0-27  grm.  cobalt 
in  100  c.c.  of  the  solution)  and  dried.  On  being  moistened  with 
a  drop  of  the  liquid  containing  zinc  sulphide  in  suspension,  the 
paper  exhibits  a  white  ring  with  a  pale-blue  margin.  As  soon 
as  the  slightest  excess  of  sodium  sulphide  is  present,  however, 
a  sharply  defined  dark  color  develops  in  the  centre  of  the  white  ring. 

The  formation  of  lead  sulphide  is  also  frequently  utilized  to 
indicate  the  end  reaction;  and  the  following  process,  which  I 


442  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  242. 

proposed  long  ago,  is  preferred  by  me  to  all  others :  *  Moisten  a 
strip  of  white  filter-paper  with  lead-acetate  solution,  place  it  on 
a  layer  of  blotting-paper,  drop  onto  it  a  little  ammonium  car- 
bonate so  that  a  thin  coating  of  lead  carbonate  may  form  on  the 
moderately  moist  paper,  allow  the  excess  of  moisture  to  be  ab- 
sorbed by  the  blotting-paper,  and  then  spread  the  lead  paper  on 
a  porcelain  plate.  As  soon  as  the  zinc  seems  to  be  all  precipitated, 
place  a  small  piece  of  filter-paper  on  the  lead  paper,  and  on 
the  former  place  a  drop  of  the  liquid  with  the  blunt  end  of  a  glass 
rod,  and  with  moderate  pressure.  So  long  as  the  sodium  sul- 
phide is  not  present  in  excess  no  brown  spot  forms  on  the  lead 
paper,  but  the  moment  a  slight  excess  is  present,  the  color  de- 
velops. 

ScHOTT  employs  sized  paper  covered  with  a  coating  of  lead 
carbonate;  this  paper  is  known  as  "Polka  Paper,"  and  is  em- 
ployed for  visiting-cards.  If  a  few  drops  of  the  liquid  containing 
the  suspended  zinc  sulphide  are  taken  out  with  a  glass  tube  and 
allowed  to  run  back  over  a  strip  of  polka  paper  into  the  beaker,  the 
paper  remains  uncolored ;  as  soon,  however,  as  the  liquid  contains 
any  sodium  sulphide,  a  brown  ring  forms  where  the  liquid  has 
flowed '  between  the  end  of  the  tube  and  the  paper. 

b.  Potassium-Ferrocyanide  Method. 

GALLETTI  f  was  the  first  to  employ  potassium  ferrocyanide  as 
a  precipitant  of  zinc  in  the  volumetric  determination  of  the  latter. 
The  precipitation  is  effected  in  an  acetic-acid  solution  at  40°; 
and  the  milky  appearance  which  the  liquid  assumes  when  the 
potassium  ferrocyanide  is  present  in  excess  serves  to  indicate  the 
end  of  the  reaction.  GALLETTI  dissolves  32-311  grm.  crystallized 
potassium  ferrocyanide  (K4Fe[CN]6  +  3H2O)  in  water  to  make  one 
litre,  and  assumes  that  100  c.c.  of  the  solution  will  precipitate  1 
grm.  of  zinc.  As,  however,  the  precipitate  is  not  pure  zinc  ferro- 
cyanide, as  he  supposed,  but  zinc-potassium  ferrocyanide, J  his 

*  Quant.  Chem.  Anal,  5th  German  edit.,  814. 
t  Zeitschr.  /.  analyt.  Chem.,  iv,  213. 

J  REINDEL,  Zeitschr.  /.  analyt.  Chem.,  vin,  460;  Neues  Handworterbuch 
der  Chemie,  in,  244. 


§  242.]  ZINC  COMPOUNDS.  443 

assumption  is  incorrect.  In  a  more  recent  communication  *  GAL- 
LETTI  modified  the  original  method  as  regards  the  separation  of 
the  iron.  RENARDf  has  altered  the  method,  in  that  he  adds 
an  excess  of  potassium-ferrocyanide  solution  of  known  strength 
to  the  ammoniacal  zinc  solution,  makes  up  the  whole  to  a  definite 
volume,  niters  off  an  aliquot  portion,  adds  considerable  hydro- 
chloric acid  (30  c.c.  to  100  c.c.  of  the  fluid),  and  determines  the 
excess  of  potassium  ferrocyanide  with  potassium  permanganate 
(comp.  Vol.  I,  p.  554,  g).  Thus  is  ascertained  the  quantity  of  potas- 
sium ferrocyanide  required  to  precipitate  the  zinc,  and  from  which 
the  latter  may  hence  be  calculated. 

C.  FAHLBERG,|  however,  has  devised  the  simplest  form  of  the 
ferrocyanide  method.  He  employs  a  potassium-ferrocyanide 
solution  1  c.c.  of  which  precipitates  0-01  gnu.  of  zinc.  The  zinc 
solution  of  known  strength  is  prepared  by  dissolving  10  grm. 
pure  zinc  in  hydrochloric  acid,  adding  50  grm.  ammonium 
chloride,  and  diluting  to  measure  1  litre.  The  addition  of  the 
ammonium  chloride  has  been  found  advantageous,  as,  when  it 
is  present,  the  precipitate  caused  by  the  ferrocyanide  is  very  fine 
and  flocculent,  and  incloses  no  potassium  ferrocyanide. 

To  determine  the  value  of  the  potassium-ferrocyanide  solution, 
prepared  by  dissolving  46  to  48  grm.  of  the  crystallized  salt  in  water 
to  make  1000  c.c.,  fill  one  burette  with  the  zinc  solution,  and  a 
second  one  with  the  ferrocyanide  solution;  introduce  50  c.c.  of 
the  zinc  solution  into  a  beaker,  add  10  to  15  c.c.  hydrochloric 
acid  (sp.  gr.  1  •  12)  and  450  c.c.  water,  and  while  diligently  stirring, 
run  in  the  ferrocyanide  solution  in  quantities  of  1  to  2  c.c.,  until  a 
drop  of  the  liquid  brought  into  contact  with  a  drop  of  uranium- 
nitrate  solution  on  a  porcelain  plate  gives  a  permanent  brownish- 
red  spot.  Now  very  cautiously  run  in  zinc  solution  until  the 
reaction  again  disappears,  and  finally  add  the  ferrocyanide  solution, 
two  drops  at  a  time,  until  it  is  again  manifested.  If,  for  example, 
there  had  been  used  4  to  8  c.c.  of  the  potassium-ferrocyanide  solution 

*  Zeitschr.  f.  analyt.  Chem.,  vni,  135,  and  xiv,  190. 
t  Ibid.,  viii,  459. 
1  Ibid.,  xin,  379. 


444  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  242. 

for  51  c.c.  of  zinc  solution,  the  former  must  be  diluted  by  adding 
3  c.c.  of  water  to  every  48  c.c. 

The  solution  of  the  ore  is  prepared  as  already  described  above. 
After  removing  the  metals  of  the  fifth  and  sixth  groups  and  the 
iron,  neutralize  500  c.c.  of  the  ammoniacal  solution  with  hydro- 
chloric acid,  add  a  further  quantity  of  10  to  15  c.c.  of  hydrochloric 
acid  (sp.  gr.  1-12),  and  then  titrate  with  ferrocyanide  solution, 
taking  no  heed  as  to  whether  manganese  is  present  or  not.  The 
fact  that  the  titrations  are  effected  in  liquids  containing  consider- 
able hydrochloric  acid,  in  which  manganese  ferrocyanide  is  soluble, 
thus  rendering  it  unnecessary  to  remove  manganese,  makes  FAHL- 
BERG'S  the  most  convenient  of  all  the  modifications  of  the  ferro- 
cyanide methods.  As  regards  accuracy,  the  differences  never  ex- 
ceed 0  •  5  per  cent. 

c.  C.  MANN'S  Method* 

This  method,  although  more  inconvenient  and  troublesome 
than  those  already  mentioned,  yet  affords  more  accurate  results; 
it  is  based  upon  the  fact  that  hydra  ted  zinc  sulphide  and  moist 
silver  chloride  readily  and  completely  react,  yielding  silver  sulphide 
and  neutral  zinc  chloride.  If,  hence,  the  chlorine  in  the  solution 
is  determined,  the  quantity  of  the  zinc  is  also  readily  ascertained. 

The  requisites  are: 

Well-washed,  moist  silver  chloride.  This  must  be  protected 
from  the  action  of  light,  and  must  be  preserved  under  water. 

Silver-nitrate  solution,  1  c.c.  of  which  contains  0-033  grm. 
silver,  corresponding  to  0-01  grm.  zinc.  It  is  prepared  by  dissolv- 
ing 33  grm.  of  pure  silver  in  nitric  acid,  boiling  off  the  nitrous  acid, 
and  diluting  the  solution  to  measure  1  litre. 

Ammonium-sulphocyanate  solution,  of  which  3  c.c.  will  just 
precipitate  1  c.c.  of  the  silver  solution. 

A  cold  saturated  solution  of  ammonio- ferric  alum. 

The  Method. 

Dissolve  0-5  to  1  grm.  of  the  ore  in  nitric  acid,  remove  the 
metals  of  the  fifth  group  with  hydrogen  sulphide,  and  iron  and 

*  Zeitschr.  /.  analyt.  Chem.,  xvm,  162. 


§  242.J  ZINC  COMPOUNDS.  445 

aluminium  by  double  precipitation  with  ammonia.  Acidulate 
the  united  filtrates  with  acetic  acid,  pass  in  hydrogen  sulphide 
until  the  zinc  is  completely  precipitated,  and  remove  the  excess  of 
hydrogen  sulphide  by  tumultuous  boiling  until  a  drop  of  the  liquid 
no  longer  colors  lead  paper;  then  let  the  liquid  settle,  decant 
while  hot,  filter,  transfer  the  filter  (without  washing)  together  with 
the  zinc  sulphide  to  a  small  beaker,  add  30  to  50  c.c.  of  hot  water, 
stir,  and  add  an  excess  of  silver  chloride ;  now  boil  until  the  super- 
natant liquid  has  become  clear,  and  to  the  boiling  liquid  finally  add 
5  to  6  drops  of  dilute  sulphuric  acid  (1:6).  A  few  minutes  suffice 
to  effect  the  complete  conversion  of  the  zinc  sulphide  into  zinc 
chloride. 

Filter  off  the  precipitate  of  silver  sulphide  and  chloride,  wash, 
and  in  the  solution  determine  the  chlorine  according  to  VOLHARD'S 
method.* 

For  this  purpose  add  to  the  zinc-chloride  solution  (which 
may  measure  200  to  300  c.c.)  5  c.c.  of  the  ammonio-ferric-alum 
solution  and  sufficient  nitric  acid  to  cause  the  disappearance  of 
the  color  of  the  iron  salt;  then  add  a  measured  quantity  of  silver 
solution,  and  in  fact  somewhat  more  than  is  necessary  to  pre- 
cipitate all  the  chlorine.  Now  run  in  ammonium-sulphocyanate 
solution  from  a  second  burette,  drop  by  drop,  without  previously 
filtering  off  the  silver  chloride  or  causing  it  to  aggregate  by  shaking 
or  boiling.  The  liquid  must  be  constantly  shaken  about  while 
the  sulphocyanate  solution  is  being  added,  so  that  the  drops  as 
they  fall  may  be  immediately  mixed  with  the  liquid.  As  soon  as  the 
latter  has  acquired  a  pale  brownish-yellow  color,  which  persists 
for  ten  minutes  on  allowing  the  liquid  to  stand  quietly,  the  pre- 
cipitation of  the  silver  is  complete.  Now  deduct  the  c.c.  of  silver 
solution  corresponding  to  the  ammonium-sulphocyanate  solution 
from  the  total  silver  solution,  and  for  every  c.c.  found  in  the  dif- 
ference (and  corresponding  to  the  chlorine  of  the  zinc  chloride) 
calculate  0-01  grm.  of  zinc. 

The  test  analyses  given  by  MANN  are  in  the  highest  degree 

*  Zeitschr.  /.  analyt.  Chem.,  xvm,  272. 


446  DETERMINATION    OF    COMMERCIAL   VALUES.  [§242. 

satisfactory/   and  in  my  laboratory   also   excellent  results  have 
been  obtained. 


J.  B.  SCHOBER'S*  method  of  determining  zinc  is  also  based 
on  the  VOLHARD  method  of  determining  silver.  SCHOBER  precipi- 
tates the  zinc  with  sodium-sulphide  solution,  decomposes  the  excess 
of  the  latter  with  silver  solution,  and  finally  determines  the  excess 
of  this  with  ammonium  sulphocyanate.  The  method  is  too  incon- 
venient, and  is  not  likely  to  be  generally  used. 

[The  following  method  by  HANDY  f  is  a  modification  of  Stolba's. 
This  process  may  be  much  more  easily  used  for  the  determination  of 
zinc  than  for  magnesium,  and  it  is  carried  out  as  follows :  To  the 
zinc  solution,  which  should  contain  ammonium  chloride,  a  large  ex- 
cess of  ammonia  is  added,  then  a  large  excess  of  sodium  phosphate. 
The  solution  remains  clear ;  but  if  the  excess  of  ammonia  is  cautiously 
neutralized,  a  white  cloud  is  formed  as  each  drop  of  acid  falls  into 
the  strong  ammoniacal  liquid.  On  stirring,  this  cloud  dissolves 
Until  nearly  all  the  ammonia  is  neutralized,  when  the  whole  solu- 
tion becomes  milky.  It  should  now  be  heated  to  about  75°  and 
stirred  constantly,  at  the  same  time  continuing  the  addition  of 
dilute  acid,  drop  by  drop.  In  a  very  few  minutes  the  precipitate 
becomes  crystalline,  and  with  care  the  liquid  may  be  almost  per- 
fectly neutralized.  It  is  a  good  plan  to  add  a  small  piece  of  litmus- 
paper  to  the  liquid;  this  should  not  turn  red,  but  should  remain 
blue  or  violet,  while  the  hot  liquid  should  have  no  odor,  or  only 
a  very  faint  odor  of  ammonia.  When  the  precipitation  is  made 
as  above,  the  zinc  ammonium  phosphate  is  easily  filtered,  which 
may  be  safely  done  after  five  minutes'  standing.  The  precipitate 
should  be  washed  with  cold  water  until  the  washings  show  only  a 
faint  trace  of  chlorides,  then  the  paper  with  the  precipitate  returned 
to  the  beaker  in  which  the  precipitation  was  made,  an  excess  of 
standard  acid  added,  a  few  drops  of  methyl  orange,  and  the  exact 
point  of  neutrality  determined  with  standard  alkali. 

*  Zeitschr.  f.  analyt.  Chem.,  xvm,  467. 

\Journ.  Amer.  Chem.  Soc.,  xxn,  31;  ibid.,  xxm,  No.  7. 


§  242.]  ZINC  COMPOUNDS.  447 

According  to  the  equation 

ZnNH4PO4 + H2SO4 = ZnSO4  +  NH4H2PQ4, 

we  see  that  1  c.c.  of  normal  acid  corresponds  to  32-7  mgrm.  zinc. 

Since  the  zinc  ammonium  phosphate  is  not  precipitated  in 
presence  of  a  large  excess  of  ammonia,  the  process  may  be  used 
in  the  presence  of  magnesium,  which  is  precipitated  in  the  strongly 
alkaline  liquid,  and  the  filtrate  from  the  precipitate  neutralized  to 
precipitate  the  zinc. 

The  process  gives  fairly  good  results  in  the  presence  of  iron, 
calcium,  and  magnesium.  Manganese,  however,  must  be  pre- 
viously separated,  best  by  the  nitric -acid  and  potassium-chlorate 
method. 

A.  C.  LANGMUIR*  describes  the  following  method:  From  0-5 
to  1  grm.  of  the  zinc  ore  is  dissolved,  and  the  metals  of  the  hydro- 
gen sulphide  group  are  separated  as  usual.  After  expulsion  of  H2S 
by  boiling,  the  solution  is  peroxidized  with  bromine  water,  and 
iron  and  manganese  are  separated  by  ammonia,  the  precipitate 
being  redissolved  and  reprecipitated  two  or  three  times.  If  the 
ore  be  free  from  lime  and  magnesia,  the  filtrate  may  at  once  be 
boiled  down  with  excess  of  nitric  acid  to  destroy  chlorides  and 
ammonium  salts;  when  the  chlorine  is  expelled,  the  solution  is 
transferred  to  a  platinum  dish,  evaporated  to  dryness,  and  ignited, 
and  the  zinc  is  weighed  as  oxide.  Otherwise  the  warm  ammoniacal 
solution  is  acidulated  with  hydrochloric  acid,  the  bromine  thus  set 
free  is  absorbed  by  the  addition  of  a  few  drops  of  sulphurous  acid, 
and  three  or  four  drops  of  methyl-orange  solution  are  added.  The 
solution  is  now  carefully  neutralized  with  ammonia,  and  ammo- 
nium sulphide  is  added,  little  by  little,  until  a  drop  of  the  liquid 
gives  a  dark  coloration  with  a  drop  of  ferric  chloride  on  a  porcelain 
plate;  the  mixture  is  warmed  on  the  water-bath  until  the  precipi- 
tate has  subsided,  when  it  is  filtered  through  a  double-ribbed  filter. 
Washing  should  be  avoided,  otherwise  the  filtrate  will  be  turbid. 
The  precipitate  is  therefore  at  qnce  dissolved  in  hot  nitric  acid 
(1:3),  or  in  dilute  hydrochloric  acid,  if  cobalt  or  nickel  is  present, 

*Journ.  Amer.  Chem.  Soc.,  1899,  xxi,  115-118. 


448  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  243. 

and  correction  is  subsequently  made  for  lime  or  magnesia,  if  any 
be  present.  The  solution  is  evaporated  in  a  porcelain  dish,  with 
the  addition  of  nitric  acid  to  expel  chlorine;  when  almost  dry  it 
is  transferred  to  a  tared  platinum  dish,  dried,  and  ignited,  at  first 
over  a  BUNSEN  burner,  and  finally,  intensely,  over  the  blowpipe, 
so  as  to  decompose  any  zinc  sulphate  present.  Ammonium  car- 
bonate may  be  added,  but  it  tends  to  cause  loss.  After  weighing, 
the  oxide  is  redissolved  in  hydrochloric  acid;  the  trace  of  iron 
present  is  thrown  down  with  ammonia,  filtered,  and  weighed,  and 
the  amount  deducted  from  the  weight  of  ZnO.  The  filtrate  is 
acidified  with  hydrochloric  acid,  and  tested  for  sulphate  with  barium 
chloride.  If  necessary,  the  barium  sulphate  is  collected  and 
weighed  and  the  SO3  determined ;  but  if  the  ignition  has  been  prop- 
erly performed,  there  should  not  be  more  than  a  trace  of  precipi- 
tated BaS04.  If  lime  or.  magnesia  be  present,  the  filtrate  from  the 
precipitate  of  iron  contained  in  the  ZnO  should  be  divided  into  two 
parts,  one  to  be  tested  for  sulphates,  the  other  to  be  used  for  the 
determination  of  the  earths. — TRANSLATOR.] 

II.    ELECTROLYTIC  DETERMINATION  OF  ZINC  IN  ZINC  ORES. 

§243. 

Quite  a  number  of  processes  have  already  been  proposed  for 
the  electrolytic  precipitation  of  zinc.*  From  these  it  may  be 
seen  that  the  electrolytic  precipitation  can  be  effected  without 
difficulty.  The  different  experimenters  differ,  however,  regard- 
ing the  best  method. 

PARODI  and  MASCAzziNif  first  proposed  the  precipitation  in 
a  solution  of  the  sulphate  to  which  an  excess  of  ammonium  acetate 
had  been  added,  but  subsequently  J  they  gave  the  following  method 
the  preference:  Dissolve  the  zinc  (0-1  to  0-25  grm.)  as  a  sulphate, 
add  4  c.c.  of  an  ammonium-acetate  solution  (naturally  a  rather 
concentrated  solution)  and  2  c.c.  of  a  (also  concentrated)  citric- 

*See  Zeitschr.  /.  analyt.  Chem.,  vm,  24;  xv,  303;  xvi,  469;  xvn,  216; 
xvin,  587;  and  xvm,  588. 
f  Ibid.,  xvi,  469. 
$  Ibid.;  xvm,  587. 


§  243.]  ZINC  COMPOUNDS.  449 

acid  solution,  dilute  to  200  c.c.,  introduce  the  electrodes*  so  that 
they  are  separated  only  a  few  millimetres,  and  close  the  circuit; 
the  platinum  cone  must  be  the  negative  electrode.  Cover  the 
beaker  with  a  glass  plate  properly  arranged.  The  current  fur- 
nished by  the  CLAMOND  thermopile  should  be  strong  enough  to 
produce  250  to  300  c.c.  of  oxy-hydrogen  mixture  per  hour.  When 
a  sample  of  the  liquid  is  no  longer  rendered  turbid  by  potassium 
ferrocyanide.  the  separation  of  zinc  may  be  considered  as  complete. 
Then  draw  off  the  liquid  with  a  siphon,  wash  the  cone  with  water, 
and  break  the  current.  Finally  wash  the  cone  with  the  adhering 
zinc  twice  with  absolute  alcohol,  dry  at  40°  to  50°  with  access  of 
air,  and  weigh. 

If  the  ore  contains  lead,  cadmium,  iron,  etc.,  these  metals  must 
first  be  removed  by  one  of  the  methods  detailed  in  §  242. 

ALF.  RICHE  f  first  removes  all  other  metals  from  the  sulphuric- 
acid  or  nitric-acid  solution  of  the  zinc  ore,  then  supersaturates 
with  ammonia  until  the  precipitate  of  hydrated  zinc  oxide  first 
formed  redissolves,  then  adds  an  excess  of  acetic  acid,  and  sub- 
mits the  solution  to  electrolysis.  The  deposited  zinc  adheres 
firmly  to  the  (negative)  platinum  cone. 

F.  BEILSTEIN  and  L.  JAWEIN  J  add  caustic  soda  to  the  sul- 
phuric-acid solution  (or  otherwise  suitably  prepared  solution) 
of  the  zinc  ore  until  a  precipitate  develops,  and  potassium  cyanide 
until  the  precipitate  redissolves  and  a  clear  solution  results.  The 
current  is  obtained  from  four  BUXSEN  elements.  If  the  liquid 
becomes  warm,  the  beaker  is  placed  in  cold  water.  When  the 
precipitation  is  considered  to  be  complete,  remove  the  electrodes 
from  the  liquid,  wash  the  cone  successively  with  water,  alcohol,  and 
ether,  dry  in  an  exsiccator  first,  then  at  100°,  weigh,  and  dissolve 
the  zinc  in  hydrochloric  or  nitric  acid.  Then  wash  and  weigh 
the  cone,  place  the  electrodes  again  in  the  liquid,  and  note  whether 
a  further  deposit  of  zinc  takes  place. 

*  As  the  electrolytic  method  is  particularly  important  in  the  precipitation 
of  copper,  the  details  will  be  described  under  the  analysis  of  the  copper 
compounds. 

t  Zeitschr.  /.  analyt.  Chem.,  xvii,  216. 

J  Ibid.,  xviii,  588. 


450  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  244. 

[For  further  processes  and  details  of  electrolytic  methods  see 
"Quantitative  Chemical  Analysis  by  Electrolysis,"  by  ALEX. 
CLASSEN,  translated  by  B.  B.  BOLTWOOD.  JOHN  WILEY  &  SONS, 
New  York,  1903.  Also  "Electro-chemical  Analysis,"  by  EDGAR 
F.  SMITH.  P.  BLAKISTON'S  SON  &  Co.,  Philadelphia,  1902.— TRANS- 
LATOR.] 

E.  METALLIC  ZINC. 
§244. 

Metallic  zinc  as  obtained  by  metallurgical  processes  contains 
various  impurities.  These  have  been  investigated  by  many  chem- 
ists, and  particularly  by  C.  W.  ELIOT  and  FR.  H.  STORER,* 
who  have  most  carefully  examined  ten  kinds  of  zinc  (German, 
English,  French,  Belgian,  and  American).  The  following  are  the 
most  important  results  of  their  investigations: 

Almost  all  zincs  (nine  out  of  the  ten  kinds)  contain  lead,  in  quan- 
tities varying  from  0-079  to  1-66  per  cent.  All  contain  small 
quantities  of  cadmium]  the  quantity  of  cadmium  oxide,  which 
in  some  zincs  contains  also  small  quantities  of  stannic  oxide 
varies  from  0-0035  to  0-4471  per  100  parts  of  zinc  All  zincs 
contain  iron,  in  quantities  varying  from  0-0549  to  0-2088  per 
cent.  Copper  was  found  in  only  one  sample.  Arsenic  does  not 
occur  so  generally  as  is  usually  believed;  quite  a  number  of  zincs 
are  free  from  it,  and  others  contain  traces,  while  some  contain 
notable  quantities.  Of  the  other  metals,  nickel,  cobalt,  man- 
ganese, and  antimony  are  only  exceptionally  found,  and  then  but 
in  very  minute  quantities.  Carbon  and  silicon  are  not,  as  a  rule, 
found  in  zinc,  but  sometimes  traces  are.  Sulphur  is  always  present 
but  only  in  slight  traces.  Phosphorus,  of  which  also  traces  may 
be  found  in  zinc,  was  not  included  in  the  investigations  of  ELIOT 
and  STORER. 

.For  ordinary  cases  it  suffices  to  quantitatively  determine  the 
lead,  iron,  and  cadmium;  regarding  the  other  impurities  it  suf- 
fices, as  a  rule,  to  test  for  them  qualitatively. 

*  Memoirs  of  the  American  Academy  of  Arts  and  Sciences,  New  Series* 
Vol.  vni,  p.  57-94. 


§  244.]  ZINC    COMPOUNDS.  451 

The  analysis  is  conducted  as  follows: 

1.  Treat  about  30  grm.  of  the  zinc  (either  granulated  or  cut 
into  small  pieces  if  sheet-zinc)  with  diluted  sulphuric  acid  (1  part 
concentrated  acid  to  4  parts  water)  with  moderate  heat.     When 
the  zinc  is  almost  completely  dissolved,  decant  or  filter  off  the 
zinc  solution  from  the  undissolved,  black  residue;  wash  the  latter, 
dissolve  in  a  little  nitric  acid  (any  residue  should  be  tested  for  tin), 
add  a  little  diluted  sulphuric  acid,  and  evaporate  until  all  the 
nitric  acid  has   been   expelled.     Treat  the  residue  again  with  the 
same  diluted  sulphuric   acid,  etc.,  and  determine   the  separated 
lead  sulphate  according  to  §  116,  3,  a,  /?. 

2.  Dilute  the  filtrate  from  the  lead  sulphate  with  water,  and 
add  to  every  100  c.c.  4  c.c.  of  hydrochloric  acid  (sp.  gr.  1-12); 
then  pass  in  hydrogen  sulphide  for  fifteen  minutes  to  precipitate 
any  cadmium  and  any  traces  of  tin  or  perhaps  copper  that  may 
be  present.     As  a  part  of  the  cadmium,  etc.,  may  also  have  passed 
into  the  main  zinc  solution,  treat  this  tco,  after  suitably  diluting 
and  adding  4  c.c.  of  hydrochloric  acid  to  every  100  c.c.  of  solution, 
with    hydrogen    sulphide  for    fifteen  minutes.     If  a  precipitate 
forms,  collect  this  in  the  small  filter  in  which  the  first  precipitate  of 
cadmium  sulphide  was  collected.     After  washing,  dissolve  the  con- 
tents of  the  filter  in  2  c.c.  brominized  hydrochloric  acid,  add  2  c.c. 
hydrochloric  acid,   dilute  with  100  c.c.  water,  expel  the  bromine 
by  heating,  and  precipitate  with  hydrogen  sulphide  as  before.    Col- 
lect, wash,  and  dry  the  precipitate;   dry  the  filter,  impregnate  it 
with  a  concentrated  ammonium-nitrate  solution,  dry  again,  in- 
cinerate, heat  the  residue  with  a  little  sulphuric  acid,  evaporate 
off  the  acid,  and  weigh  the  sulphate  obtained  (§  121,  3).     If  the 
residue  affords  with  water  and  a  slight  excess  of  ammonia  a  clear, 
colorless  solution  which  gives  a  yellow  precipitate  with  ammo- 
nium sulphide,  the  weighed  sulphate  may  be  at  once  calculated 
as  .cadmium  sulphate;    if,   on    the  other  hand,   the  ammoniacal 
solution  is  blue,  the  separation  of  the  cadmium  and  copper  salts 
must  first  be  effected  (§  163).     If  an  insoluble  residue  remains 
on  treating  the  sulphate  with  water  and  ammonia,  it  should  be 
tested  for  tin. 


452  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  245. 

3.  To  determine  the  iron,  it  is  best  to  dissolve  a  fresh  quantity 
of  at  least  10  grm.  of  the  zinc  in  pure,  diluted  sulphuric  acid  (in 
the  apparatus  Fig.  84,  Vol.  I);  pour  the  cooled  solution  into  a 
beaker,  repeatedly  wash  the  separated  spongy  lead,  and  deter- 
mine in  the  solution  the  iron  as  ferrous  sulphate,  by  means  of  a 
suitably  diluted  potassium-permanganate  solution,  according  to 
Vol.  I,  p.  318,  /?. 

The  qualitative  detection  of  arsenic  is  best  accomplished  by 
means  of  MARSH'S  method  as  modified  by  OTTO  (see  Qualit.  Anal. , 
14  ed.,  [Germ.],  188),  using  absolutely  pure  sulphuric  acid.  Any 
sulphur  present  is  most  easily  detected  by  dissolving  the  zinc  in 
hydrochloric  acid  and  testing  whether  the  gas  evolved  blackens 
an  alkaline  lead  solution  or  lead  paper.  The  greatest  care  must 
be  exercised  in  selecting  the  acid,  for  if  it  contains  traces  of  sul- 
phurous acid,  the  lead  preparations  will  be  blackened  even  if 
the  zinc  contains  no  sulphur,  while  on  the  other  hand,  if  it  con- 
tains chlorine,  the  blackening  will  not  occur  even  though  the 
zinc  contains  sulphur.  ELIOT  and  STORER  (loc.  cit.,  p.  72)  found 
these  conditions  so  difficult  to  fulfill  with  the  hydrochloric  acid 
ordinarily  obtainable,  that  they  prepared  the  acid  themselves  by 
decomposing  a  solution  of  pure  calcium  chloride  with  pure  oxalic 
acid. 

Phosphorus  in  zinc  is  best  detected  by  the  color  of  the  flame 
of  the  hydrogen  evolved  on  treating  zinc  with  pure  sulphuric 
acid  (see  Qual.  Anal,  14  ed.,[Germ.],  p.  396). 

F.  ZINC-DUST. 
§245. 

Commercial  zinc-dust,  consisting  of  more  or  less  pure  finely 
divided  zinc  intimately  mixed  with  zinc  oxide,  is  valued,  not 
according  to  its  total  zinc  content,  but  according  to  the  quantity 
of  zinc  it  contains  in  the  metallic  state,  as  the  zinc-dust  is  used 
almost  exclusively  as  a  reducer. 

For  determining  the  value  of  zinc-dust,  the  two  following 
methods  are  employed  in  my  laboratory: 


§  245.]  ZINC  COMPOUNDS.  453 

First  Method* 

This  method  is  based  upon  the  solution  of  the  zinc-dust  in  diluted 
sulphuric  or  hydrochloric  acid,  burning  the  evolved  hydrogen, 
and  \\eighing  the  water  thus  formed,  1  eq.  of  zinc  being  calculated 
for  1  eq.  of  water. 

The  apparatus  used  for  this  purpose  is  as  follows:  The  flask 
in  which  the  zinc  is  to  be  dissolved  should  have  a  capacity  of  about 
100  c.c. ,  and  be  provided  with  a  safety-tube  for  the  introduction  of 
the  acid;  also  a  screw  pinch-cock,  as  shown  in  Fig.  103,  p.  365. 
The  hydrogen  evolved  is  passed  through  a  small  cooling  apparatus 
(see  the  figure)  to  remove  the  water.  The  gas  is  then  passed  into 
the  U-tube  a,  Fig.  104,  two-thirds  filled  with  small  fragments  of 


FIG.   104. 

glass,  and  containing  besides  12  c.c.  of  pure,  concentrated  sulphuric 
acid.  b  c  is  a  combustion-tube  34  cm.  long.  Near  the  end  b  it 
contains,  between  two  copper-gauze  plugs,  a  12-cm.  long  layer  of 
asbestos  which  has  been  ignited  first  in  moist,  then  in  dry,  air;  the 
rest  of  the  tube  is  filled  with  well-ignited,  granular  cupric  oxide, 
retained  in  place  at  c  by  a  plug  of  copper-wire  gauze,  or  asbestos. 
d  is  a  U-tube  half-filled  with  glass  fragments,  and  containing 
besides  6  c.c.  pure  concentrated  sulphuric  acid;f  e  is  a  guard-tube 
containing  calcium  chloride,  and  /  is  an  aspirator. 

*  "  Ueberdie  Werthbestimmung  des  Zinkstaubes,"  R.  FRESENIUS,  Zeitschr. 
f.  analyt.  Chem.,  xvn,  465. 

f  Instead  of  this  tube  a  SCHROTTER  sulphuric-acid  tube  may,  of  course, 
be  employed,  as  described  on  page  52,  Fig.  44. 


454  DETERMINATION    OF    COMMERCIAL  VALUES.          [§  245. 

The  apparatus  is  put  together  as  shown  in  the  illustration,  but 
the  tube  b  c  is  connected  directly  (i.e.  without  interposing  d  and  e) 
with  the  aspirator.  Then  slightly  open  the  screw  pinch-cock  on 
the  safety-tube  of  the  gas-evolution  flask,  open  the  pinch-cock  g, 
draw  a  current  of  air  through  the  apparatus,  and  heat  the  whole 
length  of  the  tube  6  c  to  a  redness,  finally  al  owing  to  cool  in  a 
current  of  dry  air.  In  the  meantime  introduce  the  weighed 
quantity  of  zinc-dust  (about  3  grm.)  into  the  gas-evolution  tube, 
add  a  little  water,  weigh  the  tube  d,  close  g,  assemble  the  apparatus 
as  shown  in  the  illustration,  close  the  pinch-cock  on  the  safety- 
tube,  open  g  again,  and  thus  make  certain  that  the  apparatus  is 
tight. 

Now  heat  the  tube  b  c  to  redness  at  the  place  where  it  contains 
the  cupric  oxide,  open  the  pinch-cock  of  the  safety-tube  slightly, 
pour  diluted  sulphuric  acid,  to  which  a  drop  of  platinic-chloride 
solution  has  been  added,  into  the  funnel  ra,  and  allow  it  to  run 
into  the  gas-evolution  tube.  The  screw  pinch-cock  on  the  safety- 
tube  should  be  opened  so  far  that  single  air-bubbles  may  slowly 
pass  through  the  acid,  closing  the  lower  end  of  the  safety-tube. 
The  evolution  of  hydrogen  goes  on  quietly;  from  time  to  time 
more  acid,  but  without  platinic  chloride,  is  added,  and  until  all  the 
zinc  is  dissolved.  The  operation  requires  about  one  hour;  it  may 
be  hastened,  however,  by  a  gentle  heat.  The  mixture  of  hydrogen 
with  the  excess  of  air  is  completely  dried  in  a,  then  burned  in  b  c 
to  water,  without  the  cupric  oxide  being  permanently  reduced ;  and 
the  water  formed  is  collected  and  retained  in  d.  Toward  the  end  of 
the  operation  heat  the  evolution  flask  moderately  in  order  to  com- 
pletely expel  the  slight  quantity  of  hydrogen  still  held  in  solution 
by  the  liquid.  After  cooling,  ascertain  the  increase  in  weight  of 
the  tube  d,  and  calculate  65-4  parts  of  metallic  zinc  for  every 
18-016  parts  of  water  found.  The  apparatus  is  then  ready  for  a 
fresh  determination;  the  sulphuric  acid  in  a  and  d  should  first  be 
renewed,  however. 


§  245.]  ZINC  COMPOUNDS.  455 

Second  Method  (DREWSEN*). 

This  method  is  based  on  the  following  principle:  Zinc-dust 
hi  contact  with  a  sufficient  quantity  of  potassium  dichromate 
and  diluted  sulphuric  acid  evolves  no  hydrogen,  but  the  chromic 
acid  liberated  by  the  sulphuric  acid  is  reduced  to  chromic  oxide, 
as  follows: 

2CrO3+  6H  =  Cr2O3+  3H2O. 

The  requisites   are: 

a.  A  potassium-dichromate  solution  of  known  strength.     This 
is  prepared  by  dissolving  40  grm.  of  the  pure  fused  salt  in  water  to 
make  1  litre. 

b.  A  ferrous-sulphate  solution,  containing  about  200  grm.  of 
the  salt  in  the  litre.     The  solution  must  be  strongly  acidulated  with 
sulphuric  acid  to  prevent  oxidation. 

The  relation  between  the  two  solutions  is  first  ascertained,  as 
follows:  Measure  off  20  c.c.  of  the  ferrous-sulphate  solution 
into  a  beaker,  add  some  sulphuric  acid  and  about  50  c.c.  water, 
and  from  a  burette  run  in  the  potassium-dichromate  solution  until 
a  drop  of  the  iron  solution  is  no  longer  rendered  blue  by  potassium 
ferricyanide  (see  Vol.  I,  p.  319,  6). 

Now  place  the  weighed  zinc-dust  (about  0-05  grm.)  in  a  beaker, 
add  55  c.c.  of  the  potassium-dichromate  solution,  then  add  5  c.c. 
diluted  sulphuric  acid,  stir  thoroughly,  add  a  further  5  c.c.  of 
diluted  acid,  and  allow  to  stand  for  15  minutes  with  frequent  agi- 
tation. 

When  certain  that  all  is  dissolved  but  a  slight  residue,  which 
always  remains,  add  an  excess  of  sulphuric  acid,  100  c.c.  water, 
and  25  c.c.  ferrous-sulphate  solution,  in  order  to  reduce  the  greater 
part  of  the  excess  of  potassium  dichromate;  then  continue  to  add 
the  ferrous-sulphate  solution  in  portions  of  about  1  c.c.  each 
until  a  drop  of  the  liquid  gives  a  distinct  blue  color  with  potassium 
ferricyanide,  and  finally  titrate  back  with  the  potassium  dichro- 
mate until  the  reaction  just  ceases  to  take  place. 

*  Zeitschr.  /.  analyt.  Chem.,  xix,  50. 


456  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  246 

From  the  total  cubic  centimetres  of  the  potassium-dichromate 
solution  used  deduct  the  quantity  corresponding  to  the  ferrous- 
sulphate  solution  employed.  On  multiplying  the  difference  by 
0-66639  the  metallic  zinc  in  the  zinc-dust  is  ascertained. 


12.  MANGANESE  COMPOUNDS. 

A.  BLACK  OXIDE  OF  MANGANESE. 
§246. 

The  native  black  oxide  of  manganese  (as  also  the  regenerated 
artificial  product)  is  a  mixture  of  manganese  dioxide  with  lower 
oxides  of  that  metal,  and  with  ferric  oxide,  clay,  etc.;  it  also 
invariably  contains  moisture  and  frequently  chemically  combined 
water.  The  commercial  value  of  the  article  depends  entirely  upon 
the  amount  of  dioxide  (or,  more  correctly  expressed,  of  available 
oxygen)  which  it  contains,  hence  it  is  of  the  greatest  interest  for 
the  manufacturer  who  uses  the  substance  as  a  source  of  chlorine 
to  ascertain  this.  By  " available  oxygen'7  we  understand  the 
excess  of  oxygen  contained  in  a  manganese  over  the  1  at.  com- 
bined with  the  metal  to  monoxide;  upon  treating  the  ore  with 
hydrochloric  acid,  an  amount  of  chlorine  is  obtained  equivalent 
to  this  excess  of  oxygen.  This  available  oxygen  is  always  ex- 
pressed in  the  form  of  manganese  dioxide.  1  at.  corresponds  to 
1  mol.  manganese  dioxide,  since  MnO2  =  MnO+O. 

DE  VRY*  had  already  called  attention  to  the  importance  not 
only  of  the  drying  of  the  sample  to  be  analyzed,  but  also  to  the 
method  by  which  the  drying  should  be  effected;  and  I,  too,  have 
paid  special  attention  to  the  subject  of  drying,  as  it  may  give  rise 
to  many  differences.!  I  therefore  give  a  detailed  account  of  the 
methods  of  drying  the  manganese  dioxide  before  describing  the 
methods  of  analysis. 


*  Ann.  d.  Chem.  u.  Pharm.,  LXI,  249. 
f  DINGL.  polyt.  Journ.,  cxxxv,  277. 


§  246.]  MANGANESE    COMPOUNDS.  457 


I.    DRYING    THE    SAMPLE. 

All  analyses  of  manganese  proceed,  of  course,  upon  the  sup- 
position that  the  sample  operated  upon  is  a  fair  average  specimen 
of  the  ore.  A  portion  of  a  tolerably  finely  powdered  average 
sample  is  generally  sent  for  analysis  to  the  chemist;  in  the  case  of 
new  lodes,  however,  a  number  of  samples,  taken  from  different 
parts  of  the  mine,  are  also  occasionally  sent.  If,  in  the  latter 
case,  the  average  composition  of  the  ore  is  to  be  ascertained, 
and  not  simply  that  of  several  samples,  the  following  course 
must  be  resorted  to :  Crush  the  several  samples  of  the  ore  to  coarse 
powder  in  an  iron  mortar,  and  pass  the  whole  through  a  rather 
coarse  sieve.  Mix  uniformly,  then  remove  a  sufficiently  large  por- 
tion of  the  coarse  powder  with  a  spoon,  and  reduce  it  to  powder  in 
a  steel  mortar,  passing  the  whole  powder  through  a  fine  sieve.  Mix 
the  powder  obtained  by  this  second  process  of  pulverization  most 
intimately;  take  about  8  to  10  grm.  of  it  and  triturate,  in 
small  portions  at  a  time,  in  an  agate  mortar,  to  an  impalpable  pow- 
der. Average  samples  are  generally  sufficiently  fine  to  require 
only  the  last  operation. 

As  regards  the  temperature  at  which  the  powder  is  to  be  dried, 
if  you  desire  to  expel  the  whole  of  the  moisture  without  disturbing 
any  of  the  water  of  hydration,  the  temperature  adopted  must  be 
120°  (this  is  the  result  of  my  own  experiments;  see  Expt.  No.  89). 
In  this  case  it  is  best  to  use  the  drying-disk  described  in  §  31,  Fig. 
42,  the  finely  powdered  substance  being  placed  in  one  of  the  pans 
and  heated  to  the  temperature  indicated  for  an  hour  and  a  half. 
But  as  there  a  pears  to  be  at  present  an  almost  universal  under- 
standing in  the  manganese  trade  to  limit  the  drying  temperature 
to  100°,  the  fine  powder  is  exposed  for  6  hours  in  a  shallow  copper  or 
brass  pan  to  the  temperature  of  boiling  water,  in  a  water-bath 
(§  28,  Fig.  31).  Where  it  becomes  frequently  necessary  to  dry 
a  number  of  samples  at  the  same  time,  it  is  best  to  employ  copper 
water-baths  of  the  form  of  rather  shallow  square  boxes,  with 
4,  6,  12,  or  more  small  drying-closets  fixed  into  the  side  so  that 


458  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  247. 

they  are  surrounded  by  boiling  water  or  steam  on  all  sides  except 
the  front. 

When  the  samples  have  been  dried,  they  are  introduced,  still 
hot,  into  glass  tubes  12  to  14  cm.  long  and  8  to  10  mm.  wide,  sealed 
at  one  end;  these  tubes  are  then  corked  and  allowed  to  cool. 

In  laboratories  where  whole  series  of  analyses  of  different  ores 
are  of  frequent  occurrence,  it  is  advisable  to  number  the  drying- 
pans  and  glass  tubes,  and  to  transfer  the  samples  always  from  the 
pan  to  the  tube  of  the  corresponding  number. 


II.   DETERMINATION   OF  THE   MANGANESE   DIOXIDE. 
§247. 

Of  the  many  methods  that  have  been  proposed  for  the  valua- 
tion of  manganese  ores,  I  select  three  as  the  most  expeditious  and 
accurate.  The  first  is  more  particularly  adapted  for  technical 
purposes,  and  is  employed  almost  everywhere  for  the  purposes 
of  valuation. 

a.  FRESENIUS  and  WILL'S  Method* 

The  principle  upon  which  this  method  is  based  has  been 
already  applied  by  BERTHIER  and  THOMSON;  the  following  will 
explain : 

1.  If  oxalic  acid  (or  an  oxalate)  is  brought  into  contact  with 
manganese  dioxide  in  the  presence  of  water  and  an  excess  of 
sulphuric  acid,  manganous  sulphate  is  formed  and  carbon  dioxide 
evolved,  while  the  oxygen,  which  we  may  assume  to  exist  in  the 
manganese  dioxide  in  combination  with  the  monoxide,  combines 
with  the  elements  of  the  oxalic  acid  and  thus  converts  the  latter 
into  carbon  dioxide: 

Mn02  +  H2S04 + H2C204  =  MnSO4  +  2H2O  +  2C02. 
Each  atom  of  available  oxygen,  or,  what  amounts  to  the  same, 
*  Comp.  the  papers  mentioned  in  the  foot-note  on  p.  317,  this  vol. 


§  247.]  MANGANESE   COMPOUNDS.  459 

each  mol.  of  manganese  dioxide  =  87,  gives  2  mol.  carbon  dioxide 
=  88. 

2.  If  this  process  is  performed  in  a  weighed  apparatus  from 
which  nothing  except  the  evolved  carbonic  acid  can  escape,  and 
which,  at  the  same  time,  permits  the  complete  expulsion  of  that 
acid,  the  diminution  of  weight  will  at  once  show  the  amount  of 
carbonic  acid  which  has  escaped,  and  consequently,  by  a  very  sim- 
ple calculation,  the  quantity  of  dioxide  contained  in  the  analyzed 
manganese  ore.    As  88  parts,  by  weight,  of  carbon  dioxide  corre- 
spond to  87  of  manganese  dioxide,  the  carbon  dioxide  found  need 
simply  be  multiplied  by  87  and  the  product  divided  by  88,  or  the 
carbon  dioxide  may  be  multiplied  by 

87 

1  =  0-9887 

to  find  the  corresponding  amount  of  manganese  dioxide. 

3.  But  even  this  calculation  may  be  avoided  by  simply  using  in 
the  operation  the  exact  weight  of  ore  which,  if  the  latter  con- 
sisted of  pure  dioxide,  would  give  100  parts  of  carbon  dioxide. 

The  number  of  parts  of  carbon  dioxide  evolved  directly  ex- 
presses, in  that  case,  the  number  of  parts  of  dioxide  contained  in 
100  parts  of  the  analyzed  ore.  It  results  from  2,  that  98-87 
is  the  number  required.  Suppose  the  experiment  is  made  with 
0-9887  grm.  of  the  ore,  the  number  of  centigrammes  of  carbon 
dioxide  evolved  in  the  process  expresses  directly  the  percentage 
of  dioxide  contained  in  the  analyzed  manganese  ore.  Now,  as 
the  amount  of  carbon  dioxide  evolved  from  0-9887  grm.  of  man- 
ganese would  be  rather  small  for  accurate  weighing,  it  is  advis- 
able to  take  a  multiple  of  this  weight,  and  to  divide  afterwards 
the  number  of  centigrammes  of  carbon  dioxide  evolved  from 
this  multiple  weight  by  the  same  number  by  which  the  unit  has 
been  multiplied.  The  multiple  which  answers  the  purpose  best 
for  superior  ores  is  the  triple,  =  2  •  966 ;  for  inferior  ores  I  recom- 
mend the  quadruple,  =  3  •  955,  or  the  quintuple,  =  4  •  9435. 

4.  The  analytical  process  is  performed  in  the  apparatus  illus- 
trated in  Fig.  105. 


460  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  247. 

The  flask  A  should  hold,  up  to  the  neck,  about  120  c.c.;   B 

about  100  c.c.  The  latter  is  half 
filled  with  concentrated  sulphuric 
acid  free  from  nitric  and  nitrous 
acids;  the  tube  a  is  closed  at  b  with 
a  little  wax  ball,  or  a  very  small 
piece  of  caoutchouc  tubing,  with  a 
short  piece  of  glass  rod  inserted  in 
the  other  end. 

Place  2-966  or  3-955  or  4-9435 
grm. — according  to  the  quality  of 
the  ore — in  a  watch-glass,  and  tare 
the  latter  most  accurately  on  a 

delicate  balance;  then  remove  the  weights  from  the  watch-glass 
and  very  cautiously  replace  them  by  manganese  from  the  tube 
with  the  aid  of  a  gentle  tap  of  the  finger,  until  the  equilibrium  is 
exactly  restored.  Transfer  the  weighed  sample,  with  the  aid  of  a 
card,  to  the  flask  A,  add  5  to  6  grm.  normal  sodium  oxalate,  or 
about  7-5  grm.  normal  potassium  oxalate,  in  powder,  and  as  much 
water  as  will  fill  the  flask  to  about  one- third.  Insert  the  cork  into  A, 
and  tare  the  apparatus  on  a  strong  but  delicate  balance  by  means 
of  shot,  and  lastly,  tin-foil,  not  placed  directly  on  the  scale,  but  in 
an  appropriate  vessel.  The  tare  is  kept  under  a  glass  bell.  Test 
whether  the  apparatus  is  airtight  (Vol.  I,  pp.  488, 489) .  Then  make 
some  sulphuric  acid  flow  from  B  into  A  by  applying  suction  to  d,  by 
means  of  a  caoutchouc  tube.  The  evolution  of  carbon  dioxide  com- 
mences immediately  and  proceeds  in  a  steady  and  uniform  manner. 
When  it  begins  to  slacken,  cause  a  fresh  portion  of  sulphuric  acid 
to  pass  into  A}  and  repeat  this  until  the  manganese  ore  is  com- 
pletely decomposed,  which,  if  the  sample  has  been  very  finely 
pulverized,  requires  at  the  most  about  five  minutes.  A  too  rapid 
evolution  of  gas  must  be  avoided,  or  else  the  sulphuric  acid  will  not 
remove  all  the  water  from  the  carbon  dioxide.  The  complete 
decomposition  of  the  analyzed  ore  is  indicated,  on  the  one  hand, 
by  the  cessation  of  the  disengagement  of  carbon  dioxide,  and  its 
non-renewal  upon  the  influx  of  a  fresh  portion  of  sulphuric  into  A ; 


§  247. J  MANGANESE    COMPOUNDS.  461 

and,  on  the  other  hand,  by  the  total  disappearance  of  every  trace 
of  black  powder  from  the  bottom  of  A* 

Now  cause  some  more  sulphuric  acid  to  pass  from  B  into  A, 
to  quite  strongly  heat  the  fluid  in  the  latter,  but  not  above  70°, 
and  expel  the  last  traces  of  carbon  dioxide  therein  dissolved. 
The  apparatus  must  not  be  exposeed  to  direct  sunlight  during 
the  analysis,  otherwise  the  ferric  oxalate  may  be  decomposed 
with  evolution  of  carbon  dioxide  vLucKf).  Now  remove  the 
wax  stopper  or  india-rubber  tube  from  b  and  apply  gentle  suc- 
tion to  d  until  the  air  drawn  out  tastes  no  longer  of  carbon  dioxide. 
Let  the  apparatus  cool  completely  in  the  air,  and  place  it  on 
the  balance,  with  the  tare  on  the  other  scale,  and  restore  equilib- 
rium. The  weight  in  centigrammes  added,  divided  by  3,  4,  or  5, 
according  to  the  multiple  of  0-9887  grm.  used,  expresses  the 
percentage  of  dioxide  contained  in  the  analyzed  ore. 

5.  In  experiments  made  with  definite  quantities  of  the  ore, 
weighing  in  an  open  watch-glass  cannot  well  be  avoided,  and  the 
dried  manganese  is  thus  exposed  to  the  chance  of  a  reabsorption  of 
water  from  the  air,  which  of  course  tends  to  interfere — to  a  trifling 
extent  however — with  the  accuracy  of  the  results.     In  very  pre- 
cise experiments,  therefore,  the  best  way  is  to  analyze  an  indeter- 
minate  quantity  of   the   ore,  and  to  calculate  the  percentage  as 
shown  above.     For   this   purpose  one   of  the  little  corked  tubes 
filled  with    the    dry  pulverized    ore  is   accurately  weighed  and 
about  3  to  5  grm.  (according  to  the  quality  of  the  ore)  are  trans- 
ferred to  the  flask  A.     By  now  reweighing  the  tube,  the  exact 
quantity  of  ore  in  the  flask  is  ascertained.     To  facilitate  this  opera- 
tion it  is  advisable  to  scratch  marks  on  the  tube  with  a  file  indi- 
cating approximately  the  various  quantities  which  may  be  required 
for  the  analysis,  according  to  the  quality  of  the  ore. 

6.  If  the  manganese  ore  is  more  than  usually  difficult  to  de- 
compose, the  temperature  developed  on  mixing  the  concentrated 
sulphuric  acid  and  water  is  at  times  insufficient  to  effect  com- 

*  If  the  maganese  ore  has  been  pulverized  in  an  iron  mortar,  a  few  black 
spots  (particles  of  iron  from  the  mortar)  will  often  remain  perceptible, 
f  Zeitschr.  /.  analyt.  Chem.,-  x,  322. 


462  DETERMINATION    OF    COMMERCIAL  VALUES.          [§  247. 

plete  decomposition.  In  this  case  place  the  flask  A  of  the  ap- 
paratus on  an  iron  plate,  and  the  flask  B  on  a  board,  and  heat 
the  iron  plate.  The  temperature  must  never  be  allowed  to  ex- 
ceed 70°,  otherwise  the  oxalic  acid  may  also  be  decomposed  by 
the  ferric  sulphate  (LucK,  loc.  cit.). 

7.  With  proper  skill  and  patience  on  the  part  of  the  operator,  a 
good  balance;  and  correct  weights,  this  method  gives  most  accurate 
and  corresponding  results,  differing  in  two  analyses  of  the  same 
ore  barely  to  the  extent  of  0-2  per  cent.  I  have  never  observed 
a  greater  difference  than  this. 

If  the  results  of  two  assays  differed  by  more  than  0-2,  or  at 
most  0-3,  per  cent.,  a  third  experiment  should  be  made.  In  labo- 
ratories where  analyses  of  manganese  ores  are  matters  of  fre- 
quent occurrence,  it  will  be  found  convenient  to  use  an  aspirator 
for  sucking  out  the  carbon  dioxide.  In  the  case  of  very  moist 
air,  the  error  which  proceeds  from  the  fact  that  the  water  in  the 
air  drawn  through  the  apparatus  is  retained,  and  which  is  usually 
quite  inconsiderable,  may  now  be  increased  to  an  important  ex- 
tent. Under  such  circumstances,  connect  the  end  of  the  tube  b 
with  a  calcium-chloride  tube  during  the  suction.  It  is  needless 
to  remark  that  the  drying  and  powdering  be  properly  effected, 
and  that  the  alkali  oxalate  must  be  tested  as  to  its  purity. 

Very  accurate  determinations  may  also  be  made  by  weighing 
the  evolved  carbon  dioxide.  For  this  purpose  the  apparatus 
described  on  page  498,  Fig.  99,  Vol.  I,  is  well  adapted.  From 
0-5  to  1  grm.  ore  should  be  used  for  a  determination.  Introduce 
the  ore  and  oxalic  acid  or  oxalate  into  the  decomposing  flask,  fill 
the  flask  about  one-third  with  water,  connect  the  several  parts 
of  the  apparatus  as  for  the  determination  of  carbonic  acid,  de- 
compose the  ore  by  admitting  gradually  strong  sulphuric  acid, 
and  remove  the  evolved  C02  completely  from  the  unweighed  por- 
tion of  the  apparatus  into  the  potash  bulbs  as  described  for  the 
determination  of  CO2. 

8.  Some  ores  of  manganese  contain  carbonates  of  the  alkali- 
earth  metals,  which  of  course  necessitates  a  modification  of  the 
foregoing  process.  To  ascertain  whether  carbonates  of  the  alkali- 


§  247.]  MANGANESE    COMPOUNDS,  463 

earth  metals  are  present,  boil  a  sample  of  the  pulverized  ore  with 
water  and  add  nitric  acid.  If  any  effervescence  takes  place, 
the  process  is  modified  as  follows  (ROHR*): 

After  the  weighed  portion  of  ore  has  been  introduced  into 
the  flask  A,  treat  it  with  water,  so  that  the  flask  may  be  about  one- 
quarter  full,  add  a  few  drops  of  dilute  sulphuric  acid  (1  part,  by 
weight,  sulphuric  acid,  to  5  parts  water),  and  warm  with  agitation, 
preferably  in  a  water-bath.  After  some  time  dip  a  *od  in  and  test 
whether  the  fluid  possesses  a  strongly  acid  reaction.  If  it  does 
not,  add  more  sulphuric  acid.  As  soon  as  the  whole  of  the  car- 
bonates are  decomposed  by  continued  heating  of  the  acidified  fluid 
completely  neutralize  the  excess  of  acid  with  soda  solution  free 
from  carbonic  acid,  allow  to  cool,  add  the  usual  quantity  of  sodium 
oxalate,  and  proceed  as  above.  '  , 

If  you  have  no  soda  solution  free  from  carbonic  acid  at  hand, 
you  may  place  the  sodium  oxalate  or  oxalic  acid  (about  3  grm.)  in 
a  small  tube  and  suspend  this  in  the  flask  A  by  means  of  a  thread 
fastened  by  the  cork.  When  the  apparatus  is  tared,  and  you  have 
satisfied  yourself  that  it  is  airtight,  release  the  thread  and  proceed 
as  above. 

9.  If  the  manganese  ore  contains  magnetic  iron  oxide  f  (or 
any  ferrous  compound),  the  determination  of  its  value  in  terms 
of  manganese  dioxide,  i.e.,  the  quantity  of  chlorine  it  is  capable 
of  evolving,  will  be  inaccurate  if  the  methods  described  are  fol- 
lowed without  modification;  the  results  obtained  will  be  too  high 
because  in  carrying  out  the  method  only  the  greater  part  of  the 
ferrous  compound,  but  not  all  of  it,  is  oxidized,!  while  on  treating 
the  manganese  ore  with  hydrochloric  acid,  chlorine  is  not  evolved 
until  all  the  ferrous  iron  present  has  been  converted  into  ferric 
chloride. 

*  Zeitschr.  f.  analyt.  Chem.,  I,  48. 

f  The  presence  of  any  magnetic  iron  oxide  may  be  detected  by  the  action 
on  an  astatic  magnetic  needle.  See  MOHR,  Zeitschr.  f.  analyt.  Chem. ,  vm,  314. 

t  Compare  TESCHEMACHER  and  SMITH,  Zeitschr.  f.  analyt.  Chem.,  vm, 
509.— SHERER  and  RUMPF,  ibid.,  ix,  46.— PATTINSON,  ibid,  ix,  509.— LUCK, 
ibid.,  x,  310. 


464  DETERMINATION   OF    COMMERCIAL    VALUES.          [§  247. 

The  portion  of  the  ferrous  compound  remaining  unoxidized, 
and  hence  the  quantity  of  ferric  oxide  found  in  excess  by  the 
methods  already  described,  is  due  to  the  rapidity  with  which  the 
reaction  proceeds,  and  is  therefore  the  larger  the  more  rapid  the 
operation. 

By  slightly  modifying  the  process,  however,  perfectly  satis- 
factory results  may  be  obtained  even  with  ores  containing  ferrous 
compounds,  the  results  agreeing  well  with  those  obtained  by  other 
methods.  LUCK  *  has  shown  that  the  ferrous  compound  is  al- 
most completely  oxidized  if  some  sodium  acetate  is  introduced 
into  the  decomposition  flask. 

In  the  case  of  manganese  ores  containing  ferrous  iron,  there- 
fore, it  suffices,  according  to  LUCK,  to  introduce  as  a  rule  about 
6  c.c.  of  a  1:9  sodium-acetate  solution  into  the  decomposition 
flask,  and  to  then  conduct  the  process  as  usual.  It  is  preferable 
to  allow  the  decomposition  to  proceed  somewhat  slowly. 

Instead  of  determining  the  carbon  dioxide  from  the  loss  in 
weight  of  the  apparatus,  it  may  be  estimated  by  collecting  it  in 
a  weighed  absorption  apparatus,  as  first  recommended  by  KOLBE. 
Ths  modification  is  preferred  by  those  chemists  who  are  not 
provided  with  a  sufficiently  large  yet  very  sensitive  balance,  and 
by  those  who  prefer  weighing  on  one  balance  rather  than  on  two. 
The  most  convenient  method  to  use  is  the  one  described  in  Vol.  I, 
p.  493,  e;  a  simple  form  of  the  apparatus  may  be  used.  The 
decomposition  flask  should  hold  from  100  to  120  c.c.  up  to  the 
neck.  The  carbon  dioxide  evolved  in  it  is  passed  first  through  two 
U-tubes  the  limbs  of  which  are  170  mm.  long  and  18  mm.  wide; 
the  first  is  empty,  but  the  second  is  filled  with  calcium  chloride 
(pp.  15,  16).  The  carbon  dioxide  issuing  from  the  latter  passes 
through  two  smaller  U-tubes  the  limbs  of  which  are  110  to  120  mm. 
long  and  15  mm.  wide.  These  are  filled  £  with  granular  soda- 
lime,  and  at  the  exit  end  with  £  coarsely  granular  calcium  chloride; 
both  tubes  are  weighed  before  and  also  after  the  experiment. 
After  these  tubes  there  follows  a  small  safety-tube  the  lower  part 

*  Zeitschr.  /.  analyt.  Chem.,  x,  317. 


§  247.]  MANGANESE    COMPOUNDS.  465 

of  which  is  filled  with  soda-lime,  the  remaining  space  being  filled 
with  calcium  chloride;  then  a  small  U-tube  follows,  the  lower  part 
of  which  contains  some  water  in  order  that  the  progress  of  the 
operation  may  be  observed;  and  lastly  there  is  an  aspirator. 

Introduce  the  manganese  ore  into  the  decomposition-flask 
with  the  sodium  oxalate  (if  the  ore  contains  magnetic  iron  oxide, 
add  also  some  sodium  acetate,  as  stated  above),  and  through  a 
funnel-tube  let  run  in  diluted  sulphuric  acid  (1  vol.  concentrated 
acid  to  2  vol.  water).  Care  must  be  taken  to  avoid  exposing  the 
apparatus  to  direct  sunlight,  and  that  the  temperature  of  the 
decomposition-flask  (heated  on  an  iron  plate)  does  not  rise  above 
70°. 

If  the  manganese  ores  contain  carbonates  of  the  alkaline  earths, 
the  carbon  dioxide  in  these  may  be  first  conveniently  determined, 
by  means  of  this  method,  by  adding  a  slight  excess  of  diluted 
sulphuric  acid,  moderately  heating,  drawing  a  current  of  purified 
and  dried  air  through  the  apparatus,  and  then,  after  previously 
neutralizing  the  free  acid,  determining  the  CO2  evolved  from 
the  sodium  oxalate  by  the  action  of  sulphuric  acid  and  manganese 
ore.  It  is  almost  unnecessary  to  state  that  for  the  absorption 
of  larger  quantities  of  carbon  dioxide,  the  soda-lime  tubes  may 
be  replaced  by  a  potash  apparatus,  after  which  is  placed  a  U-tube 
half  filled  with  soda-lime,  half  with  calcium  chloride. 

b.  BUNSEN'S  Method* 

Reduce  the  ore  to  the  very  finest  powder,  weigh  off  about  0  •  4 
grm.,  introduce  this  together  with  a  few  compact  fragments  of 
magnesite  into  the  small  flask  d,  Fig.  89,  Vol.  I,  p.  425,  and  pour 
pure  fuming  hydrochloric  acid  over  it;  conduct  the  process  exactly 
as  in  the  analysis  of  chroma tes.  Boil  until  the  ore  is  completely 

*  Closely  allied  to  BUNSEN'S  method  is  that  of  GAY-LUSSAC,  very  widely 
used  in  France,  and  in  which  the  evolved  chlorine  is  passed  into  milk-of- 
lime  and  the  chlorinated-lime  solution  formed  determined  chlonmetrically 
(§  233).  SHERER  and  RUMPF  (Zeitschr.  f.  analyt.  Chem.,  ix,  48  and  51) 
in  a  critical  investigation  of  this  method  obtained  no  satisfactory  results 
whatever,  and  in  a  comparative  test  with  PERREY'S  method  (Chem.  Cen- 
tralbi,  1878,  15),  GAY-LUSSAC'S  method  gave  the  lower  results. 


466  DETERMINATION    OF   COMMERCIAL    VALUES.         [§  247. 

dissolved  and  all  the  chlorine  expelled,  which  is  effected  in  a  few 
minutes.  2  at.  of  iodine  separated  correspond  to  2  at.  chlorine 
evolved,  and  accordingly  to  1  mol.  of  manganese  dioxide.  For 
the  estimation  of  the  separated  iodine,  the  method  §  146  may  be 
employed.  Results  most  accurate,  but  only  in  skilful  hands. 

For  dissolving  the  manganese  ore,  and  absorbing  the  evolved 
chlorine  by  potassium-iodide  solution,  I  would  recommend 
the  apparatus  illustrated  by  Fig.  103,  Vol.  I,  p.  530.  There  must 
be  no  delay  in  determining  the  separated  iodine  immediately  after 
the  decomposition  is  complete,  otherwise  the  quantity  will  be  in- 
creased by  the  decomposition  of  the  hydriodic  acid  liberated, 
and  consequently  too  high  a  result  will  be  obtained. 

c.  Determination  by  means  of  Iron. 

On  heating  manganese  ore  with  hydrochloric  acid  and  a  known 
excess  of  ferrous  chloride,  the  latter  is  converted  into  ferric  chloride 
by  the  evolved  chlorine  corresponding  to  the  available  oxygen 
of  the  manganese  ore.  As  the  quantity  of  ferric  chloride  formed 
may  be  determined  by  estimating  the  unaltered  ferrous  chloride 
according  to  PENNY'S  method  (Vol.  I,  p.  319,  6),  the  effective 
value  of  the  manganese  ore,  expressed  in  terms  of  manganese 
dioxide,  may  be  readily  calculated.  This  method,  which  was 
described  in  the  5th  (German)  edition,  was  critically  examined 
in  my  laboratory  by  SHERER  and  RUMPF,*  but  the  results  ob- 
tained were  unsatisfactory,  being  somewhat  too  low  and  not 
sufficiently  concordant,  because  small  quantities  of  chlorine  es- 
cape without  acting  on  the  ferrous  chloride. 

PATTINSON  f  therefore  modified  the  method  by  employing 
sulphuric  acid  instead  of  hydrochloric  acid,  and  thereby  obtained 
good  results.  He  recommends  the  following  process:  Introduce 
into  a  600-c.c.  flask  (arranged  as  shown  in  Fig.  84,  Vol.  I,  p.  314) 
2  grm.  fine  iron  wire,  ignited  and  accurately  weighed;  dissolve 
by  the  aid  of  heat  in  90  c.c.  of  diluted  pure  sulphuric  acid  (1  part 
by  weight  concentrated  acid  and  3  of  water),  then  ad  2  grm.  of 

*  Zeitschr.  /.  analyt.  Chem.,  ix,  46.  f  Ibid.,  ix,  510. 


§  247.]  MANGANESE    COMPOUNDS.  467 

the  finely  powdered  manganese  ore,  accurately  weighed,  and 
boil  gently  until  all  is  dissolved  (soft  specimens  dissolve  very 
quickly,  but  hard  ones  require  about  fifteen  minutes  for  solution). 
When  solution  is  complete,  allow  the  water  distilled  over,  together 
with  some  additional  water,  to  run  back,  dilute  to  about  250 
to  300  c.c.,  and  after  cooling,  determine  the  excess  of  ferrous 
chloride  with  potassium  dichromate  (Vol.  I,  p.  319,  b).  The 
difference  expresses  the  quantity  of  iron  converted  by  the  oxygen 
of  the  manganese  ore  from  ferrous  to  ferric  chloride.*  This  dif- 

43-  5 

f erence  multiplied  by  ^-^  or  0  •  7782,  gives  the  quantity  of  man- 
ganese dioxide  in  the  analyzed  ore.  It  must  be  noted  that  if 
manganese  ore  contains  more  than  78  per  cent,  of  dioxide,  either 
more  iron  wire  or  less  manganese  ore  must  be  employed. 

[  The  permanganate  method  of  estimating  manganese,  although 
a  rapid  and  simple  method,  is  very  generally  ignored,  and  in  some 
cases  is  held  in  bad  repute.  The  cause  for  this,  perhaps,  is  to  be 
found  in  the  fact  that  under  certain  conditions  inconsistent  results 
can  be  easily  obtained.  The  sources  of  error  when  working  on 
ferro  and  spiegel  are  chiefly  due  to  three  causes:  first,  non- 
elimination  of  the  organic  matter  present;  secondly,  reckless 
addition  of  zinc  oxide  in  large  excess  and  in  hot  solutions;  and 
thirdly,  standardizing  the  permanganate  with  iron  instead  .of 
manganese. 

To  eliminate  these  errors,  F.  W.  DAW  f  adopted  the  following 
method,  which  he  finds  gives  very  concordant  results:  0-5  grm. 
of  ferro  or  spiegel  is  weighed  out  and  introduced  into  a  wide-mouth 
16-oz.  PHILLIPS  beaker,  and  in  the  case  of  ferro  0-4  grm.  of  pure 
iron  wire  is  added,  to  render  the  precipitation  by  zinc  oxide  easier. 
The  ferro  or  spiegel  is  dissolved  in  30  c.c.  hydrochloric  acid,  and 
the  iron  oxidized  with  a  few  c.c.  nitric  acid;  15  c.c.  of  50  per  cent, 
sulphuric  acid  are  then  added,  and  the  whole  evaporated  on  the 

*  In  very  precise  experiments,  the  weight  of  the  iron  must  be  multiplied 
by  0-996,  since  pianoforte  wire  may  always  be  assumed  to  contain  about 
0-004  impurities.  PATTINSON  takes  it  at  99-9  per  cent. 

t  Chem.  News,  LXXIX,  p.  25. 


468  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  248. 

hot  plate  till  fumes  of  sulphuric  acid  are  copiously  evolved.  When 
cool,  water  is  added,  the  sulphates  dissolved,  and  the  solution  washed 
out  into  a  1000  c.c.  conical  flask.  Cold  water  is  added  to  make  up 
to  about  500  c.c.,  the  acid  partially  neutralized  with  sodium  car- 
bonate and  zinc  oxide  gradually  added  till  the  iron  is  all  precipi- 
tated, but  a  large  excess  of  zinc  is  to  be  avoided.  The  solution 
containing  the  precipitate  is,  without  filtering,  brought  to  a  boil, 
and  standard  permanganate  run  in  till  within  a  few  c.c.  of  the  ex- 
pected amount;  the  flask  is  well  shaken,  and  the  permanganate 
run  in,  a  few  drops  at  a  time,  till  a  pink  color  appears  above  the 
precipitate.  This  is  easily  observed  by  holding  the  flask  on  one 
side,  covering  the  mouth  of  the  flask  with  a  cloth,  and  waiting  a 
few  seconds  till  the  precipitate  is  partially  settled,  when  a  pink 
color  is  easily  seen  near  the  neck. 

The  standard  permanganate  solution  is  made  up  by  dissolving 
10  grm.  KMn04  to  a  litre  of  water,  and  standardizing  it  by  means 
of  ferro-manganese  of  known  composition. 

If  iron  is  used  to  standardize  the  solution,  a  figure  is  obtained 
which  gives  low  results  when  working  on  manganese.  BREARLEY  * 
considers  this  due  to  a  small  amount  of  carbon  in  the  iron  wire 
used,  but  the  same  result  is  found  if  pure  ferrous  ammonium  sul- 
phate is  used  containing  no  carbon. — TRANSLATOR.] 

III.    ESTIMATION    OF    MOISTURE    IN    MANGANESE. 

§248. 

In  the  purchase  and  sale  of  manganese  a  certain  proportion  of 
moisture  is  usually  assumed  to  be  present,  and  often  a  percentage 
is  fixed  within  which  the  moisture  must  be  confined.  In  estimat- 
ing the  moisture  the  same  temperature  should  as  a  rule  be  em- 
ployed as  that  at  which  the  drying  for  the  purpose  of  determining 
the  dioxide  is  effected  (§  246,  I). 

As  the  amount  of  moisture  in  an  ore  may  be  altered  by  the 
operations  of  crushing  and  pulverizing,  the  experiment  should  be 
made  with  a  sample  of  the  mineral  which  has  not  yet  been  sub- 

*  Chem.  News,  Ixxv.,  15. 


§  249.]  MANGANESE  COMPOUNDS.  469 

jected  to  these  processes.  In  taking  this  it  is  best  to  use  a  round 
glass  vessel  80  to  100  mm.  in  diameter  and  30  mm.  high,  with  a 
flat  bottom,  and  closed  by  a  ground-glass  plate  of  equal  diameter, 
or  an  equally  large  tin  box  provided  with  a  well-fitting  cover.  The 
vessel  is  first  weighed  empty,  then  filled  with  the  manganese  ore 
and  covered.  After  removing  the  glass  plate  or  lid,  place  it, 
without  its  cover,  in  a  water-,  oil-,  or  air-bath,  and  continue  the 
drying  until  the  weight  remains  constant.  The  vessel  must  be 
covered  before  weighing. 

If  the  moisture  in  a  manganese  ore  is  not  to  be  estimated  on 
the  spot,  but  in  the  laboratory,  a  fair  average  sample  of  the  ore 
should  be  forwarded  to  the  chemist  in  a  strong,  perfectly  dry, 
and  well-corked  bottle. 

IV.    ESTIMATION  OF  THE  AMOUNT  OF  HYDROCHLORIC  ACID  REQUIRED 
FOR    THE    COMPLETE    DECOMPOSITION    OF    A   MANGANESE. 

§  249. 

Different  manganese  ores  containing  the  same  amount  of  avail- 
able oxygen,  or,  as  it  is  usually  expressed,  of  manganese  dioxide, 
may  require  very  different  quantities  of  hydrochloric  acid  to 
effect  their  decomposition  and  solution,  so  as  to  give  an  amount  of 
chlorine  corresponding  to  the  available  oxygen  in  them.  Thus  an 
ore  consisting  of  60  per  cent,  of  manganese  dioxide  and  40  per 
cent,  of  sand  and  clay  requires  4  mol.  hydrochloric  acid  to  1  at.  of 
available  oxygen;  whereas  an  equally  rich  ore  containing  lower 
oxides  of  manganese,"  ferric  oxide,  or  calcium  carbonate  requires  a 
much  larger  proportion  of  hydrochloric  acid. 

The  quantity  of  hydrochloric  acid  in  question  may  be  deter- 
mined by  the  following  process: 

Determine  volumetrically  the  strength  of  a  moderately  strong 
hydrochloric  acid  (of,  say,  1  •  10  sp.  gr.)  by  means  of  an  ammoniacal 
solution  of  copper  sulphate  (§  216).  Warm  10  c.c.  of  the  acid 
with  a  weighed  quantity  (about  1  grm.)  of  the  manganese  ore  in 
a  small,  long-necked  flask  fitted  with  a  reflux  condenser.  As 
soon  as  the  manganese  is  decomposed,  apply  a  somewhat  stronger 


470  DETEEMINATION    OF   COMMERCIAL   VALUES.         [§  250. 

heat  for  a  short  time,  to  expel  the  chlorine  which  still  remains 
in  solution,  but  carefully  avoid  continuing  the  application  of 
heat  longer  than  is  absolutely  necessary,  as  it  is  of  importance 
to  guard  against  the  slightest  loss  of  hydrochloric  acid.  Let  the 
flask  cool,  dilute  the  contents  with  water,  and  determine  the  free 
hydrochloric  acid  remaining  with  ammoniacal  copper-sulphate 
solution.  Deduct  the  quantity  found  from  that  originally  added; 
the  difference  expresses  the  amount  of  hydrochloric  acid  required 
to  effect  the  decomposition  of  the  manganese  ore. 


As  is  well  known,  in  the  manufacture  of  chlorinated  lime  by  the 
WELDON  method  —  treating  manganous  chloride  with  calcium 
hydroxide  and  air — there  is  obtained  a  preparation  termed  ' '  WEL- 
DON mud,"  which  is  used  over  again  as  a  sour  e  of  chlorine.  The 
effective  oxygen  value  of  WELDON  mud  (the  composition  of  which 
is  usually  CaO-2MnO2)  is  best  determined  by  BUNSEN'S  method. 
The  methods  described  under  a  and  c  are  less  suitable  because 
of  the  large  quantity  of  calcium  chloride  it  contains.  The  de- 
termination of  the  hydrochloric  acid  which  the  WELDON  mud 
requires  for  decomposition  is  effected  according  to  the  method 
detailed  in  §  249. 

B.  MANGANESE  ORES  GENERALLY. 

DETERMINATION   OF  THEIR  METALLIC    MANGANESE  CONTENT. 

§250. 

Manganese  ores  were  formerly  used  almost  exclusively  for  the 
preparation  of  chlorine,  or  as  oxidizers  in  the  manufacture  of 
glass,  but  since  they  are  also  now  used  for  the  manufacture  of 
manganese  iron,  the  quantity  of  metallic  manganese  they  contain 
has  become  of  great  importance. 

For  the  determination  of  this,  hence  quite  a  large  number  of 
new  methods  have  been  proposed  in  addition  to  those  already 
known.  These  methods,  mostly  volumetric,  are,  however,  also 


§  250.]  MANGANESE  COMPOUNDS.  471 

considered  in  connection  with  the  analysis  of  iron,  hence  they  will 
not  be  described  here,  but  in  §  255. 

I  will  detail  the  mothod  here  which  for  many  years  has  been 
used  in  my  laboratory.  It  is  true  it  is  rather  more  inconvenient 
than  is  desirable,  but  as  regards  accuracy  it  leaves  nothing  to  be 
desired,  while  at  the  same  time  it  allows  of  the  determination  of  the 
other  constituents  of  the  ore. 

Dissolve  in  hydrochloric  acid  about  1  grm.  of  the  mineral  dried 
at  100°,  evaporate  the  solution  to  dryness,  warm  the  residue  with 
hydrochloric  acid,  add  water,  filter  and  dilute  the  solution  to  about 
500  c.c.  The  entire  absence  of  manganese  from  the  residue  may 
be  ascertained  by  fusing  a  small  sample  with  sodium  carbonate 
with  access  of  air.  If  any  manganese  is  found,  the  whole  of  the 
residue  must  be  decomposed  by  fusion  with  sodium  carbonate, 
the  silicic  acid  separated  by  hydrochloric  acid,  and  the  filtrate 
from  the  silicic  acid  added  to  the  main  solution. 

//  the  solution  is  poor  in  iron,  add  ammonia  to  it  to  slight  alka- 
linity, filter  at  once  into  a  flask  containing  a  little  acetic  acid, 
dissolve  the  precipitate  (after  washing)  in  hot  hydrochloric  acid, 
heat,  allow  to  cool,  add  10  c.c.  (but  not  more)  ammonium-chloride 
solution,  and  precipitate  the  iron  as  a  basic  salt  according  to  the 
method  detailed  in  Vol.  I,  p.  644,  3,  a  [82].  If,  on  the  other  hand, 
the  solution  contains  much  iron,  add  20  c.c.  ammonium-chloride 
solution,  precipitate  the  iron  at  once  as  a  basic  salt  according 
to  the  method  given,  dissolve  the  precipitate  after  moderately 
washing  it  in  hydrochloric  acid,  add  10  c.c.  ammonium-chloride 
solution,  and  repeat  the  precipitation  of  the  basic  salt. 

After  washing  it,  fuse  a  small  portion  of  the  basic  iron  salt 
with  sodium  carbonate  with  access  of  air  in  order  to  make  certain 
that  no  manganese  is  present. 

Unite  the  filtrate  with  the  washings,  add  a  little  acetic  acid, 
concentrate  by  evaporation  to  300  c.c.,  allow  to  cool,  make  very 
weakly  alkaline  with  ammonia  (in  order  to  precipitate  any  traces 
of  aluminium),  and  at  once  filter  off  from  the  precipitate  which 
as  a  rule  is  formed.  After  washing  somewhat,  dissolve  the  pre- 
cipitate in  hot  hydrochloric  acid,  repeat  the  precipitation  with 


472  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  250. 

ammonia  as  before,  and  again  filter.  The  appearance  of  the  pre- 
cipitate— white  or  brownish — will  denote  whether  a  reprecipitation 
will  be  necessary.  Unite  the  washings  and  the  filtrate,  acidulate 
weakly  with  acetic  acid,  add  ammonium  acetate,  and  treat  with 
hydrogen  sulphide.  As  a  rule  a  black  precipitate  (cobalt  sulphide, 
etc.)  forms.  Filter  this  off,  concentrate  the  filtrate  if  necessary, 
and  precipitate  and  determine  the  manganese  as  manganese  sul- 
phide according  to  §  109,  2. 

ELECTROLYTIC  DETERMINATION. 

The  electrolytic  determination  of  manganese  has  been  worked 
out  by  LUCKOW  *  and  ALF.  RicHE.f  As,  however,  it  is  necessary 
that  the  iron  be  first  removed  and  the  liquid  then  concentrated  to 
a  very  small  volume  (the  manganese  separates  at  the  positive  pole 
as  dioxide),  while  the  separation  occurs  only  in  a  sulphuric-acid 
or  nitric-acid  solution,  this  method  offers  no  special  advantages. 

[  CLASSEN  J  could  not  confirm  the  assumption  that  manganese 
dioxide  dried  at  68°  has  the  composition  MnO2-H2O.  On  attempt- 
ing to  convert  the  hydrated  dioxide  into  anhydrous  dioxide  by 
prolonged  drying  at  a,  higher  temperature,  a  strongly  hygro- 
scopic substance  results  which  rapidly  increases  in  weight  during 
the  process  of  weighing.  It  is  therefore  necessary  to  convert  the 
dried  dioxide  into  mangano-manganic  oxide  by  ignition,  an  oper- 
ation conducted  with  ease  and  safety.  After  determining  the 
necessary  conditions  for  the  separation  of  large  quantities  of  lead 
dioxide,  the  author  found  that  strong  inorganic  acids  interfere  with 
complete  precipitation,  and  even  make  it  impossible.  Of  the 
organic  acids,  acetic  acid  alone  is  suitable,  although  the  precipi- 
tation of  large  quantities,  even  when  roughened  dishes  are  used, 
cannot  be  successfully  carried  out,  since  it  is  impossible  to  obtain 
firmly  adhering  precipitates. 

If  a  salt  other  than  acetate  is  at  hand,  it  is  best  to  precipitate  the 
manganese  as  dioxide  with  ammoniacal  hydrogen  peroxide.  The 

*  Zeitschr.  f.  analyt.  Chem.,  vm,  24.  f  Ibid.,  xvn,  216. 

J  "  Quantitative  Chemical  Analysis  by  Electrolysis."  by  ALEX.  CLASSEN, 
translated  by  B.  B.  BOLTWOOD.  JOHN  WILEY  &  SONS,  New  York,  1903. 


§  250.]  MANGANESE   COMPOUNDS.  473 

precipitate  is  washed  thoroughly  and  dissolved  in  5  c.c.  acetic  acid, 
5  c.c.  hydrogen  dioxide  (4-  to  5-per  cent.),  and  25  c.c.  water.  This 
is  especially  necessary  when  the  manganese  is  present  as  chloride 
or  when  the  solution  contains  other  chlorides.  Permanganic  acid 
is  first  reduced  to  a  manganous  salt.  In  acetic-acid  solutions, 
even  when  roughened  dishes  are  used,  the  maximum  quantity  of 
manganese  which  can  be  satisfactorily  determined  as  dioxide  is 
only  about  0-08  grm. 

A  rapid  and  complete  separation  was  secured  by  ENGELS  in 
CLASSEN'S  laboratory.  The  method  is  as  follows:  1  to  2  grm. 
of  the  manganese  salt  are  dissolved  in  about  125  c.c.  of  water, 
and  10  grm.  ammonium  acetate  and  1-5  to  2  grm.  chrome  alum 
are  also  added.  The  clear  solution  is  then  electrolyzed.  Chlorides 
must  not  be  present,  since  the  solution  of  chlorine  interferes  with 
the  separation  of  the  manganese.  If  they  are  present,  the  man- 
ganese is  converted  into  acetate  as  described  above. 

In  the  determination  of  manganese  in  the  salts  of  permanganic 
acid,  the  solution  of  the  latter  is  decomposed,  according  to  ENGELS, 
with  5  c.c.  acetic  acid  and  enough  hydrogen  dioxide  to  completely 
decolorize  it.  Since  the  presence  of  even  small  quantities  of  hydro- 
gen dioxide  prevent  the  separation  and  the  firm  adherence  of  the 
precipitate,  the  excess  of  hydrogen  dioxide  must  be  removed. 
This  may  be  most  easily  accomplished  by  the  addition  of  small 
quantities  of  chromic  acid,  until  further  addition  no  longer  causes 
the  evolution  of  gas ;  generally  0  •  3  to  0  •  5  grm.  is  sufficient. 

F.  KAEPPEL  *  has  devised  a  method  enabling  him  to  precipitate 
the  manganese  in  the  state  of  dioxide  as  a  coherent  powder,  and  at 
the  same  time  to  prevent  the  transformation  of  this  dioxide  into 
saline  oxide  by  calcination  in  a  platinum  crucible.  It  is,  of  course, 
known  that  the  platinum  is  strongly  attacked  in  this  operation. 

The  following  is  the  method; 

The  manganese  salt  (containing  manganese  equivalent  to  about 
0- 15 to  1  -6  grm.  MnO2)  is  dissolved  in  150  c.c.  of  water,  and  acetone 
is  added.  The  solution  is  kept  at  a  temperature  of  50°  to  55°, 


*Zeitschr.  f.  anorg.  Chem.,  xvi,  268;    Chem.  News,  LXXX,  195. 


474  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  251. 

and  electroly zed  with  a  current  of  4  to  4-25  volts,  and  0-7  to  1-2 
amperes;  care  must  be  taken  to  add  water  to  replace  that  which 
is  gradually  lost  by  evaporation.  At  the  end  of  from  two  to  five 
and  a  half  hours,  according  to  the  proportion  of  acetone  present 
(1-5  to  10  grm.),  the  operation  is  terminated;  the  manganese 
dioxide  is  washed  by  means  of  a  siphon  without  interrupting 
the  current;  the  electrode  is  dried  at  150°  to  180°  and  weighed. 

In  this  method  the  acetone  is  converted  into  acetic  acid,  and 
this  in  its  nascent  state  is  believed  by  KAEPPEL  to  have  a  better 
action  on  the  deposition  than  if  added  directly  to  the  electrolyte. — 
TRANSLATOR.] 

13.  NICKEL  COMPOUNDS  * 

A.  NICKEL  ORES,  NICKELSTEIN,  AND  OTHER  INTERMEDIATE 
PRODUCTS  OF  NICKEL  MANUFACTURE. 

§251. 

In  the  analysis  of  copper-nickel,  antimony-nickel,  nickelstibine, 
and  nickel  glance,  it  becomes  necessary  as  a  rule  to  separate  also 
nickel  cobalt,  iron,  arsenic,  antimony,  and  sulphur,  and  some- 
times also  lead;  in  white  nickel  pyrites  there  are  also  present 
copper  and  bismuth,  while  nickel  pyrites  contain  determinable 
quantities  of  nickel,  cobalt,  iron,  copper,  and  sulphur.  In  the 
analysis  of  nickeliferous  copper  and  iron  pyrites  also.,  only  the 
last-mentioned  elements,  as  a  rule,  have  to  be  considered,  apart 
from  silicic  acid  and  alkaline  earths,  which  may  be  present.  The 
kupfer-nickelstein,  obtained  as  an  intermediate  product  in  obtaining 
copper-nickel  or  nickel  from  nickeliferous  ores,  contains  chiefly  cop- 
per, iron,  nickel,  with  a  little  cobalt  and  sulphur,  but  it  frequently 
contains  also  arsenic,  antimony,  and  sometimes  lead.  Ores  and 

*The  cobalt  compounds  are  examined  in  exactly  the  same  way  as  the 
nickel  compounds,  and  in  fact  the  three  methods  described  in  §  251  may 
be  used  for  the  former.  Regarding  the  testing  of  nickel  and  cobalt  ores  by 
the  dry  way  by  PLATTNER'S  method  (conversion  of  the  nickel  and  cobalt  into 
arsenides)  see  MUSPRATT'S  Chemistry,  3d  Ed.,  by  KERL  and  STOHMANN,  in, 
1914. 


§  251.]  NICKEL   COMPOUNDS.  475 

metallurgical  products  contain  very  variable  quantities  of  nickel, 
and  are  frequently  the  objects  of  quantitative  analysis  since  the 
manufacture  of  nickel  has  become  of  very  great  industrial  value. 
As  a  rule  it  is  sufficient  to  determine  the  content  of  nickel  plus 
cobalt,  or  of  nickel  and  of  cobalt,  or  of  nickel,  cobalt,  and  copper. 
I  shall  here  confine  myself  to  giving  the  details  of  the  determina- 
tions of  these  metals  only,  reference  having  already  been  made  in 
the  first  part  of  this  work  to  the  further  examination  of  the  pre- 
cipitates, etc.,  obtained  during  the  operations. 

First  Method. 

Treat  a  portion  of  the  finely  powdered  mineral  or  metallurgical 
product,  containing  about  0-5  to  1  grm.  nickel,  with  hydrochloric 
acid  and  a  little  nitric  acid  until  all  the  soluble  portion  is  dissolved, 
evaporate  repeatedly  almost  to  dryness  with  hydrochloric  acid  to 
expel  the  excess  of  nitric  acid,  take  up  the  residue  with  hydrochlo- 
ric acid  and  water,  and  then  filter.  If  any  sulphur  remains,  ignite 
the  residue  in  the  air  and  treat  again  with  hydrochloric  acid  and 
a  little  nitric  acid  as  before.  If  now  too  a  residue  remains  which 
is  not  perfectly  white,  fuse  it  with  potassium  disulphate  and  treat 
the  melt  with  hydrochloric  acid  and  water,  or  fuse  it  with  sodium 
carbonate,  treat  the  melt  with  water  and  hydrochloric  acid,  and 
separate  the  silicic  acid  and  treat  it  with  hydrochloric  acid.  The 
solution  obtained  by  either  of  these  methods  is  added  to  the  main 
solution,  which  is  then  treated  as  follows: 

Add  sufficient  hydrochloric  acid  to  the  solution  (400  c.c.  of 
which  should  contain  about  40  c.c.  of  hydrochloric  acid,  sp. 
gr.  1-12),  and  pass  in  hydrogen  sulphide  to  precipitate  all  the 
metals  precipi table  by  it;  it  is  advantageous  to  pass  in  the  gas 
first  at  about  70°,  and  then  in  the  cold.  Filter  and  then  heat  the 
filtrate  gradually,  adding  nitric  acid,  so  that  all  ferrous  iron  is 
converted  into  ferric  iron.  After  the  liquid  has  cooled  somewhat 
add  ammonia  'in  excess,  filter  off  the  impure  ferric  hydroxide, 
wash  it,  dissolve  in  hydrochloric  acid,  dilute  the  solution  largely, 
add  30  c.c.  ammonium-chloride  solution,  and  then  add,  in  the  cold, 
a  dilute  ammonium-carbonate  solution  until  the  liquid  becomes 


476  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  251. 

slightly  turbid,  but  does  not  yield  a  precipitate.  The  liquid 
should  not  become  clear  on  standing,  but  the  turbidity  should 
rather  increase.  The  liquid  at  this  period  has  still  a  distinctly 
acid  reaction.  Now  heat  to  boiling,  wash  the  precipitated  basic 
ferric  salt,  first  by  decantation,  then  on  the  filter,  with  boiling 
water  containing  some  ammonium  chloride,  and  then  test  a  portion 
of  the  ferric  salt  by  dissolving  it  in  hydrochloric  acid,  reprecipitat- 
ing,  and  testing  the  filtrate  with  ammonium  sulphide  for  nickel. 
Should  a  small  quantity  of  this  be  still  found  present,  the  entire 
precipitate  must  be  dissolved  in  hydrochloric  acid  and  the  iron 
once  more  reprecipitated  as  a  basic  ferric  salt.  Mix  the  two  or 
three  filtrates  containing  the  nickel  and  cobalt,  acidulate  with 
acetic  acid,  then  make  weakly  alkaline  with  ammonia,  and  con- 
centrate by  evaporation.  If  a  small  quantity  of  a  precipitate 
(ferric  hydroxide  or  aluminium  hydroxide)  forms,  filter  it  off,  dis- 
solve in  hydrochloric  acid,  precipitate  with  an  excess  of  ammonia, 
and  repeat  the  entire  operation  once  more.  To  the  filtrate,  suit- 
ably concentrated  and  containing  all  the  nickel  and  cobalt  in 
solution,  now  add  acetic  acid  until  distinctly  acid,  and  then  add 
to  the  clear  liquid  30  to  50  c.c.  of  a  1 : 10  ammonium-acetate  solu- 
tion, warm  to  about  70°,  and  pass  in  hydrogen  sulphide  until  the 
liquid  smells  strongly  of  the  gas.  After  precipitation  is  complete, 
filter  off  the  precipitate  of  nickel  and  cobalt  sulphides,  wash,  rinse 
into  a  beaker,  and  incinerate  the  filter.  Concentrate  the  filtrate 
by  evaporation,  add  first  ammonium  hydrosulphide  and  then 
acetic  acid,  whereby  very  frequently  a  still  further  slight  quantity  of 
nickel  and  cobalt  sulphides  is  obtained.  As  a  matter  of  precau- 
tion, test  the  filtrate  again  in  like  manner  in  order  to  be  certain 
that  all  the  nickel  and  cobalt  have  been  converted  into  sulphides. 

Treat  the  nickel  and  cobalt  sulphides  which  were  washed  into 
the  beaker,  and  also  the  filter  ash,  with  hydrochloric  acid  and 
a  little  nitric  acid  added  until  completely  decomposed  and  the 
metals  are  dissolved;  then  evaporate  with  hydrochloric  acid  in 
order  to  drive  off  the  nitric  acid,  dilute  with  water,  filter,  incinerate 
the  filter,  add  the  hydrochloric-acid  solution  of  the  filter  ash  to 
the  main  solution,  and  precipitate  (best  in  a  large  platinum  dish) 


§  251.]  NICKEL    COMPOUNDS.  477 

with  pure  potassa  solution,  by  pouring  the  nickel  solution  into 
an  excess  of  the  heated  potassa  solution.  Wash  the  precipitate 
very  thoroughly,  first  by  decantation,  then  on  the  filter,  with 
boiling  water,*  and  after  partially  or  even  completely  drying, 
heat  gently  in  a  ROSE  crucible,  first  with  the  cover  on  and  then 
with  access  of  air.  Now  increase  the  heat  until  the  filter  has 
been  completely  incinerated,  conducting  the  heating  finally  in  a 
current  of  pure  hydrogen  until  the  weight  remains  constant. 
Next  treat  the  metallic  nickel  and  cobalt  in  the  crucible  with 
boiling  water;  should  this  acquire  an  alkaline  reaction,  or  con- 
tain chlorine  or  sulphuric  acid,  or  leave  a  residue  on  evaporation 
on  platinum  foil,  the  metals  must  be  exhausted  with  boiling  water 
and  again  ignited  in  a  current  of  hydrogen  and  once  more  weighed. 

Now  dissolve  the  metals  in  nitric  acid, .whereby,  as  a  rule,  a 
small  quantity  of  silicic  acid  remains  undissolved.  Collect  this 
on  a  small  filter  and  determine  its  weight.  Nearly  neutralize  the 
nitric-acid  solution  writh  ammonia,  add  an  excess  of  ammonium 
carbonate,  warm  gently  for  a  long  time,  filter  off  the  small  quan- 
tity of  precipitated  ferric  hydroxide  or  aluminium  hydroxide 
usually  obtained,  dissolve  it  in  nitric  acid,  reprecipitate  once 
more  with  ammonium  carbonate,  ignite  the  small  quantity  of 
precipitate  first  in  the  open  air,  then  in  hydrogen,  and  deduct 
its  weight,  together  with  that  of  the  silicic  acid,  from  the  weight 
of  the  metals. 

It  is  easy  to  see  that  in  most  cases  it  is  more  convenient  and 
rapid  to  incinerate  the  small  filter  with  the  silicic  acid  and  that 
containing  the  iron  and  aluminium  hydroxides,  in  the  same  crucible, 
and  then,  after  igniting  in  hydrogen,  to  weigh  both  impurities 
together.  Should  the  silicic  acid  or  the  alumina,  etc.,  exhibit  a 
bluish  color  from  the  presence  of  cobalt,  the  one  or  the  other 
must  be  fused  with  a  little  alkali  carbonate,  and  the  silicic  acid 

*  The  statements  of  FINKENER  (Handbuch  d.  analyt.  Chem.,  von  H.  ROSE, 
6.  Aufl.  von  FINKEXER,  n,  136),  and  of  BUSSE  (Zeitschr.  f.  analyt.  Chem., 
XYII,  60),  that  nickel  hydroxide  is  somewhat  soluble  in  water,  I  can  con- 
firm, but  the  traces  which  dissolve  in  water  are  so  minute  that  they  can 
have  no  appreciable  influence  on  the  result.  Comp.  Analyt.  Note,  No.  90. 


478  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  251. 

or  alumina,  etc.,  separated  in  the  pure  state  and  weighed.  As 
the  metallic  nickel  may  at  times  contain  also  slight  quantities  of 
magnesia,  it  is  necessary  to  add  a  little  ammonium  phosphate 
to  the  blue  ammoniacal  solution  obtained  when  separating  the 
impurities,  and  to  allow  the  whole  to  stand  for  a  time  in  order 
to  see  if  any  ammonium-magnesium  phosphate  separates;  if 
this  occurs,  the  precipitate  is  converted  into  and  weighed  as  mag- 
nesium pyrophosphate,  and  calculated  as  magnesia.  If  much 
Cobalt  is  present,  ammonium-cobaltous  phosphate  is  precipitated 
with  the  ammonium-magnesium  phosphate.  In  this  case,  in 
order  to  obtain  the  magnesium  salt  in  a  state  of  purity,  wash  the 
precipitate  with  water  containing  a  little  ammonia,  dissolve  in 
acetic  acid,  add  ammonium  acetate,  precipitate  the  cobalt  with 
hydrogen  sulphide  (as  above),  concentrate  the  filtrate,  and  then 
add  ammonia  and  some  ammonium  phosphate  to  precipitate 
the  magnesia. 

There  remains  now  but  to  speak  of  the  sulphuric-acid  or  hy- 
drochloric-acid solution  occasionally  obtained  by  decomposing 
the  portion  of  residue  of  ore,  etc.,  insoluble  in  hydrochloric  and 
nitric  acids,  and  containing  still  a  small  quantity  of  the  heavy 
metals  (see  above).  The  simplest  method  would  seem  to  be  to  add 
the  solution  so  obtained  to  the  main  solution  before  precipitating 
with  hydrogen  sulphide.  This  method,  however,  has  the  dis- 
advantage of  unnecessarily  introducing  a  comparatively  large 
quantity  of  alumina  into  the  solution,  which  is  very  inconvenient. 
It  is  hence  best  to  treat  the  small  quantity  of  solution  by  itself; 
first  pass  in  hydrogen  sulphide  in  order  to  separate  any  metals 
of  the  fifth  and  sixth  groups  that  may  be  present,  then  heat  the 
filtrate  with  nitric  acid,  precipitate  with  ammonia,  Wash,  dissolve 
the  precipitate  in  hydrochloric  acid,  and  precipitate  once  more 
with  ammonia.  Unite  the  filtrates  and  separate  the  small  quantity 
of  nickel  with  hydrogen  sulphide  as  in  the  case  of  the  main  solution. 
Then  dissolve  this  small  quantity  of  nickel  sulphide  with  the 
larger  quantity  in  nitric  acid  (see  above). 

If  the  nickel  and  cobalt  are  to  be  determined  separately, 
effect  the  separation  (if  comparatively  much  nickel  and  little 


§  251.]  NICKEL   COMPOUNDS.  479 

cobalt  are  present)  according  to  §  160,  9,  by  means  of  potassium 
nitrite.  If,  however,  little  nickel  but  much  cobalt  are  present, 
it  is  better  to.  operate  according  to  §  160,  10,  using  potassium 
cyanide  and  chlorine  or  bromine. 

The  most  convenient  method  is  to  make  up  to  250  c.c.  the 
solution  obtained  by  treating  the  nickel  and  cobalt  sulphides 
with  nitric  acid,  and  to  determine  in  100  c.c.  the  nickel  and  cobalt 
as  above  detailed,  while  in  a  second  100  c.c.  (or  in  the  remaining 
150  c.c.)  either  the  nickel  or  the  cobalt  is  determined,  according 
to  circumstances.  After  weighing  the  metals  treat  them  exactly 
as  above  described  for  nickel  and  cobalt,  in  order  to  remove  any 
adhering  impurities.  If  the  cobalt  has  been  precipitated  by  potassa 
solution  from  the  hydrochloric-acid  solution  of  potassium-cobalt 
nitrite,*  the  filtrate  together  with  the  washings  must  be  treated 
with  ammonium  sulphide.  If  this  yields  a  slight  precipitate  of 
cobalt  sulphide^  determine  the  cobalt  in  it  separated  as  cobaltous 
sulphate  (§  111,  2,  b).  In  order  to  avoid  this  double  determina- 
tion it  is  usually  more  convenient  to  supersaturate  with  am- 
monia the  hydrochloric-acid  solution  of  the  potassium-cobalt 
nitrite,  precipitate-  the  cobalt  with  ammonium  sulphide  as  cobalt 
sulphide,  then  to  dissolve  this  in  nitric  acid,  evaporate  the  solu- 
tion with  sulphuric  acid,  and  weigh  the  cobaltous  sulphate  (§  111, 
2,  &). 

In  case  it  is  deemed  inadvisable  to  divide  the  nickel-cobalt 
solution,  acidulate  with  acetic  acid  the  ammoniacal  solution  ob- 
tained in  purifying  the  weighed  nickel  and  cobalt,  reprecipitate 
both  metals  as  sulphides,  dissolve  these  in  nitric  acid,  and  in  the 
solution  determine  the  nickel  or  cobalt  as  already  described; 
the  metal  not  determined  may  be  estimated  in  either  case  by  dif- 
ference. 

If  very  little  cobalt  is  present  together  with  much  nickel,  all 
the  cobalt  may  be  precipitated  with  some  nickel,  and  the  separa- 
tion of  the  two  metals  then  undertaken.  For  this  purpose  dis- 
solve both  metals  in  hydrochloric  acid,  neutralize  the  solution 

*  For  another  method  of  determining  cobalt  in  potassium-cobalt  nitrite 
see  BRAUNER,  Zeitschr.  /.  analyt.  Chem.,  xvi,  195. 


480  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  251. 

as  nearly  as  possible  with  sodium  carbonate,  heat  the  liquid, 
and  then  cautiously  add  a  weakly  alkaline  solution  of  sodium 
hypochlorite,  thus  precipitating  the  cobalt  completely  and  the 
nickel  partially.  If  the  operation  is  conducted  so  that  at  least  two 
parts  of  nickel  are  present  for  one  part  of  cobalt,  the  precipitate 
will  certainly  contain  all  the  cobalt  present.  Whether  the  proper 
proportion  has  been  hit  or  not  may  be  observed  from  the  color 
of  the  hydrochloric-acid  solution  of  the  brownish-black  hydroxide; 
if  almost  colorless,  or  with  but  a  greenish  or  reddish  tinge,  all  the 
cobalt  has  been  precipitated,  but  if  the  solution  is  deep  red,  a 
further  partial  separation  is  necessary  (FLEITMANN  *).  The 
separation  is  then  effected  in  the  hydrochloric-acid  solution  by 
means  of  potassium  nitrate,  as  above  described. 

If  copper  also  is  to  be  determined  in  the  ores  or  furnace 
products,  treat  the  hydrogen-sulphide  precipitate  first  obtained 
according  to  §  261. 

Second  Method. 

According  to  CLASSEN,!  nickel,  like  zinc,  can  be  separated 
as  an  oxalate  from  iron.  I  am  not  in  a  position  to  offer  an  opinion 
regarding  this  method,  as  yet.  The  test  analyses  cited  by  CLASSEN 
show  very  satisfactory  results.  In  order  to  apply  the  method 
to  nickel  ores,  etc.,  effect  the  solution  as  in  Method  1,  and  re- 
move the  precipitable  metals  with  hydrogen  sulphide  from  the 
acid  solution  in  a  similar  manner.  Drive  off  the  hydrogen  sul- 
phide, oxidize  the  ferrous  salt  by  boiling  with  nitric  acid,  and 
evaporate  to  dryness  on  the  water-bath.  Treat  the  residue  with 
about  seven  times  its  quantity  of  a  1 : 3  solution  of  neutral  potas- 
sium oxalate,  warm  on  the  water-bath  for  fifteen  minutes,  and 
effect  solution  of  any  slight  undissolved  residue  of  ferric  oxide 
by  adding  acetic  acid  drop  by  drop.  If  sufficient  potassium 
oxalate  has  been  added  there  is  obtained  a  clear,  greenish  solution. 

Heat  the  solution  to  boiling,  and  add  at  least  an  equal  volume 
of  80  per-cent.  acetic  acid  while  stirring,  whereby  nickelous  and 

*  Zeitschr.  f.  analyt.  Chem.,  xiv,  76. 

f  Ibid.,  xvi,  471;  xvm,'  189;  xvm,  386. 


§  251. J  NICKEL   COMPOUNDS.  481 

cobaltous  oxalates  are  precipitated.  The  nickelous  oxalate  has  a 
more  or  less  crystalline  character  only  when  the  quantity  of  nickel 
present  is  small.  CLASSEN  therefore  operated  only  upon  quantities 
of  from  0-1  to  0-2  grm.  Now  heaffor  six  hours  at  50°,  filter  hot, 
and  thoroughly  wash  with  a  mixture  of  equal  volumes  of  con- 
centrated acetic  acid,  alcohol,  and  water.  After  drying  the  nickel- 
ous oxalate  and  burning  the  filter-paper  on  a  platinum  wire,  heat 
the  two  in  a  covered  platinum  crucible,  at  first  gently,  then  grad- 
ually more  strongly,  and  finally  very  strongly  with  access  of  air 
for  a  sufficiently  long  time,  and  weigh  the  nickelous  oxide  ob- 
tained. If  the  nickelous  oxalate  has  been  insufficiently  washed, 
the  nickelous  oxide  resulting  will  be  contaminated  with  potassium 
carbonate.  This  may  be  known  on  warming  the  residue  with 
water;  if  the  solution  so  obtained  gives  an  alkaline  reaction,  the 
nickelous  oxide  must  be  thoroughly  washed  with  hot  water,  and 
once  more  weighed.  If  any  cobalt  is  present,  reduce  the  ignition 
residue,  first  washed  if  necessary,  by  heating  in  a  current  of  hy- 
drogen, and  weigh  as  metal.  Regarding  the  separation  of  nickel 
and  cobalt  see  the  first  method. 

Third  Method. 

ELECTROLYTIC  SEPARATION  OF  NICKEL,  OR  OF   NICKEL  AND  COBALT. 

The  electrolytic  determination  of  nickel,  to  which  W.  GIBBS  * 
called  attention  already  in  1864,  has  been  further  extended  by  the 
labors  of  C.  LucKOW,f  the  MANSFELD  OBER-BERG-  UND  HUTTEN- 
DIRECTION,  t  HERPIN,§  F.  WRIGHTSON,||  TH.  SCHWEDER,^  and 
W.  OHL.**  These  labors  have  shown  that  nickel  and  cobalt  are 
not  precipitated  by  the  electric  current  from  solutions  containing 
free  acids,  but  that  they  are  precipitated  from  ammoniacal  solu- 
tions, or  from  solutions  of  their  cyanides  in  potassium-cyanide  solu- 

*  Zeitschr.  f.  analyt.  Chem.,  in,  334. 

f  DINGLER'S  polyt.  Journ.,  CLXXVII,  235. 

J  Zeitschr.  f.  analyt.  Chem.,  xi,  10,  and  xiv,  350. 

§  Ibid.,  xv,  335. 

||  Ibid.,  xv,  300. 

1  Ibid.,  xvi,  344. 

**  Ibid.,  xvm,  523. 


482  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  251. 

tion,  as  well  as  from  solutions  of  their  neutral  sulphates  to  which 
an  alkali  acetate,  tartrate,  or  citrate  has  been  added  (LucKOw). 
More  recently  H.  FRESENIUS  and  F.  BERGMANN*  have  most  care- 
fully studied  the  conditions  which  appear  to  be  most  favorable  for 
the  quantitative  determinations  by  this  method.  Ammoniacal 
solutions  should  be  employed,  and  they  must  contain  a  sufficient 
excess  of  free  ammonia  to  remain  strongly  ammoniacal  through- 
out. The  presence  of  ammonium  sulphate  or  of  sodium  phosphate 
(M.  S.  CHENEY  and  E.  S.  RICHARDS  f)  favor  the  separation,  while 
ammonium  chloride  hinders  or  prevents  it;  ammonium  nitrate 
also  acts  disadvantageously. 

The  most  favorable  conditions  for  the  separation  of  nickel  and 
also  cobalt  are  as  follows: 

The  strength  of  the  current  of  the  CLAMOND  pile  (comp.  §  261) 
should  be  such  as  to  liberate  300  c.c.  oxyhydrogen  gas  per  hour. 
The  nickel  or  cobalt  should  be  present  as  neutral  sulphate  in  the 
proportion  of  0-1  to  0-15  grm.  per  200  c.c.  of  aqueous  solution 
containing  2-5  to  4  grm.  ammonia  and  6  to  9  grm.  ammonium 
sulphate  (both  calculated  as  being  in  the  anhydrous  state.  The  dis- 
tance of  the  lower  edge  of  the  weighed  platinum  cone  forming  the 
negative  pole  from  the  annular  foot  of  the  platinum  spiral  form- 
ing the  positive  pole  (see  §  261)  should  be  from  3  to  5  rnm.  The 
beaker  containing  the  solution  should  be  covered  with  a  large  watch- 
glass  provided  with  suitable  openings  for  the  passage  of  the  bat- 
tery wires.  The  solution  loses  color  in  proportion  as  the  nickel 
deposits.  As  soon  as  it  appears  perfectly  colorless  test  a  few 
drops  with  potassium  sulphocarbonate ;  if  only  a  scarcely  notice- 
able rose-red  color  develops,  the  precipitation  may  be  considered 
as  complete.  Cobalt  solutions  at  first  become  darker  from  the 
absorption  of  oxygen,  but  they  gradually  become  lighter  in  color, 
and  finally  colorless;  the  sulphocarbonate  test  should  be  applied 
in  this  case  also,  discontinuing  the  operation  when  only  a  scarcely 
perceptible  wine-yellow  color  develops. 

As  soon  as  the  deposition  is  complete  draw  off  the  liquid  by 

*  Zeitschr.  f.  analyt.  Chem.,  xix,  314. 
.,  xvn,  215. 


§  252.]  NICKEL   COMPOUNDS.  483 

means  of  a  water-pump  or  aspirator  into  a  flask  provided  with  a 
doubly-perforated  stopper,  employing  the  same  simple  apparatus  for 
removing  the  washings  and  for  final  rinsings  with  the  wash-bottle. 
The  wires  must  not  be  disconnected  until  the  washing  has  been 
terminated;  then  suspend  the  cone  over  a  hot  iron  plate  until 
perfectly  dry,  allow  it  to  become  cold,  and  weigh.  The  nickel 
deposited  on  the  platinum  cone  presents  a  handsome  polished 
surface;  cobalt  is  less  lustrous. 

The  manner  of  employing  the  electrolytic  method  to  nickel  ores, 
nickelstein,  etc.,  depends  upon  the  kind  and  quantity  of  the  metals 
present  with  the  nickel  and  cobalt.  The  metals  can  always  be 
removed  according  to  Method  1,  the  nickel  and  cobalt  sulphides 
being  then  dissolved  in  nitric  acid  with  some  hydrochloric  acid 
added,  the  solution  evaporated  with  a  definite  quantity  of  sul- 
phuric acid,  and  supersaturating  with  ammonia;  if  required,  more 
ammonium  sulphate  may  be  added  in  order  to  obtain  the  favorable 
conditions  above  noted.  The  separation  of  the  foreign  metals 
may  also  at  times  be  effected  by  electrolysis  (comp.  §  264). 

B.  COMMERCIAL  METALLIC  NICKEL  (NICKEL  CUBES  AND 

GRANULAR  NICKEL). 

§252. 

Commercial  nickel  contains  about  97  to  98  per  cent,  nickel, 
besides  some  cobalt,  copper,  iron,  and  at  times  traces  of  arsenic 
and  antimony;  generally  some  calcium,  magnesium,  aluminium, 
and  silicic  acid  are  present,  and  occasionally  traces  of  alkalies; 
and  frequently  small  quantities  of  carbon  and  sulphur.  The 
analysis  is  frequently  intended  to  give  the  average  composition  of 
a  large  shipment,  in  which  case  the  analyst  receives  a  smaller  or 
greater  number  of  cubes,  each  taken  from  a  different  box.  As  in 
this  case  the  individual  cubes  cannot  be  divided,  the  only  course 
to  pursue  is  to  dissolve  them  all  in  nitric  acid  after  weighing  them. 
As  a  rule  there  remains  a  small  quantity  of  insoluble  residue, 
which  may  contain  carbon,  sulphur,  slag,  and  silicic  acid.  Collect 
the  residue  on  a  filter  dried  at  100°,  and  collect  the  filtrate  and 
washings  in  an  accurately  weighed  flask  having  a  capacity  of  J,  1, 


484  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  252. 

or  2  litres,  according  to  circumstances.  Dry  the  washed  precipi- 
tate at  100°.  and  weigh.  Dilute  the  filtrate  and  washings  up  to 
the  mark,  weigh  accurately  and  mix. 

I.   EXAMINATION   OF  THE    SOLUTION. 

a.  Measure  off  so  much  of  the  solution  as  will  contain  about 
0-5  to  1  grm.  nickel  into  a  light,  tared  glass  vessel  and  weigh 
accurately.  The  measuring  serves  merely  to  approximately  fix 
upon  the  correct  quantity,  while  the  weighing  affords  the  exact 
quantity,  since  the  total  weight  of  the  liquid  is  also  known. 
Evaporate  to  dryness  with  hydrochloric  acid,  treat  the  residue 
with  hydrochloric  acid,  separate  the  silicic  acid,  and  treat  the 
nitric-acid  free  liquid  (100  c.c.  of  which  must  contain  about  10  c.c. 
of  hydrochloric  acid)  with  hydrogen  sulphide  at  70°;  collect  the 
precipitate,  wash,  and  determine  in  it  qualitatively  the  metals 
present.  Concentrate  the  united  filtrate  and  washings  by  evapora- 
tion, and  after  driving  off  the  hydrogen  sulphide,  boil  with  a  little 
nitric  acid,  add  an  excess  of  ammonia,  filter,  wash,  dissolve  the 
precipitate  in  hydrochloric  acid,  and  then  precipitate  the  iron  as 
a  basic  salt  by  nearly  neutralizing  with  ammonium  carbonate  and 
then  boiling.  Mix  the  filtrate  with  the  first  main  ammoniacal 
filtrate,  acidulate  with  acetic  acid,  precipitate  with  hydrogen 
sulphide  in  the  heat,  and  in  this  precipitate  along  with  any  blackish 
precipitate  which  may  be  obtained  from  the  filtrate  by  adding 
ammonia,  ammonium  sulphide,  and  acetic  acid,  determine  the 
nickel  together  with  the  small  quantity  of  cobalt  according  to  the 
first  method  detailed  under  §  251,  wherein  all  the  details  are 
minutely  given.  Of  course,  the  second  or  third  method  described 
in  §  251  may  also  be  used  for  determining  the  nickel  together  with 
the  small  quantity  of  cobalt. 

6.  Measure  off  and  weigh  a  larger  volume  of  the  solution,  con- 
taining about  4  to  5  grm.  nickel,  and  separate  the  silicic  acid  and 
the  metals  of  the  fifth  and  sixth  groups,  as  in  a;  wash  the  precipi- 
tate containing  the  latter,  and  in  it  determine  the  copper,  and  also 
the  other  metals  that  may  be  present.  Treat  the  filtrate  as  de- 
tailed in  a,  but  determine  in  this  portion  any  iron  and  aluminium 


§  252.]  NICKEL  COMPOUNDS.  485 

that  may  be  present.  As,  in  consequence  of  the  excess  of  am- 
monia, aluminium  may  be  found  in  the  ammoniacal  nickel  solu- 
tion, and  as  in  the  precipitation  of  the  basic  ferric  salt  all  of  the 
alumina  is  not  completely  thrown  down,  unite  the  solutions  con- 
taining the  nickel,  acidulate  with  acetic  acid,  cautiously  add 
ammonia  in  very  slight  excess,  and  allow  to  stand  for  some  time  at 
a  gentle  heat.  If  any  flocks  of  alumina  separate,  filter  them  off 
and  add  them  to  the  basic  precipitate  before  beginning  the  separa- 
tion and  determination  of  the  iron  and  aluminium.  Acidulate 
the  solution  remaining  clear  or  filtered  from  the  flocks  of  alumina 
with  acetic  acid,  precipitate  with  hydrogen  sulphide  with  heat, 
and  filter  off  the  precipitate.  To  the  nitrate  first  add  ammonia, 
then  ammonium  sulphide,  and  then  acetic  acid  until  the  solution 
is  acid.  If  a  slight  blackish  precipitate  forms,  collect  it  after  pro- 
longed warming,  add  it  to  the  main  precipitate  thrown  dowTi  by 
hydrogen  sulphide  in  the  acetic-acid  solution,  and  then  determine 
in  this  the  cobalt,  which  will  usually  be  found  present  in  this  larger 
quantity  in  wreighable  amount.  On  deducting  the  cobalt  from  the 
nickel  plus  cobalt  found  in  1,  the  quantity  of  nickel  is  found. 

Evaporate  to  dryness  in  a  large  platinum  dish  the  nitrate  freed 
from  the  last  traces  of  nickel,  drive  off  the  ammonium  salts,  and 
in  the  residue  determine  the  calcium,  magnesium,  and  alkalies 
(§  154,  6,  and  §  153,  4,  6). 

c.  Lastly,  measure  off  another  portion  of  the  solution  repre- 
senting about  10  grm.  nickel,  drive  off  the  free  nitric  acid  so  far  as 
possible  by  evaporating,  dilute  with  water,  make  nearly  neutral 
with  ammonia,  then  add  barium  chloride  to  the  still  distinctly 
acid  solution,  and  allow  to  stand  for  a  long  time.  If  a  small  pre- 
cipitate of  barium  sulphate  forms,  determine  it;  it  corresponds 
to  the  sulphur  which  was  converted  into  sulphuric  acid  when 
effecting  solution  of  the  nickel. 

II.    EXAMINATION  OF   THE  INSOLUBLE   RESIDUE. 

Triturate  to  a  uniform  powder  the  residue  dried  at  100°  and 
weighed,  and  in  an  aliquot  portion  determine  the  sulphur  by  fusing 
with  potassium  carbonate  and  nitrate,  etc.  (Vol.  I,  p.  562,  1,  a). 


486  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  253. 

Fuse  the  residue  with  sodium  carbonate  with  the  addition  of  a 
small  quantity  of  potassium  nitrate,  and  in  the  melt  determine  the 
silicic  acid,  the  alumina,  and  any  other  substances  that  may  be 
present.  The  carbon  content  is  determined  from  the  difference. 
If  the  insoluble  residue  is  very  small,  it  is  generally  sufficient  in 
reporting  the  analysis  to  note  it  simply  as  "residue  insoluble  in 
nitric  acid.". 

14.  IRON  COMPOUNDS. 
A.  IRON  ORES. 

The  iron  ores  which  occur  most  frequently,  and  which  are 
hence  most  often  examined,  are  as  follows: 

Hematite,  limonite,  bog  iron  ore,  magnetite,  and  spathic 
iron  ore.  In  some  cases  a  complete  analysis  is  required;  in  others 
a  determination  only  of  individual  constituents  (iron,  phosphoric 
acid,  sulphuric  acid,  etc.);  in  others  again,  the  determination  of 
only  the  iron. 

I.   METHODS   FOR   COMPLETE   ANALYSIS. 

§253. 
a.  HEMATITE. 

If  the  hematite  contains  only  ferric  oxide,  moisture,  and  gangue 
insoluble  in  acids,  the  first  method  here  given  should  be  employed 
in  its  analysis;  if,  however,  it  contains  also  phosphoric  acid,  al- 
kaline-earth carbonates,  manganous  oxide,  etc.,  I  would  recom- 
mend the  second  method. 

First  Method. 

Reduce  the  ore  to  an  impalpable  powder,  and  dry  at  100°. 

a.  Weigh  off  a  portion  into  a  platinum  or  porcelain  boat, 
insert  this  into  a  porcelain  tube,*  pass  a  current  of  dry  air  through 
the  tube,  and  heat  the  mineral  until  all  the  water  is  expelled. 

*  Glass  tubes,  even  when  of  very  difficultly  fusible  glass,  are  less  ad- 
visable to  use,  as  during  the  prolonged  heating  required  the  boat  is  frequently 
fused  to  the  glass. 


§  253-]  IRON   COMPOUNDS.  487 

Allow  to  cool  in  a  current  of  air,  and  weigh.    The  loss  of  weight 
corresponds   with  the  water. 

b.  Insert  the  boat  again  into  the  porcelain  tube  and  heat  in 
a  gas- or  charcoal-furnace  (pp.  18  to  22)  for  several  hours  in  a 
current  of  pure,  dry  hydrogen,  until  no  more  water  is  formed; 
towards  the  end  heat  as  strongly  as  possible.      Allow  to  cool  in  the 
current  of  hydrogen,  and  weigh.     The  loss  of  wreight  corresponds 
with  the  oxygen  combined  with  the  iron  to  form  ferric  oxide,  hence 
from  it  the  quantity  of  the  oxide  may  be  calculated. 

c.  Fasten  a  platinum  wire  to  the  handle  of  the  boat  containing 
the  reduced  iron,  and  introduce  the  boat  in  a  250-c.c.  flask,  add 
first  some  water,  then  diluted  sulphuric  acid,  and  stopper  the 
flask,   but  not  airtight,   the    stopper   pinching  and  holding  the 
platinum  wire  in  place  in  the  neck  of  the  flask.     The  finely  divided 
iron  dissolves  with  the  evolution  of  hydrogen;    gentle  warming 
accelerates  the  process.     As  soon  as  this  is  complete,  raise  the 
boat,  rinse  it  off,  heat  the  liquid  to  gentle  boiling  in  order  to  ex- 
pel the  hydrogen,  and  allow  to  cool;  then  fill  to  the  mark,  shake, 
allow  to  settle,  take  out  100  c.c.  of  the  fluid,  and  in  it  determine 
the  iron  with  potassium  permanganate  or  dichromate  (Vol.  I,  p. 
313  and  p.  319).     The  result  must  correspond  with  that  obtained 
in  b.     If  the  results  do  not  agree  sufficiently,  the  cause  may  be 
due  to  the  ferrous  solution  having  become  slightly  oxidized.     In 
this  case  another  100  c.c.  must  be  boiled  with  a  little  zinc  (best 
in  a  current  of  carbon  dioxide)  and  the  titration  with  perman- 
ganate repeated. 

d.  Collect  the  residue  (which  has  settled  on  the  bottom  of  the 
bottle)  in  a  filter,  wash,  dry,  ignite,  and  weigh.     As  a  rule  it  con- 
sists of  silicic  acid,  but  it  may  also  contain  alumina  and  titanic 
acid,  and  occasionally  also  some  iron.     Fuse  it  with  potassium 
disulphate,  and  treat  the  melt  with  cold  water;   the  silicic  acid 
remains  undissolved.     In  the  solution  precipitate  (if  iron  is  present, 
first  pass  in  hydrogen  sulphide)   any  titanic  acid  by  prolonged 
boiling  (§  107);   and  in  the  filtrate  the  alumina,  or  the  alumina 
and   any   ferric   oxide   still   present,   by   adding   ammonia.     The 
separation  of  these  may  be  effected  according  to  §  160,  A,  2. 


488  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  253. 

Second  Method. 

This  is  the  same  as  that  employed  in  the  analysis  of  brown 
iron  ore  (limonite)  (  see  6).  If  the  hematite  is  very  finely  powdered 
and  digested  with  sufficient  fuming  hydrochloric  acid  at  an  elevated 
temperature  below  the  boiling-point,  the  decomposition  and  solu- 
tion may  be  effected  in  a  few  hours.  The  separated  silicic  acid 
should  be  tested  for  titanic  acid  according  to  p.  411;  if  this  is 
found,  some  of  it  will  have  also  passed  into  solution.  If  the 
quantity  appears  to  be  weighable,  the  titanic  acid  is  best  de- 
termined by  treating  a  separate  portion  of  the  hematite  accord- 
ing to  the  first  method. 

6.  BROWN  IRON  ORE  (LIMONITE). 

Limonite  contains,  besides  ferric  hydroxide,  occasionally  also 
small  quantities  of  ferrous  oxide,  besides  oxides  of  manganese 
and  alumina,  and  at  times  small  quantities  of  oxides  of  copper, 
zinc,  nickel,  and  cobalt,  and  frequently  small  quantities  of  lime  and 
magnesia,  silicic  acid  (combined  with  bases),  carbonic,  phosphoric, 
and  sulphuric  acids,  and  larger  or  smaller  quantities  of  quartz-sand 
or  gangue  insoluble  in  hydrochloric  acid.  Sometimes  the  limonite 
contains  also  organic  matter.* 

1.  Begin  the  analysis  by  first  finely  powdering  the  ore  and 
then  drying  it,  according  to  circumstances,  either  in  a  desiccator 
or  at  100°.     Introduce  the  powder  thus  prepared  into  a  glass 
tube  and  stopper  tightly.      The  quantity  must  be  sufficient  for 
the  entire   analysis. 

2.  To  determine  the  water  it  is  frequently  sufficient  to  ignite 
a  sample  of  the  powder  in  a  platinum  crucible.     The  water  is 
thus  determined  from  the  loss  of  weight.     If  the  iron  stone,  how- 

*  Besides  these  substances,  which  are  usually  found,  traces  of  other 
substances  are  frequently  detected  in  very  accurate  analyses.  Thus  A. 
MiiLLER  (Ann.  d.  Chem.  u.  Pharm.,  LXXXVI,  127)  found  in  a  bean-ore,  smelted 
at  Carlshiitte,  near  Alfeld,  also  weighable  traces  of  potassa,  arsenic  acid,  and 
vanadic  acid,  and  un weighable  traces  of  chromium,  copper,  and  molybdenum. 
Titanic  acid  is  also  found  occasionally.  Regarding  an  iron  ore  very  rich 
in  vanadium,  see  H.  DEVILLE  (Compt.  rend.,  XLIX,  210;  Journ.  f.  prakt 
Chem.,  LXXXIV,  255). 


§  253.]  IKON  COMPOUNDS.  489 

ever,  contains  carbonates  of  the  alkaline  earths,  ferrous  oxide, 
or  weighable  quantities  of  organic  matter,  this  method  is  inap- 
plicable. The  water  must  in  this  case  be  determined  by  direct 
weighing  (comp.  §  36  and  §  235,  I,  e). 

3.  Weigh  off  about  3  grm.  of  the  powder,  ignite  gently  in  a 
platinum  dish,  and  in  such  a  manner  as  to  insure  the  complete 
destruction  of  any  organic  matter,  that  may  be  present,  then  trans- 
fer to  a  flask  and  digest  with  fuming  hydrochloric  acid  at  a  gentle 
heat  until  completely  decomposed.     Now  add  a  little  potassium 
chlorate,  heat  for  some  time,  transfer  to  a  porcelain  dish,  add  5 
to  10  grm.  pure  sodium  chloride,  and  evaporate  to  dryhess  on  the 
water-bath.*     Now  moisten  with  hydrochloric  acid,  warm,  dilute 
with  water,  filter  into  a  500-c.c.    flask,  and  wash  the  residue. 
After  drying  this  ignite  and  weigh  it;  to  the  solution,  however, 
add  water  up  to  the  mark,  and  shake. 

4.  The  residue  consists  of  quartz-sand  or  gangue  and  separated 
silicic  acid.    This  last  may  be  separated  and  determined  by  treat- 
ing an  aliquot  portion  with  a  boiling  solution  of  sodium  carbonate 
(§  237,  2,  6).     If  it  is  desired  to  determine  more  precisely  the 
nature  of  the  gangue,  which  frequently  contains  also  a  small  quan- 
tity of  iron,   treat  the  thoroughly  washed  precipitate  insoluble 
in  sodium  carbonate,  or  else  another  aliquot  portion  of  the  original 
residue  insoluble  in  hydrochloric  acid,  according  to  the  method 
described  for  decomposing  silicates,  §  140,  II,  b.     If  the  residue 
has  a  reddish  appearance,  a  further  examination  is  absolutely 
necessary. 

5.  Dilute  250  c.c.  of  the  solution  obtained  in  3  quite  freely 
(to  about  1  litre),  add  25  c.c.  ammonium-chloride  solution,  nearly 
neutralize  with  ammonia,  then  add  a  dilute  solution  of  ammonium 
carbonate  until  the  liquid  is  permanently  slightly  turbid,  boil,  and 
thus  separate  the  ferric  oxide  and  a  part  of  the  alumina  (comp. 
§  160,  3,  and  this  volume,  p.  471).      If   the  iron  solution  is  not 
colorless  after  boiling,  add  a  few  c.c.  of  a  neutral  solution  of  am- 

*  If  a  weighable  quantity  of  arsenic  is  present,  the  evaporation  of  the 
hydrochloric-acid  solution  must  be  omitted.  Of  course,  hi  this  case,  it 
is  also  unnecessary  to  add  sodium  chloride. 


490  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  253. 

monium  acetate  and  boil  once  more.  Any  phosphoric  acid,  etc., 
is  precipitated  with  the  ferric  oxide  (see  6).  Decant  while  hot, 
filter,  and  wash  with  hot  water  containing  a  little  ammonium 
chloride.  The  precipitate  is  meanwhile  kept  moist.  If  the  iron 
ore  is  rich  in  manganese,  it  is  necessary  to  repeat  the  precipita- 
tion of  the  iron  as  a  basic  salt  (comp.  p.  471). 

6.  To  the  nitrate  or  filtrates  obtained  in  5,  and  mixed  with  the 
washings,   add  a  little  acetic  acid,   concentrate  by  evaporation, 
allow  to  cool,  add  ammonia  until  just  alkaline,  and  filter  off  the 
precipitated  aluminium  hydroxide.     Collect  the  nitrate  in  a  flask 
containing  a  small  quantity  of  acetic  acid.     After  briefly  washing, 
dissolve  the  precipitate  in  hydrochloric  acid,   again  precipitate 
with  ammonia,  filter  into  the  first  filtrate,  wash,  and  treat  the 
precipitate,  together  with  that  obtained  in  5,  according  to  7.     The 
precipitates   contain  the  ferric  oxide,    the    alumina,  and   silicic 
acid  which  were  dissolved,  as  well  as  the  phosphoric  acid  (and 
arsenic  acid).     If  necessary,  the  solution  containing  a  slight  ex- 
cess of  acetic  acid  and  filtered  off  from  the  aluminium  hydroxide 
is  slightly  concentrated  by  evaporation. 

7.  Dissolve  the  precipitates   mentioned  in   6  in  hot  hydro- 
chloric acid  and  make  up  the  solution  to  250  c.c.      If  any  silicic 
acid  remains,  filter  it  off  and  weigh  it. 

a.  Precipitate  50  c.c.  of  the  solution  with  ammonia  (Vol.  I, 
p.  278,  a) ;  the  weight  of  the  precipitate  expresses  the  sum  of  the 
following  substances  present  in  the  solution :    Ferric  oxide,  alumina, 
silicic   acid,   and  phosphoric   acid   (also   arsenic   acid).     Separate 
the  silicic  acid  by  prolonged  digestion  with  fuming  hydrochloric 
acid,  and  finally  by  fusion  with  potassium  disulphate;     lastly, 
weigh. 

b.  In  50  c.c.  determine  the  ferric  oxide  with  stannous  chloride 
(Vol.  I,  p.  327).     If  a  gravimetric  method  is  preferred,  that  given 
in  Vol.  I,  p.  642,  2,  is  recommended. 

c.  On  deducting  from  the  weighed  precipitate  obtained  in  7,  a 
the  silicic  acid,  ferric  oxide,  and  the  phosphoric  acid  determined 
in  10  (and  also  any  arsenic  acid  present),  the  weight  of  the  alu- 
mina is  obtained. 


§  253.]  IRON  COMPOUNDS.  491 

8.  To  the  solution  from  6,  containing  free  acetic  acid,   add 
ammonia  until  weakly  alkaline,  then  again  acetic  acid  until  dis- 
tinctly acid;  next  add  ammonium  acetate,  and  while  gently  warm- 
ing pass  in  hydrogen  sulphide.     If  a  slight,  usually  black,  pre- 
cipitate forms,  filter  it  off;  then  precipitate  the  manganese  in  the 
filtrate  as  manganese  sulphide,  and  determine  it  as  such  (§  109,  2). 
The  precipitate,  however,  dissolve  in  a  little  brominized  hydro- 
chloric acid,  heat  to  expel  the  free  bromine,  precipitate  any  copper 
present  with  hydrogen  sulphide,  and  in  the  filtrate  determine  the 
nickel,  cobalt,  and  zinc  present,  according  to  §  160,  6,  6. 

9.  Acidulate  the  filtrate  from  the  manganese  sulphide  with 
hydrochloric  acid,  evaporate,  drive  off  the  ammonium  salts,  and 
in  the  residue  determine  the  lime  and  magnesia  (§  154,  6). 

10.  The  remaining  250  c.c.  of  the  solution  obtained  in  3  is 
employed  for  the  determination  of  the  phosphoric  acid,  or  both 
phosphoric  and  arsenic  acids,  as  well  as  the  copper.     If  only  phos- 
phoric acid  is  to  be  determined,  and  it  is  present  in  not  too  small 
a  quantity,  evaporate  to  dryness  on  a  water-bath  with  repeated 
addition  of  nitric  acid,  take  up  the  residue  with  nitric  acid,  pre- 
cipitate with  molybdenum  solution,  and  determine  the  phosphoric 
acid  according  to  §  134,  6,  /9.     If,  however,  copper  or  arsenic  acid 
is  present  in  determinable  quantity,  or  if  the  quantity  of  phos- 
phoric acid  present  is  very  small,  subject  the  liquid  to  prolonged 
treatment  at  70°  with  hydrogen  sulphide,  filter,  and  determine  in 
the  precipitate  the  copper,  or  arsenic,  or  both  (§  164) ;  in  the  filtrate 
determine  the  phosphoric  acid  according  to  §  135,  h,  f  (Vol.  I, 
pp.  460  and  461).    The  phosphoric  acid,  which  separates  with  a 
small  quantity  of  ferric  oxide,  is  then  determined  according  to 
§  134,  6,  p. 

11.  To  determine  any  sulphuric  acid  present,  fuse  3  to  5  gnn. 
of  the  dried  ore  with  one  part  by  weight  each  of  sodium  carbonate, 
and  of  potassium  nitrate  (F.  MUCK*  in  a  platinum  crucible  over 
a  BERZELIUS  alcohol-lamp);  treat  the  melt  with  boiling  water, 
filter,  and  in  the  filtrate  determine  the  sulphuric  acid  (Vol.  I, 
p.  562,  1,  a). 

*  Zeitschr.  /.  analyt.  Chem.,  vn.  416. 


492  DETERMINATION    OF  COMMERCIAL  VALUES.  [§  253. 

12.  If  the  ore  contains  ferrous  oxide,  digest  a  suitable  quantity 
in   a   250-c.c.    flask   with  strong,  chlorine-free   hydrochloric   acid 
and  best  in  a  current   of   carbon  dioxide,  until  the  decomposi- 
tion is  complete;  then  fill  the  flask  to  the  mark,  mix,  and  in  an 
aliquot  part  determine  the  ferrous  chloride  according  to  §  112, 2,  6. 
If  the  iron  ore  can  be  decomposed  by  prolonged  heating  with  diluted, 
sulphuric   acid,   this  mode  of  decomposition  is  preferable;    the 
ferrous  oxide  is  then  determined  according  to   §  112,  2,  a.     If 
manganic  oxide  is  present,  it  must  be  remembered  in  calculating 
the  ferrous  oxide  that  the  oxygen  liberated  from  the  manganic 
oxide  during  solution  has  oxidized  a  corresponding  quantity  of  fer- 
rous oxide  to  ferric  oxide.     On  deducting  the  ferric  oxide  corre- 
sponding to  the  ferrous  oxide  from  the  quantity  found  in  7,  the 
ferric-oxide  content  of  the  mineral  is  ascertained. 

13.  If  carbonic  acid  is  present,  it  is  best  determined  according  to 
the  method  detailed  in  Vol.  I,  p.  493. 

14.  In  testing  for  titanic  acid  it  is  best  to  ignite   a  separate 
portion  of  the  mineral  in  a  current  of  hydrogen  until  the  ferric 
oxide  is  completely  reduced,  and  to  then  treat  the  residue  accord- 
ing to  the  process  described  on  page  487,  d,  this  volume.* 

15.  If  the  brown  iron  ore  contains  vanadium  and  chromium, 
as  in  the  case  of  the  bean-ore  from  Haverloh  in  the  Harz,  mix 
the  finely  powdered  ore  with  one-third  of  its  weight  of  potassium 
nitrate,  expose  to  a  low  red  heat  for  an  hour,  crush  the  mass,  and 
boil  it  with  not  too  large  a  quantity  of  water.     To  the  solution, 
which  will  have  a  yellow  color  if  chromium  is  present,  add  very 
cautiously,  and  with  constant  stirring,  diluted  nitric   acid  until 
it  is  only  just  slightly  alkaline.     (The  liquid  must  never  be  allowed 
to  become  acid,  otherwise  the  liberated  nitrous  acid  will  reduce 
the  chromic  and  vanadic  acids.)     Filter  off  the  precipitate  formed 
(silicic    acid    and    aluminium    hydroxide),    and    precipitate    with 


[*  For  the  determination  of  titanic  acid  in  iron  ores  see  also  JAS.  BRAKES 
(Journ.  Soc.  Chem.  Indust.,  xvm,  No.  12);  also  CHARLES  BASKERVILLE 
(Ibid.,  1900,  p.  419).  The  latter  gives  a  method  of  analysis  of  titaniferous 
ores  which  has  been  used  successfully  by  him  for  a  number  of  years  in  a  large 
number  of  analyses. — TRANSLATOR.] 


§  253.]  IRON  COMPOUNDS.  493 

barium  chloride,  with  the  addition  of  ammonia;  collect  the  pre- 
cipitate of  barium  chromate  and  vanadate,  wash,  and  boil  it  with 
a  not  too  large  excess  of  diluted  sulphuric  acid.  Neutralize  with 
ammonia  the  reddish-yellow  filtrate  from  the  barium  sulphate,  con- 
centrate strongly  by  evaporating,  and  place  a  piece  of  ammonium 
chloride  in  the  liquid.  In  proportion  as  the  latter  becomes  satu- 
rated with  this  salt,  ammonium  vanadate  separates  as  a  white  or 
yellow  crystalline  powder.  After  the  separation  is  complete,  filter, 
wash  with  a  saturated  solution  of  ammonium  chloride,  dry,  heat 
gradually  with  full  access  of  air,  and  thus  obtain  the  vanadium 
as  dark-red,  almost  black  vanadic  acid,  melting  to  a  red  liquid 
on  being  strongly  heated,  and  solidifying  to  a  crystalline  mass  on 
cooling  (F.  WOHLER*). 

In  the  filtrate  from  the  ammonium  vanadate  the  chromium  may 
be  precipitated  as  a  hydroxide  by  adding  sulphurous  acid.  Re- 
garding another  method  of  detecting  minute  traces  of  chromium 
in  iron  ores  see  A.  TERREIL  (Zeitschr.  /.  Analyt.  Chem.,  iv,  440). 

c.  BOG  IRON  ORE. 

The  bog  iron  ores  consist  essentially  of  sedimentary  ferric 
hydroxide  resulting  from  the  oxidation  of  ferrous  compounds  in 
waters,  the  oxidation  being  usually  assisted  by  organic  action. 
These  ores  are  characterized  by  the  invariable  presence  of  phos- 
phoric acid,  occasionally  in  quantities  up  to  4  per  cent.,  as  well  as 
by  the  presence  of  humic  acids.  In  addition,  they  always  contain 
silicic  acid  (in  combination  and  as  quartz-sand);  at  times  sul- 
phuric and  arsenic  acids  are  present;  manganic  oxide  is  always 
present,  and  ferrous  oxide,  alumina,  lime,  and  magnesia,  often. 

After  the  ore  has  been  powdered  and  dried,  ignite  a  portion  in 
an  open  platinum  crucible,  at  first  very  gently,  in  order  to  burn  off 
the  organic  acids;  then  heat  gradually  more  strongly,  and  main- 
tain this  for  some  time  with  the  crucible  placed  obliquely.  The 
loss  of  weight  corresponds  to  the  water  and  the  organic  matter. 

Treat  a  second  weighed  portion,  which  has  been  very  gently 

*" Die  Mineralanalyse  in  Beispielen,"  2d  Ed,  p.  150. 


494  DETERMINATION    OF    COMMERCIAL  VALUES.          [§  253. 

ignited,  so  as  to  destroy  the  organic  matter,  according  to  the  method 
described  under  brown  iron  ore,  b. 

If  the  organic  acids  are  to  be  detected  and  determined  boil  a 
larger  quantity  of  the  finely  powdered  ore  with  pure  potassa  solu- 
tion until  it  has  become  converted  into  a  flocculent  mass.  Then 
filter,  and  treat  the  filtrate  according  to  §  209,  10  to  12. 

d.  MAGNETIC  IRON  ORE. 

Magnetic  iron  ores  contain  the  iron  as  ferroso-ferric  oxide. 
In  analyzing  them  the  possible  presence  of  titanic  acid,  magnesia, 
and  gangue  must  not  be  overlooked;  in  the  earthy  magnetic  ores 
there  is  also  found  considerable  manganous  oxide,  and  occasion- 
ally a  small  quantity  of  cupric  oxide.  Phosphoric  acid  is  but 
seldom  found  in  magnetic  iron  ore,  and  then  only  in  small  quantity. 

The  magnetic  iron  ore  is  analyzed  in  the  same  way  as  hematite, 
and  afterwards  a  portion  is  separately  weighed  off,  dissolved  in 
hydrochloric  acid  in  a  current  of  carbon  dioxide,  and  the  ferrous 
iron  in  the  solution  determined  volumetrically  with  potassium 
dichromate  (Vol.  I,  p.  319,  b),  or  the  ferric  iron  with  stannous- 
chloride  solution  (Vol.  I,  p.  327). 

e.  SPATHIC  IRON  ORE. 

Spathic  iron  ore  contains  ferrous  carbonate,  usually  associated 
with  manganous  carbonate  and  carbonates  of  the  alkaline  earths, 
and  frequently  mixed  with  clay  and  gangue.  Occasionally  a  part 
of  the  ferrous  carbonate  is  found  already  converted  into  ferric 
hydroxide. 

The  powdered  mineral  is  dried  either  in  the  air  or  at  100°. 

a.  The  water  content  is  determined  according  to  §  36. 

b.  The  carbonic  acid  is  best  determined  as  in  Vol.  I,  p.  493. 

c.  Dissolve  a  third  portion,  about  8  to  10  grm.,  in  hydrochloric 
acid,  add  a  little  potassium  chlorate  in  order  to  convert  all  the 
ferrous  into  ferric  chloride,  boil  until  the  liquid  no  longer  smells 
of  chlorine,  and  then  proceed  as  directed  under  brown  iron  ore,  b. 

d.  In  a  fourth  portion,  dissolved  in  hydrochloric  acid  in  a 
current   of    carbon   dioxide,    determine   the   iron   volumetrically 


§  254.]  IRON  COMPOUNDS.  495 

either  as  ferric  iron  with  stannous-chloride  solution  (Vol.  I,  p.  327), 
or  as  ferrous  iron,  with  potassium  dichromate  (Vol.  I,  p.  319,  6). 

II.   DETERMINING   THE  IRON   IN   IRON   ORES. 
§254. 

1.  Volumetric  Methods. 

Many  volumetric  methods  have  been  proposed  for  determining 
the  iron  in  iron  ores,  and  adopted,  some  again  falling  into  disuse. 
The  method  long  considered  as  the  most  convenient  and  best, 
and  based  on  the  employment  of  potassium  permanganate,  sus- 
tained a  severe  set-back  when  LOWENTHAL  and  LENSSEN  showed 
that  correct  results  could  be  obtained  in  hydrochloric-acid  solu- 
tions only  when  the  conditions  of  testing,  the  effective  value  of 
the  permanganate  solution,  the  quantity  of  hydrochloric  acid 
present,  the  degree  of  dilution,  and  the  temperature,  were  identical 
(see  Vol.  I,  p.  319). 

Of  the  methods  here  described  the  first  is  especially  recom- 
mended because  of  its  simplicity  and  accuracy. 

First  Method. 

Gently  ignite  about  5  grm.  of  the  very  finely  powdered  ore 
dried  either  in  the  air  or  at  100°,  until  all  the  organic  matter  pres- 
ent has  been  destroyed,  then  heat  in  a  flask  with  hydrochloric 
acid  at  a  temperature  below  the  boiling-point  of  the  acid.  With 
hematite  fuming  hydrochloric  acid  is  absolutely  necessary;  and 
it  is  advisable  also  with  brown  iron  ore.  After  decomposition 
and  solution  are  effected  as  completely  as  possible,  add,  if  the  ore 
contains  ferrous  oxide,  some  potassium  chlorate,  heat  for  a  long  time, 
then  transfer  the  contents  of  the  flask  to  a  porcelain  dish,  rinse  out 
the  flask  into  the  dish,  and  evaporate  almost  to  dryness  on  the 
water-bath.  The  operator  may  then  be  certain  that  the  potas- 
sium chlorate  added  has  been  completely  decomposed,  and  all  the 
free  chlorine  expelled.  Now  add  to  the  residue  a  little  hydro- 
chloric acid,  then  water,  filter  into  a  500-c.c.  flask,  and  wash  the 
residue. 


496 


DETERMINATION   OF   COMMERCIAL   VALUES. 


[§  254. 


//  the  iron  stone  contains  no  ferrous  oxide,  dilute  the  contents 
of  the  flask  with  water,  filter  into  a  500-c.c.  flask,  and  wash  the 
residue.  In  either  case  now  fill  up  to  the  mark,  mix,  and,  as  a 
precaution,  test  a  small  quantity  of  the  liquid  with  potassium 
ferricyanide  to  be  sure  that  no  ferrous  chloride  is  present.  Then 
in  two  separate  portions  of  100  c.c.  each  of  the  solution  deter- 
mine the  iron  volumetrically  with  stannous  chloride  (Vol.  I,  p.  327). 
instead  of  the  apparatus  shown  in  Vol.  I,  p.  330,  Fig.  86,  the 
apparatus  here  shown,  Fig.  106,  may  be  used  for  preserving  the 


FIG.  106. 

stannous-chloride  solution,  and  particularly  if  the  solution  is 
used  only  occasionally.  In  this  apparatus  it  may  be  preserved 
unchanged  for  a  long  time.  The  solution  is  drawn  from  the  bottle 
a  by  means  of  a  siphon,  e.  The  air  which  enters  passes  first  through 
the  U-tubes  b  and  c,  then  through  the  bottle  d,  all  containing 
pumice-stone  saturated  with  a  strongly  alkaline  solution  of  potas- 
sium pyrollagate.  This  solution  is  prepared  in  the  tubes  and 
bottle  by  pouring  together  concentrated  solutions  of  potassa  and 
pyrogallic  acid  some  time  before  the  apparatus  is  required  for  use; 


I  254.]  IRON  COMPOUNDS.  497 

as  potassium  pyrogallate  rapidly  absorbs  the  oxygen  of  the  air, 
the  vessels  in  a  short  time  contain  only  pure  nitrogen.  Every- 
thing being  in  readiness,  insert  a  glass  tube  into  the  rubber  tube 
/,  fill  the  siphon  by  suction,  and  then  close  the  pinch-cock.  To 
fill  a  pipette  or  pinch-cock  burette,  insert  the  point  into  the  rubber 
tube  after  the  burette  pinch-cock  has  been  pushed  back  over  the 
delivery  tube,  then  open  pinch-cock  /,  and  allow  the  fluid  to  as- 
cend from  below.  Then  close  the  pinch-cock  /,  and  remove  the 
burette. 

Ascertain  the  iron  content  of  the  hydrochloric-acid  solution 
of  the  iron  ore  in  the  manner  detailed.  At  times  small  quantities 
of  iron  are  still  contained  in  the  residue  insoluble  in  hydrochloric 
.acid.  This  is  particularly  the  case  when  the  residue  either  before 
or  after  ignition  has  a  red  color  or  appears  reddish.  In  order 
to  determine  any  iron  present  in  the  residue  decompose  it  by 
fusion  with  sodium  carbonate,  separate  the  silicic  acid  (Vol.  I, 
p.  511,  b),  and  in  the  hydrochloric-acid  solution  determine  the 
ferric  chloride  with  stannous  chloride.  If  this  solution  is  added 
to  the  main  solution,  however,  the  necessity  for  a  special  titration 
is  avoided. 

Second  Method. 

For  the  preparation  of  the  hydrochloric-acid  solution  of  the 
iron  ore,  containing  the  iron  as  ferric  chloride,  and  perfectly  free 
from  nitric  acid  and  chlorine,  proceed  as  in  the  first  method; 
the  determination  of  the  iron,  however,  is  made  in  aliquot  por- 
tions of  the  solution  with  potassium  iodide,  as  described  hi  Vol.  I, 
p.  331,  p. 

If  the  residue  insoluble  in  hydrochloric  acid  still  contains  any 
iron  compound,  treat  it  as  in  the  first  method,  and  in  the  solution 
determine  the  ferric  chloride  similarly  with  potassium  iodide. 

According  to  my  investigations  the  first  method  yields  more 
trustworthy  results  in  the  analysis  of  iron-stone  than  the  second, 
the  latter  being  better  adapted  for  determining  smaller  quantities 
of  iron. 


498  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  254., 

Third  Method. 

Prepare  a  hydrochloric-acid  solution  as  in  the  first  method, 
dilute,  reduce  with  zinc  *  in  a  current  of  carbon  dioxide  (Vol.  I,, 
p.  325, 3,  a),  and  determine  the  ferrous  chloride  by  PENNY'S  method 
(Vol.  I,  p.  319,  6),  or  by  means  of  a  standard  potassium-perman- 
ganate solution,  observing  the  special  precautions  recommended 
for  ferrous  solutions  containing  hydrochloric  acid,  Vol.  I,  319,  f. 
If  the  residue,  insoluble  in  hydrochloric  acid,  still  contains  some 
iron,  decompose  it  as  in  the  first  method. 

Fourth  Method. 

Fuse  about  0-5  grm.  of  the  very  finely  powdered  iron  ore 
with  3  to  4  grm.  potassium  or  sodium  disulphate,  at  first  gently, 
but  gradually  more  strongly;  maintain  the  heat  for  a  long  period, 
but  yet  not  so  long  as  to  drive  off  the  second  equivalent  of  sul- 
phuric acid.  Dissolve  the  residue  in  diluted  sulphuric  acid,  re- 
duce the  solution  by  boiling  with  zinc  *  in  a  current  of  carbon 
dioxide  (Vol.  I,  p.  325,  3,  a)  and  finally  determine  the  ferrous 
iron  by  means  of  a  standard  solution  of  potassium  permanganate, 
according  to  Vol.  I,  p.  312,  2,  a.  The  difficulty  in  carrying  out. 
this  process  lies  in  the  fact  that  the  decolorization  of  the  solution 
is  no  criterion  of  the  completion  of  the  reaction.  Hence,  when 
it  appears  to  be  completed,  it  is  necessary  to  bring  a  drop  of  the 
solution  into  contact  with  a  drop  of  potassium-sulphocyanate 
solution  on  a  porcelain  plate.  If  a  distinct  redness  supervenes, 
the  reduction  is  still  incomplete.  The  reaction  between  the  sul- 
phocyanate  and  the  ferric  iron  is  so  delicate  that  no  notice  need 
be  taken  of  a  very  faint  reddening.  The  results  are  naturally 
correct  only  when  complete  decomposition  and  solution  of  the 
iron  has  been  effected. 


*  Zinc  crushed  in  a  mortar  heated  to  210°,  and  sifted  so  as  to  yield  a 
uniform,  rather  coarsely  granular  powder,  is  far  better  adapted  for  this  pur- 
pose than  granulated  zinc  or  sheet-tin  (J.  M.  BROWN,  Zeitschr.  /.  analyt. 
Chem.,  xvin,  98). 


§  254.]  IRON    COMPOUNDS.  499 

2.  Gravimetric  Methods. 

Of  these,  I  describe  only  FUCHS'S  method,*  as  the  unfavor- 
able statements  regarding  it  made  by  other  chemists  were  refuted 
by  J.  LOWE  f  and  R.  KONIG,{  in  1857.  I  would  remark,  how- 
ever, that  the  method  has  been  almost  entirely  supplanted  by 
the  volumetric  methods. 

a.  The  Ordinary  Method  (as  described  by  LOWE,  loc.  cit.). 

Heat  1  to  1  •  5  grm.  of  the  ore,  if  of  a  superior  grade,  or  2  to  3 
grm.  if  of  an  inferior  quality,  in  the  form  of  finest  powder,  in  an 
obliquely  held,  long-necked  500-c.c.  flask  with  strong  hydrochloric 
acid,  and  when  all  the  iron  is  dissolved  add  a  little  potassium 
chlorate  in  small  portions,  and  best  in  the  form  of  fused  fragments, 
until  the  liquid  has  a  decided  odor  of  chlorine;  then  continue  the 
heat  until  the  odor  of  chlorine  is  no  longer  perceptible.  Dilute 
with  water  until  the  flask  is  half  filled,  stopper  with  a  sound  cork 
bearing  a  tightly  fitting  glass  tube  about  10  inches  long,  open  at 
both  ends,  and  not  too  narrow;  support  the  flask  in  an  oblique 
position  and  maintain  at  least  fifteen  minutes  at  a  moderate  boil, 
in  order  to  make  certain  that  every  trace  of  chlorine  and  air  has 
been  expelled  rom  the  flask  and  the  water. 

While  the  solution  is  continuously  boiling  remove  the  cork  and 
slowly  lower  into  the  solution  a  strip  of  clean,  pure  copper  foil 
fastened  to  a  thin  platinum  wire.  In  doing  this,  first  suspend  the 
copper  foil  within  the  flask,  pinching  the  wire  between  the  cork 
and  the  glass,  and  until  the  copper  foil  has  become  warm;  other- 
wise the  liquid  is  very  apt  to  spirt  if  the  cold  foil  is  lowered  into 
it.  Then  remove  the  cork  again,  allow  the  foil  to  sink  down 
horizontally  and  become  completely  immersed  in  the  liquid, 
stopper  tightly,  and  secure  the  flask  obliquely  again,  taking  care 
through  all  these  operations  to  maintain  the  iron  solution  in  con- 
stant ebullition.  The  boiling  must  be  slow  and  not  too  violent, 


*Joum.  /.  prakt,  Chem.,  xvn,  160. 
t  Ibid.,  LXXII,  28. 


J  Ibid.,  LXXII,  36. 


500  DETERMINATION    OF    COMMERCIAL    VALUES.         [§   254. 

and  must  be  continued  until  the  iron  solution  has  been  completely 
reduced  and  is  therefore  either  entirely  colorless  or  at  least  so 
very  slightly  greenish  that  it  is  difficult  to  determine  its  color 
with  certainty.  As  a  rule  the  reduction  is  complete  in  two  hours, 
but  the  boiling  may  be  continued  for  three  or  even  four  hours 
without  any  effect  whatever  on  the  accuracy  of  the  result.  The 
copper  foil  must  always  be  kept  completely  covered  by  the  solu- 
tion during  the  boiling.  As  the  addition  of  water  during  the 
operation  is  quite  impracticable,  care  must  be  taken  that  suf- 
ficient water  be  added  at  the  beginning. 

The  strip  of  copper  should  weigh  about  6  grm.  It  may  be 
made  from  copper  precipitated  by  galvanic  action,  and  of  such 
a  width  and  length  as  to  conveniently  pass  into  the  flask  and  lie 
horizontally  on  the  bottom.  It  should  be  scoured  brightly  with 
sandpaper,  then  weighed,  and  attached  to  the  platinum  wire. 

When  the  reduction  of  the  ferric  chloride  is  complete,  remove 
the  cork,  quickly  withdraw  the  copper  strip  from  the  still  boiling 
solution  by  means  of  the  platinum  wire  and  immerse  it  in  a  beaker 
filled  with  distilled  water,  rinse  it  off  with  distilled  water  after 
removing  it  from  the  beaker,  dry  it  thoroughly  between  blotting- 
paper,  disconnect  it  from  the  platinum  wire,  and  weigh ;  for  every 
equivalent  of  copper  dissolved  calculate  one  equivalent  of  iron, 
according  to  the  equation:  Fe2Cl6+2Cu  =  2FeCl2+Cu2Cl2. 

The  copper  loses  its  original  lustre  during  the  operation,  and 
appears*  dull,  but  not  blackish,  as  it  usually  does  if  the  ordinary 
sheet  copper  is  used.  In  four  analyses  of  chemically  pure  ferric 
oxide,  J.  LOWE  found  by  this  method  99-7,  99-6,  99-6,  and  99-6 
per  cent,  ferric  oxide  respectively. 

KONIG'S  process  (loc.  cit.)  is  quite  similar.  He  recommends 
to  dry  the  copper  strip,  after  removing  it  from  the  boiling  liquid, 
by  keeping  it  immersed  for  some  time  in  hot  water  in  order  that 
every  portion  of  the  solution  that  may  have  penetrated  into  the 
pores  may  be  washed  out,  then  displacing  the  water  by  immersion 
in  alcohol,  and  finally  displacing  the  alcohol  with  ether.  He 
also  recommends  winding  platinum  wire  around  the  strip,  as  this 
not  only  prevents  loss  of  small  particles  of  copper  from  the  bump- 


§  255.]  IRON  COMPOUNDS.  501 

ing  of  the  metal  against  the  glass  during  ebullition,  but  also  acceler- 
ates the  reduction.  KONIG  obtained  results  in  a  series  of  ex- 
periments with  this  process,  varying  between  99-5  and  100-5 
per  cent. 

The  solubility  of  copper  hi  boiling  dilute  hydrochloric  acid 
is  so  slight  that  the  effect  on  the  accuracy  of  the  results  is  quite 
within  the  limits  of  experimental  error  (J.  LOWE  *). 

b.  Modified  Method. 

If  iron  ores  contain  any  considerable  quantity  of  titanic  acid, 
the  process  a,  according  to  FUCHS,  can  be  employed  only  with 
certain  modifications.  As  such  cases  are  comparatively  rare, 
however,  I  refer  to  the  original  paper,!  where  the  modifications 
are  described. 

If  the  iron  ore  contains  arsenic  acid  the  method  is  similarly 
inapplicable,  because  then  the  copper  becomes  covered  with 
black  scales  of  copper  arsenide.  In  this  case  the  arsenic  acid  may 
be  removed  by  fusing  the  powdered  ore  with  sodium  carbonate 
and  exhausting  the  melt  with  water,  then  dissolving  the  residue 
in  hydrochloric  acid,  and  treating  this  solution  as  in  a. 

B.   ANALYSIS  OP  VARIOUS  KINDS  OF  IRON. 

I.  CAST  IRON. 
§255. 

Cast  iron,  one  of  the  most  important  metallurgical  products, 
contains  a  whole  series  of  elements,  either  admixed  in  greater 
or  less  quantity,  or  in  combination  with  it.  Although  the  effect 
that  the  various  admixed  substances  has  on  the  character  of  the 
cast  iron  is  not  yet  accurately  known,  yet  it  is  undoubtedly  a 
fact  that  the  substances  have  a  considerable  influence  on  the 
quality  of  the  iron. 

The  analysis  of  cast  iron  is  one  of  the  more  difficult  problems 

*  Zeitschr.  f.  analyt  Chem.,  TV.,  361. 

f  Journ.  f.  prakt.  Chem.,  xvm,  495;  see  also  KONIG,  Journ.  f.  prakk 
Chem.,  LXXII,  38. 


502  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  255. 

of  analytical  chemistry.     The  following  substances  are  those  to 
which  special  attention  must  be  directed: 

Iron,  carbon  (combined  with  iron}  and  also  in  the  form  of  graphite), 
nitrogen,  silicon}  phosphorus,  sulphur,  potassium,  sodium,  lithium, 
calcium,  magnesium,  aluminium,  chromium,  titanium,  zinc,  man- 
ganese, cobalt,  nickel,  vanadium,  copper,  tin,  arsenic,  antimony, 
and  tungsten.  As  a  rule  only  those  elements  indicated  by  italics 
.are  quantitatively  determined. 

1.    CARBON    DETERMINATION. 

A.  Total  Carbon. 

Of  the  various  methods  proposed  in  former  as  well  as  in  more 
recent  times  for  determining  carbon  in  cast  iron,  only  those  afford 
invariably  accurate  results  in  which  the  carbon  is  converted 
into  carbonic  acid  and  weighed  as  such;  on  the  other  hand,  all 
those  methods  must  be  considered  as  less  reliable  in  which  the 
carbonaceous  residue  left  on  treating  the  substance  by  some 
solvent  process  is  weighed,  its  incombustible  portion  determined, 
and  the  carbon  found  from  the  difference.  The  reason  why  the 
latter  methods  are  unreliable  is  because  the  combustible  portion 
of  the  residue  is  not  as  a  rule  pure  carbon.  The  methods  here 
given  are,  hence,  almost  all  of  the  former  kind,  and  they  differ 
from  one  another  partly  in  that  the  combustion  of  the  carbon 
is  performed  either  on  the  residue  (containing  all  the  carbon) 
left  on  suitably  dissolving  the  iron,  or  upon  mechanically  divided 
iron;  or,  the  oxidation  of  the  carbon  is  effected  in  the  dry  or  in 
the  wet  way.  Under  a  I  detail  the  methods  of  obtaining  from  cast 
iron  a  residue  containing  all  the  carbon;  under  /?  the  determina- 
tion of  the  carbon  therein;  and  under  ?-,  the  determination  of 
the  carbon  by  direct  combustion  of  the  iron. 

a.   METHODS   OF   OBTAINING   A   RESIDUE    CONTAINING   ALL 
THE   CARBON   OF   CAST  IRON. 

aa.  BERZELIUS'*  Method  and  its  Modifications. 
As  on  dissolving  cast  iron  in  hydrochloric  or  sulphuric  acid 
the  combined  carbon  is  evolved  in  the  form  of  hydrocarbons, 
*  BERZELIUS'  Lehrbuch  der  Chemie,  WOHLER'S  translation,  x,  118. 


§  255.]  IRON   COMPOUNDS.  503 

BERZELIUS  employed  as  solvents  of  iron  solutions  of  neutral  metal- 
lic salts,  especially  a  solution  of  cupric  chloride  *  free  from  excess  of 
hydrochloric  acid,  or  a  solution  of  equal  equivalents  of  cupric 
sulphate  and  sodium  chloride.  He  recommends  to  allow  the 
action  to  take  place  in  the  cold  until  the  color  of  the  liquid  shows 
that  the  copper  has  been  almost  completely  precipitated,  and 
then  to  either  renew  the  cupric-chloride  solution,  or  to  add  some 
crystallized  cupric  chloride  to  it.  When  copper  is  no  longer 
precipitated,  either  in  the  cold  or  on  gently  warming,  allow  to 
stand  for  twenty-four  hours  to  make  certain.  Then  add  hydro- 
chloric acid,  and  if  necessary,  cupric  chloride,  until  all  the  pre- 
cipitated copper  has  redissolved,  collect  the  carbonaceous  residue 
in  a  filtering-tube  containing  spongy  platinum,  and  wash  it  first 
with  water,  then  with  hydrochloric  acid,  and  finally  again  with 
water. 

In  the  course  of  time  this  method  has  been  modified,  and  it 
has  been  found  especially  advantageous  to  use,  instead  of  cupric 
chloride,  ammonio-cupric  chloride  (PEARSE;!  CREATH  J),  as  this 
greatly  accelerates  the  solution  of  the  iron;  asbestos  filters  also 
are  now  usually  used  for  collecting  the  carbon. § 

The  solution  of  ammonio-cupric  chloride  is  prepared  by  dis- 


*  According  to  H.  HAHN  (Zeitschr.  f.  analyt.  Chem.,  rv,  210),  when  dis- 
solving iron  in  cupric-chloride  solution,  a  little  hydrogen,  containing  hy- 
drocarbons, is  evolved,  as  a  result  of  the  galvanic  action  induced  by  the 
contact  of  the  iron  with  the  copper  deposited,  which  causes  a  slight  loss  of 
carbon.  According  to  MAX  BUCHNER,  however  (ibid.,  iv,  211),  when  the 
cupric  chloride  used  is  perfectly  free  from  acid  the  quantity  of  gas  evolved 
is  so  small  that  the  carbon  passing  off  in  it  is  unweighable. 

j-  Eng.  and  Min.  Jvurn.,  New  York,  xxi,  151;  also  Zeitschr.  /.  analyt. 
Chem.,  xvi,  504. 

\Eng.  and  Min.  Jmtrn.,  New  York,  xxin,  168;  also  Zeitschr.  f.  analyt. 
Chem.,  xvi,  504. 

§  An  asbestos  filter  may  be  most  conveniently  made  by  placing  in  an 
ordinary  glass  funnel  a  little  glass  wool  and  pouring  on  this  asbestos  made 
into  a  pulp  with  water,  and  then  washing  until  no  more  fibres  of  asbestos 
are  washed  away.  There  is  thus  formed  a  good  filtering  layer  of  asbestos  on 
the  glass  wool  (compare  SATTER,  Zeitschr.  f.  analyt.  Chem.,  xrv,  312).  The 
asbestos  employed  must  be  ignited  in  a  current  of  moist  air  in  order  to  free 
it  from  chlorine  (compare  KRAUT,  Zeitschr.  f.  analyt.  Chem.,  in,  34). 


504  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  255. 

solving  340  grm.  crystallized  cupric  chloride  and  214  grm.  am- 
monium chloride  in  1850  c.c.  water. 

The  cast  iron  should  be  in  a  very  finely  divided  state,  in  the 
form  of  turnings,  borings,  or  very  small  pieces.  If  any  oil  from 
the  borer,  etc.,  adheres  to  the  iron,  it  must  first  be  removed  by 
washing  with  ether.  If  the  comminuted  iron  contains  any  other 
admixed  organic  matter,  separate  it  by  the  aid  of  a  magnet.  Treat 
2  to  5  grm.  of  the  suitably  purified,  finely  divided  iron  with  solu- 
tion of  ammonio-cupric  chloride,  using  about  20  to  25  c.c.  of  the 
solution  to  every  gramme  of  iron,  and  when  all  is  dissolved,  treat 
the  residue  by  one  of  the  following  methods,  according  as  to 
whether  the  carbon  is  to  be  determined  by  means  of  chromic  acid 
or  by  combustion. 

aa.  Collect  the  separated  carbon  together  with  the  metallic 
copper  in  an  ordinary  funnel  in  which  a  plug  of  asbestos  has  been 
loosely  placed,  and  preferably  by  the  aid  of  a  pump;  wash  (to  re- 
move the  precipitated  cuprous  chloride)  first  with  concentrated 
hydrochloric  acid,  and  then  with  water  or  alcohol  *  until  every 
trace  of  hydrochloric  acid  has  been  removed.  If  the  residue 
contains  any  chlorine  compound,  this,  on  treatment  with  chromic 
acid  and  sulphuric  acid,  gives  rise  to  chlorochromic  acid,  and 
the  results  are  then  too  high.  When  alcohol  has  been  used  for 
the  washing,  the  contents  of  the  funnel  must  be  thoroughly  dried. 

/?/?.  To  the  contents  of  the  vessel  add  hydrochloric  acid,  and, 
if  necessary,  a  further  quantity  of  solution  of  ammonio-cupric 
chloride  until  all  the  metallic  copper  has  dissolved,  then  collect 
the  residual  carbon  on  an  asbestos  filter,t  and  wash  it,  first  with 
a  little  hydrochloric  acid,  and  then  with  water  or  alcohol,  until 
every  trace  of  hydrochloric  acid  has  been  washed  out.  Then 
thoroughly  dry  the  contents  of  the  funnel  at  about  100°  to  110°. 

*  L.  KLEIN  (Zeitschr.  f.  analyt.  Chem.,  xvui,  p.  76)  gives  the  preference  to 
alcohol,  because  by  use  of  it  the  carbon  is  more  readily  washed  from  the 
margin  of  the  funnel,  and,  after  drying,  more  easily  removable  from  the 
funnel. 

t  See  foot-note,  p.  603. 


§  255.]  IRON  COMPOUNDS.  505 

66.  0.  ULLGREN'S  Method* 

Instead  of  using  cupric  chloride  or  aminonio-cupric  chloride, 
ULLGREN  treats  the  finely  divided  iron  with  a  solution  of  1  part 
cupric  sulphate  in  5  parts  of  water  at  a  gentle  heat ;  ELLIOT  f 
uses  the  same  method.  The  solvent  is  easily  prepared,  but  is 
far  slower  in  action  than  aminonio-cupric  chloride.  If  the  pre- 
cipitated copper  is  to  be  dissolved,  the  residue,  in  this  method 
also,  must  be  heated  with  cupric  chloride  and  hydrochloric  acid. 

cc.  BOUSSINGAULT'S  Method. I 

Triturate  the  finely  divided  iron  for  half  an  hour  in  an  agate 
or  glass  mortar  with  fifteen  times  its  weight  of  mercuric  chloride 
and  some  water  to  make  a  thin  paste.  After  adding  water,  trans- 
fer the  whole  to  a  beaker  and  heat  for  an  hour  at  80°  to  100°. 
Filter  through  an  asbestos  filter,  wash  the  residue  with  hot  water, 
dry  thoroughly  in  an  air-bath,  then  heat  in  a  platinum  boat  in  a 
current  of  dry  hydrogen,  raising  the  heat  gradually  to  redness, 
and  in  this  manner  drive  off  the  admixed  mercurous  chloride. 
In  order  to  obtain  the  hydrogen  perfectly  free  from  oxygen,  con- 
duct it  through  a  long  layer  of  spongy  platinum,  and  then  through 
sulphuric  acid.  Regarding  the  further  treatment,  see  ft  below 
(Third  Method). 

dd.  W.  WEYL'S  Method.^ 

This  excellent  method  possesses  the  great  advantage  that  it. 
is  unnecessary  to  comminute  the  iron,  during  which  operation,  as 
is  well  known,  it  is  very  apt  to  become  contaminated.  The  solu- 
tion is  effected  by  means  of  a  weak  galvanic  current,  employing  a 
BUNSEN  element,  using  the  iron  fragment  to  be  analyzed,  and 
immersed  in  diluted  sulphuric  acid,  as  the  positive  electrode.  The 
iron  dissolves  as  ferrous  chloride  without  the  evolution  of  any  gas 
from  its  surface,  and  leaves  the  carbon  behind,  while  hydrogen 

*  Ann.  d.  Chem.  u.  Phar.,  cxxiv,  59;  Zeitschr.  /.  analyt.  Chem.,  n,  430. 

f  Journ.  Chem.  Soc.,  vn,  182. 

ICompt.  rend.,  LXVI,  873;   Zeitschr.  /.  analyt.  Chem.,  vni,  506. 

§  Poggend.  Annul.,  cxiv,  507;  Zeitschr.  /.  analyt.  Chem.,  i,  112  and  250. 


506  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  255. 

is  evolved  at  the  negative  electrode.  If  a  strong  current  is  used 
the  purpose  desired  will  not  be  effected,  because  then  the  iron 
would  readily  become  passive;  in  this  case  there  would  be  liber- 
ated from  its  surface  chlorine,  which  would  oxidize  the  carbon 
already  separated,  and  would  directly  form  with  it  a  compound 
which  would  be  decomposed  by  the  galvanic  current  in  a  manner 
analogous  to  hydrochloric  acid,  carbon  as  well  as  hydrogen  separat- 
ing at  the  negative  pole.  It  is  obvious  that  in  both  cases  there 
is  a  loss  of  carbon,  as  carbonic  oxide  or  carbon  dioxide  in  the 
former  case,  and  in  the  latter  as  hydrogen  carbide,  which  may 
be  formed  from  the  hydrogen  and  carbon  simultaneously  sep- 
arated at  the  negative  electrode. 

Select  a  piece  of  iron  about  10  to  15  grm.  in  weight,  clamp  it 
in  a  pair  of  pincers  provided  with  platinum  points,  and  suspend 
it  in  diluted  hydrochloric  acid  so  that  the  points  of  contact  between 
the  iron  and  the  pincers  are  not  touched  by  the  acid  (otherwise  the 
carbon  separated  at  these  points  rapidly  impedes  the  process  of 
solution).  Connect  the  pincers  with  the  wire  from  the  positive 
pole;  immerse  also  the  platinum  foil  fastened  to  the  negative 
wire  in  the  acid,  and  regulate  the  strength  of  the  current  by 
increasing  the  distance  between  the  electrodes,  so  that  ferrous 
chloride  alone  is  formed,  but  no  ferric  chloride.  The  formation  of 
the  latter  is  immediately  recognized  by  the  yellowish  color  of  the 
streams  of  concentrated  iron  solution  which  descend  from  the 
iron.  The  piece  of  iron  changes  but  little  in  external  appearance 
during  the  process  of  solution,  as  the  carbon  remaining  retains 
the  original  form  of  the  piece  of  iron.  As  soon  as  the  immersed 
portion  of  the  iron  has  dissolved  (which  takes  about  twelve  hours) 
interrupt  the  operation,  separate  the  undissolved,  compact  piece 
of  iron  from  the  adhering  carbon,  dry,  weigh,  and  thus  ascertain 
the  quantity  of  iron  dissolved.  Collect  the  carbon  on  an  asbestos 
filter. 

When  this  method  is  employed  for  those  kinds  of  iron  which  do 
not  deposit  the  carbon  in  a  coherent  mass,  as  is  the  case  in  "  spiege- 
leisen,"  but  only  in  a  finely  divided  state,  the  negative  platinum 
electrode  becomes  colored  black  from  the  carbon  deposited  upon 


255.] 


IRON    COMPOUNDS. 


507 


it.  RINMANN  *  made  this  observation  first  when  treating  Bessemer 
steel  according  to  WEYL'S  method.  According  to  WEYI/)-  the 
method  must  be  slightly  modified  when  used  with  these  kinds  of 
iron,  the  apparatus  shown  in  Fig.  107  being  then  employed.  This 
consists  of  a  beaker  half  filled  with  diluted  hydrochloric  acid, 
and  containing  a  glass  cylinder  (held  in  place  by  a  suitable  disc), 
closed  at  the  bottom  by  a  bladder  of  parchment  paper,  and  filled 
with  the  diluted  hydrochloric  up  to  the  level  of  the  surrounding 
acid.  The  cylinder  contains  the  positive  electrode,  i.e.,  the  piece 


FIG.  107. 

of  iron,  the  negative  electrode  of  platinum  foil  occupying  the 
space  between  the  cylinder  and  the  beaker.  Otherwise  the  process 
is  similar  to  the  one  described  above.  In  this  apparatus,  too,  the 
platinum  foil  is  blackened  after  several  hours'  use,  but  the  black 
deposit  dissolves  in  hydrochloric  acid,  and  is  iron,  not  carbon. 

*Zeitschr.  /.  analyt.  Chem.,  in,  336. 
f  Ibid.,  iv,  157. 


508  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  255» 

ee.  WOHLER'S  Method.* 

WOHLER'S  method  is  based  upon  the  fact  that  upon  heating 
cast  iron  in  a  current  of  chlorine,  the  whole  of  the  iron  is  volatilized 
as  ferric  chloride,  while  all  the  carbon  remains.  The  method  is 
comparatively  rapid,  and  affords  very  good  results,  for  which 
reasons  many  chemists  prefer  it  to  all  other  methods. f  Weigh 
off  the  iron  (1  to  2  grm.)  into  a  porcelain  boat,  insert  this  into  a 
tube  of  difficultly  fusible  glass,  and  heat  it  to  faint  redness  in  a 
current  of  chlorine  gas  dried  by  previously  passing  it  over  pumice 
stone  saturated  with  concentrated  sulphuric  acid.  The  treat- 
ment is  continued  until  no  more  ferric  chloride  is  formed.  All 
the  carbon  remains  in  the  boat.  Great  care  must  be  exercised  in 
drying  the  chlorine,  for  if  it  contains  even  small  quantities  of 
moisture,  a  loss  of  carbon  may  occur  from  the  formation  of  hydro- 
carbons. 

//.  Other  Methods. 

Besides  the  methods  described  from  aa  to  ee,  several  others 
have  been  proposed,  especially  those  in  which  bromine  is  employed,]; 
and  WEYL'S  process,  in  which  dilute  chromic  acid  is  used.§  Some 
are  but  little  to  be  recommended,  while  others  have  been  less  care- 
fully studied  than  those  above  described;  a  detailed  description 
of  them  is  hence  omitted. 

/?.    DETERMINING  THE  CARBON  IN  THE  RESIDUE  FROM  a. 

The  determination  of  the  carbon  in  the  residue  obtained  from 
a  is  usually  effected  by  converting  the  carbon  into  carbonic  acid, 
and  weighing  this;  the  usual  processes  are  by  combustion  in 
oxygen  (First  Method),  or  by  oxidation  with  chromic  acid  (Second 

*  Zeitschr.  f.  analyt.  Chem.,  vin,  401. 

f  Compare  MAX  BUCHNER,  Berg-  und  Huttenmdnn.  Zeitung,  Jahrg. 
xxiv,  84;  Zeitschr.  /.  analyt.  Chem.,  iv,  211. — B.  KERL,  ibid. — E.  G.  TOSH, 
Chem.  News,  1867,  No.  401,  p.  67,  and  No.  403,  p.  94;  Zeitschr.  f.  analyt. 
Chem.,  vii,  498,  and  vm,  401. 

t  Compare  WERTHER,  Journ.  f.  prakt.  Chem.,  xci,  250;  Zeitschr.  f.  analyt. 
Chem.,  iv,  211. 

§  Zeitschr.  /.  analyt.  Chem.,  iv.,  158. 


§  255.]  IRON    COMPOUNDS.  509 

Method).     Lastly,    BOUSSINGAULT   determines   the    carbon   from 
the  loss  of  weight  on  combustion  (Third  Method). 

aa.  First  Method  (Combustion  of  the  Carbon  and 
Weighing  the  Carbonic  Add). 

If  a  residue  containing  all  the  carbon  but  free  from  copper  has 
been  obtained  according  to  cc  or  ee,  this  will  already  be  in  a  boat; 
if,  however,  it  has  been  collected  on  an  asbestos  filter,  according 
to  aa,  /?/?,  or  dd,  or  bb,  transfer  it,  together  with  the  asbestos,  to  a 
porcelain  or  platinum  boat,  remove  any  particles  of  carbon  adher- 
ing to  the  funnel  by  means  of  a  moist  pledget  of  asbestos  which  is 
also  put  into  the  boat,  and,  if  necessary,  thoroughly  dry  the  con- 
tents of  the  latter.  Now  insert  the  boat  into  a  tube,  the  hinder  end 
of  which  is  empty,  but  the  fore  part  filled  with  granular  cupric 
oxide  (p.  41  this  volume),  and  proceed  exactly  as  detailed  on  pp. 
39  to  43  this  volume.  The  absorption  apparatus  is  best  arranged 
thus :  The  end  of  the  combustion  tube  is  directly  connected  with  the 
end,  6,  of  a  tube  as  shown  in  Figs.  13,  14,  or  15,  p.  16  this  volume; 
both  limbs  of  the  tube  contain  calcium  chloride,  but  the  bend  is 
filled  with  lead  peroxide  held  between  cotton  plugs.  The  tube  so 
arranged  is  capable  of  retaining  not  only  the  water,  but  also  sul- 
phurous acid,  which  may  be  evolved  during  combustion  should 
the  residue  contain  any  sulphides.  Before  use,  conduct  through 
the  tube,  first,  dry  carbon  dioxide,  then  dry  air  continuously  until 
every  trace  of  carbon  dioxide  has  been  expelled.  The  outlet  end 
g  connect  with  two  weighed  U-tubes,  filled  with  soda-lime  and  a 
little  calcium  chloride  (p.  54  this  volume);  connect  the  second 
tube  with  a  similar  but  unweighed  safety-tube,  the  exit  limb  of 
which  is  filled  with  soda-lime,  the  other  with  calcium  chloride.  This 
safety-tube  bears  a  glass  tube  bent  at  right  angles,  and  dipping  for 
a  distance  of  a  few  centimetres  into  water;  this  enables  the  prog- 
ress of  the  operation  to  be  properly  watched.  With  regard  to 
the  heating,  it  must  be  remarked  that  the  carbon  which  was  chemi- 
cally combined  with  the  iron  burns  readily,  whereas  for  the  com- 
bustion of  graphite  there  is  required  a  more  prolonged  heating 
and  at  a  higher  temperature,  in  a  current  of  oxygen.  But  as 


510  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  255. 

even  this  does  not  always  afford  complete  combustion,  the  residue 
in  the  boat  must  always  be  carefully  examined  to  make  certain 
that  it  is  quite  free  from  graphite.  All  things  considered,  there- 
fore, it  is  preferable  to  employ  chromic  acid  for  effecting  the  oxi- 
dation of  residues  rich  in  graphite. 

If  the  combustion  method  is  employed  in  the  place  of  residues 
consisting  of  carbon  and  copper,  and  obtained  by  dissolving  iron 
in  cupric-sulphate  solution,  mix  the  residue  from  1  grm.  of  the 
iron  with  50  grm.  of  cupric  oxide,  and  conduct  the  combustion  as 
described  on  p.  43,  b,  this  volume.  I  cannot,  however,  recom- 
mend this  method  for  residues  containing  graphite,  because  it  is 
impossible  to  be  certain  of  the  complete  combustion  of  the  graphite. 
Respecting  a  modified  method  of  gasometric  determination  of 
the  carbon,  compare  PARRY  (Zeitschr.  f.  analyt.  Chem.,  xn,  225). 

[Regarding  the  determination  of  carbon  in  steel  by  combustion 
see  p.  550  this  volume. — TRANSLATOR.] 

bb.  Second  Method  (Oxidation  with  Chromic  Acid). 

The  method  first  recommended  by  the  ROGERS  brothers,  and 
later  on  by  BRUNNER,*  and  which  consists  in  oxidizing  the  carbon 
with  potassium  dichromate  and  sulphuric  acid  (hence  in  the  wet 
way)  to  carbonic  acid,  was  first  employed  by  ULLGREN  in  a  modi- 
fied form  (using  chromic  acid  instead  of  potassium  dichromate) 
for  the  determination  of  carbon  in  carbonaceous  iron  residues. 
This  method,  even  with  residues  rich  in  graphite,  insures  complete 
oxidation  of  the  carbon,  and  is  hence  particularly  to  be  recom- 
mended in  the  case  of  residues  from  gray  cast  iron. 

I  shall  first  describe  the  method  recommended  by  ULLGREN,! 
and,  because  of  its  suitableness,  shall  repeat  the  description  of 
the  process  for  effecting  the  solution  (compare  p.  505  this  volume) ; 
then  the  modifications  will  be  described. 

Treat  about  2  grm.  of  the  cast  iron  in  the  form  of  borings  if  it 
is  gray,  or  in  coarse  powder  if  it  is  white,  in  a  small  beaker  with 
a  solution  of  10  grm.  of  cupric  sulphate  in  50  grm.  water,  at  a  gentle 

*  Pogg.  Annal,  xcv,  379.— Jahresber.  von  LIEBIG  und  KOPP,  1855,  773. 
\Annal.  d.  Chem.  u.  Pharm.,  cxxiv,  59. — Zeitschr.  f.  analyt.  Chem.,  n,  430. 


§  255.] 


IRON    COMPOUNDS. 


511 


heat  and  with  stirring.  As  soon  as  the  iron  has  dissolved,  allow 
to  settle,  and  decant  the  clear  solution  from  the  deposited  carbon; 
then  transfer  the  residue,  both  liquid  and  solid,  to  the  flask  a, 
Fig.  108,  by  means  of  a  wash-bottle,  taking  care,  however,  that 


FIG.  108. 

the  volume  of  the  liquid  does  not  exceed  25  c.c.  Now  add  to  the 
contents  of  the  flask  40  c.c.  of  concentrated  sulphuric  acid  (or 
proportionally  more  if  more  wash- water  had  been  required). 
When  the  mixture  has  become  cold,  add  8  grm.  chromic  acid,* 

*  ULLGREN  chose  chromic  acid,  sulphuric  acid,  and  water  instead  of 
the  mixture  of  potassium  dichromate  and  excess  of  sulphuric  acid  recom- 
mended by  the  ROGERS  brothers  and  by  BRUNNER,  on  the  ground  that  it 
avoids  the  formation  of  anhydrous  chromium-potassium  sulphate,  which 
not  only  interferes  with  but  operates  to  conceal  the  completion  of  the  oxida- 
tion, the  salt  being  deposited  as  a  green,  muddy  powder  almost  insoluble 
in  water,  acids,  and  alkalies,  when  concentrated  sulphuric  acid  is  employed. 


512  DETERMINATION    OF    COMMERCIAL    VALUES.          [§   255. 

and  connect  the  flask  with  the  apparatus  for  absorbing  the  carbon 
dioxide.  The  carbon  dioxide  resulting  from  the  oxidation  of  the 
carbon  by  the  chromic  acid,  corresponds  with  the  total  quantity  of 
the  carbon.  The  apparatus  is  arranged  as  shown  in  Fig.  108. 
The  flask  a  has  a  capacity  of  150  c.c.,  and  stands  in  a  wire  basket, 
6;  during  the  operation  c  is  closed  by  a  glass  rod,  which,  when  air 
is  drawn  through  the  apparatus,  is  replaced  by  a  potash-tube; 
e  is  connected  with  the  bulb-tube,  d,  fused  to  the  side  of  the  flask, 
and  serves  to  condense  the  greater  part  of  the  vapors;  its  bulb 
should  have  a  capacity  of  from  70  to  80  c.c.  The  cylinder  /  holds 
about  250  c.c.,  and  contains  pumice-stone  which  has  been  satu- 
rated with  sulphuric  acid  and  then  heated  until  all  the  hydrochloric 
and  hydrofluoric  acids  (arising  from  the  presence  of  chlorides  and 
fluorides  in  the  pumice)  have  been  expelled.  The  tube  g  leading 
into  the  cylinder  ends  just  at  the  lower  surface  of  the  stopper;  the 
exit-tube,  on  the  contrary,  extends  nearly  to  the  bottom;  h  con- 
tains calcium  chloride,  and  is  0-6  metre  long;  i  i  is  a  weighed 
absorption  tube  filled  mostly  with  potassa-pumice,*  but  contain- 
ing calcium  chloride  at  the  end.  During  the  operation  it  is  con- 
nected with  a  small  guard- tube,  k}  filled  with  potassa. 

When  all  is  in  readiness,  gradually  heat  the  flask  until  the  evolu- 
tion of  gas  is  so  violent  that  the  mass  threatens  to  boil  over.  Main- 
tain the  temperature  at  this  point  so  long  as  the  gas  is  uniformly 
freely  evolved,  but  as  soon  as  it  decreases,  increase  the  heat,  so  that 
white  vapors  begin  to  rise  into  the  bulb  e.  Conduct  the  action  by 
regulating  the  heat  suitably,  and  until  the  evolution  of  gas  is  but 
very  feeble.  Now  connect  k  with  an  aspirator,  and  slightly  open 
the  cock  of  the  latter  before  connecting  c  with  the  potash  tube  (c  be- 
ing previously  pressed  down  until  its  end  dips  into  the  liquid).  Then 

*  Potassa-pumice  is  prepared  thus :  Dissolve  1  part  potassium  hydroxide 
in  3  to  4  parts  water,  warm  the  solution  in  an  iron  vessel,  and  continuously 
heat  at  a  temperature  somewhat  above  100°,  while  coarsely  granular  pumice- 
stone  is  added  under  constant  stirring,  until  the  mixture  forms  a  nearly 
dry  mass.  While  still  hot,  transfer  the  mass  to  a  glass-stoppered  bottle,  and 
shake  until  the  mass  has  become  so  cool  that  the  grains  no  longer  adhere 
to  each  other.  Potassa-pumice  very  rapidly  and  completely  absorbs  carbon 
dioxide  (according  to  ULLGREN,  more  rapidly  than  soda-lime). 


5  255.]  IRON  COMPOUNDS.  513 

'open  the  cock  of  the  aspirator  still  further.  After  5  or  6  litres  of 
water  have  run  out,  and  at  such  a  rate  that  about  two  bubbles  of 
•air  per  second  pass  through  the  liquid  in  a,  the  whole  of  the 
carbon  dioxide  will  have  been  driven  into  the  absorption  tube. 
After  this  has  cooled,  weigh  it,  but,  to  make  certain,  connect  it 
again  with  the  apparatus,  draw  air  once  more  through  the  ap- 
paratus, and  ascertain  by  weighing  whether  it  has  gained  weight. 

Instead  of  introducing  into  the  flask  a  the  residue  of  carbon 
mixed  with  precipitated  copper  obtained  by  ULLGREN'S  method 
of  solution,  the  residues  obtained  according  to  a,  aa  to  ee  may  be 
similarly  treated.  In  the  case  of  those  free  from  copper,  some- 
what less  chromic  acid  may  be  taken,  3  grm.  chromic  acid  suf- 
ficing for  the  residue  from  1  grm.  iron.  A  mixture  of  2  parts  pure 
concentrated  sulphuric  acid  and  1  part  water  is  recommended  as 
the  decomposing  fluid.  Instead  of  the  apparatus  recommended 
by  ULLGREX,  others  may,  of  course,  also  be  employed.  CLASSEN  * 
recommends  for  the  purpose  the  apparatus  .devised  by  him  for 
determining  carbon  dioxide,  and  with  which  KLEIN  f  obtained  very 
good  results.  This  apparatus  is  shown  in  Fig.  109. 

Its  chief  peculiarity  is  its  condenser,  which  effects  its  purpose 
admirably.  It  consists  of  a  tube,  b,  27  to  30  mm.  wide,  at  the  upper 
end  of  which  is  fused  a  tube  15  mm.  wide,  while  to  its  lower  end 
one  of  6  to  7  mm.  width  is  fused.  This  tube  is  placed  within  a 
wider  tube,  which  may  be  the  chimney  of  an  ARGAXD  burner  23 
cm.  long  and  45  mm.  wide,  and  through  which  is  passed  a  current 
of  cold  water.  The  condenser  so  completely  condenses  the  vapors 
ascending  from  the  200-c.c.  flask,  /,  that  the  U-tube  c  perfectly 
suffices  to  dry  the  carbon  dioxide.  This  tube  contains  glass  beads 
over  which  sufficient  pure  concentrated  sulphuric  acid  has  been 
poured  to  close  the  bend  of  the  tube,  thus  allowing  the  progress 
of  the  reaction  to  be  observed,  d  and  e  are  the  soda-lime  tubes 
for  weighing  (p.  54  this  volume).  The  sulphuric  acid  in  c  re- 
quires to  be  renewed  only  after  a  series  of  experiments. 

After  the  residue  containing  the  carbon,  the  requisite  quan- 
tity of  chromic  acid,  and  about  50  c.c.  of  the  above-mentioned 

*  Zeitschr.  f.  analyt.  Chem.,  xv,  288.  t  Ibid.,  xvm,  76. 


514 


DETERMINATION    OF    COMMERCIAL    VALUES. 


[§  255. 


mixture  of  sulphuric  acid  and  water  have  been  introduced  into  the 
flask  /;  connect  g  with  a  soda-lime  tube  and  h  with  an  aspirator, 
and  draw  a  slow,  perfectly  regular  current  of  air  through  the  ap- 
paratus in  order  to  prevent  the  stopping  up  of  the  funnel  tube. 


FIG.  109. 

Then  apply  heat,  which  increase  very  gradually,  finally  boiling 
the  contents  of  the  flask  for  about  fifteen  minutes,  and  weigh- 
ing d  and  e  when  these  have  become  perfectly  cold. 

Instead  of  CLASSEN'S  apparatus,  the  apparatus  figured  on  p.  365 
this  volume,  may  also  be  used  with  best  results,  but  naturally 
omitting  the  tubes  i  and  k.  This  apparatus  is,  in  fact,  more 


§  255.]  IRON    COMPOUNDS.  515 

rationally  constructed  than  either  ULLGREN'S  or  CLASSEN'S,  as 
in  it  the  air  entering  and  leaving  the  soda-lime  tubes  is  dried  by 
calcium  chloride,  while  in  the  others  the  air  entering  is  dried  by 
sulphuric  acid,  but  on  leaving  is  dried  by  calcium  chloride. 

cc.  Third  Method  (Determination  of  Carbon  by  loss 
of  Weight  on  Combustion). 

BOUSSINGAULT  employed  this  method  for  determining  the  carbon 
in  residues  obtained  according  to  a,  cc  (p.  505  this  volume).  Free 
the  boat  from  mercurous  chloride  and  cool  it  in  a  current  of  hy- 
drogen, then  weigh  it,  burn  the  carbon  in  it,  weigh  the  residue 
after  igniting  and  cooling  in  hydrogen,  and  calculate  the  loss  in 
weight  into  carbon  dioxide.  If  the  carbon  is  from  white  pig 
iron  (or  bar  iron  or  steel)  it  is  black,  voluminous,  easily  ignitible, 
and  burns  like  tinder;  if,  however,  it  is  from  gray  iron,  and  hence 
contains  graphite,  it  requires  prolonged  heating  in  oxygen,  and 
the  residue  must,  moreover,  be  carefully  examined  to  see  that  it 
is  perfectly  free  from  graphite.  The  fact  that  the  combustible 
portion  of  the  residue  is  not  absolutely  pure  carbon,  but  contains 
hydrogen  as  well,  causes  the  results  of  the  carbon  determination 
made  thus  to  fall  out  too  high.  According  to  BOUSSINGAULT'S  * 
investigations,  however,  the  error  is  quite  small. 

;-.  REGNAULT'S  METHOD  OF  DETERMINING  CARBON  BY  DIRECT 
COMBUSTION  OF  THE  IRON. 

In  order  to  directly  burn  the  carbon  in  cast  iron,  the  latter 
must  be  reduced  to  the  finest  powder.  This  is  effected  in  the 
case  of  the  harder  irons,  by  breaking  on  an  anvil,  crushing  in  a 
steel  mortar  (Vol.  I,  p.  52,  Fig.  25),  and  sifting  through  a  tinned- 
iron  sieve  with  very  fine  holes ;  softer  irons  are  filed  with  a  hard 
file.  For  irons  which  cannot  be  reduced  by  either  of  these 
means,  the  method  ?-  here  described  is  inappli cable. 

REGNAULT,  who  was  the  first  to  employ  the  method  of  direct 
combustion  of  carbonaceous  iron,  and  BROMEIS  f  also,  use  a 

*  Zeitschr.  f.  analyt.  Chem.,  x,  114. 

t  Annal  d.  Chem.  u.  Pharm.,  XLIH,  242. 


516  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  255 

mixture  of  lead  chromate  with  potassium  chlorate;  KUDERNATSCH,* 
who  observed  a  slight  evolution  of  chlorine  to  occur  with  this 
mixture,  prefers  pure  cupric  oxide.  H.  ROSE  recommends  mixing 
with  cupric  oxide  and  igniting  in  a  current  of  oxygen  (p.  43,  6, 
this  volume).  WOHLER  employs  the  method  described  on  p.  39,  a, 
this  volume  (combustion  of  the  iron  in  a  boat  in  a  current  of  oxy- 
gen). MEYER  recommends  the  mixture  of  potassium  dichromate 
with  lead  chromate  (§  176).  Although  the  water  is  not  deter- 
mined in  this  method,  nevertheless  place  a  calcium-chloride  tube 
between  the  combustion  tube  and  the  potash  apparatus  to  collect 
any  moisture  that  may  be  present. 

This  method  is  but  little  used,  and  is  apt  to  give  results  which  are 
too  low.  See  TOSH  f  and  PARRY. J 

B.  Determination  of  the  Graphite. 

a.  Treat  another  portion  of  the  cast  iron  with  mqderately  con- 
centrated hydrochloric  acid  at  a  gentle  heat  until  gas  is  no  longer 
evolved;  then  filter  the  solution  through  asbestos  which  has  been 
previously  ignited  in  a  current  of  moist  air,  wash  the  undissolved  resi- 
due first  with  boiling  water,  then  with  potassa  lye,  next  with  alcohol, 
and  finally  with  ether  (MAX  BUCHNER  §) ;  dry,  and  then  convert 
the  graphite  into  carbon  dioxide,  best  by  oxidation  with  chromic 
acid  (p.  510).  Direct  weighing  is  not  advisable  because  the 
graphite  is  usually  impure. 

/?.  In  order  to  determine  the  graphite  together  with  the  chemi- 
cally combined  carbon,  BOUSSINGAULT  ||  heats  the  residue  obtained 
as  on  p.  505,  by  treating  iron  with  mercuric  chloride  in  the  air  at 
a  temperature  just  below  a  dark  redness.  The  chemically  combined 
carbon  present  is  thereby  burned,  leaving  the  graphite  unchanged  ; 
the  latter  is  then  burned  in  a  current  of  oxygen.  As  BOUSSINGAULT 
determined  the  chemically  combined  carbon  and  the  graphite 

*  Journ.  f.  prakt.  Chem.,  XL,  499. 
f  Zeitschr.  f.  analyt.   Chem.,  vn,  498. 
I  Ibid.,  xii,  225. 

§  Journ.  f.  prakt.  Chem.,  LXXII,  364. 

||  Annal.  de  Chim.  et  de  Phys.  [IV],  xix,  78,  and  xx,  243;  also  Zeitschr.  f. 
analyt.  Chem.,  x,  112. 


§  255.]  IRON  COMPOUNDS.  517 

from  the  loss  in  weight,  the  residue,  consisting  chiefly  of  silicic  acid, 
must  be  heated,  after  every  combustion,  in  a  current  of  pure  hydro- 
gen, in  order  to  convert  any  iron  present  into  the  same  condition 
in  which  it  was  in  the  weighed  carbonaceous  mixture.  The  re- 
sults of  the  graphite  determination  by  this  method  may  easily 
fall  out  somewhat  too  low,  and  those  of  the  combined  carbon  some- 
what too  high,  because  finely  divided  graphite  is  not  altogether 
incombustible  when  gently  ignited  in  air. 

C.  Determination  of  the  Chemically  Combined  Carbon. 

a.  On  deducting  the  graphite  obtained  in  B,  a,  from  the  weighed 
total  carbon  obtained  in  A,  the  combined  carbon  is  ascertained. 

£1.  BOUSSINGAULT'S  method  for  determining  the  combined 
carbon  is  described  under  B,  /?. 

7-.  If  the  iron  contains  so  little  chemically  combined  carbon 
that  the  determination  by  difference  (a)  gives  insufficiently  ac- 
curate results,  the  chemically  combined  carbon  must  be  deter- 
mined directly.  The  process  devised  by  me  *  for  this  purpose 
consists  in  dissolving  the  iron  in  diluted  sulphuric  acid  with  the 
aid  of  heat,  passing  the  mixture  of  hydrogen  and  hydrocarbons 
with  air  over  red-hot  cupric  oxide,  collecting  the  carbon  dioxide, 
after  drying,  in  a  soda-lime  tube,  and  calculating  the  carbon  from 
the  increase  in  weight  of  the  tube. 

Introduce  the  iron  to  be  dissolved  (1  to  5  grm.)  into  the  flask 
a  shown  on  p.  365  this  volume.  Connect  the  small  glass  tube 
proceeding  from  the  condenser  b  by  means  of  a  rubber  tube  with  a 
descending  glass  tube  bent  at  right  angles,  the  connection  being 
made  in  such  a  manner  that  the  ground  ends  of  the  two  tubes  lie 
close  together.  Then  connect  the  horizontal  portion  of  the  right- 
angled  tube  with  the  hinder  end  of  a  combustion-tube  by  means 
of  a  cork  or  rubber  stopper.  The  combustion-tube  rests  in  a 
suitable  furnace,  and  is  about  30  cm.  long.  Fill  about  15  cm. 
of  that  portion  next  the  generating  flask  with  asbestos  ignited 
first  in  moist,  then  in  dry,  air,  and  so  as  to  leave  no  visible  empty 

*  Zeitschr.  f.  analyt.  Chem.,  iv,  73. 


518  DETERMINATION   OF    COMMERCIAL    VALUES.  [§  255. 

spaces;  then  follow  coarsely  granular  cupric  oxide  and  a  short 
asbestos  plug.  The  end  of  the  tube  farthest  from  the  generating 
flask  connect  with  a  sufficiently  large  calcium-chloride  tube,  and 
this  in  turn  connect  with  a  small,  light,  accurately  weighed  U- 
tube  filled  with  granular  soda-lime,  the  exit  end  being  filled  with 
calcium  chloride.  To  this  tube  attach  a  safety  U-tube  the  limb 
of  which  nearest  the  soda-lime  tube  is  filled  with  calcium  chloride 
while  the  other  limb  is  filled  with  soda-lime;  this  tube  is  lastly 
connected  with  an  aspirator.  After  the  combustion-tube  has 
been  heated  to  redness  in  a  current  of  carbon  dioxide,  the  ap- 
paratus tested  and  found  to  be  tight,  and  it  has  been  ascertained 
that  the  soda-lime  tube  does  not  increase  in  weight  on  igniting 
the  combustion-tube  in  a  current  of  air  free  from  carbon  dioxide, 
replace  v  (Fig.  103,  p.  365  this  volume),  which  was  first  connected 
by  means  of  the  rubber  tube  with  s,  by  the  small  funnel  tube, 
and  by  suitably  aspirating,  draw  into  the  evolution  flask  a  a  suf- 
ficient quantity  of  diluted  sulphuric  acid  (1:5)  to  effect  solution, 
pouring  the  diluted  acid  gradually  into  the  funnel-tube.  Then 
replace  the  funnel-tube  by  v,  suitably  open  the  stop-cock  s,  and 
also  the  aspirator  stop-cock,  and  thereby  draw  through  the  ap- 
paratus a  slow  current  of  air  which  must  be  maintained  through 
the  whole  process.  The  part  of  the  combustion-tube  containing 
the  cupric  oxide  is  meanwhile  kept  at  a  gentle  redness  which  must 
be  maintained  during  the  whole  process.  Now  heat  the  evolution 
flask  on  an  iron  plate  so  that  solution  may  be  easily  effected.  The 
operation  proceeds  quietly,  and  is  completed  in  from  one  and  one- 
half  to  two  hours;  towards  the  end  of  the  operation  heat  the 
contents  of  the  flask  to  boiling.  In  the  case  of  iron  poor  in  graphite 
it  is  advantageous  to  add  a  very  small  quantity  of  spongy  plat- 
inum in  order  to  facilitate  solution.  As  soon  as  hydrogen  is  no 
longer  evolved,  heat  also  that  portion  of  the  combustion-tube 
containing  the  asbestos  in  order  to  burn  up  any  condensed  hydro- 
carbons that  may  have  collected  there.  Lastly,  allow  the  ap- 
paratus to  cool  in  a  slow  current  of  air,  determine  the  increase  of 
weight  of  the  soda-lime  tube,  and  from  it  calculate  the  quantity 
of  carbon  evolved  in  the  form  of  hydrocarbons. 


§  255.]  IRON    COMPOUNDS.  519 

Of  course  this  operation  can  serve  for  the  determination  of 
chemically  combined  carbon  only  when  one  is  certain  that  this 
has  completely  volatilized  in  the  form  of  hydrocarbons.  This  is 
the  case  with  many  kinds  of  iron,  but  with  others,  hydrocarbons 
remain  behind  with  the  graphite.*  Whether  this  is  the  case  is 
readily  ascertained  on  observing  if  the  residue  remaining  in  the 
evolution  flask  yields,  after  thorough  washing  with  boiling  water, 
any  carbon  compounds  to  potassa  lye,  alcohol,  or  ether,  i.e.,  whether 
the  solvents  become  colored,  and  whether  the  alcohol  and  ether, 
the  lye  having  previously  been  displaced  by  water,  afford  an  or- 
ganic residue  on  evaporation  or  not. 

d.  For  practical  purposes,  an  exact  determination  of  the  chem- 
ically combined  carbon  is  frequently  not  attempted,  it  being  re- 
placed by  a  colorimetric  determination.  This  method,  devised 
by  EoGERTZ,t  depends  upon  the  fact  that  cast  iron  dissolves  in 
nitric  acid,  yielding  a  solution  the  color  of  which  is  deeper  brown 
the  more  combined  carbon  there  is  present.  Regarding  this 
method  compare  GRUNER,|  BRITTON,§  HERMANN,||  CREATH,!" 
and  MORRELL.** 

2.  DETERMINATION  OF  THE  SULPHUR. 

a.  Method  in  which  the  greater  part  of  the  Sulphur  is 
converted  into  Hydrogen  Sulphide. 

This  method,  which  was  devised  by  me  and  first  described 
by  LipPERT,ft  later  on  improved  by  me,Jt  and  finally  simplified 
by  my  assistant,  Mr.  J.  MOFFAT  JOHNSTON,  is  best  carried  out  by 
the  aid  of  the  apparatus  shown  in  Fig.  110. 

*  Compare  MAX  BUCHNER,  Journ.  f.  prakt.  Chem.,  LXXII,  365. 
j-  Chem.  News,  1863,  No.  182,  p.  254;  Zeitschr.  f.  analyt.  Chem.,  n,  434. 
%  Berg-  und  Huttenmdnn.  Zeit.,  1869,  52;  Zeitschr.  f.  analyt.  Chem.,  x,  245. 
§  Chem.  News,  xxn,  101 ;    Zeitschr.  f.  analyt.  Chem.,  x,  245. 
\\Journ.  Chem.  Soc.  [II],  vin,  375;    Zeitschr.  f.  analyt.  Chem.,  x,  246. 
H  Eng.  and  Min.  Journ.,  New  York,  xxm,  168;  Zeitschr.  f.  analyt.  Chem., 
xvi,  504. 

**  Amer.  Chemist,  v,  365;  Zeitschr.  f.  analyt.  Chemist,  xvi,  505. 
ft  Zeitschr.  f.  analyt.  Chem.,  n,  46. 
tJ  Ibid.,  xin,  37. 


520  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  255~ 

a  is  a  flask  holding  from  300  to  400  c.c.,  in  which  the  irorn 
is  dissolved;  b  is  a  smaller  flask,  containing  the  requisite  quantity 
of  hydrochloric  acid  used  for  effecting  solution ;  c  leads  to  a  small, 
upwardly  inclined  glass  condenser  having  a  not  too  narrow  tube. 
The  exit  tube  of  the  condenser  is  provided  with  a  U-shaped  bulb- 
tube,  and  this  latter  is  connected  in  turn  with  an  ordinary  U-tube 


FIG.  110. 

(see  Fig.  103,  p.  530,  Vol.  I)  from  which  a  rubber  tube  and  glass 
lead  into  the  open  air,  or  into  a  flask  containing  caustic  soda 
solution.  The  rubber  tube  d  is  connected  with  a  hydrogen  ap- 
paratus. The  hydrogen  is  purified  by  passing  it  first  through 
potassa  solution,  then  through  potassium-permanganate  solution, 
and  finally  through  a  solution  of  lead  oxide  in  potassa  solution. 
The  bend  of  the  U-tubes  is  filled  with  brominized  hydrochloric 
acid. 

After  introducing  about  10  grm.  of  the  finely  divided  iron  into 
a  and  adding  a  little  water,  pass  hydrogen  through  the  apparatus 
until  the  latter  is  filled  with  it,  force  down  the  greased  tube  e 
(which  up  to  now  had  not  dipped  into  the  liquid  in  6)  through  the 
rubber  stopper  until  it  dips  into  the  hydrochloric  acid.  The 
pressure  of  the  hydrogen  now  forces  a  certain  quantity  of  the 


§  255.]  IRON    COMPOUNDS,  521 

hydrochloric  acid  into  a,  and  solution  of  the  iron  then  begins. 
Now  close  the  pinch-cock  /  and  assist  the  action  of  the  acid  by 
gently  heating.  As  soon  as  the  evolution  of  the  gas  slackens, 
force  a  fresh  portion  of  the  hydrochloric  acid  from  b  into  a,  as 
before.  When  the  iron  has  dissolved,  draw  up  e  a  little  way  in 
its  stopper,  and  pass  hydrogen  through  the  liquid  in  a,  heated 
almost  to  boiling,  in  order  to  expel  all  the  hydrogen  sulphide  from  a. 

If  care  has  been  taken  to  have  sufficient  bromine  present,  no 
sulphur  will  separate  in  the  U-tubes,  but  the  oxidation  of  the  sul- 
phur will  be  complete.  When  the  operation  is  at  an  end,  evaporate 
the  brominized  hydrochloric  acid  in  a  water-bath  until  almost 
all  the  hydrochloric  acid  has  been  expelled,  dilute  the  residue 
with  water,  and  precipitate  the  sulphuric  acid  present  with  barium 
chloride. 

As  the  insoluble  residue  left  on  dissolving  iron  may  still  con- 
tain sulphur  compounds,  collect  it  on  a  filter,  wash,  dry,  and  fuse 
it  with  sodium  carbonate  and  potassium  nitrate  over  an  alcohol 
lamp;  take  up  with  water,  filter,  acidulate  the  aqueous  solution 
with  hydrochloric  acid,  evaporate  on  a  water-bath,  add  a  few 
drops  hydrochloric  acid  and  water,  filter,  and  add  to  the  solution 
some  barium  chloride.  If  a  precipitate  forms,  collect  it  on  the 
filter  together  with  the  other  barium  sulphate  obtained,  dry,  ignite, 
and  weigh. 

It  is  an  essential  condition  in  this  determination  that  the 
reagents — brominized  hydrochloric  acid,  sodium  carbonate,  potas- 
sium nitrate,  and  hydrochloric  acid — contain  no  sulphuric  acid. 
If  there  is  any  doubt,  certain  weighed  and  measured  quantities 
must  be  tested,  and  allowance  made  for  any  small  quantity  of 
sulphuric  acid  found. 

Instead  of  passing  the  hydrogen  containing  hydrogen  sulphide 
through  brominized  hydrochloric  acid,  the  gas  may  be  passed 
through  a  solution  of  lead  oxide  in  potassa  solution.  In  this 
case  collect  the  separated  lead  sulphide,  dry,  oxidize  it  with  fum- 
ing nitric  acid,  and  evaporate  the  excess  of  the  acid;  the  residue, 
together  with  that  insoluble  in  the  hydrochloric  acid,  fuse  with 
sodium  carbonate  and  potassium  nitrate,  moisten  with  water, 


522  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  255. 

and  pass  in  carbon  dioxide  to  precipitate  any  traces  of  dissolved 
lead;  then  filter,  acidulate  the  nitrate  with  hydrochloric  acid, 
evaporate  on  a  water-bath,  take  up  the  residue  with  water  and 
a  few  drops  of  hydrochloric  acid,  filter,  and  precipitate  with  barium 
chloride. 

Of  course  it  will  be  readily  understood  that  the  hydrogen 
sulphide  may  be  converted  into  sulphuric  acid  by  other  means 
also.  For  instance,  HAMILTON  *  employs  potassa  solution  and 
chlorine,  while  DROWN  f  uses  a  potassium-permanganate  solution, 
the  sulphur  being  in  both  cases  ultimately  converted  into  barium 
sulphate.  ELLIOT  J  uses  caustic-soda  solution,  and  iodometrically 
determines  the  sulphide  formed  (§  148).  M.  KOPPMAYER§  pro- 
poses a  solution  of  iodine  in  potassium-iodide  solution,  and 
determines  the  residual  iodine.  HIBSCH  ||  has  shown,  however, 
that  this  last  method  gives  inaccurate  results  because  the  hydro- 
carbons also  act  on  iodine;  and  the  same  objection  can  be  made 
against  ELLIOT'S  method. 

b.  Methods  in  which  the  Iron  is  Dissolved  in  such  a  Manner  that 
all  the  Sulphur  Remains  in  the  Insoluble  Residue. 

a.  GINTL'S  T  method.  Introduce  about  5  to  10  grm.  of  the 
moderately  fine  iron  in  a  capacious  glass  flask,  and  digest  it  for 
eight  to  ten  hours  at  a  gentle  heat  (25°  to  30°)  with  about  20  times 
the  quantity  of  a  moderately  concentrated  solution  of  ferric  chloride 
as  free  as  possible  from  excess  of  acid,  the  flask  being  fixed  obliquely 
during  the  operation. 

The  greater  part  of  the  iron  is  dissolved  as  ferrous  chloride, 
with  a  gentle  evolution  of  hydrogen.  Dilute,  and  collect  the  residue, 
which  contains,  besides  small  quantities  of  iron,  also  carbon, 
graphite,  all  the  sulphur,  phosphorus,  and  nearly  all  the  silicon. 

*  Chem.  News,  xxi,  147;  Zeitschr.  /.  analyt.  Chem.,  ix,  508. 

^Zeitschr.  f.  analyt.  Chem.,  xm,  343. 

j  Chem.  News,  xxui,  61;  Zeitschr.  /.  analyt.  Chem.,  xi,  105. 

§  DINGL.  pol.  Journ.,  ccx,  184. 

||  Ibid.,  ccxxv,  611;  Zeitschr.  f.  analyt.  Chem.,  xvin,  625. 

H  Zeitschr.  f.  analyt.  Chem.,  vn,  428. 


§  255.]  IRON    COMPOUNDS.  523 

Wash  the  residue  rapidly,  dry,  transfer  it  together  with  the  filter 
to  a  porcelain  crucible,  the  bottom  of  which  has  been  covered  with 
a  layer  of  a  mixture  of  3  parts  potassium  nitrate  and  1  part  caustic 
potassa  (of  course  both  must  be  free  from  sulphuric  acid),  and 
cover  it  with  a  layer  of  the  same  mixture.  Heat  the  crucible 
over  an  alcohol  lamp,  at  first  moderately,  then  gradually  more 
strongly.  After  oxidation  is  complete,  lixiviate  the  cooled  fused 
mass  with  water,  filter,  acidulate  with  hydrochloric  acid,  and 
precipitate  the  sulphuric  acid  with  barium  chloride,  etc.  The 
results  shown  by  test  analyses  given  by  GIXTL  do  not  differ  greatly 
from  those  obtained  by  the  first  method  (a).  E.  RICHTERS*  and 
J.  E.  HIBSCH  f  also  obtained  quite  concordant  results  with  both 
methods. 

/?.  MEINECKE  I  employs  a  process  very  similar  to  that  of  GINTL, 
but,  in  order  to  avoid  the  inconvenient  separation  of  the  basic  ferric 
salt,  he  replaces  the  ferric-chloride  solution  by  an  acid  solution 
of  cupric  chloride,  the  action  of  which  may  be  assisted  by  gently 
warming.  The  separated  copper  is  finally  dissolved  by  adding  a 
solution  of  sodium  chloride  in  cupric-chloride  solution.  Then 
filter,  and  in  the  residue,  washed  first  with  hot  sodium-chloride 
solution,  then  with  water,  determine  the  sulphur.  MEINECKE 
oxidizes  this  in  the  wet  way,  with  nitric  acid  and  potassium  chlorate 
(Vol.  I,  p.  568);  of  course  this  can  also  be  effected  by  fusing  the 
residue  with  sodium  carbonate  and  potassium  nitrate  (Vol.  I, 
p.  562). 

c.  Methods  in  which  the  iron  and  Sulphur  are  Dissolved  by  Oxi- 
dizing Agents,  and  the  Sulphuric  Acid  precipitated  from  the 
Solution  by  Barium  Chloride. 

None  of  these  methods,  whether  the  iron  is  dissolved  by  nitro- 
hydrochloric  acid  or  bromine,  or  is  converted  into  ferric  chloride 
by  chlorine  in  the  dry  way  (HIBSCH,  loc.  cit.)  are  to  be  recom- 
mended, because  on  precipitating  the  sulphuric  acid  from  the 

*  DINGL.  pol  Jaurn.,  cxcvn,  168;  Zeitschr.  f.  analyt.  Chem.,  x,  370. 
f  DINGL.  pol.  Journ.,  ccxxv,  61;  Zeitschr.  f.  analyt.  Chem.,  xvm,  625. 
i  Zeitschr.  f.  analyt.  Chem.,  x,  280. 


524  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  255- 

solutions  containing  ferric  chloride  or  ferric  bromide  a  little  barium 
sulphate  remains  dissolved,  while  on  the  other  hand  the  barium 
sulphate  obtained  contains  iron.* 

3.    DETERMINATION    OF  THE  NITROGEN. 

Nitrogen,  apart  from  that  occluded  in  the  gaseous  state  (Fr. 
C.  G.  MULLER|)  occurs  in  cast  iron  (steel  and  wrought  iron)  in 
two  conditions,  according  to  the  researches  of  Bouis,  BOUSSIN- 
GAULT,  FREMY,  and  ULLGREN.J.  In  dissolving  iron  in  hydro- 
chloric acid  a  portion  of  the  nitrogen  is  converted  into  ammonia 
by  the  nascent  hydrogen,  while  another  part  remains  in  the  insol- 
uble carbonaceous  residue.  The  methods  detailed  below  for 
determining  the  nitrogen  in  each  condition  are  taken  from  ULL- 
GREN'S  papers, §  the  most  recent  published  on  this  subject,  and  in 
which  attention  is  called  to  several  important  points  which  were 
formerly  overlooked. 

a.  Determination  of  the  Nitrogen  which  forms  Ammonia  on 
Dissolving  the  Iron  in  Hydrochloric  Acid. 

a.  Dissolve  the  iron  in  hydrochloric  acid  in  a  flask  or  tubulated 
retort,  taking  care  to  pass  the  evolved  hydrogen,  which  carries  off 
a  little  ammonia,  through  a  U-tube  containing  a  little  dilute  hydro- 
chloric acid.  When  the  solution  of  the  iron  is  complete  add  the 
contents  of  the  U-tube  to  those  of  the  flask,  and  distill  the  whole 
with  an  excess  of  calcium  hydroxide  until  about  half  the  liquid 
has  passed  over,  and  then  determine  the  evolved  ammonia  accord- 
ing to  §  99,  3,  a. 

P.  Treat  about  2  grm.  of  the  finely  divided  iron  in  a  tubulated 
retort  with  a  solution  of  10  grm.  crystallized  cupric  sulphate  and 
6  grm.  fused  sodium  chloride.  When  the  iron  has  dissolved  add 
milk-of-lime  and  proceed  as  in  a. 

*Zeitschr.  f.  analyt.  Chem.,  n,  46  and  439;   vn,  429;   and  xix,  53, 
f  Ber.  d.  deutsch.  Chem.  Gesellsch. ,  xiv,  6. 
j  Zeitschr.  f.  analyt.  Chem. ,  n,  435. 

§  Annal.  d.  Chem.  u.  Pharm.,  cxxiv,  70,  and  cxxv,  40;  Zeitschr.  f.  analyt 
Chem.,  n,  435. 


§  255.]  IKON    COMPOUNDS.  525 

ULLGREN  gives  preference  to  the  latter  method.  If  there  is  any 
neglect — as  was  formerly  the  case — to  take  note  of  the  ammonia 
carried  off  by  the  hydrogen  in  the  process  a,  some  one-fifth  to  one- 
sixth  of  the  whole  is  lost. 

b.  Determination  of  the  Nitrogen  remaining  in  the  Carbonaceous 
Residue  on  Dissolving  the  Iron. 

If  the  carbonaceous  residue  left  on  dissolving  iron  in  hydro- 
chloric acid  is  burned  with  soda-lime  (§  186),  as  recommended 
by  BOUSSINGATJLT,  unsatisfactory  results  are  obtained  according 
to  ULLGREN,  because  graphite  requires  for  its  oxidation  at  the 


FIG.  111. 

expense  of  the  water  in  sodium  hydroxide  a  temperature  much 
higher  than  that  at  which  ammonia  remains  undecomposed.  On 
this  account  it  is  necessary  to  separate  the  nitrogen  in  the  gaseous 
form.  ULLGREN  employs  for  the  Combustion  mercuric  sulphate, 
and  makes  use  of  the  apparatus  shown  in  Fig.  111.  A  is  an  ordinary 
combustion  tube  30  cm.  long,  filled  up  to  g  with  about  12  grm. 
magnesite  or  sodium  bicarbonate  * ;  at  g  an  asbestos  plug  is  placed, 
while  the  space  from  g  to  /  is  filled  with  a  mixture  of  about  0-1 

*  As  since  the  manufacture  of  ammonia-soda  commercial  sodium  bi- 
carbonate containing  ammonia  is  frequently  met  with,  it  is  necessary  to 
carefully  test  the  salt  for  ammonia  before  using  it. 


526  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  255. 

grm.  of  the  carbonaceous  residue  dried  at  130°,  with  about  3  -5  to  4 
grm.  mercuric  oxide  as  free  as  possible  from  mercurous  salt,  and 
also  the  small  quantity  of  the  mercuric  salt  used  for  rinsing  out 
the  agate  mortar.  •  Then  follow  an  asbestos  plug,  and  a  two-inch 
layer  of  coarsely  powdered  pumice-stone  (/  to  h)  which  has  been 
previously  mixed  with  mecuric  sulphate  and  a  little  water  and 
again  dried;  lastly  a  plug  of  asbestos  is  inserted.  The  fore  part 
of  the  tube  is  filled  with  pieces  of  pumice-stone  which  have  been 
boiled  with  a  concentrated  solution  of  potassium  dichromate  and 
allowed  to  cool  therein.  After  draining,  the  pieces  are  introduced, 
still  moist,  into  the  tube;  they  serve  to  absorb  sulphurous  acid, 
which  they  do  easily  and  rapidly.  The  combustion-tube  A  is  con- 
nected with  the  gas-tube  a,  which  dips  into  a  mercurial  trough 
(not  shown  in  the  illustration)  in  which  the  absorption-  and  measur- 
ing-tube B  is  inverted.  The  narrower  part,  d,  of  the  latter  is  gradu- 
ated to  hold  20  c.c.,  and  must  permit  reading  off  to  0-1  c.c.  The 
bulb  c  holds  about  40  c.c.,  and  the  lower  part  of  the  tube  b  from 
20  c.c.  to  30  c.c.  The  tube  is  at  first  filled  completely  with  mer- 
cury, then  sufficient  of  a  solution  of  1  part  potassium  hydroxide 
in  2  parts  water  is  sent  up  the  tube  so  that  the  bulb  c  is  filled  to 
within  about  10  c.c.  of  its  capacity,  and  lastly,  15  c.c.  of  a  clear, 
saturated  tannic-acid  solution.  The  level  of  the  mercury  will 
then  be  at  about  e.  When  the  apparatus  is  in  readiness,  and  that 
portion  of  the  combustion-tube  to  be  heated  has  been  surrounded 
with  a  thin  sheet  of  tinned  iron,  expel  the  air  from  the  tube  in  the 
usual  manner  by  heating  one-half  of  the  sodium  bicarbonate  in  the 
hinder  end,  then  insert  the  upturned  end  of  a  under  B,  warm  the 
part  g  f  of  the  tube,  gently  at  first  to  expel  any  moisture  deposited, 
then  heat  the  part  /  h,  containing  the  pumice-stone  impregnated 
with  mercuric  sulphate,*  and  when  this  is  red-hot  heat  the  mixture 
rapidly  to  a  bright  redness,  continuing  the  heat  until  the  evolution 
of  gas  ceases  and  the  level  of  the  column  of  liquid  in  the  measuring- 
tube  ceases  to  fall;  then  heat  the  remainder  of  the  bicarbonate. 
As  soon  as  the  tubes  are  filled  with  pure  carbon  dioxide  the  height 

*  By  employing  this  layer  of  pumice-stone  the  otherwise  possible  evolu- 
tion of  carbonic  oxide  is  prevented. 


§  255.]  IRON    COMPOUNDS.  527 

of  the  column  of  liquid  in  B  remains  constant.  Now  transfer  B 
to  a  pneumatic  trough,  allow  the  mercury  and  potassa  solution 
to  run  out  and  be  replaced  by  water,  measure  the  nitrogen  with 
due  regard  to  barometric  and  thermometric  conditions,  and  from 
the  volume  calculate  its  weight. 

4.    DETERMINATION  OF  THE  PHOSPHORUS,  OR  OF  THE  PHOSPHORUS, 
ARSENIC,   AND  COPPER. 

In  determining  the  phosphorus  the  iron  must  not  be  dissolved 
in  nitrohydrochloric  acid,  as  was  frequently  done  formerly,  because 
as  C.  STOCKMANN  *  has  shown,  a  phosphorus  compound  volatilizes,f 
and  because  the  precipitation  of  phosphoric  acid  (as  ammonium 
phosphomolybdate)  from  solutions  containing  organic  matter  is 
not  quite  complete,  and  the  results  are,  hence,  too  low.  This 
makes  necessary  a  considerable  alteration  in  the  method  of  deter- 
mining phosphorus  as  described  in  the  fifth  (German)  edition. 
Of  the  methods  here  described  I  decidedly  prefer  the  first. 

First  Method. 

This  method  (a  slight  modification  of  C.  STOCKMANN'S — loc. 
tit.)  also  permits  the  determination  of  the  arsenic  and  copper 
present.  • 

Treat  about  5  grm.  of  the  comminuted  cast  iron,  in  a  litre 
flask  in  the  neck  of  which  a  funnel  is  placed,  with  60  c.c.  of  pure 
nitric  acid  (sp.  gr.  1-2).  Add  the  acid  gradually,  and  when  the 
frothing  ceases,  gently  heat  to  boiling  until  all  the  iron  is  dissolved. 
Now  gradually  evaporate  the  contents  of  the  flask,  together  with 
the  water  used  in  rinsing  it  out,  in  a  porcelain  dish  of  from  160  c.c. 
to  200  c.c.  capacity,  and  add  about  5  grm.  ammonium  nitrate 
toward  the  end;  then  transfer  the  dish  to  a  sand-bath;  evaporate 
to  dryness  with  constant  stirring,  and  strongly  heat  the  contents 
of  the  dish  over  the  naked  flame  so  that  all  the  nitrates  and  organic 
matter  are  destroyed.  This  is  greatly  facilitated  by  the  addition 

*  Zeitschr.  /.  analyt.  Chem.,  xvi,  174. 

f  According  to  the  investigations  made  in  my  laboratory  the  quantity  of 
the  phosphorus  so  lost  is  exceedingly  small 


528  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  255. 

of  the  ammonium  nitrate,  which  modification  was  introduced  by 
me  some  time  ago.  Now  digest  the  residue  with  fuming  hydro- 
chloric acid,  employing  heat,  until  all  the  ferric  oxide  is  dissolved, 
then  dilute,  filter,  and  repeatedly  evaporate  the  solution  with 
nitric  acid  until  the  hydrochloric  acid  is  expelled.*  Then  add 
ammonium  molybdate,  and  proceed  as  described  in  Vol.  I,  p. 
446,  /?. 

As,  however,  ammonium-magnesium  arsenate  may  be  pre- 
cipitated with  the  ammonium-magnesium  phosphate,  dissolve 
the  precipitate,  after  first  washing  it  with  water  containing  ammo- 
nia, in  a  little  hydrochloric  acid,  precipitate  with  hydrogen  sul- 
phide at  70°,  filter  off  the  precipitate  of  arsenic  sulphide  and  some 
molybdenum  sulphide,  concentrate  the  filtrate  and  washings, 
and  precipitate  with  ammonia  and  some  magnesia  mixture;  then 
add  a  little  more  ammonia,  and  convert  the  now  perfectly  pure 
ammonium- magnesium  phosphate  into  magnesium  pyrophos- 
phate  (Vol.  I,  p.  445). 

If  the  arsenic  and  copper  are  also  to  be  determined,  or  if  the  quan- 
tity of  phosphorus  present  is  very  small,  modify  the  process  as  fol- 
lows :  Largely  dilute  the  solution  obtained  by  digesting  the  ignited 
evaporation-residue  with  hydrochloric  acid  and  filtering;  through 
the  solution  (to  which  is  also  to  be  added  the  hydrochloric-acid 
solution  of  the  substance  obtained  by  fusing  with  sodium  ca  bonate 
the  residue  insoluble  in  hydrochloric  acid)  pass  hydrogen  sulphide 
at  70°,  filter  and  heat  the  filtrate  until  all  the  hydrogen  sulphide 
has  been  expelled;  then  precipitate  all  the  phosphoric  acid,  to- 
gether with  a  small  part  of  the  ferric  oxide,  according  to  the  method 
given  in  Vol.  I,  p.  461,  7-  (best  with  calcium  carbonate),  dissolve 
the  precipitate  in  nitric  acid,  heat  to  boiling,  and  then  prec'pitate 
with  molybdic-acid  solution,  etc.  Vol.  I,  p.  446,  /?. 

In  the  precipitate  caused  by  the  hydrogen  sulphide,  and  con- 
sisting chiefly  of  sulphur,  separate  the  copper  and  arsenic  accord- 

*  Should  the  residue  not  be  white  it  necessitates  the  precaution  to  de- 
compose it  by  fusion  with  sodium  carbonate,  dissolving  the  melt  in  nitric 
acid,  separating  the  silicic  acid,  and  testing  the  filtrate  with  ammonium 
molybdate  to  ascertain  if  there  is  any  phosphoric  acid  present. 


§  255.]  IRON  COMPOUNDS.  529 

ing  to  §  164,  after  first  removing  the  greater  part  of  the  sulphur 
by  means  of  carbon  disulphide. 

Second  Method  (by  ANDREW  A.  BLAIR  *). 

First  treat  about  5  grm.  of  the  iron  with  nitric  acid  as  in  the 
first  method,  evaporate  the  solution  to  dryness,  add  35  c.c.  hydro- 
chloric acid,  cover,  and  heat  until  the  iron  is  dissolved;  then 
evaporate  again  to  dryness  and  heat  to  120°  to  130°  until  the  odor 
of  hydrochloric  acid  is  no  longer  noticeable;  when  cold,  dissolve 
in  35  c.c.  hydrochloric  acid,  add  50  c.c.  water,  and  boil  for  half  an 
hour  in  order  to  convert  any  pyrophosphate  that  may  have  formed 
into  orthophosphate ;  then  evaporate  the  excess  of  acid,  and  filter 
off  the  silicic  acid  and  wash  it  first  with  diluted  hydrochloric  acid 
and  then  with  hot  water. 

Dilute  the  filtrate  to  about  400  c.c.,  add  ammonium  bisulphite 
in  sufficient  quantity  to  convert  the  ferric  chloride  into  ferrous 
chloride,  heat  to  boiling,  and  nearly  neutralize  with  ammonia 
(the  reduction  is  not  complete  in  too  strongly  acid  liquids).  Now 
add  to  the  colorless  solution  50  c.c.  concentrated  hydrochloric 
acid,  boil  until  all  the  sulphurous  acid  has  been  expelled,  cool 
rapidly,  and  when  perfectly  cold  add  ammonia,  until  on  shaking 
a  slight  green  precipitate  forms.  Dissolve  this  in  a  few  drops 
acetic  acid,  add  1  or  2  c.c.  of  a  concentrated  ammonium-acetate 
solution  and  3  to  5  c.c.  diluted  acetic  acid.  Now  dilute  with  hot 
ater  to  750  c.c.,  and,  if  the  precipitate  formed  is  white,  add  drop 
by  drop  very  dilute  ferric-chloride  solution  (about  7  grm.  iron  in 
1000  c.c.  liquid)  until  the  precipitate  acquires  a  dull-red  color; 
then  heat  to  boiling,  rapidly  filter  the  hot  solution,  and  wash  the 
precipitate  with  boiling  water;  now  dissolve  it  in  hydrochloric 
acid,  evaporate  almost  to  dryness,  add  sufficient  citric  acid  to  keep 
all  the  iron  in  solution  (about  2  to  3  grm.),  then  add  ammonia 
just  to  alkalinity,  ammonium-magnesium  chloride  solution,  and 
lastly  more  ammonia.  The  quantity  of  the  liquid  must  not  exceed 

*  Zeitschr.  /.  analyt.  Chem.,  xvm,  122.  This  method  is  employed  in  the 
experimental  station  established  in  the  United  States  for  the  examination  of 
iron,  steel,  etc. 


530  DETERMINATION    OF   COMMERCIAL    VALUES.          [§  255. 

20  c.c.  to  30  c.c.  After  12  hours  collect  the  precipitate  by  filtration, 
wash  with  water  containing  ammonia,  dry,  and  ignite;  then  dis- 
solve the  residue  in  equal  parts  of  hydrochloric  acid  and  water 
in  a  platinum  crucible,  and  boil  for  half  an  hour  in  order  to  con- 
vert the  pyrophosphate  into  orthophosphate.*  Now  filter,  con- 
centrate to  20  c.c.  or  30  c.c.,  then  add  2  to  3  drops  magnesia  mix- 
ture, a  little  citric  acid,  and  some  ammonia,  and  determine  the 
now  pure  precipitate  ammonium-magnesium  phosphate  as  pyro- 
phosphate. If  the  precipitate  of  ammonium-magnesium  phos- 
phate first  obtained  is  very  small,  Blair  recommends  to  weigh 
it  after  ignition,  and  then  to  determine  the  silicic  acid  in  it  and 
deduct  its  weight,  f 

Third  Method  (by  F.  KESSLER];). 

Dissolve  5-59  grm.  of  the  sufficiently  comminuted  iron  in  a 
covered  porcelain  dish  in  60  c.c.  nitric  acid  (sp.  gr.  1-2),  evaporate, 
finally  with  stirring  over  the  direct  flame,  and  ignite;  transfer  so 
far  as  possible  to  a  platinum  crucible  and  heat  until  all  the  carbon 
is  consumed.  Now  retransfer  the  contents  of  the  crucible  to  the 
dish  and  treat  with  35  c.c.  hydrochloric  acid  (sp.  gr.  1-19).  By 
this  treatment  the  ferric  oxide  is  dissolved  while  the  silicic  acid 
remains.  If  the  latter  is  not  to  be  determined  it  need  not  be  fil- 
tered off,  but  introduce  the  ferric-chloride  solution  with  the  silicic 
acid  into  a  flask,  add  200  c.c.  water,  and  reduce  the  iron  completely 
by  passing  in  hydrogen  sulphide;  then  add  200  c.c.  of  a  solution 
of  potassium  ferrocyanide  (210  grm.  of  the  crystallized  salt  per 
litre)  and  make  up  the  volume  to  518  c.c.  (The  18  c.c.  repre- 
sent the  volume  which  the  voluminous,  bright-blue  precipitate 
of  potassium  ferri- ferrocyanide  occupies.)  After  mixing,  filter 
through  a  folded  filter  in  a  covered  funnel;  collect  the  first  por- 
tions passing  through,  and  which  are  usually  turbid,  separately, 
but  the  clear  filtrate  collect  in  a  250-c.c.  flask  and  add  20  c.c.  mag- 

*  The  conversion  js,  however,  incomplete;    compare  §74,  c. 
•j-  According  to  the  investigations  made  in  my  laboratory,  this  method 
gives  results  which  are  too  low. 

$Zeitschr.  /.  analyt.  Chem.,  xi,  106. 


§  255.]  IRON  COMPOUNDS.  531 

nesia  mixture  (Vol.  I,  p.  445).  After  12  hours  collect  the  precipi- 
tate, wash  it  with  ammoniacal  water,  dissolve  in  nitric  acid  of  sp. 
gr.  1-035,  filter  off  the  slight  insoluble  residue  of  blue  ferrocy- 
anogen  compound,  precipitate  again  with  ammonia  and  a  little 
magnesia  mixture,  and  proceed  as  described  hi  Vol.  I,  p.  445, 
According  to  the  investigations  made  in  my  laboratory,  this 
method  gives  results  with  iron  rich  in  phosphorus  which  quite 
fairly  agree  with  those  obtained  by  the  first  method;  the  method, 
in  my  opinion,  is  not  so  well  adapted,  however,  for  irons  containing 
but  little  phosphorus. 

Fourth  Method  (by  GINTL*). 

In  this  method  the  phosphorus  is  determined  together  with 
the  sulphur  (p.  522  this  volume).  For  this  purpose  treat  the  fil- 
trate from  the  barium  sulpha  e  with  sulphuric  acid  in  order  to 
remove  any  excess  of  barium,  supersaturate  the  filtrate  with  am- 
monia, remove  any  manganese  present  with  ammonium  sulphide, 
and  in  the  filtrate  precipitate  the  phosphoric  acid  with  magnesia 
mixture  (Vol.  I,  p.  445). 

E.  RiCHTERsf  thus  obtained  results  which  agreed  to  some 
extent  with  those  obtained  by  the  first  method,  but  yet  not  sat- 
isfactorily. I  would  advise,  above  all,  to  test  the  ferric-chloride 
solution  for  phosphoric  acid,  and  would  also  recommend  to  dissolve 
in  nitric  acid  the  residue  left  on  treating  the  fused  mass  with  water, 
and  to  test  the  solution  with  molybdic  solution,  as  the  ferric  oxide 
may  retain  phosphoric  acid.  It  need  scarcely  be  remarked  that 
the  phosphoric  acid  in  the  filtrate  from  the  barium  sulphate  may 
also  be  precipitated  by  molybdic  solution  (Vol.  I,  p.  446). 

*  Zeitschr.  f.  analyt.  Chem.,  vn,  428. 
t  Ibid.,  x,  370. 


532  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  255. 

5.    DETERMINING  THE    TOTAL    AMOUNT    OF    SILICON,    IRON,   MANGA- 
NESE,   ZINC,    COBALT,  NICKEL,    CHROMIUM,    ALUMINIUM, 
TITANIUM,    AND   ALSO    THE   METALS    OF    THE 
ALKALINE    EARTHS   AND   ALKALIES.* 

a.  General  Methods. 

Dissolve  5  to  10  grm.  of  the  cast  iron  in  a  covered  beaker  in 
moderately  dilute  hydrochloric  acid,  rinse  the  solution  into  a 
porcelain  dish,t  and  evaporate  to  dryness  on  the  water-bath  until 
the  mass  no  longer  has  an  odor  of  hydrochloric  acid;  then  moisten 
with  hydrochloric  acid,  warm,  add  water,  and  collect  the  precipi- 
tate, wash  and  dry;  this  we  will  call  a.  Divide  the  solution  into 
two  parts,  each  of  which  put  into  a  large  flask,  heat  with  nitric 
acid,  dilute  largely,  and  precipitate  the  ferric  oxide  by  nearly 
saturating  with  ammonium  carbonate  and  boiling,  according  to 
Vol.  I,  p.  644,  3,  a;  collect  the  precipitate,  wash  somewhat,  dis- 
solve again  in  hydrochloric  acid,  and  repeat  the  precipitation 
as  before.  Wash  the  precipitate  so  obtained  with  water  con- 
taining ammonium  nitrate,  and  dry;  we  will  call  it  b. 

Concentrate  the  nitrate  from  b,  add  ammonia  in  slight  excess, 
filter  after  standing  a  short  time,  dissolve  the  precipitate  in  hydro- 
chloric acid,  and  reprecipitate  once  more  in  the  same  way.  Then 
collect  the  precipitate,  wash,  and  dry;  we  will  call  this  c. 

Acidulate  the  filtrate  from  c  with  acetic  acid,  concentrate  it, 
make  alkaline  with  ammonia,  then  again  add  acetic  acid  until  just 
distinctly  acid ;  now  add  ammonium  acetate  and  pass  in  hydro- 
gen sulphide  at  70°.  As  soon  as  the  precipitate,  d,  has  settled, 
collect  it. 

Transfer  the  filtrate  from  d  to  a  flask,  which  it  should  almost 
fill,  make  it  alkaline  with  ammonia,  add  ammonium  sulphide, 

*  Comp.  LIPPERT,  Beitrdge  zur  Analyse  des  Roheisens,  Zeitschr.  /.  analyt. 
Chem.,  n,  39. 

f  If  it  is  desired  to  determine  the  silicon  and  aluminium  as  accurately 
as  possible,  the  solution  of  the  iron  and  the  evaporation  must  be  effected  in  a 
platinum  dish ;  but  in  this  case  the  solution  may  readily  take  up  some  plat- 
inum, whereby  the  separation  and  determination  of  the  other  metals  is 
rendered  considerably  more  difficult. 


§  255.]  IRON    COMPOUNDS.  533 

stopper  loosely,  and  allow  to  stand  for  twenty-four  hours  in  a 
warm  place.     The  precipitate  (manganese  sulphide)  is  e. 

Evaporate  the  liquid  separated  from  the  manganese  sulphide 
to  dryness  in  a  platinum  dish,  drive  off  the  ammonia  salts,  take 
up  the  residue  with  water  and  hydrochloric  acid,  filter,  and  pre- 
cipitate any  calcium  present  with  ammonium  oxalate;  then 
precipitate  any  magnesium  with  ammonium  phosphate,  and 
lastly,  after  the  phosphoric  acid  has  been  removed,  determine  any 
potassium  or  sodium  should  these  be  present  (compare  §  154,  6, 
and  §153,  4,  &*). 

We  now  proceed  to  the  further  examination  of  the  precipitates 
a  to  e. 

The  residue  a  contains  the  whole  of  the  substances  insoluble 
or  difficultly  soluble  in  hydrochloric  acid.  Besides  carbon,  silicic 
acid  and  leukon,  there  may  be  present  also  iron  phosphide,  chro- 
mium iron,  vanadium  iron,  iron  arsenide,  iron  carbide,  silicon  (?),t 
molybdenum,  etc.,  and  also  the  slag  in  a  more  or  less  altered  con- 
dition. Titanic  acid  also  may  be  found  in  the  residue.  Fuse 
the  latter  with  sodium-potassium  carbonate  and  a  little  potassium 
nitrate,  separate  the  silicic  acid  as  usual  by  evaporating  with 
hydrochloric  acid,  weigh  and  test  it  as  to  its  purity  (comp.  Vol.  I, 
p.  511),  and  specially  for  titanic  acid.  The  silicic  acid  may  have 
been  formed  partly  from  the  silicon,  or  have  been  present  partly 
as  such  in  the  slag.  In  the  filtrate  from  the  silicic  acid  separate 
by  double  precipitation  any  matter  precipitable  by  ammonia  and 
collect  the  precipitate  cf ;  acidulate  the  filtrate  weakly  with  acetic 
acid,  add  ammonium  acetate,  and  pass  in  hydrogen  sulphide 
at  70°  to  obtain  the  precipitate  d' ',  which  is  then  collected;  in  the 
filtrate  from  this  throw  down  the  precipitate  e*  by  ammonium 
sulphide,  and  lastly  test  the  filtrate  for  alkaline  earths;  any  small 


*  It  is  obvious  that  the  determination  of  the  alkalies  is  of  value  only 
when  care  has  been  taken  to  ascertain  if  the  ammonia  and  ammonia cal  salts 
used  are  free  from  fixed  alkalies,  and  when  all  the  operations  have  been 
carried  out  in  platinum  dishes.  See  my  paper  in  Zettschr.  /.  analyt.  Chem., 
iv,  69. 

f  Compare  TOSH,  Zeitschr.  /.  analyt.  Chem.,  v,  430. 


534  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  255. 

quantities  of  these  that  may  be  present  can  be  weighed  together 
with  the  somewhat  larger  quantity  obtained  above. 

The  precipitates  b,  c,  and  c1  contain  all  the  ferric  oxide  and 
alumina  and  those  portions  of  the  silicic  and  titanic  acids  that 
have  passed  into  solution.  Transfer  the  mixed,  ignited  precipi- 
tates to  several  porcelain  boats,  insert  these  in  a  porcelain  tube, 
and  subject  them  to  prolonged  ignition  in  a  current  of  pure  hydro- 
gen until  no  more  aqueous  vapor  forms.  Treat  the  boats  con- 
taining the  reduced  iron  with  very  dilute  nitric  acid  to  dissolve 
the  iron  (Vol.  I,  p.  652  [91]),  make  up  the  volume  of  the  solution 
to  1000  c.c.,  and  in  a  measured  portion  determine  the  iron  by  add- 
ing first  tartaric  acid  and  then  ammonia  and  ammonium  sulphide, 
and  finally  converting  the  ferrous  sulphide  into  ferric  oxide  (§  113, 
1,  b  *).  The  residue  insoluble  in  very  dilute  nitric  acid  fuse  with 
potassium  disulphate,  take  up  with  cold  water,  filter  off  any  in- 
soluble residual  silicic  acid  (which  is  to  be  added  to  that  found 
above)  and  pass  in  hydrogen  sulphide,  precipitate  any  titanic  acid 
present  by  boiling  while  passing  in  a  current  of  carbon  dioxide 
(§  107),  filter,  boil  the  filtrate,  or  the  solution  if  that  has  remained 
clear,  with  nitric  acid,  and  precipitate  the  alumina  by  adding 
ammonia,  and  separate  it  from  any  slight  admixed  ferric  oxide  by 
the  method  described  on  p.  247  this  volume.  Here  too,  as  before, 
regard  must  be  paid  to  any  phosphoric  acid,  for  if  this  is  present 
in  the  alumina  the  weight  of  the  latter  would  of  course  be  too 
high.  Were  any  chromium  present,  its  oxide  too  would  have  to 
be  separated  in  this  precipitate  and  determined. 

The  precipitates  d  and  d'  contain,  or  may  contain,  the  sul- 
phides of  copper,  cobalt,  nickel,  and  zinc.  Dissolve  the  precipi- 
tates in  brominized  hydrochloric  acid,  heat  until  the  excess  of 
bromine  has  been  expelled,  precipitate  the  copper  with  hydro- 
gen sulphide,  and  in  the  filtrate  separate  and  determine  the  co- 
balt, nickel,  and  zinc  according  to  §  160. 

The  precipitates  e  and  e'  consist  of  manganese  sulphide.     Treat 


*  It  is  advisable  to  determine  the  iron  in  a  separately  weighed  smaller 
quantity  only  when  the  iron  to  be  examined  is  perfectly  homogeneous. 


§  255.]  IRON  COMPOUNDS.  535 

them  according  to  §  109,  2,  and  finally  test  the  weighed  man- 
ganese sulphide  as  to  its  purity. 

6.  Special  Methods. 

a.  For  Determining  the  Total  Silicon. 

aa.  If  the  phosphoric  acid  is  determined  according  to  4  (first 
or  third  method),  the  residue  insoluble  in  hydrochloric  acid  con- 
tains all  the  silicon  as  silicic  acid.  The  latter  can  be  determined 
by  fusing  it  with  sodium  carbonate  and  a  little  potassium  nitrate 
and  proceeding  according  to  the  usual  methods. 

bb.  THOMAS  M.  DROWN  and  PORTER  W.  SHIMER  *  recommend, 
for  the  determination  of  the  total  silicon,  to  treat  the  cast  iron 
with  nitric  acid  until  everything  soluble  has  dissolved,  then  to 
evaporate  with  sulphuric  acid  until  the  nitric  acid  has  been  ah1  or 
very  nearly  all  driven  off.  Then  dilute,  collect  the  residue  consisting 
of  silicic  acid  and  carbon,  wash  it  with  water  first,  then  with  hy- 
drochloric acid,  and  finally  with  hot  water,  dry,  ignite  with  access 
of  air,  and  weigh  the  residual  silicic  acid.  So  obtained,  it  is  free 
from  titanic  acid. 

In  another  very  rapid  method  recommended  by  the  same 
authors  f  it  is  recommended  to  fuse  the  iron  with  twenty-five 
times  its  quantity  of  potassium  disulphate  in  a  very  capacious 
platinum  crucible,  treat  the  melt  with  water,  and  to  treat  the 
insoluble  residue  of  silicic  acid  with  hydrochloric  acid  and  water. 
This  method  gives  with  many  kinds  of  iron  very  serviceable  re- 
sults, but  with  others  it  gives  results  that  are  too  low,  hence  it  is 
suitable  only  for  approximate  determinations  when  these  have  to 
be  very  rapidly  made. 

/?.  Determining  Titanium. 

To  determine  titanium,  TH.  M.  DROWN  and  PORTER  W.  SHIMER  J 
heat  the  iron  in  a  porcelain  boat  in  a  glass  tube  in  a  current  of  pure, 
dry  chlorine.  The  glass  tube  must  be  sufficiently  long  to  receive  all 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  vii,  346. 
f  Ibid.,  vin. 
t  Ibid.,  vin. 


536  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  255. 

the  volatilized  ferric  chloride,  and  its  exit  end  must  be  connected 
with  three  U-tubes  containing  water.  These  tubes  retain  the 
volatilized  silicon  and  titanium  chlorides.  When  the  operation 
is  at  an  end,  transfer  the  contents  of  the  tubes  to  a  porcelain  dish, 
acidulate  strongly  with  hydrochloric  acid,  add  15  c.c.  sulphuric 
acid  of  sp.  gr.  1-23,  and  evaporate  until  all  the  hydrochloric 
acid  has  been  driven  off.  Now  collect  the  separated  silicic  acid, 
and  in  the  filtrate,  diluted  with  water,  precipitate  the  titanic  acid 
by  boiling  (§  107).  The  silicon  determinations  made  under  these 
conditions  usually  afforded  results  that  were  too  low. 

f.  Determining  the  Iron. 

The  iron  content  of  cast  iron  may,  of  course,  be  also  deter- 
mined volumetrically,  best  by  dissolving  about  10  grm.  in  the 
manner  described  on  p.  527,  4,  this  volume  (First  Method).  The 
solution  then  contains  all  the  iron  as  ferric  chloride.  Should 
it  contain  free  chlorine,  remove  this  by  evaporating  the  solution, 
then  make  up  to  1  litre,  and  in  50  c.c.  of  this  determine  the  iron 
with  stannous  chloride  according  to  Vol.  I,  p.  327.  A  variation 
of  this  latter  method  has  been  recommended  by  KESSLER.*  In 
this  stannous  chloride  is  first  added  until  all  the  ferric  chloride 
has  been  converted  into  ferrous  chloride,  then  an  excess  of  mercuric 
chloride  to  convert  the  excess  of  stannous  chloride  into  stannic 
chloride,  then  standard  potassium-dichromate  solution  until  a 
drop  test  with  potassium  ferricyanide  no  longer  gives  the  ferrocy- 
anide  reaction,  and  lastly  a  subsidiary  ferrous-chloride  solution 
until  the  ferro-ferricyanide  reaction  is  just  observable.  On  de- 
ducting the  quantity  of  dichromate  corresponding  to  the  ferrous 
chloride  used  from  the  total  dichromate,  we  find  the  quantity 
rquired  to  convert  the  ferrous  chloride  yielded  by  the  cast  iron  into 
ferric  chloride,  and  from  this  the  quantity  of  iron  can  then  be 
calculated  (Vol.  I,  p.  319,  6). 

If  the  cast  iron  contains  notable  quantities  of  arsenic  or  copper, 
the  volumetric  methods  above  mentioned  do  not  afford  very 

*  Zeitschr.  /.  analyt.  Chem.,  xi,  249. 


§  255.]  IRON    COMPOUNDS.  537 

accurate  results.    In  such  cases  KESSLER  advises  the  following 
method : 

Precipitate  the  hydrochloric-acid  solution  with  hydrogen 
sulphide  at  70°,  filter,  and  boil  the  filtrate  while  passing  in  carbon 
dioxide  in  order  to  expel  the  greater  part  of  the  hydrogen  sul- 
phide; remove  the  last  portions  of  the  gas  as  mercury  chloro- 
sulphide  by  adding  an  excess  of  mercuric  chloride,  and  then  titrate 
direct  with  potassium  dichromate  without  filtering  off  the  pre- 
cipitate. 

d.  Determining  the  Manganese. 

As  a  relatively  rapid  method  of  determining  manganese  in 
cast  iron  is  of  importance  in  iron  manufacture,  a  number  of  methods 
have  been  recommended  for  effecting  this  object  volumetrically. 
The  most  important  of  these  are  the  following : 

aa.  F.  KESSLER'S  Method* 

This  is  based  (a)  upon  the  precipitation  of  the  iron  as  basic 
ferric  sulphate,  which  is  thus  separated  from  manganese;  and  (6) 
upon  the  fact  that  on  adding  bromine  water  to  a  manganous- 
chloride  solution  to  which  zinc  chloride  and  sodium  acetate  have 
been  added,  and  then  heating,  all  the  manganese  is  precipitated  as 
peroxide,  together  with  zinc  oxide.  The  requisites  for  the  method 
are:  A  saturated  aqueous  solution  of  bromine;  a  solution  of  100 
grin,  crystallized  sodium  carbonate  in  sufficient  water  to  make 
1  litre;  a.  solution  of  100  grm.  crystallized  sodium  sulphate  in 
water  to  make  1  litre;  a  solution  of  sodium  acetate  containing 
500  grm.  crystallized  salt  per  litre;  a  dilute  solution  of  sodium 
acetate  (20  c.c.  of  the  preceding  solution  diluted  to  1  litre) ;  a 
solution  of  zinc  chloride  (200  grm.  zinc,  but  no  free  hydrochloric 
acid,  per  litre);  a  solution  of  antimony  chloride  (15  grm.  anti- 
monic  oxide  and  300  c.c.  hydrochloric  acid  of  sp.  gr.  1-19  dissolved 
in  water  to  make  1  litre);  and  a  solution  of  3-3  grm.  potassium 
permanganate  in  water  to  make  1  litre. 

Dissolve  a  suitable  quantity  of  the  iron  in  the  manner  described 

*  Zeitschr.  f.  analyt.  Chem.,  xvm,  1. 


538  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  255. 

on  p.  530  this  volume  (Third  Method) ;  the  liquid  will  then  be  free 
from  organic  substances,  and  will  contain  all  the  iron  as  ferric 
chloride,  and  all  the  manganese  as  manganous  chloride.  Dilute 
the  solution  to  about  100  c.c.  in  a  flask,  and  while  being  kept 
rapidly  rotating,  run  in  from  a  burette  the  sodium-carbonate 
solution  until  the  precipitate  formed  ceases  to  redissolve.  The 
stream  of  liquid  run  in  must  not  be  directed  against  the  sides  of 
the  vessel,  but  on  the  peripheral  part  of  the  solution.  Then  run 
in  from  another  burette,  cautiously,  and  drop  by  drop,  hydro- 
chloric acid  of  sp.  gr.  1-01  until  the  liquid  becomes  just,  but  com- 
pletely, clear,  and  this  in  not  too  short  a  time  and  after  frequent 
stirring.  Now  dilute,  add  15  c.c.  of  the  sodium-sulphate  solution 
for  every  1  grm.  of  iron,  fill  up  to  the  mark,  mix,  and  filter  through 
a  folded  dry  filter  into  a  dry  flask,  keeping  the  funnel  covered. 

Now  measure  off  a  volume  of  the  filtrate  containing  at  most 
0-11  grm.  manganese,  concentrate  it  if  necessary  to  100  c.c.,  and 
add  this  to  a  mixture  of  100  c.c.  bromine  water,  50  c.c.  of  the 
zinc-chloride  solution,  and  20  c.c.  of  the  sodium-acetate  solution 
contained  in  a  flask.  The  addition  should  be  made  in  five  equal 
portions,  and  at  intervals  of  fifteen  minutes  each.  Next  add  a 
further  20  c.c.  of  sodium-acetate  solution,  and  heat  to  boiling 
until  the  odor  of  bromine  has  entirely  disappeared  and  the  liquid 
containing  the  precipitate  in  suspension  has  become  perfectly 
colorless. 

Collect  the  precipitate,  wash  it  with  the  dilute  sodium-acetate 
solution,  and  finally  replace  it,  together  with  the  filter,  in  the  pre- 
cipitation vessel.  Now  add  antimony-chloride  solution  in  quan- 
tities of  5  c.c.  to  the  precipitate  until,  after  sufficiently  stirring 
in  the  cold,  the  residue  of  the  precipitate  is  no  longer  black,  but 
brown  or  light-brown,  then  add  25  c.c.  hydrochloric  acid,  wash 
the  solution  into  a  beaker  as  soon  as  the  precipitate  is  completely 
dissolved,  and  run  in  from  a  burette  potassium  permanganate 
until  a  reddish  color  supervenes  and  persists  for  at  least  six  seconds. 

On  now  titrating  an  equal  quantity  of  antimony  chloride  under 
similar  conditions  with  potassium  permanganate,  the  difference 
will  give  the  potassium  permanganate  equivalent  in  oxidizing 


§  255.]  IRON    COMPOUNDS.  539 

effect  to  the  manganese  dioxide  present  in  the  precipitate  (2  eq. 
KlLnO4  =  5MnO2).  The  quantity  of  manganese  that  was  present 
may  thus  be  easily  calculated.  If  the  potassium-permanganate 
Solution  has  been  standardized  against  iron  (Vol.  I,  p.  313),  10  eq. 
of  iron  (559)  will  be  the  equivalent  of  2  eq.  of  potassium  per- 
manganate (KMnO4  =  316-22)  or  5  eq.  of  manganese  dioxide  (435) 
containing  5  eq.  of  manganese  (275).  TYESSLER,  however,  prefers 
to  standardize  the  permanganate  solution  exactly  as  above  de- 
scribed, by  aid  of  a  manganese  solution  of  known  strength  and 
prepared  by  dissolving  a  weighed  quantity  of  manganous  pyro- 
phosphate  *  in  hydrochloric  acid.  The  test  analyses  cited  by 
KESSLER  are  very  satisfactory. 

bb.  VOLHARD'S  Method.^ 

This  is  based  upon  the  separation  of  ferric  oxide  from  manga- 
nous oxide  by  zinc  oxide,  and  upon  the  volumetric  determination 
of  the  manganous  oxide  in  the  filtrate  with  potassium  perman- 
ganate. Regarding  the  latter  method  of  determination  (comp. 
Vol.  1,  p.  300,  6),  VOLHARD  has  shown  that  the  precipitate  thrown 
down  by  potassium  permanganate  in  a  hot,  dilute  solution 
of  manganous  sulphate  or  chloride  is  never  pure  hydrated  manga- 
nese dioxide,  but  that  it  always  contains  some  manganous  oxide. 
If,  however,  a  salt  of  zinc,  calcium,  or  magnesium  is  added  to  the 
solution,  the  precipitate  will  contain  all  the  manganese  as  dioxide 
along  with  zinc  oxide,  lime,  or  magnesia.  The  following  equation 
shows  the  reaction: 

3MnS04  +  2KMnO4  +  7H2O  =  5MnO2  •  H2O  +  KjSO,  +  2H2SO4. 


*  To  prepare  the  manganous  pyrophosphate  mix  a  solution  of  40  gnn. 
crystallized  manganous  sulphate  with  one  of  60  grm.  crystallized  sodium 
phosphate,  add  hydrochloric  acid  until  the  precipitate  has  dissolved,  and 
then  add  ammonia  to  alkalinity.  Add  hydrochloric  acid  again  to  clarify 
the  liquid,  filter  if  necessary,  dilute  to  about  1  litre,  precipitate  with  ammo- 
nia, wash  the  precipitate  by  decantation  until  the  washings  no  longer  react 
for  chlorides;  then  dissolve  in  dilute  nitric  acid  with  the  addition  of  a  little 
sulphurous  acid,  supersaturate  with  ammonia,  clear  the  liquid  again  with 
nitric  acid,  reprecipitate  with  ammonia,  wash  the  precipitate  repeatedly 
by  decantation,  dry,  and  ignite. 

f  Annal.  d,  Chem.,  cxcvm,  318  to  354. 


540  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  255. 

Dissolve  a  suitable  quantity  of  cast  iron,  containing  say  0-3 
to  0-5  grm.  manganese,  in  nitric  acid  in  a  flask,  evaporate  to 
dryness  in  a  porcelain  dish,  adding  toward  the  end  a  little  ammo- 
nium nitrate,  heat — finally  over  the  naked  flame — until  all  the 
nitrate  has  been  decomposed  and  the  carbon  consumed,  and  digest 
with  hydrochloric  acid;  now  add  cautiously  a  sufficient  quantity 
of  concentrated  sulphuric  acid,  and  evaporate,  first  on  the  water- 
bath,  then  on  a  gas-stove,  until  the  sulphuric  acid  begins  to  pass 
off  in  fumes.  Next  rinse  into  a  litre  flask,  neutralize  the  free  acid 
with  sodium  carbonate  or  caustic  soda  free  from  manganese,  and 
then  add  sufficient  zinc  oxide  suspended  in  water*  until  all  the 
iron  is  precipitated,  i.e.,  until  the  gradually  darkening  brown-red 
solution  suddenly  coagulates  and  the  supernatant  liquid  becomes 
milky.  Now  fill  with  water  up  to  the  mark,  mix,  allow  to  settle 
for  a  while,  and  filter  through  a  dry,  folded  filter  into  a  dry  flask. 
Of  the  filtrate  acidulate  200  c.c.  in  a  flask  with  2  to  4  drops  nitric 
acid,  and  heat  to  boiling;  then  remove  the  source  of  heat  and 
run  in  potassium-permanganate  solution  (containing  about  3-8 
grm.  per  litre)  until  the  liquid  becomes  just  permanently  reddened. 
The  titration  should  be  repeated  with  another  200  c.c.  of  the 
filtrate. 

If  the  permanganate  solution  has  been  standardized  against 
iron,  as  in  Vol.  I,  p.  313,  it  must  be  noted  that  1  eq.  of  permanganic 
anhydride,  (Mn2O7),  converts  10  eq.  of  iron  from  a  ferrous  to  a  ferric 
state,  while  3  eq.  of  manganous  manganese  is  converted  into 
5  eq.  of  manganic  manganese,  thus: 

Mn2O7 +10  FeO  =  5Fe2O3+  2MnO ;  and  Mn207  +  3  MnO  =  5MnO2. 


*VOLHARD  employs  commercial  zinc  white.  This  is  strongly  heated 
for  some  time  in  a  Hessian  crucible,  with  stirring,  and  then  elutriated  with 
water.  A  test  must  be  made  of  a  small  sample  from  near  the  lowermost 
part  of  the  deposit  to  make  certain  that  it  contains  no  small  particles  of 
metallic  zinc.  The  test  is  made  by  dissolving  in  diluted  sulphuric  acid 
colored  by  a  drop  of  potassium-permanganate  solution.  The  color  must 
not  disappear  even  on  warming.  The  zinc  oxide  is  kept  mixed  with  water 
ready  for  use. 


§  255.]  IRON   COMPOUNDS.  541 

Hence  559  of  ferrous  iron  correspond  to  165  of  manganous 
manganese.  The  manganese  standard  is  therefore  obtained  from 
the  iron  standard  by  multiplying  by  Jf|  =  0-29517.  Of  course 
the  standard  of  the  potassium-permanganate  solution  may  also 
be  established  by  means  of  a  manganese  solution  of  known 
strength,  or,  as  VOLHARD  prefers,  iodometrically  (see  loc.  cit., 
p.  333) .  The  test  analyses  given  by  VOLHARD  are  very  satisfactory. 

cc.  JOHN  PATTTNSON'S  Method* 

This  is  based  upon  the  following  fact:  On  adding  chlorinated- 
lime  solution  or  bromine  water  to  a  manganous-chloride  solution 
containing  a  sufficient  quantity  of  ferric  chloride,  heating  to  from 
60°  to  70°,  and  then  adding  an  excess  of  calcium  carbonate,  all 
the  manganese  is  thrown  down  as  dioxide  in  the  precipitate.  It 
is  sufficient  if  the  solution  contains  half  as  much  iron  as  manganese, 
but  equal  quantities  are  preferable ;  an  excess  of  iron  is  not  pre ju- 
dicial. The  dioxide  is  determined  by  treating  the  precipitate  with 
an  excess  of  an  acid  solution  of  ferrous  sulphate  and  then  deter- 
mining the  excess  of  the  latter.  The  following  equation  shows 
the  reaction: 

MnO2 + 2FeSO4 + 2H2SO4  =  Fe^SO^ + MnS04  +  2H2O. 

For  carrying  out  the  process  there  are  required:  Chlorinated- 
lime  solution  (15  grm.  good  chlorinated  lime  per  litre),  the  clear 
liquid  obtained  by  subsidence  being  used;  calcium  carbonate  (ob- 
tained by  precipitating  calcium- chloride  solution  with  sodium 
carbonate  at  80°) ;  acid  ferrous-sulphate  solution,  containing  about 
10  grm.  iron  per  litre  (dissolve  53  grm.  ferrous  sulphate  in  a 
mixture  of  one  part  sulphuric  acid  and  3  parts  water  to  make  one 
litre);  a  solution  of  potassium  dichromate  (see  Vol.  I,  p.  319,  b) 
containing  exactly  14-721  grm.  per  litre.  1000  c.c.  of  this  solu- 
tion have  the  same  oxidizing  action  on  ferrous  iron  as  26-1  grm. 
manganese  dioxide,  and  correspond  with  16-5  grm.  manganese. 

*  Journ.  Chem.  Soc.,  1879,  p.  365;  Zetischr.  /.  analyt.  Chem.,  xix,  346. 


542  DETERMINATION   OF   COMMERCIAL  VALUES.         [§  255. 

Dissolve  a  quantity  of  cast  iron  containing  about  0-1  to  0-15 
gnn.  of  manganese  in  hydrochloric  acid  free  from  organic  matter 
(comp.  p.  539,  bb,  this  volume),  add  calcium  carbonate  until  the 
liquid  acquires  a  deep-red  color,  then  acidulate  again  with  a  few 
drops  hydrochloric  acid,  add  about  60  c.c.  of  the  chlorinated- 
lime  solution,  then  hot  water  until  the  temperature  is  about  60° 
to  70°,  and  lastly  about  1-5  gnn.  calcium  carbonate.  Now  stir 
until  carbon  dioxide  is  no  longer  evolved,  and  then  allow  to  settle. 
If  the  liquid  above  the  dark-brown  precipitate  (which  soon  settles) 
exhibits  a  reddish  color  from  the  presence  of  permanganic  acid, 
add  a  few  drops  alcohol  until  decolorization  is  effected.  Collect 
the  precipitate  on  a  filter  and  wash  \vith  warm-water  until  the 
washings  cease  to  react  for  chlorine  when  tested  with  potassium- 
iodide-starch  paper  (p.  379  this  volume).  Now  replace  the  pre- 
cipitate with  the  filter  in  the  beaker  in  which  the  precipitation 
was  effected  f  and*  to  the  sides  of  which  some  of  the  precipitate 
usually  still  adheres)  and  in  which  an  accurately  measured  volume 
of  the  acid  ferrous-sulphate  solution  (say  50  c.c.  to  60  c.c.)  has 
been  poured.  The  precipitate  rapidly  dissolves.  Dilute  with 
cold  water  if  necessary,  and  titrate  the  excess  of  ferrous  sulphate 
with  potassium-dichromate  solution  (Vol.  I,  p.  319).  In  order 
to  accurately  ascertain  the  relation  of  the  ferrous-sulphate  solu- 
tion to  the  potassium-dichromate  solution  a  quantity  equal  to 
that  employed  must  be  titrated  with  the  dichromate  solution,  first 
placing  in  the  liquid  a  filter  *  identical  with  the  one  used.  Lead, 
copper,  nickel,  or  cobalt  must  be  absent  from  the  liquid  being 
titrated ,  or  may  be  present  at  most  in  traces  only.  The  calculation  is 
most  simply  made  as  follows:  Deduct  from  the  number  of  c.c. 
of  dichromate  solution  corresponding  with  the  ferrous-sulphate 
solution  added,  the  number  of  c.c.  corresponding  to  the  residual 
ferrous  oxide.  The  difference  indicates  the  quantity  of  dichn> 
mate  solution  equivalent  in  oxidizing  action  to  the  manganese 


*  PATTINSON  considers  this  precaution  necessary,  as,  according  to  his 
investigations,  certain  filter-papers  exert  a  slightly  reducing  action,  which 
is  thus  eliminated. 


§  255.]  IRON  COMPOUNDS.  543 

dioxide  present,  and  the  quantity  of  manganese  is  hence  given 
(see  above)  by  the  equation: 

1000  :  16-5  ::  the  difference  in  question  :  x. 
The  test  analyses  given  by  PATTINSON  are  very  satisfactory.* 

e.  Determining  the  Chromium  and  Aluminium, 
a.  ANDREW  A.  BLAIR'S  Method^  (greatly  modified). 
Over  5  grm.  iron  in  a  500-c.c.  flask  pour  20  c.c.  of  strong  hydro- 
chloric acid  diluted  with  3  to  4  times  its  volume  of  water,  and  close 
the  flask  with  a  rubber  stopper  provided  with  a  valve  opening 
outwards.J  When  the  iron  is  all  dissolved,  replace  the  valved 
stopper  by  another,  allow  to  cool,  add  water  until  the  flask  is 
three-fourths  filled,  and  then  introduce  pure  barium  carbonate 
until  it  is  present  in  excess,  occasionally  lifting  the  stopper.  After 
twelve  hours  coll  ct  the  precipitate,  which  will  now  surely  con- 
tain all  the  chromium  and  aluminium,  and  wash  with  cold  water. 
Now  fuse  it  with  sodium  carbonate  and  potassium  nitrate,  treat 
the  melt  with  water  and  hydrochloric  acid,  separate  the  silicic 
acid,  precipitate  the  hydrochloric  acid  with  ammonia,  filter  off  the 
precipitate,  consisting  of  iron,  aluminium,  and  chromium  oxides, 
and  in  it  determine  the  chromium  and  aluminium  according  to 
Vol.  I,  p.  642,  2  [77]- 

b.  Determining  Chromium  according  to  ROD.  SCHOFFEL.  § 

If  the  iron  (or  chrome-iron  alloy)  contains  not  more  than  eight 
per  cent,  of  chromium,  dissolve  it  in  ammonio-cupric  chloride 
solution  (p.  502,  a,  aa,  this  volume),  filter,  and  fuse  with  sodium 
carbonate  and  potassium  nitrate  the  residue  which  contains  all  the 

*  Other  methods  of  determining  manganese  in  cast  iron  have  been  given 
by  THOM.  M.  CHATARD  (Zeitschr.  /.  analyt.  Chem.,  xi,  308);  CLASSEN  (Ibid., 
xviii,  175);  C.  ROSSLER  (Ibid.,  xix,  75);  F.  BEILSTEIN  and  L.  JA\YEIN 
(Ibid.,  xix,  77);  and  others. 

^'Amer.  Journ.  of  Science  and  Arts,  cxin,  421;  Zeitschr.  /.  analyt.  Chem., 
xx,  138. 

+  The  solution  may  also  be  effected  in  a*,  atmosphere  of  carbon  dioxide, 
of  course. 

§  Ber.  d.  deutsch.  chem.  Gesellsch.,  xn,  1863. 


544  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  255. 

chromium.  Digest  the  melt  with  water  until  the  residue  appears 
to  be  pulverulent,  whereby  any  manganic  acid  formed  will  be  de- 
composed, and  then  filter.  If  the  solution  contains  but  very  little 
silicic  acid,  it  may  be  very  carefully  and  accurately  neutralized 
with  nitric  acid,  and  the  chromic  acid  precipitated  as  mercurous 
chromate  (Vol.  I,  p.  423,  a,  /?) ;  if,  however,  much  silicic  acid  is  pres- 
ent, evaporate  the  solution  with  hydrochloric  acid  with  the  addition 
of  a  little  alcohol,  separate  the  silicic  acid,  and  in  the  filtrate  pre- 
cipitate the  chromium  as  chromic  hydroxide  (Vol.  I,  p.  281,  1,  a). 
After  weighing,  test  the  chromic  oxide  as  to  its  freedom  from  alu- 
mina; if  this  is  present  determine  it  and  make  the  proper  allow- 
ance. 

If  the  chrome-iron  alloy  contains  more  than  eight  per  cent, 
chromium,  the  iron  will  not  be  sufficiently  dissolved  by  treatment 
with  ammonio-cupric  chloride.  In  such  cases  dissolve  in  hydro- 
chloric acid,  filter,  fuse  the  residue  with  sodium  carbonate  and 
potassium  nitrate,  dissolve  the  melt  in  water  and  hydrochloric  acid, 
and  unite  the  solutions.  Neutralize  them  nearly,  and  add  to  the 
still  distinctly  acid  liquid  sodium  acetate  in  sufficient  excess  to 
insure  the  presence  only  of  free  acetic  acid ;  no  precipitate  should  be 
formed.  Now  add  an  excess  of  bromine,  allow  to  stand  in  a  stop- 
pered flask  for  several  hours  with  frequent  shaking,  then  boil  until 
the  excess  of  bromine  has  been  driven  off,  add  sodium  carbonate 
until  all  the  ferric  oxide  is  precipitated,  and  filter.  All  the  chromium 
is  now  in  the  filtrate  as  alkali  chromate,  and  is  then  determined 
as  described  above. 

6.    DETERMINING  THE  METALS  OF  THE   FIFTH  AND 
SIXTH   GROUPS. 

As  will  have  been  seen  above,  the  determination  of  the  copper 
and  arsenic  may  be  made  conjointly  with  that  of  the  phosphorus 
(comp.  p.  527  this  volume;.  If,  however,  there  are  other  metals 
of  the  fifth  and  sixth  groups  present  also,  or  if  the  quantity  of  the 
arsenic  or  copper  is  so  small  that  it  cannot  be  readily  determined 
in  5  grm.  iron,  a  separate  and  larger  portion  of  cast  iron  (about 
20  grm.)  must  be  employed  for  the  determination  of  the  metals  of 


§  255.]  IRON  COMPOUNDS.  545 

the  fifth  and  sixth  groups.  Dissolve  the  iron  in  nitric  acid,  add 
32  c.c.  pure  sulphuric  acid,  evaporate  until  all  the  nitric  acid  has 
been  driven  off,  dilute,  and  filter.  Fuse  the  insoluble  residue  with 
some  sodium  carbonate  and  potassium  nitrate,  take  up  the  melt 
with  water,  add  sulphuric  acid,  evaporate  until  all  the  nitric  acid 
has  been  expelled,  dilute,  filter,  unite  both  sulphuric-acid  solu- 
tions, boil  with  ammonium  bisulphite  until  the  greater  part  of 
the  ferric  oxide  is  reduced,  and  precipitate  with  hydrogen  sul- 
phide at  70°;  if  necessary,  free  the  precipitate  from  sulphur  by 
treatment  with  carbon  disulphide,  and  in  the  insoluble  residue 
determine  the  copper,  arsenic,  and  any  other  metals  of  the  fifth 
and  sixth  groups  that  may  be  present,  according  to  §§  164  and  165. 

7.   DETERMINING  TUNGSTEN. 

As  tungsten,  if  present,  cannot  be  determined  in  the  manner 
detailed  above  in  6,  a  separate  portion  of  iron  must  be  taken. 
HUD.  SCHOFFEL*  recommends  one  of  the  following  methods: 

a.  Treat  .the  very  finely  divided  iron,  or  tungsten-iron  alloy, 
with  ammonio-cupric  chloride  (p.  502,  a,  aa,  this  vol.),  filter,  fuse 
the  residue  with  sodium  carbonate,  dissolve  in  water,  filter,  nearly 
neutralize  with  nitric  acid,  precipitate  with  mefcurous  nitrate, 
filter,  dry,  ignite,  and  weigh  the  residual  tungstic  acid  containing 
silicic  acid;  fuse  this  residue  with  potassium  disulphate,  treat  the 
melt  with  water,  determine  the  residual  silica,  and  deduct  this 
from  the  weight  first  obtained.  If  chromium  is  also  present  the 
tungstic  acid  contains  chromic  oxide  also,  and  the  two  must  there- 
fore be  separated. 

6.  Treat  the  iron  or  alloy  in  very  finely  divided  form  with 
nitrohydrochloric  acid  until  all  reaction  ceases,  dilute,  and  let  stand 
for  a  day  or  two.  All  the  tungsten,  including  that  originally  dis- 
solved, will  now  be  found  in  the  insoluble  residue.  Collect  this, 
dry,  ignite  first  with  access  of  air,  then  fuse  with  sodium  carbon- 
ate, and  proceed  further  as  in  a. 

*Berichtts  der  deutschen  chem.  GeseUschaft,  xii,  1866. 


546  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  255. 

8.    DETERMINING   VANADIUM. 

Should  an  iron  contain  vanadium,  as  may  perchance  happen, 
the  determination  of  this  is  effected  by  treating  a  large  quantity 
of  the  iron  with  diluted  sulphuric  acid  until  all  reaction  ceases; 
then  filter,  dry  the  residue,  fuse  it  with  1  part  sodium  carbonate 
and  2  parts  potassium  nitrate,  extract  with  water,  and  in  the 
melt  determine  the  vanadium  according  to  p.  492,  15,  this  volume. 

9.    DETERMINATION    OF    THE     SLAG     CONTAINED    IN    IRON;     OR    THE 

SILICON,    ALUMINIUM,    AND     THE    METALS    OF    THE    ALKALINE 

EARTHS  COMBINED  AS  SUCH  WITH  THE  IRON. 

Cast  iron  not  infrequently  contains  a  small  quantity  of  slag. 
The  determination  of  this,  as  well  as  of  its  constituents,  is  not 
without  value,  as  only  after  a  knowledge  of  these  is  acquired,  can 
it  be  decided  what  part  of  the  silicon,  aluminium,  calcium,  mag- 
nesium, potassium,  etc.,  is  present  in  the  metallic  iron.  The 
methods  above  detailed  give  the  total  amount  of  the  elements, 
but  the  analysis  of  the  adhering  slag  gives  the  proportions  present 
in  oxidized  condition;  and  the  difference  gives  the  quantities 
present  combined  with  the  metallic  iron.  For  the  determination 
of  the  slag  and  its  constituents  the  following  methods  are  employed : 

a.  Heating  the  Iron  in  a  current  of  Chlorine* 

Heat  a  weighed  quantity  (about  5  grm.)  of  the  powdered  iron 
in  a  porcelain  boat  inserted  in  a  glass  tube,  in  a  current  of  per- 
fectly dry  chlorine  free  from  air  and  hydrochloric  acid.  This  is 
effected  by  first  driving  out  the  air  from  the  apparatus  by  means 
of  carbon  dioxide  before  beginning  the  operation,  and  then  passing 
through  chlorine  gas  which  has  been  first  passed  through  a  U-tube 
filled  with  fragments  of  manganese  dioxide,  and  then  through  a 
sulphuric-acid  apparatus.  The  heating  is  continued  until  no  more 
ferric  chloride,  or  chlorides  of  silicon,  sulphur,  phosphorus,  etc., 
volatilize.  To  prevent  any  stoppage  of  the  apparatus  and  any  in- 

*  See  my  memoir  "Beitrage  zur  Analyse  des  Roheisens,"  Zeitschr.  £ 
analyt.  Chem.,  iv,  72. 


§  255.]  IRON   COMPOUNDS.  547 

convenience  from  the  excess  of  chlorine,  the  glass  tube  used  should 
be  sufficiently  long  to  contain  all  the  ferric  chloride,  and  its  exit 
end  should  be  connected  by  means  of  a  rubber  tube  and  glass  tube 
with  a  carboy  containing  calcium  hydroxide.  When  cold,  treat 
the  contents  of  the  boat  with  water  to  remove  all  the  soluble 
matter  (manganous  chloride,  calcium  chloride,  etc.),  dry  the  resi- 
due, and  ignite  in  a*  current  of  oxygen  to  consume  all  the  graphite 
present.  Now  ignite  again,  for  the  sake  of  greater  certainty,  first 
in  a  current  of  hydrogen,  then  again  in  chlorine,  extract  again  with 
water,  heat,  if  necessary,  once  more  in  oxygen,  weigh  the  residual 
slag,  and  then  determine  its  constituents.  If  the  slag  obtained 
with  the  cast  iron  is  available,  it  is  preferable  to  analyze  this,  de- 
termining the  silicic  acid  in  the  residual  slag  from  the  iron,  and 
from  this,  by  comparison  with  the  slag  analysis,  determining 
the  other  slag  constituents.  The  reason  why  this  method  is  to  be 
prefered  is  because  the  slag  may  be  attacked  to  some  extent  by 
pure,  dry,  chlorine,  so  that  in  fact  water  will  extract  appreciable 
quantities  of  calcium  chloride,  etc.  The  slag  residue  then  no 
longer  contains  all  the  lime,  etc.,  that  was  in  the  slag,  but  all  the 
silicic  acid  is  left. 

b.  Treating  the  Iron  with  Solvents. 

It  may  be  readily  seen  that  the  solvents  must  be  so  chosen 
that  the  iron  will  be  dissolved,  but  that  the  slag,  will  be  not  at- 
tacked at  all,  or  only  as  little  as  possible.  The  following  solvents 
may  be  employed: 

Very  dilute  hydrochloric  acid  aided  by  a  galvanic  current*; 
iodine  or  bromine  in  the  presence  of  water  f ;  or,  mercuric-chloride 
solution,  t  The  residue  left  after  the  iron  is  dissolved  contains,  or 
may  contain,  the  combined  carbon,  graphite,  silicic  acid,  leukon, 
slag,  etc.  It  is  now  necessary,  if  the  first  mentioned  solvent  has 
been  used,  to  burn  off  the  combined  carbon  and  graphite  first, 
but  by  this  procedure  silicic  acid  may  be  introduced  into  the  slag 

*  LIPPERT,  Zeitschr.  f.  analyt.  Chem.,  n,  48. 

t  V.  EGGERTZ,  Ibid.,  vn,  500. 

J  H.  ROSE,  Handb.  d.  analyt.  Chem.,  6th  ed.,  by  R.  FINKENER,  n,  757. 


548  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  255. 

(EGGERTZ,  loc.  tit.,  p.  501).  It  is  hence  preferable  to  first  remove 
the  silicic  acid  and  the  leukon  by  heating  the  residue  with  a  satu- 
rated solution  of  pure  sodium-  carbonate.  Then  wash  the  residue, 
and  burn  off  the  carbon.  In  order  now  to  remove  the  last  traces 
of  ferric  oxide  it  is  only  necessary  to  ignite  first  in  a  current  of 
hydrogen,  and  then  in  chlorine.  Extract  the  residue  with  water, 
then  heat  again  with  a  solution  of  sodium  carbonate,  wash  again 
with  water,  and  weigh.  If  mercuric-chloride  solution  was  used 
as  the  solvent,  the  residue  must  be  washed,  and  then  treated  with 
chlorine  water  free  from  hydrochloric  acid,  or  with  bromine  water, 
to  remove  the  mercurous  chloride  formed.  It  therefore  follows 
that  the  methods  described  under  b  are  in  nowise  simpler,  while 
in  fact  less  accurate,  than  the  methods  detailed  under  a,  hence  the 
latter  are  to  be  preferred. 


II.    STEEL   AND    WROUGHT  IRON. 

Steel  and  also  wrought  iron  contain  essentially  the  same  con- 
stituents as  cast  iron,  but,  as  a  rule,  far  smaller  quantities  of  those 
elements  which  are  combined  with  the  iron.  Thus  the  total 
carbon  in  steel  varies  between  2  and  0-65  per  cent.,  and  in  wrought 
iron  between  0-6  and  0-016  per  cent.;  the  maximum  of  silicon 
in  steel  as  well  as  in  wrought  iron  is  about  0-6  per  cent.,  etc. 
The  following  are  the  elements  usually  quantitatively  determined 
in  both:  Carbon  (chemically  combined,  and  also  mechanically 
admixed,  if  this  is  present),  silicon,  sulphur,  phosphorus,  man- 
ganese, and  copper.  If  a  large  quantity  of  wrought  iron  or  steel 
is  operated  upon,  other  elements  also  present,  as  nickel,  cobalt, 
arsenic,  tungsten,  etc.,  may  be  quantitatively  determined. 

Although  the  methods  are,  on  the  whole,  identical  with  those 
used  in  cast  iron,  it  is  desirable  to  add  a  few  supplementary  re- 
marks. 

1.    DETERMINING  THE   CARBON. 

a.  If  unhardened  steel  is  dissolved  slowly  and  without  warm- 
ing, in  diluted  hydrochloric  or  sulphuric  acid,  a  carbonaceous  resi- 


§  255.]  IRON   COMPOUNDS.  549 

due  remains  (CARON,*  RINMANN  f),  whereas  the  same  unhardened 
steel  gives  no  carbonaceous  residue  when  dissolved  with  heat 
in  hydrochloric  acid  of  sp.  gr.  1  •  12,  and,  the  solution  when  com- 
plete boiled  for  half  an  hour  longer.  When  hardened,  the  same 
steel  yields  no  residue  when  dissolved  in  cold  diluted  acid;  the 
carbon  in  the  carbonaceous  residue  mentioned  cannot,  hence, 
be  graphite.  RINMANN  terms  it  "cementkohle"  (cement  car- 
bon). DEBRUNNER  J  arrived  at  the  same  conclusion,  i.e.  that 
in  steel,  and  in  various  kinds  of  iron  generally,  the  carbon  may  be 
present  in  a  third  form,  differing  from  combined  carbon  or  graphite. 
He  found,  namely,  that  on  dissolving  cast  steel  (crucible  or  Bes- 
semer steel)  in  nitric  acid  of  sp.  gr.  1  •  2,  there  forms  in  the  liquid 
a  brown,  flocculent  precipitate  which  disappears  on  heating.  On 
similarly  treating  welding-steel  (puddle-steel  or  cementation-steel) 
however,  a  black  velvety  powder  separates,  which,  while  re- 
sembling graphite  in  appearance,  completely  dissolves  on  heat- 
ing. The  carbon  thus  obtained  from  welding-steel  DEBRUNNER 
terms  semi-combined  carbon,  and  he  utilizes  the  different  be- 
havior of  steels  on  solution  in  nitric  acid  as  a  means  of  differenti- 
ating them.  I  call  attention  to  these  later  investigations  in 
order  to  point  out  that  it  must  not  be  assumed,  without  further 
inquiry,  that  the  carbon  which  remains  on  dissolving  steel  or 
wrought  iron  in  cold  dilute  hydrochloric  (or  even  nitric)  acid, 
is  graphite.  A  carbon  may  rather  be  considered  to  be  graphite 
only  when  on  rapidly  dissolving  an  iron  in  hot  hydrochloric  acid 
the  carbon  separates,  and  cannot  be  dissolved  by  continued  boiling, 
or  by  subsequent  treatment  with  alkali  and  with  alcohol.  Whether 
the  quantity  of  the  so-called  "cement  carbon"  (semi-combined 
carbon)  may  be  accurately  determined  by  dissolving  the  steel 
or  wrought  iron  in  cold  dilute  hydrochloric  acid,  whereby  it  is 
left  undissolved  with  the  graphite,  requires  further  comprehensive 
investigation. 

*  Compt.  rend.,  1863. 

f  Zeitschr.  f.  analyt.  Chem.,  iv,  159,  and  vn,  499. 

t  Iron,  xii,  775;    DINGL.  polyt.  Jvurn.,  ccxxxi,  475;   Zeitschr.  f.  analyt. 
Chem.,  xvm,  624. 


550  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  255. 

b.  To  determine  the  total  carbon  in  steel  and  wrought  iron  the 
method  most  frequently  employed  is  to  treat  with  copper  salts 
(pp.  502  to  505,  this  volume),  and  convert  the  separated  carbon 
into  carbon  dioxide  by  combustion  in  a  current  of  oxygen  or  by 
means  of  chromic  acid  (pp.  510  to  515,  this  volume).     As  the  car- 
bon content  is  considerably  smaller  than  in  the  case  of  cast  iron, 
5  to  10  grm.  should  be  operated  upon. 

c.  If  WEYL'S  method  (pp.  505  to  507,  this  volume)  is  used  for 
dissolving  the  steel  or  wrought  iron,  the  modification  described  on 
p.  507,  and  the  apparatus  shown  in  Fig.  107,  must  be  employed, 
otherwise  the  results  obtained  will  be  too  low,  because  of  the 
reasons   given  on  p.    506.     Compare   RINMANN,*    SCHNITZLER,! 
and  WEYL.J 

d.  EGGERTZ'  colorimetric  method  (p.  519,  d,  this  volume)  of 
approximately  determining  the  combined    carbon  is   excellently 
adapted  for  use  in  steel  works  where  similar  raw  materials  are 
constantly  being  worked,  and  the  steel  obtained  varies  practically 
only  in  the  amount  of  carbon  it  contains.     The  method  has  been 
variously   modified;     compare    GRUNER,§    J.  B.  BRITTON,||    and 
MORRELL^ 

[e.  Carbon  may  also  be  determined  in  steel  by  direct  combus- 
tion in  oxygen.  Although  this  simple  method  was  formerly 
decried  as  uncertain  and  yielding  too  low  results,  it  has  been 
recently  shown  that  it  is  reliable  if  the  necessary  conditions  are 
adhered  to.  LAWRENCE  DUFTY  **  states  that  if  the  drillings  used 
be  sufficiently  thin,  the  process  gives  perfectly  accurate  results, 
and  a  carbon  determination  can  be  made  in  the  remarkably  short 
time  of  forty  minutes  or  less  from  time  of  receipt  of  sample.  Thin 
curly  drillings  may  be  simply  placed  in  a  boat  and  burnt  in  oxygen 
without  any  reagent.  As  a  general  rule,  however,  especially  if 

*  Zeitschr.  f.  analyt.  Chem.,  in,  336. 

t  IUd.,  iv,  78. 

t  Ibid.,  iv,  157. 

§  Berg-  und  Huttenmdnn  Ztg.,  1869,  52. 

||  Chem.  News,  xxn,  101;  Zeitschr.  f.  analyt.  Chem.,  x,  245. 

IF  Amer.  Chemist,  v,  365;  Zeitschr.  f.  analyt.  Chem.,  xvr,  305. 

**  Chem.  News,  LXXXVII,  289. 


§  255.]  IRON   COMPOUNDS.  551 

the  drillings  are  very  small  or  inclined  to  be  powdery,  it  is  necessary 
to  mix  with  some  material  which  will  separate  the  particles  and, 
if  possible,  assist  hi  the  oxidation  of  the  sample  without  fusing 
to  a  liquid  mass,  as  is  the  case  when  using  the  oxides  of  lead 
or  bismuth,  as  recommended  by  BREARLEY*  and  LEFFLER-)-. 
ROZYETTI  used  AljOg,  RHEAD  and  SEXTON  ("Assaying  and 
Metallurgical  Analysis")  suggest  MgO,  whilst  BREARLEY  and 
IBBOTSON  ("Analysis  of  Steel  Works  Materials")  find  ZnO  satis- 
factory for  certain  alloys;  other  oxides  suggested  are  SiO2,  CaO, 
SnO2,  Mn3O4,  etc. 

The  method  adopted  by  DUFTY  was  as  follows: 

2  •  727  grm.  of  drillings  (not  exceeding  0  •  5  mm.  in  thickness  for 
hard,  and  0-25  mm.  for  mild  steels),  or  1-3636  grm.  of  pig  iron 
(gray  pig  is  powdered  until  it  all  passes  through  a  sieve  40  meshes 
to  the  inch),  are  mixed  with  0-5  grm.  of  freshly  ignited  MgO  by 
shaking  in  a  weighing  bottle,  and  then  transferring  to  a  boat  con- 
taining a  layer  of  MgO — a  further  portion  of  the  oxide  being 
spread  over  the  top  to  cover  any  drillings  exposed.  (If  the  mag- 
nesia gives  any  "blank,"  a  definite  quantity  must  always  be  used 
and  the  blank  deducted.)  Having  placed  the  boat  in  the  red-hot 
tube,  the  aspirator  is  set  working,  and  at  the  end  of  a  few  minutes 
— sufficient  time  being  given  for  the  boat  to  attain  a  red  heat — 
the  oxygen  is  turned  on,  and,  as  soon  as  the  steel  begins  to  burn, 
is  allowed  to  enter  at  a  decidedly  rapid  rate.  At  this  stage  very 
little  gas  passes  through  the  KOH  absorption  bulb,  practically  all 
the  oxygen  combining  with  the  steel.  When  the  gas  bubbles 
through  the  absorption  bulb  at  about  the  same  rate  as  that  at  which 
it  enters  the  furnace,  the  oxygea  is  turned  off  (the  combustion  of 
the  sample  being  complete),  and  about  a  litre  of  air  is  passed 
through,  the  absorption  bulb  being  then  detached  and  weighed. 
The  increase  in  weight,  minus  the  blank,  multiplied  by  10  or  20, 
according  to  the  weight  taken,  converts  the  CO2  to  carbon  per  cent. 

By  the  process  given  above,  special  steels  and  alloys,  when 
hi  the  form  of  drillings,  give  up  the  whole  of  their  carbon  almost 

*  Chem.  News,  LXXXIV,  23. 
f  Ibid.,  LXXXV,  121. 


552  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  255. 

as  readily  as  ordinary  steels.  It  is  essential,  however,  when 
chromium  is  present  to  any  appreciable  extent,  that  the  drillings 
do  not  exceed  0-25  mm.  in  thickness. 

Alloys  which  will  not  drill  after  careful  annealing,  if  powdered 
and  ground  to  a  fine  state  of  division  in  the  agate  mortar,  and 
then  well  shaken  with  MgO  or  CaO,  will  in  the  majority  of  cases 
burn  completely  in  oxygen.  Some  ferro-chromes,  even,  will 
oxidize  if  thoroughly  " floured"  in  the  mortar  and  ignited  for  a 
sufficient  length  of  time.* 

From  what  has  been  stated  it  will  be  apparent  that  the  direct 
combustion  process  is  not  only  an  alternative  to  the  usual  solution 
method,  strongly  appealing  to  the  steel- works  chemist  on  account 
of  its  reliability,  simplicity,  and  speed,  but,  as  shown,  such  a 
direct  method  is  absolutely  essential  in  the  case  of  most  special 
steels  and  some  alloys,  if  an  accurate  determination  of  the  carbon 
is  to  be  made. 

A  few  notes  on  the  process,  and  details  of  the  apparatus  used, 
may  be  of  service. 

When  a  combustion  is  finished,  the  boat  is  withdrawn,  its 
contents  turned  out  by  means  of  a  piece  of  wire  or  the  tang  of 
an  old  file,  and  then  re-charged  with  the  next  sample.  The  oxi- 
dized drillings  should  always  fit  together  in  the  form  of  a  long  cake, 
which  is  very  easily  extracted  owing  to  the  boat  being  protected 
by  the  unfused  magnesia.  If  the  steel  should  not  have  been 
completely  burnt,  the  drillings  will  be  detached  from  each  other 
— no  fritting  whatever  having  taken  place.  In  this  case  either 
thinner  drillings  are  required  or  more  heat  should  be  applied. 

Both  MgO  and  CaO  require  igniting  at  a  high  temperature 
in  the  muffle  to  completely  drive  off  CO2,  and,  in  the  case  of  lime 
that  has  been  prepared  from  marble,  it  is  advisable  to  do  a  blank 
of  each  batch  after  ignition.  As  these  oxides,  however,  absorb 
CO2  from  the  air,  their  use  has  lately  been  discarded  in  favor  of 
A12O3,  which,  after  ignition  in  the  muffle,  gives  no  blank,  nor  does 

*  For  these  very  refractory  alloys,  however,  the  use  of  Bi,O3  or  Pb3O4, 
as  recommended  by  BREARLEY  (Chem.  News,  LXXXIV,  23),  is  to  be  preferred 
as  being  quicker  and  more  certain  of  giving  the  full  carbon  contents. 


§  256.]  IRON    COMPOUNDS.  553 

it  absorb  C02;  on  this  account  it  is  preferable  to  either  of  the 
other  two,  and  is  now  regularly  used  by  the  author  as  a  standard 
reagent. 

The  combustion  tube  (porcelain,  26"XlJ")  is  covered  with 
asbestos  cloth  or  mill-board.  It  is  packed  as  usual  with  a  few  inches 
of  copper  oxide,  and  the  cooler  exit  portion  with  granular  fused 
lead  chromate  to  absorb  sulphur  compounds — the  CuO  and  PbCrO4 
being  separated  by  a  large  asbestos  plug. 

The  test  analyses  by  the  author  are  very  satisfactory. 

Regarding  methods  of  determining  carbon  in  cast  iron  by 
combustion  in  oxygen,  see  pp.  515  and  216  this  volume. — TRANS- 
LATOR.] 

2.  DETERMINING   THE   OTHER   CONSTITUENTS. 

In  regard  to  these  I  need  but  add  to  what  has  already  been 
stated  in  §  255,  that  because  of  the  small  quantities  of  these  present 
as  compared  with  the  other  elements,  the  quantity  of  iron  to  be 
taken  for  the  analysis  must  be  proportionately  increased. 

C.  PYRITES. 
§256. 

Pyrites,  which  is  now  almost  exclusively  used  for  the  prepara- 
tion of  sulphuric  acid,  is  in  consequence  very  frequently  the  subject 
of  chemical  analyses,  more  particularly  since  the  small  percentage 
of  copper  and  small  quantities  of  silver  and  gold  present  may  be 
advantageously  extracted  from  the  roasted  pyrites.  In  the  analyses 
of  pyrites  the  following  constituents,  as  a  rule,  have  to  be  con- 
sidered: Sulphur,  selenium,  sulphuric  acid,  iron  as  sulphide 
(mostly  as  FeS2),  and  at  times  also  as  ferric  or  ferrous  oxide 
copper,  zinc,  lead,  bismuth,  thallium,  cobalt,  nickel,  arsenic,  anti- 
mony, calcium,  magnesium,  carbon  dioxide,  the  portion  insoluble, 
in  acids  (gangue)  containing  occasionally  barium  sulphate  and 
carbon,  and  the  chemically  combined  water.  In  certain  pyrites 
particularly  the  Spanish,  there  are  present  also  traces  of  gold  and 
silver.  As  a  rule,  even  in  complete  analyses,  only  those  constitu- 
ents printed  in  italics  are  quantitatively  determined. 


554  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  256. 

I.    COMPLETE   ANALYSIS. 

Dry  the  very  finely  powdered  mineral  at  100°. 

1.  Determining  the  Sulphur,  Sulphuric  Acid,  and  Arsenic;  and 
testing  for  Antimony. 

Very  intimately  mix  in  a  capacious  platinum  crucible  about  1 
grm.  of  the  powdered  pyrites  with  10  grm.  of  an  intimate  mixture 
of  2  parts  pure  potassium  carbonate  and  1  part  pure  potassium 
nitrate;  cover  the  whole  with  a  layer  of  the  last-named  mixture, 
heat  gradually  over  a  BERZELIUS  alcohol-lamp,*  to  fusion,  and 
maintain  therein  for  some  time;  then  allow  to  cool,  introduce  the 
crucible  with  its  contents  into  a  beaker,  add  water,  and  heat  until 
all  soluble  matters  are  dissolved.  If  the  pyrites  contain  lead,  pass 
in  carbon  dioxide  to  precipitate  the  small  quantity  of  lead  held  in 
solution  by  the  caustic  potassa;  then  filter  the  solution  into  a 
500-c.c.  flask,  boil  the  residue  with  a  solution,  of  pure  potassium 
carbonate,  filter,  wash  with  boiling  water  to  which  a  little 
potassium  carbonate  has  been  added,  and  until  the  washings 
cease  to  react  for  sulphuric  acid.  Now  allow  to  cool,  fill  up  to  the 
mark,  and  mix  by  agitation. 

a.  To  250  c.c.  of  the  alkaline  liquid  in  a  large  flask  add  30  c.c. 
pure  concentrated  hydrochloric  acid  of  sp.  gr.  1  •  15,  warm  the 
strongly  acid  solution  until  all  the  carbon  dioxide  has  been  ex- 
pelled, evaporate  to  dryness  in  a  porcelain  dish,  add  5  c.c. 
concentrated  hydrochloric  acid,  evaporate  again,  and  in  this 
manner  free  it  from  all  nitric  acid.  Moisten  the  residue  with  two 
drops  concentrated  hydrochloric  acid,  add  some  water,  heat,  filter, 
and  precipitate  the  hot  solution  with  a  moderate  excess  of  hot 
barium-chloride  solution.  After  settling,  collect  the  precipitate, 
wash  it  very  thoroughly  with  boiling  water,  incinerate  the  filter, 
add  the  precipitate  to  the  ash,  ignite,  and  weigh.  Moisten  the 
residue  in  the  platinum  crucible  now  with  hydrochloric  acid,  add 

*  If  illuminating  gas  containing  sulphur  is  employed,  the  quantity  of 
sulphuric  acid  in  the  melt  may  be  hereby  increased,  and  give  rise  to  erro- 
neous results  (PRICE,  Zeitschr.  /.  analyt.  Chem.,  in,  483). 


§  256.]  IRON   COMPOUNDS.  555 

water,  heat,  pass  through  a  small  filter,  repeating  this  operation 
thrice;  then  evaporate  the  filtrate  (with  a  few  drops  of  barium- 
chloride  solution  added)  almost  to  dryness  on  a  water-bath,  take 
up  with  water,  filter  through  the  small  filter,  wash,  incinerate  the 
filter  in  a  platinum  spiral  over  the  platinum  crucible  containing 
the  bulk  of  the  barium  sulphate  which  has  hi  the  meantime  been 
dried,  and  then  ignite  and  weigh.  The  weight  thus  obtained 
differs,  as  a  rule,  only  by  a  few  mgm.  from  that  first  obtained, 
and  is  to  be  regarded  as  the  correct  one. 

If  the  mixture  of  the  potassium  nitrate  and  carbonate,  the 
potassium-carbonate  solution,  or  the  hydrochloric  acid,  is  not  per- 
fectly free  from  sulphuric  acid,  the  small  quantity  of  the  acid 
present  must  be  determined  in  the  reagent,  and  the  operations  car- 
ried out  with  weighed  or  measured  quantities.  Before  calculating 
the  sulphur  deduct  the  small  quantity  of  barium  sulphate  cor- 
responding with  the  sulphuric  acid  in  the  reagent  from  the  total 
barium  sulphate. 

This  method  of  determination  of  course  gives  the  total  sulphur 
in  the  pyrites.  In  order  to  determine  the  sulphur  combined  with 
the  heavy  metals,  the  sulphur  existing  as  sulphates,  if  such  are  present 
in  the  pyrites,  must  be  deducted  from  the  total  sulphur.  If  only 
barium  sulphate  is  present,  the  quantity  of  this  may  be  ascertained 
from  the  barium  content  of  the  ignition  residue,  the  determination 
being  made  by  dissolving  in  hydrochloric  acid  the  portion  of  the 
residue  insoluble  in  water,  neutralizing  any  too  great  excess  of  acid 
with  ammonia,  and  precipitating  the  barium  from  the  now  mod- 
erately acid  solution  with  sulphuric  acid  (Vol.  I,  p.  263).  The 
barium  sulphate  so  obtained  contains  a  little  iron;  if  the  quantity 
of  this  is  large  it  must,  in  order  to  obtain  accurate  results,  be  fused 
with  sodium  carbonate,  and  the  melt  treated  with  boiling  water. 
"The  operator  may  now  choose  between  determining  the  iron  in 
the  residue,  or  the  sulphuric  acid  in  the  solution. 

If  other  sulphates  (of  calcium,  ferrous  iron,  etc.)  are  present, 
determine  their  sulphuric-acid  content  by  repeatedly  boiling  a 
larger  sample  of  the  pyrites  with  dilute  hydrochloric  acid  in  a 
current  of  carbon  dioxide,  and  after  neutralizing  the  greater  part 


556  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  256. 

of  the  excess  of  acid  with  ammonia,  precipitating  with  barium 
chloride  (Vol.  I,  p.  434). 

b.  Evaporate  the  remaining  250  c.c.  with  pure  sulphuric  acid 
on  the  water-bath  until  all  the  nitric  acid  has  been  driven  off,  take 
up  the  residue  with  water  acidulated  with  hydrochloric  acid,  and 
pass  a  large  excess  of  hydrogen  sulphide  for  a  long  time  into  the 
solution  maintained  first  at  70°,  and  then  after  the  liquid  has  cooled. 
If  a  precipitate  forms,  allow  it  to  settle  in  a  moderately  warm 
place,  then  collect  it  on  a  small  filter  dried  at  110°  and  weighed, 
wash  (best  with  the  aid  of  the  water-pump)  by  filling  up  the  filter 
eight  times  with  alcohol,  four  times  with  carbon  disulphide,  and 
lastly  thrice  with  alcohol.  After  drying  at  110°,  weigh,  and 
calculate  the  precipitate  as  arsenic  pentasulphide  (BUNSEN*). 
After  weighing,  it  may  be  tested  for  antimony,  which,  as  a  rule, 
is  not  present  at  all,  or  is  so  in  unweighable  quantity.  If  it  is 
nevertheless  to  be  determined,  the  method  recommended  by 
BUNSEN  (loc.  cit.)  may  be  employed.  Dissolve  the  still  moist 
sulphide  on  the  filter,  and  before  the  treatment  with  alcohol  and 
carbon  disulphide,  in  an  excess  of  a  solution  of  pure  potassium  hy- 
droxide (purified  by  alcohol) ;  into  the  solution,  mixed  with  the 
concentrated  washings,  pass  in  chlorine  until  all  the  alkali  is  de- 
composed. Now  heat  in  the  water-bath,  gradually  add  a  large 
excess  of  concentrated  hydrochloric  acid,  carefully  avoiding  any 
loss  from  spirting,  evaporate  the  fluid  to  one-half,  replace  the 
evaporated  portion  by  an  equal  volume  of  concentrated  hydro- 
chloric acid,  and  again  evaporate  to  one-half  or  one-third,  in 
order  to  expel  all  free  chlorine.  Now  mix  with  very  dilute  hydro- 
chloric acid,  add  freshly  prepared,  saturated  hydrogen-sulphide 
water  (100  c.c.  for  each  0-1  grm.  or  less  of  the  expected  antimonic 
acid),  wait  a  short  time  until  the  precipitate  of  antimony  penta- 
sulphide has  entirely  settled,  and  then  blow  through  the  liquid  a 
strong  current  of  air,  filtered  through  cotton  and  propelled  by 
the  blowpipe  bellows,  in  order  to  remove  the  excess  of  hydrogen 
sulphide,  keeping  the  beaker  covered  meanwhile  with  a  perforated 

*  Annal.  d.  Chem.,  cxcu,  305;  Zeitschr.  /.  analyt.  Chem.,  xvni,  266. 


§  256.]  IRON  COMPOUNDS.  557 

watch-glass.  After  fifteen  or  twenty  minutes  transfer  the  pre- 
cipitate to  a  weighed  filter,  wash  with  alcohol  and  carbon  disulphide 
as  above  detailed  for  arsenic  sulphide,  dry  at  110°,  and  weigh 
the  antimony  pentasulphide.  Heat  the  arsenical  filtrate  on  the 
water-bath  after  adding  a  few  drops  chlorine  water,  and  in  it  deter- 
mine the  arsenic  as  above  described.  If  an  absolutely  complete 
separation  of  the  metals  is  to  be  effected,  dissolve  the  antimony 
sulphide,  before  washing  with  alcohol  and  carbon  disulphide,  in 
potassa  solution,  and  repeat  the  separation  in  the  manner  detailed. 
If  the  arsenic  alone  is  to  be  determined,  the  alkaline  solution 
of  the  fused  mass  may  be  treated  as  follows,  according  to  F.  MUCK:  * 
Acidulate  the  solution,  and  add  sufficient  ferric-chloride  solution 
to  yield  with  ammonia  a  reddish-brown  precipitate,  i.e.  one  con- 
taining an  excess  of  ferric  oxide,  but  avoid  any  too  great  an  excess 
by  adding  ammonia.  Now  heat  until  the  precipitate  has  settled, 
filter,  wash,  dissolve  in  hydrochloric  acid,  reduce  the  sulphurous 
acid,  and  boil  off  the  excess  of  the  latter;  then  precipitate  with 
hydrogen  sulphide,  oxidize  the  arsenic  sulphide  with  fuming 
nitric  acid,  concentrate  strongly,  and  precipitate  the  arsenic  acid 
with  magnesia  mixture,  etc.  (Vol.  I,  p.  412). 

2.  Determining  the   Iron,  Copper,  Lead,  Zinc,   etc.,   as  well  as  the 
Residue  insoluble  in  Acid. 

Digest  2  or  3  grm.  of  the  very  finely  powdered  pyrites  with 
nitro-hydrochloric  acid  until  completely  decomposed  and  all  the 
sulphur  is  dissolved,  then  repeatedly  evaporate  with  hydrochloric 
acid  to  remove  the  nitric  acid,  add  water,  and  pass  through  a  filter 
dried  at  100°  and  weighed;  now  wash  the  insoluble  residue  by  fil- 
tration and  decantation,  exhaust  it,  if  it  contains  lead  sulphate, 
by  repeated  boiling  with  a  solution  of  ammonium  acetate,  and 
wash.  Now  dry  the  filter  with  its  contents  at  100°,  weigh,  incin- 
erate the  filter,  and  weigh  again.  The  difference  in  weight  between 
the  dried  and  ignited  residue  gives  the  water  in  combination  in 
the  residue,  and,  if  the  latter  is  blackish,  also  the  carbon  content. 

*  Zeitschr.  f.  analyt.  Chem.,  v,  312. 


558  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  256. 

If  barium  sulphate  has  been  found  in  1,  deduct  its  weight  from 
that  of  the  ignited  residue,  and  calculate  the  difference  as  gangue, 
if  there  is  no  special  reason  to  subject  the  residue  to  further  analy- 
sis. If  the  residue  contains  lead,  precipitate  this  from  the  am- 
monium-acetate solution  with  hydrogen  sulphide,  dissolve  the 
lead  sulphide  obtained,  after  washing,  in  nitric  acid,  and  deter- 
mine the  lead  as  sulphate  (Vol.  I,  p.  355).  The  hydrochloric-acid 
solution  treat  with  hydrogen  sulphide  at  70°,  filter,  exhaust  the 
precipitate  with  warm  sodium-sulphide  solution,  then  dissolve 
in  nitric  acid,  and  separate  any  lead  that  may  be  present  by  evapo- 
rating with  sulphuric  acid;  then  add  first  ammonia  until  nearly 
neutral,  next  a  sufficient  excess  of  ammonium  carbonate,  warm, 
filter  if  necessary  (a  precipitate  may  contain  bismuth),  acidulate, 
precipitate  with  hydrogen  sulphide,  and  determine  the  copper  as 
sulphide  (Vol.  I,  p.  375). 

Concentrate  the  filtrate  from  the  hydrogen-sulphide  precipitate, 
oxidize  by  heating  with  nitric  acid,  and  separate  the  iron  as  on  pp. 
475  and  476  this  volume.  The  filtrate  acidulate  with  acetic  acid, 
and  add  ammonia  in  slight  excess.  If  a  slight  precipitate  of 
ferric  hydroxide  is  formed  thereby,  and  perhaps  also  of  aluminium 
hydroxide,  filter  this  off,  dissolve  it  in  hydrochloric  acid,  repre- 
cipitate  with  ammonia,  acidulate  the  ammoniacal  liquid  with 
acetic  acid,  add  ammonium  acetate,  and  precipitate  with  hydrogen 
sulphide  at  70°.  Any  precipitate  formed  is  zinc  sulphide,  fre- 
quently with  some  cobalt  and  nickel  sulphides.  The  precipitate  is 
best  weighed  in  this  state  (Vol.  I,  p.  289,  2) ;  determine  the  small 
quantities  of  cobalt  and  nickel  sulphides  in  the  not  quite  pure  zinc, 
which  may  in  this  case  be  done  with  sufficient  accuracy  by  treat- 
ing with  dilute  hydrochloric  acid  and  determining  the  small  quan- 
tity of  insoluble  residue. 

In  the  filtrate  from  the  zinc  sulphide  separate  the  manganese  by 
means  of  ammonia  and  ammonium  sulphide.  Evaporate  the  fil- 
trate finally  to  dryness,  ignite,  and  determine  in  any  residue  the 
calcium  and  magnesium,  if  these  are  present. 

The  precipitate  containing  the  ferric  oxide,  or  the  united  pre- 
cipitates in  which  alumina  may  also  be  present,  dissolve  in  hydro- 


§  256.]  IRON    COMPOUNDS.  559 

chloric  acid,  make  up  the  solution  to  500  c.c.,  and  in  100  c.c.  deter- 
mine the  iron  and  alumina  by  precipitation  with  ammonia,  and 
in  another  100  c.c.  or  200  c.c.  determine  the  iron  volumetrically 
with  stannous  chloride  (Vol.  I,  p.  327),  or  gravimetrically  accord- 
ing to  Vol.  I,  p.  642,  2. 

3.  Determination  of  any  Carbon  Dioxide  Present. 

This  is  effected  by  heating  a  suitable  quantity  of  the  finely  com- 
minuted pyrites  with  very  dilute  hydrochloric  acid,  passing  the 
evolved  gas  first  through  calcium-chloride  tubes,  then  through  tubes 
containing  pumice-copper  sulphate,  and  finally  through  weighed 
soda-lime  tubes.  The  increase  in  weight  of  the  latter  gives  the 
quantity  of  carbon  dioxide  evolved.  Regarding  the  procedure,  see 
p.  365,  d,  this  volume. 

4.  Determination  of  any  Oxygen  Compounds  of  Iron  that 
may  be  Present. 

If  the  pyrites  yields  any  ferrous  sulphate  to  water,  or  ferric  or 
ferrous  oxide  to  cold,  dilute  hydrochloric  acid,  without  hydrogen 
sulphide  being  simultaneously  evolved,  the  oxygen  compounds  of 
iron  may  be  directly  determined  in  the  solution  obtained  (Vol.  I, 
pp.  311  and  322) ;  if  this  is  not  the  case,  however,  the  direct  deter- 
mination of  the  oxygen  compounds  of  iron  must  be  abandoned, 
and  their  determination  made  by  calculation. 

5.  Testing  for  Gold  and  Silver. 

Roast  a  large  quantity  (say  about  500  grm.)  of  the  pyrites, 
best  in  a  muffle,  but  lacking  this,  in  an  inclined,  open,  Hessian  cru- 
cible, until  sulphurous  acid  is  no  longer  evolved;  heat  toward  the 
last  to  bright  redness,  powder  the  residue,  exhaust  next  with  hot 
water,  and  test  the  aqueous  extract,  by  adding  a  few  drops  hydro- 
chloric acid,  whether  it  contains  any  silver.  Collect  any  slight  pre- 
cipitate of  silver  chloride  that  may  have  settled  after  some  time 
(Precipitate  No.  I).  The  residue  left  after  exhausting  with  water 


560  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  256. 

digest  with  bromine  water*  for  a  long  time  in  the  dark,  filter  with 
exclusion  of  sunlight,  add  a  few  drops  hydrochloric  acid,  and 
evaporate  until  all  free  bromine  has  been  expelled  and  the  fluid 
measures  about  200  c.c.  To  the  liquid,  frequently  green  from 
the  presence  of  copper  salts,  add  a  clear  sulution  of  ferrous  sul- 
phate, warm,  and  into  the  warm  liquid  pass  hydrogen  sulphide, 
and  allow  to  stand  for  at  least'  24  hours  to  settle.  Collect  the 
precipitate  on  a  filter,  wash,  and  dry  (Precipitate  II).  The  residue 
extracted  with  bromine  water  heat  on  a  water-bath  for  a  long 
time  with  a  concentrated  ammonium-chloride  solution  in  order  to 
dissolve  any  silver  bromide  present.  Filter  hot  into  a  flask,  wash 
with  hot  ammonium-chloride  solution,  add  first  a  few  drops  mer- 
curic-chloride solution,!  then  some  ammonia  until  the  liquid  is 
distinctly  alkaline,  and  lastly  ammonium  sulphide  in  excess. 

Stopper  the  flask  loosely,  set  aside  in  a  warm  place  until  the  pre- 
cipitate has  completely  settled,  then  collect  it  on  a  filter,  wash, 
and  dry  (Precipitate  III). 

Heat  the  precipitates  I,  II,  III  under  a  good  draught  until 
the  filters  are  consumed  and  the  mercuric  sulphide  has  volatilized. 
Then  triturate  the  residue,  which  contains  the  whole  of  the  gold 
and  silver  that  was  present  in  the  roasted  pyrites,  with  some  anhy- 
drous borax,  transfer  the  whole  to  a  scorifier,  add  the  necessary 
quantity  of  pure  lead,  and  proceed  as  described  on  p.  579  this  vol- 
ume. After  weighing  the  gold  and  silver  button  obtained  by 
cupellation,  determine  the  gold  according  to  Vol.  I,  p.  703  [169]. 
The  silver  present  is  found  from  the  difference. 

6.  Testing  for  Thallium. 

Any  thallium  in  pyrites  may  be  often  detected  by  placing 
some  of  the  powdered  mineral  on  the  moistened  end  of  a  platinum 
wire  and  holding  it  in  the  flame  of  the  spectroscope.  The  charac- 

*  The  application  of  bromine  water  or  tincture  of  iodine  for  the  extrac- 
tion of  gold,  instead  of  the  chlorine  water  formerly  employed,  was  first  re- 
commended by  SKEY  (Chem.  News,  xxn,  245;  Zeitschr.  f.  analyt.  Chem.,  x, 
221). 

f  The  addition  of  the  mercuric  chloride  is  made  for  the  purpose  of  facili- 
tating the  deposition  of  the  usually  very  slight  precipitate  of  silver  sulphide. 


§  256.]  IRON   COMPOUNDS.  561 

teristic,  intensely  green  thallium  line  coincident  with  Ba  d  flashes 
out  transiently.  On  heating  finely  powdered  pyrites  containing 
thallium  to  bright  redness  in  a  tube  with  as  complete  exclusion 
of  air  as  possible,  thalh'um  sulphide  sublimes  along  with  the  sul- 
phur; if  the  sublimate  is  burned  away  in  the  loop  of  a  platinum 
wire,  and  the  residue  then  spectroscopically  examined,  the  green 
line  appears  very  distinctly. 

Thallium  may  be  detected  in  the  wet  way  with  the  greatest 
delicacy,  according  to  CROOKES  and  BOTTGER.  Dissolve  the 
powdered  pyrites  in  hydrochloric  acid  with  the  addition  of  the 
least  possible  necessary  quantity  of  nitric  acid  boil  with  sodium 
sulphite  until  the  ferric  oxide  is  reduced,  and  to  the  filtrate  add 
one  or  two  drops  potassium-iodide  solution.  If  thallium  is  present, 
a  light-yellow  precipitate  of  thallium  iodide  forms.  I  would  advise 
to  test  this  spectroscopically  for  the  sake  of  certainty. 

I!.  DETERMINATION  OF  SULPHUR  ONLY. 

1.  The  Dry  Method,  in  which  the  Sulphur  is  weigfied  as 
Barium  Sulphate. 

Although  this  method  has  already  been  minutely  and  completely 
described  in  A,  1,  reference  is  again  made  to  it  here  in  order  to 
remark  that  in  determining  the  sulphur  alone,  it  is  best  to  mix 
about  0-5  grm.  of  the  pyrites,  dried  at  100°,  with  10  parts  of  a 
mixture  of  2  parts  dry  sodium  carbonate*  and  1  part  potassium 
nitrate,  cover  the  whole  with  a  layer  of  the  latter  mixture,  and  to 
make  use  of  a  solution  of  pure  sodium  carbonate  with  which  to 
boil  the  residue  insoluble  in  water  in  order  to  extract  it.  In  other 
respects,  the  method  is  conducted  exactly  as  above  detailed;  the 
operator  must  never  neglect,  however,  to  test  his  reagents  for  the 
presence  of  sulphuric  acid,  and  to  deduct  the  sulphur  present  in 
the  pyrites  in  the  form  of  sulphates  from  the  total  sulphur  ob- 
tained, when  it  is  intended  to  ascertain  the  quantity  of  sulphur 
combined  with  the  heavy  metals. 

*  Sodium  carbonate  may  be  used  here  instead  of  potassium  carbonate 
because  antimony  need  not  be  considered. 


562  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  256» 

Instead  of  the  mixture  of  potassium  nitrate  and  sodium  car- 
bonate, B.  DEUTECOM*  recommends  a  mixture  containing  potas- 
sium chlorate.  He  heats  1  grm.  of  the  pyrites  with  8  grm.  of  a 
mixture  of  equal  parts  potassium  chlorate,  sodium  carbonate, 
and  sodium  chloride,  in  a  large,  covered,  porcelain  crucible,  at 
first  slowly  until  perfectly  dried,  and  then  strongly  until  homo- 
geneously fused.  When  cold  the  mass  is  treated  with  boiling 
water,  then  transferred  together  with  the  precipitate  into  a  flask, 
allowed  to  settle,  and  the  sulphuric  acid  determined  in  an  aliquot. 
part  of  the  clear  solution.  FR.  BocKMANNf  recommends  some- 
what different  proportions,  namely,  .0-5  grm.  pyrites  (or  2  grm. 
roasted  pyrites)  and  25  grm.  of  a  mixture  of  6  parts  sodium  car- 
bonate and  1  part  potassium  chlorate. 

2.  Wet  Methods,  in  which  the  Sulphur  is  weighed  as 
Barium  Sulphate. 

These  methods  consist  in  treating  the  powdered  pyrites  with 
nitrohydrochloric  acid,  or  with  hydrochloric  or  nitric  acid  with 
the  addition  of  potassium  chlorate,  or  with  similar  oxidizing 
solvents,  so  that  all  the  sulphur  combined  with  metal  is  converted 
into  sulphuric  acid,  which  is  then  precipitated  with  barium  chlo- 
ride from  the  solution  containing  the  iron  as  ferric  chloride  or 
other  ferric  salt.  In  the  Zeitschr.  f.  analyt.  Chem.,  xix,  53,  I 
published  an  exhaustive  critique  regarding  these  methods,  and 
showed  that  they  contain  two  sources  of  error,  yielding  on  the  one 
hand  more  or  less  red  barium  sulphate  containing  ferric  oxide; 
while  on  the  other  hand  the  barium  sulphate  is  not  completely 
precipitated,  because  some  of  it  remains  dissolved  in  the  acid 
liquid  containing  ferric  chloride.  These  two  sources  of  error 
counterbalance  each  other,  however,  to  some  extent,  and  more 
or  less  completely. 

In  general,  the  following  may  be  stated  regarding  this:  An 
increased  proportion  of  free  hydrochloric  acid  and  rapid  filtration 
increase  the  quantity  of  barium  sulphate  remaining  in  solution 

*  Zeitschr.  f.  analyt.  Chem.,  xix,  313. 
t  Ibid.,  xxi,  Heft  2. 


§  256.]  IRON   COMPOUNDS.  563 

and  lessen  its  iron  content,  whereas  a  much  smaller  proportion 
of  free  acid  and  filtering  after  standing  for  some  time,  lessen  the 
quantity  of  barium  sulphate  remaining  in  solution  but  increase 
the  iron  content.  A  suitable  and  equal  dilution  of  the  liquid  to 
be  precipitated  is  here  presupposed.  As  a  rule  the  results  obtained 
in  this  way  are  too  low. 

In  consequence  of  my  critique,  LUNGE  *  has  somewhat  modi- 
fied the  procedure  of  the  method  in  the  wet  way  previously  rec- 
ommended by  him,t  and  according  to  him  the  best  method  of 
determining  the  sulphur  in  the  wet  way  now  is  as  follows: 

a.  When  Economy  of  Time  is  of  More  Importance  than 
Absolute  Accuracy. 

Place  about  0-5  grm.  of  the  very  finely  powdered  and  bolted 
mineral  in  an  ERLENMEYER  flask  or  in  a  capacious  beaker,  the 
former  being  covered  with  a  funnel,  the  latter  with  a  watch-glass, 
and  pour  over  it  50  parts  of  nitrohydro  chloric  acid  (prepared  from 
1  part  fuming  hydrochloric  acid  and  3  to  4  parts  nitric  acid  of  sp.  gr. 
1-36  to  1-40).  If  the  reaction  does  not  set  in  at  once,  gently 
warm  on  the  water-bath  under  a  good  draught,  until  a  brisk  reac- 
tion sets  in,  when  the  vessel  should  at  once  be  removed  from  the 
water-bath.  When  the  reaction  becomes  very  feeble,  replace 
the  vessel  on  the  water-bath.  As  a  rule,  the  decomposition  is 
effected  in  at  most  ten  minutes;  should  it,  however,  be  incomplete 
even  after  long-continued  warming,  add  a  little  more  nitrohydro- 
chloric  acid  and  warm  anew.  If  the  object  is  even  then  not  fully 
accomplished,  or  if  any  sulphur  has  separated,  repeat  the  decom- 
position, using  a  fresh  quantity  of  substance  which  has  been  more 
finely  powdered. 

Now  evaporate  the  whole  to  dryness  with  an  excess  of  hydro- 
chloric acid,  most  safely  on  the  water-bath,  whereby  the  nitric 
acid  is  expelled  and  any  silicic  acid  that  had  become  soluble  is 
again  rendered  insoluble ;  treat  the  residue  once  more  with  some 
hydrochloric  acid,  warm,  and  observe  whether  any  vapors  of 

*  Zeitschr.  f.  analyt.  Chem.,  xix,  421. 

f  LUNGE,  Handbvch  der  Sodaindustrie,  i,  92. 


564  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  256. 

nitrohydrochloric  acid  are  evolved.  If  this  is  the  case,  repeat 
the  evaporation  with  more  hydrochloric  acid  until  the  object  is 
attained.  When  the  hydrochloric  acid  has  been  almost  com- 
pletely expelled  by  evaporation,  add  3  to  4  drops  concentrated 
hydrochloric  acid,  warm,  add  100  c.c.  water,  filter,  heat  to  boiling, 
precipitate  with  a  slight  excess  of  a  boiling  solution  of  barium 
chloride  of  known  strength  (1:10);  then  remove  the  heat,  let 
the  precipitate  settle  for  20  to  30  minutes,  decant  the  supernatant 
liquid  into  a  filter,  and  wash  the  precipitate  four  times  in  suc- 
cession by  decantation  with  boiling  water,  using  100  c.c.  each  time, 
moistening  the  precipitate  in  the  precipitation  glass  with  2  c.c. 
normal  hydrochloric  acid  each  time  before  adding  the  water  (p.  293 
this  volume).  Transfer  the  precipitate  to  the  filter,  wash  out 
thoroughly,  and  proceed  according  to  p.  554,  a,  this  volume.  The 
precipitate  remains  more  or  less  reddish  even  after  purification. 

i 

b.  When  a  High  Degree  of  Accuracy  is  of  More  Importance 
than  Economy  of  Time. 

Effect  the  decomposition  and  evaporation  with  hydrochloric 
acid  as  in  a,  treat  the  residue  with  a  little  hydrochloric  acid,  add 
water,  then  add  to  the  moderately  warm  liquid  ammonia  in  not 
too  great  excess,  filter  after  about  ten  minutes,  thoroughly  wash 
the  ferric  hydroxide  with  boiling  water  until  the  washings  cease 
to  give  a  turbidity  with  barium  chloride,  even  after  standing  a 
short  time.  Very  weakly  acidulate  the  filtrate  and  washings  with 
hydrochloric  acid,  heat  to  boiling,  add  hot  solution  of  barium 
chloride  in  slight  excess,  wash  the  precipitate  first  by  decantation 
several  times,  then  on  the  filter,  and  ignite.  As,  under  these 
circumstances,  no  salts  of  the  fixed  alkalies  are  present,  the  puri- 
fication by  treatment  with  hydrochloric  acid,  etc.,  may  be  more 
readily  effected.  The  results  obtained  with  Method  b,  according 
to  LUNGE'S  experiments,  gave  0-18  per  cent,  more  sulphur  than 
when  Method  a  was  used. 

Of  course  the  methods  in  the  wet  way  require  also  that  the 
reagents  used,  particularly  the  acids,  be  free  from  sulphuric  acid. 
'The  testing  can  be  accurately  carried  out  only  by  completely 


§  256.]  IRON   COMPOUNDS.  565 

evaporating  the  acids,  lastly  on  the  water-bath,  then  putting  a 
little  water  in  the  dish,  and  testing  the  solution  with  barium  chlo- 
ride. 

It  must  be  remarked  that  in  the  methods  by  the  wet  way  any 
barium  sulphate  that  may  be  present  is  practically  completely 
excluded  from  the  sulphur;  calcium  sulphate,  on  the  other  hand, 
goes  partly,  and  if  the  quantity  present  is  not  too  large,  entirely 
into  solution.  The  sulphur  of  the  galena  is  reckoned  in  only  to 
the  very  smallest  extent,  because  the  greater  part  of  the  lead 
sulphate  formed  remains  undissolved. 

3.  Technical    Methods    for    indirectly    (Alkalimetrically) 
determining  the  Sulphur  in  the  Wet  Way. 

a.  PELOUZE'S  Method* 

Mix  1  grm.  of  the  very  finely  powdered  pyrites  with  5  grm. 
(exactly  weighed)  perfectly  pure  anhydrous  sodium  carbonate,t 
add  7  grm.  (approximately  weighed)  potassium  chlorate,  and 
5  grm.t  (approximately  weighed)  fused,  or  at  least  anhydrous 
sodium  chloride,  mix  thoroughly,  and  gradually  heat  the  mixture 
for  eight  to  ten  minutes  to  low  redness  in  a  wrought-iron  spoon. 
When  cold  treat  it  five  or  six  times  with  hot  water,  and  transfer 
the  solution  to  a  filter  by  means  of  a  pipette.  Lastly  boil  the 
residue  with  water,  and  thoroughly  wash  it  on  the  filter  with 
boiling  water.  Then  test  the  filtrate  and  washings  as  to  their 
alkalinity  according  to  §  219  or  §  220. 

The  calculation  of  the  sulphur  content  of  the  pyrites  is  based 
upon  the  following  considerations:  To  neutralize  the  quantity  of 
the  sodium  carbonate  originally  added,  a  certain  quantity  of 
normal  acid  would  have  been  required,  and  to  neutralize  the  liquid 

*  Compt.  rend.,  Lin,  685;  Zeitschr.  f.  analyt.  Chem.,  i,  249. 

f  Should  this  not  be  at  hand,  the  experiment  may  be  made  with  sodium 
carbonate  which  is  not  quite  pure;  but  in  this  case  a  special  test  must  be 
made  to  determine  how  much  normal  acid  corresponds  to  5  grm. 

t  The  quantity  of  sodium  chloride  may  be  varied  according  to  the  nature 
of  the  pyrites,  and  may  be  increased  until  oxidation  takes  place  without 
deflagration. 


566  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  256. 

extracted  from  the  fused  mass  with  hot  water  less  is  naturally 
required,  the  quantity  being  in  fact  smaller  in  proportion  as  the 
quantity  of  sulphur  oxidized  to  sulphuric  acid  is  greater.  Hence 
the  difference  between  the  quantity  of  acid  corresponding  with 
the  quantity  of  sodium  carbonate  employed,  and  that  required  for 
neutralizing  the  liquid  extracted  from  the  fused  mass,  represents 
the  sulphur  in  the  pyrites,  calculating  1  eq.  of  sulphur  for  1  eq.  of 
acid;  1000  c.c.  of  the  standard  acid  prepared  according  to  §  219 
correspond  with  30-224  grm.  sulphur,  while  1000  c.c.  of  the  normal 
acid  prepared  according  to  §  215  correspond  with  16-035  grm. 
sulphur. 

As  a  precaution,  finally  test  a  sample  of  the  insoluble  residue 
left  on  treating  the  fused  mass  with  water,  by  treating  with  hydro- 
chloric acid,  etc.,  to  make  sure  it  contains  no  sulphur. 

The  process  requires  from  30  to  40  minutes  for  its  execution, 
and  gives  results  which,  according  to  PELOUZE,  vary  not  more 
than  1  to  1  •  5  per  cent,  from  the  truth.  Any  loss  of  sodium  car- 
bonate causes  the  sulphur  content  to  be  too  high. 

When  employing  the  method  on  roasted  pyrites,  the  sodium 
chloride  need  not  be  added.  In  this  case  5  grm.  of  the  roasted 
pyrites,  5  grm.  pure  anhydrous  sodium  carbonate,  and  5  grm. 
potassium  chlorate  are  taken. 

The  sulphur  present  in  the  form  of  sulphates  is  determined 
just  as  if  it  were  combined  with  metals. 

The  fact  that  this  method,  which  is  still  used  in  not  a  few  works, 
yields  results  that  are  not  very  reliable  has  been  demonstrated 
by  BARRESWIL,  BOTTOMLEY,  BOCHEROFF,  LUNGE,  and  with  par- 
ticular exhaustiveness  by  J.  KOLB,*  and  the  latter  has  critically 
made  clear  the  causes  of  the  inaccuracy.  The  facts  that,  in  this 
process,  chlorine  is  evolved,  that  sulphuric  acid  may  be  evolved 
from  any  ferric  sulphate  which  has  been  formed  and  not  yet  de- 
composed again,  that  sulphur  chloride  may  be  evolved,  and  also 
that  the  fused  mass  may  at  times  contain  sodium  sulphide,  may 
easily  allow  the  alkalimetric  titre  of  the  fused  mass  to  appear  too 

*  Journ.  de  Pharm.  et  de  Chim.  [iv],  x,  401;  Zeitschr.  /.  analyt.  Chem., 
IX,  407. 


§  257.]  URANIUM  COMPOUNDS.  567 

high,  and  the  sulphur  content,  consequently,  too  low,  while,  on  the 
other  hand,  arsenic,  which  is  converted  into  sodium  arsenate,  and 
silicic  acid,  which  gives  rise  to'  the  formation  of  insoluble  double 
silicates  containing  sodium  at  the  high  temperature  employed, 
makes  the  sulphur  content  too  high. 

These  errors,  which  become  so  much  the  greater  the  less  sul- 
phur the  pyrites  or  burnt  pyrites  contains,  may  be  altogether,  or 
at  least  very  largely,  avoided,  according  to  KOLB,  by  adopting  the 
following  method: 

b.  J.  KOLB'S  Method  (loc.  tit.). 

Mix  about  1  grm.  of  the  pyrites  or  5  to  10  grm.  roasted  pyrites  in 
finely  powdered  form  with  50  grm.  cupric  oxide,  also  finely  pow- 
dered, and  5  grm.  sodium  carbonate,  and  heat.  The  conversion 
of  the  sulphur  into  sodium  sulphate  takes  place,  according  to 
KOLB,  without  fusion  or  disturbance  of  the  mixture,  and  at  a 
sufficiently  low  temperature,  so  that  a  decomposition  of  the  re- 
fractory sulphates,  or  the  action  of  the  silicic  acid  on  sodium 
carbonate,  need  not  be  feared. 

The  calculation  is  made  just  as  in  PELOUZE'S  method.  I 
would  point  out,  however,  that  in  this  method  arsenic  is  deter- 
mined as  its  equivalent  of  sulphur,  and  that  easily  decomposable 
sulphates,  e.g.,  gypsum,  give  rise  to  the  same  error  as  in  PELOUZE'S 
method. 

15.  URANIUM  COMPOUNDS. 
§257. 

For  the  rapid  determination  of  uranium  in  uranium  ores, 
the  following  method,  proposed  by  A.  PATERA,*  is  recommended: 

Dissolve  the  weighed  quantity  of  ore  in  nitric  acid,  avoiding 
so  far  as  possible  an  excess  of  acid.  Dilute  the  acid  solution 
with  water,  supersaturate  with  sodium  carbonate,  heat  to  boiling 
in  order  to  completely  dissolve  the  uranic  oxide  and  to  decom- 
pose any  calcium  bicarbonate,  ferrous  oxide,  etc.,  that  may  have 
formed,  collect  the  precipitate,  and  wash  with  hot  water.  The 

*  DINGLER'S  polyt.  Journ.,  CLXXX,  242;  Zeitschr.  f.  analyt.  Chem.,  v,  228. 


568  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  258. 

filtrate  which,  besides  uranium,  may  also  contain  traces  of  foreign 
metals,  precipitate  with  soda  lye,  and  slightly  wash  and  dry  the 
orange-colored  precipitate  of  acid  sodium  uranate.  Detach  the  dry 
precipitate  from  the  filter,  ignite  in  a  platinum  crucible,  and 
add  to  this  the  ash  of  the  separately  incinerated  filter.  Now 
transfer  the  contents  of  the  crucible  to  a  small  filter,  wash  it,  dry, 
and  ignite.  It  consists  now  of  Na2U207,  100  parts  of  which  ac- 
cording to  PATERA  are  equivalent  to  88-58  parts  uranosouranic 
oxide,  U3O8.  The  results  afforded  by  this  method  are  so  satis- 
factory that  it  is  used  in  Joachimsthal  as  the  recognized  test  in 
the  purchase  of  uranium  ores. 

CL.  WINKLER,*  who  has  frequently  had  occasion  to  test  this 
method,  also  reports  that  it  is  good,  and  that  the  results  afforded 
by  it  agree  so  closely  with  those  obtained  by  other  methods  of 
analysis,  that  it  is  undoubtedly  sufficiently  accurate  for  technical 
purposes.  With  ores  rich  in  copper,  WINKLER  obtained  results 
that  were  somewhat  too  high.  In  this  case  a  small  quantity 
of  the  copper  dissolves  in  the  alkaline  solution,  and,  on  the  sub- 
sequent addition  of  caustic  soda,  is  precipitated  with  the  sodium 
uranate. 

16.  SILVER  COMPOUNDS. 

§258. 

The  silver  compounds  which  are  most  frequently  examined 
in  chemical  laboratories  are  either  ores  containing  silver,  or  silver 
alloys. 

A.  SILVER  ORES. 

Silver  ores  may  be  analyzed  both  in  the  dry  and  the  wet  way. 
If  only  the  silver  content  to  is  be  determined,  particularly  in 
the  case  of  small  quantities  of  silver,  the  dry  methods  are  usually 
the  more  direct  and  certain;  if,  however,  all  the  constituents  are 
to  be  determined,  the  wet  method  must  be  chosen,  under  all  cir- 
cumstances. An  exact  qualitative  analysis  is  first  made,  and 
then  the  individual  metals  are  separated  according  to  the  methods 

*  Zeitschr.  /.  analyt.  Chem.,  vm,  387. 


§  258.]  SILVER   COMPOUNDS.  569 

detailed  in  the  fifth  section  of  the  first  part.  If  the  ore,  on  treat- 
ment with  nitric  acid,  yields  a  solution  containing  all  the  silver, 
begin  with  this  mode  of  treatment;  in  other  cases,  particularly 
in  analyses  of  ores  containing  antimony  and  arsenic  (antimonial 
silver,  brittle  silver  ore,  ruby  silver  ore,  miargyrite,  polybasite,  fahl- 
erz,  etc.),  it  is  preferable  to  heat  the  powdered  ore  in  a  current 
of  chlorine,  and  to  thus  separate  the  volatile  metallic  chlorides 
from  the  non-volatile.  See  Vol.  I,  p.  695  [160]  (where  also  the 
apparatus  to  be  used  is  illustrated  and  described),  Vol.  I,  p.  709 
[180],  and  §  261. 

The  examination  of  the  silver  ores  by  the  dry  way  is  more 
accurately  accomplished  by  subjecting  the  ore  along  with  pure 
lead  to  a  roasting  process,  whereby  the  elements  accompany- 
ing the  silver  in  the  ore  are  either  volatilized  as  oxides  and  acids, 
or  run  into  a  slag  together  with  the  lead  oxide.  When  the  oxida- 
tion has  proceeded  sufficiently  far,  it  is  interrupted,  and  the  un- 
oxidized  lead  containing  all  the  silver  separated  from  the  slag 
and  driven  off  in  a  cupel.  Regarding  the  details  of  the  process 
I  refer  to  §  259  (Determination  of  Silver  in  Galena),  where  the 
details  are  given. 

B.  SILVER  ALLOYS. 

Of  the  silver  alloys  those  of  silver  and  copper  have,  by  far,  the 
most  frequently  to  be  examined.  That  these  may  be  analyzed 
by  the  dry  or  the  wet  way  follows  from  Vol.  I,  p.  341  et  seq.,  and 
p.  698,  11  [164].  This  is  here  again  referred  to  for  the  purpose  of 
adding  VOLHARD'S  volumetric  method,*  which  is  distinguished 
for  its  simplicity  and  also  accuracy,  as  well  as  by  the  fact,  in 
contradistinction  to  GAY-LUSSAC'S  method,  that  it  does  not  pre- 
suppose an  approximate  knowledge  of  the  silver  content  of  the 
alloy.  This  method  was  not  known  at  the  time  the  particular 
section  in  the  first  volume  was  written. 

The  method  is  based  upon  the  precipitation  of  the  silver  as 
silver  sulphocyanate  from  its  nitric-acid  solution,  the  moment 

*  Journ.  f.  prakt.  Ghent.  [N.  F.],  ix,  217;  Annal.  d.  Chem.,  cxc,  1;  Zeitschr. 
/.  analyt.  Chem.,  xiu,  171,  and  xvii,  482. 


570  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  258. 

the  ammonium  or  potassium  sulphocyanate  is  in  excess  being 
ascertained  by  the  iron-sulphocyanate  reaction. 

To  prepare  the  titrating  solution  VOLHARD  employs  ammonium 
sulphocyanate,  while  others,  as  B.  LINDEMANN,*  prefer  potassium 
sulphocyanate.  Both  salts  are  equally  stable  in  dilute  solution. 
The  presence  of  a  small  quantity  of  chlorine  in  the  sulphocyanate 
is  not  prejudicial  in  the  determination  of  silver,  but  a  large  quan- 
tity is  very  decidedly  so,  and  VOLHARD  prefers  the  ammonium 
sulphocyanate  on  the  ground  that  it  is  much  more  readily  ob- 
tained free  from  chlorine  than  is  the  potassium  salt.| 

Dissolve  7-5  to  8  grm.  ammonium  sulphocyanate  (approxi- 
mately weighed)  in  water  to  make  one  litre,  and  then  ascertain  its 
effective  value  by  standardizing  it  against  a  silver  solution  of 
accurately  known  strength.  For  this  purpose  weigh  off  accurately 
10  grm.  chemically  pure  silver,  dissolve  in  160  to  200  c.c.  pure 
nitric  acid  of  sp.  gr.  1  •  2,  expel  all  the  nitrous  acid,  when  solution 
is  complete,  by  prolonged  heating,  allow  to  become  cold,  dilute 
to  one  litre,  and  pipette  off  50  c.c.  (containing  0-5  grm.  silver). 
Dilute  these  50  c.c.  with  about  150  c.c.  water,  and  add  5  c.c.  of 
a  cold  saturated  solution  of  ammonio-ferric  alum;  if  the  color 
of  the  ferric  salt  is  observable,  add  a  little  nitric  acid  until  the 
color  disappears.  Now  run  in  the  sulphocyanate  solution  from 
a  burette.  At  first  only  a  white  precipitate  forms  and  remains 
suspended  in  the  liquid,  and  imparts  to  it  a  milky  appearance. 
On  the  further  addition  of  the  ammonium  sulphocyanate,  the 
drops,  as  they  fall  into  the  liquid,  produce  a  blood-red  cloud  which 
rapidly  disappears  on  shaking.  When  the  point  of  complete 
precipitation  of  the  silver  is  approached,  the  precipitated  silver 
sulphocyanate  collects  in  flocks,  and  the  liquid  begins  to  become 
clear  without,  however,  becoming  perfectly  so,  so  long  as  a  trace 
of  silver  still  remains  in  the  solution.  As  soon,  however,  as  all 

*  Zeitschr.  /.  analyt.  Chem.,  xvi,  352. 

f  As  the  ammonium  sulphocyanate  is  prepared  from  materials  which 
are  nearly  or  altogether  free  from  chlorine,  it,  as  a  rule,  contains  no  chlorine 
compounds,  or  only  minute  quantities,  from  which  it  may  be  easily  freed 
by  a  single  recrystallization  from  boiling  water.  The  commercial  potassium 
sulphocyanate  always  contains  more  chlorine  than  the  ammonium  salt 
(VOLHARD,  loc.  cit.\ 


§  258.]  SILVER  COMPOUNDS.  571 

the  silver  is  precipitated,  the  flocculent  precipitate  subsides;  con- 
tinue to  add  the  sulphocyanate  solution  at  last  drop  by  drop, 
until  the  liquid  becomes  clear,  and  acquires  a  very  pale,  brownish 
tint  which  does  not  disappear  even  on  frequent  shaking.  The 
color  is  best  observed  if  the  liquid  is  held,  not  against  the  light, 
but  away  from  the  window  and  against  a  white  wall.  Repeat 
the  experiment,  and,  if  the  results  correspond,  dilute  the  am- 
monium-sulphocyanate  solution  on  the  basis  of  the  results  ob- 
tained, so  that  50  c.c.  of  it  accurately  correspond  with  50  c.c.  of 
the  silver  solution,  when  1  c.c.  of  the  sulphocyanate  solution  will 
correspond  to  0-01  grm.  silver. 

To  determine  the  silver  in  alloys,  proceed  exactly  as  just  de- 
scribed in  titrating.  If  exactly  1  grm.  of  the  alloy  is  taken,  then 
every  0-1  c.c.  of  the  sulphocyanate  solution  will  indicate  1  per 
1000  of  silver. 

In  using  this  method  the  following  points  must  be  observed: 

1.  Nitrous  acid  must  never  be  present,  either  in  the  solution 
or  in  the  nitric  acid  which  is  subsequently  added.     If,  therefore, 
the  nitric  acid  contains  nitrous  acid,  remove  this  by  boiling,  and 
protect  the  purified  acid  from  exposure  to  bright  light. 

2.  The  action  of  the  sulphocyanate  solution  must  take  place 
in  the  cold,   as,  when  warm,   sulphocyanic  acid    is  decomposed 
by  nitric  acid,  and  the  color  of  the  iron  sulphocyanate  is  destroyed. 

3.  The  solution  of  the  ammonio-ferric  alum  must  always  be 
employed  in  large  excess,  and  in  approximately  the  same  pro- 
portion to  the  total  quantity  of  liquid. 

4.  It  makes  no  difference  on  the  result  whether  the  quantity 
of  free  nitric  acid  present  is  greater  or  less. 

5.  Copper,  if  present,  has  no  disturbing  influence  on  the  result, 
so  long  as  the  alloy  does  not  contain  more  than  70  per  cent,  of 
copper.     In  the  case  of  alloys  containing  more  than  this,  weigh 
off  a  suitable  quantity  of  silver  and  add  it  to  the  sample,  taking 
care  that  the  copper  content  of  sample  weighed  (1  grm.)  does  not 
exceed  0-7  grm. 

6.  Mercury  must  not  be  present.     If  an  alloy  contains  mer- 
cury, this  must  be  first  expelled  by  ignition. 


572  DETERMINATION   OF    COMMERCIAL   VALUES.          [§  258. 

7.  Palladium  makes  the  titration  of  silver  inexact,  as  it  is  indi- 
cated as  silver. 

8.  If  nickel  or  cobalt  is  present,  the  recognition  of  the  end 
of  the  reaction  requires  practice;  otherwise  a  few  drops  too  much 
of  sulphocyanate  may  be  easily  added.     On  carefully  titrating 
back  with  silver  solution,  the  pure  color  of  the  nickel  or  cobalt 
solution  appears   so   suddenly   and  sharply   that    the  end-point 
of  the  reaction  is  easily  observed  on  again  titrating  back,  when 
the  color  of  the  solution  has  become  yellowish  brown  from  the 
admixture  of  the  ferric  sulphocyanate. 

[PisANi's  method*  is  adapted  for  the  determination  of  very 
small  quantities  of  silver.  The  method  is  based  upon  the  fact  that 
on  adding  iodine  to  a  dilute  neutral  solution  of  silver  nitrate  there 
are  formed  silver  iodide  and  silver  hypoiodite  or  iodate,  as  follows  r 

2AgN03+  21+  H20  =  Agl+  AgIO+  2HNO3. 
6AgNO3+  61+  3H2O  =  5AgI+  AgIO3+  6HNO3. 

If  a  solution  of  starch  iodide  is  used  instead  of  iodine  solution, 
the  blue  color  of  the  solution  will  continue  to  disappear  until  all 
the  silver  has  combined  with  the  iodine,  the  quantity  of  iodine 
used  up  being  proportional  to  the  quantity  of  silver  present.  The 
effective  value  of  the  iodine  solution  is  determined  directly  by 
means  of  a  solution  of  known  silver  content. 

The  starch-iodide  solution  is  prepared  by  triturating  2  grm. 
iodine  with  15  grm.  starch  and  6  to  8  drops  of  water,  heating  the 
mixture  in  a  closed  vessel  on  a  water-bath  for  about  one  hour, 
and  then  dissolving  in  water.  To  standardize  this  solution,  add 
to  10  c.c.  of  a  neutral  silver-nitrate  solution  (1  grm.  Ag  per  litre) 
sufficient  pure,  precipitated  calcium  carbonate  to  neutralize  the 
nitric  acid  liberated,  and  run  in  the  blue  iodide  solution  until  the 
mixture  assumes  a  bluish-green  color.  Dilute  the  starch-iodide 
solution  so  that  50  to  60  c.c.  of  it  will  correspond  to  10  c.c.  of  the 
silver  solution.  Very  dilute  silver  solution,  however,  should  be 
concentrated  so  that  from  50  to  100  c.c.  of  the  iodide  solution  may 

*  Annal.  des  Mines,  1856,  83;  Jahresber.  von  LIEBIG  und  KOPP,  1856,  749. 


§  258.]  SILVER  COMPOUNDS.  573 

be  used  up.  There  must  be  no  substances  present  which  will 
decompose  starch  iodide,  e.g.,  reducers,  mercuric  and  mercurous 
salts,  stannous  and  antimonic  salts,  arsenites,  ferrous  and  man- 
ganous  salts,  gold  chloride,  etc.  Lead  and  copper  salts  have 
no  disturbing  influence  on  the  reaction. 

ELECTROLYTIC   DETERMINATION   OF   SILVER. 

CLASSEN  *  states  that  silver  can  be  obtained  as  a  white,  strongly 
adhering  deposit  on  roughened  dishes  by  electrolyzing  a  solution 
containing  1  to  2  c.c.  of  nitric  acid  (sp.  gr.  1-4)  and  5  c.c.  of  alcohol 
at  55°  to  60°,  if  the  potential-difference  between  the  electrodes 
is  carefully  regulated  so  as  to  be  within  the  limits  1  •  35-1  •  38  volts. 
The  time  required  for  precipitation  is  from  6  to  8  hours,  and 
depends  but  little  on  the  amount  of  silver  contained  in  the  solu- 
tion. A  quantity  of  from  0-1  to  0-5  grm.  of  silver  is  convenient, 
but  may  be  as  great  as  2  grm.  The  chief  factor  of  importance 
is  the  potential-difference,  which  must  be  kept  within  the  limits 
specified,  since  an  increase  to  even  1-4  volts  causes  the  silver  to 
separate  in  a  spongy  state,  which  is  useless  for  quantitative  deter- 
mination. 

For  other  electrolytic  methods  of  determination,  as  well  as 
separation  of  silver  from  other  metals,  see  u  Electro-chemical 
Analysis,"  by  EDGAR  F.  SMITH.  P.  BLAKISTON'S  SON  &  Co., 
Philadelphia,  1902;  CLASSEN'S  "Quantitative  Chemical  Analysis 
by  Electrolysis,"  B.  B.  BOLTWOOD.  JOHN  WILEY  &  SONS,  New 
York,  1903;  and  also  "Electrolytic  Determinations  and  Separa- 
tions," LILY  G.  KOLLOCK  (Journ.  Amer.  Chem.  Soc.,  xxi,  No.  10). 
— TRANSLATOR.] 

*  "Ausgewahlte  Methoden,"  p.  3. — CLASSEN'S  "Quantitative  Chemical 
Analysis  by  Electrolysis,"  p.  199.  B.  B.  BOLTWOOD.  JOHN  WILEY  &  SONS, 
NTew  York,  1903. 


574  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  259» 


17.  LEAD  COMPOUNDS. 

§  259. 
A.  GALENA. 

Galena,  the  most  widely  distributed  and  most  important  of 
all  the  lead  ores,  contains,  besides  lead  and  sulphur,  frequently, 
or  occasionally,  smaller  or  larger  quantities  of  zinc,  copper,  anti- 
mony, arsenic,  iron,  silver,  traces  of  gold,  and  usually  more  or 
less  gangue  insoluble  in  acids. 

In  the  following  are  described  (1)  the  determination  of  all  the 
constituents  of  the  galena;  (2)  the  determination  of  the  lead 
alone;  and  (3)  the  dete  mination  of  the  silver  in  galena,  by  the 
dry  way,  and  (4  in  the  wet  way. 

1.    DETERMINATION  OF  ALL  THE  CONSTITUENTS  OF  GALENA. 

a.  Oxidize  a  weighed  quantity  (1  or  2  grm.)  with  very  concen- 
trated, red,  fuming  nitric  acid  free  from  chlorine  and  sulphuric 
acid  (Vol.  I,  p.  567,  a).  For  this  purpose  make  use  of  a  capacious 
flask,  which  is  to  be  kept  covered  with  a  watch-glass  during  the 
operation;  the  small  tube  in  which  the  galena  has  been  weighed 
must  not  be  put  into  the  flask.  If  the  acid  is  sufficiently  strong 
all  the  sulphur  will  be  oxidized.  After  warming  gently  for  some 
time,  rinse  the  contents  of  the  flask  into  a  porcelain  dish,  add  3 
to  4  c.c.  pure,  concentrated  sulphuric  acid  which  has  been  pre- 
viously diluted  wi  h  a  little  water,  and  heat  on  the  water-bath 
until  all  the  nitric  acid  has  been  evaporated  off.  Now  dilute  with 
50  to  60  c.c.  water,  filter,  wash  the  residue  with  water  acidulated 
with  sulphuric  acid,  and  displace  the  latter  by  alcohol.  Collect 
the  alcoholic  washings  separately. 

a.  When  the  residue  is  dry  ignite  it  and  weigh  (Vol.  I,  p.  355,  3). 
It  consists  of  lead  sulphate,  gangue  undecomposed  by  the  acid, 
silicic  acid,  etc.  Heat  the  residue,  or  an  aliquot  portion,  to  boiling 
with  hydrochloric  acid  and  filter  after  some  time,  but  in  such  a 
manner  that  the  precipitate  does  not  come  on  the  filter;  treat  the 
precipitate  with  a  fresh  portion  of  hydrochloric  acid,  boil  again, 


§  259.]  LEAD  COMPOUNDS.  575 

and  repeat  the  operations  until  all  the  lead  sulphate  has  been 
dissolved;  finally  transfer  everything  to  the  filter,  wash  with 
boiling  water  until  every  trace  of  lead  chloride  has  been  removed, 
and  then  dry,  ignite,  and  weigh  the  residue.  Deduct  the  weight 
found  from  that  of  the  original  residue;  the  difference  expresses 
the  quantity  of  lead  sulphate  the  latter  contained.  Instead  of 
using  hydrochloric  acid,  the  lead  sulphate  may  be  dissolved  by 
heating  with  an  aqueous  solution  of  ammonium  tartrate  or  acetate 
to  which  some  ammonia  has  been  added,  or  with  sodium  acetate; 
or  it  may  be  converted  into  lead  carbonate  by  digestion  with  a 
solution  of  sodium  carbonate,  then  washed  and  dissolved  in  di- 
luted nitric  acid.  One  of  the  methods  just  mentioned  must  be 
employed  for  separating  the  lead  sulphate  from  the  gangue  if 
there  is  any  fear  that  the  latter  may  be  attacked  by  hydrochloric 
acid. 

/?.  The  sulphuric-acid  solution  will  contain  no  weighable  trace 
of  lead,  if  the  operation  has  been  properly  carried  out,  but  in  it 
will  be  found  the  metals  which  were  present  in  the  ore  with  the 
lead.  Add  first  some  hydrochloric  acid,  to  test  for  silver.  If  a 
cloudiness  or  precipitate  forms,  set  the  liquid  aside  in  a  warm 
place  for  some  time  until  the  silver  chloride  has  settled,  then  collect 
it  on  a  small  filter,  and  determine  it  according  to  Vol.  I,  p.  338, 
In  the  case  of  very  small  quantities,  I  prefer  to  proceed  as  follows: 
Incinerate  the  filter  with  the  silver  chloride  in  a  porcelain  crucible, 
ignite  the  residue  for  a  short  time  in  a  current  of  hydrogen,  dis- 
solve the  trace  of  metallic  silver  in  nitric  acid,  evaporate  the  solu- 
tion in  a  crucible  to  dryness,  take  up  the  residue  with  water,  and 
in  the  solution  determine  the  silver  by  PISANI'S  method  (Vol.  I, 
p.  349).  As  a  rule,  however,  galena  contains  so  little  silver  that 
an  accurate  determination  of  the  quantity  in  1  or  2  grm.  of  the  ore 
is  impossible,  hence  for  silver  determinations  a  larger  quantity  must 
be  operated  upon,  according  to  §  259,  3  or  4. 

The  clear  liquor,  or  that  filtered  off  from  the  silver  chloride, 
precipitate  with  hydrogen  sulphide;  the  precipitate  contains 
usually  a  little  copper  sulphide  and  antimony  sulphide,  and  at  times 
also  other  sulphides.  Separate  these,  as  well  as  the  metals  in  the 


576  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  259. 

solution  precipitable  by  ammonium  sulphide  (iron,  zinc,  etc.), 
according  to  the  methods  described  in  Section  V  of  the  First  Part. 
Regarding  the  separation  of  antimony  from  arsenic  see  also  pp. 
556  and  557  this  volume. 

b.  To  determine  the  sulphur  take  a  fresh  portion  of  the  finely 
powdered  galena  and  proceed  exactly  as  described  in  Vol.  I,  p. 
562,  1,  b.  Do  not  neglect,  as  there  pointed  out,  to  treat  the  solu- 
tion of  the  fused  mass  with  carbon  dioxide  before  filtering.  If 
a  wet  method  is  preferred,  that  detailed  in  Vol.  I,  p.  568,  b}  is  to 
be  recommended. 

2.  DETERMINATION  OF  LEAD  ALONE  IN  GALENA. 

The  method  of  analyzing  lead  salts  given  by  F.  STOLBA  *,  i.e., 
separation  of  the  lead  by  zinc  in  the  wet  way,  has  also  been  recom- 
mended by  STORER  f  and  MASCAZZINI  J  for  the  determination  of 
lead  in  galena.  Both  weigh  the  separated  lead  as  such,  the  former 
after  drying  in  a  current  of  illuminating-gas,  the  latter  after  fusing 
with  a  reducing  flux.  The  former  brings  the  powdered  galena 
directly  together  with  hydrochloric  acid  and  zinc,  while  the  latter 
first  converts  the  galena  into  lead  sulphate  by  ignition  with  ammo- 
nium sulphate  before  acting  on  it  with  zinc  and  hydrochloric 
acid.  These  methods  do  not,  however,  appear  to  deserve  com- 
mendation, at  least  G.  C.  WITTSTEIN  and  A.  B.  CLARK,  JR.;§  when 
testing  STORER' s  method,  obtained  very  unsatisfactory  results, 
and  FR.  MOHR  ||  in  his  investigations  also  obtained  unsatisfactory 
results  on  weighing  the  separated  lead  after  drying,  or  after  fusing 
with  reducing  fluxes. 

FR.  MOHR  (loc.  cit.)  has,  however,  based  the  following  method 
for  determining  lead  in  galena,  on  the  decomposition  of  the  latter 
by  zinc :  Weigh  off  about  2  grm.  of  the  finely  powdered  ore,  intro- 
duce into  a  small  porcelain  dish  or  casserole,  treat  it  with  ordinary 

*  Journ.  f.  prakt.  Chem.,  ci,  150;  Zeitschr.  /.  analyt,  Chem.,  vn,  102. 
f  Chem.  News.,  xxi,  137;  Zeitschr.  /.  analyt.  Chem.,  ix,  514. 
j  Zeitschr.  f.  analyt.  Chem.,  x,  491. 
§  Ibid.,  xi,  460. 
D  Ibid.,  xii,  143. 


S  259.]  LEAD  COMPOUNDS.  577 

hydrochloric  acid  of  sp.  gr.  1  •  12,  cover  with  a  convex  glass,  and 
heat,  finally  to  boiling.  Hydrogen  sulphide  is  evolved,  and  lead 
chloride  separates.  When  the  acid  ceases  to  act  because  the  unde- 
composed  galena  becomes  covered  with  a  layer  of  lead  chloride, 
and  the  hydrochloric  acid  becomes  saturated  with  lead  chloride, 
drop  in  a  small  ball  of  zinc.  Hydrogen  is  at  once  briskly  evolved, 
and  lead  is  precipitated  on  the  zinc.  On  gently  warming,  fresh 
portions  of  the  lead  chloride  dissolve  and  become  decomposed 
until  finally  no  more  hydrogen  sulphide  is  evolved,  and  the  liquid 
appears  clear  and  colorless.  Decant  the  liquid  then,  and  thor- 
oughly wash  the  lead  with  water;  *  this  may  be  easily  done  by 
simple  decantation.  Dissolve  the  separated  lead  in  dilute  nitric 
.acid,  filter  the  solution  from  the  undissolved  gangue,  concentrate 
;by  evaporation  with  sulphuric  acid,  and  proceed  with  the  deter- 
mination of  lead  according  to  Vol.  I,  p.  355,  a,  /?. 

3.    DETERMINATION    OF  THE    SILVER   IN    GALENA,  AND   TESTING   FOR 
GOLD    IN    THE    DRY    WAY. 

As  already  mentioned,  the  method  described  in  §  259,  1,  does 
not  suffice  to  detect  and  determine  very  small  quantities  of  silver  f 
and  the  very  small  traces  of  gold  which,  according  to  PERCY  and 
SMITH  I  are  frequently  found  in  galena.  To  effect  this,  it  is,  as  a 
rule,  advisable  to  first  obtain  a  button  which  will  contain  all  or  a 
part  of  the  lead  of  the  galena,  but  surely  all  the  gold  and  silver, 
and  to  then  treat  the  button  in  the  dry  way. 

PREPARATION   OF  THE   BUTTON. 

a.  Methods  suitable  for  poor  Argentiferous  Galenas, 
a.  Mix  20  grm.  of  the  finely,  powdered  galena,  60  grm.  anhy- 
drous sodium  carbonate,  and  6  grm.  potassium  nitrate,  introduce 

*  According  to  STOLBA  (Zeitschr.  f.  analyt.  Chem.,  vii,  103)  distilled 
water  is  unsuitable  for  washing  the  spongy  lead,  because,  even  when  pre- 
viously boiled  and  cooled  with  exclusion  of  air,  it  dissolves  a  little  lead. 
He  therefore  recommends  spring-water  for  the  washing. 

f  Argentiferous  galenas  usually  contain  from  0-03  to  0-18  per  cent,  of 
silver,  and  rarely  above  0-5  per  cent.;  very  many  galenas,  however,  contain 
less  silver  than  the  minimum  mentioned. 

J  Phil.  Mag.,  vn,  126;  Journ.  f.  prakt.  Chem.,  LXI,  435. 


578  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  259. 

the  mixture  into  a  Hessian  crucible,  cover  it  with  an  8-mm.  deep 
layer  of  decrepitated  sodium  chloride,  and  fuse,  finally  at  a  bright- 
red  heat,  so  that  the  slag  flows  well.  After  slowly  cooling,  break 
the  crucible,  flatten  the  button,  which  must  be  clean  and  compact, 
on  an  anvil,  and  cleanse  it  by  boiling  with  water.  According  to 
BERTHIER  (and  my  own  investigations)  there  is  thus  obtained 
from  75  to  78  per  cent,  of  lead  from  pure  galena,  instead  of  the 
86  •  6  per  cent,  which  it  contains,  but  all  the  silver  is  found  in  the 
lead.  In  order  to  understand  the  process,  it  must  be  remembered 
that,  on  fusing  galena  with  sodium  carbonate  out  of  contact  with 
air,  there  are  obtained  lead,  and  a  slag  consisting  of  lead  and  sodium 
sulphide  and  sodium  sulphate,  thus:  4Na2CO;j+7PbS  =  4Pb  + 
3(PbS.Na2S)+Na2SO4  +  4CO2.  The  addition  of  the  potassium 
nitrate  serves  to  decompose  the  sulpho-salt,  the  lead  being  sepa- 
rated, and  the  sodium  and  sulphur  oxidized. 

/?.  Mix  20  grm.  of  the  powdered  galena,  40  grm.  black  flux,* 
and  5  or  6  grm.  very  small  iron  nails,  and  fuse  the  mixture  in  a 
Hessian  crucible  at  a  bright  redness.  If  a  refractory  gangue  is 
present,  add  2  to  3  grm.  borax  glass.  The  galena  is  first  decom- 
posed by  the  carbonate  and  the  carbon  with  the  separation  of  lead 
and  the  formation  of  lead  and  potassium  sulphide,  the  latter  being 
then  desulphurized  by  the  iron  at  a  higher  temperature,  when  the 
fused  lead  separates.  After  cooling,  break  the  crucible,  and  pro- 
ceed as  in  a.  Care  must  be  taken  that  the  lead  incloses  no  nails. 
According  to  BERTHIER  this  method  yields  72  to  79  per  cent, 
lead;  from  pure  galena,  however,  85-5  per  cent,  may  be  obtained 
if  the  temperature  is  not  too  high.f 

b.  Method  more  particularly  suitable  for  rich  Argentiferous 
Galenas  (Scorification  j) . 

For  this  process  there  are  required  scorifiers  of  baked  clay, 

*  Prepared  by  deflagrating  1  part  potassium  nitrate  with  2£  parts  potas- 
sium bitartrate. 

f  "  Probirkunst,"  by  KERL,  Leipzig,  A.  FELIX,  1866,  p.  155. 

J  Compare  the  excellent  work  by  BODEMANN,  A  nleitung  zur  Probirkunst, 
edited  by  KERL,  2d  ed.,  CLAUSTHAL,  1857,  p.  287;  also  M etallurgische 
Probirkunst,  by  KERL.  Leipzig,  A.  FELIX,  18fi6,  p.  241;  and  Probirkunst, 
by  C.  A.  M.  BALLING,  Braunschweig,  FR.  VIEWEG  u.  SOHN,  1879,  p.  299. 


§  259.]  LEAD    COMPOUNDS.  579 

Fig.   112,  and  a  properly  constructed  muffle  furnace  with  good 
draught.* 

Mix  4  grm.  of  the  finely  powdered  ore  with  16  grm.  of  silver- 
free  leadf  in  a  scorifier,  and  cover  the  mixture  uniformly  with 
16  grm.  more  of  the  lead.  According  to  the  nature  of  the  im- 
purities present,  there  must  be  added  borax,  quartz,  or  glass. 
Borax  is  added  when  the  galena  contains  much  calcium,  mag- 
nesium, zinc,  etc.,  the  quantity  to  be  added  varying  according  to 
the  quantities  of  the  foreign  bases,  and  amounting  at  times  up  to 
2  •  5  grm.  No  borax  is  added  to  ores  that  contain  quartz  or  silicates, 
or  only  a  little — not  more  than  0-5  grm.  To  ores  which  contain 
little  or  no  silicic  acid,  whether  free  or  combined,  add  a  very  small 
quantity  of  glass  or  quartz. 


FIGO  112. 


FIG.  115. 


FIG.  116.  FIG.  113.  FIG.  114. 

The  above  proportions  between  ore  and  lead  may  be  considered 
as  normal;  if  the  ore,  however,  contains  a  considerable  quantity 
of  zinc  blende  or  pyrites,  48  grm.  or  even  64  grm.  of  lead  are  used 
instead  of  32  grm.,  and  if  copper  or  tin  compounds  are  present, 
even  more  must  be  taken. 

*  The  construction  such  a  furnace  should  have  is  not  detailed  here,  but 
it  is  accurately  described  in  the  above-named  works. 

j-  This  may  be  prepared  in  the  laboratory  most  conveniently  by  pre- 
cipitating lead-acetate  solution  with  zinc. 


580  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  259. 

The  scorifiers,  charged  as  above,  are  placed  into  the  muffle, 
Fig.  116,  previously  heated  to  bright  redness,  and  the  mouth  of 
the  muffle  is  closed  with  live  coal  in  order  to  rapidly  effect  the 
fusion  of  the  lead.  The  lead  melts  while  the  lighter  ore  floats  on 
its  surface  and  is  roasted.  The  character  of  the  vapors  evolved 
during  the  roasting  varies  according  to  the  nature  of  the  prod- 
ucts evolved;  the  fumes  of  sulphur  are  light-gray,  those  of  zinc 
are  dense- white,  those  o  arsenic  grayish- white,  and  those  of 
-antimony  bluish. 

After  15  to  20  minutes  a  fluid  slag  forms,  which  completely 
surrounds  the  fused  metal  at  the  edges,  and  from  which  dense 
fumes  of  lead  arise.  Refractory  samples  require  35  minutes  or 
more  until  this  point  is  reached  and  the  surface  of  the  fused  metal 
has  become  smooth. 

Now  remove  the  live  coal  from  the  mouth  of  the  muffle,  close  the 
damper  of  the  furnace,  and  .allow  the  lead  to  be  oxidized  by  the 
access  of  air  until  the  scoriae  completely  or  nearly  cover  the  metal, 
then  heat  again  very  strongly  for  five  minutes  in  order  to  render 
the  slag  very  fluid.  The  process  of  scorification  requires,  as  a 
rule,  half  an  hour,  or  at  most  one  hour. 

Now  remove  the  samples  from  the  muffles  with  suitable  tongs 
about  three  feet  long,  Fig.  113,  and  pour  the  metal  and  slag  into 
a  mould,  which  may  be  made  of  sheet-iron  or  sheet-copper  with 
hemispherical  depressions  3  to  6  cm.  in  diameter;  the  mould  should 
be  warmed,  and  the  depressions  rubbed  with  reddle  or  chalk. 

The  lead  alloy  obtained  must  form  a  single  button,  which 
must  readily  separate  from  the  slag.  Now  hammer  down  the 
button  so  that  it  may  easily  be  held  with  the  three-foot  tongs 
shown  in  Fig.  114,  and  subsequently  placed  on  the  cupel  without 
projecting  over  the  edge. 

In  the  operation  here  described,  the  ore  is  first  roasted  and 
litharge  produced,  the  latter  decomposing  the  metallic  sulphides 
the  sulphur  being  oxidized  to  sulphurous  acid  and  the  metals 
separating;  the  lead  oxide  formed  in  addition  dissolves  the  earths 
and  foreign  oxides  present  and  removes  them  as  slag. 


§  259.]  LEAD    COMPOUNDS.  581 

Determining   the  Silver  in  the  Argentiferous  Lead  Button. 

The  silver  in  the  lead  button  may  be  determined  either  in  the 
wet  -or  the  dry  way.  In  laboratories  where  suitable  muffle  fur- 
naces are  not  at  hand,  the  determination  is  frequently  made  hi 
the  wet  way  (§  259,  4,  a),  whereas  in  metallurgical  laboratories 
the  dry  way  (cupellation)  is  invariably  used.* 

For  this  operation  there  are  required  small  cups  or  cupels  of 
compressed  bone-ash,  Fig.  115,  which  are  generally  obtainable. 
Although  1  part  of  the  porous  cupel  mass  can  absorb  the  oxide 
from  2  parts  of  lead,  it  is  usual  to  calculate  that  it  takes  up  the 
oxide  from  only  1  part  of  lead ;  hence  the  button  must  not  be  much 
heavier  than  the  cupel.  As  soon  as  half  of  the  bottom  of  the 
muffle,  Fig.  116,  is  at  a  white  heat,  it  is  ready  for  the  cupellation. 
Introduce  the  empty  cupels,  and  gradually  push  them  toward 
the  back  until  they  are  at  a  bright-red  heat;  for  it  is  necessary 
that  the  lead-silver  alloy  now  to  be  introduced  should  rapidly 
melt,  otherwise  small  particles  of  lead  are  prone  to  adhere  to  the 
upper  edge  of  the  cupel.  If  the  furnace  is  very  hot,  the  separation 
soon  begins;  if  not,  place  live  coal  in  the  mouth  of  the  muffle  in 
order  to  more  rapidly  effect  the  separation.  As  soon  as  the  surface 
of  the  lead  is  in  motion,  close  the  damper  of  the  furnace  and  leave 
only  one  small  coal  at  the  mouth  of  the  muffle.  It  must  now  be 
the  object  to  properly  effect  complete  separation  at  the  lowest 
possible  temperature,  for  at  too  high  a  heat  the  cupel  will  absorb 
some  of  the  silver  with  the  litharge.  Too  low  a  temperature 
must  equally  be  avoided,  as  in  this  case  the  lead  will  be  chilled, 
and  even  though  the  heat  is  subsequently  raised  to  the  proper 
point,  the  results  are  not  reliable. 

If  the  cupellation  is  properly  conducted,  the  lead  fumes  slowly 
rise  in  curls  to  the  middle  of  the  muffle,  and  at  the  margin  of  the 
cupel,  now  at  a  reddish-brown  heat,  there  forms  a  ring  of  imperfect 
crystals  of  lead.  If  the  lead  fumes  disappear  just  above  the  cupels 
while  these  are  at  a  bright-red  heat,  and  if  no  crystals  form  at  the 

*  The  description  of  this  interesting  and  important  operation  is  taken 
from  BODEMANN-KERL'S  work  already  mentioned. 


582  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  259. 

edges,  the  heat  is  too  strong.  If  the  lead  fumes,  on  the  other 
hand,  rise  to  the  vault  of  the  muffle,  and  if  the  edges  of  the  cupels 
appear  dark  brown,  the  heat  is  insufficient,  and  the  sample  is 
very  apt  to  solidify. 

Toward  the  end  of  the  cupellation  the  heat  must  again  be 
raised,  as  the  bead  becomes  less  fusible  as  the  proportion  of  silver 
in  it  increases,  and  the  last  portions  of  lead  are  entirely  converted 
into  litharge  and  absorbed  by  the  cupels  only  at  a  higher  tem- 
perature. The  heat  must  not,  however,  be  raised  too  soon,  and 
then  only  gradually,  nor  must  it  be  so  high  as  to  remelt  the  ring 
of  lead  crystals.  At  the  end  of  the  process,  the  residual  net-like 
film  of  litharge  disappears  from  the  surface  of  the  metal,  the  irri- 
descence  ceases  at  the  same  time,  and  the  globule  of  silver  is  sud- 
denly visible  in  all  its  purity — the  assay  flashes.  Allow  to  cool 
slowly  in  order  to  avoid  the  spitting  of  the  silver,  and  which  is 
caused  by  the  violent  escape  of  the  oxygen  absorbed  by  the  fused 
silver.  « 

The  surface  of  the  silver  globule  must  be  silvery  white  and 
perfectly  lustrous,  and  hemispherical  or  round,  and  readily  detach- 
able from  the  cupel  by  aid  of  a  small  pair  of  pincers;  and  the 
surface  which  was  in  contact  with  the  cupel  must  be  clean  and 
silvery  white,  though  not  lustrous,  after  brushing.  Beads  having 
projections  of  any  kind  on  the  lower  surface,  due  to  fissures  or 
depressions  in  the  cupel,  must  be  rejected,  as  these  projections 
always  contain  lead.  After  cleaning,  the  silver  bead  is  weighed. 
If  the  lead  added  was  not  absolutely  free  from  silver  a  correction 
must  be  made,  the  silver  in  the  lead  being  first  determined,  and 
the  quantity  allowed  for. 

After  weighing,  the  silver  bead  may  be  tested  for  the  presence 
of  gold,  and  the  quantity  of  this  determined  if  possible  according 
to  Vol.  I,  p.  703  [169]. 

A  small  quantity  of  silver  is  invariably  lost  in  cupellation. 
From  investigations  made  by  BURBIDGE  HAMBLY  *  it  appears  that 
the  loss  increases  with  the  proportion  of  the  lead  to  the  silver; 
thus  with  1  part  silver  to  1  part  lead  the  loss  of  silver  was  5-5 

*  Chem.  Gazette,  p.  1856,  185;  Chem.  Centralblatt,  1857,  p.  509. 


§  259.]  LEAD  COMPOUNDS.  583 

per  100  parts  of  silver;  with  1  part  silver  to  15  parts  lead  the  loss 
was  16-2;  and  with  1  part  silver  to  35  parts  lead  it  was  18-8  parts 
silver. 

4.    DETERMINING    THE    SILVER   IN   GALENA   IN  THE   WET  WAY. 

a.  Prepare  a  lead  button  containing  the  whole  of  the  silver, 
according  to  §  259,  3,  a,  a  or  3,  purify  it  so  far  as  possible,  dissolve 
in  chlorine-free,  moderately  diluted  nitric  acid,  dilute  the  solution 
largely,  and  add  a  little  very  dilute  hydrochloric  acid  or  solution 
of  lead  chloride.  Set  aside  the  turbid  liquid  in  a  warm  place  until 
the  silver  chloride  has  settled,  then  collect  it,  wash  thoroughly 
with  boiling  water,  and  finally  determine  it  as  metallic  silver 
(p.  575,  /?,  this  volume).  This  method  afforded  me  very  satisfac- 
tory results  in  cases  where  the  quantity  of  silver  present  was  not 
too  small  (Analytical  Supplement,  91),  but  with  exceedingly  small 
quantities  this  method  is  inapplicable  because  very  small  traces  of 
silver  chloride  remain  dissolved  in  the  liquid  containing  much 
lead  nitrate  (HAMPE*).  Regarding  the  concentration  of  silver 
in  lead,  see  p.  589  this  volume. 

6.  Treat  the  nitric-acid  solution  of  the  regulus  according  to 
PISANI'S  method,  p.  349.  Take  care  that  the  sulphuric  acid  used 
for  precipitating  the  lead,  and  the  calcium  carbonate  used  for 
neutralizing  the  acid,  are  both  perfectly  free  from  chlorine  com- 
pounds. I  have  had  no  experience  with  this  method. 

c.  C.  A.  M.  BALLING  f  recommends  the  following  method,  which 
dispenses  with  the  preparation  of  a  regulus:  Mix  2  to  5  grm.  of 
the  finely  powdered  galena  with  3  to  4  times  its  weight  of  a  mix- 
ture of  equal  parts  of  sodium  carbonate  and  potassium  nitrate, 
introduce  the  whole  into  a  porcelain  crucible  of  suitable  size, 
cover,  heat  the  contents  to  fusion,  and  stir  well  with  a  hot 
glass  rod.  When  cold  place  the  crucible  in  a  porcelain  dish,  soften 
the  mass  with  water,  and  empty  the  contents  of  the  crucible  into 
the  porcelain  dish;  then  warm,  filter,  and  wash  the  residue,  trans- 
fer again  to  the  dish,  dissolve  the  lead  oxide  containing  silver  in 
diluted  pure  nitric  acid,  and  evaporate  to  dry  ness ;  now  take  up 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  221.         f  Chem.  CentralbL,  1879,  p.  490. 


584  DETERMINATION    OF   COMMERCIAL    VALUES.          [§  259- 

the  residue  with  water  acidulated  with  a  little  nitric  acid,  warm,, 
filter  the  solution  into  a  flask,  wash  with  hot  water,  allow  to  cool, 
add  ammonio-ferric  alum  solution,  and  titrate  the  silver  accord- 
ing to  VOLHARD'S  method  with  ammonium-sulphocyanate  solu- 
tion (compare  p.  570,  this  volume).  The  ammonium-sulpho- 
cyanate solution  should  be  diluted  so  that  1  c.c.  should  be  equiva- 
lent to  1  c.c.  of  a  solution  containing  1  grm.  metallic  silver  per 
litre.  1  c.c.  of  the  sulphocyanate  solution  will  thus  represent 
1  mgm.  silver.  I  have  had  no  personal  experience  with  this 
method. 

B.  VARIETIES  OF  METALLIC  LEAD. 

The  purity  of  the  metallic  lead  which  has  to  be  examined 
varies  greatly.  In  the  following  paragraphs  are  detailed  the- 
analyses  of  refined  lead  (soft  lead),  crude  lead,  and  hard  lead. 

a.   ANALYSIS   OF   REFINED   LEAD    (SOFT   LEAD). 

This  contains  from  99-96  to  99-99  per  cent,  metallic  lead, 
hence  only  very  minute  quantities  of  other  metals,  such  as  silver, 
copper,  bismuth,  cadmium,  antimony,  arsenic,  iron,  nickel,  cobalt, 
zinc,  and  manganese. 

First  Method* 

1.  Cut  up  the  lead  to  be  analyzed  into  large  pieces,  and  scrape 
the  surfaces  of  each  with  a  bright  knife  until  they  are  perfectly 
clean  and  bright;   then  warm  them  with  dilute  hydrochloric  acid, 
wash  with  hot  water,   and  dry  them  rapidly.     If  this  cleaning 
process  is  omitted,  there  is  danger  that  the  mechanically  adhering 
impurities  may  appreciably  affect  the  accuracy  of  the  results. 

2.  Weigh  off  exactly  200  grm.  of  lead  cleaned  as  in  1,  and  dis- 
solve (in  a  flask  of  1000  to  1500  c.c.  capacity)  in  pure  diluted  nitric 
acid,  of  which  about  500  c.c.  acid  of  sp.  gr.  1-2  are  required,  with 
the  addition  of  enough  water  (about  500  c.c.)  to  prevent  the  separa- 
tion of  any  lead  nitrate.     Solution  is  assisted  by  suitably  warming; 

*  R.  FRESENIUS,  "On  the  Analysis  of  Soft  or  Refined  Lead,"  Zeitschr. 
/.  analyt.  Ghent.,  vm,  148. 


§  259.]  LEAD  COMPOUNDS.  585 

an  unnecessary  excess  of  nitric  acid  must  be  avoided.    Allow  the 
solution  to  stand  for  from  12  to  24  hours. 

As  200  grm.  of  lead  yield  practically  320  grm.  lead  nitrate, 
(Fb[NOJ2),  and  as  the  latter  requires  about  two  parts  of  water 
for  solution,  no  lead  nitrate  will  crystallize  out  if  the  solution  be 
diluted  to  1  litre.  Should  this  nevertheless  be  the  case,  it  is  the 
result  of  using  too  large  an  excess  of  nitric  acid,  as  it  is  well  known 
that  lead  nitrate  is  far  more  insoluble  in  dilute  nitric  acid  than  in 
water. 

3.  As  a  rule  (i.e.,  in  the  case  of  all  pure  soft  leads)  the  solutions 
are  and  remain  clear.     It  is  only  in  the  case  of  leads  which  are 
rather  rich  in  antimony  that  there  forms  a  more  or  less  decided 
quantity  of  a  white  precipitate,  either  immediately  or  on  standing. 
These  less  usual  cases  are  treated  as  under  15;  we  here  presuppose 
that  the  solution  has  remained  clear. 

4.  Transfer  the  solution  completely  to  a  2-litre  flask,  add  115 
grm.  (about  62  to  63  c.c.)  of  perfectly  pure,  concentrated  sulphuric 
acid  (approximately  measured  or  weighed),  allow  to  cool,  fill  up 
to  the  mark,  mix  thoroughly  by  shaking,  and  allow  to  settle.    The 
quantity  of  sulphuric  acid  added  should  be  so  adjusted  that  there 
will  remain  an  excess  of  from  about  10  to  12  grm.    After  the 
precipitated  lead  sulphate  has  subsided,  siphon  off  the  clear,  or 
nearly  clear,  supernatant  fluid  by  means  of  a  siphon  previously 
filled  with  a  small  quantity  of  the  liquid.     In  this  manner  over 
1750  c.c.  of  the  liquid  may  be  easily  siphoned  off.     Of  course  the 
siphoning  may  be  replaced  by  filtration  through  a  dry  filter,  but 
the  method  of  siphoning  deserves  the  preference,  as  it  excludes 
any  impurities.     Measure  off  exactly   1750  c.c.  of  the  clear  or 
nearly  clear  liquid,  and  evaporate  it  under  a  perfectly  clean  draught 
hood,  and  without  covering  the  dish  with  paper,  until  sulphuric- 
acid  vapors  are  freely  evolved — a  sign  that  the  nitric  acid  has 
been  driven  off.     Allow  to  cool,  add  about  60  c.c.  water,  collect 
the  slight  quantity  of  separated  lead  sulphate  on  a  small  filter 
previously  thoroughly  washed  with  hydrochloric  acid  and  water, 
and  then  wash  the  precipitate  with  water. 

5.  The  small  quantity  of  lead  sulphate  so  obtained  frequently 


586  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  259. 

contains  slight  quantities  of  antimony.  Dissolve  it  in  hydro- 
chloric acid,  dilute  with  at  least  ten  times  as  much  hydrogen- 
sulphide  water  as  the  hydrochloric  acid  employed  for  solution, 
heat,  and  treat  with  hydrogen  sulphide.  After  subsidence,  collect 
the  precipitate,  wash,  spread  out  the  filter  in  a  dish,  and  treat  the 
precipitate  for  a  short  time  at  near  the  boiling-point  with  a  solu- 
tion of  pure  potassium  sulphide  or  ammonium  sulphide,  with  the 
addition  of  a  small  quantity  of  pure  sulphur.  Filter  off,  wash, 
acidulate  the  filtrate  with  hydrochloric  acid,  and  allow  the  precipi- 
tate to  subside  at  a  gentle  heat. 

6.  Into  the  sulphuric-acid  solution  obtained  in  4,  and  which, 
if  necessary,  is  diluted  with  water  to  200  c.c.,  pass  hydrogen  sul- 
phide until  the  precipitate  subsides,  keeping  the  temperature  at 
about  70°;  then  allow  to  stand  in  a  warm  place  for  12  hours,  pass 
through  a  small  filter,  and  wash  the  precipitate.     Treat  the  filtrate 
and  washings  according  to  9,  but  the  precipitate  heat  with  potas- 
sium-sulphide solution  with  the  addition  of  a  trace  of  sulphur  as 
in  5.      Acidulate  the  filtrate  containing  potassium   sulphide   with 
hydrochloric  acid,  and  allow  the  precipitate  to  subside  at  a  gentle 
heat. 

7.  The  small  quantity  of  precipitate  insoluble  in  potassium 
sulphide,  and  containing  the  metals  of  the  fifth  group,  treat,  after 
spreading  out  the  filter  in  a  small  dish,  with  diluted  nitric  acid  (about 
1   part  nitric  acid  of  sp.  gr.  1-2  and  2  parts  water)  at  near  the 
boiling-point.     When  the  precipitate  has  dissolved,  filter,  wash 
the  filter,  dry  it,  and  incinerate;   add  the  ashes  to  the  nitric-acid 
solution,  and  evaporate  this  after  adding  2  c.c.  diluted  sulphuric 
acid,  until  all  the  nitric  acid  has  been  driven  off;  then  add  a  little 
water,  filter  off  the  trace  of  lead  sulphate  which  will  have  separated, 
nearly  neutralize  with  pure  potassa  lye,  then  add  sodium  carbonate 
and  a  little  potassium  cyanide  free  from  potassium  sulphide,  and 
gently  heat.     If  a  precipitate  forms,  dissolve  it,  after  washing, 
in  dilute  nitric  acid,  and  in  the  solution  determine  the  bismuth 
by   precipitating   with   ammonium   carbonate    and   weighing   as 
oxide.     To  the  solution  filtered  from  the  bismuth,  or  which  has 
remained  clear  after  adding  potassium  cyanide,  add  first  a  further 


§  259.]  LEAD    COMPOUNDS.  587 

quantity  of  potassium  cyanide,  and  then  a  few  drops  potassium- 
sulphide  solution.  If  a  precipitate  forms  it  may  contain  cadmium 
sulphide  or  silver  sulphide.  Collect  it,  dissolve  in  hot  dilute  nitric 
acid,  precipitate  any  silver  present  by  adding  a  few  drops  hydro- 
chloric acid,  evaporate  the  filtrate  almost  to  dryness,  and  test  with 
sodium  carbonate  to  see  if  any  cadmium  is  precipitated.  If  this 
is  the  case,  determine  the  cadmium*  as  oxide,  the  best  method 
being  to  dissolve  the  well-washed  precipitate  in  nitric  acid,  evapo- 
rate, ignite,  and  weigh  the  residue.  To  the  liquid  filtered  from  the 
silver  and  cadmium  sulphides,  or  which  has  remained  clear  on  adding 
potassium  sulphide,  add  a  little  sulphuric  and  nitric  acids  and 
a  few  drops  hydrochloric  acid,  and  evaporate  until  the  odor  of 
hydrocyanic  acid  has  altogether  disappeared;  then  precipitate 
the  clear,  or,  if  necessary,  filtered,  solution  with  hydrogen  sulphide, 
and  determine  the  copper  as  sulphide  (Vol.  I,  p.  375).  If  the 
quantity  of  copper  is  very  small,  control  the  determination  by 
a  volumetric  analysis,  by  again  dissolving  the  copper  sulphide  in 
nitric  acid,  evaporating  the  solution  to  dryness  with  sulphuric 
acid,  and  decomposing  the  cupric  sulphate  with  potassium  iodide 
{Vol.  I,  p.  377,  a). 

If  no  cadmium  is  present,  the  separation  of  bismuth  from  copper 
by  means  of  ammonia  and  ammonium  carbonate  is  simpler;  if, 
however,  it  is  present,  which  cannot,  as  a  rule,  be  known,  the 
analysis  is  thereby  rendered  more  difficult,  because  the  cadmium 
may  be  partly  thrown  down  with  the  bismuth  precipitate,  and 
partly  retained  in  solution  with  the  copper.  It  must  never  be 
forgotten  to  test  the  acid  copper  solution  for  silver  by  adding 
hydrochloric  acid  before  the  final  precipitation  with  hydrogen 
sulphide,  as  otherwise  the  copper  sulphide  may  be  contaminated 
with  silver  sulphide 

8.  The  precipitates  obtained  in  5  and  6  by  acidulating  the 
potassium-sulphide  solutions  with  hydrochloric  acid  collect  on 
a  small  filter,  dissolve  in  an  excess  of  potassa  lye  while  still  moist, 
treat  with  chlorine,  and  separate  and  determine  the  antimony 
and  arsenic  according  to  BUNSEN'S  method  (pp.  556  and  557  this 
volume).  The  antimony  sulphide  may  be  advantageously  col- 


588  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  259. 

lected  in  an  asbestos  filter-tube  according  to  Vol.  -I,  p.  397,  and 
Weighed  as  black  antimony  trisulphide. 

9.  Unite  the  filtrate  from  6  with  the  washings,  and  if  they  exceed 
500  c.c.  concentrate  by  evaporation,  then  transfer  to  a  flask,  make 
alkaline  with  ammonia,   and  add  ammonium  sulphide.     Fill  up 
the  flask  to  the  neck,  stopper,  and  set  aside  for  at  least  twenty-four 
hours.     In  any  case,  filter  only  when  the  slight  precipitate  has 
completely  subsided.     Add  acetic  acid  to  the  filtrate  just  to  acidity, 
then  add  ammonium  acetate,  and  evaporate  at  a  gentle  heat  so 
that  if  a  trace  of  nickel  sulphide  is  still  retained  in  solution  by  the 
ammonium  sulphide,  it  may  be  precipitated  together  with  the 
sulphur.     After  subsidence,  collect  this  sulphur  on  a  filter. 

10.  Treat  the  precipitate  afforded  by  ammonium  sulphide  in  9, 
just  after  collecting,  and  on  the  filter,  with  a  mixture  of  about 
6  parts  hydrogen-sulphide    water  and  1  part  hydrochloric  acid  of 
sp.  gr.  1  •  12,  and  pour  the  filtrate  repeatedly  back  onto  the  filter. 
By  this  treatment  the  iron  and  zinc  sulphides  are  dissolved,  while 
the  nickel  and  cobalt  sulphides  remain.   This  filter,  and  that  obtained 
in  9.  the  sulphur  of  which  may  contain  nickel,  incinerate  together, 
treat  with  a  little  nitrohydrochloric  acid,  evaporate  to  a  small  bulk, 
make  just  alkaline  with  ammonia    add  a  little  ammonium  carbo- 
nate, filter,  and  heat  the  ammoniacal  liquid  with  a  slight  excess 
of  pure  potassa  lye  in  a  platinum  dish  until  ammonia  is  no  longer 
evolved.     If  weighable  flocks  separate,  collect  them,  wash    dry, 
incinerate,   ignite,   weigh,    and  test  with   the  blowpipe  whether 
the  nickelous  oxide  contains  any  cobaltous  oxide. 

11.  The  filtrate  obtained  in  10  by  treating  the  ammonium- 
sulphide  precipitate  with  very  dilute  hydrochloric  acid,  concen- 
trate by  evaporation,  and  finally  with  the  addition  of  a  little  nitric 
acid ;  then  precipitate  with  ammonia,  warm,  and  collect  the  flocks 
of  ferric  hydroxide;    redissolve  this  in  hydrochloric  acid,  again 
precipitate  with  ammonia,  wash,  dry,  incinerate,  and  weigh  the 
ferric  oxide.     As  a  control  the  oxide  may  be  fused  with  potassium 
disulphate,  reduced  with  zinc,  and  the  ferrous  oxide  determined 
volumetrically  with  potassium  permanganate. 

12.  To  the  filtrate  from  the  ferric  hydroxide  add  a  little  ammo- 


§  259.]  LEAD  COMPOUNDS.  589 

nium  sulphide,  and  allow  to  stand  for  at  least  twenty-four  hours 
at  a  gentle  heat.  If  weighable  flocks  separate,  collect  them,  wash, 
and  treat  at  once  upon  the  filter  with  diluted  acetic  acid  in  order 
to  dissolve  out  any  admixed  manganese  sulphide.  If  a  trace  of 
zinc  sulphide  remains  on  the  filter,  it  is  best  weighed  by  converting 
the  sulphide  into  oxide  by  VOLHARD'S  method  (see  p.  432  this 
volume).  Evaporate  the  acetic-acid  solution,  however,  to  a  small 
volume,  and  test  with  caustic  potassa  for  any  manganese  that  may 
be  present. 

13.  In  calculating  the  constituents  found  thus  far,  it  must  not 
be  forgotten  that  the  quantities  obtained  correspond  with  179  grm. 
of  lead,  and  not  200  grm.     These  figures  result  from  the  fact  that 
the  2-litre  flask,  when  filled  to  the  neck,   contains  45  c.c.  lead 
sulphate  and  1955  c.c.  solution,  and  that  of  the  latter  only  1750  c.c. 
have  been  used ;   hence  1955  c.c. :  200  grm. : :  1750  c.c. :  179  •  03,  or  in 
round  numbers,  179  grm. 

14.  The  silver  *  is  best  determined  by  cupellation  (pp.  581  and 
582   this   volume),    because    exceedingly   slight   traces   of   silver 
cannot  be  precipitated  by  hydrochloric  acid  from  the  nitric-acid 
solution  of  lead  (p.  583,  4,  a,  this  volume).     As  many  soft  leads, 
e.g.,  the  Oberharz  refined  lead  (HAMPE),  contain  only  0-0005  per 
cent,  silver,  200  grm.  of  the  lead  must  be  cupelled  in  order  to 
obtain  1  mgm.  of  silver.      If  the   operator  lacks  the  facilities  for 
the  cupellation  of  so  large  a  quantity  of  metal,  the  volume  of  the 
metal  may  be  reduced,  according  to  MERRicK,f  by  fusing  the  lead 
in  a  rather  capacious  Hessian  crucible  and  adding  half  its  weight 
of  potassium  nitrate.     Then  increase  the  heat  until  the  crucible 
is  white-hot  up  to  its  margin,  stir  the  contents  with  a  pointed  iron 
rod,  remove  from  the  heat  before  the  lead  oxide  has  eaten  through 

*  The  cause  of  the  difference  in  the  silver  in  lead  bars  is  often  due  to  the 
unequal  distribution  of  the  silver  in  the  bars.  The  silver  collects  to  a  greater 
extent  in  the  portions  which  solidify  first  than  in  those  that  remain  fluid 
longer,  hence  the  outer  and  upper  portions  are  richer  in  silver  than  the  middle 
and  lower  portions.  SCHWEITZER  (Zeitschr.  f.  analyt.  Chem.,  xvi,  504) 
found  from  this  cause,  in  a  bar  of  lead,  differences  between  79-83  oz.  (middle 
portion)  and  104-54  oz.  (upper  length)  per  ton  of  lead. 

t  Zeitschr.  f.  analyt.  Chem.,  x,  494. 


590  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  259. 

the  crucible,  allow  to  cool,  and  break  the  latter.  In  this  manner 
the  silver  in  lead  may  be  concentrated  so  that  its  determination 
is  rendered  possible  by  the  wet  way. 

15.  Lastly,  there  remain  to  be  considered  those  cases  in  which 
the  leads  contain  rather  more  antimony.     In  these  there  is  formed. 
even  during  the  solution,  or  on  its  standing,  a  white  precipitate  of 
antimony  oxide  and  antimonic  antimonate,  which  may,  however, 
also  contain  arsenic  and  traces  of  other  metals.     Collect  the  pre- 
cipitate,  wash,   dissolve  in  hydrochloric  acid,   dilute  exactly  to 
100  c.c.  with  water  acidulated  with  tartaric  acid,  and  of  the  solu- 
tion take  a  quantity  in  the  proportion  of  1955 : 1750  (see  above,  13), 
i.e.,  89-5  c.c.,  and  precipitate  this  with  hydrogen  sulphide;    mix 
the  precipitate  formed  with  that  obtained  in  6  by  precipitation 
with  hydrogen  sulphide  and  treat  both  together  as  already  de- 
scribed. 

16.  If  other  metals  besides  those  already  noted  above  are  present 
in  soft  leads,  the  processes  must,  of  course,  be  correspondingly 
modified. 

17.  The  quantity  of  lead  is  found  from  the  difference.     It  is 
useless  to  make  a  direct  determination  of  lead  because  it  would 
in  no  way  control  the  accuracy  of  the  determinations  of  the  foreign 
metals  present. 

Second  Method  (by  W.  HAMPE  *). 

1.  Beat  out  the  carefully  cleaned  metal  on  a  steel  anvil  with 
a  polished  steel  hammer,  into  thin  sheets,  and  cut  these  into  small 
strips  with  a  pair  of  scissors.  To  determine  the  foreign  metals, 
excepting  silver,  present  in  the  lead,  400  grm.  are  used.  200  grm. 
each  are  dissolved  in  large  covered  beakers,  in  a  mixture  of  500 
c.c.  nitric  acid  of  sp.  gr.  1-2,  and  500  cc.  water,  and  to  the  still 
hot,  clear  solutions  add  70  c.c.  of  pure  concentrated  sulphuric 
acid  mixed  with  a  little  water  to  precipitate  the  lead.  Decant 
the  clear  liquids  from  both  beakers,  so  far  as  possible,  into  a  porce- 
lain dish,  and  wash  the  united  precipitates  with  water  acidulated 

*  Zeitschr.  /.  das  Berg-,  Hutten-,  und  Salinenwesen  in  dem  preussischen 
Staate,  xviu,  195;  Zeitschr.  /.  analyt.  Chem.,  xi,  215. 


§  259.]  LEAD    COMPOUNDS.  591 

with  sulphuric  acid,  either  by  decantation  8  to  10  times  or  on  a 
vacuum  filter,  the  platinum  cone  of  which  is  fitted  with  a  very 
small  filter.  Concentrate  the  washings  by  evaporation,  add  to 
the  decanted  liquid,  and  lastly  evaporate  the  whole,  continuing 
the  heat  until  the  greater  part  of  the  sulphuric  acid  is  driven  off. 

2.  When  the  residue  obtained  hi  1  is  cold,  mix  it  with  water, 
whereby  a  still  further  small  quantity  of   lead  is  precipitated; 
then  boil  the  strongly  acid  liquid  for  some  time  so  that  no  basic 
bismuth  sulphate  will  remain  with  the  lead  sulphate,  add  a  drop 
of  hydrochloric  acid  in  order  to  precipitate  the  silver,  filter,  and 
wash  with  diluted  sulphuric  acid. 

3.  The  precipitate  obtained  in  2,  and  containing  some  admixed 
lead  antimonate,  boil  with  potassium-sulphide  solution,  and  filter. 
The  solution  we  will  term  A. 

4.  The  solution  filtered  off  from  the  lead  sulphate  and  silver 
chloride  in  2,  treat  as  in  the  First  Method  (6  and  7)  hi  order  to 
precipitate  the  metals  of  the  fifth  and  sixth  groups.     There  are 
thus  obtained  a  filtrate  containing  the  metals  of  the  fourth  group, 
and  a  precipitate.     On  treating  the  latter  with  potassium-sulphide 
solution,  however,  there  is  obtained  an  insoluble  residue,  and  a 
potassium-sulphide  solution  containing  the  remainder  of  the  anti- 
mony and  arsenic  (B). 

5.  Treat  the  solutions  A  and  B  obtained  in  3  and  4  with  diluted 
sulphuric  acid  to  precipitate  the  metallic  sulphides,  remove  the 
hydrogen  sulphide  by  evaporation,   filter,   and  wash  with  water 
to  which  has  been  added  a  little  ammonium  nitrate  and  a  few 
drops  nitric  acid  (because  on  washing  antimony  sulphide  with 
pure  water  the  washings  may  easily  pass  through  the  filter  turbid). 
Remove  any  excess  of  sulphur  from  the  precipitate  by  treatment 
with  carbon  disulphide,  dissolve  the  residue  in  freshly  prepared, 
strong  ammonium-sulphide  solution,  evaporate  the  solution  on  a 
water-bath,  treat  the  residue  with  hydrochloric  acid  and  potas- 
sium chlorate  at  a  moderate  heat,  and  separate  the  arsenic  and 
antimony  according  to  Vol.  I,  p.  720  [204].     The  antimony  sulphide 
precipitated  by  hydrogen  sulphide  in  the  filtrate  from  the  am- 
monium-magnesium  arsenate,   dissolve,   after  washing  in  warm 


592  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  259. 

freshly  prepared  ammonium  sulphide,  evaporate  the  solution  in 
a  weighed  porcelain  crucible,  at  first  only  at  a  moderate  heat  on  a 
water-bath,  then  oxidize  the  evaporation-residue  with  fuming 
nitric  acid,  ignite,  and  weigh  the  antimony  antimonate  obtained. 

6.  The  separation  of  the  metals  of  the  fifth  group,  the  sulphides 
of  which  constitute  the  residue  insoluble  in  potassium-sulphide 
solution  obtained  in  4;  is  effected  as  in  the  First  Method  (7) ;   but 
HAMPE  prefers  to  dissolve  the  carbonates  of  bismuth  and  cadmium 
in  hot  nitric  acid,  evaporate  the  solutions  in  small  weighed  porcelain 
crucibles,  ignite  the  residues,  and  weigh  the  oxides  thus  obtained. 

7.  Evaporate  the  filtrate  obtained  in  4,  add  ammonia  to  alka- 
line reaction,  and  precipitate  the  metals  of  the  fourth  group  with 
ammonium  sulphide;   if  the  solution  is  brown  from  the  presence 
of  dissolved  nickel  sulphide,  boil  until  the  brown  color  has  dis- 
appeared, filter,  wash  first  with  water,  then  with  alcohol,  remove 
any  admixed  sulphur  by  treatment  with  carbon  disulphide,  and 
separate  nickel,  cobalt,  iron,  manganese,  and  zinc  as  in  the  First 
Method  (9  to  12).     Lastly  separate  the  cobalt  and  nickel  by  means 
of  potassium  nitrite. 

8.  The  silver  is  determined  by  cupellation. 

b.    ANALYSIS    OF    CRUDE    LEAD   AND    HARD    LEAD. 

Crude  lead  contains  from  95  to  99  per  cent,  lead,  0-01  to  0-18 
silver,  and  somewhat  larger  quantities  than  this  of  the  other 
metals  that  have  been  considered  in  the  analysis  of  soft  lead. 
Hard  lead  differs  from  the  other  varieties  of  lead  chiefly  in  its 
containing  a  relatively  large  quantity  of  antimony,  which  ranges 
from  about  2  to  6  per  cent.  In  the  analysis  of  crude  lead  quan- 
tities of  from  50  to  200  grm.  are  taken,  according  to  the  degree  of 
purity;  in  the  case  of  hard  lead,  from  5  to  10  grm.  are  sufficient. 
Treat  either  of  the  leads  with  a  warm  mixture  of  equal  parts  of 
nitric  acid  of  sp.  gr.  1-2  and  water  until  all  soluble  matter  is  dis- 
solved, dilute  with  water,  allow  to  settle,  and  filter  off  the  white 
precipitate  which  nearly  always  remains,  and  which  consists 
chiefly  of  oxygen  compounds  of  antimony  and  of  lead  antimonate. 
After  washing,  separate  the  precipitate  from  the  filter,  without 


§  259.]  LEAD    COMPOUNDS.  593 

destroying  the  latter,  by  careful  washing,  or  by  drying  and  rubbing; 
in  the  former  case  evaporate  the  water  in  the  precipitate  in  a 
porcelain  crucible,  and  fuse  the  residue  with  3  to  4  parts  sulphurated 
potassa  in  the  covered  crucible.  Dissolve  the  melt  in  hot  water, 
pass  through  the  filter  first  used,  ahd  then  treat  this,  together 
with  the  precipitate  thrown  down  from  the  sulpho-salt  solution 
by  diluted  sulphuric  acid,  and  also  the  precipitate  insoluble  in 
the  sulphurated-potassa  solution,  and  consisting,  according  to 
HAMPE,  of  lead,  silver,  and  bismuth  sulphides,  together  with 
the  analogous  precipitates  to  be  obtained  from  the  sulphuric- 
acid  solution. 

Precipitate  the  lead  from  the  nitric-acid  solution  by  adding 
a  moderate  excess  of  sulphuric  acid,  allow  the  precipitate  to  sub- 
side, decant  the  solution,  wash  the  precipitate  by  decantation  or  on 
a  vacuum  filter  (see  a,  Second  Method,  1,  p.  481),  and  evaporate 
until  the  greater  part  of  the  excess  of  sulphuric  acid  has  been  ex- 
pelled. The  residue  is  then  best  treated,  according  to  HAMPE, 
as  follows:  Add  a  little  water  and  hydrochloric  acid,  boil,  then 
allow  to  cool,  add  alcohol,  filter  after  twelve  hours,  and  wash 
with  alcohol  acidulated  with  hydrochloric  acid.  In  this  manner 
all  the  arsenic,  antimony,  copper,  bismuth,  cadmium,  iron,  etc., 
besides  small  quantities  of  lead,  are  obtained  in  solution.  Evap- 
orate off  all  the  alcohol,  precipitate  with  hydrogen  sulphide,  sep- 
arate the  metals  of  the  fifth  and  sixth  groups  by  fusing  with  potas- 
sium sulphide,  and  then  determine  the  individual  metals  accord- 
ing to  the  methods  employed  for  soft  lead.  If  BUNSEN'S  method 
is  used  for  the  separation  of  arsenic  from  antimony,  it  is  advisable, 
as  the  quantity  of  antimony  present  is  large,  to  again  dissolve  in 
potassa  lye  the  antimony  sulphide  first  precipitated,  and  to  repeat 
the  separation,  in  order  to  obtain  the  antimony  sulphide  per- 
fectly free  from  arsenic.  The  determination  of  the  iron,  zinc,  and 
silver  is  effected  as  in  a,  this  section. 


594  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  259. 

[C.  ELECTROLYTIC    SEPARATION    AND    DETERMINATION    OF    LEAD. 

According  to  A.  HOLLARD  *  the  estimation  of  lead  by  elec- 
trolysis in  the  state  of  dioxide  is  of  incomparable  exactness  and 
simplicity,  provided  that  a  certain  number  of  precautions  are  ob- 
served very  closely,  such  as  density  of  current,  composition  of 
the  electrolyte,  temperature  of  desiccation  of  the  deposit  of  lead 
dioxide,  etc.  The  author  has  also  laid  down  the  conditions  under 
which  the  method  may  be  applied  to  the  most  widely  divergent 
alloys.  It  is  only  after  experiments  carried  out  under  the  most 
varying  conditions  and  methods  of  control,  during  the  course  of 
several  years,  that  the  author  publishes  this  method,  believing 
that  it  will  be  found  to  be  of  great  service. 

The  deposits  of  lead  dioxide  which  occur  exclusively  on  the 
anode  are  very  adherent,  and  correspond  exactly  to  the  formula 
PbO2 ;  further,  no  trace  of  metallic  lead  is  deposited  on  the  cathode. 

The  quantity  of  lead  submitted  to  estimation  need  not  be  more 
than  0-2  grm. ;  with  a  larger  quantity,  in  fact,  there  is  a  danger 
of  the  deposit  not  being  sufficiently  adherent. 

Electrolytic  Apparatus. 

The  electrodes  consist  of  a  truncated  cone  of  platinum  which 
serves  as  anode,  and  on  which  the  lead  dioxide  is  deposited;  the 
cathode  is  a  spiral  of  platinum  wire  fixed  on  a  stand.  They  are, 
in  fact,  LUCKOW'S  apparatus  modified  as  to  construction  and 
dimensions;  the  truncated  cone  is  made  of  a  sheet  of  pure  platinum; 
its  upper  diameter  is  18  mm.  and  its  lower  diameter  45  mm.,  its 
generatrix  63  mm.  A  hard  platinum  wire  is  gold-soldered  to  the 
trunk  of  the  cone.  Each  electrode  weighs  about  20  grm. 

The  vessels  containing  the  electrolytes  are  of  ordinary  cylin- 
drical Bohemian  glass,  about  6-5  cm.  diameter,  holding  about 
370  to  400  c.c.  The  solution  of  the  alloy,  as  well  as  the  electrolysis 
of  the  lead,  is  conducted  in  the  same  beaker;  the  whole  operation 
does  not  require,  as  will  be  seen,  either  decantation  or  filtration. 
During  the  a' tack  with  acid  the  beaker  must  be  covered  with  a 

*  Bull.  Soc.  Chim.  [3],  xiv,  No.  22.—Chem.  News,  LXXX,  123. 


§  259.]  LEAD    COMPOUNDS.  595 

unnel,  the  edge  of  which  should  rest  just  inside  the  edge  of  the 
beaker,  forming  a  little  gutter  in  which  a  few  drops  of  water  will 
make  a  perfect  hydraulic  joint;  all  loss  by  projection  is  thus  avoided. 
The  distance  from  the  lower  edge  of  the  cone  to  the  foot  of  the 
spiral  should  be  about  6  mm.  For  better  receiving  the  electrolytic 
deposit  of  lead  the  cone  should  not  be  polished,  but  dull,  so  that 
the  deposit  will  adhere  to  it  more  easily.  This  can  be  effected 
by  immersing  the  platinum  hi  aqua  regia  for  a  few  hours. 

Estimation  of  Pure  Lead. 

The  lead  is  dissolved  in  dilute  nitric  acid.  The  solution,  diluted 
to  about  350  c.c.,  should  contain  80  c.c.  of  ordinary  pure  nitric 
acid  in  the  free  state.  With  a  less  quantity  of  acid  there  is  a  lia- 
bility to  deposit  part  of  the  lead  on  the  cathode.  The  electrolysis 
is  effected  at  the  ordinary  temperature  with  a  current  of  0-15 
ampere.  The  voltage  cannot  be  denned;  it  depends  on  the  quan- 
tity of  lead  hi  the  electrolyte,  and,  hi  the  case  of  alloys,  on  the 
nature  and  proportion  of  foreign  metals  present.* 

The  cone  should  be  plunged  completely  into  the  bath,  and  the 
foot  of  the  spiral  should  be  as  near  as  possible  to  the  bottom  of 
the  beaker.  The  electrolysis  goes  on  at  the  ordinary  temperature. 
At  the  end  of  twenty-four  hours  the  precipitation  is  complete  and 
the  deposit  very  adherent.  The  cone  is  then  plunged  successively 
into  two  beakers  filled  with  distilled  water,  and  then  placed  in  an 
oven  and  heated  gradually  to  200°,  which  temperature  should  be 
maintained  for  a  quarter  of  an  hour.  This  temperature  is  abso- 
lutely necessary  to  obtain  a  deposit  corresponding  exactly  with  the 
formula  PbO2. 

In  CH.  MARIE'S  f  method  the  lead  in  the  form  of  sulphate  or 
chloride  is  placed  in  the  beaker  in  which  it  is  to  be  electrolyzed, 
and  attacked  with  nitric  acid  to  which  crystals  of  ammonium 
nitrate  are  gradually  added.  To  hasten  the  solution  it  is  heated 
on  a  water-bath.  When  all  the  sulphate  is  dissolved  the  solution 

*  For  0-2  grm.  of  pure  lead  under  the  conditions  described  above  the 
electromotive  force  should  be  from  2-'6  to  2-7  volts. 

t  Bull.  Soc.  Chim.  [3],  xxiu,  No.  12. — Chemical  News,  LXXXI,  p.  51. 


596  DETERMINATION   OF   COMMERCIAL    VALUES.  [§   259- 

is  diluted  with  warm  water,  and  the  electrolysis  is  proceeded  with 
in  the  ordinary  manner,  keeping  the  temperature  up  to  60 — 70° 
The  quantities  of  the  reagents  necessary  are  as  follows: — For  0-3 
grm.  of  sulphate  it  is  necessary  to  have  5  grm.  of  ammonium 
nitrate;  as  for  the  nitric  acid,  its  quantity  is  determined  by  this 
condition,  viz.,  that  after  dilution  the  liquid  ought  to  contain  10 
per  cent,  of  free  acid. 

As  the  sulphate  dissolves  more  easily  in  acid  which  has  been 
slightly  diluted  than  in  concentrated  acid,  it  is  as  well,  before  adding 
the  latter,  to  pour  a  little  water  over  the  sulphate.  In  three  hours, 
with  an  unpolished  platinum  electrode  having  a  surface  of  90 
square  cm.,  and  with  a  current  of  0-3  ampere  intensity,  0-4  grm. 
of  lead  dioxide  can  easily  be  deposited. 

This  method  allows  of  the  application  of  electrolysis  to  the  analy- 
sis of  lead  glass.  It  is  sufficient  to  attack  the  finely  powdered 
glass  with  hydrofluoric  acid  containing  the  necessary  quantity  of 
sulphuric  acid  to  transform  the  bases  into  sulphates.  Too  great 
an  excess  of  sulphuric  acid  will  prevent  the  solution  of  the  sulphate 
of  lead,  which  should  be  carried  out  as  described  above.  After 
the  electrolysis  we  can  proceed  immediately  to  the  estimation  of 
the  alkaline  metals,  if  the  material  under  examination  contains 
no  metal  of  the  iron  group,  or  of  the  alkaline-earthy  group. 

The  chromates  of  lead  dissolve  still  more  easily  than  the  sul- 
phates in  the  mixture  of  nitric  acid  and  nitrate  of  ammonia.  For 
0-5  grm.  of  chromate  2  grm.  of  nitrate  suffice;  as  for  the  nitric 
acid,  it  is  sufficient  for  the  final  solution  to  contain  10  per  cent. 

The  electrolysis  is  conducted  as  in  the  case  of  the  sulphate; 
the  chromic  acid,  during  the  operation,  is  completely  brought  into 
the  state  of  chromium  sesquioxide  directly  precipitable  by  am- 
monia. 

From  the  simplicity  of  the  analytical  method  and  the  exact- 
ness of  the  results  furnished,  this  method  will  be  very  useful  for 
the  analysis  of  such  important  commercial  products  as  the  silicates 
and  chromates  of  lead. — TRANSLATOR.] 


§  259.]  LEAD    COMPOUNDS.  597 

C.  LEAD  OXIDES  AND  SALTS. 

The  lead  oxides  and  salts  met  with  in  commerce,  e.g.  mas- 
sicot, litharge,  white  lead,  and  lead  sulphate,  present  no  difficulties 
in  analysis.  The  analysis  of  minium  and  of  the  more  impure 
varieties  of  lead  acetate,  however,  require  a  brief  mention. 

a.  MINIUM. 

Minium  is  frequently  the  subject  of  analysis  in  technical  labora- 
tories, and  it  is  by  no  means  a  question  of  simply  detecting  the 
impurities  and  adulterations,  but  the  determination  in  particular 
of  also  the  relation  between  the  lead  peroxide  and  the  lead  oxide. 
The  impurities  insoluble  in  acids  remain  behind  on  dissolving  the 
minium  in  diluted  nitric  acid  to  which  is  added  some  alcohol, 
sugar,  or  oxalic  acid.  If  the  nitric-acid  solution  is  made  up  to 
a  definite  volume,  an  aliquot  portion  may  be  qualitatively  tested 
for  any  dissolved  foreign  metals,  while  another  portion  may  be 
used  for  the  quantitative  determination  of  the  lead  according  to 
Vol.  I,  p.  355,  3.  Any  carbonic  acid  present  may  be  determined 
by  the  method  in  Vol.  I,  p.  493,  employing  a  larger  quantity  of 
minium,  and  using  nitric  acid  for  the  expulsion  of  the  carbon 
dioxide.  The  lead-peroxide  content  can  be  determined  in  the 
same  manner  as  the  manganese  dioxide  is  determined  in  manganese 
ores,  and  in  fact  by  means  of  oxalic  and  sulphuric  acids  according 
to  p.  458,  and  pp.  462  and  463  this  volume,  and  also  iodometrically, 
according  to  p.  465,  6,  this  volume. 

FR.  Lux,*  finally  has  devised  the  following  process  for  rapidly 
determining  the  value  of  minium,  with  sufficient  accuracy  for 
commercial  purposes;  the  process  is  also  based  on  the  action  of 
oxalic  acid  on  lead  peroxide,  thus: 

PbO2  +  C2H2O4  =  PbO  +  2C02  +  H20. 

If  the  quantity  of  oxalic  acid  originally  added  is  known,  and  a 
determination  made  of  the  acid  remaining  after  the  reaction  is 
complete,  which  may  be  easily  done  with  a  solution  of  potassium 
permanganate  after  dissolving  the  lead  oxalate  formed  in  nitric 

*  Zeitschr.  f.  analyt.  Chem.,  xrx,  153. 


598  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  259. 

acid,  the  difference  will  give  the  quantity  of  oxalic  acid  decom- 
posed, and  from  this  the  lead  dioxide  present  may  be  calculated, 
since  1  eq.  of  C2H2O4  corresponds  to  1  eq.  of  lead  dioxide. 

It  is  convenient  to  employ  a  one-fifth  normal  oxalic-acid  solu- 
tion, hence  containing  12-605  grm.  crystallized  oxalic  acid  (H2C2O4 
+  2H2O)  per  litre,  and  an  equivalent  solution  of  potassium  per- 
manganate, of  which  1  c.c.  corresponds  with  1  c.c.  of  the  oxalic- 
acid  solution  (Vol.  I,  pp.  316  and  317).  Place  2-069  grm.  of  the 
minium  (the  one-hundredth  part  of  the  lead  equivalent  expressed  in 
grammes)  to  be  tested  in  a  porcelain  dish  of  about  300  c.c.  capacity, 
pour  over  it  20  to  30  c.c.  diluted  nitric  acid  (of  sp.  gr.  1-2)  and 
stir  while  warming  gently.  In  a  few  minutes  the  minium  will 
have  been  decomposed  into  lead  monoxide,  which  dissolves,  and 
dioxide,  which  remains  undissolved.  Now  add  50  c.c.  of  the 
oxalic-acid  solution,  and  heat  to  boiling;  the  lead  dioxide  is  im- 
mediately decomposed  and  dissolved,  while  any  insoluble  im- 
purities (barytes,  lead  sulphate,  clay,  sand,  ferric  oxide,  larger 
quantities  of  gypsum)  remain.  Maintain  the  solution  at  the  boiling- 
point,  and,  without  removing  any  insoluble  residue,  add  at  once 
5  to  10  c.c.  of  the  potassium-permanganate  solution.  As  soon 
as  this  is  decolorized  add  fresh  portions,  until  all  the  oxalic  acid 
present  has  been  decomposed.  The  titration  may  be  considered 
at  an  end  when  the  pink  color  afforded  by  two  drops  of  the  perman- 
ganate solution  does  not  completely  disappear  within  half  a  minute. 
(If  the  permanganate  solution  is  added  at  first  only  in  drops,  the 
decomposition  of  the  oxalic  acid  takes  place  but  very  slowly.) 
On  deducting  the  number  of  c.c.  of  permanganate  solution  used 
from  50,  the  difference  will  give  the  quantity  of  lead  dioxide  present 
expressed  in  per  cents. 

After  the  liquid  has  been  decolorized  by  a  few  drops  oxalic- 
acid  solution,  add  first  ammonia  almost  to  neutrality,  and  then 
ammonium  or  sodium  acetate  in  sufficient  quantity,  and  determine 
the  lead  volumetrically  with  potassium  chromate  solution  ac- 
cording to  Vol.  I,  p.  360,  6.  On  deducting  the  lead  dioxide  from 
the  total  lead  we  find  the  lead  present  in  the  minium  as  lead  mon- 
oxide. The  determination  of  the  lead  dioxide  is  not  interfered 


§  259.]  LEAD    COMPOUNDS.  599 

with  by  any  of  the  impurities  or  adulterants  present  in  the  min- 
ium; that  of  the  lead,  however,  can  only  be  properly  made  in 
the  manner  described  when  barium  carbonate  is  absent  (and  this 
should  scarcely  ever  be  present  in  minium). 

6.    LEAD   ACETATE    (SUGAR    OF   LEAD). 

Besides  the  crystallized,  almost  pure  lead  acetate,  the  properties 
and  composition  of  which  may  be  decided  usually  without  a  quan- 
titative analysis,  other  varieties  of  lead  acetate  occur  in  com- 
merce regarding  which  this  cannot  be  said,  and  which,  according 
to  their  method  of  preparation,  contain  more  or  less  lead  and 
acetic  acid.  To  these  belong  the  so-called  amorphous  white 
lead  acetate  as  well  as  the  yellow  and  brown  acetates  (which  are 
obtained  by  dissolving  litharge  in  impure  acetic  acid  made  from 
wood  vinegar,  or  in  rectified  or  crude  pyroligneous  acid). 

All  kinds  of  lead  acetates  may  now  be  simply  analyzed  by  a 
process  devised  by  me,*  and  which  is  a  suitable  combination  of 
gravimetric  with  volumetric  analysis.  The  principle  of  the  method 
is  as  follows: 

On  dissolving  the  lead  acetate  to  be  examined  in  water  in  a 
flask,  and  adding  normal  sulphuric  acid  in  slight  excess,  all  the 
lead  will  be  obtained  in  the  precipitate  as  lead  sulphate,  and  all 
the  acetic  acid  together  with  the  excess  of  sulphuric  acid  in  the 
solution.  On  now  filling  the  flask  to  the  mark,  and  adding  a 
volume  of  water  equal  to  that  displaced  by  the  lead  sulphate 
(and  which  can  be  ascertained  with  sufficient  accuracy  as  the 
lead  content  of  lead  acetate  varies  only  between  certain  'limits) , 
the  above-named  acids  are  obtained  in  a  known  volume  of  liquid. 
If  now  the  excess  of  sulphuric  acid  is  determined  in  a  measured 
quantity  of  the  clear  liquid  by  means  of  barium  chloride,  the 
entire  quantity  of  lead  present  may  be  readily  calculated;  for 
since  the  total  quantity  of  sulphuric  acid  is  known,  and  that  re- 
maining is  determined,  the  difference  will  give  that  which  has  com- 
bined with  the  lead,  and  thus,  calculating  1  eq.  of  the  sulphuric 
acid  for  1  eq.  of  lead,  also  the  quantity  of  the  latter. 

*  Zeitschr.  f.  analyt.  Chem.,  xin,  30. 


600  DETERMINATION    OF    COMMERCIAL  VALUES.          [_§  259. 

In  an  equally  simple  manner  the  quantity  of  acetic  acid  (together 
with  the  small  quantities  of  propionic  and  butyric  acids,  etc.) 
may  be  ascertained,  for,  on  determining  the  number  of  c.c.  of 
normal  soda  solution  required  to  neutralize  a  measured  quantity 
of  the  liquid  containing  the  acetic,  etc.,  acids,  and  the  excess  of 
sulphuric  acid,  and  deducting  from  this  the  quantity  of  soda 
solution  required  to  neutralize  the  already  known  excess  of  sul- 
phuric acid,  the  difference  will  correspond  to  the  acetic  acid,  etc., 
from  which  the  quantity  of  the  latter  may  hence  be  easily  calcu- 
lated. 

The  following  simple  method  is  recommended  in  practice: 
Weigh  off  10  grm.  of  the  lead  acetate  to  be  examined,  dissolve 
it  in  water  in  a  500-c.c.  flask,  add  60  c.c.  normal  sulphuric  acid, 
fill  the  flask,  which  has  also  a  mark  at  501-3  c.c.,  to  the  latter 
mark,  close  with  a  rubber  stopper,  shake  thoroughly,  and  allow 
to  settle. 

1.  In  100  c.c.  of  the  clear  solution  determine  the  sulphuric 
acid  with  barium  chloride,  calculate    the  quantity  for  the  500  c.c., 
deduct  the  result  from  the  sulphuric  acid  contained  in  the  60  c.c. 
of  normal  solution  (i.e.  2-943  grm.  H2SO4,  or  2-402  grm.  SO3),  and 
from  the  difference  calculate  the  equivalent  lead.     As  this  refers 
to  10  grm.  the  percentage  will  be  obtained  by  multiplying  the  result 
by  10. 

2.  To  another  100  c.c.  of  the  clear  solution  add  a  few  drops 
litmus  tincture,  then  add  normal  soda  solution  to  neutrality,  cal- 
culate the  number  of  c.c.  used  to  the  500  c.c.,  and  deduct  from 
this  nUmber  of  c.c.  of  soda  solution  corresponding  with  the  sul- 
phuric acid  found  in  1  and  contained  in  the  500  c.c.  of  liquid; 
from  the  difference  the  acetic  acid  contained  in  the  10  grm.  of  lead 
acetate  is  then  calculated. 

[M.  LIEBIG  *  recommends  the  following  method  for  the  deter- 
mination of  the  proportion  of  lead  dioxide  in  minium.  This  method 
is  very  convenient,  and  can  be  generally  recommended  on  account 
of  the  sharpness  of  the  end  of  the  reaction: 

0-5  gramme  of  finely  powdered  minium  is  placed  in  a  small 

*  Zeitschr.  f.  angew.  Chem.,  1901,  p.  528. — Chem.  News,  LXXXV,  229. 


§  260.]  MERCURY    COMPOUNDS.  601 

Lrlenmeyer  flask,  with  a  little  distilled  water.  By  means  of  a 
burette  25  c.c.  of  a  decinormal  solution  of  sodium  thiosulphate 
are  added,  then  10  c.c.  of  about  30-per  cent,  acetic  acid.  On 
well  shaking,  the  mass  goes  into  solution.  Then  add  10  c.c.  of  a 
10-per  cent,  potassium-iodide  solution,  and  2  or  3  c.c.  of  a  solu- 
tion of  zinc  iodide  and  starch,  and  titrate  the  excess  of  thio- 
sulphate with  a  decinormal  solution  of  iodine.  By  multiplying 
the  number  of  c.c.  of  iodine  used  by  238-92  (the  molecular  weight 
of  lead  dioxide),  we  obtain  the  proportion  of  dioxide  present  in 
the  minium. 

The  end  of  the  reaction  is  recognized  by  the  change  of  color 
caused  by  the  lead  iodide  formed  from  citron-yellow,  as  it  is  at 
first,  to  a  deep  dirty  yellow. 

As  above  stated,  the  reaction  is  very  sharp  and  rapid,  and  it 
is  not  necessary  to  have  a  very  practised  eye  to  perform  the  opera- 
tion.— TRANSLATOR.] 

18.  MERCURY  COMPOUNDS. 

§260. 
A.  MERCURY  ORES. 

The  analysis  of  mercury  ores  scarcely  requires  special  mention, 
as  all  that  is  necessary  has  been  detailed  in  §§  118,  162,  163,  and 
164.  As  a  rule  the  method  described  in  §  118,  1,  a,  is  the  best 
and  most  rapid  for  the  determination  of  mercury.  Mention  may, 
however,  here  be  made  of  A.  ESCHKA'S  method  *  for  determining 
mercury  in  ores,  and  which  is  fairly  rapid,  while  giving  sufficiently 
accurate  results  for  technical  purposes,  particularly  in  testing 
poor  ores. 

For  this  method  a  porcelain  crucible  is  required,  with  an  even 
rim,  ground  if  necessary,  and  provided  with  a  tightly  fitting,  very 
highly  concave  bevel-edged  cover  of  gold  plate.  Introduce  the 
powdered  ore  into  the  crucible,  taking  about  5  grm.  if  the  ore  con- 
tains from  1  to  10  per  cent.,  2  grm.  if  it  contains  from  10  to  30  per 

*  Oesterr.  Zeitschr.  /.  Berg-  u.  Hiittenwesen,  1872,  No.  9;  DINGLER'S  polyt. 
Journ.,  cciv,  47;  Zeitschr.  f.  analyt.  Chem.,  xi,  344. 


602  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  260. 

cent.,  or  1  grm.  if  it  contains  above  30  per  cent.,  of  mercury.  Mix 
the  powdered  ore  with  half  its  weight  of  clean  iron  filings,  perfectly 
free  particularly  from  oil,  with  the  aid  of  a  glass  rod,  cover  the 
mixture  with  a  uniform  layer  of  iron  filings  0-5  to  1  cm.  in  thick- 
ness, and  place  the  previously  weighed  gold  cover  in  position;  fill 
the  concavity  of  the  gold  cover  with  distilled  water  to  keep  it  cool, 
and  then  heat  the  crucible  for  ten  minutes  with  a  flame  the  tip 
of  which  plays  around  the  bottom.  Heating  for  this  length  of 
time  suffices  to  volatilize  all  the  mercury  from  the  ore  and  to  cause 
it  to  collect  on  the  gold  cover.  Now  remove  the  cover,  pour  out 
the  water  from  it,  wash  the  mercury  mirror  on  the  convex  sur- 
face with  alcohol,  dry  at  100°,  and  weigh  after  it  has  become  per- 
fectly cold  in  the  desiccator.  The  increase  in  weight  of  the  cover 
represents  the  weight  of  the  mercury  contained  in  the  ore  exam- 
ined. The  gold  cover  is  weighed  by  placing  it  on  a  porcelain 
crucible  as  a  support,  and  weighing  this  each  time  with  it. 

When  the  test  has  been  completed,  heat  the  cover  under  a 
good  draught,  at  first  very  gently,  but  finally  to  bright  redness,  in 
order  to  free  it  from  mercury  and  prepare  it  for  the  next  assay. 
The  weight  of  the  cover  changes  but  very  little  with  repeated 
use,  provided  the  necessary  care  is  exercised  in  heating  it. 

If  larger  quantities  of  mercury  have  been  volatilized  during  the 
examination,  a  mobile  amalgam  is  obtained  which  flows  about  on 
inclining  the  cover.  Should  this  occur,  the  alcohol  used  in  washing 
must  be  collected,  of  course,  in  order  not  to  lose  any  mercury. 

From  the  test  analyses  given  by  ESCHKA  it  appears  that  this 
method  gives  results  that  are  always  too  low.  The  loss,  for  in- 
stance, amounted  :to  0-002  grm.  mercury  in  0-083  grm.  cinnabar, 
and  to  0-005  grm.  mercury  in  0-2855  cinnabar. 

B.  METALLIC  MERCURY. 

The  analysis  of  commercial  mercury  offers  certain  difficulties 
because  quite  considerable  quantities  must  be  taken  to  be  oper- 
ated upon  in  order  to  detect  and  determine  the  frequently  very  small 
quantities  of  admixed  foreign  metals.  According  to  my  investi- 
gations *  the  object  may  be  best  attained  by  the  following  method: 
*  Zeitschr.  /.  analyt.  Chem.,  n,  343. 


§260.]  MERCURY    COMPOUNDS.  603 


1.  Dissolve  100  grm.  of  the  mercury  to  be  tested  in  a  flask  in 
an  excess  of  pure,  moderately  strong  nitric  acid,  and  heat  for  a 
long  time  to  boiling  in  order  to  convert  the  mercurous  salt  first 
formed  entirely  into  a  mercuric.     If  any  insoluble  residue  remains, 
collect  it  by  filtration,  wash,  dry,  fuse  it  with  potassium  sulphide, 
treat  the  melt  with  water,  filter  off  any  lead  sulphate,  etc.,  and 
acidulate  the  solution  with  hydrochloric  acid. 

After  settling,  filter  through  an  asbestos  filter  tube,  wash,  dry, 
and  heat  in  a  current  of  chlorine  (Vol.  J,  p.  716  [196]).  Treat 
the  metallic  chlorides  in  the  receiver  with  hydrogen  sulphide,  and 
preserve  the  precipitate  for  a  while ;  the  contents  of  the  filter-tube, 
however,  treat  with  nitrohydrochloric  acid,  and  test  the  solution 
for  gold  (Vol.  I,  p.  392,  b,  0). 

2.  Add  to  the  solution  of  mercuric  nitrate  56  grm.  pure,  con- 
centrated sulphuric  acid  mixed  with  120  grm.  water,  evaporate 
to  dryness  in  a  porcelain  dish,  and  continue  the  heat  until  all  the 
nitric  acid  has  been  expelled.     Dilute  the  residue  now  with  water, 
and  wash  the  whole  into  a  stoppered  flask  of  3  or  4  litres  capacity. 
We  now  have  all  the  mercury  in  the  flask,  partly  dissolved  as 
mercuric   sulphate,    partly   undissolved   as   basic   sulphate;    and 
with  these  are  present  all  the  foreign  metals  as  sulphates,  either 
dissolved  or  undissolved. 

3.  Add  ammonia  to  the  contents  of  the  flask  to  alkalinity, 
then  add  ammonium  sulphide  until  it  strongly  predominates,  and 
digest  for  24  hours  a    a  gentle  heat  with  frequent  stirring.     The 
liquid  above  the  dense,  black  precipitate  must  be  yellow  in  color, 
and  smell  strongly  of  ammonium   sulphide.     If  this  is  not  the 
case,  a  little  more  ammonium  sulphide  must  be  added,  and  the 
digestion    prolonged.      Pass    the    ammonium-sulphide    solution, 
containing  the  metals  of  the  sixth  group  (antimony,  tin,  arsenic, 
etc.),  through  a  large,  smooth   filter,  and  wash  the  dense  black 
precipitate  of  mercuric  sulphide  with  water  to  which  some  ammo- 
nium sulphide  has  been  added. 

4.  Acidulate  with  hydrochloric  acid  the  liquid  containing  the 
ammonium  sulphide,   add  the  precipitate  (reserved  from  1)    ob- 
tained from  the  solution  of  the  metallic  chlorides  volatilized  in 


604  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  260. 

the  current  of  chlorine,  allow  to  stand  2  or  3  days,  siphon  off  the 
clear,  supernatant  liquid  from  the  precipitate,  and  collect  the  latter 
consisting  chiefly  of  sulphur,  on  a  filter.  After  washing  this  first 
with  water  and  then  with  alcohol,  treat  it  with  carbon  disulphide. 
The  residue  which  usually  remains  treat  once  more  with  warm 
ammonium  sulphide,  in  order  to  remove  any  possible  traces  of 
mercury  and  copper,  and  then  determine  in  the  filtrate  any  tin, 
antimony,  and  arsenic,  if  such  are  present,  by  one  of  the  methods 
detailed  in  §  165.  Regarding  a  convenient  method  of  separating 
arsenic  and  antimony,  see  p.  556,  b,  this  volume. 

5.  If  the  presence  of  alkalies  and  alkaline  earths  is  suspected, 
these  are  to  be  tested  for  in  the  filtrate  from  the  precipitated 
sulphur  and  metallic  sulphides  obtained  in  4. 

6.  Rinse  into  a  flask  the  precipitate  of  mercuric  sulphide  ob- 
tained in  3,  together  with  any  traces  of  lead,  copper,  and  mercuric 
sulphides  obtained  in  1  and  4      If  much  water  has  been  required 
for  this  purpose,  allow  to  settle,  pass  the  supernatant  liquid  through 
a  small  filter,  and  rinse  the  small  quantity  collected  into  the  main 
precipitate.     Now  add  50  c.c.  of  pure  nitric  acid  of  sp.  gr.  1-2  and 
about  1  grm.  ammonium  nitrate  to  the  500  c.c.  or  so  of  liquid 
in  the  flask,  and  keep  the  whole  boiling  gently  for  an  hour.     Allow 
the  liquid  to  become  clear,  filter,  wash,  evaporate  the  nitric-acid 
solution  to  a  small  bulk,  dilute,  and  precipitate  any  silver  present 
by  adding  a  few  drops  diluted  hydrochloric  acid.      To   the  clear 
liquid,  or  the  filtrate  from  any  silver  chloride  deposited  on  long 
standing,  add  pure  sulphuric  acid  in  excess,  evaporate  until  all 
the  nitric  acid  has  been  expelled,  then  dilute,  heat,  filter  off  the 
precipitated   lead  sulphate,  wash   it   first  with  water   acidulated 
with   sulphuric    acid,  then  with  alcohol,  and  determine  the  lead 
according  to  Vol.  I,  p.  355,  a,  ft.    Add  a  little  hydrochloric  acid 
to  the  filtrate   from   the   lead    sulphate,  precipitate  with  hydro- 
gen sulphide,  and  in  the  precipitate  determine  the  bismuth,  copper, 
and  cadmium,  should  these  be  present,  as  detailed  on  p.  586,  7,  this 
volume. 

7.  To  the  filtrate  from  the  precipitate  obtained  by  hydrogen 
sulphate  in  6,  and  contained  in  a  flask  which  it  must  nearly  fill, 


§  261.]  COPPER    COMPOUNDS.  605 

add  ammonia,  ammonium  chloride,  and  ammonium  sulphide, 
allow  to  stand  24  hours,  and  in  the  precipitate  formed  determine 
the  metals  of  the  fourth  group,  particularly  zinc.  The  iron  which 
is  found  here  can  be  considered  as  originating  in  the  mercury  only 
when  all  the  reagents  and  filters  are  absolutely  free  from  iron. 

8.  Lastly,  exhaust  a  sample  of  the  mercuric  sulphide  with  boil- 
ing diluted  nitric  acid,  dry,  and  ignite  under  a  good  draught  in  a 
porcelain  crucible.     If  the  operation  has  been  properly  conducted, 
no  residue  should  remain. 

9.  If,  on  shaking  with  diluted  hydrochloric  acid,  mercury  yields 
a   solution   containing   mercuric    chloride,   the   mercury   contains 
mercuric  oxide.     The  quantity  of  this  may  be  ascertained  from 
the  mercury  contained  in  the  hydrochloric-acid  solution. 


[Regarding  the  electrolytic  determination  of  mercury,  as  well 
as  separations  from  other  metals,  see  CLASSEN'S  "Quantitative 
Chemical  Analysis  by  Electrolysis,"  B.  B.  BOLTWOOD  (JOHN  WILEY 
&  SONS,  New  York,  1903);  "Electro-Chemical  Analysis,"  EDGAR 
F.  SMITH  (P.  BLAKISTON'S  SON  &  Co.,  1902);  and  "Electrolytic 
Determinations  and  Separations,"  by  LILY  G.  KOLLOCK  (Jour. 
Amer.  Chem.  Soc.,  xxi,  No.  10). — TRANSLATOR.] 

19.  COPPER  COMPOUNDS. 

A.  COPPER  ORES. 

§261. 

Of  the  copper  ores  those  that  contain  metallic  copper,  cuprous 
oxide,  cupric  oxide,  or  copper  salts  require  no  special  considera- 
tion; but  detailed  accounts  are  necessary  of  the  complicated 
analyses  of  the  sulphuretted  copper  ores  (copper  pyrites,  purple 
copper  ore,  copper-glance,  etc.),  as  well  as  of  those  containing 
large  quantities  of  antimony  and  arsenic  (fahlerz). 

I.    METHODS   OF    COMPLETE    ANALYSIS. 

A    Sulphuretted  Copper  Ores. 

The  sulphuretted  copper  ores,  of  which  copper  pyrites  is  the 
most  frequently  subjected  to  analysis,  always  or  nearly  always 


606  DETERMINATION    OF    COMMERCIAL    VALUES.         [§    261. 

contain  copper,  iron,  sulphur,  and  gangue.  Whether  any  other 
metals  (nickel,  cobalt,  zinc,  manganese,  arsenic,  antimony,  sil- 
ver, etc.)  are  also  present  must  be  ascertained  by  qualitative 
analysis. 

Dry  the  very  finely  powdered  mineral  at  100°. 

1.  The  sulphur  content  is  best  determined  according  to  the 
method  detailed  for  pyrites  (p.  554,  1;  and  561,  1). 

2.  To  determine  the  copper,  iron,  and  gangue,  treat  about  1 
grm.  of  the  ore  with  concentrated  nitric  acid  in  an  inclined,  long- 
necked  flask,  add   some   strong  hydrochloric   acid   after  a  while, 
digest  until  entirely  decomposed,  and  evaporate  nearly  to  dryness 
at  a  gentle  heat.     If  the  hydrochloric  acid  added  does  not  suffice 
to  remove  all  the  nitric  acid,  .add  a  further  small  quantity  and 
evaporate    again    as    described.     Add    hydrochloric    acid    to    the 
residue,  warm,  dilute  with  water,  filter,  and  dry,  ignite,  and  weigh 
the  residual  gangue. 

If  the  ore  contains  any  admixed  galena,  the  residue  may  con- 
tain lead  sulphate.  In  such  a  case  this  must  be  removed  by 
digestion  with  ammonium  acetate  or  tartrate  before  the  drying 
and  ignition. 

Dilute  the  hydrochloric-acid  solution,  precipitate  hot  with 
hydrogen  sulphide,  filter  after  settling,  wash  the  copper  sulphide 
with  water  containing  hydrogen  sulphide,  spread  out  the  filter  in 
a  dish,  and  warm  with  sodium-sulphide  solution;  dilute,  filter, 
wash,  dissolve  the  copper  sulphide  in  nitrohydrochloric  acid,  dilute, 
and  filter;  incinerate  the  washed  filter  paper,  treat  the  ash  also 
with  a  little  nitrohydrochloric  acid,  strongly  concentrate  the 
solutions  containing  the  copper,  add  ammonia  until  the  free  acid 
is  neutralized,  then  add  ammonium  carbonate,  allow  to  stand  for  a 
long  time  at  a  gentle  heat,  filter,  acidulate  with  hydrochloric  acid, 
precipitate  hot  with  hydrogen  sulphide,  and  determine  the  copper 
according  to  Vol.  I  p.  375,  3,  a. 

The  filtrate  from  the  still  impure  copper  sulphide  first  precipi- 
tated by  hydrogen  sulphide  concentrate  by  evaporation,  oxidize 
with  nitric  acid,  precipitate  the  iron  according  to  Vol.  I,  p.  644  [82], 
and  determine  it  in  the  hydrochloric-acid  solution  of  the  precipi- 


§  261.]  COPPER    COMPOUNDS.  607 

tate  either  according  to  Vol.  I,  p.  642  [77],  or  volumetrically  accord- 
ing to  p.  327,  a. 

3.  To  determine  the  constituents  present  in  small  quantity, 
treat  about  10  grm.  of  the  finely  powdered  ore  with  fuming  nitric 
acid,  evaporate  with  a  slight  excess  of  sulphuric  acid  in  order  to 
remove  the  nitric  acid,  and  until  vapors  of  sulphuric  acid  begin 
to  be  evolved,  then  allow  to  cool,  add  water,  warm,  filter  into  a 
weighed  flask  of  about  one  litre  capacity,  and  wash  the  residue 
with  water  acidulated  with  sulphuric  acid.  Any  lead  that  may 
have  been  present  is  now  found  in  the  residue  as  lead  sulphate. 
Extract  the  residue  with  a  hot  solution  of  ammonium  acetate  to 
which  has  been  added  some  ammonia,  and  in  the  solution  deter- 
mine the  lead  by  precipitating  with  hydrogen  sulphide  and 
converting  the  lead  sulphide  into  lead  sulphate.  Exhaust  the 
residue  with  ammonium  acetate,  heat  with  hydrochloric  acid, 
dilute,  filter,  add  the  filtrate  to  the  sulphuric-acid  solution  first 
obtained,  and,  whether  clear  or  rendered  turbid  by  the  separation 
of  a  small  quantity  of  silver  chloride,  precipitate  hot  with  hydrogen 
sulphide,  add  water  until  the  flask  is  almost  filled,  mix,  let  stand 
for  a  long  time  to  settle,  and  weigh  the  whole.  The  weight  of  the 
empty  flask  and  that  of  the  copper  sulphide  from  2  being  known, 
the  difference  gives  the  weight  of  the  solution  in  the  flask.  Siphon 
off  as  much  of  the  dear  liquid  from  the  flask  as  possible,  and  again 
weigh  the  flask  with  the  residue.  Filter  the  liquid,  the  weight  of 
which  is  now  known;  and  should  it  not  be  absolutely  clear,  boil 
an  aliquot  portion  of  the  solution  so  obtained  w  th  some  nitric  acid, 
then  precipitate  with  an  excess  of  ammonia,  dis  olve  the  slightly 
washed  precipitate  in  hydrochloric  acid,  and  again  precipitate  the 
ron  as  a  basic  salt  according  to  Vol.  I,  p.  644  [82];  test  the  filtrate 
by  adding  ammonia  to  it  to  see  if  a  further  precipitate  of  alumina 
forms,  filter  from  this  should  it  occur,  acidulate  the  solution  with 
acetic  acid,  and  in  the  liquid  determine  nickel,  cobalt,  zinc,  and 
manganese,  should  such  be  present,  according  to  Vol.  II,  p.  491,  8. 
In  the  precipitates  afforded  by  ammonium  carbonate,  and  sub- 
sequently perhaps  by  ammonia,  determine  any  alumina  according 
to  Vol.  I,  p.  642  [78].  As  the  weights  of  the  alumina,  nickel,  cobalt, 


608  DETERMINATION    OF   COMMERCIAL    VALUES.         [§  261. 

etc.,  are  obtained  from  only  a  part  of  the  solution,  it  must  not  be 
forgotten  to  calculate  them  for  the  total  solution. 

To  the  residue  containing  copper  sulphide,  and  remaining  in 
the  flask,  add  first  potassa  or  soda  lye  to  alkaline  reaction,  then 
potassium-  or  sodium-sulphide,  and  warm  for  a  long  time.  Dilute 
with  water  until  the  flask  is  nearly  filled,  mix,  allow  to  cool,  and 
weigh.  On  deducting  from  this  weight  that  of  the  flask,  of  the  cop- 
per sulphide,  and  of  the  iron  sulphide  here  present,  the  weight  of 
the  alkaline  solution  containing  the  metals  of  the  sixth  group  is 
ascertained.  Siphon  off  as  much  of  the  clear  liquid  as  possible, 
determine  the  weight  of  the  liquid  siphoned  off  by  weighing  the 
flask  with  the  residue,  filter  the  solution  if  necessary,  precipitate 
with  hydrochloric  acid,  and  allow  the  precipitate  to  subside;  then 
collect  it,  wash,  digest  with  brominized  hydrochloric  acid,  filter, 
remove  the  excess  of  bromine  by  cautiously  adding  sulphurous 
acid,  precipitate  with  hydrogen  sulphide  at  70°,  and  separate  and 
determine  the  arsenic  and  antimony  according  to  pp.  556  and  557 
this  volume ;  calculate  the  values  so  obtained  from  the  part  to  the 
whole.  If  the  ore  contains  any  mercury,  this  would  pass,  in  the 
form  of  mercuric  sulphide,  into  the  solution  containing  sodium  or 
potassium  sulphide,  and  would  be  obtained  together  with  the 
antimony  and  arsenic  sulphides,  hence  it  would  have  to  be  separ- 
ated from  these  by  ammonium  sulphide. 

4.  Should  any  other  metals  of  the  fifth  group  be  present  besides 
copper,  lead,  and  mercury,  the  copper  must  ultimately  be  washed, 
dissolved  in  nitric  acid,  and  this  solution  employed  for  the  deter- 
mination of  the  other  metals  of  the  fifth  group.     Compare  §  263. 
Any  small  quantity  of  silver  present  may  be  best  determined  by 
cupellation  (pp.  579  and  580  this  volume). 

5.  In  regard  to  the  testing  for  thallium,  see  p.  560,  6,  this  volume. 

b.  Ores  containing  Antimony  and  Arsenic  (Fahlerz). 

In  the  analysis  of  fahlerz  (gray  copper  ore)  the  determination 
of  copper,  silver,  mercury,  iron,  zinc,  antimony,  arsenic,  lead, 
sulphur,  and  gangue,  must  be  kept  in  mind,  even  though  certain 
kinds  of  fahlerz  do  not  contain  all  the  metals  mentioned.  The 


§  261.]  COPPER  COMPOUNDS.  609 

analysis  is  best  conducted  by  heating  about  1  grm.  of  the  finely 
powdered  ore  in  a  slow  current  of  chlorine.*  For  this  purpose 
the  apparatus  shown  on  p.  695,  Vol.  I,  is  used,  but  modified  to  the 
extent  only  that  the  bulb-tube  D  is  replaced  by  a  similar  one  with 
two  bulbs.  Introduce  the  powdered  ore  into  the  bulb  connected 
with  the  chlorine-evolution  apparatus,  and  after  almost  completely 
expelling  all  the  air  from  the  evolution  flask  and  drying  apparatus, 
connect  the  bulb-tube,  which  is  fixed  slightly  inclined  downwards, 
with  C.  Charge  the  tubes  E  and  F  with  a  solution  of  tartaric 
acid  to  which  a  little  hydrochloric  acid  has  been  added.  The 
decomposition  of  the  fahlerz  begins  at  once,  the  bulb  becoming 
heated  thereby,  and  the  volatile  chlorides  are  carried  partly  as  far 
as  the  at  first  empty  second  bulb  of  the  bulb-tube,  partly  as  far 
as  E  and  F.  When  the  bulb  containing  the  ore  has  become  almost 
cold,  heat  it  very  gently  with  a  small  flame  while  passing  a  slow 
current  of  chlorine  through  it  in  order  to  drive  all  the  volatile 
chlorides  into  the  second  bulb.  It  is  inadvisable  to  continue  the 
heating  until  all  the  ferric  chloride  has  passed  into  the  second  bulb, 
but  rather  to  stop  when  the  vapor  of  ferric  chloride  alone  begins 
to  come  over.  As  soon  as  the  piece  of  tubing  between  the  two 
bulbs  has  become  clean,  and  the  apparatus  has  become  cold,  cut 
the  tube  between  the  two  bulbs  by  means  of  a  file  mark  and  a  piece 
'of  ignited  charcoal,  and  close  that  portion  attached  to  the  bulb 
containing  the  sublimate  with  a  short  glass  tube  sealed  at  one 
end  and  moistened  internally  with  water.  Allow  the  apparatus 
to  stand  for  twenty-four  hours  in  order  that  the  sublimate  may 
absorb  moisture  and  thus  be  rendered  soluble  in  water  without 
disengagement  of  heat.  Then  treat  the  contents  of  the  bulb  with 
a  dilute  solution  of  tartaric  acid  to  which  some  hydrochloric  acid 
is  added.  Should  the  liquid  be  turbid  from  the  separation  of 
oxygen  compounds  of  antimony,  warm  it  until  they  dissolve;  if 
sulphur  has  separated,  filter  the  liquid. 

The  analysis  now  resolves  itself  into  an  examination  of  the 

*  Compare  H.  ROSE,  Handbuch  der  analyt.  Chemie,  6th  edit.,  by  R. 
FIXKENER,  n,  479. — F.  WOHLER,  Die  Mineralanalyse  in  Beispielen,  2d  edit., 
p.  73. 


610  DETERMINATION    OF   COMMERCIAL    VALUES.  [§  261. 

residue  remaining  in  the  first  bulb  of  the  solution  of  the  volatile 
chlorides,  and  lastly  into  the  separate  determination  of  the  sul- 
phur. 

1.  The  residue  contains  or  may  contain  the  chlorides  of  silver, 
lead,  and  copper,  a  portion  of  the  ferric  chloride,  all  or  nearly  all 
the   zinc   chloride,   and   gangue.     Digest  it   with   diluted   hydro- 
chloric acid  for  a  long  time,  dilute  with  much  water,  allow  to  stand 
for  quite  a  while,  and  filter  off  the  silver  chloride;  wash  this  with 
boiling  water  until  all  the  lead  chloride  has  been  removed,  if  neces- 
sary separate  the  silver  chloride  from  the  gangue  by  means  of 
ammonia,  precipitate  the  silver  chlor  de  in  the  ammoniacal  solu- 
tion by  means  of  nitric  acid,  and  determine  the  silver  in  the  pre- 
cipitate according  to  p.  342,  Vol.  I.     Precipitate  the  filtrate  with 
hydrogen  sulphide  (Vol.  I    p.  677),  and  in  the  precipitate  then 
separate  the  lead  and  copper  according  to  Vol.  I,  p.  689,  2  [146]. 
Preserve  the  filtrate  for  a  while  however. 

2.  The  solution,  which  contains  the  mercury,  antimony,  arsenic, 
and  a  portion  of  the  iron,  precipitate  with  hydrogen  sulphide  at 
70°,  filter,  and  wash.     In  the  precipitate  separate  the  mercuric 
sulphide  from  antimony  and  arsenic  sulphides  by  means  of  ammo- 
nium sulphide  (Vol.  I,  p.  701,  2  [167]),  and  determine  the  mercury 
as  sulphide  (Vol.  I,  p.  366,  3).     Arsenic  and  antimony,  however, 
are  best  separated  according  to  BUNSEN'S  method  (pp.  556  and 
557  this  volume).     Boil  the  mercuric  sulphide  obtained  with  di- 
luted nitric  acid,  and  in  the  filtrate  determine  any  slight  quantity 
of  lead  that  may  be  present. 

The  liquid  filtered  off  from  the  precipitate  thrown  down  by 
hydrogen  sulphide,  add  to  the  similar  solution  obtained  from  the 
residue  in  1,  and  determine  therein  the  iron  and  zinc  (pp.  557  to 
559  this  volume),  and  also  any  alkaline  earths,  should  these  be 
present. 

3.  The  sulphur  is  best  determined  by  fusing  a  fresh  sample 
of  the  ore  with  sodium  carbonate  and  potassium  nitrate,  as  in  the 
case  of  pyrites  (p.  561,  1,  this  volume). 


§  261.]  COPPER    COMPOUNDS.  611 

II.    DETERMINATION    OF   THE    COPPER    CONTENT   OF 
COPPER    ORES. 

1.  By  Ordinary  Gravimetric  Analysis. 

The  process  is  conducted  exactly  as  in  §  261,  I,  af  weighing 
the  copper  as  sulphide,  and  omitting  the  determination  of  the 
other  metals,  etc. 

2.  Determination  of  the  Copper  by  Electrolysis. 

When  it  is  a  question  of  making  a  number  of  copper  deter- 
minations daily  in  ores  of  a  simliar  character  the  electrolytic 
method  is  preferable  to  all  others. 

This  was  first  described  by  WOLCOTT  GIBBS,*  and  by  LucKOW,f 
and  introduced  into  general  use  by  the  MAXSFELD  Ober-Berg-  und 
Hiittendirection  in  Eisleben,  for  ores  containing  no  antimony, 
arsenic,  or  bismuth.];  The  method  is  unsuitable  for  ores  contain- 
ing these  metals,  because  they  are  precipitated  on  the  copper  and 
blacken  it. 

Further  references  to  the  electrolytic  determination  of  copper 
are  given  in  the  foot-note.§ 

a.  Production  of  the  Current. 

For  the  production  of  the  current  MEIDINGER'S  element  was 
first  made  use  of  in  the  laboratories  of  the  MANSFELD  Ober-Berg- 
und  Hiittendirection,  and  later  on  PINKUS'  modified  MEIDINGER'S 
element,  but  now  the  MURE  and  CLAMOND  ||  thermopile  as  im- 
proved by  CLAMOND. *[  HERPIN  who  also  operated  with  the  BUNSEN 
battery,  a  fmall  GRAMME  machine,  and  the  CLAMOND  thermopile, 

*  Zeitschr.  /.  analyt.  Chem.,  in,  334. 

•j-  DINGL.  polyt.  Journ.,  CLXXVII,  296;  also,  Zeitschr.  f.  analyt.  Chem., 
xix,  1. 

|  Zeitschr.  f.  analyt.  Chem.,  vin,  23;  xi,  1 ;  and  xiv,  350. 

§  MERRICK,  Americ.  Chem.,  n,  136. — WRIGHTSON,  Zeitschr.  f.  analyt. 
Chem.,  xv,  299. — HERPIN,  "'bid.,  xv,  335. — OHL,  ibid.,  xvni,  523. — A.  CLASSEN 
and  M.  A.  v.  REIS,  Berichte  der  deutsch.  chem.  Gesellsch.,  1881,  No.  13> 
p.  1627. — A.  RICHE,  Zeitschr.  f.  analyt.  Chem.,  xvn,  216,  and  xxi,  116.  . 

11  DINGL.  polyt.  Journ.,  ccvii,  125. 

Tf  Ibid.,  ccxv,  427;  Zeitschr.  f.  analyt.  Chem.,  xiv,  350. 


612  DETERMINATION   OF    COMMERCIAL   VALUES.          [§  261. 

4 


FIG.  117. 


FIG.  118. 


§  261.]  COPPER  COMPOUNDS.  613 

recommends  the  use  of  the  last  by  preference.  For  use  in  the 
chemical  laboratory  the  CLAMOND  thermopile  is  undoubtedly  the 
most  convenient  apparatus  for  the  production  of  a  suitable  cur- 
rent. I  would  therefore  refer  to  the  reports. of  the  MANSFELD 
Ober-Berg-  und  Hiittendirection  *  for  particulars  regarding  the 
MEIDINGER-PINKUS  element  and  its  working,  and  will  here  confine 
myself  to  a  description  of  the  CLAMOND  thermopile  f  only.  This 
apparatus  is  illustrated  by  Figs.  117,  118,  and  119. 

Fig.  117  is  a  perspective  view;  Fig.  118  a  vertical  section, 
showing  also  the  armatures;  and  119,  a  cross-section  of  the  bars 
and  the  armatures  in  position. 

The  elements  are  composed  of  iron,  and  an  alloy  of  zinc  and 
antimony.  In  order  to  impart  greater  durability  to  the  latter 
the  bars  must  be  cast  in  molds  heated  to  a  temperature  slightly 
below  the  melting-point  of  the  alloy;  nor  should  the  alloy  itself 
be  strongly  overheated.  The  elements  are  arranged,  as  shown 
in  Fig.  119,  radially  around  a  centre,  several  such  superimposed 
rings  constituting  one  pile. 

In  Fig.  119  B  denotes  the  bars  of  zinc-antimony  alloy,  while 
L  denotes  the  tinned-iron  plate; 
the  latter  serve  as  conductors 
from  one  element  to  another, 
hence  they  are  laid  on  the  upper 
surfaces  of  the  bars  B.  As  the 
bars  B  expand  much  more  than 
the  iron,  the  contact  increases  on 
heating.  The  individual  ele- 
ments are  insulated  by  layers  of 
asbestos  (r,  Fig.  118),  and  so  are 
also  the  different  superimposed 

rings  of  elements  B.  The  whole  forms  a  cylinder,  all  the  junctions 
being  directed  toward  the  inner  side;  the  junctions  are  protected 
from  the  direct  action  of  the  gas-flame  by  lining  the  inner  cylinder 
with  asbestos.  The  heating  is  effected  by  means  of  gas,  and  for 
this  purpose  a  porcelain  tube,  A,  perforated  with  holes,  Figs.  118 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  4.  f  Ibid.,  xv,  334. 


614 


DETERMINATION    OF    COMMERCIAL    VALUES.         [§  261. 


and  119,  is  placed  within  the  cylinder.  The  gas  passes  first  through 
a  GIKOUD  regulator,  C  (Fig.  118),  in  order  to  secure  a  uniform 
flame  under  varying  pressures,  and  thus  obtain  a  constant  cur- 
rent; it  then  passes  through  the  tube  T,  into  which  air  flows 
through  various  apertures,  and  reaches  A,  at  the  perforations  of 
which  the  mixture  of  gas  and  air  burns,  any  further  quantity  of 
air  necessary  for  perfect  combustion  entering  from  below  by  the 
annular  space  D  between  the  tube  A  and  the  inner  walls  of  the 


FIG.  120. 


FIG.  121. 


cylinder  (Fig.  118).    The  burner  is  lighted  from  above,  the  cover 
being  first  removed. 

The  individual  elements  of  a  ring  are  connected  in  series,  but 
the  rings  themselves  can  be  made  up  variously,  according  to  the 
external  resistance.  For  this  purpose  the  poles  of  each  ring 
terminate  in  binding-screws  arranged  on  two  vertical  metallic 
strips  as  shown  in  Fig.  117.  In  the  illustration  the  elements  are 
shown  combined  in  series,  while  in  the  sketch  plan  to  Fig.  118  the 
rings  are  made  up  in  compound  circuit. 


§  261.] 


COPPER   COMPOUNDS. 


615 


6.  Form  of  the  Electrodes. 

Regarding  the  form  of  the  electrodes  used  in  electrolytic  deter- 
minations, LUCKOW  at  first  employed  a  cylinder  of  platinum  foil 
as  the  negative  electrode,  and  a  spiral  of  stout  platinum  wire  as 
the  positive  electrode.  Repeated  experiments  in  the  laboratory 
of  the  MANSFELD  Ober-Berg-  und  Hiittendirection  at  Eisleben 


FIG.  122. 

have  resulted  in  the  adoption  of  the  electrodes  having  the  form 
shown  in  Figs.  120  and  121.  The  hollow  truncated  cone  weighs 
20  grin,  and  is  75  mm.  high,  9  mm.  in  diameter  at  the  top,  and 
58  mm.  in  diameter  at  the  base.  The  platinum  cone  is  provided 
with  several  openings  in  the  sides  in  order  to  allow  the  escape  to 
the  outer  surface  of  the  cone  of  the  oxygen  liberated  when  electro- 
lyzing  solutions  containing  much  iron ;  this  is  indispensable  in  order 
to  prevent  the  partial  reduction  with  a  current  of  sufficient  strength 


616  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  261. 

of  ferric  to  ferrous  salts,  and  of  free  nitric  acid  to  nitric  oxide,  and 
to  thereby  avoid  the  black-brown  coloration  which  the  liquid 
would  otherwise  acquire.  The  platinum  spiral  weighs  16  grm. 

In  the  laboratory  of  CHRISTOFLE  &  Co.,  of  Paris,  where,  in  the 
analysis  of  copper-nickel  alloys  and  German  silver,  it  is  necessary 
to  operate  with  concentrated  solutions,  another  form  of  electrode 
is  used;  this  is  described  by  HERPIN  (loc.  cit.),  and  is  shown  in 
Figs.  122  and  123.  The  apparatus  consists  of  a  platinum  dish, 
A,  supported  on  a  tripod,  B,  and  connected 
with  negative  pole  of  the  thermopile;  the 
positive  electrode  is  formed  by  the  platinum 
spiral,  C.  The  whole  is  covered  with  the  glass 
funnel,  D,  in  order  to  prevent  any  loss  of  sub- 
stance by  reason  of  the  escape  of  the  gas 
evolved. 

FIG.  123.  A.   CLASSEN   and  M.   A.   VON  REIS  *   also 

employ  as  negative  electrode  a  rather  deep 
platinum  dish  covered  with  a  watch-glass;  and  for  the  positive 
electrode  they  use  a  disc  of  platinum  foil  about  4-5  cm.  in  diameter, 
and  fastened  to  a  rather  stout  platinum  wire  by  means  of  a  plati- 
num screw. 

RICHE  t  employs  in  the  electrolysis  of  small  quantities  of  fluid 
a  platinum  crucible  which  at  the  same  time  acts  as  the  positive 
electrode.  The  negative  electrode  is  a  platinum  cone,  Fig.  124, 
open  at  both  ends,  and  corresponding  as  nearly  as  possible  to  the 
form  of  the  crucible.  Elongated  openings  are  cut  in  the  sides 
of  the  cone  so  that  the  concentration  may  be  maintained  as  uni- 
form as  possible.  The  distance  between  the  cone  and  the  crucible 
may  be  from  2  to  4  mm.  Fig.  125  shows  the  entire  arrangement 
and  requires  no  further  description,  except  that  the  rod  A  is  made 
of  some  non-conducting  material,  like  glass.  If  the  current  is 

*  Ber.  d.  deutsch.  chem.  Gesellsch.,  1881,  No.  13,  p.  1623;  also,  Quanti- 
tative Analyse  auf  electrolytischem  Wege,  by  AL.  CLASSEN,  Aachen,  J.  A.  MAYER, 
1882. 

f  Ann.  de  chim.  et  de  Phys.  [5  s6r.]  xm,  508;  Zeitschr.  /.  analyt.  Chem., 
xxi,  116. 


§  261.] 


COPPER    COMPOUNDS. 


617 


to  act  in  a  warm  liquid,  the  crucible  is  set  in  a  basin  of  water  which 
is  then  heated.  If  the  deposition  must  be  effected  in  larger  quan- 
tities of  liquid  in  a  beaker,  RICHE  employs  as  a  negative  electrode 


FIG.  124. 


FIG.  125. 


a  platinum  cylinder,  and  as  a  positive  a  piece  of  platinum  gauze 
bent  into  a  cylindrical  form;  and  the  rapidity  of  action  is  in- 
creased by  employing,  besides  the  platinum  gauze  outside  the 
platinum  cylinder,  a  supplementary  positive  electrode  in  the  form 
of  a  platinum  spiral  placed  within  the  cylinder. 

[F.  A.  GOOCH  and  H.  E.  MEDWAY  *  employ  as  a  cathode  an  or- 
dinary 20-c.c.  platinum  crucible  rotating  at  a  speed  of  from  600 
to  800  revolutions  a  minute.  The  crucible  is  driven  by  a  small 
inexpensive  electric  motor  fastened  so  that  its  shaft  is  vertical. 
Upon  this  shaft  the  crucible  is  fixed  by  pressing  it  over  a  rubber 
stopper  bored  centrally  and  fitted  tightly  on  the  end  of  the  shaft 
(Fig.  125a).  To  secure  electrical  connection  between  crucible  and 
shaft,  a  narrow  strip  of  sheet  platinum  is  soldered  to  the  shaft 
and  then  bent  upward  along  the  sides  of  the  stopper,  thus  putting 
the  shaft  in  contact  with  the  inside  of  the  crucible  when  the  latter 


*  Amer.  Journ.  of  Science,  xv,  320. 


618 


DETERMINATION    OF    COMMERCIAL    VALUES.          [§  261. 


is  pressed  over  the  stopper.  The  shaft  is  made  in  two  parts  as  a 
matter  of  convenience  in  removing  the  crucible,  and  is  joined, 
with  care  to  make  a  good  contact  between  the  two  pieces  of  shaft- 
ing, by  a  rubber  connector  of  sufficient  thickness  to  prevent  the 
crucible  from  wobbling  when  rotated. 

The  solution  to  be  electrolysed  is  placed  in  a  beaker  upon  a 
small  adjustable  stand,  so  that  the  crucible  may  be  dipped  into  the 
liquid  to  any  desired  depth.  A  platinum  plate  is  employed  as  an 


FIG.  125  a. 

anode,  and  this  is  connected  with  the  positive  pole  of  a  series  of  four 
storage  batteries,  while  the  negative  pole  of  this  series  is  connected 
with  the  bearing  in  which  the  shaft  rotates,  thus  allowing  the  current 
to  go  from  the  platinum  plate  through  the  solution  to  the  crucible; 
up  the  shaft  of  the  motor  and  back  to  the  batteries.  The  powrer 
to  run  the  motor  is  taken  from  the  incandescent  light  circuit  of 
the  street. 

From  results  obtained  in  a  number  of  experiments,  it  has  been 
found  that  nickel  also,  like  copper  and  silver,  may  be  deposited 
with  rapidity  and  completeness. 

The  metallic  deposits  of  these  metals  obtained  by  means  of  the 


§  261.]  COPPER  COMPOUNDS.  619 

revolving  cathode  are  sufficiently  coherent  and  compact  to  permit 
accurate  manipulation  and  weighing,  even  when  the  current  den- 
sity on  the  cathode  is  very  considerable,  and  variable  within  wide 
limits.  Other  metals  have  been  found  to  behave  similarly. 

The  advantages  claimed  for  this  rotating  cathode  in  analytical 
operation  are:  The  process  as  described  is  rapid,  exact,  and  very 
simple;  the  apparatus  required,  moreover,  is  inexpensive,  and, 
if  it  is  required  to  make  many  determinations  simultaneously,  a 
single  motor  may  be  made  to  drive  a  running  belt  over  any  reason- 
able number  of  rotating  shafts. — TRANSLATOR.] 

c.  Dissolving  the  Ore  (or  Lode)  and  Preparing  the  Solutions 
for  Electrolysis* 

a.  If  the  Ores  contain  no  Silver. 

The  electrolysis  is  always  effected  in  nitric-acid  solution; 
small  quantities  of  free  sulphuric  acid,  such  as  occur  when  a  nitric- 
acid  solution  of  neutral  copper  sulphate  is  electrolyzed,  are  not 
prejudicial,  but  hydrochloric  acid  must  never  be  present  in  the 
solution,  otherwise  the  copper  will  not  be  deposited  on  the  nega- 
tive electrode — the  platinum  cylinder — with  its  usual  handsome 
color,  but  will  be  blackish. 

If  the  ores  contain  bitumen,  they  are  roasted  before  proceeding 
to  dissolve  them.  If  nitric  acid  suffices  to  effect  solution,  employ 
only  this  acid,  evaporate  the  excess,  and  dissolve  the  residue  by 
the  aid  of  20  c.c.  nitric  acid  of  sp.  gr.  1-2  and  water  to  make 
200  c.c.  of  liquid.  This  volume  of  liquid,  and  also  the  proportion 
of  acid  to  water,  must  be  adhered  to  in  all  electrolytic  determinations 
of  copper. 

If  nitric  acid  alone  does  not  suffice,  nitric  acid,  or,  better,  nitro- 
hydrochloric  acid,  with  the  addition  of  sulphuric  acid,  is  em- 
ployed. 

*  The  directions  given  under  c  are  taken  from  the  above  cited  reports 
of  the  MANSFELD  Ober-Eerg-  und  Hiittendirection,  in  the  laboratory  of 
which  the  electrolytic  determination  of  copper  has  been  practiced  for  about 
twelve  years.  On  p.  623,  /,  are  described  various  modifications  recommended 
by  others. 


620  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  261. 

In  the  case  of  ores  or  lodes  rich  in  copper,  take  about  2  grm., 
effecting  solution  in  a  hemispherical  porcelain  dish  14  cm.  in 
diameter  and  6  cm.  deep,  and  using  40  c.c.  nitric  or  nitrohydro- 
chloric  acid,  and  4  c.c.  concentrated  sulphuric  acid,  which  is 
previously  diluted  with  an  equal  volume  of  water.  Cover  the 
dish  with  a  glass  cover  while  effecting  the  solution,  this  being 
assisted  by  heating  on  a  sand-bath.  After  rinsing  off  the  glass 
cover  into  the  porcelain  dish,  cautiously  evaporate  the  con- 
tents of  the  latter  to  dryness,  drive  off  the  excess  of  sulphuric 
acid,  and,  if  any  sulphur  has  separated,  burn  it  off.  Dissolve 
the  residue  in  20  c.c.  nitric  acid  of  sp.  gr.  1-2,  dilute  with 
water,  and  filter  into  a  beaker  8  cm.  inside  diameter  and  12  cm. 
high;  the  beaker  should  bear  a  mark  to  show  where  it  will  hold 
200  c.c.,  and  it  should  also  be  provided  with  an  opening  11  mm. 
wide  and  9-5  cm.  from  the  bottom,  through  which  the  acid  liquid 
may  be  removed  when  the  electrolysis  is  complete.  After  washing 
the  undissolved  residue,  dilute  the  solution  to  the  mark.  If, 
after  separating  the  copper,  the  liquid  is  to  be  used  for  the  deter- 
mination of  other  substances  present,  such  beakers  must  be  selected 
as  are  provided  with  a  glass  tube  bent  at  right  angles  and  inserted 
at  a  distance  of  20  mm.  from  the  upper  edge. 

/?.  For  Ores  containing  Silver. 

If  the  ores  contain  silver,  the  latter,  when  chlorine-free  nitric 
and  sulphuric  acids  are  employed  as  the  solvents,  will  pass  com- 
pletely into  solution  with  the  copper,  and  will  be  thrown  down 
and  weighed  with  it.  The  silver  must  hence  be  determined  in 
a  separate  quantity  of  ore  and  its  weight  deducted.  If  this  is 
not  desired,  the  silver  may  be  separated  from  solutions  prepared 
with  pure  nitric  acid  by  adding  an  accurately  known  quantity 
of  very  dilute  hydrochloric  acid,  1  c.c.  of  which  will  be  the  equiv- 
alent of  0-001  grm.  silver.  If  nitric  acid  alone  does  not  suffice 
to  effect  the  solution,  use  nitrohydrochloric  acid,  but  in  this  case 
evaporate  to  dryness,  treat  the  residue  with  nitric  acid,  dilute 
with  water,  and  filter.  The  solution,  now  free  from  silver,  evapo- 
rate to  dryness  with  the  addition  of  sulphuric  acid  and  proceed 
as  in  a. 


§  261.]  COPPER   COMPOUNDS.  621 

d.  Electrolytic  Precipitation  of  Copper. 

After  the  solution  has  been  well  stirred,  introduce  first  the 
platinum  spiral  (positive  electrode),  then  the  platinum  cylinder 
(negative  electrode).  The  distance  of  the  latter  from  the  base 
of  the  spiral  should  be  barely  5  mm.  in  the  case  of  strongly  ferru- 
ginous liquids;  in  solutions  very  rich  in  copper  the  distance  may 
be  10  mm. 

Before  connecting  the  electrodes  with  the  thermopile,  it  must 
be  ascertained  whether  the  current  is  of  the  right  strength.  In  this 
connection  it  must  be  noted  that  for  samples  containing  small  quan- 
tities of  copper,  the  current  should  be  of  such  strength  as  to  yield 
from  16  to  25  c.c.  of  oxyhydrogen  gas  in  thirty  minutes  on  decom- 
posing water  acidulated  with  sulphuric  acid.  If,  however,  larger 
quantities  of  copper  are  to  be  deposited,  the  strength  of  the  current 
in  case  of  solutions  poor  in  iron  must  be  such  as  to  yield  from 
75  to  100  c.c.,  and  with  those  rich  in  iron,  from  100  to  120  c.c., 
of  the  oxyhydrogen  gas  in  thirty  minutes.  The  strength  of  the 
current  may,  of  course,  be  measured  by  the  tangent  galvanometer 
instead  of  by  a  voltmeter. 

The  copper  begins  to  deposit  on  the  platinum  cylinder  soon 
after  the  electrodes  are  connected  with  the  thermopile.  If  the 
deposit  is  pure,  it  exhibits  the  fine  light  color  of  copper,  and  if  the 
current  strength  is  correct,  the  deposit  is  bright  and  adherent. 
The  time  required  for  the  deposition  varies  according  to  the  copper 
content.  Solutions  very  rich  in  copper  require  more  than  twelve 
hours  for  complete  deposition,  hence  hi  such  cases  the  current 
must  be  allowed  to  act  for  about  eighteen  hours. 

When  the  deposition  appears  to  be  complete,  raise  the  level 
of  the  water  in  the  beaker  by  adding  water.  If  the  clean  portion 
of  the  platinum  cylinder  which  was  previously  above  the  liquid, 
but  which  is  now  submerged,  exhibits  no  reddish  deposit  after 
the  lapse  of  half  an  hour,  the  precipitation  is  complete.  Further 
assurance  of  this  is  obtained  by  pipetting  off  a  small  quantity  of 
the  liquid  and  testing  with  hydrogen-sulphide  water. 

Now,  while  the  current  is  still  acting,  introduce  a  current  of 


622  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  201. 

water  at  the  bottom  of  the  beaker  so  as  to  completely  expel  the 
acid  liquid.  As  soon  as  the  water  running  off  no  longer  has  an 
acid  reaction,  loosen  the  binding  screws,  remove  the  platinum 
cylinder,  wash  it  with  alcohol,  dry  at  90°  to  95°,  and  weigh  when 
cold.  The  increase  in  weight  gives  the  quantity  of  copper  deposited. 

e.  Procedure  when  the  Deposited  Copper  is  Blackish. 

If  the  copper  solutions  contain  arsenic,  antimony,  selenium,  or 
bismuth,  the  copper  becomes  covered  with  a  brown  to  blackish 
deposit,  and  the  accuracy  of  the  results  is  interfered  with.  A 
grayish-black  or  occasionally  peacock-like  color  may  also  occur 
if  the  solution  contains  traces  of  hydrochloric  acid. 

If  the  elements  causing  the  black  deposit  are  present  in  very 
small  quantity  only,  and  if  they  rnay  be  volatilized  by  heating  to 
redness  with  access  of  air,  as  in  the  case  with  arsenic,  antimony, 
or  selenium,  then  wash  the  platinum  electrode  on  which  the  black 
deposit  has  formed  with  alcohol,  dry,  and  heat  to  redness  in  a 
gas-  or  alcohol-flame,  or  in  a  muffle.  Arsenic  and  antimony  vola- 
tilize, but  the  copper  is  converted,  without  any  loss  whatever,  into 
cupric  and  cuprous  oxides.  Now  place  the  platinum  electrode, 
thus  treated,  in  a  beaker,  suspend  over  it  a  similar  but  larger 
and  weighed  platinum  electrode,  connect  the  latter  with  the  nega- 
tive and  the  former  with  the  positive  pole  of  the  battery,  and  pour 
a  sufficient  quantity  of  diluted  nitric  acid  (1  part  of  acid  to  6  parts 
of  water)  into  the  beaker.  The  copper  oxides  dissolve,  and  the 
pure  copper  is  deposited  on  the  outer  platinum  electrode;  it  is 
then  determined  in  the  usual  way.  If  the  elements  causing  the 
black  color  are  present  in  larger  quantities,  the  moment  when  they 
begin  to  be  deposited  must  be  watched  for;  the  acid  liquid  is  then 
at  once  expelled,  and  the  platinum  electrode  bearing  the  only 
slightly  blackened  deposit  treated  as  described  above. 

If  the  copper  solution  contains  lead,  the  latter  is  not  deposited 
with  the  copper  at  the  negative  pole,  but  separates  at  the  positive 
pole  as  lead  dioxide,  and  may,  if  the  quantity  is  not  too  large,  be 
determined  by  the  increase  in  weight  of  the  spiral  dried  at  100°. 
If  larger  quantities  of  lead  are  present,  only  a  part  of  the  lead 


§  261.]  COPPER  COMPOUNDS.  623 

dioxide  adheres  to  the  platinum  spiral,  while  the  rest  separates 
in  the  form  of  thin  flakes. 


/.  Methods  differing  from  those  adopted  by  the  MANSFELD  Works. 

Under  this  heading  I  call  attention  to  several  modifications 
of  the  process  described  above. 

a.  WRIGHTSON*  effects  the  deposition  in  ordinary  beakers,  and 
while  the  current  is  acting,  siphons  off  the  acid  liquid  while  pure 
water  is  being  constantly  added;  he  does  not  dry  the  copper  spiral 
with  alcohol,  but  simply  dries  it  at  100°  to  120°. 

/?.  AL.  CLASSEN  and  M.  A.  VON  REIS  f  deposit  the  copper  from 
solutions  containing  it  in  the  form  of  ammonio-cupric  oxalate 
with  a  considerable  excess  of  ammonium  oxalate.  For  the  deter- 
mination of  large  quantities  of  copper,  a  current  is  employed  capable 
of  evolving  330  c.c.  of  oxyhydrogen  gas  per  hour,  and  which  will 
hence  deposit  0-15  grm.  copper  in  about  twenty-five  minutes. 
For  separating  copper  from  zinc,  AL.  CLASSEN  J  prefers  to  deposit 
from  acid  sulphuric-acid  solutions  rather  than  from  acid  nitric- 
acid  solutions.  Compare  also  p.  630,  e,  this  volume. 

f.  RICHE  §  employs  a  BUNSEN  element  for  the  deposition  of 
copper.  The  sulphuric-acid  or  nitric-acid  solution  is  evaporated 
almost  to  dryness,  the  residue  taken  up  with  water,  and  ths  liquid 
electrolyzed  at  60°  to  90°.  The  copper  rapidly  deposits  as  a 
handsome,  red,  adherent  coating.  When  the  deposition  is  com- 
plete, the  cone  is  removed  from  the  crucible  without  interrupting 
the  current  (comp.  p.  616  this  volume),  and  immediately  sub- 
merged in  distilled  water;  it  is  then  dried  at  50°  to  60°,  and  weighed. 
RICHE  in  this  manner  effects  the  deposition  of  1  grm.  copper  in 
three  and  one  half  hours.  If  iron  is  present,  the  decomposition 
must  be  conducted  at  a  temperature  not  exceeding  70°. 

*  Zeitschr.  f.  analyt.  Chem.,  xv,  299. 

t  Berichte  der  deutsch.  chem.  Gesellsch.,  xrv,  No.  13,  1627. 

t  Quantitative  Analyse  auf  elektrolytischem  Wege,  by  Dr.  AL.  CLASSEN, 
Aachen,  J.  A.  MATER,  1882,  p.  12. 

§  A*in.  de  chim.  tt  de  phys.  [5  s£r.],  xni,  508;  Zeitschr.  f  analyt.  Chem., 
xxi,  )  8. 


624  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  261. 

d.  LECOQ  DE  BOISBAUDRAN  *  employs  the  following  process  for 
determining  copper  in  solutions  containing  much  ferrous  sulphate: 
For  the  production  of  the  current  he  uses  three  BUNSEN  elements, 
weakly  charged,  and  for  the  negative  electrode  a  platinum  crucible, 
a  semicylindrical  piece  of  platinum  foil  serving  as  the  positive 
electrode.  In  order  to  prevent  the  ferric  salt  separated  at  the 
positive  pole  from  corroding  the  copper,  which  may  easily  happen 
in  acid  solutions,  he  rapidly  siphons  off  the  iron  solution  when 
the  deposition  is  complete,  while  the  positive  electrode  is  mean- 
while lowered  very  close  to  the  bottom  of  the  crucible,  so  that  the 
current  continues  to  pass  while  the  liquid  is  being  removed.  The 
copper  is  then,  without  interrupting  the  current,  repeatedly  washed 
first  with  diluted  sulphuric  acid  and  then  with  boiling  hot  water. 

[Regarding  the  commercial  analysis  of  copper  see  A.  HoLLARD'sf 
paper  on  this  subject.  The  electrolytic  determination  of  copper  and 
its  separation  from  other  metals  electrolytically  is  al  o  fully  treated 
of  by  EDGAR  F.  SMITH,  "Electro-Chemical  Analysis,"  and  CLASSEN'S 
"Quantitative  Analysis  by  Electrolysis,"  translated  by  B.  B.  BOLT- 
WOOD.  JOHN  WILEY  &  SONS,  New  York,  1903. — TRANSLATOR.] 

3.    OTHER    METHODS    OF    DETERMINING    COPPER. 

a.  FR.  MOHR  J  recommends  the  following  methods  of  determin- 
ing copper  in  ores: 

a.  For  Oxidized  Ores  (Cupric  and  Cuprous  Oxides,  Malachite, 
and  Cupric  Phosphate). 

Treat  5  grm.  of  a  rich,  or  10  grm.  of  a  poor,  ore,  in  fine 
powder,  with  some  sulphuric  acid,  water,  and  nitric  acid  in  a 
porcelain  dish  of  10  cm.  diameter,  and  after  covering  the  dish 
with  a  large  watch  glass,  heat  to  boiling.  As  soon  as  the  mass 
is  nearly  dry,  and  has  ceased  to  spirt,  remove  the  watch-glass 
and  increase  the  flame.  Sulphuric  acid  and  sulphuric  anhydride 

*  Bull.  mens.  de  la  soc.  chim.  de  Paris,  1869,  p.  35;  Zeitschr.  f.  analyt. 
Chem.,  ix,  102. 

t  "Commercial  Analysis  of  Copper"  (Bull.  Soc.  Chim.,  [3],  xxiu,  No.  8; 
Chem.  News,  LXXXI,  258). 

|  Zeitschr.  f.  analyt.  Chem.,  i,  143. 


§  261.]  COPPER   COMPOUNDS.  625 

are  evolved  from  the  ferric  sulphate  only  at  a  high  temperature; 
the  heat  must  be  increased  to  a  point  until  no  more  fumes  are 
given  off;  then  allow  to  cool,  add  distilled  water,  heat  to  boiling, 
filter  into  a  small  platinum  dish,  wash  with  hot  water,  transfer 
the  evaporated  and  concentrated  washings  to  the  platinum  dish, 
and  lastly,  after  making  certain  that  the  residue  insoluble  in 
water  yields  no  copper  to  acids,  precipitate  the  copper  by  means 
of  zinc  according  to  Vol.  I,  p.  373.  The  bright-red  color  of  the 
copper  indicates  that  this  is  pure.  It  is  seen  that  the  object  of 
this  method  is  to  remove,  so  'far  as  possible,  the  metals  precipi- 
table  by  zinc  (lead,  antimony,  and  tin). 

/?.  For  Sulphuretted  Ores,  Mixed  Metallurgical  Products, 
and  Ore-furnace  Regulus,. 

The  substance  must  be  powdered  with  special  care;  it  is  then 
treated  as  in  a,  taking  5  grm.  of  the  ore,  and  heating  as  before  with 
sulphuric  acid,  water,  and  a  larger  quantity  of  nitric  acid.  The 
action  must  be  allowed  to  go  on  at  a  gentle  heat  in  a  covered 
porcelain  dish,  during  which  considerable  spirting,  and  condensation 
of  liquid  from  the  watch-glass  will  take  place.  A  large  quantity 
of  sulphur  separates,  which  collects  and  incloses  some  of  the  pow- 
dered ore.  It  is  therefore  necessary  to  evaporate  the  liquid  to 
dryness  with  a  stronger  heat,  remove,  increase  the  heat  until  the 
sulphur  is  burned  off,  and  volatilize  the  free  acid.  When  cold, 
add  a  fresh  quantity  of  nitric  acid  and  a  very  little  sulphuric  acid; 
the  evolution  of  red  fumes  points  to  the  presence  of  ore  still  un- 
decomposed.  Evaporate  to  dryness  as  before,  allow  to  cool, 
moisten  once  more  with  nitric  acid,  and  burn  off  the  sulphur  a 
second  time.  If  the  ore  is  very  rich  in  copper,  it  is  necessary  to 
repeat  the  entire  operation  once  more.  The  extraction  of  the 
residue  and  the  copper  determination  are  made  as  detailed 
under  a. 

b.  STOKER  *  and  PEARSON  f  in  order  to  obtain  a  solution 
free  from  separated  sulphur,  heat  the  finely  powdered  ore,  pre- 
viously mixed  with  potassium  chlorate,  with  strong  nitric  acid 


*  Zeitschr.  f.  analyt.  Chem.,  ix,  71.  f  Ibid-t  IX»  l01- 


626  DETERMINATION   OF    COMMERCIAL    VALUES.  [§  261. 

on  the  water-bath,  and,  at  short  intervals,  add  more  chlorate  and 
acid,  until  no  more  separated  sulphur  is  visible.  When  cold, 
strong  hydrochloric  acid  is  added  in  sufficient  excess,  the  whole 
evaporated  to  dryness  on  the  water-bath,  and  the  residue  treated 
with  hydrochloric  acid  and  water,  and  filtered. 

PEARSON  precipitates  the  copper  with  iron/  and,  in  order  to 
obtain  the  solution  perfectly  free  from  nitric  acid,  washes  the 
evaporation  residue  with  water  into  a  beaker,  heats  almost  to 
boiling,  adds  about  25  c.c.  of  a  concentrated  ferrous-sulphate 
solution  weakly  acidulated  with  sulphuric  acid,  and  heats  for 
about  five  minutes  nearly  to  boiling.  If  any  ferrous  salt  still 
remains  at  the  end  of  this  time,  and  which  may  be  ascertained 
by  testing  a  drop  with  potassium  ferricyanide,  the  object  is  at- 
tained; if  otherwise,  the  heating  must  be  continued  with  the  ad- 
dition of  more  ferrous  sulphate.  The  metallic  copper  is  finally 
precipitated  in  the  filtered  solution  by  the  introduction  of  a  piece 
of  sheet  iron,  and  is  then  ignited  in  a  current  of  hydrogen  in  a 
porcelain  crucible,  and  weighed. 

c.  Solutions  containing  all  the  copper  may  be  prepared  by 
various    fusion    methods.    Thus    FLEISCHER,*    for    decomposing 
sulphuretted  ores,   recommends  fusing  the  finely  powdered  ore 
with  a  mixture  of  exactly  5  parts  potassium   chlorate,  4  parts 
sodium  carbonate,  and  3  parts  sodium  chloride,  until  the  mass 
flows  quietly,  and  then  dissolving  the  melt  in  water.    W.  GIBBS,  f 
on  the  other  hand,  recommends  mixing  the  finely  powdered  ore 
in  a  porcelain  crucible  with  three  or  four  times  its  Weight  of  a 
mixture  of  equal  parts  of  potassium  disulphate  and  potassium 
nitrate,  and  gradually  heating  to  a  low  red  heat,  preferably  in  a 
muffle,  by  which  procedure  oxidation  is  effected  without  frothing. 
Sufficient  sulphuric  acid  is  then  added  to  the  cooled  mass  to  con- 
vert all  the  potassium  sulphate  into  disulphate,  and  the  whole 
is  again  carefully  heated  until  the  contents  of  the  crucible  have 
fused  to  a  clear  mass  which,  after  cooling,  is  dissolved  in  water. 

d.  When  all  the  copper  has  been  brought  into  solution  in  one 

*  Zeitschr.  f.  analyt.  Chem.,  ix,  258. 
f  Ibid.,  vii,  257. 


§  261.]  COPPER  COMPOUNDS.  627 

way  or  another  (according  to  p.  606,  2,  this  volume),  or  according 
to  3,  a,  b,  or  c,  it  may  also  be  determined  volumetrically.  The  older 
volumetric  methods  have  already  been  described  in  Vol.  I,  pp.  377 
to  382;  of  the  new  or  improved  methods  I  would  mention  the 
following : 

a.  FR.  WEIL  *  supplements  his  method  described  in  Vol.  I, 
p.  380,  by  the  following  special  instructions:  Dissolve  5  grm.  of 
the  mineral  in  hydrochloric  or  sulphuric  acid  free  from  nitric 
acid,  and  dilute  to  250  c.c.  Dissolve  4-5  to  5  grm.  crystallized 
stannous  chloride  in  about  100  c.c.  water  with  the  addition  of 
about  30  c.c.  hydrochloric  acid,  and  dilute  the  solution  to  500  c.c. 
with  a  mixture  of  about  40  c.c.  hydrochloric  acid  and  100  c.c. 
water.  Prepare  also  a  normal  copper  solution,  each  10  c.c.  of 
which  contains  0  •  1  grm.  copper.  To  determine  the  effective  value 
of  the  stannous-chloride  solution,  allow  this  to  act,  in  a  flat-bot- 
tomed flask,  upon  10  c.c.  of  the  normal  copper  solution  to  which 
25  c.c.  of  hydrochloric  acid  have  been  added,  and  the  whole  heated 
to  boiling.  In  a  simila*  manner  allow  the  stannous-chloride 
solution  to  act  upon  10  c.c.  of  the  copper-ore  solution  also  mixed 
with  25  c.c.  hydrochloric  acid  and  heated  to  boiling.  If  it  has 
been  necessary  to  employ  nitric  or  nitrohydrochloric  acid  to  effect 
solution,  evaporate  to  dryness,  dissolve  the  residue  in  hydro- 
chloric acid,  dilute  to  250  c.c.,  pipette  off  10  c.c.,  evaporate  to 
dryness  with  5  to  10  c.c.  hydrochloric  acid,  dissolve  the  residue, 
which  is  now  certainly  free  from  nitric  acid,  in  25  c.c.  hydrochloric 
acid,  and  proceed  as  above.  During  the  titration  at  the  boiling 
temperature  the  flask  is  full  of  hydrochloric-acid  vapors,  and  this 
circumstance  prevents  oxidation  by  the  atmosphere. 

The  procedure  to  follow  when  the  copper  solution  contains 
ferric  chloride  or  sulphate,  was  described  in  Vol.  I,  p.  381. 

If  the  ore  contains  antimony,  effect  solution  with  hydro- 
chloric acid  or  a  mixture  of  much  hydrochloric  acid  with  a  little 
nitric  acid,  add  potassium  permanganate  until  a  red  tint  persists, 
and  boil  until  the  redness  has  disappeared  and  the  vapors  evolved 

*  Zeitschr.  f.  analyt.  Chem.,  xvn,  438;  Precedes  FR.  WEIL  pour  le  dosage 
vol  du  cuivre,  du  fer,  et  de  Vantimoine. 


628  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  261. 

DO  longer  render  potassium-iodide  starch  paper  blue.  Then  dilute 
the  liquid  to  250  c.c.  with  an  aqueous  solution  of  tartaric  acid 
containing  5  to  10  per  cent,  of  the  acid,  or  with  water  to  which 
the  necessary  quantity  of  hydrochloric  acid  has  been  added.  The 
solution  contains  the  copper  as  cupric  chloride,  and  the  antimony 
as  antimonic  acid.  On  now  mixing  10  c.c.  of  the  solution  with 
25  c.c.  of  hydrochloric  acid  and  boiling,  and  then  titrating  with 
the  standardized  stannous-chloride  solution,  the  cupric  chloride 
will  be  reduced  to  cuprous  chloride,  and  the  antimony  penta- 
chloride  to  trichloride,  and  the  volume  of  stannous-chloride  solu- 
tion used  up  will  therefore  show  the  quantity  of  copper  and  anti- 
mony present,  according  to  the  following  equations:  SbCl5+SnCl2 
=  SbCl3+SnCl4;  and  2CuCl2+SnCl2  =  Cu2Cl2+SnCl4.  Under  the 
conditions  stated,  the  reducing  effect  of  the  stannous  chloride 
is  the  same  for  2  eq.  of  copper  (2X63-6=127-2)  as  for  1  eq.  of 
antimony  (120-4).  In  order  to  now  ascertain  the  quantity  of 
copper  alone,  allow  the  reduced  liquid  to  stand  in  a  shallow  porce- 
lain dish  for  twelve  hours  exposed  to  the  air;  by  this  treatment 
all  the  cuprous  chloride  will  have  been  reconverted  into  cupric 
chloride.  On  now  titrating  again  with  stannous-chloride  solution, 
the  copper  alone  will  be  found,  from  the  difference  between  the 
volume  of  stannous-chloride  solution  employed  and  that  corre- 
sponding to  the  antimony,  and  from  this  the  latter  also  is  found. 
Arsenic  acid,  according  to  WEIL,  is  not  reduced  during  the  short 
time  required  for  titration. 

ft.  VOLHARD  *  determines  the  copper  volumetrically  by 
precipitating  it  as  sulphocyanate  and  determining  the  residual 
excess  of  ammonium-sulphocyanate  solution  (see  the  method  of 
silver  determination  based  on  the  same  principle,  pp.  569  to 
571  this  volume).  He  employs  decinormal  solutions,  hence  a 
silver-nitrate  solution  containing  10-792  grm.  per  litre,  and  a 
solution  of  ammonium  sulphocyanate  so  standardized  against  the 
silver  solution  that  on  mixing  equal  volumes  of  the  two  solutions 
ferric  sulphate  will,  if  present,  afford  only  a  barely  perceptible 


*  Zeitschr.  f.  analyt.  Chem.,  xvm,  285. 


§  261.]  COPPER    COMPOUNDS.  629 

color;   1  c.c.  of  the  ammonium-sulphocyanate  solution  will  hence 
correspond  with  0-00636  grm.  copper. 

Dissolve  the  copper  in  sulphuric  or  nitric  acid,  and  drive  off 
the  excess  of  acid  by  evaporation.  If  the  excess  is  not  very  large, 
it  may  be  neutralized  with  sodium  carbonate  until  a  permanent 
cloudiness  forms.  Place  the  liquid  to  be  titrated  in  a  300-c.c. 
flask,  add  aqueous  solution  of  sulphurous  acid  until  the  liquid 
smells  strongly  of  it,  whereby  any  precipitate  of  basic  cupric  car- 
bonate which  may  have  been  produced  is  dissolved,  heat  to  boil- 
ing, and  run  in  from  a  burette  sulphocyanate  solution  until  a 
further  addition  develops  no  more  change  of  color ;  then  for  the 
sake  of  safety,  add  3  or  4  c.c.  more,  and  note  the  total  quantity 
taken.  Allow  the  liquid  containing  the  precipitated,  almost 
white,  copper  sulphocyanate  to  cooi,  fill  with  water  up  to 
the  mark,  mix,  and  filter  through  a  dry  filter  into  a  dry  flask; 
pipette  off  100  c.c.,  add  to  this  10  c.c.  cold,  saturated  solution 
of  ammonio-ferric  alum  and  a  little  nitric  acid,  titrate  with  silver 
solution  until  the  liquid  has  become  colorless,  and  then  cautiously 
run  in  from  a  pipette  or  burette  graduated  in  -fa  c.c.  ammonium- 
sulphocyanate  solution  until  a  just  permanent  reddish  color  de- 
velops. The  number  of  c.c.  of  silver  solution  used,  after  deducting 
the  sulphocyanate  solution  used  in  retitration,  is  multiplied  by 
3,  and  deducted  from  the  sulphocyanate  solution  originally  added; 
the  difference  gives  the  number  of  c.c.  of  sulphocyanate  solution 
required  for  precipitation  of  the  copper. 

In  the  presence  of  iron  the  point  of  complete  precipitation  of 
the  copper  cannot  be  recognized  by  the  absence  of  any  color 
change.  Ferric  oxide,  even  when  all  the  copper  is  precipitated, 
affords  a  dark  coloration  at  the  point  where  the  sulphocyanate 
solution  falls  into  the  liquid,  but,  on  shaking,  it  disappears 
through  the  action  of  the  sulphurous  acid.  Hence,  in  order  to 
ascertain  when  the  precipitation  of  the  copper  is  complete,  it  is 
necessary  to  transfer  some  of  the  fairly  clear  liquid  above  the 
precipitate  to  a  test-tube,  and  while  warming,  to  allow  a  drop 
of  sulphocj^anate  solution  to  fall  in  from  a  burette.  If  the  tur- 
bidity does  not  increase,  all  the  copper  has  been  precipitated. 


630  DETERMINATION    OF    COMMERCIAL  VALUES.          [§   261. 

Then  return  the  sample  to  the  main  bulk  of  the  solution,  and 
proceed  as  above  detailed.  In  the  presence  of  halogens,  silver,  and 
mercury  the  method  is  inapplicable. 

e.  CLASSEN  *  employs  the  oxalic-acid  method  already  described 
for  zinc  (p.  434  this  volume)  and  nickel  (p.  480  this  volume),  for 
determining  copper  in  solutions  which,  as  in  the  case  of  copper- 
ore  solutions,  contain  ferric  chloride,  antimonous  chloride,  ar- 
senous  chloride,  etc.  If  but  little  antimony  is  present,  evaporate 
to  dryness  the  nitric-acid  solution,  add  a  concentrated  solution 
of  potassium  oxalate  in  excess,  filter  hot,  and  wash  the  residue 
with  water  to  which  potassium  oxalate  has  been  added.  Con- 
centrate the  filtrate  to  about  50  c.c.,  whereby  almost  the  entire 
quantity  of  copper  crystallizes  out  as  potassio-cupric  oxalate  in 
the  form  of  blue  needles,  add  2  volumes  of  80-per  cent,  (about) 
acetic  acid,  and  allow  to  stand  for  some  time.  Then  filter,  wash 
the  precipitate  with  a  mixture  of  equal  parts  of  acetic  acid,  al- 
cohol, and  water,  dry,  and  ignite  gently  in  a  platinum  crucible; 
dissolve  the  residue  in  sulphuric  acid,  and  in  this  solution  precip- 
itate the  copper  electrolytically,  whereby  it  is  obtained  free  from 
zinc,  nickel,  magnesium,  etc. 

If  considerable  quantities  of  antimony  are  present  beside 
arsenic,  mix  the  finely  powdered  substance,  or  the  evaporation- 
residue  of  the  solution  with  about  four  times  its  quantity  of  am- 
monium chloride,  and  heat  very  gently  in  a  covered  crucible.  By 
this  treatment  nearly  all  the  arsenic  and  antimony,  as  well  as 
considerable  ferric  chloride,  are  votalilized.  The  copper  can  be 
determined  in  the  residue  in  the  manner  above  described. 

[  /.  Copper  is  also  determined  colorimetrically  by  the  so-called 
"Heine's  method/'  in  poor  copper  ores  and  slags.  It  consists 
in  bringing  the  copper  into  ammoniacal  solution,  and  comparing 
the  color  of  the  solution  so  obtained  with  that  of  a  copper  solution 
of  known  strength.  Although  the  method  appears  simple,  it  is, 
nevertheless  important  to  observe  the  precautions  detailed  by 
HEATH  f  as  the  result  of  many  years'  experience  with  this  method. 

*  Zeitschr.  f.  analyt.  Chem.,  xvm,  390  and  391. 
t  Journ.  Amer.  Chem.  Soc.,  xix,  24,  1897. 


§  261.]  COPPER    COMPOUNDS.  631 

In  the  first  place  it  is  necessary  to  so  prepare  and  preserve  the 
standard  solution  that  it  will  remain  unchanged  for  at  least  one 
year;  secondly,  the  solution  to  be  compared  must  be  prepared 
in  a  manner  to  easily  permit  of  the  separation  of  the  notable  quan- 
tities of  silica,  ferric  oxide,  alumina,  and  lime  present  with  the 
small  quantity  of  copper.  The  first  requisite  is  accomplished  by 
using  copper  sulphate  instead  of  nitrate,  adding  a  sufficient  quan- 
tity of  ammonia  to  the  solution  to  obtain  a  clear,  blue  solution, 
and  then  preserving  the  latter  so  stoppered  as  to  prevent  any  loss 
whatever  of  ammonia. 

To  prepare  the  standard  solution,  dissolve  about  0.3  grm.  pure 
copper  hi  5  c.c.  nitric  acid  of  sp.  gr.  1-4,  with  the  addition  of  5  c.c. 
concentrated  sulphuric  acid  of  sp.  gr.  1-84,  and  evaporate  the 
solution  until  vapors  of  sulphuric  acid  begin  to  be  evolved.  When 
cold,  add  25  c.c.  of  water,  and  then  sufficient  strong  ammonia  to 
yield  a  clear  solution.  The  latter  is  then  diluted  with  ammonia 
water  (1  vol.  stronger  ammonia  and  6  vols.  water)  so  that  1  c.c. 
of  the  resulting  liquid  will  accurately  represent  0  •  0025  grm.  copper. 
This  copper  solution,  which  we  will  term  A,  serves  for  the  prepa- 
ration of  a  scale  of  colors  representing  from  0-1  to  1-3  per  cent, 
of  copper.  As  2  •  5  grm.  of  the  substance  to  be  examined  is  always 
taken,  and  made  up  into  200  c.c.  of  solution,  the  latter  will  contain 
exactly  0-0025  grm.  copper,  assuming  the  substance  to  contain 
0  •  1  per  cent,  of  copper.  The  standard  copper  solution  correspond- 
ing with  this  strength  is  prepared  by  diluting  1  c.c.  of  the  solution 
A  with  sufficient  of  the  diluted  ammonia  (1  +  6)  to  measure  200  c.c. 
Similarly  a  standard  solution  of  2  c.c.  solution  A  in  200  c.c.  corre- 
sponds to  a  copper  content  of  0-2  per  cent.,  always  assuming,  of 
course,  at  2-5  grm.  of  the  substance  to  be  examined  be  taken. 
Standard  solutions  prepared  in  like  manner,  and  corresponding 
to  from  0-1  to  1-3  per  cent,  copper,  are  filled  into  cylindrical 
flasks  of  thin,  colorless  glass,  and  most  carefully  closed  with  ground- 
glass  stoppers  to  prevent  any  and  all  escape  of  ammonia.  HEATH 
gives  as  the  most  suitable  dimensions,  a  length  of  about  180  mm. 
to  the  neck,  and  a  diameter  of  about  44  mm. ;  and  the  flasks  should 


632  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  261. 

bear  a  scratch  at  the  200-c.c.  point.  The  dimensions  and  the 
thickness  of  the  glass  must  be  uniform  throughout;  and  the  flasks 
must  be  preserved  in  a  rather  cool  place,  and  protected  from  ex- 
posure to  direct  sunlight. 

The  determination  is  made  as  follows:  Powder  the  substance 
Very  finely,  weigh,  and  sift.  If  any  pieces  remain  in  the  sieve, 
and  which  are  usually  of  a  metallic  nature,  determine  their  weight, 
and  analyze  them  separately.  Moisten  2-5  grrn.  of  the  powder 
(if  this  contains  over  1  •  2  per  cent,  copper,  only  1  •  25  grm.  is  taken) 
with  water  in  a  porcelain  dish,  add  15  c.c.  nitric  acid  of  sp.  gr. 
1-42,  and  heat  gently  with  occasional  stirring  until  completely 
decomposed.  Then  add  5  c.c.  concentrated  sulphuric  acid,  and 
heat  until  the  mass  acquires  a  doughy  consistency,  whereby  the 
silica  is  dehydrated,  and  the  copper  is  converted  into  sulphate. 
Now  dissolve  in  70  c.c.  water,  add  an  excess  of  ammonia  all  at  once 
(as  a  rule  30  c.c.  suffice),  filter,  wash  twice  with  10  c.c.  diluted 
ammonia  (1:10),  and  wash  the  precipitate  back  again  into  the 
dish  as  completely  as  possible  with  the  aid  of  50  c.c.  water.  After 
the  ferric  oxide  and  alumina  have  been  brought  into  solution  by 
the  addition  of  sulphuric  acid,  drop  by  drop,  repeat  the  precipita- 
tion with  20  to  25  c.c.  of  ammonia  of  sp.  gr.  0-9,  filter,  and  wash 
with  diluted  ammonia.  Now  pour  the  solution  into  one  of  the 
flasks,  make  up  to  200  c.c.  with  the  1 :6  ammonia  water,  and  com- 
pare the  color  with  those  of  the  standard  solutions,  the  comparison 
being  made,  however,  with  only  one  standard  solution  at  a  time. 
HEATH  recommends  not  to  compare  three  flasks  together,  as  in 
such  a  case  the  color  of  the  middle  flask  appears  too  light.  The 
determination  permits  of  an  accuracy  up  to  0  •  03  per  cent. 

If  the  ammoniacal  copper  solution  has  a  greenish  tint,  this 
may  be  due  to  the  presence  of  organic  matter,  which  impairs  the 
complete  precipitation  of  ferric  oxide  by  the  ammonia.  In  mak- 
ing comparisons  with  a  greenish  liquid,  too  high  a  copper  content 
is,  as  a  rule,  found,  nevertheless  the  difference  is  usually  within 
the  limits  of  experimental  error.  Should  the  green  tint  be  too 
pronounced,  it  is  better  to  ignite  the  weighed  sample  for  a  short 


§  262.]  COPPER   COMPOUNDS.  633 

time  in  a  porcelain  crucible  before  proceeding  to  dissolve  it. — 
TRANSLATOR.] 

B.  VARIETIES  OF  COPPER. 

I.    CEMENT    COPPER. 

§262. 

Since  Spanish  pyrites  containing  copper  is  being  so  largely  used, 
particularly  in  the  manufacture  of  sulphuric  acid,  and  as  cement 
copper  is  prepared  from  the  waste,  this  cement  copper  comes  into 
the  market  in  large  quantities;  and  as  it  exhibits  great  variations 
as  regards  both  its  copper  and  moisture  contents,  it  is  frequently 
the  subject  of  analysis. 

The  commercial  varieties  are,  as  a  rule,  fine,  homogeneous, 
and  either  red  with  a  content  of  from  5  to  15  per  cent,  of  moisture, 
or,  if  precipitated  by  cast  iron  instead  of  wrought  iron,  or  if  de- 
prived of  its  water  by  heating  at  a  high  temperature,  it  is  black; 
in  the  latter  case  it  is  almost  anhydrous.  At  times,  however, 
cement  copper  is  met  with  consisting  partly  of  fine,  partly  of  me- 
dium fine,  powder  and  larger  lumps  of  copper.  The  homogeneous 
and  irregular  kinds  must  be  treated  differently  if  the  results  of 
the  analysis  are  to  correctly  express  their  average  composition. 
1.  Fine  Homogeneous,  Red  or  Black  Cement  Copper, 
a.  Determination  of  Water. 

Dry  about  75  grm.  of  the  uniformly  mixed  cement  copper  at 
100°  to  constant  weight.  I  employ  for  this  purpose  a  semicylindri- 
cal  tin  box,  like  that  shown  in  Fig.  126,  16  cm.  long,  40  nun.  wide, 


FIG.  126 

and  22  mm.  deep,  and  provided  with  a  sliding  cover.*    The  box, 
without  the  cover,  is  inserted  in  a  slightly  larger  copper  tube 

*  I  use  this  box  not  only  for  the  determination  of  water  in  cement  copper, 
but  also  for  the  determination  of  moisture  in  minerals  and  other  substances 
of  which  it  is  necessary  to  take  large  quantities  in  order  to  obtain  a  correct 
average  of  the  quantity  of  moisture  contained. 


634  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  262. 

which  is  fixed  crosswise  and  slightly  inclined  in  a  box-shaped 
copper  water-bath  in  such  a  manner  as  to  be  completely  surrounded 
by  boiling  water  or  steam  at  100°.  After  several  hours  remove 
the  box  from  the  tube,  slide  the  lid  in  place,  allow  to  cool  in  a 
desiccator,  and  weigh;  then  remove  the  cover,  insert  the  box 
again  in  the  tube,  and  ascertain  if  the  weight  remains  constant 
after  heating  for  an  hour;  when  this  is  the  case,  the  determination 
is  completed. 

b.  Copper  Determination. 

Treat  about  60  grm.  of  the  copper  dried  at  100°,  or,  if  the  water 
determination  and  the  solution  are  to  be  made  in  one  operation, 
of  the  undried  copper,  with  hydrochloric  acid  of  sp.  gr.  1-12,  to 
which  nitric  acid  is  gradually  added,  and  apply  heat  until  all 
reaction  ceases;  then  dilute  and  filter  into  a  weighed,  two-litre- 
flask.  Wash  the  residue,  which  is  mostly  carbonaceous,  and  ignite 
with  access  of  air  until  all  the  combustible  matter  is  consumed, 
then  treat  with  hydrochloric  acid  at  a  gentle  heat  with  the  addition 
of  nitric  acid,  dilute,  filter  this  solution  into  the  main  solution, 
allow  to  cool,  fill  to  the  mark,  mix  thoroughly,  and  weigh.  In 
an  aliquot  part  of  the  liquid  now  determine  the  copper.  The 
method  to  be  described  next  allows  all  the  foreign  metals  that 
may  be  present  to  be  separated,  and  hence  gives  thoroughly  re- 
liable results  under  all  circumstances.  It  will  of  course  be  under- 
stood that  the  copper  determination  may  be  effected  by  one  of 
the  simpler  methods  described  in  §  261,  II,  but  it  must  always 
be  remembered  that  cement  copper  may  contain  impurities  (lead, 
antimony,  iron,  etc.)  which  affect  the  accuracy  of  the  determina- 
tion. 

a.  Measure  off  30  c.c.  of  the  solution  with  a  pipette  into  a  light, 
glass-stoppered  flask  (which  is  to  be  weighed  with  its  stopper) 
and  weigh.  The  weight  of  the  solution  alone  is  here  the  desider- 
atum, the  measuring  of  the  solution  being  merely  for  the  purpose 
of  enabling  the  operator  to  take  a  suitable  quantity  for  the  analysis. 

ft.  Rinse  the  contents  of  the  weighing-flask  into  a  400-  or  500- 
c.c.  flask,  add  20  c.c.  hydrochloric  acid  of  sp.  gr.  1  •  12,  precipitate 


§  262.]  COPPER   COMPOUNDS.  635 

hot  with  hydrogen  sulphide,  collect  the  precipitate;  and  wash  it 
with  water  to  which  a  little  hydrogen-sulphide  water  and  some 
acetic  acid  are  added.  The  washing  is  to  be  considered  completed 
when  the  washings  cease  to  afford  a  precipitate  or  color  on  adding 
ammonia  and  ammonium  sulphide. 

f.  Transfer  the  precipitated  copper  sulphide,  together  with  the 
filter,  to  a  beaker,  and  add  10  or  20  c.c.  sodium-sulphide  solution 
and  about  50  c.c.  water;  heat  about  five  minutes,  dilute  with 
about  100  c.c.  water,  filter,  and  wash  with  water  to  which  some 
sodium-sulphide  solution  has  been  added.  Acidulate  the  filtrate 
and  washings  with  hydrochloric  acid  in  order  to  make  certain 
that  the  sulphur  precipitated  contains  no  copper  sulphide,  and 
which  is  recognized  by  the  color  of  the  precipitate. 

d.  Transfer  the  copper  sulphide  and  the  filter  back  again  to 
the  beaker  in  which  the  treatment  with  sodium  sulphide  was 
effected,  add  20  c.c.  nitric  acid  of  sp.  gr.  1-2,  and  20  to  30  c.c. 
water,  warm  until  the  copper  sulphide  is  dissolved,  dilute,  filter 
into  a  flask,  and  wash  the  filter.  Then  cautiously  incinerate  the 
dried  filter  in  a  porcelain  crucible,  warm  the  residue  with  a  little 
hydrochloric  and  nitric  acids,  dilute,  and  filter  into  the  other 
solution.  Should  this  be  turbid  in  consequence  of  the  separa- 
tion of  a  slight  quantity  of  silver  chloride,  it  must  be  given  suf- 
ficient time  to  settle;  then  filter.  As  a  rule,  however,  this  is 
unnecessary.  Now  add  ammonia  to  the  clear  or  filtered  liquid 
until  weakly  alkaline,  then  add  ammonium  carbonate,  allow 
to  stand  for  twelve  hours  at  a  moderately  warm  temperature, 
filter,  acidulate  the  filtrate  with  acetic  acid,  precipitate  hot  with 
hydrogen  sulphide,  and  determine  the  copper  as  cuprous  sulphide 
according  to  Vol.  I,  p.  375. 

£.  Should  the  cement  copper  contain  a  relatively  large  quan- 
tity of  lead,  it  is  preferable  to  separate  this  by  adding  an  excess 
of  diluted  sulphuric  acid  to  the  nitric-acid  solution  first  obtained 
from  the  evaporated,  weighed  quantity. 

2.  Non-homogeneous  Cement  Copper. 

If  the  cement  copper  consists  of  portions  of  very  unequal 
character,  i.e.,  fine  and  moderately  fine  powder,  and  coarser  lumps, 


636  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  263. 

an  average  sample  cannot  be  properly  obtained  by  mere  mixture.* 
In  such  a  case,  after  the  moisture  in  the  entire  sample  has  been 
determined,  the  unequal  portions  must  be  separated  by  sifting, 
each  grade  again  dried  at  100°,  and  then  an  aliquot  part  of  each, 
say  one-tenth,  accurately  weighed,  and  these  portions  used  for 
preparing  the  solution.  In  the  case  of  the  cement  copper  referred 
to  in  the  foot-note,  a  sample  weighing  4358-7  grm.  consisted  of 
3197-5  grm.  fine  powder,  747  grm.  moderately  fine  powder,  and 
414-2  grm.  in  lumps.  One-tenth  of  each  was  weighed  off  and 
the  435-87  grm.  of  sample  thus  obtained  dissolved  in  nitric  acid; 
the  solution  weighed  7845-3  grm.,  and  the  copper  was  determined 
in  aliquot,  weighed  portions. 

ii.  COARSE  COPPER;  REFINED  COPPER. 
§263. 

Although  in  the  analysis  of  cement  copper  the  determination 
of  the  copper  content  is,  as  a  rule,  sufficient,  in  the  case  of  coarse 
copper  a  determination  of  all  the  constitutents  must  be  made. 
The  carrying  out  of  such  an  analysis  becomes  the  more  difficult 
the  greater  the  number  of  foreign  elements  to  be  determined, 
and  which  are  usually  present  in  very  small  quantities,  and  in 
order  to  form  an  opinion  regarding  the  copper  it  does  not  suffice 
to  simply  ascertain  what  these  are  and  their  quantities,  but  the 
forms, in  which  they  exist  in  combination  in  the  copper  must  also 
be  ascertained;  this  was  first  accomplished  by  the  exhaustive  in- 
vestigation carried  out  with  the  most  extreme  care  by  W.  HAMPE.f 

The  foreign  elements  that  usually  occur,  or  may  occur,  are 
silver,  gold,  arsenic,  antimony,  tin,  bismuth,  lead,  iron,  cobalt, 
nickel,  zinc,  sulphur,  phosphorus,  and  oxygen. 

In  the  following  I  shall  first  describe  two  methods  which  are 
suitable  for  the  quantitative  determination  of  these  elements, 
which  usually  altogether  amount  only  to  0-5  to  1-0  per  cent.; 

*  Compare  my  communication  regarding  this  in  Zeitschr  f.  analyt.  Chem., 
xv,  63. 

t  "  Beitrage  zur  Metallurgie  des  Kupfers,"  Zeitschr.  /.  Berg-,  Hutten-  und 
Salinenwesen,  xxvii,  205;  'Zeitschr.  f.  analyt.  Chem.,  xui,  176. 


§  263.]  COPPER    COMPOUNDS.  637 

then  will  follow  methods  for  determining  the  forms  in  which  the 
combinations  of  the  foreign  elements  are  present. 

a.  First  Method,  in  which  the  Copper  is  not  Precipitated 
Electrolytically. 

1.  Treat  100  grm.  of  the  carefully  cleaned  copper  with  a  suf- 
ficient quantity  of  perfectly  pure  nitric  acid  of  sp.  gr.  1«2  (in  the 
case  of  copper  turnings  with  addition  of  water),  to  effect  solution 
until  even  when  warmed  there  is  no  longer   any  reaction;   then 
dilute  with  water,  filter,  and  wash  the  undissolyed  residue.     Col- 
lect the  filtrate  in  a  tared  two-litre  flask,  fill  this  up  to  the  mark, 
and  mix. 

2.  Rinse  the  residue  into  a  porcelain  dish,  add  to  it  the  filter 
ash,  evaporate  to  dryness,  transfer  to  a  porcelain  crucible,  re- 
move any  adhering  particles  by  rubbing  with  a  little  sodium  car- 
bonate,  introduce  this   also  into  the   crucible,   add  sulphurated 
potassa,  and  fuse  with  exclusion  of  air;   after  cooling,  treat  with 
water,  filter  the  yellow  solution  from  the  black  residue,  and  wash 
the  latter. 

3.  Heat  the  black  residue  obtained  in  2,  together  with  the 
filter,  with  moderately  dilute  nitric  acid,  filter,  wash,  incinerate 
the  filter,  heat  the  filter  ash  with  nitric  acid,  dilute,  and  filter; 
add  the  filtrate  to  the  solution  first  obtained,  incinerate  the  filter, 
and  preserve  the  filter  ash,  which  may  contain  a  portion  of  the 
gold  present.     To  the  solution,  however,  add  a  small  quantity  of 
hydrochloric  acid ;  if  a  precipitate  of  silver  chloride  forms,  allow  it 
to  settle,  then  filter,  and  convert  the  silver  chloride  into  silver 
for  the  purpose  of  weighing,  finally  testing  its  purity.     Evapo- 
rate the  clear  or  filtered  solution  with  some  sulphuric  acid  to 
separate  the  lead,  and  precipitate  the  copper  and  bismuth  if  these 
are  present;  precipitate  the  solution  with  hydrogen  sulphide,  and 
in  the  filtrate  from  this  separate  any  metals  of  the  fourth  group  by 
adding  ammonium  sulphide. 

4.  Precipitate  the  sulphurated-potassa  solution  from  2  with 
hydrochloric    acid,   filter,   treat   the   precipitate,   which   contains 
much    admixed    sulphur,    together   with    the    filter,    with    bro- 


638  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  263. 

minized  hydrochloric  acid  until  everything  soluble  is  dissolved; 
then  filter,  wash,  remove  the  free  bromine  present  with  ammonia, 
acidulate  with  hydrochloric  acid,  and  precipitate  with  hydrogen 
sulphide  at  70°;  collect  the  precipitated  sulphides,  dissolve  in 
weak  yellow  ammonium  sulphide,  filter,  evaporate  the  solution 
to  dryness  in  a  porcelain  crucible,  cautiously  oxidize  the  residue 
with  fuming  nitric  acid,  evaporate  to  dryness,  add  caustic  soda 
and  a  small  quantity  of  sodium  nitrate,  fuse,  and  effect  the  sepa- 
ration of  antimony,  tin,  and  arsenic,  if  these  are  present,  according 
to  ROSE'S  method,  Vol.  I,  p.  718  [201].  After  washing,  incinerate 
the  filter  through  which  the  ammonium-sulphide  solution  of  the 
sulphides  and  the  sodium  antimonate  dissolved  by  the  hydro- 
chloric and  tartaric  acids  have  been  filtered,  add  to  it  the  filter 
ash  of  the  filter  preserved,  and  treat  with  nitrohydrochloric  acid. 
Dilute,  filter,  evaporate  with  hydrochloric  acid  in  order  to  drive  off 
the  nitric  acid,  and  after  evaporating  the  solution  to  a  small 
bulk,  precipitate  the  gold  by  adding  ferrous  chloride. 

If  tin  is  not  present,  remove  the  free  bromine  from  the  bromin- 
ized  hydrochloric-acid  solution,  and  in  the  liquid  then  separate 
the  antimony  and  arsenic  most  conveniently  by  BUNSEN'S  method 
(see  pp.  556  and  557  this  volume).  The  weighed  metallic  sulphides 
must,  however,  be  tested  for  gold. 

5.  In  about  20  grm.  of  the  solution  obtained  in  1  determine  the 
copper  by  the  method  described  for  cement    copper,  p.  633  this 
volume. 

6.  Add  four  drops  hydrochloric  acid  to  one  litre  of  the  liquid 
obtained  in  1,  and  representing  50  grm.  copper.     If  a  turbidity  or 
precipitate  forms,  due  to  silver  chloride,  allow  it  to  subside  in  a 
warm  place,  add  a  few  more  drops  of  hydrochloric  acid,  and  observe 
whether  all  the  silver  has  been  precipitated.     If  a  further  turbidity 
develops,  a  couple  of  drops  more   acid  must  be  added;  any  con- 
siderable excess  of  acid  must,  however,  be  avoided.     Convert  the 
silver  chloride  most  conveniently  into  metallic  silver  for  the  pur- 
pose of  weighing.     The  quantity  found  and  multiplied  by  2,  and 
added  to  that  found  in  3,  gives  the  percentage  of  silver. 

7.  The  liquid  from  6,  which  remained  clear  on  adding  the  hydro- 


§  263.]  COPPER    COMPOUNDS.  639 

chloric  acid,  or  that  filtered  off  from  the  silver  chloride,  transfer 
to  a  porcelain  dish,  cautiously  add  85  grm.  pure,  concentrated 
sulphuric  acid  which  has  previously  been  diluted  with  water,  and 
evaporate  until  all  the  nitric  acid  has  been  expelled;  then  add 
water,  warm  until  all  the  cupric  sulphate  has  dissolved,  filter  the 
liquid  into  a  two-litre  flask,  wash  the  undissolved  residual  lead 
sulphate  first  with  water  acidulated  with  sulphuric  acid  and  then 
with  alcohol  (which  must  be  collected  and  preserved  apart),  weigh 
(Vol.  I,  p.  355),  and  test  its  purity  by  boiling  with  a  solution  of 
ammonium  acetate  containing  a  small  quantity  of  free  ammonia; 
if  an  insoluble  residue  remains  even  after  repeated  boiling,  it  must 
be  deducted  from  the  lead  sulphate  and  tested  further. 

8.  Make  up  to  two  litres  the  liquid  filtered  off  from  the  lead 
sulphate  in  7,  mix,  and  transfer  500  c.c.  to  each  of  four  flasks  of 
about  1500  c.c.  capacity.*  Dilute  the  contents  of  each  flask  with 
about  500  c.c.  water,  add  50  c.c.  hydrochloric  acid  of  sp.  gr.  1-12 
to  each,  warm  to  about  70°,  and  precipitate  with  hydrogen  sul- 
phide. When  cold,  transfer  the  contents  of  the  four  flasrs  to  a 
weighed  flask  of  about  six  litres  capacity  and  provided  with  a  glass 
stopper,  repeatedly  rinse  the  flasks  with  hydrogen-sulphide  water 
so  that  the  whole  of  their  contents  are  brought  into  the  large  flask, 
then  mix  well  and  weigh  the  flask.  The  weight  of  the  solution  in 
the  flask  is  ascertained  by  deducting  from  the  total  weight  the 
tare  of  the  flask  together  with  the  weight  of  the  cupric  sulphide, 
the  quantity  of  which  can  be  calculated  from  the  weight  of  the 
copper.  After  settling,  siphon  off  the  supernatant  liquid  from 
the  precipitate  so  far  as  possible,  weigh  the  flask  with  the  precipi- 
tate and  the  remainder  of  the  solution,  and  thus  ascertain  the  weight 
of  'the  liquid  siphoned  off.  Filter  the  latter,  evaporate  in  a  porce- 
lain dish  until  by  far  the  greater  part  of  the  sulphuric  acid  has 
been  expelled,  heat  finally  with  a  little  nitric  acid,  add  ammonia, 
and  filter;  dissolve  the  precipitate  in  hydrochloric  acid,  repre- 
cipitate  with  ammonia,  and  in  the  precipitate  determine  any  iron 

*  The  reason  for  recommending  the  measuring  of  the  contents  of  each 
flask  is  that  in  case  of  accident  to  one  of  them  the  whole  labor  may  not  be 
lost. 


640  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  263. 

present  according  to  Vol.  I,  p.  642  [77].  Add  to  the  filtrate 
ammonium  acetate,  acidulate  with  acetic  acid,  and  then  precipi- 
tate nickel,  cobalt,  and  zinc,  which  separate  and  determine  ac- 
cording to  the  methods  described  on  pp.  431,  476  and  477,  and 
478  and  479  this  volume.  Finally,  the  quantities  of  iron,  nickel, 
cobalt,  and  zinc  obtained  must  be  calculated  from  the  part  to  the 
whole,  since  they  are  obtained  from  only  a  part  of  the  solution 
drawn  off  from  the  cupric  sulphide. 

9.  To  the  precipitate,  together  with  the  remainder  of  the  solu- 
tion left  in  the  large  flask,  add  first  caustic-potassa  or  soda  solu- 
tion until  the  liquid  is  strongly  alkaline,  then  a  solution  of  potas- 
sium or  sodium  sulphide  containing  some  disulphide,  and  in  suffi- 
cient quantity  to  make  certain  of  dissolving  all  the  antimony  and 
arsenic  sulphides,  and  warm  gently  for  some  time.     Then  dilute 
copiously  with  water,  mix,  weigh,  siphon  off  the  liquid  so  far  as 
possible,  weigh  the  flask  with  the  precipitate  and  the  remainder 
of  the  solution,  and  thus  ascertain  the  weight  of  the  liquid  siphoned 
off.     Filter  the  latter,  acidulate  with  hydrochloric  acid,  and  allow 
to  settle.     From  the  explanation  given  in  8,  it  follows  that  the 
copper  content  of  the  sulphides  of  the  sixth  group  precipitated 
from  the  alkali-sulphide    solution  can  be  readily  calculated.     As 
these  sulphides  contain  considerable  sulphur  admixed,  collect  it 
after  it  has  settled,  wash,  treat  it  while  still  moist  with  brominized 
hydrochloric  acid,  dilute,  filter,  add  ammonia  until  the  solution 
has  become  colorless,  then  gently  heat  for  a  long  time,  and  finally 
add  hydrochloric  acid.     In  the  clear  liquid  now  precipitate  the 
metals  of  the  sixth  group  with  hydrogen  sulphide,  and  separate 
them  as  detailed  in  4.     The  weights  obtained  must  be  calculated 
from  the  part  to  the  whole. 

10.  The  precipitated  cupric  sulphide  separated  from  the  main 
bulk  of  the  liquid  in  9  containing  the  alkali  sulphide,  now  bring 
onto  the  filter  through  which  the  liquid  has  been  filtered,  wash  it 
with  water  containing  some  potassium  or  sodium  sulphide,  then 
dissolve  in  hydrochloric   acid  with  the   addition  of  nitric   acid, 
filter,  and  evaporate  the  solution,  with  the  addition  of  hydro- 
chloric acid  in  excess,  to  dryness  on  a  water-bath;   take  up  the 


§  263.]  COPPER  COMPOUNDS.  641 

saline  mass  with  water  and  filter  after  long  settling.  Dissolve 
the  insoluble  residue,  containing  all  the  bismuth  as  basic  bismuth 
chloride,  in  hydrochloric  acid,  add  caustic-potassa  solution  until  the 
liquid  is  alkaline,  and  then  add  an  excess  of  potassium  cyanide  and 
potassium  sulphide.  The  bismuth  is  thus  separated  as  bismuth 
sulphide,  while  the  copper  present  with  it  remains  in  solution.  As 
the  bismuth  sulphide  may  contain  some  nickel  sulphide,  dissolve 
it  in  nitric  acid,  precipitate  the  solution,  after  dilution,  with  hy- 
drogen sulphide,  and  now  determine  the  pure  bismuth  sulphide 
either  as  such  (Vol.  I,  p.  385,  3)  or  after  conversion  into  bismuth 
oxide. 

11.  To  400  c.c.  of  the  solution  obtained  in  1,  and  corresponding 
to  20  grm.  copper,  add  ammonia  until  the  greater  part  of  the  free 
nitric  acid  present  has  been  neutralized,  then  add  a  few  drops  of 
a  solution  of  barium  nitrate  and  allow  to  stand  for  a  long  time  in  a 
warm  place.  If  the  copper  contains  any  considerable  traces  of 
sulphurous  acid  (any  sulphur  present  in  coarse  copper  is  in  this 
state  —  HAMPE*),  a  slight  precipitate  of  barium  sulphate  forms, 
and  is  to  be  collected  and  determined.  Very  slight  quantities 
of  sulphurous  acid  cannot,  however,  be  detected  in  this  manner, 
as  barium  sulphate  is  not  altogether  insoluble  in  the  solution  of 
copper  nitrate.  For  the  detection  of  very  small  quantities,  there- 
fore, the  copper  (about  30  to  40  grm.)  must  be  treated,  accord- 
ing to  HAMPE  f,  in  a  current  of  pure,  dry  chlorine,  and  the 
sulphuric  acid  determined  in  the  volatile  products.  For  this 
purpose  the  copper  is  placed  in  a  tube  of  refractory  Bohemian 
glass  which  is  bent  at  its  exit  end  at  first  downwards  and  then 
upwards.  The  tube  is  fixed  in  a  slightly  inclined  position,  with 
the  exit  end  lowermost,  and  connected  with  a  PELIGOT  bulb-tube, 
which  in  turn  is  connected  with  another.  Vulcanized  india- 
rubber  must  be  altogether  avoided  in  setting  up  this  apparatus. 
The  PELIGOT  tubes  are  partly  filled  with  water  which  is  saturated 
with  chlorine  gas  before  beginning  the  operation.  In  order  that 
the  gas  may  be  pure  and  free  from  moisture  it  must  be  well  washed 


*Zeitschr.  /.  analyt.  Chem.,  xm,  222.  f  *&*&»  XIII»  223- 


642  DETERMINATION   OF  COMMERCIAL   VALUES.         [§  263. 

and  dried  by  passing  over  calcium  chloride.  When  the  apparatus 
is  set  up,  warm  the  copper  for  a  short  time;  it  then  becomes  red- 
hot  as  it  combines  with  the  chlorine  to  form  cuprous  chloride, 
which  flows  down  the  bent-down  portion  of  the  tube.  As  soon 
as  only  a  little  copper  remains  unattacked,  warm  the  tube  again, 
and  at  the  same  time  moderate  the  current  of  gas.  After  the 
experiment  is  at  an  end,  unite  the  contents  of  the  receivers,  heat 
until  all  the  chlorine  has  been  expelled,  and  determine  the  sulphuric 
acid  with  barium  chloride. 

For  other  methods  of  determining  the  sulphurous  acid  present 
in  refined  copper,  see  13. 

12.  Evaporate  400  c.c.  of  the  solution  obtained  in  1  repeatedly 
with  hydrochloric  acid  to  remove  the  nitric  acid,  dilute  with  about 
1200  c.c.  water,  precipitate  with  hydrogen  sulphide  at  70°,  bring 
the  whole  into  a  weighed  flask  of  about  two  litres  capacity,  rinse, 
mix,  and  weigh;   allow  to  settle,  siphon  off  as  much  as  possible 
of  the  supernatant  liquid,  weigh  the  flask  with  the  precipitate  and 
the  remainder  of  the  solution,  and  thus  ascertain  the  quantity  of 
copper  corresponding  to  the  liquid  siphoned  off  (compare  8).    Filter 
the  latter,  evaporate  to  a  small  bulk  with  repeated  addition  of 
nitric  acid,  and  determine  any  phosphoric  acid  arising  from  the 
presence  of  phosphorus  in  the  copper,  according  to  Vol.  I,  p.  446/2. 

13.  To  determine   any  oxygen   present  in  coarse   copper,  and 
which,  as  HAMPE  (loc  cit.)  has  shown,  is  combined  partly  with 
copper  as  cuprous  oxide,  partly  with  other  metals  as  oxides  and 
acids,  and  partly  with  sulphur  as  sulphuric  acid,  the  following 
method,  described  by  HAMPE,*  yields  very  accurate  results  if  all 
the  precautions  given  are  observed,  but  not  otherwise : 

Reduce  the  perfectly  bright  copper  to  filings  by  means  of  a  not 
too  coarse  file,  sift  through  a  hair  sieve,  extract  any  particles  of 
iron  that  may  be  present  by  means  of  a  magnet,  and  boil  the 
comminuted  copper  with  caustic-potassa  solution,  whereby  any 
traces  of  fat  are  dissolved,  and  paper  fibres  are  washed  away. 
Then  wash  the  purified  copper  thoroughly  and  dry  rapidly. 

The  oxygen  is   determined  by  ascertaining  the  loss  in  weight 

*  Zeitschr.  /.  analyt.  Chem.,  xm,  202. 


§  263.]  COPPER   COMPOUNDS.  643 

the  powdered  copper  sustains  on  being  ignited  in  a  current  of  hydro- 
gen. The  reduction  is  effected  in  a  Bohemian  glass  bulb-tube 
drawn  out  at  both  ends.  Heat  the  tube  in  a  current  of  dry  air, 
allow  to  cool  in  it,  and  immediately  close  both  ends  with  small 
rubber  tubes  closed  by  small  glass  rods;  then  weigh,  introduce  the 
dried  powdered  copper  (about  30  grm.)  into  the  bulb,  and  weigh 
again.  Now  pass  perfectly  pure,  dry  carbon  dioxide  through  the 
tube,  the  gas  being  evolved  from  marble  *  by  hydrochloric  acid  in 
a  constant-delivery  apparatus.  The  evolution  apparatus  is  set  in 
operation  about  two  hours  before  it  is  required  for  use;  and  to  purify 
and  dry  the  gas,  conduct  it  first  through  a  solution  of  sodium  bi- 
carbonate, then  through  a  tube  containing  lumps  of  the  salt,  a  wash- 
bottle  containing  a  solution  of  silver  nitrate,  a  tube  filled  with 
pieces  of  pumice-stone  impregnated  with  the  same  solution,  a  flask 
containing  concentrated  sulphuric  acid,  and  lastly  through  a  tube 
containing  porous  calcium  chloride.  After  the  carbon  dioxide  has 
passed  for  five  minutes  through  the  bulb-tube  containing  the 
copper,  heat  the  latter  very  moderately  in  order  to  remove  every 
trace  of  moisture.  Empyreumatic  products  should  not  in  this 
case  be  evolved.  Too  strong  heating  of  the  copper  must  be 
avoided,  as  otherwise,  if  the  copper  contains  arsenates,  a  sublimate 
of  arsenous  acid  may  form. 

After  cooling  in  the  current  of  carbon  dioxide,  displace  the 
latter  by  dry  air,  stopper  the  tube,  and  weigh  it.  The  difference 
between  this  weight  and  that  obtained  before  will  be  but  a  few 
milligrammes.  Now  pass  a  very  slow  current  of  pure  hydrogen 
over  the  copper  and  heat  at  first  gently,  and  later  until  the  whole 
of  the  copper  is  red-hot,  maintaining  this  temperature  for  about 
fifteen  minutes.  During  the  heating  water  forms,  and  in  the  case 
of  impure  copper,  there  forms  in  the  upper  part  of  the  bulb  and 
close  behind  it  a  black  sublimate  of  arsenic,  antimony,  and  lead. 
On  this  account  the  end  of  the  tube  must  be  sufficiently  long,  and 
the  current  of  hydrogen  so  slow  that  in  no  case  may  any  of  the 
sublimate  leave  the  tube. 

*  The  air  contained  in  marble  may  be  easily  removed,  according  to  A. 
BERNTHSEN  (Zeitschr.  /.  analyt.  Chem.,  xxi,  63). 


644  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  263. 

In  the  case  of  copper  containing  sulphurous  acid,  some  hydrogen 
sulphide  is  evolved  with  the  water  vapor.  As  it  is  necessary  to 
ascertain  its  quantity,  conduct  the  evolved  gas  through  an  alkaline 
lead  solution,  or  through  brominized  hydrochloric  acid,  and  deter- 
mine it  as  detailed  on  pp.  520  and  521  this  volume.* 

After  the  copper  has  become  perfectly  cold  in  a  current  of 
hydrogen,  and  this  gas  has  been  displaced  by  dry  air,  close  the 
tube  and  weigh  it.  The  loss  in  weight  minus  that  of  the  sulphur 
evolved  as  hydrogen  sulphide  gives  the  quantity  of  oxygen. 

b.  Second  Method,  in  which  the  Copper  is  Electrolytically 

Deposited.     (According  to  HAMPE.f) 

1.  For  the  main  analysis,  the  copper  is  used  in  the  form  of 
clean,  chiselled  pieces,  two  portions  of  25  grm.  each  being  weighed 
off.  Treat  each  portion  in  a  beaker  with  a  mixture  of  175  to 
180  c.c.  nitric  acid  of  sp.  gr.  1-2,  and  200  c.c.  water  at  a 
gentle  heat,  until  everything  soluble  has  dissolved;  then,  without 
previously  filtering  off  any  insoluble  residue,  evaporate  each  liquid 
to  dryness  on  a  water-bath  after  adding  25  c.c.  pure  concentrated 
sulphuric  acid  which  has  been  previously  diluted  with  water;  then 
heat  more  strongly  until  all  the  free  sulphuric  acid  is  volatilized. 
Now  cover  each  perfectly  cold  dish  with  a  glass  cover,  and  cau- 
tiously and  gradually  add  20  c.c.  nitric  acid  of  sp.  gr.  1  -2,  and  350 
c.c.  of  water.  When  all  the  cupric  sulphate  is  dissolved  add  an 
accurately  measured  quantity  of  standard  hydrochloric  acid 
(1  c.c.  =  0-001  grm.  silver)  sufficient  to  exactly  precipitate  the 
silver  present,  and  the  quantity  of  which  has  been  previously  ascer- 
tained by  scorification  and  cupellation  (pp.  579  and  580  this  vol- 
ume). Allow  to  stand  for  twenty-four  hours,  and  collect  the 
precipitate,  consisting  of  lead  sulphate,  silver  chloride,  and  anti- 
monic  acid  or  antimonates,  on  a  small  filter,  and  thoroughly  wash 
the  dishes  and  filter.  These  precipitates  we  will  designate  I,  a  and  b. 
Rinse  out  the  dishes  with  hot  concentrated  hydrochloric  acid  in 

*  The  quantities  of  sulphur  obtained  agreed  very  well  in  the  results 
published  by  HAMPE  (Zeitschr.  /.  analyt.  Chem.,  xm,  226)  with  those  ob- 
tained by  heating  the  copper  in  a  current  of  chlorine. 

•\  Zeitschr.  /.  analyt.  Chem.,  xin,  180. 


§  263.]  COPPER   COMPOUNDS.  645 

order  to  remove  any  adhering  particles  of  antimonic  acid,  unite 
both  solutions,  dilute  with  water,  precipitate  with  hydrogen  sul* 
phide,  and  for  the  present  set  aside  the  liquid  and  the  precipitate 
of  antimony  sulphide,  etc.,  which  we  will  designate  as  II. 

2.  The  two  copper  solutions  from  1,  and  the  washings,  each 
amounting  to  from  400  to  450  c.c.,  place  in  separate  glass  vessels 
9-2  cm.  wide  and  15  cm.  high,  and  precipitate  the  copper  electrolyt- 
ically  (p.  621  this  volume).       The  current  employed  must  be  of 
a  strength  sufficient  to  yield  130  c.c.  of  oxyhydrogen  gas  in  thirty 
minutes  from  diluted  sulphuric  acid  (1 :22) ;  and  it  is  important  to 
maintain   the  current   approximately  at  this  strength.     The  pre- 
cipitation  of  the  copper  from  the  solution  requires  about  seventy- 
two  hours.     When  the  liquid  has  become  colorless  or  nearly  so, 
and  deposits  but  a  trace  of  copper  on  a  freshly  immersed  portion 
of  the  platinum  electrode  on  continuing  the  current,  run  off  the 
liquid,  while  still   maintaining  the  current,  into  a  large  flask  of 
about  four  litres  capacity,  wash  out  until  the  evolution  of  gas 
at  the  positive  pole  ceases,  and  the  liquid  is  therefore  no  longer  acid. 
Now  interrupt  the  current,  and  wash  the  cone  bearing  the  deposited 
copper  first  with  water,  then  with  alcohol,  dry  rapidly  (best  by  sus- 
pension in  a  current  of  hot  air  ascending  from  a  large  platinum  or 
silver  dish  heated  from  below),  and  weigh  the  copper.     The  two 
copper  determinations  carried  out  in  this  manner  check  each  other. 
If  the  copper  has  a  bright,  pure  color  it  is  a  certain  indication 
that  no  antimony  or  arsenic  has  yet  been  deposited  upon  it,  as 
would  be  the  case  if  the  current  were  allowed  to  pass  after  complete 
precipitation  of  the  copper.    As  the  copper  must  be  tested  for 
bismuth  (see  p.  648,  8,  this  volume),  it  must  be  preserved  for  a 
while. 

3.  Rinse  the  siphon  and  platinum  spirals  used  in  2  with  water 
into  the  large  flask,  dissolve  the  slight  quantities  of  lead  dioxide 
adhering  to  the  platinum  spiral  in  hot  hydrochloric  acid  over  one 
and  the  same  porcelain  dish,  evaporate  to  dry  ness  with  sulphuric 
acid  the  solution  containing  also  a  small  quantity  of  platinic  chloride, 
ignite  the  residue,  dissolve  the  lead  sulphate  in  hot  hydrochloric 
acid,  add  ammonia  to  alkalinity,  then  nitric  acid  until  just  acid, 


646  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  263. 

precipitate  with  hydrogen  sulphide,  and  reserve  for  the  present 
the  liquid  with  the  precipitate,  which  we  will  designate  as  III. 

4.  The  liquid  in  the  large  flask,  and  obtained  in  2,  boil,  and 
then  evaporate  in  a  porcelain  dish,  at  first  on  the  water-bath; 
finally  heat  more  strongly,  until  the  free  sulphuric  acid  is  almost 
completely  expelled,   and  but  a  few  drops  remain  in   the  dish. 
When  cold,  add  concentrated  hydrochloric  acid,  warm,  dilute,  filter 
off  from  the  small  quantity  of  silicic  acid  derived  from  the  vessels, 
saturate  with  hydrogen  sulphide,  and  allow  to  stand  for  twenty- 
four  hours  at  75°;  repeat  the  saturation  with  the  gas,  and  expel 
the  excess  by  applying  a  gentle  heat,  in  order  to  effect  complete 
precipitation  of  the  arsenic.     Now  filter  through  a  suitable  filter: 
a,  the  precipitate  of   lead    sulphide,    III    (see    3);   6,  the   pre- 
cipitate  of    antimony  sulphide,  etc.,    II    (see   1);  and  c   (after 
previously  removing  the  filtrates  from  III  and  II),  the  precipitate 
caused  by  hydrogen  sulphide  in  the  electrolyzed  liquid.      Wash 
the  precipitate  well,  but  do  not  dry  it  (term  it  IV) ;  the  filtrate, 
however,  evaporate  until  all  hydrogen  sulphide  is  expelled,  boil 
with  a  little  nitric  acid,  and  add  ammonia  in  excess.     If  a  pre- 
cipitate of  ferric  hydroxide  forms,  redissolve  it  in  hydrochloric 
acid,  reprecipitate  with  ammonia,  weigh  as  ferric  oxide,  and  con- 
trol the  gravimetric  determination  of  the  iron  by  a  volumetric 
determination.     Precipitate  the  nickel  and  cobalt  electrolytically 
from  the   ammoniacal  solution  (p.  481  this  volume),  and  then 
separate  them  by  means  of  potassium  nitrite  (Vol.  I,  p.  655,  9). 

5.  Now  remove  the  precipitates  I,  a  and  b  (see  1),  and  which 
are  to  be  united,  as  completely  as  possible  from  the  filters,  treat 
with  fuming  nitric  acid  in  a  porcelain  crucible,  evaporate  to  dry- 
ness,  add  a  little  ammonium  nitrate  to  completely  destroy  the 
organic  matter  present,  and  heat  cautiously;   when  cold,  transfer 
the  precipitates  removed  from  the  filters  to  the  crucible,  and  fuse 
the  whole  with  three  times  its  quantity  of  a  mixture  of  sodium 
carbonate  and  sulphur,  with  exclusion  of  air  as  much  as  possible. 
Allow  the  melt  to  disintegrate  in  water  as  completely  as  possible, 
filter  the  hot  yellow  solution  through    the   filter  containing   the 
still    moist   precipitate  IV  (see  4),   and  wash,  first  with  dilute 


§  263.]  COPPER   COMPOUNDS.  647 

potassium-sulphide  solution,  and  then  with  hydrogen-sulphide 
water.  The  filtrate  contains  all  the  arsenic,  antimony,  and  tin 
(also  any  traces  of  gold  that  may  be  present)  in  the  form  of 
sulpho-salts,  while  the  precipitate  (V)  contains  all  the  lead  and 
silver  and  the  portions  of  bismuth  and  copper  here  present. 

6.  Precipitate   the  solution  of    the   sulpho-salts  obtained    in 
5  with  diluted  sulphuric  acid,  filter,  dissolve  the  precipitate  in 
freshly  prepared  ammonium  sulphide,  and  evaporate  the  solution 
to  dryness. 

If,  now,  only  antimony  and  arsenic  are  present,  heat  the  residue 
with  hydrochloric  acid  and  potassium  chlorate,  add  tartaric  acid, 
then  ammonia,  filter,  and  precipitate  the  arsenic  acid  with  mag- 
nesia mixture;  after  long  standing  dissolve  the  precipitate  in 
hydrochloric  acid,  again  precipitate  with  ammonia,  and  weigh  either 
as  ammonium-magnesium  ar senate  (Vol.  I,  p.  412, 2),  or  dissolve  in 
hydrochloric  acid,  precipitate  the  arsenic  with  hydrogen  sulphide, 
determine  the  magnesium  as  pyrophosphate  in  the  filtrate  after  con- 
centration (Vol.  I,  p.  275,  2),  and  from  the  quantity  found  calcu- 
late the  arsenic  acid.  HAMPE  recommends  the  latter  method  par- 
ticularly when  rather  large  quantities  of  arsenic  are  present.  Acid- 
ulate the  filtrate  from  the  magnesium  arsenate,  precipitate  the 
antimony  with  hydrogen  sulphide,  and  determine  small  quantities 
as  antimony  tetroxide  (Sb2O4)  (Vol.  I,  p.  398,  2),  but  larger  quan- 
tities determine  as  anhydrous  antimony  sulphide  (Vol.  I,  p.  397). 
If  zinc  is  present  (a  case  of  which  HAMPE  takes  no  special  note), 
the  residue  obtained  by  evaporating  the  ammonium-sulphide 
solution  containing  all  three  sulphides  must  be  reoxidized  with 
fuming  nitric  acid,  and  the  antimony,  tin,  and  arsenic  separated 
according  to  Vol.  I,  p.  718,  a  [201]. 

7.  Dissolve  the  precipitate  V  from  5  in  a  covered  funnel  in 
warm,  moderately  dilute  nitric  acid  by  repeatedly  pouring  it  back, 
then  wash,  dry,  and  incinerate  the  filter,  transfer  the  ash  to  the 
nitric-acid  solution,  boil,  filter,  and  if  but  little  bismuth  is  present, 
precipitate  the  silver  with  hydrochloric  acid;   determine  the  lead 
by  evaporating  with  sulphuric  acid,  and  lastly  separate  the  copper 
and  bismuth  in  the    filtrate    by    ammonium    carbonate.     In  the 


648  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  263. 

case  of  larger  quantities  of  bismuth  neutralize  the  nitric-acid 
solution  with  sodium  carbonate,  add  potassium  cyanide  in  excess, 
filter  off  the  precipitate  containing  the  lead  and  bismuth  oxides, 
precipitate  the  silver  in  the  nitrate  as  silver  cyanide  by  cautiously 
acidulating  with  nitric  acid  (Vol.  I,  p.  341,  3),  evaporate  the  filtrate 
to  dryness  with  sulphuric  acid  in  order  to  decompose  the  cyanogen 
compounds,  and  in  the  hydrochloric-acid  solution  of  the  copper 
precipitate  the  latter  as  cupric  sulphide.  The  mixture  of  lead 
and  bismuth  oxides,  however,  dissolve  in  hot  hydrochloric  acid, 
evaporate  to  a  small  bulk,  and  pour  into  a  large  volume  of  water. 

After  twenty-four  hours  collect  the  precipitate  containing  all 
the  bismuth  as  basic  chloride,  dissolve  it  in  nitric  acid,  precipi- 
tate the  bismuth  with  ammonium  carbonate,  boil,  filter  after 
twenty-four  hours,  and  determine  the  bismuth  as  oxide  (Vol.  I, 
p.  383,  1,  a).  In  the  filtrate,  however,  precipitate  the  lead  with 
ammonium  sulphide,  and  convert  the  lead  sulphide  into  lead 
sulphate. 

8.  The  bismuth  determined  in  7  was  that  left  in  the  residue 
on  dissolving  the  copper  in  nitric  acid ;  the  bismuth  that  had  passed 
into  the  nitric-acid  solution,  on  the  other  hand,  is  precipitated 
with  the  electrolytically  deposited  copper,  and  must  be  determined 
in  this.    Hence  dissolve  this  in  nitric  acid  (using  about  350  c.c. 
nitric  acid  of  sp.  gr.  1-2  for  every  50  grm.  copper),  and  boil  the 
solution  in  a  large  flask  with  a  large  excess  of  hydrochloric  acid, 
and  until  all  the  nitric  acid  has  been  expelled.     Evaporate  to 
dryness  on  a  water-bath  until  the  excess  of  hydrochloric  acid  has 
been  driven  off  and  the  residue  has  acquired  a  brown  color,  and 
then  pour  into  a  large  volume  of  boiling  water.     All  the  bismuth 
is  thereby  separated  as  basic  chloride,  mixed  with  a  little  basic 
copper  salt.     Filter  after  twenty-four  hours,  and  separate  the  two 
metals  either  directly,  or  after  reprecipitating  the  hydrochloric- 
acid  solution  with  ammonium  carbonate. 

9.  The    methods    recommended    by    HAMPE    for    determining 
the  sulphur  and  the  total  oxygen  I  have  already  described  above 
(pp.  640  to  643).     HAMPE  has  not  touched  upon  the  determina- 
tion of  phosphorus  in  his  paper. 


§  263.]  COPPER   COMPOUNDS.  649 

c.  Ascertaining  the  Forms  of  Combination  in  which  the  Foreign 

Metals  occur  in  Coarse  Copper,  etc.  (HAMPE  *). 
It  was  formerly  assumed  that  the  foreign  metals  in  coarse 
copper  were  present  in  the  metallic  form;  it  is  now  known,  how- 
ever, that  they  are  present  partially  in  the  form  of  oxides  and  acids. 
This  fact  was  first  pointed  out  by  FLEITMANN  f  on  the  basis  of  a 
research  carried  out  by  REISCHAUER,!  but  HAMPE, §  after  making 
a  comprehensive  investigation,  elaborated  the  methods  detailed 
below,  which  render  it  possible  to  determine  in  what  form  the 
foreign  metals  are  present  in  coarse  copper,  etc.  The  examina- 
tion requires  two  sets  of  experiments,  i.e.  the  quantitative 
analysis  of  the  residues  remaining  on : 

1.  Treating  the  copper  with  nitric  acid;  and 

2.  Treating  the  copper  with  silver  nitrate. 

In  addition  to  this,  the  quantity  of  the  oxygen  must  be  known 
or  else  ascertained,  i.e.  the  total  quantity,  and  that  combined  with 
copper  as  cuprous  oxide  in  the  rough  copper,  etc. 

As  regards  the  basis  of  the  analytical  method  I  refer  to  HAMPE'S 
original  paper,  as  here  the  process  only  will  be  described. 

1.  Treat  300  grm.  of  bright  filed  pieces  of  copper  in  a  ten-litre 
flask  with  a  mixture  of  4  litres  water  and  2-5  litres  nitric  acid  of 
sp.  gr.  1-2,  at  a  moderate  heat.  When  all  the  copper  has  dis- 
appeared allow  to  settle,  and  pour  off  the  perfectly  clear  liquid 
into  another  vessel;  the  precipitate,  however,  rinse  into  a  beaker, 
and  wash  it  by  decantation,  but  pass  the  liquid  through  a  small 
filter  in  order  to  prevent  any  loss.  After  washing  the  contents 
of  the  filter  into  the  undissolved  residue,  boil  repeatedly  with 
concentrated  nitric  acid,  whereby  a  little  more  copper  is  dissolved ; 
then  remove  the  gold  in  the  residue  with  chlorine  water,  and  any 
slight  quantity  of  silver  chloride  by  repeated  extraction  with 
ammonia  water.  As  the  residue  may  contain,  in  addition  to 
antimonates,  also  hydra  ted  antimonic  acid,  the  latter  derived  from 

*  Zeitschr.  f.  analyt.  Chem.,  xin,  188. 

f  DINGL.  polyt.  Journ.,  CLXXV,  32. 

J  Ibid.,  CLXXIII,  195;  Journ.  f.  prakt.  Chem.,  xcii,  508. 

§  Zeitschr.  /.  analyt.  Chem.,  xm,  188. 


650  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  263. 

the  metallic  antimony  contained  in  the  rough  copper,  treat  it,  in 
order  to  remove  the  hydrated  antimonic  acid,  with  hot,  rather 
strong,  hydrochloric  acid  containing  some  tartaric  acid,  and  until 
the  nitrate  no  longer  gives  a  reaction  for  antimony  on  testing  with 
hydrogen  sulphide.  Finally,  collect  the  residue  thus  treated  and 
thoroughly  washed,  on  a  filter  dried  at  100°,  and  weigh.  Lastly, 
shake  it  so  far  as  possible  into  a  porcelain  crucible,  weigh  the  filter 
with  the  particles  still  adhering,  and  thus  ascertain  the  quantity 
remaining  for  further  analysis.  Fuse  this  with  three  times  its 
quantity  of  a  mixture  of  equal  parts  sodium  carbonate  and  sulphur, 
extract  the  melt  with  water,  and  in  the  solution  determine  the 
antimony  and  any  arsenic  and  tin  that  may  be  present,  according 
to  the  method  detailed  in  §  263,  b.  The  residue,  however,  dis- 
solve in  nitric  acid,  separate  the  silicic  acid  by  evaporation,  and 
treat  the  residue  with  nitric  acid;  then  precipitate  the  solution 
with  hydrogen  sulphide,  filter,  dissolve  the  precipitate  in  nitric 
acid,  evaporate  the  solution  with  hydrochloric  acid  almost  to 
dryness,  and  dilute  with  much  water.  Dissolve  the  separated 
basic  bismuth  chloride  in  nitric  acid,  precipitate  with  ammonium 
carbonate,  and  determine  the  bismuth  as  oxide.  The  lead,  copper, 
nickel,  cobalt,  and  iron  are  determined  according  to  the  methods 
detailed  in  §  263,  b. 

In  HAMPE'S  analysis  of  toughened  copper  and  dry  copper  from 
Oker,  the  residue  insoluble  in  nitric  acid  consisted  of  about  75 
per  cent,  bismuth  antimonate,  Bi(SbO3)3,  the  remainder  being 
lead,  cuprous,  ferric,  nickelous,  and  cobaltous  antimonates.  The 
small  quantity  of  silicic  acid  found  appeared  to  have  been 
derived  from  the  glass  vessels.  That  the  antimonates  existed 
ready  formed  in  the  copper,  and  were  not  formed  from  the  latter 
by  treatment  with  nitric  acid,  was  shown  by  HAMPE  in  the  varieties 
1  of  copper  examined  by  him  in  that  he  treated  50  grm.  of  each  to 
fusion  in  a  current  of  hydrogen,  and  dissolved  the  residual  copper 
in  nitric  acid;  it  dissolved  completely,  with  the  exception  of  only 
a  trace  of  gold.  This  test  must  be  carried  out  in  the  same  way 
with  all  varieties  of  copper,  if  it  is  desired  to  know  with  certainty 
the  state  of  combination  of  the  foreign  metals. 


§  263.J  COPPER   COMPOUNDS.  651 

2.  For  many  metals,  particularly  arsenic,  lead,  and  iron,  the 
method  detailed  under  1  does  not  suffice  to  determine  whether  they 
are  present  in  the  copper  in  the  metallic  form,  or  in  the  form  of 
oxides  or  salts.  The  examination  in  1  may  therefore  be  supple- 
mented as  follows: 

Cover  8  to  10  grm.  of  the  copper,  in  the  form  of  thin,  rolled 
sheet,  or  less  preferably  as  filings  (these  must  be  freed  from  mechan- 
ically admixed  iron  by  means  of  a  magnet,  and  from  any  adherent 
grease  by  boiling  with  diluted  potassa  solution),  with  100  to  150 
times  its  weight  of  distilled  water  containing  rather  more  than 
sufficient  pure  silver  nitrate  hi  solution  to  completely  displace  the 
copper;  stir  for  a  long  time,  until  no  more  particles  of  copper 
are  visible,  and  repeat  the  stirring  from  time  to  time  during  the 
next  twenty-four  hours.  Then  collect  on  a  filter,  wash  thoroughly 
by  aid  of  the  pump,  dry,  remove  from  the  filter,  add  the  filter 
ash,  treat  with  nitric  acid,  filter  off  from  any  slight  residual  pow- 
der, and  precipitate  the  silver  with  hydrochloric  acid,  avoiding 
any  considerable  excess.  Dilute,  decant,  filter,  evaporate  the 
filtrate  to  a  small  volume,  dilute,  and  precipitate  warm  with  hy- 
drogen sulphide.  In  the  precipitate  determine  the  arsenic,  anti- 
mony, lead,  bismuth,  and  copper  according  to  the  methods  de- 
tailed in  §  263,  b,  bearing  in  mind,  however,  that  the  precipitate 
may  still  contain  a  little  silver  sulphide. 

Regarding  the  antimony  here  found,  it  must  be  noted  that  if 
the  whole  of  the  antimony  is  not  found  in  the  copper  in  the  form 
of  insoluble  antimonates,  some  antimony  from  the  antimony  com- 
pounds in  the  silver  precipitate  passes  into  the  nitric-acid  solu- 
tion; as  regards  the  copper  here  found,  it  must  be  noted  that  it 
is  derived  from  the  cuprous  oxide  of  the  rough  copper,  and  serves  for 
the  quantitative  determination  of  the  former  (see  4,  below). 

In  the  filtrate  from  the  hydrogen-sulphide  precipitate  finally 
determine  the  iron  which  was  contained  in  the  copper  as  ferric 
oxide  or  as  a  salt. 

The  examination  of  the  filtrate  from  the  silver  precipitate, 
and  containing  the  excess  of  silver  nitrate,  and  cupric  nitrate, 
together  with  the  nickel,  cobalt,  and  arsenic,  which  were  present 


652  DETERMINATION   OF   COMMERCIAL    VALUES.  [§  263. 

in  the  copper  in  metallic  form,  is  superfluous.  It  may,  however. 
be  carried  out  for  the  purposes  of  control. 

3  The  determination  of  the  total  oxygen  is  effected  according 
to  the  method  detailed  on  p.  642  this  volume. 

4.  To  determine  the  oxygen  present  in  the  form  of  cuprous 
oxide,  and  hence  also  the  quantity  of  the  latter,*  it  is  necessary 
to  know  the  reaction  which  occurs  when  cuprous-oxide  acts  upon 
a  neutral  solution  of  silver  nitrate.  H.  ROSE  has  already  studied 
this  subject,  and  shown  that  cuprous  oxide,  in  this  connection, 
behaves  exactly  as  a  mixture  of  equal  equivalents  of  copper  and 
cupric  oxide  would,  i.e.,  that  a  mixture  of  metallic  silver  and 
a  basic  cupric  salt  is  precipitated.  HAMPE,  who  carefully  studied 
this  reaction,  found  that  the  basic  cupric  salt  formed  possesses  a 
definite  composition  (4CuO-N2O5  +  3H2O),  and  expresses  the  reac- 
tion in  the  cold  by  the  following  equation: 


3Cu20  +  4AgN03  +  zH2O  =  (4CuO  -  N2O5  +  3H2O)  +  2CuNO3  +  4Ag 
+  (x-3)  H20. 

In  accordance  with  this  the  copper  existing  as  cuprous  oxide 
is  found  by  multiplying  by  1  •  5  the  copper  in  the  precipitate  from  2. 
Again,  this  copper  multiplied  by  1  •  6886,  gives  the  weight  of  cuprous 
oxide  ;  or  by  0  •  1887,  the  quantity  of  oxygen  in  the  latter. 

5.  The   sulphur   found   in   rough    copper    containing   oxygen 
compounds  is  not  in  the  form  of  copper  sulphide,  as  this  would 
react  with  the  cuprous  chloride  in  molten  copper,  nor  would  it  give 
rise  to  the  evolution  of  hydrogen  sulphide,  which  has  been  ob- 
served  by  HAMPE,  and    also  previously  by  ABEL  f  and  DICK  J; 
when  heating  rosette  copper  in  a  current  of  hydrogen  (see  p.    643 
this  volume). 

6.  In  order  to  show  how  the  true  constitution  of  the  rough 

*  HAMPE  (Zeitschr.  /.  analyt.  Chem.,  xni,  215)  criticises  the  method  given 
by  AUBEL  V^BERGGEIST,  xn,  279;  Zeitschr.  f.  analyt.  Chem.,  vi,  456)  for 
determining  the  cuprous  oxide  in  refined  copper,  and  gives  an  account  of 
the  not  generally  applicable  method  of  determining  cuprous  oxide  volu- 
metrically  (ibid.,  221). 

t  Polyt.  Centralbl,  1864,  904. 

J  Berg-  und  Huttenmdnnische  Zeit.,  1856,  329. 


§263.] 


COPPER   COMPOUNDS. 


653 


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654  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  263. 

copper  may  be  calculated  from  the  results  obtained,  I  give  on 
p.  653  the  composition  of  a  refined  copper  from  Oker,  according  to 
HAMPE'S  *  analysis  and  arrangement  of  results,  and  point  out, 
where  necessary  in  the  accompanying  notes,  the  analytical  de- 
terminations on  which  the  results  are  based. 

Notes  to  the  accompanying  Table. 

From  the  residue  obtained  in  c  1,  it  may  be  seen  that  the  nickel, 
cobalt,  and  antimony  are  present  in  oxidized  form  (if  the  antimony 
is  not  present  as  decomposable  antimonate) ;  also  that  the  bismuth 
is  present  as  bismuthic  antimonate.  From  the  residue  obtained 
in  c  2,  the  quantities  of  nickel,  cobalt,  arsenic,  iron,  and  lead  pres- 
ent in  an  oxidized  form,  as  well  as  the  quantity  of  copper  present 
as  cuprous  oxide,  are  ascertainedc 

From  this  we  find: 

1.  The  difference  between  the  total  copper  found  in  b  2  and 
that  found  as  cuprous  oxide  in  c  4. 

2.  Determined  according  to  c  4. 

3.  The  difference  between  the  total  arsenic  found  in  b  6  and 
that  present  as  arsenic  acid  in  c  1  or  c  2. 

4.  Determined  according  to  c  2. 

5.  Difference  between  the  total  antimony  found  in  b  6  and 
that  present  as  antimonic  acid  in  c  1. 

6.  Determined  according  to  c  1. 

7.  8,  and  9.     Determined  according  to  c  1  and  c  2,  in  agree- 
ment with  the  results  from  b  4,  b  7,  and  b  8. 

10  and  12.     Difference  between  the  total  cobalt  and  nickel 
found  in  6  4  and  that  of  these  metals  present  as  oxides  obtained 
from  c  1. 

11  and  13.     Determined  according  to  c  1. 

*  Zeitschr.  f.  analyt.  Chem.,  xin,  228. 


§  264.]  COPPER   COMPOUNDS.  655 

C.  COPPER  ALLOYS. 
§264. 

Of  the    copper   alloys,  brass,  nickel-coin,  and  German  silver 
will  be  here  treated  of.     Regarding  the  analysis  of  silver-c«        r 
alloys  I  refer  to  Vol.  I,  pp.  342  and  686,  and  also  this  volui. 
569.     The  copper-tin  alloys  will  be  treated  of  under  the  tin  i   .a- 
pounds 

I.    BRASS. 

Brass  consists  of  from  25  to  40  per  cent,  of  zinc  and  75  to  60 
per  cent,  copper.  In  addition  it  contains,  as  a  rule,  also  small 
quantities  of  lead,  and  occasionally  small  quantities  of  tin  and 
traces  of  iron.  Its  analysis  may  be  conducted  in  very  different 
ways. 

First  Method. 

1.  Dissolve  about  2  grm.  in  nitric  acid,  evaporate  the  solution 
to  dryness  in  a  water-bath,  moisten  the  residue  with  nitric  acid, 
add  a  little  water,  warm,  dilute  still  further,  and  filter  off  any 
residual  stannic  oxide  which  is  to  be  determined  according  to 
Vol.  I,  p.  405,  1,  a.    To  the  filtrate,  or  to  the  solution  itself,  if 
tin  is  either  not  present  or  is  so  only  in  unweighable  quantity,  add 
about  20  c.c.  pure  diluted  sulphuric  acid,  evaporate  on  the  water- 
bath  to  dryness,  add  50  c.c.  water,  and  warm.     If  any  undissolved 
lead  sulphate  remains,  collect  it,  and  wash   it  with  water  acidu- 
lated with  sulphuric  acid.     Then  remove  the  beaker  containing 
the  filtrate  and  washings,  completely  displace  the  diluted  sulphuric 
acid  by  alcohol,   and  determine  the  lead  sulphate  according  to 
Vol.  I,  p.  355,  3. 

2.  In  the  sufficiently  diluted  filtrate  precipitate  the  copper, 
after  adding  aqueous  sulphurous  acid,  with  potassium  sulphocya- 
nate,  and  convert  the  copper  sulphocyanate  into  cuprous  sulphide 
for  weighing;  see  Vol.  I,  p.  376,  6.     I  call  attention  to  the  fact  that 
the  ash  of  the  filter  on  which  the  copper  sulphocyanate  is  collected 
must  be  heated  with  access  of  air  for  a  long  tune  in  order  to  make 
sure  that  all  the  carbonized  filter  is  consumed;   and  that  it  is  best 


656  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  264. 

to  heat  the  copper  sulphocyanate  first  in  air  before  mixing  it 
with  sulphur  and  then  igniting  in  hydrogen.* 

3.  Heat  the  filtrate  from  the  copper  sulphocyanate  in  a  capacious 
flask,  adding  nitric  acid  gradually  until  the  carbon  dioxide  and 
nitric-oxide  gas  evolved  by  the  decomposition  of  the  excess  of 
sulphocy anic  acid  ceases ;  then  evaporate  nearly  to  dryness,  dilute, 
filter  if  necessary,  neutralize  the  free  acid  in  a  flask  (to  avoid 
loss  from  spirting),  heat  the  almost  neutral  liquid  until  the  carbon 
dioxide  is  expelled,  transfer  the  liquid  to  a  porcelain  dish,  and 
precipitate  the  zinc  with  sodium  carbonate  according  to  Vol  I, 
p.  287,  1,  a.  Make  certain,  on  the  one  hand,  that  the  filtrate  con- 
tains no  weighable  quantities  of  zinc,  by  testing  with  ammonium 
sulphide ;  and,  on  the  other  hand,  test  the  weighed  zinc  oxide  as 
to  its  purity.  For  this  purpose  boil  it  repeatedly  with  water, 
filter  into  a  platinum  dish,  evaporate  to  dryness,  gently  ignite  the 
slight  residue  of  alkali  salts,  and  deduct  its  weight  from  that  of 
the  zinc  oxide,  provided  it  is  completely  soluble  in  water,  other- 
wise it  must  be  filtered  and  the  clear  solution  again  evaporated. 
Then  ascertain  if  the  zinc  oxide  is  completely  soluble  in  hydrochlo- 
ric acid,  and  if  necessary  determine  any  residual  silicic  acid,  and 
deduct  its  weight  also  from  that  of  the  zinc  oxide;  finally  super- 
saturate the  cold  zinc-chloride  solution,  after  diluting  it,  with 
ammonia,  in  order  to  ascertain  whether  any  weighable  trace  of 
ferric  oxide  remains  undissolved.  If  necessary,  this  is  collected, 
washed,  again  dissolved  in  hydrochloric  acid,  and  the  solution  re- 
precipitated  with  ammonia  in  order  to  obtain  the  ferric  hydroxide 
free  from  zinc. 

Instead  of  determining  the  zinc  in  the  manner  above  detailed 
it  may  be  determined  by  ZIMMERMANN'S  method,  precipitating 
as  zinc  sulphide  and  weighing  as  such  (see  p.  661,  First  Method). 

Second  Method. 

2.  Proceed  just  as  in  the  first  method,  but  effect  the  separation 
of  the  copper  and  zinc  by  hydrogen  sulphide,  according  to  Vol.  I, 
p.  677.  I  make  use  of  this  opportunity  to  point  out  that  according 

*  Compare  BUSSE  (Zeitschr.  f.  analyt.  Chem.,  xvn,  156). 


§  264.J  COPPER   COMPOUNDS.  657 

to  GERH.  LARSEN  *  the  complete  separation  of  copper  and  zinc 
may  be  effected  by  a  single  precipitation  with  hydrogen  sulphide 
if  the  cupric  sulphide  has  been  washed  first  with  hydrochloric  acid 
of  sp.  gr.  1  •  05  previously  saturated  with  hydrogen  sulphide,  and 
afterwards  with  pure  hydrogen-sulphide  water. 

Third  Method  (Partly  Electrolytic). 

Dissolve  about  2  giro,  brass  in  nitric  acid,  evaporate  the  solu- 
tion, dissolve  the  residue  in  20  c.c.  nitric  acid  of  sp.  gr.  1-2,  dilute 
with  a  little  water,  filter  off  any  residual  undissolved  stannic  oxide, 
dilute  further  to  200  c.c.,  and  electrolyze  according  to  p.  621  this 
volume.  The  copper  is  obtained  at  the  negative  pole;  the  lead 
as  dioxide  at  the  positive  pole.  Dry  the  latter  at  100°  and  weigh 
(comp.  pp.  621  and  622  this  volume).  Evaporate  the  solution 
free  from  lead  and  copper,  nearly  to  dry  ness,  take  up  the  residue 
with  water,  and  determine  the  zinc  as  in  the  first  method  by  pre- 
cipitating with  sodium  carbonate,  etc. 

Fourth  Method  (Entirely  Electrolytic). 

As  reliable  methods  for  electrolytically  separating  zinc  are  now 
known,  the  analysis  of  brass  may  be  effected  by  electrolytic  methods 
altogether.  The  many  different  ways  recommended  for  the 
electrolytic  deposition  of  zinc  show,  however,  that  these  methods 
are  not  as  simple  nor  so  easily  carried  out  as  in  the  case  of  copper. 
After  separating  the  copper  and  lead  as  in  the  third  method,  the 
electrolytic  separation  of  the  zinc  is  proceeded  with.  I  here  give 
the  method  which  has  been  found  to  be  the  best  of  all  those  pro- 
posed, f  i.e.,  that  of  H.  REIXHARDT  and  R.  IHLE,|  which  differs  from 

*  Zeitschr.  /.  analyt.  Chem.,  xvii,  312. 

f  Compare  LUCKOW'S  treatise  on  electro-metallic  analysis  in  DINGL.  polyt. 
Journ.,  177  and  178;  also  Zeitschr.  f.  analyt.  Chem.,  xix,  16;  PARODI 
and  MASCAZZIXI,  Zeitschr.  f.  analyt.  Chem.,  xvi,  469,  and  xviu,  587;  RICHE, 
ibid.,  xvii,  216,  and  xxi,  119;  BEILSTEIN  and  JAWEIN,  ibid.,  xviu,  588;  A. 
CLASSEN  and  M.  A.  VON  REIS,  Ber.  d.  deutsch.  chem.  Gesellsch.,  xiv,  1625, 
and  Zeitschr.  f.  analyt.  Chem.,  xxi,  255;  also  Quantitative  Analyse  auf  elek- 
trolytischem  Wege,  by  A.  CLASSEN,  Aachen,  J.  A.  MAYER,  1882,  p.  12. 

J  Journ.  f.  prakt.  Chem.  [N.  F.],  xxiv,  193;  Zeitschr.  f.  analyt.  Chem., 
xxi,  255. 


658  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  264. 

that  recommended  by  CLASSEN  and  VON  REIS  (see  foot-note  on 
previous  page)  only  in  that  in  the  former  the  deposition  is  effected 
in  a  solution  of  zinc  and  potassium  oxalate,  while  in  the  latter  a 
zinc  and  ammonium  oxalate  solution  is  employed.  ,:  ,: , 

For  the  analysis  take  about  2  grm.  brass,  separate  tin  (should 
this  be  present),  copper  and  lead  according  to  the  third  method, 
siphon  off  the  nitric-acid  solution  from  the  copper  and  lead  dioxide, 
add  sulphuric  acid,  and  evaporate  to  expel  the  nitric  acid;  then 
neutralize  with  potassa  solution,  add  to  the  solution  (and  which 
measures  about  10  c.c.)  50  c.c.  of  a  1:6  potassium-oxalate 
solution  and  100  c.c.  of  a  saturated  solution  of  potassium  sul- 
phate, and  then  submit  to  the  action  of  the  current.  A  current 
capable  of  yielding  90  c.c.  of  oxy hydrogen  gas  per  hour  is  sufficiently 
strong.  The  zinc  oxalate  is  decomposed  by  the  current  into  zinc 
and  carbon  dioxide,  and  the  potassium  oxalate  into  potassium 
and  carbonic  acid;  as,  however,  the  potassium  decomposes  water, 
a  copious  evolution  of  hydrogen  occurs  at  the  negative  pole  during 
the  experiment.  The  potassa  simultaneously  produced  is  con- 
verted into  bicarbonate  by  the  carbonic  acid  given  off  at  the  posi- 
tive pole.  When  the  evolution  of  gas  at  the  positive  electrode 
has  altogether  or  nearly  ceased,  and  a  small  sample  of  the  liquid 
gives  no  precipitate  with  ammonium  sulphide,  the  precipitation  of 
the  zinc  may  be  considered  completed.  As  the  potassium  carbonate 
formed  offers  considerable  resistance  to  the  passage  of  the  current, 
it  is  advisable  to  occasionally  add  some  pure  neutral  potassium 
sulphate  in  order  to  heighten  the  conductivity  of  the  liquid.  The 
separated  zinc  is  bluish-white,  and  adheres  firmly  to  the  electrode. 
This  can  be  removed  at  once  and  washed  first  with  hot  water,  then 
repeatedly  with  cold,  air-free  water,  then  with  alcohol,  and  finally 
in  pure,  acid-free  ether,  and  dried  in  a  desiccator  (according  to 
REINHARDT  and  IHLE),  or  in  an  air-bath  (CLASSEN). 

As  the  zinc  cannot  be  completely  removed  from  the  platinum 
without  difficulty,*  it  is  advisable  to  copper  the  negative  platinum 

*If  the  zinc  is  dissolved  off  from  uncoppered  platinum  with  acids,  a 
dark-gray  residue,  rough  to  the  touch,  generally  remains.  This  is  best  re- 
moved by  fused  potassium  disulphate  (LUCKOW). 


§  264.]  COPPER    COMPOUNDS.  659 

electrode  before  using  it  (with  about  5  grm.  copper).  After  weigh- 
ing, immerse  the  electrode  in  rather  dilute,  cold  nitric  acid.  The 
zinc  dissolves  in  this  rapidly  even  at  ordinary  temperatures, 
while  the  copper  deposit  is  but  very  slightly  attacked,  and  retains 
a  perfectly  bright  surface,  so  that  after  washing  and  drying,  the 
electrode  may  be  used  again  at  once.  If  the  copper  deposit. is 
not  perfectly  bright,  the  zinc  will  appear  covered  with  numerous 
black,  loosely  adherent  granules  which  are  easily  detached  on 
washing,  and  thus  give  rise  to  loss.  When  coppered  electrodes 
are  used,  the  point  when  the  zinc  is  completely  deposited  may 
be  readily  known  by  lowering  the  cone  somewhat  further  in  the 
liquid  and  observing  whether  any  light-gray  deposit  of  zinc  forms 
on  the  reddish  surface  of  copper. 

II.   NICKEL-COINAGE   METAL. 

The  so-called  " nickel  coins"  of  the  German  Empire  consist  of 
75  per  cent,  copper  and  25  per  cent,  nickel.  A  variation  of  more 
than  0-5  per  cent,  in  the  nickel  content,  or  the  presence  of  more 
than  1  per  cent,  of  foreign  metals,  is  forbidden  by  law.  On  em- 
ploying about  1  grm.  of  the  alloy  for  analysis,  which  quantity 
suffices  for  the  legal  determination,  the  exact  determination  of 
the  other  elements  (sulphur,  lead,  iron,  zinc,  arsenic,  etc.)  pres- 
ent in  small  quantities  must  be  abandoned.  If  these,  too,  are  to 
be  accurately  determined,  one  of  the  following  methods  must  be 
selected  for  the  main  analysis,  while  the  foreign  elements  present 
in  smaller  quantities  are  to  be  determined  by  the  methods  de- 
tailed in  §§  252  and  263. 

First  Method. 

Dissolve  about  1  grm.  of  the  metal  in  nitric  acid;  if  black 
specks  of  nickel  sulphide  float  on  the  surface  of  the  solution,  heat 
for  a  long  time  until  they  are  dissolved,  adding  some  hydrochloric 
acid  if  necessary.  Evaporate  the  solution  with  a  slight  excess 
of  sulphuric  acid,  in  order  to  remove  the  nitric  acid  (1  c.c. 
of  concentrated  sulphuric  acid  suffices  for  1  grm.  of  the  alloy), 
precipitate  the  copper  as  sulphocyanate  (compare  Vol.  I,  p.  376, 
and  p.  655  this  volume),  decompose  the  excess  of  sulphocyanic 


660  DETERMINATION   OF    COMMERCIAL   VALUES.  [§  264. 

acid  in  the  filtrate  by  cautiously  heating  with  nitric  acid,  expel 
the  greater  part  of  the  free  nitric  acid  by  evaporation,  and  deter- 
mine the  nickel  according  to  p.  476  this  volume.  If  weighable 
quantities  of  iron  are  found  when  separating  the  impurities  in  the 
weighed  nickel,  separate  the  iron  by  a  double  precipitation  with 
ammonia,  and  determine.  It  must  be  noted  that  the  ferric  hy- 
droxide may  contain  a  small  quantity  of  aluminium  hydroxide, 
derived  from  the  potassa  solution  and  the  vessels  used.  See  BUSSE 
(Zeitschr.  f.  analyt.  Chem.,  xvn,  62). 

Second  Method. 

Dissolve  as  in  the  first  method,  precipitate  the  copper  elec- 
trolytically  (compare  p.  621,  and  p.  529,  third  method,  this  volume), 
and  in  the  liquid,  after  siphoning  it  off,  determine  the  nickel 
after  evaporating  off  the  excess  of  nitric  acid,  either  as  in  the 
first  method,  or  electrolytically,  according  to  p.  481  this  volume. 

AL.  CLASSEN  and  M.  A.  VON  REIS*  employ  for  the  electro- 
lytic separation  of  the  nickel  the  clear  solution  of  nickelous  ammo- 
nium oxalate  prepared  by  adding  an  excess  of  ammonium  oxalate; 
and  AL.  CLASSEN  f  gives  the  following  method  for  the  analysis  cf 
copper-nickel  alloys: 

Electrolytically  separate  the  copper  in  the  sulphuric-acid  solu- 
tion obtained  by  evaporating  the  nitric-acid  solution  with  sul- 
phuric acid,  siphon  off  the  liquid,  concentrate,  by  evaporation, 
neutralize  with  ammonia  or  potassa  lye,  add  an  excess  of  ammo- 
nium oxalate,  heat,  add  3  or  4  grm.  more  of  ammonium  oxalate 
and  electrolyze  hot.  ^The  nickel  rapidly  separates  as  an  adherent, 
bright  layer. 

III.    ARGENTAN    (GERMAN    SILVER). 

German  silver  consists  of  copper,  zinc,  and  nickel  in  varying 
proportions,  but,  apart  from  the  very  small  quantity  of  impuri- 
ties these  metals  may  contain,  it  occasionally  also  contains  small 
proportions  of  lead,  iron,  and  more  rarely  tin,  which  are  intention- 
ally added.  The  following  methods  of  analysis  may  be  used: 

*  Berichte  der  deutsch.  chem.  Gesellsch.,  xiv,  1624. 

•\  See  p.  22  of  CLASSEN'S  work  mentioned  on  p.  657,  this  volume. 


§  265.]  BISMUTH    COMPOUNDS.  661 

First  Method. 

Dissolve  about  2  grm.  in  nitric  acid  and  separate  any  tin  ac- 
cording to  Vol.  I,  p.  706;  the  lead,  however,  separate  by  evaporat- 
ing the  filtrate  with  a  slight  excess  of  sulphuric  acid  (Vol.  I,  p.  689). 
Then  precipitate  the  copper  as  sulphocyanate  with  ammonium 
sulphocyanate  (compare  p.  655,  2,  this  volume),  expel  the  sul- 
phurous acid  by  heating,  neutralize  as  nearly  as  possible  with 
sodium  carbonate,  and,  after  adding  a  further  quantity  of  ammo- 
nium sulphocyanate,  precipitate  the  zinc  with  hydrogen  sulphide 
according  to  ZIMMERM ANN'S  method  (p.  431  this  volume).  In 
the  filtrate  decompose  the  excess  of  sulphocyanic  acid  by  cautiously 
heating  with  nitric  acid,  and  in  doing  which  it  is  advisable  to  add 
the  filtrate  to  the  heated  dilute  nitric  acid.  Then  expel  the  greater 
part  of  the  excess  of  nitric  acid,  and  determine  the  nickel,  and  also 
any  iron  present,  according  to  p.  659,  this  volume  (first  method). 

Second  Method. 

Dissolve  in  nitric  acid  and  separate  any  tin  present  as  in  the 
first  method;  the  copper  and  lead,  however,  separate  electrolyt- 
ically  (p.  657,  this  volume).  Then  precipitate  the  zinc  according 
to  Vol.  I,  p.  650  [88],  Vol.  I,  p.  658  [100],  or  as  in  the  first  method; 
and  in  the  filtrate  determine  the  nickel  electrolytically  (p.  660, 
this  volume,  second  method),  first  separating  if  necessary,  any  iron 
that  may  be  present.  If  the  zinc  also  is  to  be  separated  electro- 
lytically, dissolve  the  zinc  sulphide  in  hydrochloric  acid,  and  pre- 
cipitate the  zinc  according  to  p.  657,  this  volume  (Fourth  Method), 

20.  BISMUTH  COMPOUNDS. 

§265. 

A.  BISMUTH  ORES. 

Of  the  bismuth  ores  the  more  common  are  native  bismuth, 
bismuth  glance,  copper-bismuth  glance,  and  bismuth  ochre.  In 
the  analysis  of  these,  particularly  the  first  three  mentioned,  atten- 
tion must  be  directed  to  the  presence  or  possible  presence  of  bis- 
muth, lead,  copper,  silver,  gold,  antimony,  arsenic,  tin,  iron,  cobalt 
nickel,  zinc,  sulphur,  and  tellurium.  It  is  therefore  advisable  to 


662  DETERMINATION    OF    COMMERCIAL    VALUES.  [§   265. 

make  an  accurate  qualitative  analysis  before  proceeding  to  the 
quantitative  analysis. 

In  the  following,  the  procedure  in  the  case  of  an  ore  of  the  most 
complex  composition  possible  has  been  detailed,  as  the  analytical 
process  will  then  meet  all  cases.  It  is  of  course  evident  that  the 
analysis  will  be  greatly  simplified  when  but  a  few  of  the  elements 
above  named  are  to  be  determined,  or  when  only  the  bismuth 
content  is  to  be  ascertained: 

The  finely  powdered  ore  is  first  dried  at  100°. 

1.  Treat  from  2  to  5  grm.  of  the  ore  with  pure  nitric  acid  of 
sp.  gr.  1-2,  at  first  in  the  cold,  then  for  a  long  time  with  the  appli- 
cation of  heat,  if  necessary,  with  the  addition  of  stronger  nitric 
acid,  until  all  is  dissolved,  then  dilute  with  water  acidulated  with 
nitric   acid.     If   an   insoluble    residue   remains,    collect   it,   wash 
thoroughly,  warm  the  filter  containing  the  residue  with  hydro- 
chloric acid,  dilute  with  water  containing  a  little  tartaric  acid,  filter, 
wash  the  residue  thoroughly  with  water,  dry,  ignite,  and  weigh  the 
residual  gangue.     As  this  may  contain  some  gold,  treat  it,  after 
ignition,  with  nitrohydrochloric  acid,  dilute,  filter,  evaporate  with 
nitric  acid,  and  test  with  ferrous  chloride  for  the  presence  of  gold. 

2.  The   hydrochloric    acid   solution    containing   tartaric    acid, 
and  obtained  in  1,  precipitate  with  hydrogen  sulphide  at  70°,  and 
set  aside  the  precipitate  (a)  for  a  while. 

3.  Add  hydrogen-sulphide  water  to   the   nitric-acid   solution 
obtained  in  1,  and  then  pass  in,  without  warming,  hydrogen  sul- 
phide.    After  standing  for  a  long  time,  filter,  wash  with   water 
containing    hydrogen    sulphide,    and   treat   the  filter   containing 
the  precipitate  (6),  together  with  the  precipitate  a  (from  2)  which 
has  been  collected  meanwhile,  with  warm  potassium-  or  sodium- 
sulphide  solution .     After  diluting,  filter,  and  in  the  filtrate  pre- 
cipitate the  metallic  sulphides  of  the  sixth  group  by  adding  hy- 
drochloric acid,  and  let  the  precipitate  (c)  stand  for  a  while. 

4.  The    metallic   sulphides  of  the  fifth  group  obtained  in  3 
dissolve  by  heating  with  diluted  nitric  acid,  filter,  incinerate  the 
washed  filter,  warm  the  residue  with  nitric  acid,  and  filter  this 
solution  into  the  one  first  obtained.     If  a  slight  residue  is  still 


§  265.]  BISMUTH  COMPOUNDS.  663 

left,  it  may  be  lead  sulphate;  this  should  then  be  weighed,  and 
tested  by  treating  with  ammonium  acetate  to  see  if  it  is  lead  sul- 
phate. Add  sodium  carbonate  to  the  united  nitric-acid  solutions 
until  a  just  permanent  precipitate  forms,  then  add  potassium 
cyanide,  digest  for  some  time  at  a  gentle  heat,  and  filter.  The 
washed  precipitate,  consisting  of  lead  and  bismuth  carbonates 
containing  alkali,  dissolve  in  nitric  acid,  and  separate  the  lead 
and  bismuth  according  to  Vol.  I,  p.  689  [146],  or  p.  692  [152]. 

5.  The  nitrate  from  4,  and  containing  potassium  cyanide,  must 
now  be  examined  for  silver,  copper,  and  small  quantities  of  bis- 
muth.    Add  to  it  a  little  potassium-  or  sodium-sulphide,  collect 
the  resulting  black  precipitate,  wash  it,  dissolve  in  nitric  acid,  and 
precipitate  any  silver  present  by  cautiously  adding  hydrochloric 
acid;  collect  the  silver  chloride,  wash  it  first  with  water  acidulated 
with  hydrochloric  acid,  then  with  pure  water,  and  in  the  filtrate 
determine  any  small  quantity  of  bismuth  that  may  be  present  as 
sulphide  (Vol.  I,  p.  385).     In  the  filtrate  containing  the  potassium 
cyanide,   lastly   determine   the   copper   and   also   any  silver  that 
may  possibly  be  here,  according  to  Vol.  I,  p.  690  [148]. 

6.  The  liquid  filtered  off  from  the  precipitate  6  in  3,  contains 
the  metals    of  the  fourth  group;    it  will  also,  as  a  rule — having 
been    precipitated    in    the    cold    only — contain    arsenic.     Hence 
evaporate  it  to  dryness  with  an  excess  of  sulphuric  acid  in  order 
to  expel  the  nitric  acid,  take  up  the  residue  with  hydrochloric 
acid  and  water,  treat  with  hydrogen  sulphide  at  70°,  collect  the 
precipitate,  and  wash  it;   in  the  filtrate  determine  the  iron,  cobalt, 
nickel,  and  zinc.     For  this  purpose  concentrate  the  liquid  by  evap- 
oration, then  heat  with  nitric  acid,  precipitate  cold  with  an  excess 
of  ammonia,   dissolve  the  precipitate  in  hydrochloric  acid,  and 
precipitate  the  iron  as  a  basic  salt  according  to  Vol.  I,  p.  644  [82]. 
Make  the  united  ammoniacal  solutions  just  acid  with  acetic  acid, 
possibly  after  the  removal  of  an  aluminium  precipitate  by  filtra- 
tion, and  treat  while  warm  with  hydrogen  sulphide.     If  a  precipitate 
forms,  it  may  contain  the  sulphides  of  zinc,  cobalt,  and  nickel, 
which   may  be  separated  according  to  Vol.   I,   p.    650  [88],   or 


664  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  265. 

this  volume,  p.  558.  If  the  precipitate  obtained  by  the  double 
precipitation  is  pure  ferric  hydroxide,  determine  the  iron  by  simply 
igniting;  if  it,  however,  contains  alumina,  this  must  be  separated 
from  the  iron  according  to  Vol.  I,  p.  642  [77]. 

7.  Collect  the  precipitate  c  obtained  in  3,  on  the  same  filter 
that  was  used  in  6  for  filtering  the  supplementary  precipitate  of 
arsenic  sulphide;   then  treat  the   filter,  after  washing,  with  bro- 
minized  hydrochloric  acid,  filter,  add  ammonia,  warm,   acidulate 
with    hydrochloric    acid,    precipitate   warm   with    hydrogen   sul- 
phide, and  lastly  separate  the  arsenic  and  antimony  when  only 
these  are  present,  according  to  pp.  556  and  557    this  volume; 
if,  however,  tin  is  present,  employ  the  method  described  on  p.  637, 
4,  this  volume. 

8.  To  determine  the  sulphur,  employ  a  separate  portion  of 
the  ore,  and  proceed  according  to  p.  561,  1,  this  volume. 

9.  To  test  for  tellurium,  and  to  determine  it  if  necessary,  one 
of  the  following  methods  may  be  selected: 

a.  Heat  the  finely  powdered  ore  in  a  bulb-tube  in  a  current  of 
chlorine,  using  the  apparatus  shown  on  p.  695,  Vol.  I,, and  collect 
the  volatilized  chlorides  in  the  receivers  containing  hydrochloric 
acid;  then  evaporate  the  hydrochloric-acid  solution  to  dryness  on 
the  water-bath,  take  up  the  residue  with  hydrochloric  acid  and 
water,  and  precipitate  the  tellurium,  now  present  as  tellurous 
acid,  by  adding  a  concentrated  aqueous  solution  of  sulphurous 
acid.  If  hereby  there  is  produced  a  white  precipitate  of  basic 
bismuth  chloride,  hydrochloric  acid  must  be  added  until  it  is 
redissolved.  If  the  liquid  contains  tellurous  acid,  a  black  pre- 
cipitate of  tellurium  gradually  forms;  allow  it  to  stand  first  for 
a  few  days  in  a  warm  place,  and  then  filter  (H.  ROSE*).  As 
the  precipitate  may  contain  bismuth,  dissolve  it  in  sodium-hypo- 
chlorite  solution  with  the  addition  of  hydrochloric  acid,  evaporate, 
reprecipitate  with  sulphurous  acid  as  above,  rapidly  wash  the 
tellurium,  dry  it  at  100°,  and  weigh. 

6.  Intimately  mix  the  finely  powdered  ore  with  three  times 

*  His  Handbuch  der  analyt.  Chem.,  6  ed.,  R.  FINKENER,  n,  439. 


§  265.]  BISMUTH    COMPOUNDS.  665 

its  weight  of  carbonized  potassium  bitartrate,  and  expose  the 
mixture  to  a  moderate  red  heat  in  a  luted  crucible;  by  this  treat- 
ment any  tellurium  present  is  converted  into  potassium  telluride. 
Comminute  the  mass  when  cold,  place  on  a  filter,  and  thoroughly 
wash  it  with  water  that  has  been  rendered  air-free  by  boiling, 
and  allowed  to  become  cold.  If  any  tellurium  is  present,  the 
washings  are  red,  and  on  exposure  to  air  gradually  deposit  the  tel- 
lurium as  a  gray  powder  (WOHLER  *). 

B.  BISMUTH  ALLOYS. 

As  an  example  of  these,  WOOD'S  metal,  consisting  of  tin,  lead, 
bismuth,  and  cadmium,  may  be  taken. 

1.  Treat  a  weighed  sample  with  nitric  acid  of  sp.  gr.  1-2  until 
all  reaction  ceases,  evaporate  to  dryness  on  the  water-bath,  warm 
the  residue  with  nitric  acid  and  water,  filter  off  the  impure  hy- 
drated  metastannic  acid  (containing   lead  and  bismuth  oxides), 
ignite,  and  weigh.     Then  fuse  with  sodium  carbonate  and  sul- 
phur, or  with  sulphurated  potassa  with  exclusion  of  air  (Vol.  I, 
p.  703,  /?),  treat  the  melt  with  water,  collect  the.  residual  undis- 
solved  lead  and  bismuth  sulphides  and,  after  washing,  dissolve 
in  hot  diluted  nitric  acid.     Should  any  stannic  oxide  remain  undis- 
solved,  it  must  be  once  more  fused  with  sulphurated  potassa, 
etc.     The  lead  and  bismuth  which  passed  into  the  nitric-acid  solu- 
tion, separate  and  determine  according  to  Vol.  I,  p.  689  [146],  deduct 
the  weight  of  the  oxides  from  that  of  the  impure  stannic  oxide,  and 
thus  ascertain  the  quantity  of  the  pure  stannic  oxide. 

2.  In  the  nitric-acid  solution  filtered  off  from  the  hydrated 
metastannic  acid  separate  from  each  other  the  greater  part  of  the 
lead    and    bismuth  contained,  and  from  the  cadmium    according 
to  Vol.  I,  p.  692  [152];  or,  separate  the  lead  as  sulphate  (Vol.  I, 
p.  689    [146],    precipitate  the  bismuth  as  basic  chloride  (Vol.  I, 
p.  386,  4),  and  determine  the  cadmium  in  the  evaporated  filtrate 
according  to  Vol.  I,  p.  388,  1  or. 2. 

Instead  of  converting  the  basic  bismuth  chloride   into   metal 

*  His  Die  Mineral-Analyse  in  Beispiekn,  2d  ed.,  p.  109. 


666  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  265. 

by  fusing  with  potassium  cyanide,  this  can  be  accomplished  elec- 
trolytically.  For  this  purpose,  according  to  CLASSEN  and  VON 
REIS,*  dissolve  the  basic  bismuth  chloride  in  hydrochloric  acid, 
evaporate  the  solution  with  an  excess  of  sulphuric  acid,  take  up 
with  water,  add  an  excess  of  ammonium  oxalate,  and  electrolyze. 
The  platinum  dish  serving  as  the  negative  electrode  (comp.  p.  616 
this  volume)  must  be  filled  to  the  brim  in  order  to  secure  as  large  a 
depositing  surface  as  possible.  As  a  rule  a  deposition  of  bismuth 
peroxide  is  observed  at  the  positive  electrode  (compare  also 
LucKOwf)  but  it  slowly  disappears.  In  order  to  protect  the 
reduced  metal  from  oxidation,  it  is  necessary  to  remove  the  last 
traces  of  water  by  copious  washing  with  alcohol  and  anhydrous 
ether. 

Cadmium  also  may  be  electrolytically  separated  in  the  fil- 
trate from  the  basic  bismuth  chloride.  Expel  the  free  hydro- 
chloric acid  by  evaporation,  add  an  excess  of  ammonium  oxalate, 
and  electrolyze.  The  cadmium  separates  as  a  gray,  not  very 
adherent  film,  hence  care  must  be  exercised  during  washing  in 
order  to  avoid  loss  (CLASSEN  and  VON 


C.  BISMUTH  SALTS. 

As  an  example  of  these  we  may  take  the  basic  bismuth  nitrate 
(magistery  of  bismuth,  or  bismuth  white),  which  is  frequently  the 
subject  of  analysis,  as  it  not  only  contains  impurities  but  is  fre- 
quently adulterated  with  barytes,  talc,  etc.,  and  an  intentional 
admixture  with  basic  bismuth  chloride  is  frequently  met  with 
in  the  commercial  product. 

I.    COMPLETE   ANALYSIS. 

The  substances  to  be  considered  in  making  a  complete  analy- 
sis are,  in  addition  to  the  normal  constituents,  e.g.,  bismuth 
oxide,  nitric  acid,  and  water,  as  follows:  Of  the  bases,  lead,  zinc, 

*  Berichte  der  deutsch.  chem.  Gesellsch.,  xiv,  1626;  Zeitschr.  /.  analyt. 
Chem.,  xxi,  256;  also,  CLASSEN,  Quant.  Analyse  auf  elektrolyt.  Wege,  p.  18. 

t  Zeitschr.  f.  analyt.  Chem..  xix,  16. 

J  Berichte  der  deutschr.  chem.  Gesellsch.,  xiv,  1628  ;  CLASSEN,  Quant. 
Anal  auf  elektrolyt.  Wege,  p.  23. 


§  265.]  BISMUTH    COMPOUNDS.  667 

iron,  calcium,  and  magnesium;  and  of  the  acids,  arsenic,  hydro- 
chloric, sulphuric,  and  carbonic.  Finally  there  may  be  present 
adulterants  insoluble  in  nitric  acid. 

1.  Dry  a  sample  at  100°,  and  determine  the  water  expelled 
at  this   temperature.    (According   to    PHILLIPS    and   MENIGAUD, 
the  total  water  is  expelled  at  100°,  but  according  to  L.  GMELIN, 
about  3  per  cent,  still  remains  behind.*) 

2.  If  the  quantity  of  water  still  retained  after  drying  at  100° 
is  to  be  determined,  heat  to  redness  a  weighed  portion  in  a  glass 
tube  while  passing  a  slow  current  of  dry  carbon  dioxide,  and  pass 
the  vapors  first  over  red-hot  copper  turnings,  then  through  a 
weighed  calcium-chloride  tube  (p.  56  this  volume). 

3.  Treat  1  to  2  grm.  of  the  substance  dried  at  100°  with  about 
eight  times  its  quantity  of  cold  nitric  acid  of  sp.  gr.  1-2.     If  carbon 
dioxide  is  evolved,  this  must  be  determined  in  a  separate  portion; 
if  any  insoluble  residue  remains,  it  indicates  the  presence  of  one 
of  the  adulterants  named;    in  this  case  collect  it  by  filtration, 
wash  it  first  with  water '  acidulated  with  nitric  acid,  then  with 
pure  water,  then  ignite  and  weigh. 

4.  To  the  nitric-acid  solution  obtained  in  3  add  some  hydro- 
gen-sulphide water,  then  pass   in   hydrogen  sulphide  in  the  cold, 
allow  to  settle,  and  filter;  wash  the  precipitate   (a),  and  treat 
it  with  ammonium  sulphide  while  warming,  dilute,  filter,  wash, 
dissolve  the  black  precipitate  in  warm,  dilute  nitric  acid,  and 
separate    the  lead  and  bismuth  according  to  Vol.  I,  p.  689  [146]; 
to   the   ammonium-sulphide   filtrate,   however,   add   hydrochloric 
acid  in  slight  excess,  and  for  the  time  being  reserve  the  precipitate 
(6)  of  arsenic  sulphide  that  may  be  produced. 

5.  The  filtrate  obtained  in  4  from  the  precipitate  a  evaporate 
with  a  slight  excess  of  sulphuric  acid  to  remove  the  nitric  acid, 
dilute,  and  precipitate  with  hydrogen  sulphide  at  70°;   should  a 
precipitate  (c)  form,  collect,  wash,  transfer  it  to  the  filter  contain- 
ing the  precipitate  b  obtained  in  4,  dissolve  the  contents  of  the 
filter  in  potassa  solution,  and  finally  determine  the  arsenic  in  it 
according  to  p.  556  6,  this  volume. 

*  L.  GMELIN,  Handb.  der  Chem.,  4.  ed.  n,  858. 


668  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  265. 

6.  In  the  filtrate  from  the  precipitate  c  (or  the  clear  liquid  if 
there  was  no  precipitate)  precipitate  the  iron  and  zinc  with  ammo- 
nium sulphide,  and  in  the  filtrate  from  this  determine  the  calcium 
and  magnesium.     The  former  are  separated  according  to   §  160, 
and  the  alkaline  earths  according  to  the  methods  detailed  in  §  154. 

7.  If   qualitative   analysis    has    shown    chlorine    or   sulphuric 
acid  to  be  present,  fuse  a  fresh  sample  with  four  times  its  quantity 
of  potassium-sodium  carbonate,  filter,  wash  with  hot  water  con- 
taining a  little  sodium  carbonate,  make  up  the  filtrate  to  a  definite 
volume,  and  in  half  of  this  determine  the  chlorine  (Vol.  I,  p.  521) ; 
in  the  other  half  the  sulphuric  acid  (Vol.  I,  p.  434). 

8.  The  nitric-acid  content  is,  as  a  rule,  ascertained  by  deduct- 
ing the  quantity  of  water  found  in  2  from  the  loss  which  the  sub- 
stance, dried  at  100°,  undergoes  on  being  ignited.     Should  this 
method  not  be  applicable,  from  one  cause  or  the  other,  the  nitric 
acid  must  be  determined  by  one  or  other  of  the  methods  detailed 
in  §  149. 

II.    BUISSON    AND    FERRAY'S  *    METHOD    OF    DETERMINING 

THE    BISMUTH   PRESENT   AS   BASIC   NITRATE   IN   THE 

SUBNITRATE    (BISMUTH    WHITE). 

This  is  a  volumetric  method,  based  upon  the  precipitation 
of  bismuth  from  an  acetic-acid  solution  by  means  of  iodic  acid. 
The  white  precipitate  of  bismuth  iodate  formed  is  insoluble  in 
water  and  in  dilute  acids,  and  free  acetic  acid  in  particular  dis- 
solves not  even  a  trace  of  it. 

There  are  required  a  solution  of  iodic  acid  1  litre  of  which  con- 
tains about  30  grm.  of  the  crystallized  acid;  a  saturated  solution 
of  pure  potassium  iodide;  and  a  solution  of  sodium  thiosulphate 
of  such  strength  that  30  to  40  c.c.  will  be  required  to  convert 
into  hydriodic  acid  the  iodine  liberated  from  potassium  iodide 
by  10  c.c.  of  iodic-acid  solution. 

The  sodium-thiosulphate  solution  is  first  standardized  against 
the  iodic-acid  solution  by  adding  a  sufficient  excess  of  diluted 

*  Moniteur  scientifigue  [3d  Ser.],m,900;  Zeitschr.  /.  analyt.  Chern.,  xiu,  61. 


§  266.]  ANTIMONY    COMPOUNDS.  669 

sulphuric  acid  and  potassium  iodide  to  10  c.c.  iodic-acid  solution, 
and  ascertaining  how  much  of  the  thiosulphate  solution  is  re- 
quired to  destroy  the  color  of  the  iodine,  or  if  starch  paste  has 
been  used,  that  of  the  starch  iodide  (Vol.  I,  p.  545).  Then 
determine  the  titre  of  the  iodic-acid  solution  thus:  Dissolve 
about  0-3  grm.  pure  bismuth,  or  about  0-4  grm.  pure  bismuth 
oxide,  in  nitric  acid,  dilute  with  some  water,  add  sodium  bicar- 
bonate until  a  just  permanent  precipitate  forms,  dissolve  this 
in  a  sufficient  excess  of  acetic  acid  in  order  to  prevent  a  partial 
subsequent  precipitation  by  water,  transfer  to  a  250-c.c.  flask, 
add  25  c.c.  of  the  iodic-acid  solution,  fill  with  water  to  the  mark, 
mix,  allow  to  settle,  and  filter  through  a  dry  filter.  To  100  c.c. 
of  the  clear  filtrate  add  diluted  sulphuric  acid,  then  as  much  potas- 
sium-iodide solution  as  may  be  required  to  dissolve  the  liberated 
iodine,*  and  lastly  sodium  thiosulphate  until  the  iodine  (or  starch- 
iodide)  color  has  disappeared.  By  this  last  titration  there  is 
ascertained  the  quantity  of  the  iodic  acid  still  remaining  in  solution, 
and  from  the  difference  the  volume  of  iodic-acid  solution  required 
to  precipitate  the  bismuth. 

To  test  the  bismuth  subnitrate  dissolve  about  0-5  grm.  in  a 
few  drops  nitric  acid  and  proceed  as  above  detailed;  but  boil 
after  adding  the  acetic  acid.  If  an  insoluble  residue  remains — 
basic  bismuth  chloride,  or  even  basic  ferric  salts — filter  the  whole 
into  a  250-c.c.  flask  and  then  proceed  in  the  manner  already 
described  for  standardizing  the  iodic-acid  solution.  From  the 
iodic  acid  required  for  precipitation,  then  calculate  the  bismuth 
present  as  basic  nitrate. 

21.  ANTIMONY  COMPOUNDS. 

§266. 

A.  ANTIMONY  ORES. 

Of  the  antimony  ores,  the  most  widely  distributed  and  im- 
portant, antimony  glance  (stibnite),  may  serve  as  an  example. 
In  it  are  usually  found,  besides  antimony  and  sulphur,  also  lead, 

*  The  decomposition  is  represented  by  the  following  equation : 
2HIO3+  lOKI-f  5H2S04=  5K2SO4+ 12 1-f  6H2O. 


670  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  266. 

iron,  and  arsenic,  and  occasionally  also   copper,  and  frequently 
gangue  insoluble  in  acids. 

I.    COMPLETE  ANALYSIS. 

If  the  lead  content  is  high,  decompose  the  ore,  powdered  and 
dried  at  100°,  by  heating  in  a  current  of  chlorine,  and  proceed 
exactly  as  in  the  case  of  fahlerz  (p.  608  this  volume);  if  the  lead 
content,  however,  is  small,  the  following  method  in  the  wet  way 
will  accomplish  the  object: 

1.  Introduce  about  2-5  grm.  of  the  ore,  finely  powdered  and 
dried  at  100°,  into  a  flask,  add   three  or  four  times  its  quantity 
of  potassium  chlorate,  and  then,  without  warming,  hydrochloric 
acid  of  sp.  gr.  1-12  (but  not  stronger,  as  otherwise  slight  explo- 
sions will  occur).     The  liquid  acquires  a  yellow  color,  and  the  ore 
gradually   dissolves.     After   prolonged   action   in   the   cold,   heat 
gently  on  the  water-bath  until  all  the  ore  has  disappeared.     Now 
add  a  concentrated  solution  of  tartaric  acid,  and  then  dilute  with 
water.     As  a  rule  a  little  gangue,  and  frequently  also  a  little  sul- 
phur, remain  unoxidized.     Pass  the  liquid  through  a  filter  dried  at 
100°  and  weighed,  into  a  250-c.c.  flask,  wash,  dry  at  100°,  weigh, 
then  ignite,  weigh  again,  and  thus  find  the  weight  of  the  gangue 
as  well  as  that  of  the  residual  undissolved  sulphur. 

2.  Dilute  the  solution  obtained  in   1   up  to  the  mark,  mix, 
measure  off  100  c.c.,  dilute  it,  and  pass  in  hydrogen  sulphide  at 
70°.     After  settling,  filter,  and  in  the  filtrate  determine  the  iron 
and  any  other  heavy  metals,  earths,  or  alkaline  earths  that  may 
be  present.     The  precipitate,  however,  after  washing,  treat  with 
potassium-  or  sodium-sulphide  solution  at  a  gentle  heat  until  all 
the  antimony  sulphide  is  dissolved;    then  dilute,  filter,  wash  the 
residue,  and  precipitate  the  filtrate  with  hydrochloric  acid;  collect 
the  precipitate,  wash  it,  then  dissolve  in  potassa  lye,  pass  in  chlo- 
rine, and  determine  the  antimony  and  arsenic  as  on  pp.  556  and  557 
this  volume. 

3.  Dissolve  the  residual  lead  sulphide  from  2,  and  which  may 
contain  admixed  cupric  sulphide,  in  hot,  dilute  nitric  acid,  and 
separate  the  lead  and  copper  according  to  Vol.  I,  p.  689  [146]. 


§  266.]  ANTIMONY    COMPOUNDS.  671 

4.  Partially  neutralize  the  excess  of  acid  in  100  c.c.  of  the 
solution  obtained  in  1,  then  precipitate  with  barium  chloride, 
gently  ignite  the  barium  sulphate  with  access  of  air,  and  treat  the 
residue  with  very  dilute  hydrochloric  acid  in  order  to  extract  any 
barium  carbonate  that  may  have  been  formed  from  the  admixed 
barium  tartrate;  then  wash,  ignite,  and  weigh.  The  major  por- 
tion of  the  sulphur,  which  was  dissolved  as  sulphate  on  treating 
the  ore  with  hydrochloric  acid  and  potassium  chlorate,  is  thus 
ascertained. 

II.   METHOD  FOR   DETERMINING   ONLY  THE  ANTIMONY  IN  ORE. 

First  Method. 

This  method  is  based  upon  the  fusion  of  the  finely  powdered  ore 
with  sodium  carbonate  and  sulphur  (recently  again  recommended 
by  FR.  BECKER*),  with  sodium  thiosulphate  recently  and  carefully 
dehydrated  (recommended  by  A.  FROEHDE  f,  and  recently  by 
ED.  DONATH  J  for  the  decomposition  of  antimony  ores),  or  with 
sulphurated  potassa.  The  fusion  is  effected  in  a  covered  porcelain 
crucible.  The  melt,  extracted  with  hot  water,  yields  a  yellow  liquid 
containing  all  the  arsenic  and  antimony  in  the  form  of  sulphur 
salts.  Precipitate  these  with  hydrochloric  acid,  collect  the  pre- 
cipitate, wash  it  thoroughly,  close  the  funnel  below,  fill  it  with 
a  solution  of  ammonium  carbonate,  and  allow  to  stand  for  twelve 
hours;  then  remove  the  stopper  from  the  stem  of  the  funnel,  allow 
the  solution  containing  the  arsenic  sulphide  to  run  off,  wash  the 
residue  on  the  filter  with  water  containing  ammonium  carbonate, 
and  determine  the  antimony  either  as  antimony  tetroxide  (Vol. 
I,  p.  398  §),  or  better,  as  black  antimony  sulphide  (Vol.  I,  p.  396). 

*  Zeitschr.  /.  analyt.  Chem.,  xvn,  185. 

f  Poggend.  Annal.,  cxix,  317;   Zeitschr.  /.  analyt.  Chem.,  n,  362. 

J  Zeitschr.  f.  analyt.  Chem.,  xix.,  23. 

§  From  BUNSEN'S  more  recent  work  on  the  determination  of  antimony 
(LIEBIG'S  Annal.  d.  Chem.,  cxcn,  305;  Zeitschr.  f.  analyt.  Chem.,  xvm, 
267)  it  follows  that  the  method  previously  recommended  by  him  for  deter- 
mining antimony  by  converting  the  sulphide  into  antimony  tetroxide  (comp. 
Vol.  I,  p.  398)  is  not  adapted  for  accurate  determinations,  because  the  tem- 
perature at  which  the  antimonic  acid  is  converted  into  antimony  tetroxide, 


672  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  266. 

In  the  latter  case  the  precipitate  must  be  collected  on  a  filter,  dried 
at  100°,  and  after  washing  with  ammonium  carbonate,  drying  at 
100°  and  weighing,  so  that  an  aliquot  part  may  be  heated  in  a  cur- 
rent of  carbon  dioxide. 

Second  Method  (by  FR.  WEIL  *). 

Although  this  method  follows,  to  a  certain  extent,  from  what 
has  already  been  stated  on  p.  627  this  volume,  it  will  never- 
theless be  useful  to  once  more  briefly  describe  the  process.  For  it 
there  are  required  the  normal  cupric-chloride  solution  mentioned 
in  the  place  stated,  and  also  the  stannous-chloride  solution  stand- 
ardized against  it. 

Dissolve  about  2  to  5  grm.  of  the  ore  in  a  large  quantity  of 
hydrochloric  acid  with  the  addition  of  a  small  quantity  of  potassium 
chlorate,  add  potassium  permanganate  until  permanent  redness, 
and  boil  until  the  red  color  has  disappeared,  and  the  vapors  no 
longer  render  potassium-iodide  starch  paper  blue.  Now  dilute 
the  liquid  with  an  aqueous  5-  or  10-per  cent,  tartaric-acid  solution 
to  250  c.c.,  mix,  introduce  10  c.c.  into  a  porcelain  dish,  add  10  c.c. 
of  the  normal  cupric-chloride  solution,  evaporate  to  about  half  the 
volume,  add  25  c.c.  hydrochloric  acid,  and  then  run  in  from  a 
burette  stannous  chloride  until  decolorization.  From  the  volume 
used  deduct  the  quantity  corresponding  with  the  cupric-chloride 
solution,  and  thus  ascertain  the  quantity  which  served  to  reduce 
antimony  pentachloride  to  trichloride;  and  from  this  calculate  the 
antimony  according  to  the  equation  on  p.  628  this  volume. 

Third  Method  (by  TAMM|). 

This  is  based  upon  the  fact  that  when  antimony  is  present  as 
antimonous  chloride  in  a  concentrated  but  only  slightly  acid  solu- 
tion, it  is  completely  precipitated  by  gallic  acid  as  antimonic  gallate, 
whereas  under  similar  conditions  other  metals  are  not  precipitated. 

and  that  at  which  the  latter  is  decomposed  into  oxygen  and  antimonic  oxide, 
lie  very  close  together.  Different  weights  are  therefore  obtained,  varying 
with  the  temperature  and  the  duration  of  the  ignition. 

*  Procedes  FR.  WEIL  pour  de  dosage  volumetrique  du  cuirrc,  du  fer  et  de 
rantimoine  (printed  as  MS.). 

t  Chem.  News,  xxiv,  207  and  221;  Zeitschr.  /.  analyt.  Chem.,  xiv,  351. 


§  266.]  ANTIMONY    COMPOUNDS.  673 

Dissolve  about  1  grm.  of  the  ore  in  hydrochloric  acid  with  the 
addition  of  a  small  quantity  of  potassium  chlorate,  expel  the  free 
chlorine  from  the  liquid  by  gently  warming,  add  potassium  iodide 
(to  reduce  the  antimonic  to  antimonous  chloride),  heat,  drive 
off  the  liberated  iodine  by  heating,  and  at  the  same  time  concen- 
trate the  liquid  to  the  proper  point  by  evaporation.  According  to 
TAMM  the  potassium  chloride  present  prevents  any  loss  of  anti- 
mony from  volatilization.  Now  add  a  concentrated,  freshly  pre- 
pared solution  of  gallic  acid  in  moderate  excess,  and  allow  to  settle. 
That  an  excess  of  gallic  acid  is  present  is  readily  known  by  placing 
a  drop  of  the  liquid  from  above  the  precipitate  on  a  piece  of  filter- 
paper  and  touching  the  moistened  spot  with  a  drop  of  ammonia, 
and  observing  whether  a  reddish  color  develops.  The  white 
precipitate  of  antimonic  gallate  can  not  be  washed  on  the  filter. 
The  washing  must  be  effected  by  decanting  three  or  four  times 
with  hot  water,  pouring  the  water  through  a  double  filter,  and 
finally  bringing  the  precipitate  on  to  the  filter  and  washing  it 
thereon  once  or  twice  more.  When  dried  at  100°  it  has  the  com- 
position, according  to  TAMM,  of  SbO  •  C7H5O5,  and  is  very  prone  to 
attract  moisture,  and  contains  39-42  per  cent,  of  antimony;  if 
dried  at  80°,  however,  it  contains  2  eq.  more  water  and  then  con- 
tains 35-26  per  cent,  of  antimony.  The  antimony  gallate  may, 
of  course,  be  dissolved  in  hydrochloric  acid,  tartaric  acid  added, 
the  solution  diluted,  hydrogen  sulphide  passed  in,  and  the  anti- 
mony determined  as  antimony  sulphide.  If  the  other  metals  are 
also  to  be  determined  they  must  be  precipitated  in  the  liquid, 
containing  the  excess  of  gallic  acid  by  means  of  hydrogen  sulphide 
or  ammonium  sulphide. 

Fourth  (Electrolytic)  Method. 

The  electrolytic  separation  of  antimony  has  been  studied  by 
PARODI  and  MASCAZZINI.*  LucKOW,f  and  CLASSEN  and  v.  REIS.J 
The  separation  of  the  metal  on  the  electrode  in  the  form  of  an 

*  Zeitschr.  f.  analyt.  Chem.,  xvin,  587. 
t/6iW.,  xix,  13. 

%Benchte  d.  deutsch.  Chem.  Gesellsch.,  xiv,  1629;  Zeitschr.  /.  analyt. 
Chem.,  xxi,  257;  CLASSEN,  Quant.  Anal.  auf.  elektrolyt.  Wege,  pp.  T5  and  42. 


674  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  266. 

adherent  coating  is  best  accomplished  in  a  solution  of  an  antimony 
sulpho-salt.  If  the  solution  has  hence  been  made  by  treating 
antimony  ore  with  hydrochloric  acid,  with  the  addition  of  potassium 
chlorate,  adding  tartaric  acid,  diluting  the  solution,  precipitating 
with  hydrogen  sulphide  in  the  cold,  washing  the  precipitate  first 
with  water,  and  then  with  a  solution  of  ammonium  carbonate  to 
remove  any  arsenic  sulphide  that  may  have  been  precipitated, 
and  then  washing,  it  is  only  necessary  to  treat  the  precipitate  with 
a  solution  of  yellow  potassium-  or  sodium  sulphide  at  a  gentle 
heat,  and  filter  off  the  residual  undissolved  metallic  sulphides  of 
the  fifth  group,  in  order  to  be  able  to  then  at  once  electrolytically 
deposit  the  antimony  from  the  solution  of  the  sulpho-salt.  After 
washing  the  electrode  with  its  deposit  with  water,  alcohol,  and 
ether,  it  is  dried  and  then  weighed. 

B.  ANTIMONY  ALLOYS. 

As  an  example  we  may  select  type  metal,  the  most  important  of 
all  the  antimony  alloys,  and  which  consists  either  of  lead  and 
antimony,  or  of  lead,  antimony,  and  tin;  occasionally  it  also 
contains  a  slight  quantity  of  copper.- 

Treat  the  comminuted  alloy  with  nitric  acid  with  the  addition 
of  tartaric  acid,  add  an  excess  of  ammonia,  then  yellow  ammonium 
sulphide,  and  digest  in  a  closed  flask  until  certain  that  all  the  anti- 
mony and  tin  sulphides  are  dissolved.  Collect  the  lead  sulphide, 
which  may  possibly  contain  some  admixed  cupric  sulphide,  wash, 
and  determine  the  lead,  or  separate  the  lead  and  copper,  according 
to  Vol.  I,  pp.  355  or  689  [146],  or  this  volume,  p.  657  (Third 
Method). 

When  only  antimony  is  present  in  the  filtrate  it  may  be  at 
once  deposited  electrolytically  (compare  p.  673  this  volume). 
We  may,  however,  also  precipitate  the  filtrate  by  means  of  hydro- 
chloric acid,  and  determine  the  antimony  according  to  Vol.  I, 
p.  396  as  black  antimony  sulphide.  If  tin  is  present  with  anti- 
mony, proceed  as  detailed  on  p,  637,  4,  this  volume.  CL.  WINKLER'S 
method  of  separating  antimony  and  tin  will  be  described  in  §  267. 


§  267.]  ,TIN    COMPOUNDS.  675 

22.  TIN  COMPOUNDS. 

§267. 

A.  TIN  ORES. 

Of  the  tin  ores  only  the  two  most  important,  tinstone  and  tin 
pyrites,  will  be  here  considered.  In  the  analysis  of  the  former 
it  must  be  borne  in  mind  that  stannic  oxide  is  frequently  accom- 
panied by  ferric  and  manganic  oxides,  alumina,  and  silicic  acid. 
In  many  tinstones  lead  oxide,  tantalic  acid,  tungstic  acid,  and 
small  quantities  of  silver  have  also  been  found.  Tin  pyrites,  on 
the  other  hand,  always  contains,  besides  tin  and  sulphur,  some 
iron  and  zinc,  and  frequently  gangue  also. 

I.   TINSTONE. 

As  tinstone  is  insoluble  in  acids,  its  analysis  must  always  be 
preceded  by  its  decomposition.  This  may  be  effected  by  fusion 
with  caustic  potassa  or  caustic  soda  in  a  silver  crucible,  or  by  the 
aid  of  sulphurated  potassa.  The  latter  is  the  method  usually 
preferred. 

1.  The  tinstone  must  be  reduced  to  an  exceedingly  fine  powder. 
According  to  ROSE,*  mix  it  with  3  parts  of  sodium  carbonate  and 
3  parts  of  sulphur,  and  fuse  it  in  a  well-covered  porcelain  crucible. 
Instead  of  using  the  mixture  stated  the  decomposition  may  also 
be  effected  by  means  of  the  ready  prepared  sulphurated  potassa. 
When  cold,  treat  the  melt  with  water,  filter  the  yellow  solution 
from  the  black  residue,  and  wash  the  latter  with  water  containing 
ammonium  sulphide. 

2.  Treat  the  residue  obtained  in  1  with  hot,  somewhat  diluted, 
nitric  acid.    Should  there  be  any  residue  of  undecomposed  tinstone 
left  it  must  be  collected,  fused   again  with  sulphurated  potassa, 
and  the  melt  treated  as  described.     In  the  nitric-acid  solution 
qualitatively   ascertain  the   constituents  belonging  to  the  third, 
fourth,   and    fifth   groups;    and  separate  them  by  the  methods 
described  in  §§  160  to  164.     Any  residue  insoluble  in  nitric  acid 
remaining  after  the  second  fusion  may  be  tantalic  acid  and  gangue. 

*  Handb.  der  analyt.  Chem.,  von  H.  ROSE,  6th  ed.,  by  R.  FINKENER,  n,  275. 


676  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  267. 

Fuse  it  with  potassium  disulphate,  treat  with  water,  and  test  for 
alumina  by  adding  ammonia.  After  reweighing  the  insoluble 
residue  treat  it  with  hydrofluoric  and  sulphuric  acids.  If  any 
residue  now  remains  it  is  to  be  regarded  as  tantalic  acid,  but  of 
course  it  must  be  further  tested.  The  silicic  acid  is  determined 
from  the  difference. 

3.  The  solutions  of  the  tin  sulpho-salt  obtained  in  1  and  also  in 
2,  precipitate  with  hydrochloric  acid,  allow  to  settle,  collect  the 
tin  sulphide,  wash  it,   dissolve  in  brominized  hydrochloric  acid, 
precipitate  the  solution  with  ammonium  nitrate,  and  determine 
the  tin  as  stannic  oxide,  according  to  Vol.  I,  p.  405,  b.    If  the  tinstone 
contains  tungstic  acid  the  greater  part  of    the  tungsten  will  be 
found  with  the  tin  sulphide.     In  this  case  the  metals  must  be 
separated  according  to  one  of  the  methods  described  on  pp.  677 
to  679  this  volume. 

4.  As  the  filtrate  from  the  tin  sulphide  may  still  contain  silicic 
and  tungstic  acids,  since  tungsten  is  not  completely  precipitated 
by  acids  as  sulphide  from  solutions  of  its  alkali  sulpho-salts,  evap- 
orate the  solution  to  dryness,  heat  the  residue  to  120°,  treat  again 
with  hydrochloric  acid  and  water,  evaporate  once  more  to  dryness, 
and  repeat  this  operation  several  times.     On  now  treating  the 
residue  with  hydrochloric  acid  and  water  all  the   tungstic    acid 
remains  behind  (H.  ROSE),  together  with  silicic  acid,  if  it  is  present. 
Collect   the   insoluble    residue,    wash   with    diluted   hydrochloric 
acid,  ignite,  weigh,  and  then  separate  the  tungstic  acid  from  the 
silicic  acid  by  fusing  with  potassium  disulphate  and  treating  the 
melt  with  water;    the  insoluble  silicic  acid  remains  behind. 

II.    TIN    PYRITES. 

1.  Treat  2  to  3  grm.  of  the  finely  powdered  mineral,  dried 
at  100°,  with  hydrochloric  acid  with  the  addition  of  potassium 
chlorate,  or  with  nitrohydrochloric  acid,  until  the  tinstone  is 
completely  decomposed,  dilute,  heat  to  drive  off  the  free  chlorine, 
filter  through  a  filter  dried  at  60°,  into  a  250-c.c.  flask,  and  in 
the  residue,  dried  at  60°  and  weighed,  separate  the  sulphur  and 
gangue  by  heating. 


§  267.]  TIN    COMPOUNDS.  677 

2.  Make  up  the  solution  to  250  c.c.,  mix,  and  in  100  c.c.  de- 
termine the  sulphur  which  dissolved  as  sulphuric  acid  by  first 
neutralizing  the  greater  part  of  the  free   acid  with    ammonia, 
adding  barium  chloride,  and  then  determining  the 'barium  sulphate. 
As  this  may  contain  stannic  oxide  determine  the  sulphuric  acid 
in  it  either  according  to  Vol.  I,  p.  441,  6,  a,  or,  after  igniting,  boil 
with  a  frequently  renewed  solution  of  sodium  carbonate  in  order 
to  completely  decompose  the  barium  salt.     As  soon  as  the  liquid 
filtered  off  no  longer  contains  sulphuric  acid,  wash  the  precipitate, 
and  dissolve  the  barium  carbonate  in  dilute  nitric  acid.     If  it  con- 
tains stannic  oxide  this  remains  undissolved ;   this  must  then  be 
washed,  ignited,  and  weighed,  and  its  weight  deducted  from  that 
of  the  impure  barium  sulphate. 

3.  A  further  100  c.c.  of  the  pyrites  solution  mentioned  in  2 
are  used  for  the  determination  of  the  metals.     For  this  purpose 
precipitate  warm  with  hydrogen  sulphide,  wash  the  precipitate, 
and  in  it  separate  the  copper  and  tin  by  means  of  potassium  sul- 
phide, according  to  Vol.  I,  p.  701  [167];  in  the  filtrate,  however, 
separate  the  iron  and  zinc  according  to  Vol.  I,  p.  644  [82]. 

B.  VARIETIES  OF  TIN. 

Tin  occurs  in  commerce  in  varying  degrees  of  purity.  The 
purest  kinds,  such  as  Banca  tin,  contain  99-9  to  99-96  per  cent, 
of  tin,  while  crude  tin  is  frequently  found  to  contain  only  about 
94  per  cent,  of  tin.  The  foreign  elements,  of  which  note  is  to  be 
taken,  are  the  following:  Lead,  copper,  bismuth,  antimony,  ar- 
senic, tungsten,  molybdenum,  iron,  zinc,  manganese,  nickel, 
chromium,  and  sulphur.  As,  in  order  to  determine  the  very  small 
quantities  of  foreign  metals  present,  it  is  necessary  to  operate  on 
large  quantities  of  tin,  a  complete  analysis  of  tin  is  by  no 
means  an  easy  task.  If  it  is  only  a  question  of  determining  those 
foreign  metals  which  are  present  in  larger  quantity,  as  copper, 
lead,  and  iron,  the  following  method  answers  well: 

Treat  about  3  grm.  of  the  finely  powdered  tin  with  nitric  acid 
until  all  the  tin  is  oxidized,  evaporate  in  a  large  porcelain  crucible 
to  dryness,  and  fuse  with  about  10  grm.  sulphurated  potassa  with 


678  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  267. 

as  complete  exclusion  of  air  as  possible.  Now  treat  the  cooled 
melt  with  warm  water,  and  thus  obtain  the  tin  (together  with 
any  antimony  and  arsenic  that  may  be  present)  in  solution  as  a 
sulpho-salt,  while  the  metals  of  the  fourth  and  fifth  groups  remain 
undissolved.  The  analysis  is  then  further  proceeded  with  as  in 
the  case  of  tinstone  (p.  676  this  volume). 

If  a  tin  contains  tungsten,  this  also  goes  into  the  sulpho-salt 
solution,  and  on  precipitating  the  latter  with  diluted  sulphuric 
acid  (which  is  preferable  to  hydrochloric  acid  when  the  tin  sul- 
phide is  to  be  directly  converted  into  stannic  oxide),  the  tin  sul- 
phide obtained  contains  tungsten  sulphide.  On  converting  the 
sulphides  into  oxides  by  moistening  with  nitric  acid  and  igniting, 
the  tin  may  be  completely  volatilized  as  a  chloride  by  repeatedly 
heating  the  residue  with  ammonium  chloride,  while  the  tungstic 
acid  remains  behind  (H.  ROSE*).  According  to  TALBOTT  f  the 
separation  of  stannic  oxide  from  the  tungstic  acid  may  also 
be  effected  by  fusing  the  oxides  with  five  times  their  quantity 
of  potassium  cyanide  and  treating  the  melt  with  water.  The 
tin  remains  behind  as  metal,  while  the  potassium  tungstate  goes 
into  solution;  tungstic  acid  in  the  latter  is  most  simply  deter- 
mined according  to  the  method  described  above  on  p.  676. 

The  method  of  determining  small  quantities  of  antimony  and 
arsenic  in  metallic  tin  has  already  been  mentioned  in.  Vol.  I,  p.  726, 
c  and  d.  Regarding  the  separation  of  the  arsenic  and  antimony 
precipitated,  see  also  pp.  556  and  557  this  volume. 

If  it  is  desired  to  determine,  in  metallic  tin,  small  quantities  of 
metals  the  chlorides  of  which  are  not  volatile  at  all,  or  are  so  only 
at  a  relatively  high  temperature,  this  may  be  done  by  fusing  the 
tin  in  a  current  of  chlorine  in  a  retort,  or  distributed  in  boats  in 
a  tube.  The  tin,  together  with  the  antimony,  arsenic,  etc.,  vola- 
tilize as  chlorides,  which  may  be  collected  in  cooled  receivers, 
while  the  chlorides  of  copper,  lead,  etc.,  remain  behind  (Vol.  I, 
p.  694,  9,  and  this  volume,  p.  608,  &). 

The  stannous  oxide  and  also  the  tungsten  and  molybdenum  in 

*  ROSE'S  Handbuch  der  analyt.  Chem.,  6th  ed.,  by  FINKENER,  p.  352. 
f  Zeitschr.  f  analyt.  Chem.,  x,  343. 


§  267.]  TIN    COMPOUNDS. 


679 


metallic  tin  can  be  determined,  according  to  BALLING,*  as  follows: 
Treat  10  to  20  grm.  of  the  finely  reduced  metal  with  about  1  litre 
of  an  acid-free  solution  of  ferric  chloride  (containing  20  grm.  iron 
per  litre),  warmed  to  30°,  and  digest  the  mixture  at  the  ordinary 
temperature  sufficiently  long  (about  24  hours)  stirring  occasion- 
ally, and  adding  more  ferric  chloride,  if  necessary,  until  all  the 
tin  has  dissolved  as  stannous  chloride.  Then  filter  off  the  un- 
dissolved,  dark  residue,  consisting  of  finely  granular  stannous 
oxide,  which  may  show  whitish  flecks  of  tungstic  and  molybdic 
acids,  and  also  of  antimonic  oxide,  and  which,  in  the  case  of  tin 
rich  in  lead,  may  contain  lead  as  well.  If  the  residue  is  free  from 
other  metals,  wash  it,  convert  it  into  stannic  oxide  by  igniting 
with  access  of  air,  and  weigh.  If  it  contains  lead,  a  separation 
must  be  effected  (see  Vol.  I,  p.  703,  /?) ;  if  it,  however,  contains 
tungstic  or  molybdic  acid,  BALLING  recommends  to  treat  the 
undissolved  stannous  oxide  with  aqueous  ammonia;  the  acids 
dissolve,  while  the  stannous  oxide,  together  with  any  antimonic 
oxide  present,  remain  behind.  On  evaporating  the  ammoniacal 
solution  in  a  porcelain  crucible,  and  moderately  heating  the  resi- 
due, the  tungstic  and  molybdic  acids  remain,  and  may  be  weighed. 

Their  separation  may  be  effected,  according  to  H.  RosE,f  as  fol- 
lows: Add  tartaric  acid  to  the  ammoniacal  solution  of  the  acids, 
then  add  hydrochloric  acid,  and  precipitate  the  molybdenum  in 
the  solution  by  prolonged  treatment  with  hydrogen  sulphide  in 
the  warm;  filter,  evaporate  to  dryness,  ignite  the  residue  with 
access  of  air,  and  if  necessary,  with  the  addition  of  ammonium 
nitrate,  until  all  the  carbon  has  been  consumed,  and  then  weigh 
the  residual  tungstic  acid.  If  it  is  desired  to  separate  only  the 
stannic  oxide  from  tungstic  acid,  the  mixture  may  be  ignited  re- 
peatedly with  ammonium  chloride  until  all  the  tin  has  volatilized 
as  chloride;  or  TALBOTT'S  method  of  separation  may  be  resorted 
to  (p.  678  this  volume). 

If  the  tin  contains  sulphur,  determine  this  by  warming  the 

*  Oesterr.  Zeitschr.  /.  Berg-  und  Hiittenwesen,  1878,  p.  169. 

f  ROSE'S  Handbuch  der  analyt.  Chem.,  6th  ed.,  by  FINKENER,  n,  p.  358. 


680  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  267. 

tin  with  hydrochloric  acid  until  dissolved,  and  determining  the 
hydrogen  sulphide  in  the  hydrogen  evolved  according  to  one  of 
the  methods  detailed  for  determining  sulphur  in  cast  iron,  p.  519 
this  volume. 

C.  TIN  ALLOYS. 

Of  the  tin  alloys,  one,  WOOD'S  metal,  has  already  been  treated 
of  (p.  665  this  volume).  The  analysis  of  a  few  others  will  be  here 
given. 

I.   ALLOYS     CONSISTING     CHIEFLY     OF     COPPER     AND     TIN     (ANTIQUE 

BRONZE,  PATENT  BRONZE,  BELL  METAL,  SPECULUM  METAL, 

MEDAL  AND  COIN  BRONZE,  PHOSPHOR-BRONZE,  ETC.). 

The  above-named  highly  important  alloys  contain  tin  and 
copper  in  varying  proportions.  Other  elements  are  found  in  them, 
either  because  the  alloyed  metals  were  impure,  or  because  they 
were  purposely  added  in  order  to  impart  special  properties  to  the 
bronze. 

In  making  the  analysis,  attention  must  be  directed  to  the  fol- 
lowing elements  in  addition  to  copper  and  tin:  Lead,  silver,  bis- 
muth, antimony,  arsenic,  iron,  cobalt,  nickel,  and  zinc.  At  times 
the  alloys  also  contain  small  quantities  of  sulphur.  Phosphor- 
bronze  also  contains  phosphorus  as  an  important  constituent. 
For  the  analysis  of  bronzes  several  quite  different  methods  may 
be  employed. 

First  Method. 

1.  Treat  about  2  to  5  grm.  of  the  comminuted  alloy  with  nitric 
acid  as  detailed  in  Vol.  I,  p.  405,  1,  a.  Evaporate  almost  to  dry- 
ness,  treat  the  residue  with  water,  and  filter  the  solution  from  the 
residual  undissolved  metastannic  acid.  BUSSE  *  recommends 
in  the  analysis  of  bronze  coins  (an  alloy  poor  in  tin),  to  treat  1 
grm.  of  the  alloy  in  the  form  of  cuttings  with  6  c.c.  nitric  acid  of 
sp.  gr.  1-5  in  a  beaker,  then  to  slowly  add  3  c.c.  water,  and  to 
quickly  cover  the  vessel.  In  proportion  as  the  water  mixes  with 

*  Zeitschr.  /.  analyt.  Chem.,  xvn,  64. 


§  267.]  TIN  COMPOUNDS.  681 

the  acid,  solution  takes  place;  when  this  is  complete,  heat  to  boil- 
ing, then  add  50  c.c.  boiling  water,  allow  to  settle,  and  filter. 

Whether  the  alloy  has  been  treated  by  one  or  other  of  these 
methods  with  nitric  acid,  or  even  according  to  BRUNNER'S  method, 
detailed  in  Vol.  I,  p.  706,  the  stannic  oxide  which  is  obtained  on 
thoroughly  washing,  igniting,  and  weighing  the  undissolved  meta- 
stannic  acid  must  be  further  tested,  as  it  may  contain  the  oxides 
of  lead,  copper,  and  iron,  and  other  oxides  of  the  fourth  and  fifth 
groups,  besides  arsenic,  phosphoric,  and  silicic  acids.  Hence 
powder  it,  and  fuse  an  aliquot  portion  with  sulphurated  potassa 
according  to  Vol.  I,  p.  703,  /?,  in  order  to  determine  in  any  residue 
that  may  remain  on  treating  the  melt  with  water,  the  oxides  of 
copper,  lead,  and  iron,  etc.,  retained  by  the  stannic  oxide;  then- 
weight  is  to  be  deducted  from  that  of  the  impure  stannic  oxide. 
Test  a  second  aliquot  portion  for  silicic  acid  according  to  KHITTEL'S 
method  (Vol.  I,  p.  707) .  If  the  bronze  contains  weighable  quanti- 
ties of  arsenic  and  antimony,  the  portions  of  these  carried  down 
with  the  stannic  oxide  will  be  found  in  the  solution  of  the  sulpho- 
salts.  In  this  case  precipitate  the  solution  with  dilute  hydro- 
chloric acid  and  separate  the  tin  from  arsenic  and  antimony 
(p.  637,  4,  this  volume). 

If  the  bronze  contains  phosphorus  this  will  all  be  found  as 
phosphoric  acid  with  the  stannic  acid  (compare  Vol.  I,  pp. 
448  and  449).  Its  weight,  as  ascertained  in  3,  must  therefore  be 
deducted  from  that  of  the  impure  stannic  oxide. 

2.  If  the  nitric-acid  solution  contains  all  the  metals  above 
mentioned  which  occur  in  bronzes,  their  separation  must  be  effected 
according  to  the  methods  detailed  for  copper,  p.  637,  a,  this  volume. 
If,  however,  as  is  usually  the  case,  only  copper,  lead,  iron,  and 
zinc  are  to  be  determined  in  the  solution,  proceed  as  detailed  in 
the  case  of  brass  (p.  655  this  volume). 

3.  If   the   bronze  contains  phosphorus,  dissolve  it  by  treating 
it  with  nitric  acid  in  the  manner  described  in  1.     After  removing 
the  greater  part  of  the  nitric  acid  by  evaporation,  moisten  the 
residue  with  fuming  hydrochloric  acid,  and  leave  in  contact  with 
this  at  the  ordinary  temperature,  or  slightly  warming,  and  fre- 


682  DETERMINATION    OF    COMMERCIAL    VALUES.          [§   267. 

quently  stirring.  Then  add  water,  in  which,  if  the  operation  has 
been  properly  carried  out,  everything  will  dissolve.  Now  precipi- 
tate the  metals  of  the  fifth  and  sixth  groups  with  hydrogen  sul- 
phide in  the  warm,  filter,  wash  the  precipitate,  evaporate  the  fil- 
trate repeatedly  with  nitric  acid,  precipitate  the  phosphoric  acid 
resulting  from  the  phosphorus  with  molybdic  acid,  and  deter- 
mine it  as  in  Vol.  I,  p.  446,  /?. 

4.  If  the  bronze  contains  a  small  quantity  of  sulphur,  deter- 
mine it  as  in  the  third  method. 

Second  Method. 

Dissolve  the  alloy  as  in  Vol.  I,  p.  707,  and  precipitate  the  tin 
according  to  LOWENTHAL'S  method  with  ammonium  nitrate,  or 
according  to  ROSE'S  method  by  means  of  diluted  sulphuric  acid, 
diluting  very  largely  (Vol.  I,  p.  406).  In  the  filtrate  all,  or  nearly 
all,  the  other  metals  will  be  found.  In  this  method  the  weighed 
stannic  oxide  must  also  be  further  tested  as  directed  in  1  of  the 
first  method. 

Third  Method. 

1.  Treat  the  comminuted  alloy  in  a  current  of  chlorine  at  a 
gentle  heat,  as  described  in  Vol.  I,  p.  709,  8,  and  this  volume,  p.  609; 
effect  the  separation,   on  the  one  hand,  of  the  readily  volatile 
chlorides  of  tin,  antimony,  arsenic,  .bismuth,  etc.,  which  collect  in 
the  receiver,  and,  on  the  other,  the  residual  non-volatile  or  diffi- 
cultly volatile  chlorides   of   copper,  lead,   etc.,  according  to  the 
methods  detailed  in  Vol.  I,  Section  V. 

2.  The  treatment  of  the  alloy  in  the  current  of  chlorine  is 
adapted  also  for  the  determination  of  small  quantities  of  sulphur 
in  bronze.     The  contents  of  the  receiver  then  contain  the  sulphur 
in  the  form  of  sulphuric  acid.     All  the  precautions  detailed  in  this 
volume,  p.  641,  must  be  taken.     As  the  barium  sulphate  obtained 
may  easily  contain  stannic  oxide,  the  sulphuric  acid  in  it  must  be 
determined  according  to  Vol.  I,  p.  441,  6,  a. 


§    267.]  TIN   COMPOUNDS.  683 

Fourth  Method,  by  CLASSEN,*  based  upon  the  Electrolytic  Separation 

of  Tin,  presupposing  the  Presence  of  only  Copper  and  Tin,  or 

of  Copper,  Tin,  Phosphorus,  and  Zinc. 

1.  Treat  the  alloy  with  nitric  acid  as  in  the  first  method,  filter 
off  the  metastannic  acid,  wash  it,  digest  with  strong  hydrochloric 
acid,  evaporate  off  the  greater  part  of  the  latter,  add  water,  and 
thus  effect  the  solution  of  the  metastannic  chloride.     In  this  solution 
separate   the  tin  electrolytically,  which  can  easily  be  done,  and 
wash   without   interrupting   the    current.     The    liquid   separated 
from   the  tin,   evaporate  repeatedly  with  nitric  acid,  unite  with 
the  nitric-acid  solution  first  obtained,  and  determine  in  it  the  cop- 
per (p.  611,  2,  this  volume). 

2.  If  the  bronze  contains  phosphorus,  the  whole  of  this  will  be 
found  as  phosphoric  acid  in  the  liquid  from  which  the  tin  has  been 
electrolytically  deposited.     Add  the  liquid  to  the  nitric-acid  solu- 
tion first  obtained  and  containing  the  greater  portion  of  the  copper, 
evaporate  off  the  free  acids  on  the  water-bath,  convert  the  copper 
into   ammonio-cupric   oxalate   (p.  623,  /?,  this   volume),  separate 
it  electrolytically,  and  in  the  liquid  separated  from  it  determine 
the  phosphoric  acid. 

3.  If  the  bronze  contains  zinc,  it  is  precipitated  together  with 
the  copper  by  the  method  given  in  2.     Then  determine  the  weight 
of  both  metals,  bring  these  into  solution  as  nitrates  or  sulphates, 
precipitate  the   copper  electrolytically,   and  from  the  difference 
ascertain  the  zinc. 

II.  ALLOYS   CONSISTING  CHIEFLY  OF  LEAD  AND  TIN 
(FINE  SOLDER,  ETC.). 

First  Method. 

Treat  about  1-5  grm.  of  the  comminuted  alloy  with  nitric  acid 
according  to  Vol.  I,  p.  405,  1,  a,  evaporate  almost  to  dryness,  and 
filter  off  the  metastannic  acid.  Add  some  pure,  diluted  sulphuric 
acid  to  the  filtrate,  evaporate  until  the  nitric  acid  has  been  driven 
off,  and  then  determine  the  lead  as  lead  sulphate  according  to  Vol. 

*  Quantitative  Analyse  auf  elektrolytischem  Wege,  p.  19. 


684  DETERMINATION    OF    COMMERCIAL  VALUES.          [§  267. 

I,  p.  355,  3,  a,  /?.  If  the  alloy  contains  also  other  metals,  these  are 
found,  at  least  in  part,  in  the  liquid  filtered  off  from  the  lead 
sulphate;  hence  this  filtrate  must  be  tested  with  hydrogen 
sulphide  and  ammonium  sulphide. 

Convert  the  metastannic  acid  into  stannic  oxide,  and  weigh 
this  (Vol.  I,  p.  405,  1).  Next  fuse  an  aliquot  portion  with  sulphu- 
rated potassa  or  with  sulphur  and  ammonium  carbonate  (Vol.  I, 
p.  703,  /?),  treat  the  melt  with  water,  dissolve  the  residual  lead 
sulphide,  after  washing  it,  in  hot  dilute  nitric  acid,  determine  in 
the  solution  the  lead  as  lead  sulphate,  and  test  whether  the  filtrate 
contains  any  iron,  etc.  If  any  residue  is  left  on  heating  the  lead 
sulphide  with  nitric  acid,  it  must  be  once  more  fused  with  sulphu- 
rated potassa,  etc.,  after  having  been  ignited.  Test  another  aliquot 
portion  of  the  stannic  oxide  for  silicic  acid  according  to  KHITTEL'S 
method  (Vol.  I,  p.  707),  deduct  the  weight  of  the  lead  oxide  with 
that  of  the  silicic  acid  here  found  from  the  weight  of  the  impure 
stannic  oxide,  and  thus  ascertain  the  weight  of  the  pure  stannic 
oxide. 

Second  Method. 

Fuse  the  finely  divided  alloy  with  3  parts  sulphur  and  3  parts 
sodium  carbonate,  or  with  4  parts  sulphurated  potassa,  with 
exclusion  of  air,  and  warm  the  melt  with  water.  From  the  solu- 
tion so  obtained  precipitate  the  tin  sulphide  mixed  with  sulphur 
by  adding  diluted  sulphuric  acid,  and  after  washing  and  drying, 
convert  it  by  suitable  ignition  into  stannic  oxide  (Vol.  I,  p.  405). 
The  residual  lead  sulphide  left  on  treating  the  melt  with  water, 
heat  with  diluted  nitric  acid,  separate  the  lead  in  the  solution  by 
evaporating  the  latter  with  sulphuric  acid,  etc.  (Vol.  I,  p.  355, 
3,  a,  /?),  and  test  the  filtrate  for  the  possible  presence  of  other 
metals. 

Third  (Electrolytic)  Method  (CLASSEN'S*). 
Treat  the  alloy  with  nitric  acid,  and  proceed  exactly  as  in  the 
first  method;    the  metastannic   acid,   containing  lead,   however, 
digest  with  strong  hydrochloric  acid,  evaporate  off  the  greater 

*  Quantitative  Analyse  auf  elektrolytischem  Wege,  p.  17. 


§  267.]  TIN   COMPOUNDS.  685 

part  of  the  acid,  add  water,  then  add  an  excess  of  ammonium 
oxalate  to  the  solution  thus  obtained,  and  then  subject  the  mix- 
ture to  electrolysis.  The  tin  is  thus  obtained  at  the  negative 
electrode,  and  the  lead  (which  it  still  contains)  as  dioxide  at  the 
positive  electrode.  Dry  the  electrodes  at  100°,  weigh,  and  from 
their  increase  in  weight  ascertain  the  weight  of  the  metals  de- 
posited. 

III.  ALLOYS  CONSISTING  CHIEFLY  OF  TIN  AND  ANTIMONY 

(BKITTANNIA  METAL,  PEWTER,  ETC.). 

The  widely  employed  tin-antimony  alloys  contain  both  metals 
in  varying  proportions.  In  their  analysis  attention  must  be  paid 
to  the  lead,  copper,  bismuth,  zinc,  and  nickel  which  are  some- 
times intentionally  added  to  the  alloy;  and  in  very  accurate 
investigations  also  to  the  small  quantities  of  other  elements  which 
are  present  as  impurities  in  tin  and  antimony,  specially  arsenic. 
One  of  the  following  methods  may  be  employed  for  the  analysis : 

First  Method. 

Proceed  exactly  as  detailed  in  Vol.  I,  p.  718,  a  [201].  If  the 
alloy  contains  other  metals  besides  antimony,  tin,  and  arsenic,  they 
are  found  in  part  with  the  sodium  antimonate,  e.g.,  cupric,  bismuth, 
ferric,  and  nickelous  oxides;  and  in  part  in  the  alkaline  nitrate 
containing  the  stannic  oxide  and  arsenic  acid,  e.g.,  lead  and  zinc. 
It  will  be  easily  seen  that  on  further  treatment  the  copper  and 
bismuth  are  obtained  as  sulphides  together  with  the  antimony 
sulphide,  but  that  the  iron  and  nickel  will  remain  in  the  liquid 
filtered  off  from  the  antimony  sulphide;  lead  and  zinc  may,  how- 
ever, be  precipitated  from  the  solution  still  containing  the  large 
excess  of  soda,  by  the  cautious  addition  of  sodium  sulphide,  before 
adding  hydrochloric  acid  and  passing  in  hydrogen  sulphide. 

Second  Method  (CL.  WINKLER'S  *). 

Dissolve  from  1  to  1-5  grm.  of  the  comminuted  alloy  in  a 
mixture  of  4  parts  hydrochloric  acid,  1  part  nitric  acid,  and  5  parts 
water,  with  the  addition  of  some  tartaric  acid,  dilute  to  300  to 

*  Zeitschr.  f.  analyt.  Chem.,  xiv,  163. 


686  DETERMINATION    OF  COMMERCIAL  VALUES.  [§  267. 

400  c.c.  (if  sufficient  tartaric  acid  is  present  the  liquid  will  not 
become  turbid),  and  add  calcium-chloride  solution  in  such  quan- 
tity that  there  will  be  8  parts  lime  present  to  1  part  of  tin;  then 
neutralize  with  potassium  carbonate,  add  potassium  cyanide,  and 
then  more  potassium  carbonate,  until  all  the  calcium  is  precipitated. 
Now  heat  the  mixture  to  boiling,  allow  to  settle,  decant  through 
a  filter,  boil  the  precipitate  once  more  with  fresh  wate'r,  allow  to 
settle,  and  filter  the  supernatant  liquid  into  the  first.  In  this 
manner  the  main  portion  of  the  antimony  is  obtained  in  the  fil- 
trate. In  order  to  bring  also  the  remainder  completely  into 
solution,  dissolve  the  residue  in  a  little  concentrated  hydrochloric 
acid,  add  some  tartaric  acid,  neutralize  with  potassium  carbo- 
nate, and  once  more  precipitate  with  potassium  cyanide,  with 
the  subsequent  addition  of  a  further  quantity  of  potassium  car- 
bonate. Boil,  decant  through  the  filter,  boil  thrice  with  fresh 
quantities  of  water,  decanting  through  the  filter,  and  finally  transfer 
the  precipitate  to  the  filter  and  complete  the  washing.  All  the 
antimony  and  arsenic  will  now  be  had  in  the  filtrate,  and  all  the 
tin  as  stannic  hydroxide,  together  with  considerable  calcium 
carbonate,  in  the  precipitate.  Dry  the  latter,  heat  it,  together 
with  the  filter  ash,  to  bright  redness  in  a  porcelain  crucible,  transfer 
to  a  beaker,  and  add  some  water,  followed  by  diluted  nitric  acid 
in  which  the  calcium  dissolves,  while  the  stannic  oxide  remains. 
Collect  this,  ignite,  and  weigh. 

In  the  filtrate  determine  the  antimony  as  antimony  sulphide. 
If  arsenic  is  also  present,  the  separation  is  best  effected  by  BUN- 
SEN'S  method  (pp.  556  and  557  this  volume). 

IV.    ALLOYS    USED    FOR    BEARINGS     ( WHITE  BEARING-METAL). 

White  metals  as  a  rule  contain  tin  as  the  chief  constituent, 
but  in  other  respects  they  differ  greatly.  Some  contain,  besides 
tin,  also  antimony,  others  zinc.  Copper  and  lead  are  usually 
present  in  small  quantities,  but  occasionally,  however,  also  in 
very  large  quantity;  many  white  metals  contain  also  mercury, 
and  a  few  nickel.  The  other  metals  which  are  met  with,  as  arsenic 
and  iron,  are  as  a  rule  to  be  regarded  only  as  impurities.  Phos- 


§  267.]  TIN  COMPOUNDS.  687 

phorus  is  met  with  only  when  phosphor-bronze  has  been  em- 
ployed in  making  the  white  metal.  It  is  hence  evident  that  the 
quantitative  analysis  of  white  metal  must  necessarily  be  preceded 
by  a  qualitative  examination. 

The   quantitative    analysis  is  most    conveniently    conducted 
as  follows: 

1.  Treat  from  1-5  to  3  grm.  with  nitric    acid  according  to 
Vol.  I,  p.  405,  1,  a,  evaporate  almost  to  dryness  on   the  water- 
bath,  and  treat  the  residue  with  diluted  nitric  acid.     If  the  pre- 
cipitate does  not  subside,  add  a  little  ammonium  nitrate.     Collect 
the  impure  metastannic  acid  and  wash  it  with  water  to  which  a 
little  ammonium  nitrate  may  be  advantageously  added. 

2.  The  undissolved  residue  contains  all  the  tin,  almost  all  the 
antimony,  and,  as  a  rule,  small  quantities  of  lead,  copper,  zinc, 
etc.     Separate  these  from  the  filter,  saturate  the  latter  with  a 
solution  of  ammonium  nitrate,  dry,  and  incinerate  it;    add  the 
filter  ash  to  the  precipitate,  ignite,  weigh,  then  fuse  with  sodium 
carbonate  and  sulphur  (Vol.  I,  p.  703,  /?) ;  treat  the  melt  with  water, 
filter,  wash  the  undissolved  residue,  extract  it  with  hot,  diluted 
nitric  acid,  fuse  any  residue  again  with  sodium  carbonate  and 
sulphur,  and  repeat  the  operations  just  described. 

3.  In  the  nitric-acid  solution   obtained   in  2,   determine  the 
small  quantities  of  lead,  copper,  zinc,  and  iron,  usually  present, 
according  to  the  methods  described  for  brass  (p.  655  this  volume). 

4.  Acidulate  with  sulphuric  acid  the  solution  of  the  sulpho- salts 
obtained  in  2,  allow  to  settle,  filter,  and  wash  the  precipitate, 
evaporate  the  filtrate,  and  determine  the  phosphoric  acid  result- 
ing from  any  phosphorus  originally  present,  by  precipitating  with 
molybdic  acid,  etc.     The  quantity  of  the  tin  is  ascertained  on 
deducting  the  combined  weight  of  the  small  quantities  of  the 
metallic  oxides  found  in  3,  and  that  of  the  phosphoric  acid  found 
in  4,  from  the  weight  of  the  impure  stannic  oxide.     The  tin  may 
also  be  directly  determined  by  converting  the  tin  sulphide  into 
stannic  oxide  and  weighing  the  latter  (Vol.  I,  p.  406,  c). 

5.  If  antimony  is  present,  and  perhaps  also  arsenic,  the  tin 
sulphide  obtained  in  4,   and  containing  sulphur  and   antimony 


688  DETERMINATION    OF    COMMERCIAL  VALUES.          [§  267- 

sulphide,  and  perhaps  also  arsenic  sulphide,  must  be  oxidized  with 
fuming  nitric  acid.  After  evaporating  off  the  excess  of  the  acid, 
the  separation  and  determination  of  the  metals  is  then  proceeded 
with  according  to  Vol.  I,  p.  718,  a  [201]. 

6.  The  nitric-acid  solution  filtered  from  the  metastannic  acid 
in  1,  evaporate  with  an  excess  of  dilute  sulphuric  acid  in  order  to 
separate  and  determine  the  lead  (Vol.  I,  p.  689,  2).     To  the  solution 
filtered  from  the  lead  sulphate,  however,  add  about  12  per  cent,  of 
hydrochloric  acid  of  sp.  gr.  1-1,  and  pass  in  hydrogen  sulphide  at 
70°;   collect  the  precipitate,  wash,  treat  with  a  solution  of  sodium 
sulphide,  or,  if  mercury  is  present,  of  ammonium  sulphide,  filter, 
and  add  hydrochloric  acid  to  the  filtrate.     The  precipitate,  which 
consists  chiefly  of  sulphur,  but  which  may  contain  the  rest  of  the 
antimony  and  arsenic,  treat  with  some  brominized  hydrochloric 
acid,  filter,    add    an    excess    of    ammonia,  and    after    prolonged 
digestion,  acidulate  with  hydrochloric    acid  and  precipitate  with 
hydrogen  sulphide.     The  small  quantity  of  antimony  sulphide  so 
obtained  collect  in  a  small  asbestos  filtering-tube  and  determine 
according  to  Vol.  I,  p.  398.     If  arsenic  is  present,  it  is  generally 
sufficient  to  treat  the  moist  precipitate  with  ammonium  carbonate 
in  order  to  separate  the  two. 

7.  The  insoluble   residue  in  6   left  after  the  treatment  with 
sodium  or  ammonium  sulphide,  and  which  as  a  rule  still  contains 
some  zinc  sulphide,  dissolve  in  brominized  hydrochloric  acid,  in 
order  to  complete  the  separation  of  the  metals  of  the  fifth  group 
from  zinc,  digest  with  an  excess  of  ammonia,  add  12  per  cent, 
hydrochloric  acid  of  sp.  gr.  1-1,  and  again  precipitate  with  hydro- 
gen sulphide  at  70°;    filter,  unite  the  filtrate  with  the  analogous 
filtrate  from  6,  concentrate  by  evaporation,  and  separate  the  zinc 
from  the  iron,  and  if  necessary  from  the  nickel,  according  to  ZIM- 
MERMANN'S  method  (p.  431  this  volume). 

8.  The  precipitate  thrown  down  by  hydrogen  sulphide  in  7,  if 
it  consists  only  of  cupric  sulphide,  convert  into  cuprous  sulphide 
according  to  Vol.  I,  p.  375,  a,  and  weigh;   if,  however,  it  contains 
also  mercuric  sulphide,  separate  the  two  according  to  Vol.  I,  p.  691, 
3,c[i49]. 


§  267.]  TIN  COMPOUNDS.  689 

9.  The  determination  of  the  mercury  as  detailed  in  8  usually 
gives  too  low  a  result,  because  a  small  portion  of  the  mercury  may 
be  retained  by  the  precipitate  of  metastannic  acid  and  lost  in  the 
further  treatment  of  the  latter.  It  is  hence  advisable  to  under- 
take the  determination  of  the  mercury  in  a  separate  portion  of 
the  white  metal,  and  to  heat  this  in  a  current  of  hydrogen  in  a 
small  boat  inserted  into  a  glass  tube.  The  loss  in  weight  of  the 
sample  corresponds  exactly  with  the  quantity  of  mercury. 

D.  PREPARATIONS  OF  TIN. 

The  method  of  analyzing  tin  preparations  follows  from  what 
has  been  detailed  in  §  126;  regarding  the  testing  of  crystallized 
stannous  chloride  ("tin  salt")*  a  few  new  methods  are  added. 

1.  To  test  tin  salt  for  adulterations  (zinc  sulphate,  magnesium 
sulphate,  sodium  chloride,  etc.),  G.  MERZ  *  recommends  the  follow- 
ing process:  Cover  a  weighed  quantity,  about  2  grm.,  with  five  tunes 
its  weight  of  absolute  alcohol  and  stir  for  five  minutes.     If  the  tin 
sdt  is  free  from  the  usual  additions  insoluble  in  alcohol,  and  has 
been  recently  prepared,  a  clear  solution  will  be  obtained;   if,  on 
the  other   hand,  it   has   absorbed   oxygen   from   the   air,  a  fine, 
pulverulent    or    flocculent    precipitate    appears,  which,   however, 
when  slight,  dissolves  on  heating  the  solution,  but  if  rather  large, 
dissolves  on  adding  a  solution  of  hydrochloric-acid  gas  in  alcohol 
If  the  tin  salt  contains  any  of  the  frequently  added  adulterants, 
these  would  remain  undissolved  as  fragments  of  crystals,  which 
may  be  filtered  off,  washed  with  alcohol,  and  weighed. 

2.  If  the  quantity  of  stannous  chloride  present  in  tin  salt  is 
to  be  determined,  the  following  methods  recommended  by  FR. 
GOPPELSRODER  and  W.  TRECHSEL  |  may  be  used  instead  of  the 
methods  detailed  in  Vol.  I,  p.  408: 

a.  Dissolve  a  weighed  quantity  of  potassium  dichromate  in  a 
little  water,  add  hydrochloric  acid  to  the  hot  but  not  boiling  solu- 
tion, and  then  the  weighed  quantity  of  the  tin  salt  which  must 

*  Pharm.  Centralhalle,  xvii,  105;  Zeitschr.  /.  analyt.  Chem.,  xn,  487. 
f  Butt,  de  la  Soc.  industr.  de  Mulhouse,  xuv,  297;   Zeitschr.  /.  analyt. 
Chem.,  xvi,  364. 


690  DETERMINATION    OF    COMMERCIAL   VALUES.  [§   268. 

be  so  adjusted  as  not  to  reduce  all  the  chromic  acid.  As  soon  as 
this  has  dissolved,  add  a  larger  quantity  of  hydrochloric  acid,  heat, 
conduct  the  chlorine  evolved  into  a  potassium-iodide  solution, 
and  determine  the  iodine  liberated  according  to  Vol.  I,  p.  424. 
Its  quantity  corresponds  with  the  potassium  dichromate  not  re- 
duced by  the  tin  salt,  while  that  reduced  by  the  tin  salt  corre- 
sponds wioh  the  following  equation: 

3SnCl2 + K2Cr207  +  14HC1 = 3SnCl4  +  2CrCl3 + 2KC1 + 7H20. 

b.  Dissolve  the  tin  salt  in  cold  hydrochloric  acid  in  a  glass- 
stoppered  flask,  add  a  known  quantity  of  potassium  dichromate, 
and  when  the  reaction  has  ceased,  add  an  excess  of  potassium- 
iodide  solution,  allow  to  stand  for  five  minutes,  and  then  titrate 
the  liberated  iodine  with  sodium  thiosulphate.  This  process 
is  based,  hence,  on  K.  ZULKOWSKY'S  *  method  of  determining 
chromic  acid,  the  absolute  reliability  of  which  is  still  somewhat 
questionable  (see  loc.  cit.f  p.  76).  According  to  GOPPELSRODER 
and  TRECHSEL'S  investigations  one  and  the  same  sample  of  tin 
salt,  repeatedly  analyzed  by  method  b,  gave  quite  concordant 
results,  the  greatest  difference  amounting  to  0-51  per  cent,  in  a 
content  of  about  96  per  cent,  of  crystallized  stannous  chloride. 

3.  If  the  total  tin  content  of  a  tin  salt  is  to  be  determined, 
dissolve  the  salt  in  hydrochloric  acid  with  the  addition  of  some 
potassium  chlorate,  neutralize  the  greater  part  of  the  free  acid, 
and  determine  the  tin  by  precipitating  with  ammonium  nitrate 
(Vol.  I,  p.  405) ;  or  dissolve  in  hydrochloric  acid  and  determine 
the  tin  electrolytically  (p.  683  this  volume). 

23.  ARSENIC  COMPOUNDS. 

§268. 

The  determination  of  arsenic  and  its  separation  from  other  ele- 
ments has  been  already  so  fully  described  in  §§  127,  164,  and  165 
(Vol.  I),  as  well  as  in  the  analysis  of  arsenical  ores,  alloys,  etc.,  and 
also  in  their  respective  places  in  this  volume,  particularly  under  py- 
rites (p.  557),  fahlerz  (p.  608),  varieties  of  copper  (pp.  638  and  647), 

*  Zeitschr.  /.  analyt.  Chem.,  vni,  74. 


§  268.]  ARSENIC   COMPOUNDS.  691 

bismuth  ores  (p  663),  and  antimony  ores  (p.  670),  that  there 
is  no  need  to  again  take  up  the  analysis  of  arsenical  compounds 
in  this  place.  The  only  reason  for  reverting  to  the  subject  here 
is  to  call  attention  to  a  method  which  is  specially  adapted  for 
determining  small  quantities  of  arsenic  in  large  quantities  of 
ochres  and  other  pigments  which  contain  the  arsenic  as  an  im- 
purity, i.e.,  to  solve  the  problem  frequently  presented  of  late  years 
to  chemists,  when  it  becomes  a  question  to  determine  whether 
such  a  pigment  may  or  may  not  be  used  for  wall-paper,  etc. 

To  solve  this  problem  it  is  usually  necessary  to  operate  on 
large  quantities  of  the  substance — e.g.,  50  to  100  grm. — i.e.,  quanti- 
ties that  are  not  adapted  for  fusion  with  alkali  carbonates  and 
nitrates  or  with  sulphurated  potassa  or  treatment  with  hydrogen 
sulphide  in  solutions  effected  by  the  aid  of  strong  acids. 

In  such  a  case  it  is  best  to  employ  the  distillation  method  of 
SCHNEIDER  *  and  FYFE  f  which,  as  is  well  known,  has  been  fre- 
quently investigated  by  others ;  J  and  particularly  HAGER'S  §  modi- 
fication, which  has  recently  been  again  recommended  by  EMIL 
FISCHER  ||  and  tested  by  him  with  reference  to  the  simultaneous 
presence  of  antimony  and  tin.  By  these  modifications  it  is  ren- 
dered possible,  as  is  well  known,  to  volatilize  the  arsenic  chloride 
and  collect  it  in  the  distillate,  when  the  arsenic  is  present  as  arsenic 
acid. 

The  substance  (about  100  grm.)  is  first  placed  in  a  long-necked, 
round-bottomed  flask  of  about  600  c.c.  capacity,  and  then  covered 
with  100  c.c.  of  fuming  hydrochloric  acid  of  sp.  gr.  1  •  15  and  per- 
fectly free  from  arsenic.  If  there  is  reason  to  fear  that  this  treat- 
ment is  insufficient  to  effect  the  complete  decomposition  and  so- 
lution of  the  arsenical  compound,  add  a  few  grammes  potassium 
chlorate.  After  prolonged  action  in  the  cold,  add  50  c.c.  water, 
.and  warm  gently  for  some  time,  and  until  everything  that  is  sol- 

*  Wiener  akadem.  Berichte,  vi,  409;   POGGEND.  Annal.,  LXXXV,  433. 

f  J&urn.  f.  prakt.  Chem.,  LV,  103. 

J  Zeitschr.  f.  analyt.  Chem.,  xiV;  250  et  seq. 

§  HAGER,  Handbuch  der  pharmac.  Praxis,  I,  492. 

11  Zeitschr.  f.  analyt.  Chem.,  xxi,  266. 


692  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  268. 

uble  has  passed  into  solution.  If  potassium  chlorate  has  been 
employed  for  effecting  solution,  add  a  solution  of  ferrous  chloride  * 
perfectly  free  from  arsenic  until  it  is  present  in  excess,  and  then 
add  a  further  20  c.c.  of  the  ferrous-chloride  solution.  If  hydro- 
chloric acid  alone  has  been  used,  a  single  addition  of  20  c.c.  of 
ferrous-chloride  solution  is  sufficient.  Now  subject  the  mixture 
to  distillation,  employing  for  the  purpose  a  tubulated  retort,  as 
cork  connections  are  very  prone  to  cause  blackening  of  the  dis- 
tillate, and  even  rubber  stoppers  are  best  avoided.  The  neck  of 
the  retort  should  be  directly  obliquely  upwards,  and  near  the  end 
it  should  be  drawn  out,  the  drawn-out  part  being  bent  obliquely 
downwards  so  that  it  may  be  conveniently  inserted  to  a  suffi- 
cient depth  into  the  tube  of  the  condenser.  A  small  flask,  into 
which  the  lower  end  of  the  condenser-tube  is  inserted,  serves  as 
the  receiver.  Now  heat  the  contents  of  the  flask  to  boiling  so 
that  from  2  to  3  c.c.  of  distillate  pass  over  per  minute,  and  con- 
tinue the  distillation  until  but  30  to  40  c.c.  of  liquid  are  left  in  the 
retort.  When  cooled  somewhat,  int  oduce  another  100  c.c.  of 
quite  arsenic-free  hydrochloric  acid  of  sp.  gr.  1-1  into  the  retort, 
and  again  distil  as  before ;  repeat  the  operation  a  third  time  with  a 
further  addition  of  100  c.c.  of  the  same  hydrochloric  acid,  but  this 
time  collect  the  distillate  separately. 

The  distillates,  diluted  with  water,  treat  separately  with 
hydrogen  sulphide;  when  the  portion  last  obtained  no  longer  gives 
a  yellow  precipitate,  all  the  arsenic  will  be  contained  in  the 
first  distillate.  If,  however,  the  last  distillate  still  gives  a  precipi- 
tate, the  distillation  must  be  repeated  with  the  addition  of  a  fur- 

*  To  prepare  the  ferrous-chloride  solution,  treat  an  excess  of  small  nails, 
or  iron  filings,  with  hydrochloric  acid  of  sp.  gr.  1-12;  as  soon  as  the  first 
turbulent  disengagement  of  hydrogen  has  ceased,  warm  until  almost  no 
more  hydrogen  is  evolved,  and  then  filter.  To  the  solution  so  obtained 
add  100  c.c.  of  pure  hydrochloric  acid  of  sp.  gr.  1-1,  and  heat  to  boiling  in  a 
retort  fitted  with  a  condenser  and  receiver,  and  until  about  80  c.c.  of  dis- 
tillate have  been  collected.  If  the  distillate,  on  dilution  with  water,  gives 
no  arsenical  reaction  when  hydrogen  sulphide  is  passed  through  it,  the 
ferrous-chloride  solution  is  ready  for  use;  if  otherwise,  it  must  be  heated 
again  with  fresh  quantities  of  hydrochloric  acid  until  the  final  distillate  is 
free  from  arsenic. 


§  268.]  ARSENIC   COMPOUNDS.  693 

ther  quantity  of  hydrochloric  acid  of  sp.  gr.  1-1,  until  the  distillate 
is  free  from  arsenic. 

Collect  the  whole  of  the  arsenic  sulphide  on  a  small  filter,  wash, 
digest  with  a  concentrated  solution  of  ammonium  carbonate, 
filter,  and  acidulate  with  hydrochloric  acid;  pass  in  hydrogen 
sulphide  for  a  short  time,  collect  the  arsenous  sulphide  so  obtained 
on  a  small  filter  dried  at  100°  and  weighed,  and  then  wash,  dry, 
and  weigh  (Vol.  I,  p.  414). 

If  the  substance  under  examination  contains  any  lead,  copper, 
bismuth,  cadmium,  and  mercury,  these  are  wholly  retained  in 
the  distillation  residue  on  conducting  the  process  as  detailed;  if, 
however,  it  contains  antimony  or  tin,  small  portions  of  these  pass 
over  in  the  distillate.  In  this  case,  therefore,  the  latter  must  be 
again  distilled,  with  the  addition  of  a  few  cubic  centimetres  of 
ferrous-chloride  solution,  until  about  20  c.c.  of  residue  remains; 
all  the  arsenic  will  then  be  obtained  in  the  distillate  free  from  tin 
and  antimony,  while  the  two  latter  will  be  retained  in  the  united 
distillation  residues.  In  order  to  attain  this  object  with  certainty, 
it  is  advisable,  according  to  FISCHER,  to  distil  down  the  first  half 
of  the  total  distillate  first  obtained,  and  which  contains  by  far  the 
greater  part  of  the  arsenic,  by  itself  with  the  addition  of  from 
3  to  5  c.c.  ferrous-chloride  solution  until  but  30  c.c.  of  residue 
remain,  and  then  to  add  the  second  half  and  concentrate  to  the 
same  volume. 

[DETECTION  AND  ESTIMATION  OF  ARSENIC  IN  ORGANIC  MATTER. 

§  268,  a. 
GAUTIER'S  Method  simplified  by  JOHNSON  and  CHITTENDEN. 

The  following  method  for  the  detection  and  estimation  of 
arsenic  in  organic  matter  is  a  modification  of  the  process  recently 
described  by  GAUTIER.*  GAUTIER'S  method  consists  in  treating 
the  substance  with  certain  quantities  of  nitric  acid,  and  afterwards 
of  sulphuric  acid,  at  a  high  temperature,  whereby  the  organic 
matters  are  partly  destroyed  and  converted  into  slightly  soluble 

*  Bulletin  de  la  Societe  Chimique,  24,  250. 


694  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  268. 

humus-like  bodies,  from  which  all  the  arsenic  may  be  extracted  by 
boiling  water.  GAUTIER  treats  the  brown  solution  thus  obtained 
with  "sodium  bisulphate,  throws  down  the  arsenic  in  a  state  of 
sulphide  with  hydrogen  sulphide,  transforms  this  sulphide  into 
arsenic  acid  by  known  means,"  treats  the  solution  thus  obtained  in 
the  MARSH  apparatus,  and  finally  weighs  the  arsenic  in  the  metallic 
state  as  below  described. 

JOHNSON  and  CHITTENDEN  dispense  with  the  use  of  all  reagents 
but  sulphuric  acid,  nitric  acid,  and  zinc  alloyed  with  a  little  plati- 
num, which  are  not  difficult  to  obtain  in  a  state  of  absolute  freedom 
from  arsenic,  and  they,  together  with  DONALDSON,  have  demon- 
strated that  the  method,  thus  essentially  simplified,  gives  exact 
results.  The  following  account  of  the  process  is  from  a  paper  by 
CHITTENDEN  and  DONALDSON.* 

I.  REAGENTS  AND  APPARATUS. 

The  reagents  required  are  pure  granulated  zinc  alloyed  with  a 
small  quantity  of  platinum,  pure  concentrated  nitric  and  sulphuric 
acids,  and  three  dilute  sulphuric  acids  of  increasing  strength,  which, 
for  the  sake  of  convenience,  may  be  prepared  in  considerable  quan- 
tities : 

Acid  No.  1.  180  c.c.  pure  cone.  H2S04+ 1000  c.c.  H20. 
Acin  No.  2.  260  c.c.  pure  cone.  H2S04+  1000  c.c.  H2O. 
Acid  No.  3.  425  c.c.  pure  cone.  H2SO4+  1000  c.c.  H20. 

The  form  of  MARSH  apparatus  used  is  shown  by  Fig.  127. 

The  flask,  a  BUNSEN'S  wash-bottle,  of  200  c.c.  capacity,  is  pro- 
vided with  a  small  separatory  funnel  of  65  c.c.  capacity,  with 
glass  stop-cock.  This  is  a  very  material  aid  to  obtaining  a 
slow  and  even  evolution  of  gas,  and  is  nearly  indispensable  in 
accurate  quantitative  work.  The  gas  generated  is  dried  by  pass- 
ing through  a  calcium-chloride  tube,f  and  then  passes  through  a 

*  American  Chemical  Journal,  vol.  n,  p.  235. 

f  OTTO  and  also  DRAGENDORFF  recommend  to  pass  the  gas  first  over 
fragments  of  caustic  potassa.  We  find,  however,  in  accordance  with  DORE- 
MUS,  that  arsenic  is  arrested  by  caustic  alkali. — S.  W.  J.  and  R.  H.  C. 


§  268.] 


ARSENIC    COMPOUNDS. 


695 


tube  of  hard  glass,  heated  to  a  red  heat  by  a  furnace  of  three 
BUNSEN  lamps  with  spread  burners,  so  that  a  continuous  flame 
of  six  inches  is  obtained ;  and  with  a  proper  length  of  cooled  tube 
not  a  trace  of  arsenic  passes  by.  The  glass  tube  where  heated  is 
wound  with  a  strip  of  wire  gauze,  both  ends  being  supported  upon 
the  edges  of  the  lamp  frame,  so  that  the  tube  does  not  sink  down 


FIG.  127. 

when  heated.  The  small  furnace  is  provided  with  two  appropriate 
side  pieces  of  sheet  metal,  so  that  a  steady  flame  is  always  ob- 
tained. When  the  quantity  of  arsenic  is  very  small  the  tube  is 
naturally  so  placed  that  the  mirror  is  deposited  in  the  narrow 
portion,  but  when  the  arsenic  is  present  to  the  extent  of  0-005 
grm.,  the  tube  should  be  6  mm.  in  inner  diameter  and  so  arranged 
that  fully  two  inches  of  this  large  tube  are  between  the  flame  and 
the  narrow  portion.  When  the  quantity  of  arsenic  is  less  the 
tube  can  naturally  be  smaller. 


696  DETERMINATION    OF   COMMERCIAL   VALUES.         [  §268. 


II.  PROCESS. 

a.  Method  for  the  complete  extraction  of  arsenic  from 
organic  matter. 

100  grm.  of  the  material  to  be  examined,  cut  into  small  pieces, 
are  placed  in  a  porcelain  casserole  of  600  c.c.  capacity  and  provided 
with  a  stirring-rod  of  stout  glass.  23  c.c.  of  pure  concentrated 
nitric  acid  are  added  and  the  dish  placed  on  a  small  air-bath* 
provided  with  a  thermometer  and  a  single  BUNSEN  burner.  The 
mixture  is  then  heated  at  150°  to  160°  C.,  with  occasional  stirring. 
At  first  the  tissue  takes  on  a  yellowish  color,  then  swells  up  some- 
what, becoming  finally  quite  thick ;  it  soon  changes  again,  becoming 
liquid,  and  then  generally  requires  heating  from  1J  to  2  hours,  the 
temperature  sometimes  being  raised  to  180°  C. 

At  this  point  the  mass,  being  now  quite  thick  again,  usually 
takes  on  a  deeper  yellow  color  or  orange  shade.  When  this  change 
of  color  is  noticed  the  casserole  is  taken  from  the  bath  and  3  c.c.  of 
pure  concentrated  sulphuric  acid  added  and  the  mixture  stirred 
vigorously.  The  addition  of  concentrated  sulphuric  acid  to  the 
viscid  residue  rich  in  nitric  acid  and  nitro-compounds  naturally 
gives  rise,  especially  at  this  temperature,  to  a  considerable  com- 
motion; the  mass  becomes  brown,  swells  up,  nitrous  fumes  are 
copiously  evolved,  immediately  followed  by  dense  white  fumes  of 
suffocating  odor,  while  the  residue  in  the  dish  is  changed  either  into 
a  dry,  carbonaceous  mass,  or  a  black,  sticky,  tar-like  mass.  Although 
the  oxidation  is  so  powerful,  no  deflagration  takes  place,  and  the 
carbonization  is  effected  in  this  manner  without  the  volatilization 
of  any  arsenic.  The  casserole  is  again  placed  on  the  bath  and 

*  For  air-bath  an  ordinary  flat-bottomed  tin  basin,  7  inches  in  diameter, 
3  inches  deep,  is  used,  with  a  cover  provided  with  an  opening  5  inches  in 
diameter.  The  bath  is  set  in  an  iron  ring  fastened  to  a  stout  lamp-stand, 
while  the  end  of  the  thermometer  passes  through  a  small  hole  near  the  edge 
of  the  cover  a  short  distance  into  the  bath,  so  that  the  temperature  can  be 
regulated. 


§  268.]  ARSENIC  COMPOUNDS.  x        697 

heated  for  a  few  minutes  at  180°  C.,  then,  while  still  on  the  bath, 
8  c.c.  of  pure  concentrated  nitric  acid  are  added  drop  by  drop  with 
continual  stirring,  the  object  being  to  destroy  more  completely 
the  organic  matter;  and  at  the  same  time,  the  nitric  acid  falling  drop 
by  drop  on  the  carbonaceous  residue  tends  to  prevent  the  formation 
of  sulphurous  acid  and  the  consequent  formation  of  insoluble 
arsenous  sulphide. 

After  the  addition  of  the  nitric  acid,  the  dish  is  heated  at  200°  C. 
for  fifteen  minutes,  and  when  cold  a  hard,  carbonaceous  residue 
is  the  result,  entirely  free  from  nitric  acid.  In  working  with  dif- 
ferent kinds  of  tissue,  slight  deviations  from  the  above  description 
will  frequently  be  observed.  When  much  bony  matter  is  present 
the  last  residue  takes  on  a  somewhat  different  character,  owing  to 
the  presence  of  calcium  sulphate,  and  occasionally  when  the  3  c.c. 
of  sulphuric  acid  are  added  the  oxidation  does  not  at  once  take 
place,  but  requires  a  little  longer  heating  on  the  air-bath.  When 
such  is  the  case,  the  mixture  needs  constant  watching  in  order  to 
remove  the  dish  from  the  bath  at  the  first  approach  of  the  oxida- 
tion. 

The  arsenic  now  exists  as  arsenic  acid,  readily  soluble  in  water. 
The  carbonaceous  residue  is  thoroughly  extracted  with  boiling 
water,  and,  in  order  to  avoid  all  loss,  is  not  previously  pulverized, 
but  the  casserole  in  which  the  oxidation  took  place  is  filled  with 
water  and  heated  on  the  water-bath  for  several  hours.  The  hard 
mass  soon  softens,  and  by  repeated  treatment  in  this  manner 
readily  gives  up  all  its  arsenic  to  the  aqueous  solution ;  it  is,  how- 
ever, better  to  have  the  carbonaceous  residue  in  contact  with 
different  portions  of  warm  water  for  about  24  hours  to  insure 
the  complete  extraction  of  the  arsenic. 

The  reddish-brown  fluid  containing  some  organic  matter  and 
arsenic  acid  is  now  evaporated  on  the  water-bath  to  dryness,  care 
being  taken  that  the  entire  residue  is  finally  obtained  in  one  cas- 
serole. This  residue  *  of  organic  matter  and  arsenic  is  warmed 


*  When  the  residue  left  by  the  evaporation  of  the  water  is  quite  large,  it 
is  sometimes  better  to  reoxidize  it.     This  is  quickly  accomplished  by  adding 


698  DETEKMINATION    OF    COMMERCIAL    VALUES.  [§  268. 

with  45  c.c.  of  sulphuric  acid  No.  1,  and  the  clear  solution  so  ob- 
tained, or,  as  more  frequently  happens,  the  fluid  with  organic 
matter  in  suspension,  is  then  ready  for  introduction  into  the  MARSH 
apparatus. 

b.  Method  for  the  conversion  of  arsenic  acid  into  arsenetted 
hydrogen  and  then  into  metallic  arsenic. 

25  to  35  grm.  of  granulated  zinc  previously  alloyed  with  a  small 
quantity  of  platinum  are  placed  in  the  generator,  and  everything 
being  in  position,  the  MARSH  apparatus  is  filled  with  hydrogen  by 
the  use  of  a  small  quantity  of  acid  No.  1.  After  a  sufficient  time 
has  elapsed  the  gas  is  lighted  at  the  jet  and  the  glass  tube  heated 
to  a  bright  redness.  The  45  c.c.  of  acid  No.  1  containing  the 
arsenic  are  then  poured  into  the  separatory  funnel,  from  which  the 
acid  is  allowed  to  flow  into  the  generator  at  such  a  rate  that  the  en- 
tire fluid  is  introduced  in  one  hour  or  one  hour  and  a  half;  40  c.c.  of 
acid  No.  2  are  then  poured  into  the  casserole,  to  which  considerable 
organic  matter  usually  adheres,  and  then  transferred  to  the  sepa- 
rating funnel  and  allowed  to  flow  slowly  into  the  generator,  and 
lastly  45  c.c.  of  acid  No.  3.  In  this  manner  we  are  sure  to  have 
all  of  the  arsenic  acid  dissolved  and  thus  carried  into  the  generator, 
while  at  the  same  time  the  stronger  acids  Nos.  2  and  3  serve  as  a 
rinse  fluid  and  thereby  prevent  mechanical  loss,  while,  at  the 
same  time,  the  increasing  strength  of  acid  added  counteracts  the 
diluting  effect  on  the  reaction  so  that  the  strength  of  acid  remains 


a  few  cubic  centimetres  of  concentrated  nitric  acid  to  the  contents  of  the 
casserole  and  heating  on  the  air-bath  at  150°  to  180°  C.  until  a  reddish  solution 
is  obtained.  Then  3  to  5  c.c.  of  concentrated  sulphuric  acid  are  added  and  the 
mixture  heated  at  the  above  temperature  until  the  nitric  acid  is  completely 
driven  off.  The  thin  black  fluid  is  then  carefully  mixed  with  the  requisite 
quantity  of  No.  1  acid  and  introduced  into  the  MARSH  apparatus.  Fre- 
quently quite  a  heavy,  flocculent  precipitate  separates  from  the  sulphuric- 
acid  solution.  This  does  not  interfere,  but  is  poured,  together  with  the 
fluid,  directly  into  the  receiving  bulb,  which  is  purposely  provided  with  a 
delivery-tube  of  large  calibre. 


§  268.]  ARSENIC   COMPOUNDS.  699 

about  the  same  during  the  entire  process  of  2J  to  3  hours, 
and  thereby  insures  a  regular  flow  of  gas.  The  time  required 
will  vary  with  the  quantity  of  arsenic;  2  to  3  mgrms.  of  arsenic 
will  require  about  two  to  three  hours  for  entire  decomposition, 
while  4  to  5  mgrms.  will  need  perhaps  three  to  four  hours.  Where 
the  quantity  of  arsenic  is  small,  only  25  grm.  of  zinc  are  needed, 
and  but  45  c.c.  of  acid  No.  1,  30  c.c.  of  acid  No.  2,  and  30  c.c.  of 
acid  No.  3;  but  when  4  to  5  mgrms.  of  arsenic  are  present, 
it  is  better  to  take  the  first-mentioned  quantities  of  zinc  and 
acids. 

The  arsenic  being  thus  collected  as  a  large  or  small  mirror  of 
metal,  the  tube  is  cut  at  a  safe  distance  from  the  mirror,  so  that  a 
tube  of  perhaps  2  to  6  grm.  weight  is  obtained.  This  is  carefully 
weighed  and  then  the  arsenic  removed  by  simple  heating;  or,  if 
the  arsenic  is  to  be  saved  as  in  a  toxic  case,  dissolved  out  with 
strong  nitric  acid.  The  tube  is  then  cleaned,  dried,  and  again 
weighed,  the  difference  giving  the  weight  of  metallic  arsenic,  from 
which  by  a  simple  calculation  the  amount  of  arsenous  oxide  can 
be  obtained.  The  delicacy  of  the  method  is  shown  by  the  fact 
that  0-00001  grm.  As2O3  when  introduced  into  100  grm.  of  beef 
yielded  by  this  method  a  distinct  mirror  of  metallic  arsenic.  In  a 
similar  manner  0-000001  grm.  As2O3  yielded  a  faint  mirror  of  ar- 
senic, this  quantity  appearing  to  be  the  limit. 

In  conducting  these  experiments  with  organic  matter,  after 
"the  zinc  is  placed  in  the  generator,  15  drops  of  olive  oil  are  allowed 
to  flow  down  the  side,  and  this,  as  the  fluid  is  introduced,  floats 
on  top  and  thereby  prevents  any  troublesome  frothing.  The 
only  other  thing  to  be  guarded  against  is  the  too  rapid  introduc- 
tion of  the  acids,  whereby  loss  as  well  as  frothing  of  the  mixture 
may  ensue,  and  secondly  the  heating  of  the  flask  by  the  chemical 
reaction.  If  necessary,  this  latter  can  be  prevented  by  placing 
the  generator  in  a  glass  or  other  dish  so  that  a  stream  of  cold 
water  can  continually  play  about  it,  which  will  keep  the  flask 
sufficiently  cool  to  prevent  the  formation  of  any  hydrogen  sul- 
phide which  might  sometimes  show  itself  in  slight  quantity. 

The  following  results  show  the  accuracy  of  the  method: 


700  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  269. 


QuantityofArsenicIntroduced. 

100  grm.  beefsteak  with  0  -  004  grm.  As2O3  0  •  00300  0  •  00303 

"     "           "           "     0-004     "  "  0-00300  0-00303 

"     "           "           "     0-004     "  "  0-00290  0-00303 

"     "           "           "    0-003     "  "  0-00219  0-00227 

"     "                        "     0-005     "  "  0-00369  0-00378 

"     "           "           "    0-005     "  "  0-00372  0-00378] 


24.  PHOSPHORUS  COMPOUNDS. 
§269. 

RED  (AMORPHOUS)  PHOSPHORUS. 

Red  phosphorus,  which  is  manufactured  on  a  large  scale,  and 
which  is  now  used  in  considerable  quantities,  is,  as  a  rule,  not 
perfectly  pure.  It  frequently  contains  a  smaller  or  larger  quantity 
of  ordinary  white  phosphorus,  and  as  this  gradually  oxidizes  on 
contact  with  the  air,  varying  quantities  of  phosphoric  and  phos- 
phorous acids  are  formed,  whereby  the  substance  acquires  an  acid 
reaction  and  becomes  moist  from  the  taking  up  of  water. 

For  the  determination  of  these  constituents  the  following 
method,  devised  by  E.  LUCK  and  myself,  is  adapted:* 

1.  Determination  of  the  Phosphoric  and  Phosphorous  Acids 
in  Amorphous  Phosphorus. 

Place  about  5  grm.  of  the  red  phosphorus  to  be  examined 
evenly  in  an  asbestos  filter-tube,  crushing  any  small  lumps,  and 
wash  with  water,  best  by  the  aid  of  the  water-pump,  so  long  as  the 
washings  have  an  acid  reaction;  then  make  up  the  liquid  to 
250  c.c. 

1.  Add  5  c.c.  concentrated  nitric  acid  to  100  c.c.  of  the  above 
solution  and  evaporate  on  the  water-bath  until  a  residue  of  about 
1  c.c.  remains,  then  add  a  few  drops  of  red,  fuming  nitric  acid,  heat 
again  for  a  short  time,  and  then  throw  down  the  phosphoric  acid 
with  magnesia  mixture  in  the  usual  manner.  (If,  in  certain  cases, 
a  slight  turbidity  occurs  on  supersaturating  with  ammonia  before 
precipitating  with  magnesia,  i.e.,  if  the  phosphoric  acid  to  be  deter- 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  63. 


§  269.]  PHOSPHORUS   COMPOUNDS.  701 

mined  is  impure,  it  is  advisable  to  first  precipitate  with  molybde- 
num solution,  Vol.  I,  p.  446,  ,5.) 

From  the  weighed  magnesium  pyrophosphate  calculate  the 
quantity  of  phosphoric  acid  originally  present  and  that  formed 
from  the  oxidation  of  the  phosphorous  acid. 

2.  Transfer  a  second  100  c.c.  of  the  original  washings  to  a 
beaker,  add  a  little  hydrochloric  acid  and  an  excess  of  mercuric- 
chloride  solution,  and  gradually  heat  on  a  water-bath  for  some 
time,  and  until  temperature  of  about  60°  is  reached.  Pour  off 
some  of  the  clear  liquid,  add  to  it  a  further  quantity  of  mercuric- 
chloride  solution,  and  ascertain  whether  a  further  precipitation 
occurs  on  warming,  in  which  case  the  complete  precipitation  must 
be  effected  by  adding  a  further  quantity  of  mercuric  chloride  to 
the  contents  of  the  beaker. 

Collect  the  precipitated  mercurous  chloride  on  a  weighed  filter, 
dry  at  100°,  and  calculate  the  phosphorous  acid  corresponding  to 
the  mercurous  chloride  according  to  the  following  equation: 

H3PO3 + 2HgCl2  +  H2O  =  Hg2Cl2 + 2HC1 + H3PO4. 

1  eq.  of  mercurous  chloride  =  470  •  9,  hence  corresponds  with  J  eq. 
of  phosphorous  anhydride,  P2O3  =  55,  or  1  eq.  of  phosphorous 
acid,  H3PO3=82-024. 

During  the  precipitation  of  the  mercurous  chloride  direct  sun- 
light must  be  excluded,  otherwise  the  mercurous  chloride  would 
acquire  a  gray  color  from  the  separation  of  metallic  mercury. 

On  calculating  the  phosphorous  acid  found  to  phosphoric  acid, 
and  deducting  this  from  the  total  phosphoric  acid  found  in  1,  the 
difference  gives  the  phosphoric  acid  originally  present  as  such  in 
the  phosphorus. 

2.  Determination  of  the  Total  Amount  of  Red  and  White 
Phosphorus. 

Wash  about  0-5  grm.  of  the  phosphorus  as  before  in  an  asbestos 
filter- tube  with  water  in  order  to  remove  phosphorous  and  phos- 
phoric acids,  and  then  introduce  it  together  with  the  asbestos 


702  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  269. 

into  a  flask  connected  with  a  U-tube  by  means  of  a  glass  tube 
bent  twice  at  right  angles.  The  U-tube  contains  5  c.c.  red,  fuming 
nitric  acid.  Heat  the  phosphorus  with  nitric  acid  of  sp.  gr.  1-2, 
gradually  to  boiling  and  until  dissolved.  Then  transfer  the  solu- 
tion, together  with  the  nitric  acid  in  the  U-tube,  to  an  evaporating- 
dish,  evaporate,  add  some  fuming  nitric  acid  again  to  the  residue 
and  evaporate  once  more,  and  take  up  the  viscid  residue  with 
water.  Then  filter,  precipitate  with  magnesia  mixture,  and  from 
the  phosphoric  acid  found  calculate  the  total  of  both  modifications 
of  the  phosphorus. 

3.  Determination  of  the  Red  Phosphorus. 

Wash  0-5  grm.  of  the  sample  as  before  in  an  asbestos  tube 
with  water  until  the  washings  cease  to  have  an  acid  reaction,  then 
place  the  tube  over  a  second  flask,  and  displace  the  water  which 
moistens  the  phosphorus  by  washing  first  with  absolute  alcohol 
and  finally  with  anhydrous  ether.  Reserve  the  alcoholic  and 
ethereal  washings,  and  now  treat  the  phosphorus  (which  has,  by 
the  foregoing  proceeding,  been  rendered  capable  of  being  moistened 
with  carbon  disulphide) ,  with  the  disulphide  until  a  few  drops  evapo- 
rated on  a  watch-glass  in  a  dark  place  no  longer  exhibits  a  lumi- 
nosity. Collect  the  carbon-disulphide  solution  of  the  white  phos- 
phorus in  a  dry  flask  and  set  it  aside  for  further  use. 

Through  the  tube  containing  the  washed  red  phosphorus  pass 
a  current  of  dry  carbon  dioxide,  at  first  at  the  ordinary  tempera- 
ture, but  later  at  40°  to  50°,  and  determine  the  red  phosphorus 
either  direct  or,  better,  after  its  conversion  into  phosphoric  acid 
by  nitric  acid,  in  the  form  of  magnesium  pyrophosphate. 

4.  Determination  of  the  Ordinary  (White)  Phosphorus. 

Transfer  the  carbon-disulphide  solution  obtained  in  3  to  a 
tubulated .  retort  fitted  with  a  condenser,  add  sufficient  iodine  to 
impart  a  violet  tint,  and  then  distil  in  a  water-bath  nearly  to 
dryness.  The  carbon  disulphide  passing  over  must  contain  a  slight 
quantity  of  iodine  in  order  to  make  certain  that  the  quantity  of 


§  270.]  SULPHUR  COMPOUNDS.  703 

iodine  used  was  sufficient.  (For  every  equivalent  of  phosphorus 
at  least  3  eq.  of  iodine  should  be  used.) 

Add  to  the  residue  in  the  retort  the  alcoholic-ethereal  filtrate 
which  had  served  to  remove  the  water  from  the  phosphorus, 
and  distil  this  off  also.  The  white  phosphorus  soluble  in  carbon 
disulphide  will  now  be  found  in  the  residue  in  the  form  of  phos- 
phorus triiodide,  but  the  slight  quantity  of  water  present  in 
the  alcoholic-ethereal  solution  usually  suffices  to  decompose  the 
triiodide  into  hydrogen  iodide,  HI,  and  either  phosphorous  acid, 
H3PO3,  or  phosphoric  acid,  H3PO4.  Add  some  more  water,  distil 
off  a  part  of  the  excess  of  iodine  with  it,  transfer  the  contents 
of  the  retort  to  an  evaporating-dish,  add  some  nitric  acid,  heat  on 
a  water-bath  until  all  the  iodine  has  been  driven  off,  and  take  up 
with  a  little  water;  now  precipitate  the  phosphoric  acid  with 
molybdenum  solution,*  determine  it  as  magnesium  pyrophosphate, 
and  from  this  calculate  the  quantity  of  white  phosphorus. 

5.  Any  foreign  admixtures  in  the  commercial  article,  such  as 
sand,  etc.,  are  best  determined  by  treating  the  samples  in  a  flask 
with  iodine  and  water,  separating  the  undissolved  residue  by 
filtration,  and  weighing. 

When  the  quantities  of  both  modifications  of  the  phosphorus, 
the  phosphorous  and  phosphoric  acids,  and  also  the  mechanical 
admixtures,  are  known,  the  water  in  the  sample  may  be  ascer- 
tained by  the  difference. 

25.  SULPHUR  COMPOUNDS. 

§270. 
A.  COMMERCIAL  SULPHUR. 

Sulphur  comes  into  the  wholesale  market  as  crude  sulphur 
(prepared  from  native  sulphur,  metallic  sulphides,  soda  waste 
from  the  LE  BLANC  soda  process,  etc.)  or  as  refined  sulphur  (roll 

*  Commercial  iodine  frequently  contains  a  small  quantity  of  iron  which, 
on  precipitating  the  phosphoric-acid  solution  directly  with  magnesia  mix- 
ture, causes  the  result  to  be  inaccurate. 


704  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  270* 

sulphur,  flowers  of  sulphur).  Refined  sulphur  contains  as  a  rule 
but  slight  quantities  of  impurities,  whereas  crude  sulphur  con- 
tains a  much  larger  quantity  of  these.  The  method  of  examina- 
tion here  detailed  covers  all  the  admixtures  which  usually  occur  in 
sulphur. 

1.  To  determine  the  water,  introduce  from  3  to  5  grm.  of  the 
coarsely  ground  sulphur  into  a  small  weighing  flask,  dry  at  70° 
(but  not  longer  than  is  just  necessary),  and  determine  the  loss  in 
weight.     If  the  determination  of  the  water  is  to  be  made  in  a 
larger  quantity,  the  tin  box  described  on  p.  633,  Fig.  126,  is  em- 
ployed. 

2.  To  determine  the  arsenic,  dissolve  about  10   grm.  of   the 
sulphur  in  pure  potassa  lye,  and  pass  in  chlorine  (evolved  from 
pure,  arsenic-free  substances)  until  the  liquid  above  the  precipi- 
tated sulphur  is  clear.     Add  hydrochloric  acid  to  the  filtrate,  and 
determine  the  arsenic  (and  also  any  antimony  present)  according 
to  BUNSEN'S  method  (p.  556  this  volume). 

If  arsenic  has  been  found,  an  examination  must  be  made  as  to 
whether  it  is  present  as  arsenpus  acid  or  as  arsenic  sulphide.*  For 
this  purpose  treat  a  fresh  sample  of  the  ground  sulphur  with  diluted 
hydrochloric  acid  at  a  gentle  heat  for  a  long  time,  filter,  and  test 
whether  the  solution  affords  arsenic  sulphide  on  treatment  with 
hydrogen  sulphide.  Any  arsenic  so  obtained  was  present  in  sul- 
phur as  arsenous  acid.  If  the  sulphur  contains  arsenic  also  in 
the  form  of  arsenic  sulphide,  this  may  be  extracted,  although  with 
difficulty,  from  the  sulphur  treated  with  diluted  hydrochloric 
acid,  by  aqueous  ammonia,  then  acidulating  the  ammoniacal 
filtrate  with  hydrochloric  acid,  and  precipitating  with  hydrogen 
sulphide. 

3.  To  determine   any  sulphuric  acid  and  chlorine  present,  as 
well  as  to  detect  any  sulphurous  and  thiosulphuric  acids,  shake 
100  grm.  of  the  finely  ground  sulphur  with  500  c.c.  water,  allow 
to  settle,  and  filter. 


*  Compare  H.   HAGER,  Pharm.   Centralb.,  xv,   149;    Zeitschr.  f.  analyt. 
Chem.,  xra,  346. 


§  270.]  SULPHUR  COMPOUNDS.  705 

a.  To  100  c.c.  of  the  liquid  add  some  nitric  acid  and  silver  ni- 
trate, and  convert  any  precipitate  of  silver  chloride  that  may  form 
into  metallic  silver  for  the  purpose  of  weighing  (Vol.  I,  p.  341).     If 
the  silver  chloride  appears  blackish  from  the  admixture  of  silver 
sulphide,  treat  it  with  ammonia,  filter,  acidulate  with  nitric  acid, 
and  then  convert  the  silver  chloride  thus  purified  into  silver. 

b.  Make  100  c.c.  of  the  liquid  just  acid  with  hydrochloric  acid, 
and  determine  any  sulphuric  acid  present  by  means  of  barium 
chloride  (Vol.  I,  p.  434). 

c.  Test  100  c.c.  first  as  to  its  reaction,  then  add  a  few  drops  of 
starch  iodide  to  test  for  the  presence  of  sulphurous  or  thiosul- 
phuric  acid.     These  acids  may  be  later  quantitatively  determined 
in  another  100  c.c.  of  the  filtrate  by  means  of  standard  iodine  solu- 
tion (Vol.  I,  pp.  431  and  432). 

4.  To  determine  the  non-volatile  substances  (bitumen,  salts), 
carefully  heat  10  or  15  grm.  of  the  sulphur  in  a  porcelain  crucible 
on  a  sand-bath  until  nearly  all  the  sulphur  has  been  volatilized 
(ignition  of  the  sulphur  must  be  avoided).    Now  cover  the  crucible 
with  a  perforated  lid,  pass  pure,  dry  hydrogen  gas  into  the  cru- 
cible, and  heat  again,  until  all  the  sulphur  has  volatilized.     The 
residue,  consisting  of  the  carbon  from  organic  substances  and  salts, 
is  weighed.     Now  heat  it  carefully  with  access  of  air,  weigh  after 
cooling,  and  thus  ascertain  the  inorganic   admixtures,  and   from 
the   difference,    the    carbon   from   the   organic   substances.     The 
inorganic   admixtures  are  to  be  subsequently  further  examined 
(for  their  content  of  iron,  calcium,  magnesium,  sodium,  etc.). 

5.  To  determine  any  selenium  present,  one  of  the  following 
methods  may  be  employed : 

a.  Heat  the  very  finely  powdered  sulphur  with  a  large  excess 
of  potassium-cyanide  solution  for  a  long  time,  but  not  so  strongly 
that  the  sulphur  will  cake  together,  and  finally  boil,  and  filter  off 
the  undissolved  sulphur.  The  solution  contains  potassium  sul- 
phocyanate  and,  if  selenium  is  present,  potassium  selenocyanate. 
Supersaturate  it  with  hydrochloric  acid,  whereby  the  selenium  is 
precipitated;  it  must  be  remembered,  however,  that  this  sepa- 
rates from  dilute  solutions  but  very  slowly,  and  requires  several 


706  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  270. 

days  for  its  complete  precipitation.  Collect  it  on  a  weighed  filter, 
dry  it  at  a  temperature  a  little  below  100°,  and  weigh  (OPPEN- 
HEIM;*  H.  ROSE  f). 

6.  If  the  nature  of  the  sulphur  is  such  as  to  give  rise  to  a  doubt 
as  to  whether  the  selenium  has  been  completely  dissolved  by 
heating  with  the  potassium-cyanide  solution,  fuse  the  sulphur  with 
eight  to  ten  times  its  quantity  of  potassium  cyanide  in  a  long- 
necked  flask  into  which  a  current  of  hydrogen  is  conducted,  and 
proceed  as  described  in  Vol.  I,  p.  430,  c. 

c.  Mix  the  sulphur  with  3  parts  potassium  nitrate  and  3  parts 
sodium  carbonate,  and  introduce  the  mixture  in  small  portions  into 
a  crucible  heated  to  low  redness.  The  melt,  containing  all  the 
sulphur  as  alkali  sulphate,  and  all  the  selenium  as  alkali  selenate, 
heat  with  water,,  and  filter;  supersaturate  with  hydrochloric  acid, 
and  heat  with  this  for  some  time  in  order  to  convert  all  the  selenic 
acid  into  selenous  acid,  and  lastly  precipitate  the  selenium  by 
sulphurous  acid  (Vol.  I,  p.  430). 

B.  FUMING  SULPHURIC  ACID. 

Fuming  sulphuric  acid,  which  of  late  years  is  being  extensively 
employed  in  the  color  industry  and  for  various  other  purposes, 
now  comes  into  the  market  containing  much  more  anhydride  than 
it  formerly  did;  and,  as  the  anhydride  content  is  very  variable, 
and  is  the  only  basis  upon  which  the  price  is  fixed,  the  acid  is 
frequently  the  subject  of  analysis.  As  this  presents  some  diffi- 
culties, the  following  introductory  remarks  will  be  found  useful: 

1.  If  the  fuming  sulphuric  acid,  as  often  happens,  is  either 
wholly  or  partially  solid,  it  must  be  first  liquefied  in  order  that  an 
average  sample  may  be  obtained.  This  is  best  effected  by  very 
carefully  warming  the  flask  containing  the  acid  on  a  sand-bath,  or 
on  an  iron  plate  (warming  in  water  I  consider  far  more  dangerous). 
During  the  warming  the  stopper  should  be  only  loosely  fitted  on 
the  bottle.  When  the  acid  is  liquid,  and  is  uniformly  mixed  by 

*  Journ.  f.  prakt.  Chem.,  LXXI,  280. 

•f  POGGEND.  AnnaL,  cxm,  621 ;  Zeitschr.  /.  analyt.  Chem.,  I,  76. 


§   270.]  SULPHUR   COMPOUNDS.  707 

cautiously  shaking,  transfer  portions  of  it  (about  25  grm.)  by 
means  of  a  pipette,  to  two,  weighed,  light,  thin  weighing  flasks  with 
wide  necks,  immediately  stopper  the  flasks  with  their  light,  hollow 
stoppers,  which  must  be  well  fitted,  allow  to  cool,  if  necessary,  and 
weigh. 

Now  place  one  or  both  of  the  weighing  flasks,  according  as  the 
examination  is  to  be  single  or  in  duplicate,  into  a  beaker  of  about 
1  litre  capacity,  remove  the  glass  stoppers,  place  them  also  in  the 
beaker,  and  introduce  water  into  the  beaker  by  means  of  a  large 
pipette,  but  not  so  much  as  to  impair  the  steadiness  of  the  flasks 
containing  the  acid;  care  must  also  be  exercised  that  no  water 
comes  into  contact  with  the  sulphuric  acid.  Now  cover  the  beaker 
with  a  closely-fitting  glass  plate  moistened  on  the  inner  side  with 
water,  and  allow  to  stand  for  at  least  24  hours  in  order  to  give  the 
acid  time  to  absorb  water.  When  this  end  has  been  attained,  intro- 
duce more  water  into  the  beaker,  and  overturn  the  flasks  in  such  a 
manner  as  to  bring  the  acid  into  contact  with  the  entire  quantity 
of  water  at  once,  the  beaker  being  meanwhile  kept  well  covered. 

There  are  many  and  varied  opinions  held  as  to  the  best  manner 
of  effecting  the  solution  in  water,  and  it  is  often  desirable  to  more 
quickly  effect  the  solution  than  is  possible  by  the  method  above 
detailed.  Thus  FR.  BECKER  *  recommends  weighing  the  acid 
in  a  10-c.c.  platinum  crucible  provided  with  a  well-fitting  cover; 
the  crucible,  after  raising  the  cover,  is  sunk  with  its  contents  into  a 
beaker  containing  about  100  c.c.  water,  the  beaker  being  imme- 
diately covered.  CL.  WINKLER  f  advises  weighing  the  products 
rich  in  anhydride  in  a  glass-stoppered  flask  containing  accurately 
weighed  quantities  (10  to  15  c.c.)  of  concentrated  sulphuric  acid 
of  known  acidity,  and  then  allowing  the  acid  to  run  into  water, 
or  employing  the  tap-tube,  Fig.  128,  devised  by  him.!  The  cock 
on  the  tube  must  fit  tightly  without  the  need  of  grease,  and 
the  point  of  the  tube  must  be  uniformly  drawn  out.  Fill  the 

*  Chemiker-Zeitung,  iv,  600;  Zeitschr.  /.  analyt.  Chem.,  xx,  302. 
t  Chem.  Industr.,  1880,  No.  6;  Zeitschr.  f.  analyt.  Chem.,  xx,  302. 
J  LUNGE,  Taschenbuch  fur  Soda-,  etc.,  Fabrikation,  Berlin,  JUL.  SPRINGER, 
1883,  p.  120. 


708 


DETERMINATION   OF   COMMERCIAL   VALUES.         [§  270. 


lower  portion  one-half  or  two-thirds  full  by  means  of  a  suitable  suc- 
tion apparatus,  close  the  cock,  turn  the  tube  point  upwards,  clean 
the  outside  by  wiping  with  paper,  weigh  in  a  hori- 
zontal position,  then  place  the  tube,  point  down- 
wards, in  water,  or,  in  the  case  of  acids  very  rich  in 
anhydride,  in  a  layer  of  crystallized,  coarsely  broken, 
perfectly  neutral  sodium  sulphate,  and  allow  the 
contents  to  slowly  run  out.  Finally,  spirt  a  drop  of 
water  from  above  into  the  tap-tube,  allow  to  stand 
for  a  short  time,  and  then  rinse  out  the  tube.  LUNGE 
(loc.  cit.)  recommends  this  method  of  weighing  as  the 
most  convenient.  If  such  a  tap-tube  is  not  at  hand, 
the  weighing  may  be  done  in  a  bulb-tube  about  2 
cm.  diameter,  and  both  ends  of  which  terminate  in 
capillary  tubes.  Suck  up  3  to  5  grm.  of  the  acid  into 
the  bulb-tube,  which  should  not  be  quite  half-filled, 
clean  one  of  the  capillary  ends,  fuse  it,  weigh  in  a 
horizontal  position  (best  on  a  platinum  crucible 
having  notches  cut  in  its  edge),  and  then  empty  the 
contents,  by  breaking  off  the  point,  in  a  manner 
similar  to  that  used  in  emptying  the  tap-tube. 
FIG  128  Similar  glass  tubes  are  also  used  by  CLAR  and 

GAIER.*  For  weighing  off  the  anhydride  they  recom- 
mend a  glass  flask,  58  mm.  high  and  17  mm.  wide,  with  a  high, 
ground  stopper,  expanded  into  a  bulb  at  the  top,  and  having  at 
the  point  a  small  aperture  closed  by  a  small  glass  stopper.  The 
inside  of  the  stopper  is  filled  with  slightly  moistened  glass  wool. 
The  weighed  flask,  with  its  contents,  is  placed  upside  down  in  an 
obliquely  supported  flask  of  about  2  litres  capacity  and  containing 
about  500  c.c.  water  of  50°  to  60°.  After  mixing  has  been  effected 
through  the  small  aperture  in  the  stopper,  and  after  the  cooling 
and  absorption  of  the  vapors,  make  up  the  liquid  to  1  litre. 

Whichever  of  the  methods  detailed  has  been  employed,  all  the 
sulphuric  acid,  and,  if  any  sulphurous  acid  is  present,  also  a  part 

*  Chem.  Industr.,  iv,  251;  Zeitschr.  /.  analyt.  Chem.,  xxi,  441. 


§  270.]  SULPHUR   COMPOUNDS.  709 

of  the  latter  will  be  obtained  in  solution,  the  remainder  of  the 
sulphurous  having  been  volatilized  by  the  heat  engendered  in  the 
liquid.  Taking  first  the  simplest  case,  in  which  sulphurous  acid 
is  absent,  transfer  the  diluted  acid,  when  perfectly  cold,  to  a  meas- 
uring flask,  dilute  to  the  mark,  mix,  accurately  titrate  aliquot  por- 
tions with  normal  soda  solution  (p.  302  this  volume),  and  from  the 
soda  solution  used  calculate  its  equivalent  of  sulphuric  anhydride 
(SO3)  in  the  entire  liquid,  and  deduct  the  value  so  obtained  from 
the  fuming  acid  taken ;  the  difference  gives  the  water  of  hydration, 
and  from  this  the  quantity  of  monohydrate  may  be  ascertained. 
On  finally  deducting  the  weight  of  the  latter  from  that  of  the 
fuming  acid,  the  quantity  of  sulphuric  anhydride  present  therein 
as  such  is  ascertained. 

The  influence  exerted  by  any  sulphurous  acid  present  will  now 
be  considered. 

a.  If  the  whole  of  the  sulphurous  acid  has  remained  in  the  acid 
liquid,  calculate  from  the  soda-lye  used  the  quantity  of  sulphuric 
anhydride  equivalent  to  the  total  sulphuric  and  sulphurous  acids 
present.     On  deducting  this  total  acid  from  the  fuming  acid  taken, 
the  difference  will  be  a  number  which  will  be  too  low  to  represent 
water  of  hydration,  and  therefore  also  that  for  a  monohydrate,  and 
consequently  the  number  for  the  anhydride  will  be  too  high. 

If,  on  the  other  hand,  we  suppose: 

b.  That  the  sulphurous  acid  is  completely  volatilized  from  the 
acid  solution,  then  instead  of  the  water  of  hydration,  we  obtain 
this   together  with   the  sulphurous   acid.      The   monohydrate   in 
this  case  will  be  calculated  too  high,  and  the  anhydride  too  low. 

As  in  reality,  however,  by  the  methods  of  determination  above 
detailed,  a  part  of  the  sulphurous  acid  volatilizes,  the  result  obtained 
will  be  between  a  (too  high)  and  b  (too  low),  i.e.,  only  an  approxi- 
mately correct  result;  and  as  the  determination  of  the  sulphurous 
acid  is  considered  to  be  too  tedious,  the  analyst  usually  accepts  the 
results  so  obtained. 

If  greater  accuracy  is  required,  not  only  must  the  acidity  of  the 
acid  liquid  be  determined,  but  also  the  sulphurous  acid  in  a  separate 
portion,  which  may  be  done  according  to  Vol.  I,  p.  131,  with  iodine 


710  DETERMINATION    OF  COMMERCIAL   VALUES.          [§  271. 

solution,  or  with  potassium-permanganate  solution  standardized 
against  an  iron  solution  ( WINKLER  *) .  As  the  operations  are 
carried  out  with  very  dilute  solutions,  it  is  advisable  to  deduct  from 
the  titrating  fluid  used  the  quantity  of  starch  iodide  or  potassium 
permanganate  required  for  coloring  an  equal  volume  of  acidulated 
water. 

The  calculation  is  made  as  follows:  After  the  acidity  of  the 
acid  solution  and  its  content  of  sulphurous  acid  have  been  ascer- 
tained, calculate  the  latter  to  sulphuric  anhydride,  and  deduct  this 
from  the  equivalent  quantity  corresponding  to  the  soda  solution 
used.  On  now  subtracting  the  sum  of  the  sulphuric  anhydride 
and  of  the  sulphurous  acid  from  the  weight  of  the  fuming  acid,  we 
ascertain  the  water  of  hydration  present,  and  from  this  the  mono- 
hydrate  may  be  found.  On  finally  deducting  the  latter,  together 
with  the  sulphurous  acid,  from  the  fuming  acid  taken,  the  differ- 
ence will  give  the  content  of  sulphuric  anhydride. 

This  method,  however,  can  yield  accurate  results  only  when  the 
solution  of  the  fuming  acid  is  so  carefully  effected,  and  with  exclu- 
sion of  air,  that  the  whole  of  the  sulphurous  acid  present  in  the 
fuming  acid  is  also  retained  in  the  acid  solution. 

26.  NITROGEN  COMPOUNDS. 
§271. 

A.    NlTROSE. 

"Nitrose"  is  the  term  applied  to  the  acid  issuing  from  the  foot 
of  the  GAY-LUSSAC  towers  in  the  manufacture  of  sulphuric  acid. 
The  acid  consists  chiefly  of  a  solution  of  the  so-called  lead-chamber 
crystals  (nitrosulphonic  acid  or  nitrosyl-sulphonic  acid)  in  sulphuric 
acid  of  about  76  per  cent,  monohy drate ;  it  may,  however,  also 
be  regarded  as  a  solution  of  nitrous  acid  in  sulphuric  acid  of  the 
above-named  concentration.  Normal  nitrose  contains  no  nitric 
acid,  according  to  LUNGE .f  As  the  nitrous-acid  content  varies 
between  1  and  2-5  per  cent,  by  weight,  and  a  knowledge  of  this 

*  Zeitschr.  f.  analyt.  Chem.,  xx,  304. 

t  Berichte  der  deutsch.  chem.  Gesellsch.,  x,  1078. 


§  271.]  NITROGEN    COMPOUNDS.  711 

quantity  is  of  importance  in  operating  the  chamber  process,  the 
nitrose  is  often  the  subject  of  chemical  investigation. 

To  determine  the  nitrous-acid  content,  one  of  the  following 
methods  will  answer: 

1.  FELDHAUS'   method    (comp.   Vol.   I,  p.  433),   modified  by 
LUNGE,  *    requires  a  solution  of   potassium    permanganate    con- 
taining exactly  15-811  grm.  of  the  salt  per  litre.     1  c.c.  of  this 
solution  is  capable  of  yielding  0  •  004  grm.  oxygen  for  oxidizing  pur- 
poses, and  will  hence  convert  0-00951  grm.  N203  into  N2O5. 

To  carry  out  the  determination  heat  100  c.c.  water  to  40°,  or 
at  most  45°,  add  20  c.c.  of  the  permanganate  solution,  and  from  a 
burette  provided  with  a  glass  cock  run  in  the  nitrose  to  be  tested, 
very  gradually  and  with  constant  stirring  or  frequent  shaking, 
until  the  solution  just  becomes  colorless.  Since  20  c.c.  of  the 
permanganate  solution  correspond  with  0-1902  grm.  N2O3,  the 
quantity  of  nitrose  required  to  effect  the  decolorization  contained 
0-1902  grm.  In  the  case  of  very  strong  nitrose  it  is  better  to  take 
40  c.c.  of  the  permanganate  solution,  diluted  with  200  c.c.  of  water. 

It  is  evident  that  the  method  can  give  satisfactory  results  only 
when  other  substances  which  reduce  potassium  permanganate 
(arsenous  or  sulphurous  acid)  are  either  absent,  or  present  only 
in  traces.  LUNGE'S  modification  consists  in  adding  the  nitrose 
to  the  permanganate  solution  until  decolorization  ensues,  whereas 
FELDHAUS  adds  the  permanganate  solution  to  the  very  dilute 
nitrous-acid  solution. 

2.  WALTER  CRUM'S  method,  which  was  further  improved  by 
JOHN  WATTS,  and  recommended  by  DAVIS,  is  now  very  conve- 
niently carried  out  by  means  of  the  nitrometer  devised  by  LUNGE. f 
The  process  is  based  upon  the  fact  that  the  nitrogen  acids,  when 
dissolved  in  sulphuric  acid,  are  reduced  by  metallic  mercury  to 
nitric  oxide,  the  volume  of  which  serves  to  determine  their  quan- 

*  Berichte  der  deutsch.  chem.  Gesellsch.,  x,  1075. — LUNGE,  Taschenbuch 
fur  die  Sodafabrikation,  etc.,  Berlin,  JUL.  SPRINGER,  1883,  p.  114. 

t  LUNGE,  Handbuch  der  Sodaindustrie,  I,  59,  and  n,  ;  also  932  his  Taschen- 
buch  fur  die  Sodafabrikation,  etc.,  p.  116;  Berichte  der  deutsch.  chem.  Gesellsch., 
xi,  438;  Zeitschr.  f.  analyt.  Chem.,  xix,  207. 


712 


DETERMINATION   OF  COMMERCIAL   VALUES. 


[§  271. 


tity.  It  follows,  therefore,  that  the  method  will  give  the  correct 
content  of  nitrous  acid  only  when  no  other  oxygen  compound  of 
nitrogen  is  present;  and  that  when  both  nitrous  and  nitric  acids 
are  present,  the  nitrogen  of  both  is  obtained  as  nitric  oxide. 

The  LUNGE  nitrometer  is  shown  in  Fig.  129.    The  cylindrical 


FIG.  129. 

measuring-tube  a  has  a  capacity  of  50  c.c.,  and  is  graduated  in 
0-1  c.c.  The  stopper  of  the  glass  cock  has  two  holes  bored  in  it; 
one  straight,  affording  a  communication  between  the  funnel  and 
the  measuring  tube,  and  a  second,  bent  so  as  to  allow  the  contents 
of  the  funnel  to  flow  out  at  the  side.  The  latter  may,  however,  be 
also  turned  so  that  the  funnel  communicates  with  neither  hole.  In 
order  to  prevent  any  possibilit>  of  the  stopper  falling  out,  it  is 
fastened  to  the  constriction  of  the  funnel  with  fine  copper  wire ;  and 
to  render  it  air-tight,  it  is  smeared  with  a  little  petrolatum,  but  in 


§  271.]  NITROGEN  COMPOUNDS.  713 

such  a  manner  that  none  enters  the  holes  of  the  stopper,  b  is  a 
strong  glass  tube  of  approximately  the  same  diameter  and  capacity 
as  a.  Both  tubes  are  connected  by  a  thick-walled  rubber  tube. 
The  rest  of  the  details  may  be  gathered  from  the  illustration. 

In  operating  with  the  apparatus,  place  the  tube  b  so  that  its 
lower  end  is  somewhat  higher  than  the  stop-cock  on  a,  and,  the 
cock  being  open,  pour  mercury  into  b  until  it  ascends  into  a.  Then 
close  the  stop-cock,  allow  the  excess  of  mercury  to  run  out  through 
the  side  opening  in  the  cock,  and  lower  b;  then,  by  means  of  a  very 
fine  pipette,  introduce  a  measured  quantity  of  the  nitrose  (2  to 
5  c.c.  in  the  case  of  weaker  nitroses,  or  only  0-5  c.c.  if  very  strong) 
into  the  funnel,  allow  it  to  flow  into  a  by  cautiously  opening  the 
stop-cock,  and  so  that  no  air  may  be  carried  along  with  it,  and 
rinse  the  funnel  twice  with  concentrated,  pure  sulphuric  acid  in  a 
similar  manner,  using  2  to  3  c.c.  the  first  time,  and  1  to  2  c.c.  the 
second.  It  is  not  advisable  to  have,  altogether,  more  than  8  to  10 
c.c.  of  acid  in  the  apparatus,  and  it  is  better  to  operate  with  less. 
The  volume  of  nitric  oxide  must  in  no  case  exceed  50  c.c.,  and  the 
vacant  space  in  the  tube  a  below  the  graduation  must  be  great 
enough  to  prevent  any  acid  entering  the  rubber  tube,  even  when  50 
c.c.  of  nitric  oxide  are  evolved.  In  any  case,  for  the  reaction  to  be 
successful,  an  excess  of  strong  sulphuric  acid  must  be  present,  and, 
when  the  acid  being  analyzed  is  rich  in  nitrogen  acids,  quite  a  large 
quantity,  about  5  c.c.,  of  concentrated  sulphuric  acid  must  be  used 
for  rinsing,  as  otherwise  the .  unavoidable,  but  usually  harmless, 
separation  of  mercurous  sulphate  soils  the  measuring-tube  too 
much. 

Now  remove  the  tube  a  from  the  spring  clamp,  and  shake  it 
thoroughly.  The  evolution  of  gas  begins  at  once,  the  acid  acquiring 
a  violet  color.  (In  the  case  of  sulphuric  acid  containing  nitric  acid 
instead  of  nitrous  acid  as  in  the  case  of  nitrose,  the  evolution  of 
gas  begins  only  after  shaking  a  few  times.)  The  evolution  is 
facilitated  by  inclining  the  tube  several  times  to  a  nearly  horizontal 
position,  and  then  quickly  raising  it  to  a  vertical  position  so  that 
the  mercury  falls  through  the  acid.  As  soon  as  some  gas  has 
collected,  the  shaking  becomes  easy.  In  from  one  to  two  minutes 


714  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  271. 

(five  minutes  are  seldom  necessary)  the  reaction  is  complete.  When 
the  acid  has  become  clear  and  cool,  and  the  froth  has  disappeared, 
which  as  a  rule  does  not  take  long,  raise  the  tube  b  so  that  the  level 
of  mercury  in  it  will  be  so  much  higher  than  in  a  as  will  correspond 
with  the  sulphuric  acid  (1  mm.  height  of  mercury  is  equivalent 
to  7  mm.  of  sulphuric  acid),  read  off  the  volume  of  nitric  oxide, 
reduce  it  to  0°  and  760  mm.  pressure,  and  from  this  ascertain  the 
content  of  nitrous  acid  (or,  in  the  case  of  liquids  containing  nitric 
acid,  the  latter),  calculating  1-699  mgrm.  N2O3  (or  2-413  mgrm. 
N2O5)  for  each  c.c.  of  nitric  oxide  at  0°  and  760  mm.* 

When  the  reading  off  is  finished,  check  the  accuracy  of  the 
compensation  of  the  acid  layer  by  the  column  of  mercury,  by 
opening  the  stop-cock.  If  the  level  of  the  acid  rises,  the  pressure 
has  been  too  great,  and  hence  a  larger  volume  of  gas  should 
have  been  read  off;  if  the  level  falls,  the  pressure  was  too  low, 
and  the  volume  read  off  consequently  too  large.  If,  for  exam- 
ple, 15-3  c.c.  have  been  read  off,  and  the  acid  rises  to  15-2  c.c. 
when  the  stop-cock  is  opened,  it  follows  that  the  correct  volume  is 
15-3  +  0-1  =  15-4.  Now  raise  the  tube  b  so  as  to  drive  into  the 
funnel  first  the  nitric  oxide,  and  then  the  acid  rendered  turbid  by 
the  mercurous  oxide.  When  the  mercury  just  enters  the  funnel, 
close  the  stop-cock,  allow  the  acid  to  run  off  through  the  side-open- 
ing in  the  stopper  into  a  vessel  placed  to  receive  it,  remove  the  last 
traces  with  blotting  paper,  and  turn  the  cock  so  as  to  shut  off  the 
funnel  both  from  a  and  the  side  opening;  the  apparatus  is  now 
ready  for  a  fresh  analysis.  The  accuracy  of  the  result  is  not  affected 
by  any  arsenous  acid,  organic  acid,  etc.,  present  in  the  acid  to  be 
analyzed.  If  notable  quantities  of  sulphurous  acid  are  present, 
add  to  the  acid  in  the  funnel  of  the  nitrometer  a  little  powdered 
|  potassium  permanganate. 

*  LUNGE  has  calculated  special  tables  for  use  with  the  nitrometer,  both 
for  reducing  the  gas  volume  to  normal  temperature  and  pressure,  as  also 
for  calculating  the  nitric  oxide  so  reduced,  into  oxygen  compounds  of  nitro- 
gen. See  DINGLER'S  Polyt.  Journ.,  ccxxxi,  522,  and  LUNGE'S  Handb.  der 
Sodaindustrie,  n,  922-932. 


§  271.]  NITROGEN    COMPOUNDS.  715 

B.  CHAMBER  ACID,  ETC. 

Under  this  heading  are  discussed  the  products  containing  nitrous 
and  nitric  acids  resulting  from  the  manufacture  of  sulphuric  acid, 
as  is  the  case,  for  example,  with  chamber  acid.  Liquids  containing 
nitrogen  tetroxide,  N204,  may  also  be  regarded  as  if  consisting  of 
1  eq.  of  nitrous  anhydride  and  1  eq.  of  nitric  anhydride  (N2O3+ 
N205  =  2NA). 

The  determination  of  the  nitrogen  acids  in  nitrous  acid  in  sul- 
phuric acid  containing  nitrous  and  nitric  acids,  always  requires  two 
separate  analyses,  one  for  determining  the  nitrous-acid  content, 
the  other  for  determining  the  sum  of  both  acids,  expressed  either  as 
nitrous  acid  or  as  nitric  acid. 

1.  Determination  of  the  Nitrous  Acid. 

The  method  employed  is  simply  that  described  in  §  271,  A,  1. 
If  the  acid  contains  other  substances  which  reduce  potassium  per- 
manganate (e.g.,  arsenous  acid,  sulphurous  acid,  etc.),  the  deter- 
mination will  of  course  be  exact  only  when  these  are  separately 
determined  and  the  corresponding  corrections  made.  This  cir- 
cumstance must  be  considered,  of  course,  not  only  when  determin- 
ing nitrous  acid  with  permanganate,  but  also  to  an  equal  extent  in 
all  methods  based  upon  the  conversion  of  nitrous  acid  into  nitric 
acid  (chromic-acid  method,  chlorinated-lime  method).* 

2.  Determination  of  the  Nitrous  and  Nitric  Acids. 

This  is  most  simply  accomplished  according  to  the  method 
detailed  in  §  271,  A,  2,  using  the  LUNGE  nitrometer.  It  may  also 
be  effected  in  nearly  all  the  ways  recommended  in  §  149,  and  par- 
ticularly according  to  §  149,  d,  a,  or  /?  (Vol.  I,  pp.  575  and  577),  or 
§  149,  e  (Vol.  I,  p.  584).  In  using  PELOUZE'S  method,  §  149,  d,  a, 
LUNGE  f  employs  ferrous  sulphate  instead  of  the  ferrous  chloride, 
and  in  the  following  manner: 

An  iron  solution  is  used  containing  100  grm.  of  pure  ferrous 
sulphate  and  50  grm.  of  pure,  concentrated  sulphuric  acid  per 

*  See  LUNGE,  Handbuch  der  Soda-industrie,  i,  58  and  59. 
t  Ibid.,  FR.  VIEWEG  und  SOHN,  i,  pp.  49-51. 


716 


DETERMINATION    OF    COMMERCIAL   VALUES. 


[§  271. 


litre;  and  for  titrating,  a  solution  of  potassium  permanganate 
containing  15-811  grin,  per  litre,  the  strength  of  which  is  to  be 
checked  as  in  Vol.- 1,  p.  313,  a,  a.  The  first  step  is  to  ascertain 

how  much  of  the  permanganate  solution 
is  required  to  oxidize  25  c.c.  of  the 
ferrous-sulphate  solution.  Then  intro- 
duce 25  c.c.  of  the  latter  solution  into 
a  flask  (Fig.  130)  provided  with  a  glass 
tube  and  a  BUN  SEN  rubber  valve,*  and 
add  the  solution  obtained  from  the  de- 
termination of  the  nitrous  acid  in 
§  271,  B,  1  (and  now  containing  all 
the  nitrogen  combined  with  oxygen  in 
the  form  of  nitric  acid),  together  with 
FIG.  130.  a  further  and  not  too  small  quantity 

of  pure  sulphuric  acid;  now  add  1  to  2  grm.  sodium  bicar- 
bonate in  order  to  drive  out  the  air  by  the  carbon  dioxide 
evolved.  After  quickly  inserting  the  stopper  carrying  the  rubber 
valve,  heat  to  boiling,  which  continue  for  some  time  (often  for  an 
hour),  until  all  the  nitric  oxide  has  been  expelled,  and  the  liquid 
has  in  consequence  become  lighter  in  color.  Now  cool,  dilute, 
and  titrate  again  with  the  permanganate  solution.  From  the 
difference  between  the  quantity  used  up  now  and  that  required 
in  the  previous  titration,  calculate  the  quantity  of  nitric  acid 
(1  c.c.  of  the  permanganate  of  the  above  strength  corresponds  to 
0.009  grm.  N2O5). 

So  far  as  the  calculation  is  concerned,  the  following  must  be 
considered:  If  both  the  nitrogen  acids  have  been  determined  as 
nitric  acid,  as  in  LUNGE'S  modification  of  PELOUZE'S  method,  just 
described,  or  in  any  of  the  other  methods  in  which  the  nitrogen 
of  the  nitrogen  acids  is  converted  into  ammonia  or  nitric  oxide, 


*  This  may  be  simply  made  from  a  piece  of  thick  rubber  tubing  closed  at 
the  top  by  a  small  piece  of  glass  rod,  and  with  a  long  slit  in  the  side.  The 
cut  is  made  by  bending  the  tube  over  the  index  finger  of  the  left  hand,  and 
making  an  incision  10  to  15  mm.  long  with  a  sharp  razor  moistened  with 
water.  See  also  KRONIG  (Zeitschr.  /.  analyt.  Chem.,  iv,  95). 


§  272.]         .  CARBON    COMPOUNDS.  717 

from  which  in  turn  the  nitric  acid  is  calculated,  then  the  quantity 
of  nitrous  acid  found  as  in  1  is  increased  in  the  proportion  of 
76-08: 108:08  (or  9-51: 13-51),  i.e.,  it  is  calculated  into  nitric  acid; 
the  weight  of  this  deducted  from  the  total  nitric  acid  found  gives, 
as  a  difference,  the  nitric  acid  originally  present  as  such ;  if,  however, 
one  of  the  methods  has  been  employed  based  upon  the  oxidation 
of  iron  with  a  separate  sample  of  the  unaltered  acid,  then  the  cal- 
culation is  most  simply  made  by  considering  the  oxidation  as 
if  effected  by  nitrous  acid,  i.e.,  for  every  111-8  parts  of  iron 
(2  at.)  converted  from  ferrous  into  ferric  iron,  calculate  76-08 
parts  of  N2O3  (1  mol.),  and  deduct  from  the  nitrous  acid  so  found 
the  quantity  found  in  1 ;  and,  in  order  to  ascertain  the  content  of 
nitric  acid,  reduce  the  difference  in  the  proportion  of  228  •  24 : 108  •  08, 
i.e.,  in  the  proportion  of  3  eq.  of  N2O3  to  1  eq.  of  N2O5,  since  3  eq. 
of  N203  yield  as  much  oxidizing  oxygen  as  1  eq.  of  N2O5. 

27.  CARBON  COMPOUNDS. 
§272. 

Under  this  heading  the  analysis  of  graphite,  coal,  and  coke  is 
detailed. 

A.  GRAPHITE. 

Natural  graphite,  which  is  used  for  many  purposes,  particu- 
larly for  the  manufacture  of  graphite  crucibles  and  pencils,  is 
found  in  very  different  grades  of  purity,  and  is  hence  not  infre- 
quently the  subject  of  chemical  analysis.  This  alone  does. not, 
however,  give  the  value  of  the  various  sorts  of  graphites,  as  the 
carbon  present  is,  according  to  its  degree  of  fineness,  more  or  less 
adapted  for  the  manufacture  of  lead  pencils,  and  also  exhibits 
very  great  differences  in  degree  of  combustibility,  which  is  of  im- 
portance in  the  manufacture  of  crucibles.  It  is  hence  necessary 
to  supplement  the  chemical  analysis  by  a  practical  examination 
based  upon  the  purposes  for  which  the  graphite  is  to  be  used. 

I.    METHOD  FOR  COMPLETE  AND  ACCURATE  ANALYSES. 

1.  To  determine  the  moisture  dry  a  sample  at  about  150°. 
If  the  drying  is  effected  in  a  bulb-tube  (Vol.  I,  p.  64),  the  same 


718  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  272. 

portion  of  substance  can  also  be  used  for  determining  the  water 
chemically  combined  (and  partly  present  in  the  clay).  For  this 
purpose  heat  the  contents  of  the  bulb-tube  in  a  current  of  dry 
air  to  low  redness,  and  collect  the  water  in  a  calcium-chloride  tube 
(Vol.  I,  p.  76). 

2.  The  carbon  in  the  graphite  may  be  most  surely  (as  the 
method  may  be  used  for  all  kinds  of  graphite)  oxidized  to  carbon 
dioxide  by  means  of  chromic  acid  and  sulphuric  acid,  and  the  CO2  col- 
lected in  weighed  soda-lime  tubes.     The  operation  is  carried  out  in 
one  of  the  forms  of  apparatus  shown  on  pp.  510  to  514  this  volume, 
and  by  the  method  given  on  p.  513,  i.e.,  using  a  sulphuric  acid 
obtained   by  mixing  2  parts   by  weight    concentrated   sulphuric 
acid  and  1  part  by  weight  of  water,  and  an  excess  of  chromic  acid 
(about  5  to  10  grm.  chromic  acid  to  about  0-25  grm.  to  0-5  grm. 
graphite). 

In  many  kinds  of  graphite  the  carbon  may  also  be  determined 
by  heating  in  a  current  of  oxygen,  as  in  the  ordinary  combustion 
(p.  39  et  seq.,  this  volume).  Before  this  method  can  be  adopted 
with  safety,  however,  a  preliminary  test  must  be  made  in  order  to 
make  certain  whether  the  carbon  in  the  graphite  in  question  will 
be  completely  consumed  under  the  conditions  prevailing  in  ordinary 
combustion.  If  the  graphite  contains  carbonates,  e.g.,  calcium 
carbonate,  the  carbonic  acid  must  be  determined  and  deducted 
from  the  total  obtained  by  the  oxidation  with  chromic  and  sul- 
phuric acids,  or  by  combustion,  before  calculating  the  carbon  of 
the  graphite  from  the  carbon  dioxide  obtained. 

3.  The  total  mineral  constituents   of   a   graphite  is  indirectly 
found  by  deducting  from  100  the  carbon,  moisture,  and  chemically 
combined  water,  expressed  in  per  cents.     If  a  direct  determination 
is  required,  it  suffices,  for  many  kinds  of  graphite,  to  place  a  small 
quantity  (about  0-5  grm.)  of  the  finely  powdered  substance  in  a 
platinum  crucible,  and  expose  it,  with  free  access  of  air,  to  the 
long-continued  and  strong  heat  of  a  BUNSEN  or  MASTE  gas  burner 
(see  Vol.  I,  p.  116,  Fig.  77).     F.  STOLBA*  recommends  a  platinum 

*  DINGLER'S  polyt.  Journ.,  cxcvni,  213;  Zeitschr.  /.  analyt.  Chem.,  x,  369. 


§  272.]  CARBON  COMPOUNDS.  719 

crucible  provided  with  a  projecting  perforated  lid,  the  round  hole 
in  which  is  5  mm.  in  diameter.  The  crucible  is  fixed  in  an  inclined 
position,  and  the  cover  is  so  placed  on  that  about  one-quarter  of 
the  opening  is  left  uncovered.  The  combustion  of  the  carbon  is 
facilitated  by  exposing  a  fresh  surface  of  the  graphite  by  turning 
the  crucible  round  occasionally,  or  stirring  the  contents  with  a 
platinum  wire.  As  the  operation  requires  from  3  to  4  hours  for 
its  completion,  and  as  the  weight  of  the  platinum  crucible  may  be 
affected  by  so  prolonged  a  heating,  the  crucible  must  be  weighed 
again.  If  a  muffle  is  available,  the  combustion  of  the  carbon  may 
also  be  accomplished  in  a  platinum  dish  placed  in  the  muffle  heated 
to  redness.  This  method,  which  permits  of  the  incineration  of 
large  quantities  of  graphite,  is  particularly  to  be  recommended 
when  the  ash  is  to  be  further  analyzed. 

If  the  graphite  contains  calcium  carbonate,  the  carbonic  acid 
is  naturally  expelled  during  the  ignition;  in  order  to  replace  it, 
the  ash  must  be  repeatedly  moistened  with  a  concentrated  solu- 
tion of  ammonium  carbonate,  dried,  and  gently  ignited.  A  com- 
plete agreement  between  the  quantity  of  the  mineral  constituents 
directly  determined  and  that  directly  found  can  not  always  be 
expected  even  after  the  treatment  with  ammonium  carbonate,  e.g., 
when  the  graphite  contains  iron  sulphide  or  ferric  hydroxide. 
J.  STIXGL*  has  called  attention  to  this  circumstance,  and  has 
given  examples. 

STOLE  A  (loc.  cit.)  failed  to  obtain  favorable  results  in  his  attempts 
to  burn  graphite  in  a  current  of  oxygen,  because  some  of  the  min- 
eral constituents  were  carried  off  by  the  current  of  gas,  and  during 
the  fusion  there  were  also  formed  small  globules  which  enveloped 
particles  of  graphite.  As  a  check  to  make  certain  that  the  graphite 
ash  no  longer  contains  carbon,  a  weighed  portion  of  the  finely 
powdered  ash  may  be  mixed  with  pure  mercuric  oxide  and  ignited 
under  a  good  draught  hood,  and  again  weighed;  carbon-free  ash 
should  suffer  no  loss  of  weight.  The  most  certain  test,  however, 
that  the  ash  is  free  from  carbon,  consists  in  treating  a  sample  of  the 

*  Berichte  der  deutsch.  chem.  Gesellsch.  zu  Berlin,  vi,  391 ;  Zeitschr.  /. 
analyt.  Chem.,  xiv,  397. 


720  DETERMINATION   OF   COMMERCIAL   VALUES.         [§  272. 

ash  with  chromic  and  sulphuric  acids  according  to  2,  and  observing 
whether  carbon  dioxide  is  obtained  or  not. 

4.  To  determine  the  individual  mineral  constituents,  so  far  as  the 
silicic  acid,  aluminium,  iron,  etc.,  are  concerned,  the  ash  obtained 
in  3  may  be  employed,  and  treated  according  to  the  method  de- 
tailed for  silica  (Vol.  I,  p.  511,  b),  or  the  graphite  itself  may  be 
decomposed  by  some  method.     WITTSTEIN  *  recommends  for  this 
purpose  the  following  method:   Mix  about  1  grm.  of  the  finely 
powdered  graphite  with  about  3  grm.  sodium-potassium  carbonate 
in  a  platinum  crucible,  place  upon  the  surface  of  the  mixture  about 
1  grm.  potassium  hydroxide,  and  slowly  heat  to  redness.     From 
time  to  time  break  the  crust  formed  during  the  fusion  with  a  stout 
platinum  wire.     After  half  an  hour's  fusion,  allow  to  cool,  macerate 
the  mass  with  water,  heat  for  fifteen  minutes  to  boiling,  filter,  and 
wash  the  residue.     Treat  the  contents  of  the  filter  together  with 
the  filter  ash  with  hydrochloric  acid  of  sp.  gr.  1  •  12,  and  after  digest- 
ing for  half  an  hour,  add  water,  filter  off  from  the  insoluble  residue 
of  carbon,  unite  the  hydrochloric-acid  solution  so  obtained  with  the 
alkaline  liquid  first  obtained,  and  add  hydrochloric  acid  in  excess; 
then  evaporate  to  dryness  on  a  water-bath,  separate  the  silicic  acid, 
and  in  the  hydrochloric-acid  filtrate  determine  the  bases  (Vol.  I, 
pp.  509  and  510).     In  order  to  make  certain  that  the  carbon  filtered 
off  contains  no  mineral  constituents,  it  is  burnt.     It  is  of  no  use  to 
weigh  this  carbon,  as  it  does  not  represent  the  entire  quantity  of 
carbon  present,  but  only  about  four-fifths. 

5.  If  the  graphite  contains  carbonates,  determine  the  carbonic 
acid  in  a  separate,  somewhat  larger,  sample,  according  to  Vol.  I, 
p.  493. 

6.  If  metallic  sulphides  (iron  or  copper  pyrites)  are  present, 
determine  the  sulphur  in  a  sample  according   to  pp.  561,   1,  or 
562,  2,  this  volume.      It  must  not  be  considered  strange  if,  when 
using  the  first  method,  the  carbon  of  the  graphite  remains  partly 
or  wholly  unoxidized,  since  many  kinds  of  graphite  are  not  at- 
tacked by  fused  potassium  nitrate  (RAMMELSBERG  f) . 

*  DINGLER'S  polyt.  Journ.,  ccxvi,  45;  Zeitschr.  /.  analyt.  Chem.,  xiv,  395. 
t  His  Handbuch  der  Miner 'alchemic,  2  ed.,  Leipzig,  W.  ENGELMANN,  n,  2. 


§  272.]  CARBON   COMPOUNDS.  721 

II.   METHODS   OF   DETERMINING   THE   CARBON   ONLY. 

Of  the  methods  proposed  for  the  rapid  determination  of  carbon 
in  graphite,  that  of  GINTL  *  alone  will  be  here  described.  In  this 
process  there  is  required  a  stout  tube  of  refractory  glass,  10  to  12 
cm.  long,  about  1  cm.  wide,  and  sealed  at  one  end,  and  which  may 
be  advantageously  blown  out  to  a  moderately  sized  bulb.  Into  this 
introduce  0-05  to  0-1  grm.  of  the  graphite  dried  at  150°  to  180°, 
add  1  •  5  to  3  grm.  of  pure,  powdered  lead  oxide,  previously  ignited, 
weigh,  and  carefully  mix  the  lead  oxide  with  the  graphite  by  means 
of  a  mixing-wire;  then  heat  that  part  of  the  tube  containing  the 
mixture,  at  first  over  a  BUNSEN  burner,  and  finally  with  a  blowpipe- 
lamp  until  the  contents  are  completely  fused  and  froth  is  no  longer 
visible.  According  to  GINTL  the  operation  is  complete  in  ten  min- 
utes. Allow  to  cool,  weigh,  and  from  the  loss  in  weight  (the  carbon 
dioxide  expelled)  calculate  the  carbon.  Of  course  the  results  ob- 
tained by  this  method  are  serviceable  only  when  the  graphite  con- 
tains neither  water  chemically  combined  or  capable  of  expulsion  at 
150°  to  180°,  nor  carbonates,  and  when  all  the  carbon  is  oxidized 
by  fusion  with  the  lead  oxide. 

GINTL' s  method  is  a  modification  of  that  devised  by  SCHWARZ,! 
in  which  the  lead  which  separates  on  fusing  graphite  with  an  excess 
of  litharge  is  weighed  (also  of  BERTHIER'S  method  of  determining 
the  calorific  value  of  combustibles  applied  to  graphite).  GINTL 
(loc.  cit.,  p.  423)  did  not  obtain  satisfactory  results  with  this 
method. 


Regarding  the  pyrometric  determination  of  pure  graphite,  as 
well  as  of  that  containing  clay  and  silicic  acid,  consult  BISCHOF'S}: 
paper. 

B.  COAL  AND  COKE. 

Coal,  being  one  of  the  most  important  industrial  factors,  is  fre- 
quently the  subject  of  chemical  analysis,  both  in  its  unchanged 

*  Zeitschr.  /.  analyt.  Chem.,  vn,  425. 

f  Breslauer  Gewerbeblatt,  1863,  No.  18;  Zeitschr.  /.  analyt.  Chem.,  in,  215. 

J  DINGLER'S  polyt.  Journ.,  cciv,  139. 


722  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  272. 

state  and  as  coke,  as  it  varies  greatly  in  character,  and  its  value  and 
applicability  for  various  uses  cannot  be  sufficiently  determined  by 
its  external  characteristics.  If,  however,  such  an  examination  is  to 
be  of  any  value,  it  is  absolutely  necessary  to  obtain  samples  which 
will  truly  represent  the  average  composition  of  the  coal  or  coke. 
This  requires  that  a  relatively  large  quantity  must  be  coarsely 
ground  and  uniformly  mixed.  By  further  comminuting  a  portion 
of  this  mixture,  samples  consisting  of  fragments  about  the  size  of 
a  bean  (or  for  coke,  of  a  hazel  nut)  are  obtained,  and  these  are  to 
be  preserved  in  glass-stoppered  bottles. 

1.    DETERMINATION  OF  WATER. 

Coal,  when  heated  to  a  high  temperature,  first  yields  water, 
and  later  other  volatile  constituents;  many  kinds  are  also  prone 
to  absorb  oxygen  at  higher  temperatures.  As,  however,  dried  coal 
is  besides  prone  to  abstract  moisture  from  the  atmosphere,  an 
accurate  determination  of  the  water  content  is  not  at  all  easy. 
As  a  rule  it  is  considered  sufficient  to  determine  the  water  from  the 
loss  in  drying,  although  BRITTON  *  has  pointed  out  that  the  results 
afforded  by  this  method  are  doubtful,  not  only  because  of  the 
reasons  above  mentioned,  but  also  because  the  water  present  in 
the  coal  is  more  or  less  combined  and  firmly  retained. 

To  determine  the  water  in  coal  from  the  loss  in  weight,  the  tin 
boxes  described  on  p.  633,  Fig.  126,  this  volume,  are  adapted,  a  few 
of  these  being  half-filled  with  the  coal  reduced  to  the  size  of  a 
bean.  The  boxes  are  then  weighed  together  and  dried  at  100° 
in  the  water-bath  as  described  on  p.  633  this  volume,  and  weighed 
hourly  until  they  cease  to  lose  weight. 

100°  is  the  temperature  recommended  as  most  suitable  by 
MucK,t  whereas  LUNGE  J  recommends  105°  and  HINRICHS  §  115°. 

*  Engineering  and  Mining  Journal,  xxn,  No.  7;  Zeitschr.  f.  analyt.  Chem., 
xvi,  501. 

f  POST'S  Chem.-Techn.  Analyse,  Brunswick,  FR.  VIEWEG  u.  SOHN,  1881 , 
p.  16. 

J  His  Taschenbuch  fur  die  Soda-,  etc.;  -Fabrikation,  Berlin,  J.  SPRINGER, 
p.  82. 

§  Zeitschr.  f.  analyt.  Chem.,  vin,  133. 


§  272.J          CARBON  COMPOUNDS.  723 

To  directly  determine  the  water  in  coal,  a  current  of  dry  air 
must  be  passed  over  the  coal  heated  in  a  glass  tube  in  an  air-bath, 
and  then  passed  through  a  weighed  calcium-chloride  tube;  the 
water-content  is  then  ascertained  from  the  increase  in  weight  of 
the  latter.  In  this  method  the  temperature  may  be  raised  con- 
siderably above  100°,  but  it  should  never  be  allowed  to  reach  a 
point  at  which  other  permanently  gaseous  decomposition  products 
are  evolved. 

The  water-content  of  coke  may  with  certainty  be  determined 
from  the  loss  in  weight  on  drying.  MUCK  (loc.  tit.)  recommends 
drying  at  a  temperature  which  may  approach  200°,  while  LUNGE, 
(loc.  cit.)  advises  110°.  In  the  case  of  coke  there  is  of  course  no 
danger  of  volatile  decomposition  products  being  formed  and  passing 
off  with  the  water  during  drying. 

2.    DETERMINATION    OF    THE    ASH. 

The  determination  of  the  mineral  constituents  of  coal  and  coke 
is  an  operation  which  is  very  frequently  performed.  Before  des- 
cribing the  best  methods  of  incineration,  attention  must  be  called 
to  the  fact  that  the  yield  of  ash  in  one  and  the  same  powdered 
coal  may  vary  greatly,  since  the  mineral  constituents  present  may 
be  left  in  varying  states  of  combination  according  to  the  tem- 
perature, duration  of  the  heating,  and  admission  of  air.  This 
may  be  especially  the  case  with  coal  rich  in  sulphur,  in  which 
the  calcium  carbonate  is  converted  into  calcium  sulphate,  the  iron 
sulphide  more  or  less  completely  into  ferric  oxide,  etc.  According 
to  MUCK,*  however,  the  differences  arising  from  this  cause  do  not 
exceed  0-1  to  0-2  per  cent. 

When  incinerating,  the  caking  of  the  coal  must  above  all  be 
prevented,  as  the  caking  renders  complete  combustion  of  the 
carbon  much  more  difficult.  When  the  incineration  is  effected 
over  the  gas  lamp,  therefore,  place  from  1  grm.  to  3  grm.  of  the 
very  finely  powdered  coal  dried  at  100°  in  a  covered  platinum 
crucible,  or  in  a  covered  platinum  dish,  and  subject  it  at  first  to 
a  gentle  heat  for  a  long  time,  whereby  not  only  decrepitation,  with 

*  Zeitschr.  f.  analyt.  Chem.,  xix,  137. 


724  DETEKMINATION   OF   COMMERCIAL   VALUES.  [§  272. 

its  possible  attendant  slight  loss,  but  also  the  subsequent  caking 
of  the  coal,  are  avoided;  then  heat  to  low  redness  with  access  of 
air  for  a  prolonged  period,  until  all  the  carbon  appears  to  be  con- 
sumed. In  order  to  shorten  this  otherwise  tedious  operation, 
LUNGE  *  recommends  placing  the  platinum  crucible  in  the  round 
opening  of  an  inclined  clay  tile  or  asbestos  disk,  and  to  heat  that 
part  of  the  crucible  projecting  below.  The  air  required  for  oxida- 
tion does  not  then  mix  with  the  gases  from  the  flame,  and  hence  acts 
more  energetically.  Now  add  to  the  apparently  pure  ash  a  little 
alcohol,  when  the  unconsumed  particles  of  carbon  will  be  readily 
recognized  by  their  color  as  well  as  by  their  buoyancy  in  the  liquid 
(MucK,  loc.  cit.,  p.  133).  After  burning  off  the  alcohol,  ignite 
again,  and  until  the  object  is  fully  attained,  and  finally  check  the 
weight  of  the  platinum  vessel. 

If  a  muffle  is  at  hand,  a  number  of  samples  may  be  incinerated 
at  the  same  time.  They  are  placed  in  the  cold  muffle  in  shallow 
platinum  or  porcelain  dishes,  but  most  conveniently  in  square 
platinum  trays,  and  then  slowly  warmed,  gradually  raising  the 
temperature  to  and  maintaining  it  at  redness. 

Coke  requires  a  much  higher  heat  for  the  complete  combustion 
of  its  carbon.  For  its  incineration,  therefore,  it  is  best  to  use  the 
muffle;  the  object  may,  however,  also  be  attained  by  heating  the 
sample  in  a  boat  in  a  current  of  oxygen. 

3.  DETERMINATION  OF  THE  SULPHUR. 

Coal  may  contain  sulphur  in  three  different  forms  of  com- 
bination; namely,  as  metallic  sulphides,  as  sulphates,  and  in  the 
organic  matter  of  the  coal.  The  method  of  determining  sulphur 
must  hence  be  differentiated  into  such  as  give  the  total  sulphur 
present,  and  such  as  give  the  sulphur  present  only  in  certain  forms 
of  combination. 

a.  Determination  of  the  Total  Sulphur. — For  this  purpose 
ESCHKA'S  method,  described  on  p.  115  this  volume,  is  especially 
well  adapted.  MucKf  recommends  to  ignite  with  magnesia  and 

*  His  Taschenbuch  fur  Soda-,  etc.,  Fabrikation,  p.  83. 
t  POST'S  Chem.-Techn.  Analyse,  Brunswick,  FR.  VIEWEG  u.  SOHN,  1881, 
p.  21. 


§  272.]  CARBON  COMPOUNDS.  725 

sodium  carbonate,  then  to  treat  the  mass  with  hot  water,  and  to 
add  bromine  water  until  the  liquid  has  a  faint  yellowish  color. 
Then  boil,  decant  through  a  niter,  wash  with  hot  water,  acidulate 
the  filtrate  with  hydrochloric  acid,  boil  until  the  liquid  is  decolor- 
ized, and  finally  precipitate  the  sulphuric  acid  (and  corresponding 
to  the  total  sulphur  in  the  coal)  with  barium  chloride. 

If  the  reagents  employed  are  not  quite  free  from  sulphuric  acid, 
their  acid-content  must  be  ascertained  and  deducted  from  the 
result. 

6.  Determination  of  the  Sulphur  Combined  with  Metals  and  that 
Contained  in  Organic  Combination. — These  quantities  of  sulphur 
may  be  determined  either  indirectly,  by  deducting  that  found 
as  sulphates  in  c  from  the  total  sulphur  found  in  a;  or  directly , 
according  to  one  of  the  methods  described  on  p.  100,  5,  this  volume. 
According  to  TSCHIRIKOW,*  it  is  advisable,  when  employing 
SAUER'S  method,  to  insert  plugs  of  platinum  gauze  both  hi  the 
fore  part  of  the  combustion  tube,  as  well  as  behind  the  platinum 
boat,  particularly  when  determining  sulphur  in  coal  rich  in  volatile 
substances.  This  ensures  complete  combustion,  and  hence  pre- 
vents the  passing  over  of  organic  decomposition  products  into  the 
receiver. 

c.  Determination    of   the   Sulphur   Present   as   Sulphates    (and 
Particularly  as  Gypsum). — For  this  purpose  the  GRACE  CALVERT 
method  is  employed  (see  p.  116  this  volume). 

d.  Determination  of   the   Total  Sulphur  Present  as   Sulphides 
and  Sulphates. — In   order  to    effect  this    determination,  and  to 
thus  obtain  also  the  organically  combined  sulphur  by  difference, 
the  following  method    may,  according    to  TH.  M.  DROWN,!  be 
employed  (but  of  which  I  have  had  no  personal  knowledge): 
There  is  required  for  it  a  saturated  solution  of  bromine  in  soda 
lye  of  1-25  sp.  gr.,  and  to  which  sodium  hydroxide  is  then  added 
until  it  no  longer  gives  off  free  bromine.    Moisten  about  1  grm.  of 
the  very  finely  powdered  coal  with  about  10  c.c.  of  this  liquid,  heat, 
and  add  hydrochloric  acid  just  to  acidity.    At  intervals  of  ten 

*  Pharm.  Zeit.  fur  Russland,  xix,  333;  Zeitschr.  /.  analyt.  Ghent.,  xx,  304. 
f  Ghent.  News,  XLIII,  89;  Zeitschr.  f.  analyt.  Chem.,  xxi,  440. 


726  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  272. 

minutes,  and  while  the  liquid  is  kept  hot,  add  two  portions  of 
20  c.c.  each  of  the  bromine  solution,  acidulating  after  each  addi- 
tion. Now  evaporate  to  dryness,  heat  to  from  110°  to  115°  to 
separate  the  silicic  acid,  heat  with  hydrochloric  acid,  dilute,  and 
precipitate  the  sulphuric  acid  with  barium  chloride.  By  this  mode 
of  treatment  the  organically  combined  sulphur  is  not  attacked. 
I  would  point  out,  however,  that  should  the  barium  sulphate 
have  a  reddish  tint,  i.e.,  contain  iron,  it  must  be  purified  accord- 
ing to  Vol.  I,  p.  435,  by  fusing  with  sodium  carbonate,  etc. 

4.    DETERMINATION    OF   THE    PHOSPHORUS. 

This  is  best  effected  in  the  ash.  Hence  incinerate  a  suitable 
quantity  of  coal,  digest  the  ash  for  a  considerable  time  with 
strong  hydrochloric  acid  on  the  water-bath,  and  evaporate  to  dry- 
ness;  then  add  first  hydrochloric  acid,  then  some  water,  warm, 
filter,  evaporate  with  repeated  additions  of  nitric  acid  almost  to 
dryness,  take  up  with  water  with  a  little  nitric  acid  added,  pre- 
cipitate with  molybdenum  solution,  and  determine  the  phosphorus 
according  to  §  134,  6,  /?. 

5.    DETERMINATION     OF    THE    NITROGEN. 

This  is  effected  according  to  one  of  the  methods  detailed  on 
pp.  82  to  94  this  volume,  using  coal  dried  at  100°. 

6.    DETERMINATION  OF  THE   CARBON,    HYDROGEN,    AND  OXYGEN. 

For  this  purpose  the  coal  dried  at  100°  may  be  burned  with  lead 
chromate  (p.  95  this  volume)  or  in  boats,  using  a  current  of  oxygen 
(p.  39  this  volume).  If  the  latter  method  is  adopted,  introduce 
into  the  fore  part  of  the  combustion  tube  a  10-cm.  layer  of  lead 
chromate  (or,  according  to  MUCK,  of  pea-sized  pieces  of  pumice- 
stone  which  have  been  thoroughly  mixed  with  powdered  lead 
chromate,  and  which  are  of  course  perfectly  free  from  water),  so 
that  the  combustion  products  first  pass  .over  the  glowing  granu- 
lated cupric  oxide,  then  over  the  lead  chromate,  which  is  to  be 
maintained  at  a  low  red  heat.  This  suffices  as  a  rule  to  retain  all 
the  sulphurous  acid ;  otherwise,  in  the  case  of  coal  very  rich  in  sul- 


§  722.]          CARBON  COMPOUNDS.  727 

phur,  a  lead-dioxide  tube  would  also  have  to  be  used  (p.  95  this 
volume). 

Before  the  carbon  and  hydrogen  can  be  calculated  from  the 
carbon  dioxide  and  water  obtained  by  the  ultimate  analysis,  it 
must  be  ascertained  whether  the  coal  or  coke  contains  any  car- 
bonates, and  whether  the  coal  dried  at  100°  contains  any  water. 
In  such  a  case  the  quantities  of  carbon  dioxide  and  water  found  in 
the  sample  on  combustion  (and  which  must  be  determined  in  sepa- 
rate portions)  must  be  deducted  from  those  obtained  in  the  ultimate 
analysis. 

The  oxygen  is  obtained  by  difference;  as  the  values  for  ash,  sul- 
phur, nitrogen,  hydrogen,  and  carbon,  as  well  as  the  possible  con- 
tent of  water,  in  the  coal  dried  at  100°,  have  an  influence  on  this,  it 
may  be  readily  seen  that  the  determination  of  the  oxygen  by  differ- 
ence cannot  be  exact.  Regarding  the  direct  determination  of  the 
oxygen,  compare  §  192. 
• 

7.    DETERMINATION  OF  THE  YIELD  OP  COKE. 

By  this  is  understood  the  determination  of  the  non-gasifiable 
residue  left  on  heating  the  coal  in  a  loosely  covered  crucible  until 
the  evolution  of  combustible  gases  ceases.  Experience  shows  that 
the  results  obtained  by  this  means  may  vary  considerably,  according 
as  the  operation  is  conducted  with  larger  or  smaller  quantities  of 
coal,  the  kind  of  crucible  employed,  and  the  mode  of  heating. 

MUCK,*  who  has  thoroughly  studied  this  question,  gives  the 
following  rules,  which  must  be  followed  in  order  to  obtain  constant 
results:  Never  use  more  than  1  grm.  of  coal,  and  if  the  coal  cakes 
strongly,  take  even  less;  select  a  platinum  crucible  with  a  closely 
fitting  lid  of  large  surface,  and  which,  for  coal  which  swells  up 
greatly,  must  be  over  3  cm.  in  height;  place  this  crucible  on  a  plati- 
num triangle,  so  that  the  bottom  is  3  cm.  from  the  top  of  the  tube 
of  a  BUNSEN  burner  fitted  with  a  chimney,  and  heat  it  with  a  flame 
not  less  than  18  cm.  high,  until  any  flame  issuing  from  between  the 
crucible  and  lid-edge  has  almost  completely  disappeared.  By 

*  Chemische  Beitrage  zur  Kentnisse  der  Steinkohlen,  Bonn,  MAX  COHEN 
u.  SOHN,  1876,  p.  14. 


728  DETERMINATION    OF  COMMERCIAL   VALUES.  [§  273. 

observing  these  rules  the  variations  in  the  yield  of  coke  are  gener- 
ally far  below  1  per  cent.  Stronger  heating  over  the  blowpipe 
lowers  the  yield  of  coke  but  very  slightly. 

In  order  to  obtain  comparative  results,  the  yield  of  coke  must 
be  calculated  to  coal  free  from  ash.  Regarding  the  influence  of 
mineral  constituents  on  the  extent  of  the  yield  of  coke,  see  MUCK, 
loc.  tit.,  p.  15. 

I  have  omitted  the  method  of  gravimetric  analysis  of  gases  con- 
taining carbon  dioxide  and  hydrocarbons,  devised  by  me,  and 
which  it  had  been  my  intention  to  insert  in  this  place  (see  Vol.  I, 
p.  480)  in  view  of  the  appearance  of  CL.  WINKLER'S  excellent  treatise . 
"Anleitung  zur  chemischen  Untersuchung  der  Industriegase,"  in 
which  a  full  description  of  the  method  is  given ;  see  the  second  part 
of  the  aboVe-named  work,  p.  192. 

28.  HYDROGEN  COMPOUNDS. 
§273. 

HYDROGEN  DIOXIDE. 

As  hydrogen  dioxide  has  of  late  come  into  use  as  a  bleaching; 
agent,  and  is  also  used  in  surgery  and  medicine,  and  consequently 
is  manufactured  on  a  large  scale,  its  aqueous  solutions,  which  are 
found  in  the  market  in  varying  strengths,  are  frequently  the 
subject  of  chemical  analysis.  Before  proceeding  to  describe  the 
methods  of  determination,  it  must  be  stated  that  solutions  of  hydro- 
gen dioxide  are  not  as  unstable  as  was  formerly  believed,  but  if  kept 
in  a  dark  place  and  at  a  temperature  below  30°,  they  lose  but  a  very 
small  porportion  of  their  hydrogen-dioxide  content.* 

Of  all  the  methods  of  determining  hydrogen  dioxide  in  liquids 
containing  no  organic  matter,  the  simplest  and  most  accurate  has 
been  found  to  be  that  based  upon  the  decomposition  of  the  dioxide 
by  potassium  permanganate  in  acid  solution.  The  reaction  takes 

*  See  P.  EBELL,  "Das  Wasserstoff-hyperoxid  und  seine  Verwendung  in 
der  Technik,  Chirugie  und  Medicin,"  a  paper  read  before  the  Hanover  Section 
of  the  Societ}'  of  German  Engineers,  Dec.  9,  1881;  Zeitschr.  des  Vereins 
deutsch.  Ingenieure,  xxvi. 


§  273.]  HYDROGEN   COMPOUNDS.  729 

place  according  to  the  following  equation:  2KMn04+5H2O2+ 
3H2SO4=K2S04+2MnSO4+8H2O+10  0;  it  was  first  observed  by 
BRODIE,  and  used  by  SCHONBEIN  for  the  approximate,  and  by 
ASCHOFF  for  the  accurate,  determination  of  hydrogen  dioxide. 
Among  many  other  chemists,  E.  SCHONE  *  in  particular  deserves 
credit  for  critically  testing  this  method,  as  well  as  all  others  pro- 
posed for  the  determination  of  hydrogen  dioxide. 

This  method  requires  a  solution  of  potassium  permanganate 
the  strength  of  which  must  be  proportional  to  that  of  the  hydro- 
gen-dioxide solution.  For  testing  the  ordinary  commercial  solu- 
tions, one  containing  about  3  grm.  of  potassium  permanganate  per 
litre  is  suitable.  The  effective  value  of  the  permanganate  solution 
is  ascertained  by  means  of  metallic  iron  (Vol.  I,  p.  313).  In  the  cal- 
culation it  must  be  noted  that  100  c.c.  of  a  permanganate  solution 
capable  of  converting  0  •  559  grm.  of  iron  from  a  ferrous  to  a  ferric 
state  corresponds  to  0-18016  grm.  H2O2. 

The  operation  is  very  simple.  By  means  of  a  pipette  introduce 
a  suitable  quantity  of  the  hydrogen-dioxide  solution  (about  2  to 
10  c.c.)  into  a  beaker  containing  about  300  c.c.  of  water  stongly 
acidulated  with  sulphuric  acid,  and  then,  while  stirring,  run  in  the 
permanganate  solution  until  the  liquid  acquires  a  just  permanent 
reddish  tint.  Occasionally,  according  to  SCHONE,!  and  partic- 
ularly if  the  solution  has  been  exposed  to  sunlight,  the  first  por- 
tions of  permanganate  added  are  not  immediately  decolorized 
(this  is  also  observed  when  titrating  with  oxalic  acid,  Vol.  I,  p.  316) ; 
when  the  reaction  has  once  begun,  however,  the  fresh  additions  of 
permanganate  are  decolorized  immediately.  BRODIE,  who  was 
the  first  to  make  this  observation, J  believed  this  to  be  due  to  the 
dilution  of  the  solution,  but  SCHONE  observed  it  also  in  relatively 
strong  solutions. 

The  method  of  determination  with  permanganate  is  adapted,  not 
only  for  concentrated,  but  also  for  very  dilute  solutions  of  hydro- 
gen dioxide;  and  SCHONE  obtained  good  results  with  solutions 
containing  but  a  few  grammes  per  litre  (loc.  tit.,  p.  142). 

*  Zeitschr.  f.  analyt.  Chem.,  xvin,  133. 

t  Ibid.,  xvin,  140. 

J  POGGEND.  AnnaL,  cxx,  318. 


730  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  273. 

Besides  this  method,  there  are  others  that  may  be  employed; 
e.g.,  the  hydrogen-dioxide  solution  may  be  brought  into  con- 
tact with  potassium  iodide  in  an  acid  solution,  and  the  liberated 
iodine  determined  with  sodium  thiosulphate;  or  it  may  be  decom- 
posed by  platinum-black,  and  the  oxygen  evolved  measured  (in 
SCHEIBLER'S  apparatus,  Fig.  101,  Vol.  I,  p.  501);  these  methods, 
however,  are  neither  simpler  nor  more  accurate  than  titration 
with  permanganate. 

If,  however,  the  hydrogen  dioxide  is  to  be  determined  in  liquids 
containing  organic  matter,  then  the  platinum-black  deserves  the 
preference.  Regarding  this  method,  it  may  be  remarked  that 
according  to  EBELL'S  investigations  (see  foot-note,  p.  728)  platinum- 
black  that  has  not  been  ignited  decomposes  hydrogen  dioxide  very 
rapidly,  whereas  when  ignited,  its  action  is  slower,  but  otherwise 
equally  as  complete. 

If  the  hydrogen  dioxide  is  to  be  determined  in  atmospheric 
deposits,  in  which  it  occurs  in  exceedingly  minute  quantities, 
the  methods  above  described  are  inapplicable.  SCHONE,*  who 
has  occupied  himself  with  the  solution  of  this  problem,  makes 
use  of  a  colorimetric  method  based  upon  the  separation  of  iodine 
from  neutral  potassium  iodide  by  hydrogen  dioxide,  without  the 
addition  of  ferrous  sulphate  or  any  other  similar  excitant.  Re- 
garding the  details  I  refer  to  the  original  treatise. 

SUPPLEMENT  TO  SECTION  II. 

I.  DETERMINATION  OF  GRAPE-SUGAR  (DEXTROSE),  FRUIT-SUGAR 
(LEVULOSE),  INVERT-SUGAR,  MALTOSE,  MILK-SUGAR,  CANE- 
SUGAR  (SACCHAROSE),  STARCH,  AND  DEXTRIN. 

As  the  determination  of  these  substances  is  frequently  required 
in  the  analysis  of  agricultural  and  technical  products,  and  also 
pharmaceutical  preparations;  and  as  it  is  also  of  some  importance 
in  the  examination  of  diabetic  urine,  a  few  of  the  best  methods 
for  the  purpose  are  here  given. 

*  Berichte  der  deutsch.  chem.  Gesellsch.,  vn,  1693;  Zeitschr.  f.  analyt.  Chem., 
xiv,  90,  and  91  and  above  all  xvin,  154. 


§  273.]  DETERMINATION    OF    GRAPE-SUGAR,  ETC.  731 

Apart  from  the  purely  physical  processes,  which  are  based 
either  upon  the  specific  gravity  of  the  saccharine  solutions,*  or 
upon  their  behavior  toward  polarized  light,f  the  following  methods 
serve  for  the  determination  of  the  various  kinds  of  sugars : 

A.  Methods   based   upon  the   reduction   of   cupric    oxide    to 
cuprous  oxide. 

B.  Methods  based  upon  the  reduction  of  mercury  compounds. 

C.  Methods  based  upon  the  decomposition  of  sugar  by  alcoholic 
fermentation. 

These  methods  are  detailed  in  the  f  olio  wing  sections : 

*  For  the  determination  of  cane-sugar  from  the  specific  gravity  of  the 
solution,  the  BALLING  or  BALLING-BRIX  tables  are  most  generally  used. 
These  tables  are  found  in  many  works,  e.g.,  in  the  Handworterbuch  der  reinen 
und  angewandten  Chemie,  by  LIEBIG,  POGGENDORFF,  and  WOHLER  (Brunswick, 
FR.  VIEWEG  und  SOHN,  1859,  vii,  4) ;  OTTO'S  Lehrbuch  der  rationetten  Praxis 
der  landwirthschaftlichen  Gewerbe,  5th  ed.,  1860-1862,  i,  233;  STAMMER'S 
Lehrbuch  der  Zuckerfabrikation,  1874,  38;  MUSPRATT'S  Chemie,  3d  ed.,  by 
KERL  und  STOHMANN  (Brunswick,  SCHWETSCHKE  und  SOHN,  1874,  i,  194, 
and  vii,  694) ;  BOLLEY'S  Handbuch  der  techn.  chem.  Untersuchungen,  4th  ed., 
by  E.  KOPP  (Leipzig,  FELIX,  1874,  p.  679) ;  FRUHLING  and  SCHULZ,  Anleitung 
zur  Untersuchung  der  fur  die  Zuckerindustrie  in  Betracht  kommenden  Rohma- 
terialien,  etc.  (Brunswick,  FR.  VIEWEG  und  SOHN,  1876,  p.  16);  POST'S 
chem.  techn.  Analyse,  1881,  p.  694.  The  BALLING-BRIX  tables,  although 
compiled  only  for  cane-sugar,  are  also  frequently  employed  for  grape-sugar, 
because  the  difference  in  density  between  sugar  solutions  and  grape-sugar 
solutions  of  equal  strength  is  but  slight — see  GRAHAM,  HOFMANN  and  RED- 
WOOD, Jahresber.  der  Chem.,  1852,  803;  POHL,  Ber.  der  Wien.  Akad.,  1854, 
xi,  664;  HOPPE-SEYLER,  Zeitschr.  f.  analyt.  Chem.,  xiv,  305.  A  compara- 
tive table,  by  which  the  difference  in  densities  may  be  seen,  may  also  be 
found  in  BOLLEY'S  Handbuch  (see  above),  p.  681.  A  special  table  for  the 
determination  of  grape-sugar  from  the  specific  gravity  of  its  aqueous  solutions 
was  prepared  by  SALOMON  (Ber.  d.  deutsch.  chem.  Gesellsch.,  xiv,  2711),  and 
a  corresponding  one  for  invert-sugar  by  CHANCEL  (LIPPMANN,  Die  Zuckerarten, 
etc..  Brunswick,  FR.  VIEWEG  und  SOHN  1882,  p.  73). 

f  The  determination  of  sugar  by  the  polariscope  will  also  be  found  de- 
scribed in  the  above-named  works,  but  the  most  complete  description  is 
given  in  LANDOLT'S  work,  Das  optische  Drehungsvermogen  organischer  Sub- 
-stanzen,  etc.,  Brunswick,  FR.  VIEWEG  und  SOHN,  1879. 


732  DETERMINATION    OF   COMMERCIAL   VALUES.  [§274. 

A.  METHODS  BASED  UPON  THE  REDUCTION  OF  CUPRIC  OXIDE. 

§274. 

I.    GENERAL   PRINCIPLES. 

The  fact  that  a  solution  of  cupric  sulphate  to  which  potassium- 
or  sodium  tartrate,  and  caustic  potassa  or  soda  have  been  added 
(and  which,  if  these  are  added  in  proper  proportion,  remains  un- 
altered when  boiled)  is  decomposed  by  grape-sugar  at  the  boiling 
temperature,  with  separation  of  cuprous  oxide,  was  first  utilized  by 
BARRESWIL*  for  the  determination  of  sugar.  Subsequently  the 
method  was  thoroughly  investigated,  particularly  by  FEHLING,! 
who  also  greatly  improved  upon  BARRESWIL' s  formula  for  the  prep- 
aration of  the  alkaline  copper  solution,!  and  established  the  rule, 
later  on  confirmed  by  NEUBAUER§  and  others,  that  1  equivalent 
of  grape-sugar,  C6H12O6=  180-096  reduces  5  equivalents  of  cupric 
oxide,  5CuO  =  398.  This  important  method  has  in  course  of 
time  been  widely  investigated,  and  variously  modified.  More 
recently  SOXHLET,||  in  particular  has  subjected  the  method  to  a 
most  thorough  investigation;  and  amongst  others  who  have  done 

*  Arch,  d'anatomie,  1846,  p.  50;  Journ.  de  Pharm.,  vi,  361;  BERZELIUS' 
Jahresber.,  xxv,  556. 

f  Annal  d.  Chem.  u.  Pharm.,  LXXII,  106,  and  cvi,  75. 

JThe  original  formula  for  FEHLING'S  solution  is  as  follows:  Dissolve 
40  grm.  pure,  crystallized  copper  sulphate  free  of  adhering  moisture,  in 
about  600  c.c.  water;  further,  dissolve  in  a  separate  vessel  160  grm.  neutral 
potassium  tartrate  in  a  little  water,  add  600  to  700  grm.  of  a  solution  of  pure 
caustic  lye  of  sp.  gr.  1-12;  gradually  pour  the  first  solution  into  the  latter, 
and  dilute  the  deep-blue  solution  until  it  measures  exactly  1154-4  c.c.  at  15°. 
Calculated  down  to  1000  c.c.  and  sodium  hydroxide,  and  moreover,  substi- 
tuting for  the  equivalent  of  copper  sulphate  formerly  used  (124-75)  that 
based  upon  the  atomic  weights  used  in  this  book  (CuSO4-5H2O=249-75), 
we  obtain  the  quantities  34-669  grm.  cupric  sulphate,  138-6  grm.  potassium 
tartrate,  and  54-58  to  63-67  sodium  hydroxide. 

§  Archiv  der  Pharm.   [2],  LXXII,  278. 

II  Chem.  Centralbl  [3],  ix,  218,  and  236;  Journ.  f.  prakt.  Chem.,  N.  S.,  xxi, 
227;  Zeitschr.  f.  analyt.  Chem.,  xvm,  348,  and  xx,  425. 


§  274.]  DETERMINATION    OF   GRAPE-SUGAR,    ETC.  733 

important  work  on  this  subject  are  GRATAMA,*  ULBRicHT,f 
MARCKER,  BEHREND  and  MORGEN,J  RODEWALD  and  TOLLENS,§ 
ALLIHN,||  DEGENER,^]"  and  MEISSL.** 

As  the  fruit  of  all  these  exhaustive  investigations  the  laws  laid 
down  by  SOXHLET  are  here  given : 

1.  The  assumption  that  1  equivalent  of  grape-sugar  (180-096) 
reduces  5  equivalents  of  cupric  oxide  and  that  therefore  10  c.c.  of 
the  FEHLING'S  solution  correspond  with  0-05  grm.  of  anhydrous 
grape-sugar,  is  only  correct,  or — more  accurately,  nearly  correct — 
at  the  degree  of  dilution  prescribed  by  FEHLING  (10  c.c.  copper 
solution +  40  c.c.  water),  and  when  a  0-5-  to  1-per  cent,  solution 
of  sugar  is  used.     SOXHLET  found  that  when  using  a  1-per  cent, 
sugar  solution,  the  proportion  is  1  equiv.  :  5  •  055  instead  of  1:5. 
Hence  10  c.c.  of  FEHLING'S    solution  under  these  circumstances 
do  not  correspond  with   0-05  grm.  grape-sugar,  but  only  with 
0-0495  grm. 

2.  On  altering  the  degree  of  concentration,  the  reducing  action 
of  the  solution  is  also  changed;  thus  SOXHLET  found  that  on  em- 
ploying undiluted  FEHLING'S   solution  and  a  1-per  cent,  grape- 
sugar  solution,  the  proportion  was  1  equiv.  :  5  •  26  equiv. 

3.  The  quantity  of  the  sugar  solution  acting  upon  the  copper 
solution  also  influences  the  reducing  action.     Hence,  on  allowing 
the  sugar  solution  to  run  into  the  boiling  copper  solution,  the  first 
portions,  coming  into  contact  with  a  large  excess  of  copper,  will 
reduce  more  than  the  succeeding  portions.      The   proportion  in 
which  the  reduction  takes  place  is    hence,  under  these  circum- 
stances, not  constant  but  gradually  diminishes. 

4.  Grape-sugar,  fruit-sugar,  invert-sugar,  and  maltose,  have  not 

*  Zeitschr.  f.  analyt.  Chem.,  xvii,  155. 

f  Chem.  Centralbl.  [3],  ix,  392;  Landwirthschaftl.  Versuchsstat.,  xxvii,  81. 

t  Ibid.  [3],  ix,  584. 

§  Zeitschr.  f.  analyt.  Chem.,  xvni,  605. 

||  Neue  Zeitschr.  f.  Rubenzuckerindustrie,  in,  230,  and  Zeitschrift  des  Vereins 
fur  Rubenzuckerindustrie,  xix,  865;  Zeitschr.  f.  analyt.  Chem.,  xx,  434,  and 
xxii,  448. 

^f  Zeitschrift  des  Vereins  fur  Rubenzuckerindustrie,  xvin,  349 ;  Zeitschr.  f. 
analyt.  Chem.,  xxn,  444. 

**  Zeitschr.  des  Vereins  f.  Rubenzuckerindustrie,  1879,  1034. 


734  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  274. 

identical,  but  different  reducing  effects.  Thus,  using  the  propor- 
tions stated  in  1,  i.e.,  a  FEHLING'S  solution  diluted  with  four  vol- 
umes of  water  and  a  1-per  cent,  sugar  solution, 

10  c.c.  FEHLING'S  solution = 0-0495  grm.  grape-sugar,  C6H1206. 
"    "  "  "       =0-0515    "     invert-sugar,  C6H1206. 

"    "  "  "       =0-0740    "     maltose,  C12H22On. 

That  the  reducing  action  of  milk-sugar  differs  considerably  from 
that  of  grape-sugar  was  already  known  long  ago,  but  opinions  dif- 
fered as  to  the  extent  of  the  difference.  SOXHLET  found  that  10 
c.c.  of  FEHLING'S  solution  corresponded  with  0-0676  grm.  of  milk- 
sugar,  C12H22011-H20,  and  further,  that  with  milk-sugar  the  dilu- 
tion of  the  copper  and  sugar  solutions  had  no  effect,  or  only  an 
inappreciable  one,  on  the  results. 

5.  On  allowing  1-per  cent,  solutions  of  the  different  sugar  solu- 
tions to  act  on  undiluted  FEHLING'S  solution,  the  following  results 
were  obtained  by  SOXHLET: 

50  c.c.  FEHLING'S  solution= 0-2375  grm.  grape-sugar,  C6H12O6. 

"    "  "  "       =0-2470    "     invert-sugar,  C6H12O6. 

"    "  "  "       =0-2572    "     levulose,  C6H13O6. 

"    "  "  "       =0-3890    "     maltose,  C12H22On. 

11    "  "  "       =0-3380    "     milk-sugar,  C12H22On  H2O. 

6.  The  reducing  action  of  the  different  sugars  on  FEHLING'S 
solution  at  the  boiling  temperature  varies  greatly,  thus: 

Grape-sugar  required  boiling  for          2  minutes. 
Invert-sugar        "  il       il  2       " 

Levulose  "  "       "  2       " 

Maltose  "  "       "    3  to  4       " 

Milk-sugar  "  "       "    6  to  7       " 

Bearing  these  newly-ascertained  facts  in  mind,  SOXHLET  has  so 
modified  FEHLING'S  method  of  volumetric  analysis,  that  the  results, 
so  far  as  accuracy  is  concerned,  leave  nothing  to  be  desired,  while 
MARCKER  in  conjunction  with  BEHREND  and  MORGEN  have  shown, 
SOXHLET  recognized,  and  ALLIHN  as  well  as  MEISSL,  more  accurately 
demonstrated,  that  accurate  determinations  may  also  be  obtained 
by  gravimetric  methods. 


§  274.]  DETERMINATION   OF   GRAPE-SUGAR,   ETC.  735 

II.    METHODS  OF  DETERMINING  SUGAR. 

There  will  be  here  described: 

1.  FEHLING'S  volumetric  method  of   determining  grape-sugar, 
in  its  original  or  but  slightly  modified  form,  as  this  method  is  still 
adapted   for   the   approximate   determination   of  grape-sugar  in 
must,  diabetic  urine,  etc. 

2.  SOXHLET'S  modification  of  FEHLING'S  method,  for  the  more 
accurate  determination  of  the  various  sugars. 

3.  Gravimetric  methods  of  determining  sugar. 

1.  FEHLING'S  Method. 

Instead  of  the  copper  solution  originally  employed  by  FEHLING, 
the  preparation  of  which  was  described  in  the  foot-note  on  p.  732, 
and  the  stability  of  which  leaves  much  to  be  desired,  it  is  advan- 
tageous to  employ  two  solutions:  a. — An  aqueous  cupric-sulphate 
solution  containing  34-669  *  grm.  of  pure,  crystallized  cupric  sul- 
phate per  liter;  and  6. — A  solution  prepared  by  dissolving  153 
grm.  crystallized  potassium  and  sodium  tartrate  in  water  in  a  litre 
flask,  adding  572  grm.  of  soda  lye  of  sp.  gr.  1-12  (containing  60 
grm.  sodium  hydroxide),  and  filling  up  to  the  mark;  or,  which  is 
as  a  rule  preferable  in  the  case  of  6  (which  does  not  remain  long 
unchanged),  by  dissolving  43-3  grm.  potassium  and  sodium  tar- 
trate in  water  in  a  250-c.c.  flask,  adding  143  c.c.  soda  lye  of  sp.  gr. 
1  •  12,  or  15  grm.  sodium  hydroxide,  and  making  up  to  250  c.c. 

It  will  be  seen  that  similar  proportions  of  mixture  and  dilution 
are  obtained  in  both  cases,  e.g.,  in  i,  10  c.c.  of  the  original  FEHLIXG'S 
solution  (see  foot-note,  p.  732)  diluted  with  40  c.c.  of  water,  or  n, 
mixing  10  c.c.  of  the  alkaline  solution  of  potassium  and  sodium 
tartrate  b  described,  with  10  c.c.  of  the  pure  aqueous  cupric- 
sulphate  solution  a,  and  diluting  with  30  c.c.  of  water. 

Either  of  the  two  liquids  therefore  corresponds,  under  given 
conditions  (see  §  274,  i,  1),  almost  exactly  to  0-05  grm.  grape-sugar. 

*  The  figure  given  by  the  author  is  34  •  639,  but  recalculated  on  the  basis 
of  the  atomic  weights  used  in  this  book,  c  is  as  given  in  the  text. — TRANS- 
LATOR. 


736 


DETERMINATION   OF   COMMERCIAL   VALUES. 


[§  274. 


Now  dilute  the  sugar  solution  to  be  tested  so  that  it  will  contain 
between  0-5  and  1  per  cent,  of  sugar;  this  can  generally  be  done  by 
determining  the  specific  gravity.  In  order  to  afford  the  necessary 
data  for  this  purpose  for  use  in  ordinary  cases,  I  give  the  following 
abstract  from  SALOMON'S  table: 

GRAMMES  OF   ANHYDROUS    GRAPE-SUGAR  IN    100  C.C.   OF  AN  AQUEOUS 
SOLUTION   AT   17-5°. 


Grammes 
Grape-sugar. 

Sp.  Gr. 

Grammes 
Grape-sugar. 

Sp.  Gr. 

Grammes 
Grape-sugar. 

Sp.  Gr. 

1 

•00375 

10 

1-0381 

19 

1-0725 

2 

•0075 

11 

1-0420 

20 

1-0762 

3 

•0115 

12 

1-0457 

21 

1-0800 

4 

•0153 

13 

1-0495 

22 

1-0838 

5 

•0192 

14 

1-0533 

23 

1-0876 

6 

1-0230 

15 

1-0571 

24 

1-0910 

7 

1-0267 

16 

1-0610 

25 

1-0946 

8 

1-0305 

17 

1-0649 

26 

1-0985 

9 

1-0342 

18 

1-0687 

Heat  to  gentle  boiling  a  quantity  of  the  above-mentioned 
diluted  copper  solution,  i  or  n,  corresponding  with  0-05  grm.  grape- 
sugar,  in  a  small  flask,  and  from  a  burette  calibrated  in  0-1  c.c. 
run  in  the  sugar  solution  slowly  and  in  small  portions  at  a  time. 
After  the  addition  of  the  first  few  drops  the  liquid  appears  greenish- 
brown,  owing  to  the  cuprous  hydroxide  and  cuprous  oxide  sus- 
pended in  the  blue  liquid;  in  proportion  as  more  sugar  solution  is 
added,  the  more  voluminous  and  redder  does  the  precipitate 
become,  and  the  more  rapidly  does  it  settle.  As -soon  as  the  pre- 
cipitate appears  deep-red,  remove  the  source  of  heat,  allow  the  pre- 
cipitate to  settle  somewhat,  and  place  the  flask  on  a  sheet  of  white 
paper,  or  hold  it  up  between  the  eye  and  the  window,  in  order  to 
observe  the  liquid  by  transmitted  light;  the  slightest  bluish-green 
color  may  thus  be  easily  detected.  In  order  to  make  absolutely 
certain,  however,  pour  a  small  portion  of  the  supernatant  clear 
liquid  into  a  test-tube,  add  a  few  drops  sugar  solution,  and  heat ;  if 
the  slightest  trace  of  undecomposed  salt  copper  is  still  present, 
there  will  form  at  first  a  flocculent,  yellowish-red  precipitate.  If 
this  forms,  return  the  contents  of  the  test-tube  to  the  flask,  and 
add  more  sugar  solution  until  the  reduction  is  complete.  The  vol- 


$  274.]  DETERMINATION    OF   GRAPE-SUGAR,    ETC.  737 

ume  of  sugar  solution  used  up  will  have  contained  0-05  grm. 
grape-sugar. 

When  the  experiment  is  finished,  test  the  liquid  to  ascertain 
whether  the  precise  point  at  which  reduction  is  complete  has  been 
struck,  i.e.,  whether  the  solution  contains  any  copper,  sugar>  or 
a  brown  decomposition  product  of  the  latter.  For  this  purpose 
rapidly  filter  off  a  sample  of  the  still  hot  liquid.  If  the  exact 
point  has  been  hit,  the  filtrate  must  be  colorless  or  only  very  faint- 
ly yellowish,  and  not  brownish;  and  samples  of  the  liquid  must 
remain  unchanged  when  heated  either  with  a  drop  of  the  copper 
solution  or  with  some  of  the  sugar  solution;  or  on  acidulating 
with  hydrochloric  acid  and  treating  with  hydrogen  sulphide;  or 
on  acidulating  with  acetic  acid  and  adding  potassium  ferrocyanide. 
If  it  is  found  that  there  is  a  notable  excess  of  copper  or  of  sugar 
present,  the  experiment  must  be  repeated.  As  a  rule,  the  first 
determination  will  give  only  approximately  correct  results.  In 
the  second  experiment  it  is  best  to  add  to  the  cold  copper  solution 
all  but  a  little  of  the  entire  quantity  of  sugar  solution  as  ascer- 
tained in  the  first  test,  then  to  heat,  maintain  boiling  for  two 
minutes,  and  then  to  continue,  cautiously  adding  two  drops  at  a 
time  until  the  operation  is  complete. 

The  results  are  quite  concordant,  and  are  approximately 
correct.  That  the  sugar  solution  was  of  the  proper  degree  of 
dilution  will  be  evidenced  by  the  fact  that  from  5  to  10  c.c.  of  it 
will  have  been  required  for  the  determination.  Care  must  be  taken 
that  the  copper  solution  is  always  strongly  alkaline.  If  the  sugar 
solution  is  acid,  it  must  be  rendered  feebly  alkaline  before  diluting 
to  the  requisite  volume. 

If  this  method  is  employed  for  diabetic  urine,  it  must  be  remem- 
bered that  on  boiling  the  urine  with  caustic  soda,  ammonia  is 
liberated,  and  that  this  will  retain  cuprous  oxide  in  solution.  As 
such  a  solution  turns  blue  on  exposure  to  air,  this  must  be  pre- 
vented so  far  as  possible,  and  the  hot  liquid  must  hence  be  allowed 
to  stand,  for  the  determination  of  its  color,  only  so  long  as  is  un- 
avoidably necessary  to  see  through  the  liquid  free  from'  cuprous 
oxide.  For  the  same  reason  it  is  inadvisable  to  filter  the  liquid 


738  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  274, 

when  determining  sugar  in  urine ;  nor  is  it  of  any  use  to  test  the 
nitrate  with  hydrogen  sulphide  or  potassium  ferrocyanide,  as 
copper  (dissolved  in  the  ammonia  as  cuprous  oxide)  may  be,  and 
often  is,  present  in  it,  even  when  all  the  cupric  oxide  has  been 
reduced  by  the  sugar. 

2.  SOXHLET' s  Modification  of  FEHLING'S  Method.    - 

a.  Dissolve  34-669*  grm.  cupric  sulphate  f  in  sufficient  water 
to  make  500  c.c. 

b.  Dissolve  173  c.c.  grm.  of  crystallized  potassium  and  sodium 
tartrate  in  400  c.c.  water,  and  add  100  c.c.  caustic-soda  solution 
containing  500  grm.  sodium  hydroxide  in  the  litre.     It  will  be 
evident  that  if  such  a  caustic-soda  solution  is  not  at  hand,  the 
solution  may  be  also  more  simply  prepared  by  dissolving  173  grm. 
of  the  potassium  and  sodium  tartrate  in  about  400  c.c.  of  water, 
adding  50  grm.   of  sodium  hydroxide,  and  when  perfectly  cold, 
filling  up  to  the  mark  and  mixing. J 

c.  Mix  25  c.c.  of  the  copper-sulphate  solution  a,  and  25  c.c.  of 
the  alkaline  Rochelle-salt  solution  b,  in  a  deep  porcelain  dish,| 


*  The  author's  figures  are  34-639,  but  when  recalculated  according  to 
the  values  adopted  in  this  work  (Cu=63-6;  8=32-07;  H=  1-008;  O=16) 
the  figures  are  as  stated  in  the  text,  since  grape-sugar,  C6H12O6=  180-096, 
and  5CuSO4-5H2O=  1248-75,  from  which  it  follows  that  5  grm.  grape-sugar 
are  the  equivalent  of  34-669  grm.  cupric  sulphate. — TRANSLATOR. 

f  SOXHLET  advises  to  recrystallize  the  commercial  so-called  chemically 
pure  cupric  sulphate  by  stirring  the  hot,  saturated,  and  filtered  solution 
until  it  cools ;  the  crystalline  powder  dried  between  filter-paper,  and  exposed 
for  24  hours  in  a  thin  layer  in  a  dry  place,  will  then  have  the  proper  water 
content. 

J  SOXHLET  prepares  the  alkaline  solution  of  potassium  and  sodium  tar- 
trate fresh  every  time,  and  states  that  "the  use  of  Rochelle-salt  solution 
which  has  been  kept  for  some  time  should  be  avoided  just  as  much  as 
the  employment  of  ready-made  FEHLING'S  solution  which  has  been  kept 
on  hand  for  some  time,  even  though  the  container  has  been  kept  ever  so  well 
stoppered." 

§  It  will  be  evident  that  the  50  c.c.  of  liquid  contained  in  the  dish  will 
contain  exactly  as  much  cupric  sulphate  and  Rochelle  salt  in  solution  as 
50  c.c.  of  the  solution  prepared  by  FEHLING'S  original  formula. 


§  274.]  DETERMINATION    OF   GRAPE-SUGAR,   ETC.  739 

heat  to  boiling,  and  add  the  sugar  solution  in  small  portions  until 
the  liquid,  after  sufficient  boiling,  the  duration  of  which  must 
depend  upon  the  kind  of  sugar  (§  274,  i,  6),  no  longer  appears 
blue.  From  this  preliminary  test  calculate,  according  to  §  274, 
i,  5,  the  approximate  quantity  of  the  sugar  corresponding  with 
50  c.c.  of  FEHLING'S  solution,  and  then  dilute  the  solution  so  as 
to  contain  about  1  per  cent,  of  sugar. 

d.  Now  heat  a  fresh  mixture  of  25  c.c.  of  copper-sulphate 
solution  a,  and  25  c.c.  Rochelle-salt  solution  6,  without  diluting  it 
with  water,  but  with  a  quantity  of  the  approximately  1  per  cent, 
sugar  solution  corresponding  with  the  preliminary  test  (i.e.,  about 
23  c.c.  grape-sugar,  24  c.c.  invert-sugar,  25  c.c.  levulose-,  38  c.c. 
maltose-,  or  33  c.c.  milk-sugar  solution)  so  long  as  is  necessary 
for  the  particular  kind  of  sugar  (§  274,  i,  6),  and  then  pour  the 
whole  through  a  sufficiently  large  folded  filter.  If  the  filtrate  is 
green  or  appreciably  greenish,  it  is  of  course  unnecessary  to  test 
further  for  copper;  if,  however,  it  is  yellow,  some  copper  may 
still  be  present.  In  order  to  ascertain  this,  acidulate  about  one- 
third  of  the  filtrate  with  acetic  acid,  and  add  potassium  ferro- 
cyanide.  A  dark-red  color  indicates  the  presence  of  large  quan- 
tities of  copper,  while  a  pale  pink  indicates  traces;  if  there  is  no 
change  in  color  all  the  copper  has  been  precipitated.  If  copper 
was  found  in  the  solution,  make  a  fresh  test  in  exactly  the  same 
way  as  before,  but  use  a  larger  quantity  of  sugar  solution,  propor- 
tional to  the  intensity  of  the  copper  reaction  observed;  if,  on  the 
other  hand,  no  copper  was  found,  take  about  1  c.c.  less  sugar  solu- 
tion for  the  second  test. 

These  trials  are  repeated  until  two,  differing  in  the  quantity 
of  sugar  used  only  by  0-1  c.c.,  yield  filtrates  one  of  which  contains 
copper  while  the  other  is  free  from  it.  The  mean  between  the 
two  is  regarded  as  the  exact  quantity  of  sugar  solution  required 
to  decompose  50  c.c.  FEHLING'S  solution.  As  a  rule  5  or  6  such 
tests  will  suffice  to  attain  the  object.  The  calculation  is  then  made 
on  the  basis  of  the  comparative  figures  given  in  §  274,  i,  5.  For 
instance,  were  24  cc.  of  grape-sugar  solution  used,  these  would 


740  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  274. 

contain  0-2375  grm.  grape-sugar;  if  40  c.c.  maltose  solution  have 
been  employed,  these  contained  0  •  389  grm.  maltose. 

In  colored  liquids  it  is  more  difficult  to  detect  any  copper  in 
the  filtrate  by  means  of  potassium  ferrocyanide,  and  the  hydrogen 
sulphide  gives  even  still  more  uncertain  results.  In  such  cases 
SOXHLET  advises  to  boil  the  liquid  in  the  beaker  with  a  few  drops 
of  sugar  solution  for  about  one  minute,  and  to  then  allow  to  stand 
quietly  for  3  to  4  minutes.  On  now  pouring  the  liquid  from  the 
beaker,  and  wiping  the  bottom  of  the  latter  with  a  piece  of  white 
blotting-paper  wrapped  around  a  glass  rod,  the  paper  will  be  colored 
red  by  any  adherent  cuprous  oxide.  Larger  quantities  of  copper 
in  the  filtrate  may  be  easily  detected  by  the  red  deposit  on  the 
sides  and  bottom  of  the  glass  vessel. 

e.  SOXHLET' s  modification  of  FEHLING'S  method  is  also  gen- 
erally applicable  to  diabetic  urine;  the  operator  must,  however, 
be  content  with  boiling  two  minutes,  and  allowing  to  settle  for 
a  very  short  time,  to  determine  whether  the  supernatant  liquid 
is  green  or  not,  as  the  testing  for  copper  in  the  filtrate  is  impracti- 
cable (see  above,  FEHLING'S  method). 

/.  As  in  SOXHLET' s  modification  the  period  of  boiling  is  defi- 
nitely fixed,  and  must  not  be  prolonged  longer  than  is  necessary 
it  can  yield  serviceable  results  only  when  reducing  sugars  are 
present  with  substances  which  reduce  FEHLING'S  solution  only 
after  prolonged  action.  Hence  grape-sugar  or  invert-sugar  may 
be  determined  by  this  method  in  solutions  containing  also  cane- 
sugar  (compare  §  277,  I). 

3.  Gravimetric  Methods  of  Sugar  Determination. 

a.  Determination  of  Grape-sugar. 

This  is  based  upon  the  fact,  ascertained  by  MARCKER,  that 
when  grape-sugar  acts  upon  FEHLING'S  solution  at  the  boiling  tem- 
perature, there  is  no  proportional  relation  between  the  quantity 
of  grape-sugar  and  the  cuprous  oxide  precipitated,  but  that  a 
definite  relation  exists  when  in  all  cases  equal  quantities  of  copper 
solution  act  under  like  conditions.  The  method  rests,  therefore, 


§  274.]  DETERMINATION    OF   GRAPE-SUGAR,    ETC.  741 

upon  a  purely  empirical  basis.  MARCKER  based  the  formula  for 
the  calculation  on  three  determinations  only,  and  with  different 
quantities  of  sugar.  ALLIHN  placed  the  method  on  a  more  secure 
foundation  by  making  eleven  determinations;  he  also  greatly 
facilitated  the  performance  of  the  method  by  calculating  a  table 
based  upon  his  determinations,  from  which  the  relations  between 
the  copper  thrown  down  as  cuprous  oxide  and  the  grape-sugar 
may  be  directly  ascertained.  In  order  that  the  table  may  apply, 
the  details  of  ALLIHN' s  method  must  be  strictly  adhered  to,  as  it 
rests  upon  a  purely  empirical  basis.  The  reagents  required  are: 

a,  a  copper  sulphate  solution,  prepared  by  dissolving  34-6  grnu 
crystallized  copper  sulphate  in  sufficient  water  to  measure  500  c.c.; 

b,  a  Rochelle-salt  solution,  prepared  by  dissolving  173  grm.  Ro- 
chelle  salt  and  125  grm.  potassium  hydroxide  in  water  to  make 
500  c.c.    The  solutions  are  kept  separate. 

Now  mix  30  c.c.  of  the  alkaline  Rochelle-salt  solution  6,  and 
30  c.c.  of  the  copper-sulphate  solution  a,  in  a  300-c.c.  beaker,  and 
heat  to  boiling  over  the  naked  flame  or  on  a  sand-bath.  For  each 
test,  run  into  the  boiling  liquid  from  a  burette  25  c.c.  of  the  sugar 
solution  (which  must  not  contain  more  than  1  per  cent,  of  sugar)  > 
boil  the  mixture  up  once  more,  and  immediately  filter  off  the- 
precipitated  cuprous  oxide.  SOXHLET  directs  an  asbestos  filter- 
tube  to  be  used  for  filtering.  ALLIHN  recommends  to  prepare  it 
from  a  piece  of  combustion  tubing  10  cm.  long,  drawn  out  to  about 
one-half  the  width  at  one  end,  and  the  wider  part  one-fourth 
filled  with  freshly  ignited,  long-fibred,  soft  asbestos.  Under  the 
asbestos  layer,  in  the  conical  part  of  the  filter-tube  (shown  in 
Fig.  131,  a),  place  a  small  plug  of  glass  wool,  so  that  no  particles 
of  asbestos  can  be  carried  away  during  filtration.  The  asbestos 
must  be  packed  neither  too  loosely  nor  too  tightly,  as  in  the  former 
case  some  cuprous  oxide  might  easily  run  through  with  the  liquid, 
while  in  the  second  place  the  filtration  would  be  too  slow.  It 
is  well  to  place  a  loose  plug  of  asbestos  upon  the  rather  tightly 
packed  asbestos  mass.  The  cuprous  oxide  in  this  case  dis- 
tributes itself  in  the  former,  instead  of  forming,  as  it  otherwise 
does,  a  compact  layer,  which  hinders  filtration. 


742  DETERMINATION   OF   COMMERCIAL    VALUES.         [§  274 

The  prepared  filter-tube  is  now  carefully  heated  with  the  lamp 
while  a  current  of  dry  air  is  drawn  through  it 
in  order  to  remove  all  moisture;  after  cooling  in 
the  exsiccator  it  is  weighed.  When  in  use,  a 
small  funnel  is  fitted  into  the  filter-tube  by 
means  of  a  perforated  cork,  and,  in  order  to 
facilitate  filtration,  the  flask  for  receiving  the 
nitrate  is  connected  with  a  pump.  After  repeated 
decantation,  bring  the  cuprous  oxide  on  to  the 
filter,  wash  with  cold  water,  and  finally  rinse 
with  alcohol  and  ether  to  facilitate  the  drying. 
The  traces  of  cuprous  oxide  adhering  to  the 
beaker  remove  with  a  glass  rod  over  the  end  of 
which  a  short  piece  of  rubber  tubing  has  been 
slipped.  The  drying  is  best  effected  by  heating 
in  an  air-bath;  it  requires  scarcely  15  minutes. 

Now  proceed  to  reduce  the  cuprous  oxide,  as  the 
metallic  copper  resulting  has  to  be  weighed.  For 
this  purpose  fix  the  filter-tube  in  an  inclined  po- 
sition and  pass  a  current  of  pure,  dry  hydrogen 
FIG.  131.  through  it  while  gently  heating.  The  reduction  is 
effected  even  at  a  moderate  heat  (according  to  SOXHLET'S  investi- 
gations already  at  130°  to  135°).  It  is  hence  unnecessary  for  the 
flame  to  touch  the  glass  tube,  and  special  care  must  be  taken  not 
to  directly  heat  that  part  of  the  tube  wherein  the  glass  wool  is 
placed,  in  order  that  the  lead  oxide  it  contains  may  not  be  reduced. 
As  soon  as  the  precipitate  exhibits  the  characteristic  color  of 
copper,  and  droplets  of  water  cease  to  form  at  the  cold  end  of  the 
tube  (which  usually  is  the  case  in  a  few  minutes),  the  object  is 
attained.  Now  allow  to  cool  in  the  current  of  hydrogen,  then  pass 
a  current  of  dry  air  through  the  tube  for  a  short  time,  and  weigh. 
The  quantity  of  copper  found  (in  milligrammes)  is  now  sought  in 
the  following  table,  and  the  corresponding  quantity  of  grape-sugar 
read  off  in  the  adjacent  column: 


1274.] 


DETERMINATION    OF  GRAPE-SUGAR,   ETC. 


743 


TABLE  FOR  CALCULATING  THE  GRAPE-SUGAR  FROM  THE  QUANTITY  OF  COPPER 
DETERMINED    BY    GRAVIMETRIC   ANALYSIS. 


Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

10 

6-1 

59 

30-3 

108 

55-0 

157 

80-1 

11 

6-6 

60 

30-8 

109 

55-5 

158 

80-7 

12 

7-1 

61 

31-3 

110 

56-0 

159 

81-2 

13 

7-6 

62 

31-8 

111 

56-5 

160 

81-7 

14 

8-1 

63 

32-3 

112 

57-0 

161 

82-2 

15 

8-6 

64 

32-8 

113 

57-5 

162 

82-7 

16 

9-0 

65 

33-3 

114 

58-0 

163 

83-3 

17 

9-5 

66 

33-8 

115 

58-6 

164 

83-8 

18 

10-0 

67 

34-3 

116 

59-1 

165 

84-3 

19 

10-5 

68 

34-8 

117 

59-6 

166 

84-8 

20 

11-0 

69 

35-3 

118 

60-1 

167 

85-3 

21 

11-6 

70 

35-8 

119 

60-6 

168 

85-9 

22 

12-0 

71 

36-3 

120 

61-1 

169 

86-4 

23 

12-5 

72 

36-8 

121 

61-6 

170 

86-9 

24 

13-0 

73 

37-3 

122 

62-1 

171 

87-4 

25 

13-5 

74 

37-8 

123 

62-6 

172 

87-9 

26 

14-0 

75 

38-3 

124 

63-1 

173 

88-5 

27 

14-5 

76 

38-8 

125 

63-7 

174 

89-0 

28 

15-0 

77 

39-3 

126 

64-2 

175 

89-5 

29 

15-5 

78 

39-8 

127 

64-7 

176 

90-0 

30 

16-0 

79 

40-3 

128 

65-2 

177 

90-5 

31 

16-5 

80 

40-8 

129 

65-7 

178 

91-1 

32 

17-0 

81 

41-3 

130 

66-2 

179 

91-6 

33 

17-5 

82 

41-8 

131 

66-7 

180 

92-1 

34 

18-0 

83 

42-3 

132 

67-2 

181 

92-6 

35 

18-5 

84 

42-8 

133 

67-7 

182 

93-1 

36 

18-9 

85 

43-4 

134 

68-2 

183 

93-7 

37 

19-4 

86 

43-9 

135 

68-8 

184 

94-2 

38 

19-9 

87 

44-4 

136 

69-3 

185 

94-7 

39 

20-4 

88 

44-9 

137 

69-8 

186 

95-2 

40 

20-9 

89 

45-4 

138 

70-3 

187 

95-7 

41 

21-4 

90 

45-9 

139 

70-8 

188 

96-3 

42 

21-9 

91 

46-4 

140 

71-3 

189 

96-8 

43 

22-4 

92 

46-9 

141 

71-8 

190 

97-3 

44 

22-9 

93 

47-4 

142 

72-3 

191 

97-8 

45 

23-4 

94 

47-9 

143 

72-9 

192 

98-4 

46 

23-9 

95 

48-4 

144 

73-4 

193 

98-9 

47 

24-4 

96 

48-9 

145 

73-9 

194 

99-4 

48 

24-9 

97 

49-4 

146 

74-4 

195 

100-0 

49 

25-4 

98 

49-9 

147 

74-9 

196 

100-5 

50 

25-9 

99 

50-4 

148 

75-5 

197 

101-0 

51 

26-4 

100 

50-9 

149 

76-0 

198 

101-5 

52 

26-9 

101 

51-4 

150 

76-5 

199 

102-0 

53 

27-4 

102 

51-9 

151 

77-0 

200 

102-6 

54 

27-9 

103 

52-4 

152 

77-5 

201 

103-1 

55 

28-4 

104 

52-9 

153 

78-1 

202 

103-7 

56 

28-8 

105 

53-5 

154 

78-6 

203 

104-2 

57 

29-3 

106 

54-0 

155 

79-1 

204 

104-7 

58 

29-8 

107 

54-5 

156 

79-6 

205 

105-3 

744 


DETERMINATION    OF   COMMERCIAL   VALUES. 


[§  274. 


TABLE  FOR  CALCULATING  THE  GRAPE-SUGAR  FROM  THE   QUANTITY  OF  COPPER 
DETERMINED    BY   GRAVIMETRIC   ANALYSIS.        (Continued.) 


Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

206 

105-8 

255 

131-9 

304 

158-7 

353 

186-0 

207 

106-3 

256 

132-4 

305 

159-3 

354 

186-6 

208 

106-8 

257 

133-0 

306 

159-8 

355 

187-2 

209 

107-4 

258 

133-5 

307 

160-4 

356 

187-7 

210 

107-9 

259 

134-1 

308 

160-9 

357 

188-3 

211 

108-4 

260 

134-6 

309 

161-5 

358 

188-9 

212 

109-0 

261 

135-1 

310 

162-0 

359 

189-4 

213 

109-5 

262 

135-7 

311 

162-6 

360 

190-0 

214 

110-0 

263 

136-2 

312 

163-1 

361 

190-6 

215 

110-6 

264 

136-8 

313 

163-7 

362 

191-1 

216 

111-1 

265 

137-3 

314 

164-2 

363 

191-7 

217 

111-6 

266 

137-8 

315 

164-8 

364 

192-3 

218 

112-1 

267 

138-4 

316 

165-3 

365 

192-9 

219 

112-7 

268 

138-9 

317 

165-9 

366 

193-4 

220 

113-2 

269 

139-5 

318 

166-4 

367 

194-0 

221 

113-7 

270 

140-0 

319 

167-0 

368 

194-6 

222 

114-3 

271 

140-6 

320 

167-5 

369 

195-1 

223 

114-8 

272 

141-1 

321 

168-1 

370 

195-7 

224 

115-3 

273 

141-7 

322 

168-6 

371 

196-3 

225 

115-9 

274 

142-2 

323 

169-2 

372 

196-8 

226 

116-4 

275 

142-8 

324 

169-7 

373 

197-4 

227 

116-9 

276 

143-3 

325 

170-3 

374 

198-0 

228 

117-4 

277 

143-9 

326 

170-9 

375 

198-6 

229 

118-0 

278 

144-4 

327 

171-4 

376 

199-1 

230 

118-5 

279 

145-0 

328 

172-0 

377 

199-7 

231 

119-0 

280 

145-5 

329 

172-5 

378 

200-3 

232 

119-6 

281 

146-1 

330 

173-1 

379 

200-8 

233 

120-1 

282 

146-6 

331 

173-7 

380 

201-4 

234 

120-7 

283 

147-2 

332 

174-2 

381 

202-0 

235 

121-2 

284 

147-7 

333 

174-8 

382 

202-5 

236 

121-7 

285 

148-3 

334 

175-3 

383 

203-1 

237 

122-3 

286 

148-8 

335 

175-9 

384 

203-7 

238 

122-8 

287 

149-4 

336 

176-5 

385 

204-3 

239 

123-4 

288 

149-9 

337 

177-0 

386 

204-8 

240 

123-9 

289 

150-5 

338 

177-6 

387 

205-4 

241 

124-4 

290 

151-0 

339 

178-1 

388 

206-0 

242 

125-0 

291 

151-6 

340 

178-7 

389 

206-5 

243 

125-5 

292 

152-1 

341 

179-3 

390 

207-1 

244 

126-0 

293 

152-7 

342 

179-8 

391 

207-7 

245 

126-6 

294 

153-2 

343 

180-4 

392 

208-3 

246 

127-1 

295 

153-8 

344 

180-9 

393 

208-8 

247 

127-6 

296 

154-3 

345 

181-5 

394 

209-4 

248 

128-1 

297 

154-9 

346 

182-1 

395 

210-0 

249 

128-7 

298 

155-4 

347 

182-6 

396 

210-6 

250 

129-2 

299 

156-0 

348 

183-2 

397 

211-2 

251 

129-7 

300 

156-5 

349 

183-7 

398 

211-7 

252 

130-3 

301 

157-1 

350 

184-3 

399 

212-3 

253 

130-8 

302 

157-6 

351 

184-9 

400 

212-9 

254 

131-4 

303 

158-2 

352 

185-4 

401 

213-5 

§274.] 


DETERMINATION   OF   GRAPE-SUGAR,    ETC. 


745 


TABLE  FOR  CALCULATING  THE  GRAPE-SUGAR  FROM  THE  QUANTITY  OF  COPPER 
DETERMINED   BY  GRAVIMETRIC  ANALYSIS.       (Concluded.) 


Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

Copper. 
Mg. 

Grape- 
sugar. 

Mg. 

'     402 

214-1 

418 

223-3 

434 

232-8 

450 

242-2 

403 

214-6 

419 

223-9 

435 

233-4 

451 

242-8 

404 

215-2 

420 

224-5 

436 

233-9 

452 

243-4 

405 

215-8 

421 

225-1 

437 

234-5 

453 

244-0 

406 

216-4 

422 

225-7 

438 

235-1 

454 

244-6 

407 

217-0 

423 

226-3 

439 

235-7 

455 

245-2 

408 

217-5 

424 

226-9 

440 

236-3 

456 

245-7 

409 

218-1 

425 

227-5 

441 

236-9 

457 

246-3 

410 

218-7 

426 

228-0 

442 

237-5 

458 

246-9 

411 

219-3 

427 

228-6 

443 

238-1 

459 

247-5 

412 

219-9 

'428 

229-2 

444 

238-7 

460 

248-1 

413 

220-4 

429 

229-8 

445 

239-3 

461 

248-7 

414 

221-0 

430 

230-4 

446 

239-8 

462 

249-3 

415 

221-6 

431 

231-0 

447 

240-4 

463 

249-9 

416 

222-2 

432 

231-6 

448 

241-0 

417 

222-8 

433 

232-2 

449 

241-6 

b.  Determination  of  Invert-sugar. 

Although  invert-sugar  behaves  in  other  respects  just  like  grape- 
sugar  towards  alkaline  copper-sulphate  solution  containing  an 
alkali  tartrate,  its  reducing  effect,  however,  as  SOXHLET  has 
shown,  is  different  from  that  of  grape-sugar;  hence  ALLIHN'S 
tables  for  grape-sugar  cannot  be  used  for  invert-sugar,  and  a  new 
set  of  empirical  tables  must  necessarily  be  constructed.  For  such 
a  one  we  are  indebted  to  MEISSL.* 

In  the  gravimetric  process  of  determining  invert-sugar,  proceed 
exactly  in  the  manner  detailed  for  grape-sugar,  using,  however, 
the  table  on  p.  746  for  ascertaining  the  quantity  of  invert-sugar 
from  the  copper  obtained. 

Examples  in  the  Use  of  this  Table. 

The  weight  of  the  copper  =  0-175  grm.  According  to  the  table 
0-1705  Cu  =  0-09  grm.  invert-sugar;  hence  0-175-0-1705= 
0-045  Cu,  =  1*|T  invert-sugar =0-0025  grm.  invert-sugar.  Hence 
0-175  grm.  Cu= 0-09  +  0- 0025 =0-0925  grm.  invert-sugar. 

*  Zeitschrift  des  Vereins  fur  Rubenzuckerindustrie,  1879,  1034. 


746  DETERMINATION    OF   COMMERCIAL  VALUES.          [§  274. 

TABLE  FOR  SOLUTIONS  OP  PURE  INVERT-SUGAR. 


Mgrms. 
Invert-sugar. 

Mgrms. 
Reduced 
Copper. 

1  Mgrm. 
Invert-sugar 
corresponds 
with  Mgrm. 
Reduced  Cu. 

Mgrms. 
Invert-sugar. 

Mgrms. 
Reduced 
Copper. 

1  Mgrm. 
Invert-sugar 
corresponds 
with  Mgrm. 
Reduced  Cu. 

50 

96-0 

140 

259-4         ) 

55 

105-4 

145 

268-1       [ 

1-744 

60 

114-8 

1C7A 

150 

276-8       ) 

65 

124-2 

-  o/O 

155 

285-2       1 

70 

133-5 

160 

293-6 

75 

142-9 

165 

302-1    y 

1-684 

80 

152-1       1 

170 

310-5 

85 

161-3 

175 

318-9      J 

90 

170-5        V 

1-840 

180 

327-2       1 

95 

179-7 

185 

335-5 

100 

188-9       I 

190 

343-7        \ 

1-656 

105 

197-8      1 

195 

352-0 

110 

206-6 

200 

360-3       J 

115 

215-5        Se 

1-772 

205 

368-2       1 

120 

224-4 

210 

376-2 

125 

233-2       J 

215 

384-2        I 

1-592 

130 
135 

241-9       \ 
250-6       J 

1-744 

220 
225 

392-4 
400-1       J 

c.  Determination  of  Milk-sugar. 

In  the  case  of  milk-sugar,  the  degree  of  dilution,  according  to 
SOXHLET'S  experiments,  has  no  effect  on  the  reducing  action,  but 
the  quantity  of  copper  solution,  whether  smaller  or  larger,  has. 
The  latter  fact  has  also  been  confirmed  by  RODEWALD  and  TOLLENS, 
hence  the  gravimetric  determination  of  milk-sugar  must  also  be 
based  upon  proportions  empirically  ascertained.  The  following 
table  has  been  prepared  by  SOXHLET,  and  presupposes  the  carrying 
out  of  the  following  directions: 

Mix  25  c.c.  of  the  copper  solution  a,  p.  738,  and  25  c.c.  of  the 
alkaline  Rochelle-salt  solution,  6,  p.  738,  with  20  to  60  c.c.  of  an 
approximately  0-5-per  cent,  milk-sugar  solution,  and  make  up 
the  volume  to  150  c.c.  with  water.  Then  heat  to  boiling  for  6 
minutes,  collect  the  cuprous  oxide  in  an  asbestos  filter- tube,  and 
weigh  the  reduced  copper,  just  as  in  the  case  of  grape-sugar.  The 
quantity  of  milk-sugar  is  then  ascertained  from  the  weight  of  the 
copper,  by  completing  SOXHLET'S  table  by  interpolating: 


274.]  DETERMINATION   OF   GRAPE-SUGAR,    ETC.  747 


Weight  of  Copper 

in  Mgrms.  Sugar  in  Mgrms> 

392-7  ........  co  ............................  300 

363-6,  .....................................  275 

333-0  ......................................  250 

300-8  ........  o.o  ..........................  225 

269-6  .........  o  ...........................  200 

237-5  ......  o  ..............................   175 

204-0  ......  .  ..............................   150 

171-4...  .............  ,  ....................   125 

138-3  ................  o  ....................   100 

If  the  milk-sugar  in  milk  is  to  be  determined,  first  precipitate 
the  albumin  (and  fat)  by  means  of  cuprous  sulphate  and  caustic- 
potassa  solution  in  the  manner  described  by  RITTHAUSEN.*  For 
this  purpose  dilute  25  c.c.  milk  with  400  c.c.  water,  add  10  c.c. 
of  the  cuprous-sulphate  solution  described  on  p.  738  (and  containing 
34-669  grm.  in  500  c.c.).  then  add  6-5  to  7-5  c.c.  of  a  potassa  lye 
of  such  strength  that  one  volume  will  exactly  precipitate  the 
copper  from  one  volume  of  copper  solution.  The  liquid  must  still 
have  an  acid  reaction  after  the  alkali  has  been  added,  and  may 
contain  some  dissolved  copper.  Now  make  up  the  liquid  to  500  c.c. 
and  filter  through  a  dry,  folded  filter.  Mix  100  c.c.  of  the  approx- 
imately 0-25-per  cent,  milk-sugar  solution  with  25  c.c.  of  the 
alkaline  Rochelle-salt  solution  and  25  c.c.  of  the  cuprous-sulphate 
solution  (p.  738)  in  a  beaker,  cover  the  latter,  place  on  a  double- 
wire  gauze,  and  heat  to  boiling.  After  boiling  for  six  minutes, 
filter,  and  proceed  as  described  above.  Assuming  with  SOXHLET 
that  0-294  grm.  copper  is  obtained,  this  would  correspond  with 
0-2236  grm.  milk-sugar. 

d.  Determination  of  Maltose. 

As,  according  to  SOXHLET'  s  investigations,  an  excess  of  undiluted 
PEHLING'S  solution  (but  only  when  undiluted)  does  not,  as  hi  the 

*  Journ.  /.  prakt.  Chem.,  N.  S.,  xv,  332. 


748  DETERMINATION   OF   COMMERCIAL  VALUES.         [§  274. 

case  of  other  sugars,  increase  the  reducing  action  of  maltose,  and  as 
hence  a  definite  quantity  of  maltose  reduces  the  same  quantity  of 
cupric  oxide,  irrespective  of  the  quantity  of  the  copper  excess  present^ 
the  gravimetric  determination  of  maltose  is  simpler  than  that  of  the 
other  sugars,  because,  when  an  approximately  1-per  cent,  maltose 
solution  is  used,  only  one  relation  has  to  be  considered,  namely,  that 
determined  by  SOXHLET,  i.e.,  113  of  copper  =100  of  anhydrous 
maltose,  CuHttOn.  In  carrying  out  the  determination,  the  oper- 
ator need  only  observe  that  the  mixture  of  equal  volumes  of  the 
cupric-sulphate  solution  a  and  of  alkaline  Rochelle-salt  solution  6, 
p.  738,  be  used  undiluted,  and  in  excess.  The  liquids  are  mixed  cold, 
then  boiled  for  four  minutes,  and  filtered  (see  Grape-sugar). 

A  passing  glance  at  the  literature  on  the  subject  suffices  to  show 
that,  besides  the  above-named  investigators,  many  others  have 
worked  with  modifications  of  FEHLING'S  test.  The  variations  are 
confined  in  part  to  the  preparation  of  the  copper  solution,  and  in 
part  to  the  manner  of  determining  the  precipitated  cuprous  oxide. 
Regarding  the  former  point,  I  would  mention  the  work  by  J.  LOWE,* 
who  recommends  a  glycerinic  cupric-soda  solution;  those  of  LA- 
GRANGE  t  and  of  DEGENER,J  who  give  preference  to  solutions  of 
cupric  tartrate  in  caustic-soda  solutions,  and  prepared  in  different 
ways;  and  that  of  PAVY,§  who  employs  a  FEHLING'S  solution  to 
which  ammonia  is  added.  Regarding  the  latter  point,  however,  I 
would  mention  the  work  of  FR.  MOHR;||  who  collects  the  cuprous 
oxide  and  dissolves  it  in  a  solution  of  acid  ferric  sulphate,  and 
determines  the  ferrous  sulphate  formed  with  potassium  perman- 
ganate; that  of  W.  PILLITZ,!"  who  replaces  the  ferric  sulphate  by  a 
solution  of  sodium  chloride  in  diluted  sulphuric  acid,  and  oxidizes 

*  Zeitschr.  f.  analyt.  Chem,,  ix,  20,  and  x,  452. 
f  Compt.  rend.,  1874,  1005;  Zeitschr.  f.  analyt.  Chem.,  xv,  111. 
J  Zeitschrift  des  Vereins   fur  Rubenzuckerindustrie,  xviu,  349,  and  xix, 
736;  Zeitschr.  f.  analyt.  Chem.,  xxu,  444. 

§  Chem.  News,  xxxix,  77;  Zeitschr.  f.  analyt.  Chem.,  xix,  98. 
II  Zeitschr.  f.  analyt.  Chem.,  xn,  296. 
IT  Ibid.,  xvi.  48. 


§  275.]  DETERMINATION  OF   GRAPE-SUGAR,   ETC.  749 

the  cuprous  oxide  directly  with  permanganate ;  of  FR.  WEIL,*  who 
titrates  the  residual  excess  of  cupric  oxide  in  the  solution  with 
stannous-chloride  solution  (see  Vol.  I,  p.  380,  d)  and  thus  finds  the 
cuprous  oxide  from  the  difference;  that  of  HOLDEFLEISS  f  and  of 
GRATAMA,{  who  convert  the  cuprous  oxide  collected  into  cupric 
oxide  by  means  of  nitric  acid;  and  that  of  ARNOLD,§  who  dissolves 
the  cuprous  oxide  in  nitric  acid  and  determines  it  by  VOLHARD'S 
method  (p.  628  this  volume). 

These  modifications,  however,  offer  no  advantages,  and  all  those 
that  require  filtration  of  the  excess  of  FEHLING'S  solution  through 
paper  have  the  disadvantage  besides,  that  the  filter-paper  retains 
some  copper,  the  quantity  of  which  varies  according  to  the  con- 
centration and  copper  content  of  the  solution. 

B.  METHODS  BASED  UPON  THE  REDUCTION  OF  MERCURY 
COMPOUNDS. 

§275. 

On  this  basis  three  methods  are  founded: 

1.  KNAPP'S;||  2,  SACHSSE'S  ;  1"  and  3,  H ACER'S,**  of  which  the 
first  two  have  been  repeatedly  and  critically  studied,  particularly 
.by  SoxHLET.ft 

1.  KNAPP'S  Method. 

This  was  employed  by  KNAPP,  at  the  suggestion  of  LIEBIG,  for 
the  quantitative  determination  of  grape-sugar.  The  mercury 
solution  required  is  obtained  by  dissolving  10  grm.  pure,  dry  mer- 
curic cyanide  in  water,  adding  100  c.c.  of  caustic-soda  solution 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  284. 
f  Landwirthschaftl.  Jahrbiicher,  1877,  Suppl.  Heft. 
j  Zeitschr.  f.  analyt.  Chem.,  xvii,  155. 
§  Ibid.,  xx,  231. 

H  Annal.  d.  Chem.  u.  Pharm.,  CLIV,  252;    Zeitschr.  f.  analyt.  Chem.t  ix,  395. 
f  Pharmaceut.  Zeitschr.  f.  Russland,  1876,  549 ;  Zeitschr.  f.  analyt.  Chem., 
xvi,  121. 

**  Pharm.  Centralhalle,  xvm,  313;  Zeitschr.  f.  analyt.  Chem.,  xvn,  380. 
tf  Journ.  f.  prakt.  Chem.  [2],  xxi,  300;  Zeitschr.  f.  analyt.  Chem.,  xx,  447. 


750  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  275^ 

of  1  •  145  sp.  gr.,  and  diluting  to  measure  1000  c.c.  The  sugar 
solution  employed  should  have  a  strength  of  about  0  •  5-per  cent. 

As,  according  to  BRUMME'S  *  observation,  confirmed  by  SOXH- 
LET,  the  reducing  effect  of  sugar  is  greater  when  the  sugar  solu- 
tion is  added  all  at  once,  and  less  when  added  in  separate  portions, 
KNAPP'S  method  in  its  original  form,  in  which  the  sugar  solution 
is  gradually  added  to  the  boiling  mercury  solution  until  all  the 
mercury  has  been  precipitated,  does  not  give  satisfactory  results 
according  to  SOXHLET.  Concordant  and  accurate  results  may  be 
obtained,  however,  according  to  him,  by  proceeding  in  a  manner 
analogous  to  that  employed  in  his  modification  of  FEHLING'S 
method,  i.e.,  when  the  whole  of  the  sugar  solution  (whether  in  0  •  5- 
or  1-per  cent,  solution  is  quite  immaterial)  is  added  all  at  once  to 
the  mercury  solution — most  conveniently  to  100  c.c. — the  liquid 
boiled  for  two  or  three  minutes,  then  tested  as  to  whether  it  still 
contains  any  mercury,  and  then  making  other  tests  with  fresh 
portions  of  the  mercury  solution  and  larger  or  smaller  quantities  of 
sugar  solution,  until  two  experiments  are  made  in  which  the  quan- 
tities of  sugar  contained  differ  but  very  little,  -one  of  which  con- 
tains, however,  a  slight  quantity  of  mercury,  the  other  being  free 
from  it. 

To  determine  the  quantity  of  dissolved  mercury  the  reaction 
introduced  by  SACHSSE  is  to  be  usually  recommended.  It  consists 
in  removing  a  few  drops,  or  towards  the  end,  about  5  c.c.  of  the 
liquid  above  the  precipitated  mercury,  and  mixing  it  in  a  small 
porcelain  dish  with  an  alkaline  stannous-oxide  solution.  If  fairly 
large  quantities  of  mercury  are  present,  a  black  precipitate  forms; 
if  very  small  quantities,  a  brown  color  only  develops.  The  alka- 
line stannous-oxide  solution  is  made  simply  by  supersaturating  a 
stannous-chloride  solution  with  caustic-soda  solution.  HAAS  f 
recommends  to  filter  the  solution  to  be  tested  for  mercury  through 
a  triple  filter. 

By  operating  in  this  manner,  the  following  relations,  according 
to  SOXHLET,  are  to  be  recognized  as  existing  between  KNAPP'S 

*  Zeitschr.  f.  analyt.  Chem.,  xvi,  12 le 
f  Ibid.,  xxn,  216. 


§  275.]  DETERMINATION   OF   GRAPE-SUGAR,    ETC.  751 

solution  and  the  various  sugars,  and  should  be  used  in  calculating. 
100  c.c.  KNAPP'S  solution  are  reduced  by  the  following  quantities 
of  sugar  when  a  0-5-per  cent,  sugar  solution  is  employed: 

Grape-sugar,  CeH^Oe 202  mgnn. 

Invert-sugar,  C^Oe 200      " 

Levulose,  C^Oe 198      " 

Maltose,  C^H^ 308      " 

Milk-sugar,  C^H^On  •  H2O 311      " 

Accurate  results  may,  however,  also  be  obtained  by  adding 
0-5-  to  1-per  cent,  sugar  solutions  gradually,  according  to  WORM 
MULLER  and  J.  HAGEN,*  and  more  recently  confirmed  by  further 
investigations  by  WORM  MULLER  f  and  J.  G.  OTTO.t  They  advise 
the  following  procedure:  For  a  1-per  cent,  sugar  solution  take 
100  c.c.,  or  for  a  0-5-per  cent,  take  50  c.c.,  of  KNAPP'S  solution, 
dilute  it  with  three  to  four  volumes  of  water,  heat  to  boiling,  add 
the  sugar  solution,  the  larger  bulk  in  portions  of  about  2  c.c.  each,, 
and  boil  for  one-half  to  one  minute  between  each  addition.  W. 
MULLER  employs  the  end  reaction  used  by  PILLITZ,§  but  OTTO 
employs  that  recommended  by  LENSSEX.|| 

Operating  in  the  manner  stated,  the  above-named  chemists 
confirmed  the  relation  of  reducing  power  stated  by  KNAPP,  in 
which  100  c.c.  of  KNAPP'S  solution  correspond  to  0-25  grm.  grape- 
sugar,  while  on  the  other  hand  SOXHLET'S  results  were  also  con- 
firmed when  operating  according  to  his  method. 

2.  R.  SACHSSE'S  Method. 

An  alkaline  solution  of  mercuric  iodide  serves  as  the  mercury 
solution  in  this  method.  It  is  prepared  by  dissolving  on  the  one 

*  PFLUGER'S  Archiv  fur  die  gesammte  PhysioL,  xvi,  569  and  590,  and 
xxin,  220. 

f  Journ.  f.  prakt.  Chem.  [2],  xxvi,  78. 

t  Ibid.,  xxvi,  87. 

§  Zeitschr.  f.  analyt.  Chem.,  x,  459.  PILLITZ  places  a  drop  of  the  solution 
on  a  piece  of  Swedish  filtering-paper  and  exposes  the  spot  first  to  the  vapors 
of  hydrochloric  acid,  and  then  to  hydrogen  sulphide. 

H  Zeitschr.  f.  analyt.  Chem.,  ix,  455.  LENSSEN  acidulates  a  filtered 
sample  with  acetic  acid  and  tests  for  mercury  with  hydrogen  sulphide. 


752  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  275. 

hand  18  grm.  of  pure,  dried  mercuric  iodide  with  25  grm.  potas- 
sium iodide  in  water,  and  on  the  other  dissolving  80  grm.  caustic 
potassa  in  water.  The  latter  solution  is  added  to  the  former,  and 
the  whole  diluted  to  1000  c.c.  According  to  SACHSSE  the  sugar 
solution  should  be  added  in  portions  to  the  boiling  mercury  solu- 
tion until  all  the  mercury  is  precipitated.  As,  however,  SOXHLET 
found  that  titrations  made  by  adding  the  sugar  solution  gradually 
and  in  portions  give  results  which  differ  from  those  obtained  when 
all  the  sugar  solution  is  added  at  once,  it  is  necessary,  in  order 
to  obtain  exact  results,  to  proceed  in  the  same  manner  when 
using  SACHSSE'S  mercury  solution  as  prescribed  by  SOXHLET  for 
KNAPP'S  solution. 

It  is  noteworthy  that  the  action  of  sugar  solution  when  added 
gradually  or  all  at  once  is  quite  different  in  KNAPP'S  and  SACHSSE'S 
methods.  In  the  former,  when  the  sugar  solution  is  added  gradu- 
ally, more  sugar  is  required  to  effect  reduction,  and  in  the  latter, 
less.  This  must,  of  course,  be  taken  into  consideration  when 
determining,  from  the  preliminary,  the  quantity  of  sugar  solution 
with  which  it  is  advisable  to  begin  the  actual  experiment. 

In  carrying  out  SACHSSE'S  method  it  must  be  further  borne  in 
mind  that  the  reducing  action  of  sugar  differs  according  as  a 
1-per  cent,  or  0-5-per  cent,  solution  is  used.  Hence  a  concen- 
tration of  0-5-per  cent,  must  not  be  appreciably  departed  from. 

In  operating,  it  is  convenient  to  employ  100  c.c.  of  SACHSSE'S 
solution ;  the  boiling  should  be  continued  for  two  or  three  minutes, 
and  the  test  for  any  mercury  present  in  the  solution  made  with 
alkaline  stannous-oxide  solution. 

Under  the  conditions  determined  by  SOXHLET  the  relation 
between  SACHSSE'S  solution  and  the  different  sugars  is  as  below. 

100  c.c.  of  SACHSSE'S  solution  are  reduced  by  the  following 
quantities  of  sugar  when  in  0'5-per  cent,  solution: 

Grape-sugar,  CflH12O6 325  mgrm. 

Invert-sugar,  C6H12Ofl 269     " 

Levulose,  C6H12Ofl 213     " 

Maltose,  C^H^Ou 491     " 

Milk-sugar,  C12H22On  •  I^O 387     " 


§  275.]  DETERMINATION    OF    GRAPE-SUGAR,    ETC.  753 

With  reference  to  both  of  the  methods  based  upon  the  precipi- 
tation, it  must  be  remarked  that  the  values  obtained  by  SOXHLET 
hold  good,  of  course,  for  sugars  in  a  perfectly  pure  state.  With 
such,  uniform  results  will  be  obtained  by  using  the  empirically 
found  values  under  the  given  conditions,  whether  FEHLING'S, 
KNAPP'S,  or  SACHSSE'S  method,  as  modified  by  SOXHLET,  is  em- 
ployed. The  case  is  different,  however,  if  the  various  methods 
are  employed  with  sugar  solutions  which — as  for  example  com- 
mercial grape-sugar — contain  products  intermediate  between 
dextrin  and  grape-sugar,  or  as  wine  extract  which  contains 
glycerin,  as  both  the  latter  as  well  as  the  intermediate  products 
reduce  mercury  solutions  (at  least  HAAS  found  this  to  be  the  case 
in  SACHSSE'S  method),  but  not  FEHLING'S  copper  solution.* 
When  SACHSSE'S  method  is  hence  employed  with  such  impure 
sugar  solutions  (and  this  is  probably  true  with  KNAPP'S  method), 
the  results  obtained  are  too  high.  It  is  therefore  decidedly  pref- 
erable to  make  use  of  SOXHLET'S  modification  of  FEHLING'S 
method  for  determining  the  sugar  in  such  cases. 

3.  H.  H  ACER'S  Gravimetric  Method. 

Up  to  the  present  time  this  method  has  been  proposed  only  for 
determining  grape-sugar,  and,  so  far  as  I  am  aware,  has  not  yet 
been  tested  for  other  sugars. 

A  solution  made  as  follows  serves  as  the  reagent:  Triturate 
30  grm.  mercuric  oxide  with  30  grm.  sodium  acetate,  transfer  to  a 
flask,  add  25  grm.  concentrated  acetic  acid  (or  100  c.c.  diluted 
acetic  acid  of  1-04  sp.  gr.),  then  add  50  grm.  sodium  chloride  and 
sufficient  warm  water  to  make  up  to  1000  c.c.  Solution  is  facili- 
tated by  shaking  and  gently  warming.  When  cold,  filter  the 
liquid  and  preserve  it  in  a  cool  place  protected  from  light. 

To  determine  the  sugar,  introduce  the  sugar  solution  together 
with  an  excess  of  the  mercury  solution  (about  200  c.c.  of  the  mer- 
cury solution  should  be  used  for  every  gramme  of  grape-sugar)  into 
a  glass  flask  provided  with  a  perforated  cork  carrying  a  glass  tube 

*  HAAS  states  that  2-1618  grm.  glycerin  reduces  20  c.c.  of  SACHSSE'S 
mercury  solution. 


754  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  276. 

about  15  cm.  long,  and  heat  the  flask  either  in  a  water-bath  or 
over  the  naked  flame  for  from  one  to  two  hours,  taking  care  that 
the  liquid  always  remains  acid.  In  proportion  as  the  sugar  acts 
mercurous  chloride  precipitates.  The  reaction  is  complete  when  a 
small  portion  of  the  clear  liquid,  because  of  the  presence  of  some 
mercuric  acetate,  is  rendered  turbid  by  ammonia,  while  the  filtrate 
remains  clear  on  further  boiling.  Collect  the  precipitated  mer- 
curous chloride  on  a  filter  dried  at  100°  and  weighed,  wash  it. 
first  with  5-per  cent,  hydrochloric  acid,  then  with  water,  and 
finally  with  alcohol,  then  dry  on  the  water-bath  and  weigh.  As, 
according  to  HAGER,  2  equivalents  of  grape-sugar  (2X180-096  = 
360-192)  decompose  9  equivalents  of  mercuric  oxide  (9X216  = 
1944),  yielding  4J  equivalents  of  mercuous  chloride  (4^Hg2Cl2  = 
4^X470-90=2119-05),  it  follows  that  1  grm.  of  grape-sugar, 
CcH12Oti,  is  represented  by  5-883  grm.  of  mercurous  chloride, 
Hg2Cl, 

The  acid  solution  of  mercuric  acetate  containing  sodium 
chloride  does  not  act  upon  cane-sugar,  glycerin,  gum  arabic, 
dextrin,  or  uric  acid,  but  it  does  act  upon  other  constituents  of 
urine,  hence  the  method  is  not  applicable  for  the  determination  of 
sugar  in  diabetic  urine. 

C.  METHOD  BASED  UPON  THE  DECOMPOSITION  OF  SUGAR  BY 
ALCOHOLIC  FERMENTATION.* 
§276. 

1.  When  a  liquid  containing  grape-sugar  and  some  ferment  or 
yeast  is  exposed  to  a  suitable  temperature  it  undergoes  alcoholic 
fermentation.  It  was  formerly  believed  that  1  equivalent  of  the 
anhydrous  grape-sugar  yielded  2  equivalents  of  alcohol  and  2 
equivalents  of  carbon  dioxide,  thus:  C6H12O6  =  2(C2H6O)  +  2CO2. 

According  to  this  assumption  48-86  parts  of  carbon  dioxide 
would  correspond  with  100  parts  of  anhydrous  grape-sugar.  PAS- 
TEUR^ however,  has  shown  that  this  assumption  is  incorrect,  as 

*  Compare  KROCKER,  "Ueber  die  Bestimmung  des  Starkemehlgehaltes 
in  vegetabilishchen  Nahraingsmitteln,"  Annal.  d.  Ghent,  u.  Pharm.,  LVIII,  212. 
f  Compt.  rend.,  XLVIII,  1149;  Journ.  /.  prakt.  Chem.,  LXXXV,  465. 


§  276.]  DETERMINATION    OF   GRAPE-SUGAR,   ETC.  755 

during  the  alcoholic  fermentation  a  number  of  other  products  are 
formed  from  the  elements  of  sugar,  namely,  glycerin,  succinic  acid, 
cellulose,  and  fats,  and  also  very  small  quantities  of  other  sub- 
stances, the  formation  of  which  was  already  known,  e.g.,  amyl 
alcohol,  butyl  alcohol,  etc. 

If,  therefore,  the  quantity  of  carbon  dioxide  evolved  during  the 
alcoholic  fermentation  is  to  serve  for  the  determination  of  the  sugar 
decomposed,  the  determination  cannot  be  made  by  calculation,  but 
must  be  made  from  the  practical  results  obtained  by  experiments. 
As,  however,  the  quantity  of  the  individual  decomposition  products 
is  by  no  means  a  constant  one,  it  may  be  easily  seen  that  the  method 
of  determining  sugar  from  the  carbon  dioxide  evolved  during  alco- 
holic fermentation  can  make  no  claim  to  absolute  accuracy. 
According  to  PASTEUR'S  experiments  (loc.  tit.),  of  100  parts  of  grape- 
sugar  95  parts  are  decomposed,  as  in  the  above  equation,  into  alco- 
hol and  carbon  dioxide;  the  balance  of  the  sugar  decomposes  into 
2-5  to  3-6  glycerin,  0-4  to  0-7  succinic  acid,  0-6  to  0-7  carbon 
dioxide,  and  1-2  to  1-5  cellulose,  fat,  and  other  still  undetermined 
substances.  Consequently  we  shall  not  depart  very  far  from  the 
truth  if  we  assume  every  47  parts  of  carbon  dioxide  obtained  by 
alcoholic  fermentation  to  represent  100  parts  of  anhydrous  grape- 
sugar. 

2.  To  determine  the  carbon  dioxide  evolved  during  the  fer- 
mentation, the  apparatus  shown  on  p.  494,  Fig.  97,  Vol.  I,  may  be 
employed,  omitting  the  copper-sulphate  pumice  tube,  I,  and  taking 
care  that  the  tubes  n  and  o  contain  a  sufficient  quantity  of  soda- 
lime  to  surely  retain  all  the  carbon  dioxide  evolved.  If  it  is  desired 
to  determine  the  carbon  dioxide  from  the  loss  in  weight  of  the  appa- 
ratus, employ  a  flask  arranged  as  shown  in  A,  Fig.  93,  p.  489,  Vol.  I. 
In  order  to  prevent  the  liquid  from  returning  backwards,  replace 
the  flask  B  by  a  U-tube  filled  with  pumice-stone  saturated  with 
sulphuric  acid.  The  quantity  of  sulphuric  acid  must  be  so  adjusted 
that  the  bend  of  the  U-tube  may  be  just  closed  by  the  liquid.  The 
outer  limb  of  the  U-tube  is  connected  with  a  calcium-chloride  tube 
(not  weighed  with  the  apparatus),  so  that  the  sulphuric  acid  hi  the 
U-tube  may  not  absorb  moisture  from  the  atmosphere. 


756  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  276. 

3.  Take  of  the  saccharine  liquid  a  quantity  which  will  contain 
about  2  to  3  grm.  anhydrous  sugar.     If  much  more  is  taken,  the 
fermentation  takes  too  long,  while  if  much  less  is  taken,  the  deter- 
mination, will  be  inaccurate — at  least  if  the  carbon  dioxide  is  deter- 
mined from  the  loss  in  weight — because  then  the  volume  of  the 
evolved  carbon  dioxide  will  be  too  small. 

4.  As  regards  the  concentration  of  the  liquid,   the  solution 
should  contain  about  4  or  5  parts  of  water  to  1  part  of  sugar ;  when 
solutions  are  more  dilute,  they  should  therefore  be  concentrated  by 
evaporation  on  the  water-bath. 

5.  Introduce  the  sugar  solution  into  the  flask,  add  a  few  drops 
of  tartaric-acid  solution,  and  a  comparatively  large,  weighed  por- 
tion of  washed  yeast,  say  20  grm.  fresh,  or  a  corresponding  quantity 
of  pressed  yeast.     As  yeast  itself  also  generally  evolves  some  carbon 
dioxide,  a  parallel  experiment  may  be  made  at  the  same  time  with 
a  larger,  weighed  quantity  of  the  yeast  in  a  similar  apparatus,  in 
order  to  determine  the  carbon  dioxide  it  evolves,  and  to  be  thus 
able  to  allow  for  that  evolved  by  the  20  grm.  of  yeast. 

6.  When  the  apparatus  has  been  arranged  and  the  weight  taken, 
place  it,  or  the  flask  containing  the  sugar  solution  and  yeast,  in  a 
place  where  a  fairly  constant  temperature  of  25°  is  maintained. 
Fermentation  soon  sets  in,  and  is  rapid  at  first,  but  slackens  later 
on,  becoming  slower  and  slower.     When  bubbles  of  gas  are  no 
longer  formed,  which  is  the  case  in  four  or  five  days,  the  process  is 
complete.     Then  heat  the  flask  to  100°,  exhaust  the  carbon  dioxide 
still  remaining  in  the  flask,  allow  to  cool,  and  weigh.     The  increase 
of  weight  of  the  carbonic-acid  apparatus,  or  the  loss  in  weight  of  the 
fermentation  apparatus  and  drying  tube,  corresponds  to  the  carbon 
dioxide  evolved.     For  every  47  parts  of  carbon  dioxide  found  cal- 
culate, as  above  stated,  100  parts  of  anhydrous  grape-sugar. 


§  277.]  DETERMINATION   OF   GRAPE-SUGAR,    ETC.  757 

D.  DETERMINATION  OF  CANE-SUGAR,  DEXTRIN,  AND  STARCH.* 

§277. 

1.    CANE-SUGAR. 

Cane-sugar  is  usually  determined  optically  or  araeometrically- 
(see  p.  731  this  volume). f  Of  the  other  methods  the  inversion- 
method  particularly,  and  hi  many  cases  also  the  fermentation, 
method,  is  well  adapted. 

a.  The  inversion  is  as  a  rule  most  simply  effected  by  heating  the- 
cane-sugar  with  very  dilute  hydrochloric  acid.  The  most  favorable^ 
proportions  were  ascertained  by  NICOL,{  and  hi  the  main  confirmed. 
by  SOXHLET.§ 

NICOL  recommends  to  dissolve  1-25  grm.  of  sugar  in  200  c.c.. 
water  hi  a  250-c.c.  flask,  add  10  drops  of  hydrochloric  acid  of  1- 11 
sp.gr.,  and  to  heat  on  a  water-bath  for  half  an  hour  at  100°.  Then 
neutralize  the  liquid  with  sodium  carbonate,  fill  the  flask  to  the 
mark  with  water,  and  thoroughly  mix  the  liquid.  If  the  heating 
is  continued  for  a  longer  period,  a  part,  although  only  a  very  small 
one,  of  the  in  vert-sugar  is  decomposed;  and  this  will  hence  lower 
the  reducing  action  of  the  solution  somewhat.  According  to  SOXH- 
LET,  for  example,  on  heating  for  an  hour  and  a  half  the  propor- 
tion will  be  100:  99-3.||  The  latter  recommends  for  the  purpose  of 
conversion  the  following  proportions  which,  if  pure,  dry  sugar  is: 
used,  are  adapted  for  yielding  a  solution  of  invert-sugar  100  c.c.  of 
which  contain  exactly  1  grm.  or  0-5  grm.  of  invert-sugar:  Dissolve 

*  See  also  Appendix  I,  Section  III. 

f  Regarding  the  optical  determination  of  cane-sugar  in  the  presence  of 
other  sugars  or  the  ordinary  carbohydrates,  see  CLERGET  (Annales  de  chim. 
et  de  Phys.  [3],  xxvi,  175);  H.  REICHARDT  and  C.  BITTMANN  (Zeitschr.  des 
Vereins  f.  d.  Rubenzuckerindustrie,  1882,  764) ;  S.  CASAMAJOR  (Chem.  News, 
XLV,  150);  K.  ZULKOWSKY  (Ber.  der  osterr.  Gesellsch.  zur  Forderung  der  chem. 
Industrie,  n,  1883) ;  J.  KJELDAHL  (Meddelelser  fra  CARLSBERG  Laboratoriet 
Part.  3,  Copenhagen,  H.  HAGERUP);  also  Zeitschr.  /.  analyt.  Chem.,  xxii, 
588,  Part  4. 

t  Zeitschr.  f.  analyt.  Chem.,  xiv,  177. 

§  Journ.  f.  prakt.  Chem.  [2],  xxi,  228. 

II  Ibid.  [2],  xxi,  235. 


758  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  277. 

9-5  grm.  cane-sugar  in  700  c.c.  of  hot  water,  add  100  c.c.  one-fifth- 
normal  hydrochloric  acid  (containing  0-729  HC1),  heat  for  30  min- 
utes on  a  water-bath  at  100°,  accurately  neutralize  with  standard 
caustic-soda  solution,  and  make  up  the  volume  to  either  1000  c.c. 
or  2000  c.c.  In  either  of  the  solutions  thus  obtained  then  determine 
the  invert-sugar  volumetrically  according  to  SOXHLET'S  method,  or 
gravimetrically  according  to  MEISSL'S  method,  pp.  738  and  745  this 
volume,  and  for  every  100  parts  of  invert-sugar,  C6H1206,  calculate 
95  parts  of  cane-sugar,  C^H^On. 

If  the  method  is  to  be  employed  for  determining  the  sugar  in 
beet-juice,  in  the  aqueous  extract  of  the  residue  left  after  extraction, 
etc.,  add  first  some  lead  acetate  to  the  weighed  or  measured  quan- 
tity of  the  liquid  until  a  precipitate  no  longer  forms,  then  filter, 
remove  the  excess  of  lead  by  means  of  sodium  sulphate,  and  then 
invert  the  sugar  by  heating  with  hydrochloric  acid. 

If  it  is  feared  that  other  substances  present  besides  sugar  may 
be  converted,  by  heating  with  hydrochloric  acid,  into  products 
which  also  reduce  FEHLING'S  solution,  e.g.,  dextrin  into  grape- 
sugar,  effect  the  conversion  by  J.  K  ELDAHL'S  method*  with 
invertin  (the  inverting  ferment  of  yeast).  The  invertin  is  em- 
ployed in  the  form  either  of  an  aqueous  extract  of  the  previously 
well- washed  yeast,  or  as  a  mixture  of  the  well-washed  yeast  with 
a  little  of  an  alcoholic  solution  of  thymol,  the  addition  of  which 
completely  checks  the  fermentative  power  of  the  yeast,  while  it 
is  entirely  without  influence  on  the  invertin. 

Invertin  easily  and  completely  changes  cane-sugar  into  invert^ 
sugar  without  acting  on  most  of  the  other  carbohydrates,  f  The 
most  favorable  temperature  is  between  52°  and  56°.  The  presence 
of  salts  of  the  alkalies  hinders  the  action  of  invertin,  while  smol1 
quantities  of  acid  increase  it. 

If  cane-sugar  is  to  be  determined  in  the  presence  of  grape-sugar, 
the  latter  is  determined  in  a  separate  portion  of  the  solution  by 

*  Meddelelser  fra  CARLSBERG  Laboratoriet,  Copenhagen,  H.  HAGERUP, 
1881,  339,  and  189;  Zeitschr.  f.  analyt.  Chem.,  xxn,  588. 

•j-  With  the  exception  of  a  few  sugars  which  but  rarely  occur,  synanthrose 
is  the  only  one  which  is  changed  by  invertin. 


§  277.]  DETERMINATION  OF   GRAPE-SUGAR,    ETC.  759 

SOXHLET'S  volumetric  method  (p.  738  this  volume).  An  equal 
quantity  of  the  solution  is  then  inverted  in  the  manner  above 
detailed  by  heating  with  hydrochloric  acid  or  by  means  of  in- 
vertin.  In  this  solution  there  will  then  be  found  all  the  invert- 
sugar  from  the  cane-sugar,  together  with  the  unchanged  grape- 
sugar.  The  quantity  of  FEHLING'S  copper  solution  reduced  by 
the  solution  is  now  ascertained  by  SOXHLET'S  method,  and  the 
quantity  corresponding  to  that  required  for  the  grape-sugar  de- 
ducted from  the  total;  the  difference  gives  the  quantity  corre- 
sponding to  the  invert-sugar.  Finally  calculate  95  parts  of  cane- 
sugar  for  every  100  parts  of  invert-sugar  found. 

In  a  similar  manner  cane-sugar  may  be  determined  in  ike  presence 
of  invert-sugar.  KJELDAHL.  (loc.  cit.},  employing  inversion  with 
invertin,  determined  in  this  manner  cane-sugar  not  only  in  the 
presence  of  grape-sugar  and  invert-sugar,  but  also  in  the  presence 
of  maltose,  dextrin,  and  inulin. 

This  method  presupposes  that  cane-sugar  when  present  is 
without  effect  on  the  reducing  action  of  grape-  or  invert-sugar,  an 
-assumption  which  SOXHLET  admitted  in  view  of  the  short  time 
the  boiling  is  continued  in  his  process  of  determining  sugar;  but 
according  to  MEISSL'S  experiments  this  assumption  is  not  abso- 
lutely correct.  At  all  events  it  holds  good  only  for  SOXHLET'S 
method,  but  in  no  way  for  the  gravimetric  processes  for  deter- 
mining invert-sugar  (and  also  grape-sugar).  Nevertheless  in 
order  to  render  possible  a  gravimetric  determination  of  invert- 
sugar  in  the  presence  of  cane-sugar,  MEISSL  *  has  prepared  a 
special  table  in  which  allowance  is  made  for  the  influence  of  cane- 
sugar.  This  table  was  subsequently  still  further  extended  by 

ZuLKOWSKY.f 

6.  Fermentation  Method. — The  method  detailed  on  p.  754  this 
volume,  for  determining  sugar  from  the  carbon  dioxide  evolved 
during  alcoholic  fermentation,  may  also  be  employed  for  cane- 
sugar.  The  fermentation  of  the  latter  is  more  difficult  to  effect 

*  Zeitschr.  des  Vereins  f.  Riibenzuckerindustrie,  1879,  1034. 
•j-  Bericht  der  osterreich.  Gesettsch.  zur  Forderung  der  chemisch.  Industr.,  n, 
1883. 


760  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  277. 

than  that  of  grape-sugar,  hence  a  larger  quantity  of  yeast  must 
be  taken. 

This  acts  by  the  ferment  in  it,  invertin,  first  inverting  the  cane- 
sugar;  then  the  dextrose  ferments,  and  later  the  levulose.  The 
products  of  the  fermentation  of  cane-sugar  are  the  same  as  in 
the  case  of  grape-sugar.  For  49  parts  of  carbon  dioxide  calculate 
100  parts  of  cane-sugar.  The  number  49  is  the  average  of  the 
values  48-889  and  49-20,  directly  determined  by  BALLING  and 
PASTEUR. 

2.   DEXTRIN  AND  STARCH. 

Of  the  various  methods  which  may  be  used  for  determining 
dextrin  and  starch  only  those  based  upon  the  conversion  of  these 
into  grape-sugar  will  be  here  described.  The  conversion  was 
formerly  effected  by  the  aid  of  sulphuric  acid  in  pressure-flasks 
on  a  salt-bath  (MuscuLus),  or  in  sealed  tubes  (PILLITZ*).  The 
object  may,  however,  be  effected  more  simply  and  completely 
by  heating  with  hydrochloric  acid.  R.  SACHSSE  f  recommends 
for  this  purpose  the  following  method :  Heat  2  •  5  to  3  grm.  of  starch 
in  a  flask  with  200  c.c.  of  water  and  20  c.c.  of  hydrochloric  acid  of 
1  •  125  sp.  gr.,  on  a  water-bath  maintained  briskly  boiling  for  three 
hours,  under  a  reflux  condenser.  According  to  SACHSSE  the  con- 
version is  then  complete,  i.e.,  no  change  in  the  proportions,  whether 
of  water,  acid,  time,  or  heat,  will  produce  more  dextrose  from  a 
given  weight  of  starch  than  will  be  afforded  by  adhering  to  the 
above  rules.  When  through  heating,  filter,  almost  completely 
neutralize  with  caustic-soda  solution  (alkalinity  must  be  avoided), 
dilute  to  500  c.c.,  and  in  a  portion  then  determine  the  grape-sugar 
formed,  either  volumetrically  or  gravimetrically,  and  for  every 
1080  parts  of  grape-sugar  found  calculate  990  parts  of  starch,  i.e., 
for  every  100  parts  of  grape-sugar  91-67  parts  of  starch.  This 

*  Zeitschr.  f.  analyt.  Chem.,  xi,  57.  See  also  the  extended  investigations 
of  ALLIHN  (Journ.  /.  prakt.  Chem.  [2],  xxn,  84  et  seq.) ;  according  to  him, 
under  the  most  favorable  conditions  (0-5-per  cent,  sulphuric  acid  at  108°), 
only  94-5-per  cent,  of  starch  are  converted  into  sugar  in  14  hours. 

f  Chem.  Centralbl,  1877,  732;  Zeitschr.  f.  analyt.  Chem.,  xvii,  231. 


§  277.]  DETERMINATION    OF   GRAPE-SUGAR,   ETC.  761 

proportion,  which  was  obtained  by  SACHSSE  in  his  experiments 
with  potato-starch,  does  not  correspond  with  the  formula  usually 
assigned  to  starch,  C6H10O5,  but  with  the  formula  CsaH82O81, 
assigned  to  it  by  W.  NAGELI.  If  the  calculation  is  based  upon 
the  usual  formula  for  starch,  then  90  parts  of  starch  must  be 
calculated  for  every  100  parts  of  grape-sugar,  i.e.,  the  same  pro- 
portion as  is  used  in  calculating  dextrin  from  the  grape-sugar 
found. 

SALOMON  *  found,  when  using  SACHSSE'S  method  of  inversion 
on  potato-starch  dried  at  120°,  and  determining  the  grape-sugar 
formed  according  to  ALLIHN,  that  the  quantity  of  grape-sugar 
obtained  (100  parts  equivalent  to  90  parts  starch)  corresponded 
with  the  formula  generally  accepted  for  starch,  C6H10O5,  and  ascribed 
the  difference  in  SACHSSE'S  results  partly  to  insufficient  dehydra- 
tion of  the  starch  (drying  only  at  100°  to  110°),  and  partly  to 
the  mode  of  determining  the  sugar. 

While  it  was  formerly  assumed  that  starch  from  different 
plants  exhibited  a  like  behavior  on  being  heated  with  acids,  and 
that  equal  weights  of  starch,  from  any  source,  afforded  equal 
weights  of  grape-sugar,  it  must  now  be  accepted,  if  the  labors  of 
SACHSSE  and  SALOMON  f  are  to  be  considered  as  conclusive  and 
comparative,  that  this  is  not  the  case,  or  at  least  not  with  the 
commercial  starches.  SACHSSE  and  SALOMON  found,  namely,  that 
on  treating  rice-  and  wheat-starches  less  grape-sugar  was  formed 
than  from  an  equal  quantity  of  potato-starch. 

The  question  whether  the  starches  of  different  plants  exhibit 
differences  in  behavior,  is  not  hereby  decided,  because  the  differ- 
ences in  behavior  of  the  commercial  starches  may  also  be  ascrib- 
able  to  their  manner  of  preparation.  On  the  basis  of  his  experi- 
ments, SALOMON  assumes  that  the  differences  noted  are  due  to 
the  fact  that  while  certain  starches,  e.g.,  rice-starch,  on  heating 
with  diluted  acids,  are  completely  dissolved,  it  is  true,  a  part  of 

*  Repertor.  d.  analyt.  Chem.,  i,  274,  and  Journ.  f.  prakt.  Chem.  [a],  xxv, 
348;  Zeitschr.  f.  analyt.  Chem.,  xxii,  111. 

\Journ.  f.  prakt.  Chem.  [a],  xxvi,  324;  Zeitschr.  f.  analyt.  Chem.,  xxn, 
594. 


762  DETERMINATION    OF    COMMERCIAL  VALUES.  [§  277. 

the  starch,  however,  is  not  converted  into  grape-sugar,  but  into 
other  substances  which  do  not  reduce  FEHLING'S  solution.  The 
proportional  figures  found  by  SALOMON  for  rice-starch  are  as  fol- 
lows: 100  parts  of  grape-sugar  formed  correspond  with  93-5  parts 
rice-starch. 

In  the  case  of  wheat-starch,  L.  SCHULZE*  found  the  relation 
recently  to  be  100  of  grape-sugar  =90  starch.  I  therefore  do  not 
consider  the  question  as  settled  for  rice-starch. 

On  employing  the  above-described  method  of  determining 
starch  in  grain,  the  results  obtained  are,  according  to  G.  FRANCKE,| 
too  high,  because  cellulose  also  is  converted  into  sugar  on  heating 
with  hydrochloric  acid.  The  treatment  of  starch  with  malt 
infusion  (diastase)  at  temperatures  up  to  65°,  readily  effects  com- 
plete solution  of  the  starch,  it  is  true,  but  either  does  not  effect  a 
complete  conversion  into  maltose  or  does  so  but  very  slowly. 
The  solution  always  contains,  besides  maltose,  also  dextrin,  or, 
more  accurately,  various  dextrins,  and  in  fact  in  proportion  varying 
with  the  temperature  at  which  the  diastase  acts  (O'SuLLiVAN  J). 
If  it  is  desired  to  make  a  direct  determination  of  starch  on  this 
basis,  therefore,  one  of  the  following  methods  more  recently  pro- 
posed may  be  adopted: 

a.  FAULENBACH  §  makes  use  of  the  following  solution  of  diastase : 

Crush  3  •  5  kilos  of  fresh,  green  malt,  treat  with  a  mixture  of  two 
litres  water  and  4  litres  glycerin,  and  allow  to  stand  for  eight  days 
with  occasional  stirring;  then  express  and  filter.  Five  drops  of 
the  liquid  so  obtained  dissolve  1  grm.  starch,  and  15  drops  con- 
tain a  quantity  of  carbohydrates  corresponding  with  1  mgrm. 
grape-sugar.  The  solution  is  very  stable.  In  testing  the  nutrient, 
which  may  contain  about  2  grm.  starch,  gelatinize  the  starch 
first,  and  then  effect  solution  by  adding  15  drops  of  the  diastase 
solution,  and  digesting  at  about  63°;  then  filter  off  the  undissolved 

*  Journ.  f.  prakt.  Chem.  [2],  xxvin,  311. 

f  Zeitschr.  f.  Spiritusindustr.,  1882,  306;  Berichte  der  deutsch.  chem. 
Gesellsch.,  xvi,  976. 

J  Journ.  Chem.  Soc.  [2],  x,  579 ;  [3],  I,  478,  and  n,  125. 

§  Zeitschr.  f.  physiol  Chem.,  vn,  510;  Chem.  CentralbL,  1883,  p.  632. 


§  278.]  DETERMINATION    OF    ALCOHOL.  763 

cellulose,  etc.,  heat  the  solution  with  20  c.c.  hydrochloric  acid  on 
a  water-bath  for  three  hours,  just  neutralize  with  caustic-soda 
solution,  determine  the  grape-sugar,  deduct  1  mgrm.,  and  then 
calculate  the  starch  from  the  sugar. 

b.  O'SuLLiVAN  *  employs  pure  diastase,f  and  in  determining 
starch  in  cereal,  treats  5  grm.  of  the  finely  ground  substance  suc- 
cessively with  ether,  with  alcohol  at  35°  to  40°,  and  with  water 
(at  the  same  temperature)  so  as  to  remove  the  fat,  sugar,  soluble 
albuminates,  and  soluble  carbohydrates.  The  residue  is  then 
boiled  for  a  few  minutes  at  62°  to  63°  to  gelatinize  the  starch, 
and  then  allowed  to  cool;  0-025  to  0-035  grm.  of  the  diastase 
dissolved  in  a  little  water  is  now  added,  and  the  whole  maintained 
for  an  hour  at  a  temperature  of  62°  to  63°.  Then  heat  to  boiling, 
filter,  wash  with  hot  water,  make  up  the  filtrate  when  cool  to 
100  c.c.  and  in  it  determine  on  the  one  hand  the  maltose  (§  274), 
and  on  the  other  hand  the  dextrin  by  polarization,  deducting 
from  the  total  polarization  that  due  to  the  action  of  the  maltose. 
Both  maltose  and  dextrin  are  then  calculated  into  starch  and  the 
results  added. 

II.  DETERMINATION  OF  ALCOHOL.  J 

§278. 

The  determination  of  alcohol  (ethyl  alcohol)  in  mixtures  of 
alcohol  and  water  is  almost  exclusively  accomplished  arseomet- 
rically,  either  by  the  aid  of  an  alcoholometer,  from  which  the  per- 
centage by  weight  or  volume  may  be  directly  read  off,  or  by  using 
an  ordinary  araeometer  and  ascertaining  the  alcohol  content  from 
the  specific  gravity,  for  which  purpose  numerous  tables  have  been 

*J&urn.  Chem.  Soc.,  1884,  p.  1. 

t  This  is  prepared  as  follows :  Pour  sufficient  water  over  2  or  3  kilos  of 
finely  crushed  pale  barley  malt  to  just  cover  it.  After  3  or  4  hours,  express, 
filter  the  solution,  and  add  alcohol  of  0  •  83  sp.  gr.  until  the  liquid  above  the 
flocculent  precipitate  becomes  opalescent  or  milky.  Collect  the  precipitate, 
wash  it  first  with  alcohol  of  0-86  to  0-88  sp.  gr.,  then  with  absolute  alcohol, 
then  press  it  between  linen,  and  finally  dry  it  completely  in  a  vacuum  over 
sulphuric  acid. 

I  See  also  Appendix  I,  Section  V. 


764  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  278. 

compiled  for  facilitating  the  object  in  view.  The  tables  compiled 
by  O.  HEHNER,*  and  based  upon  FOWNE'S  tables  (which  only 
give  the  percentage  in  whole  numbers)  are  very  convenient,  as 
they  afford  complete  readings  of  percentages  by  both  weight  and 
volume. 

This  simple  method  of  determining  the  alcohol  needs  no  more 
extended  discussion  here,  nor  is  it  necessary  to  dilate  upon  the 
use  of  the  vaporimeter,  the  utility  of  the  results  of  which  depends 
entirely  on  the  proper  adjustment  of  the  instrument. f  In  the 
following  I  will  describe  only  those  methods  of  determining 
alcohol  which  are  used  in  the  analysis  of  wines  and  other  liquids 
obtained  by  alcoholic  fermentation.  It  will  be  readily  seen  that 
the  method  described,  and  which  has  been  in  use  in  my  laboratory 
for  a  long  time,  is  quite  independent  of  the  accuracy  of  special 
apparatus. 

The  principle  of  the  method  is  well  known.  The  alcoholic 
liquid  is  distilled  until  all  the  alcohol  has  passed  over  into  the 
distillate,  taking  care  that  the  latter  contains  no  notable  quantities 
of  other  volatile  substances;  the  absolute  weight  and  specific 
gravity  are  then  taken,  and  from  these  data,  using  the  alcohol 
tables,  the  quantity  of  alcohol  in  the  distillate,  and  hence  which 
was  originally  present  in  the  liquid,  is  calculated. 

The  distillation  may,  of  course,  be  carried  out  in  various  forms 
of  apparatus;  the  form  shown  in  Fig.  132,  which  scarcely  requires 
further  explanation,  may  be  recommended,  because  it  takes  up 
but  little  space  and  requires  no  renewal  of  the  condensing  water.J 

If  a  large  quantity  of  the  alcoholic  liquid  to  be  examined,  and 
containing  presumably  not  more  than  20  per  cent,  of  alcohol  by 
volume,  is  available,  introduce  150  c.c.  or  grm.  into  the  flask, 

*  Zeitschr.  /.  analyt.  Chem.,  xix,  485.  The  tables  are  published  separately 
by  C.  W.  KREIDEL,  Wiesbaden,  1881,  and  in  English  by  J.  and  A.  CHURCHILL, 
London,  1880. 

t  Compare  A.  KRAFT,  Zeitschr.  f.  analyt.  Chem.,  xn,  50;  and  A.  SALOMON, 
Annal.  d.  Oenologie,  I,  374. 

t  An  apparatus  that  admits  of  the  simultaneous  distillation  of  several 
samples  of  wine  has  been  described  by  B.  LANDMANN,  Zeitschr.  /.  analyt. 
Chem.,  xxn,  394. 


278.] 


DETERMINATION   OF   ALCOHOL. 


765 


a,  and  to  prevent  frothing  in  wines,  etc.,  add  a  little  tannin,  then 
distil  and  collect  the  distillate  in  a  weighed  or  tared  flask,  b, 
having  a  capacity  of  200  c.c.  to  the  mark  on  the  neck  (i.e.,  about 
two-thirds  of  the  liquid  taken).  As  soon  as  the  distillate  reaches 
the  mark,  it  may  be  safely  assumed  that  it  will  contain  all  the 


FIG.  132. 

alcohol.     Now  weigh  the  flask,  6,  together  with  its  contents,  and 
thus  ascertain  the  absolute  weight  of  the  latter. 

To  ascertain  the  specific  gravity  of  the  distillate,  which  must, 
of  course  be  done  only  after  thoroughly  mixing,  a  pyknometer, 
shown  at  c  in  Fig.  132,  and  having  a  capacity  of  25  to  60  c.c.,  may 
be  employed.  The  neck  of  the  flask  should  have  a  diameter  of  5 
to  6  mm.  Its  weight,*  and  the  number  of  grammes  of  distilled 
water  it  holds  at  15-5°,  must  be  previously  ascertained  by  re- 
peated experiments.  Fill  the  pyknometer  to  a  little  above  the 
mark  with  the  distillate  by  aid  of  a  small  funnel  with  very  narrow 

*  In  order  to  dry  such  a  pyknometer,  heat  it,  and  exhaust  the  moist  air 
by  means  of  a  narrow  glass  tube.  The  neck  may  be  finally  dried  with  filter- 
paper. 


766  DETERMINATION    OF  COMMERCIAL   VALUES.  [§  278. 

stem,  and  place  it  in  water  of  15-5°  (see  Fig.  132,  d).  As  soon 
as  certain  that  the  contents  of  the  pyknometer  have  the  same 
temperature  as  the  surrounding  water,  remove  the  excess  of  dis- 
tillate, by  the  aid  of  a  strip  of  filtering  paper,  until  the  pyknometer 
is  filled  exactly  to  the  mark;  then  dry  and  weigh.  On  dividing 
the  weight  of  the  distillate  in  the  flask  by  the  known  weight  of 
the  distilled  water  contained  at  15-5°,  the  specific  gravity  of  the 
distillate  is  ascertained,  and  from  this  the  alcohol  content  may 
be  found  by  the  aid  of  HEHNER'S  tables  above  mentioned.* 

If  only  a  limited  quantity  of  the  liquid  to  be  tested  is  at  com- 
mand, distill  only  50  c.c.  or  grm.  The  mark  on  the  receiver, 
6,  must  then  be  at  a  height  where  the  flask  will  hold  about 
35  c.c.  It  is,  of  course,  evident  that  in  this  case  the  pyknometer 
used  must  have  a  capacity  of  25  to  30  c.c.,  or  a  suitable  quantity  of 
water  must  be  added  to  the  distillate,  before  weighing,  in  order  to 
fill  a  larger  pyknometer. 

An  example  will  make  this  clear:  150  c.c.  of  wine  yielded  102 
grm.  distillate  having  a  specific  quantity  of  0-9809  at  15-5°. 
Hence,  according  to  HEHNER'S  tables,  100  grm.  distillate  contained 
12-46  grm.  absolute  alcohol.  If  100  grm.  contained  12-46  grm., 
then  102  grm.  will  contain  12  •  709  grm.  As  all  the  alcohol  passed 
over  into  the  distillate,  the  latter  quantity  represents  the  quantity 
present  in  the  150  c.c.  of  wine.  But,  if  150  c.c.  contain  12-709 
grm.,  100  c.c.  contain  8-47  grm.  alcohol.  If  it  is  also  desired  to 
ascertain  how  many  grammes  of  alcohol  are  present  in  100  grm.  of 
wine,  the  specific  gravity  of  the  wine  must  be  ascertained  in  order 
to  find  the  weight  of  100  c.c.  of  wine. 

When  it  is  a  question  of  determining  the  alcohol  content  of  liq- 
uids containing  comparatively  small  quantities  of  alcohol,  collect 
the  distillate  in  an  un weighed  flask.  When  all  the  alcohol  has 
passed  over,  redistil  the  distillate,  and  then  determine  the  absolute 
weight  and  specific  gravity  as  above  in  the  last  obtained  distillate. 

When  liquids  are  so  viscid  that  direct  distillation  is  difficult,  it 
is  advisable  to  accomplish  the  first  distillation  by  steam  (see  p.  388, 

*  See  also  the  alcohol  tables  in  Appendix  I,  Section  V. 


§  279.]  DETERMINING  TANNIN.  767 

6,  this  volume).  The  distillate  so  obtained  is  then  again  distilled, 
as  above  detailed.  E.  BORGMANN  *  employed  this  method  with 
best  results  in  the  determination  of  small  quantities  of  alcohol  in 
American  malt  extracts. 

If  the  liquids  to  be  distilled  contain  much  free  carbon  dioxide, 
as,  for  instance,  in  the  case  with  new  or  sparkling  wines,  or  beer, 
first  remove  the  greater  part  of  the  carbon  dioxide  by  shaking  in  a 
half-filled  flask,  then  add  a  little  milk-of-lime  until  the  liquid  is 
just  alkaline,  and  then  distil.  The  last-named  addition  is  also 
made  when  the  liquid  to  be  examined  contains  any  notable  quan- 
tity of  acetic  acid  or  other  volatile  acid.  In  distilling  with  milk- 
of-lime,  however,  care  must  be  taken  that  the  distillate  contains  no 
ammonia  which  will,  of  course,  be  present  when  the  liquid  being 
distilled  contains  ammonium  salts.  Should  the  distillate  contain 
any  ammonia,  add  to  it  an  aqueous  solution  of  tartaric  acid  until 
the  liquid  is  acid,  and  then  rectify  the  distillate. 

III.  DETERMINING  TANNIN.! 

§279. 

The  determination  of  tannin  in  oak-barks  and  other  tanning 
materials,  in  extracts  containing  tannin,  and  also  in  commercial 
tannins,  is  of  such  frequent  occurrence  in  chemical  laboratories 
that  a  description  of  the  methods  most  useful  for  the  purpose  may 
properly  find  a  place  here.  Of  the  great  number  proposed  I  select 
only  those  which  are  at  present  considered  as  most  reliable. 

A.    LOWENTHAL'S  Method^ 

This  method  is  based  upon  the  oxidation  of  the  tannin  in  sul- 
phuric-acid solution  by  potassium  permanganate  (formerly  chlor- 
inated lime  was  used)  in  the  presence  of  a  large  quantity  indigo- 
carmine.  If  care  is  taken  that  the  liquid  is  properly  diluted,  the 
oxidations  are  normal, §  and  if  the  indigo  solution  has  been  added 

*  Zeitschr.  /.  analyt.  Chem.,  xxn,  534. 
f  See  also  Appendix  I,  Section  VIII. 

t  This  method  in  its  earliest  form  is  described  in  the  Journ.  f.  prakt. 
Chem.,  1860,  m,  150. 

§  Compare  FR.  GAUHE,  Zeitschr.  f.  analyt.  Chem.,  in,  p.  123. 


768  DETERMINATION    OF   COMMERCIAL   VALUES.  [§  279. 

in  such  quantity  as  to  require  about  twice  as  much  of  the  oxidizing 
agent  as  is  required  for  the  tannin,  the  operator  may  be  certain  that 
the  last  portion  of  the  tannin  will  be  oxidized  with  the  last  portion 
of  indigo. 

At  first  it  was  assumed,*  with  LOWENTHAL,  that  of  the  sub- 
stances contained  in  tannin  extracts,  only  the  tannin  was  oxidized, 
but  it  was  soon  proved  that  certain  other  substances  passing  into 
solution,  and  which  for  brevity  we  will  designate  as  non-tannins, 
use  up  a  determinable  quantity  of  potassium  permanganate.! 
NEUBAUER  {  hence  so  modified  the  method  that,  on  the  one  hand 
both  the  tannin  and  the  non-tannins  were  determined,  while  on  the 
other,  he  determined  the  non-tannins,  after  first  precipitating  the 
tannin  with  animal  charcoal,  and  from  the  difference  calculated 
the  tannin.  LOWENTHAL,§  after  further  investigating  the  method, 
retained  the  principle  of  NEUBAUER'S  method,  but  for  the  animal 
charcoal  used  in  precipitating  the  tannin,  he  substituted  a  solution 
of  glue  containing  much  sodium  chloride,  or  the  animal  hide  pre- 
pared for  tanning  and  reduced  to  powder  (see  Method  B)  first  used 
by  HAMMER — the  so-called  "Blosse."  As  he  gave  preference  to 
the  glue,  the  improved  LOWENTHAL  method  was  almost  exclusively 
carried  out  with  glue  or  gelatin. 

After  SIEMAND,!)  however,  had  found  that  the  improved  LOW- 
ENTHAL method  afforded  concordant  results  with  uniform  con- 
centrations while  with  varying  concentrations  the  results  also 
varied  widely,  due  to  a  slight  solubility  of  the  glue  (or  gelatin) 
tannate,  he  showed  that  the  method  could  be  further  improved 
by  determining  the  quantity  of  potassium  permanganate  used  up 
by  the  dissolved  glue  (gelatin)  tannate,  and  deducting  this  from 
the  total  required  for  the  combined  tannin  and  non-tannins. 

As,  however,  this  correction,  the  value  of  which  must  be  deter- 
mined by  experiment  each  time  for  different  dilutions,  makes  the 

*Journ.  f.  prakt.  Chem.,  1860,  150;  Zeitschr.  f.  analyt.  Chem.,  in,  122. 
t  Compare  FR.  GAUHE,  Zeitschr.  f.  analyt.  Chem.,  in,  125. 
t  Zeitschr.  f.  analyt.  Chem.,  x,  1. 
§  Ibid.,  xvi,  33  and  201 ;  also  xx,  91. 

H  DINGLER'S  polyt.  Journ.,  CCXLIV,  390;  Zeitschr.  /.  analyt.  Chem.,  xxn, 
595. 


$  279.]  DETERMINING    TANNIN.  769 

method  inconvenient,  SIEMAND  finally  reverted  to  HAMMER'S 
principle,  already  applied  by  LOWENTHAL,  of  removing  the  tannin 
by  means  of  a  solid  substance  capable  of  combining  with  it.  In 
the  experiments  which  were  made  to  ascertain  the  substance  most 
suitable  for  this  purpose,  he  finally  found  that  the  glue-yielding 
tissue  of  bones,  horn  cartilage  (the  so-called  "Hornschlauche"),  is 
preferable  to  the  "  blosse"  proposed  by  HAMMER  and  employed  by 
LOWENTHAL,  as  the  former  is  easier  to  obtain,  gives  up  less  soluble 
matter  to  water  on  digestion,*  and  effects  the  precipitation  of  the 
tannic  acid  more  rapidly. 

LOWENTHAL' s  method,  in  consequence  of  these  improvements, 
has  gained  greatly  in  reliability  over  its  earlier  form,  and  I  will 
hence  confine  myself  to  a  description  of  its  latest  and  best  form. 

I.    REQUISITES. 

The  method  requires  the  following: 

1.  A  Potassium-Permanganate  Solution. — Dissolve  1  grm.  of  the 
pure  salt  in  sufficient  water  to  make  1  litre. 

2.  Indigo-carmine  Solution. — Dissolve  40  grm.  of  purest  indigo- 
carmine  paste  in  water,  add  60  c.c.  sulphuric  acid,  dilute  with 
water  to  1  litre,  and  filter. 

3.  Glue-yielding  tissue  of  Bones  or  Horn  Cartilage. 

a.  The  former  is  prepared  according  to  SIEMAND,  as  follows: 
Hollow  bones,  from  which  the  ends  have  been  cut  and  the  marrow 
removed,  are  broken  into  large  pieces  and  digested  for  two  days 
with  a  5-per  cent,  sodium-carbonate  solution,  then  brushed,  and 
washed  repeatedly  with  water  with  which  they  are  left  in  contact 
each  time  for  several  hours.  Then  break  the  bones  hi  to  pieces  the 
size  of  a  nut,  and  treat  with  diluted  hydrochloric  acid,  8  litres  of 
which  contain  1  litre  of  commercial  hydrochloric  acid,  until  they 

*  SIEMAND,  on  treating  each  10  grm.  of  the  substance  for  forty-eight 
hours  with  200  c.c.  of  water  and  evaporating  100  c.c.  of  the  filtrate,  obtained 
the  following  residues:  From  blosse,  0*25;  from  extracted  bones,  0-008; 
and  from  "hornschlauche "  (horn  cartilage)  0-004  grm.  The  aqueous 
solutions  of  all  three  substances,  however,  contained  no  substances  appre- 
ciably oxidizable  by  potassium  permanganate. 


770  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  279. 

become  soft.  Then  wash  them  with  water  until  nearly  free  from 
acid,  and  grind  them  while  moist  in  a  small  mill.*  In  order  to 
remove  the  last  traces  of  calcium  salts  and  also  ferric  oxide,  digest 
the  comminuted  mass  repeatedly  with  diluted  (1:20)  hydrochloric 
acid,  then  thoroughly  wash  first  with  rain-  or  spring-water  until  no 
longer  acid,  and  then  with  distilled  water,  then  press,  and  dry.  It 
is  convenient  to  sort  the  preparation  by  sifting,  and  using  each 
size  separately. 

b.  Horn  Cartilage  (the  bony,  vascular  nucleus  of  cattle  horn). 
This  is  freed  from  calcium  salts  in  the  same  manner  as  the  bone- 
preparation.  When  softened  by  water,  the  preparation  appears 
cartilaginous. 

Instead  of  these  substances,  hide  prepared  for  tanning  may, 
as  already  remarked,  also  be  employed,  but  the  former  are  pref- 
erable. The  prepared  hide  is  best  obtained  from  a  tannery;  for 
its  further  preparation,  see  below,  Method  B. 

II.    PROCEDURE. 

1.  Prepare  an  aqueous  solution  of  the  tanning  material  suitable 
for  tannin  determination,  taking  care  to  take  sufficient  of  the  sub- 
stance, the  tanning  principle  of  which  is  to  be  brought  into  solu- 
tion, to  afford  a  solution  containing  about  0-5  to  1  grm.  of  the 
tanning  principle  per  litre. 

For  this  purpose,  the  following  quantities  of  the  substances 
mentioned  should  be  weighed  off: 

Pine  bark from  about  10  to  15  grm. 

Oak  bark "         "       8  to  10    " 

Spanish  chestnut  wood "         "       6  to    8    " 

Valonia "         "        3  to    4    " 

Sumach "          "        6  to    8    " 

Extract  the  vegetable  substance  by  boiling  at  least  four  times 
with  water,  and  then  make  up  the  liquid  to  one  litre.  In  the  case 
of  wood,  as,  for  example,  Spanish  chestnut,  care  must  be  taken 

*  According  to  experiments  made  in  my  laboratory  the  object  is  better 
attained  by  grinding  the  dry  preparation. 


§  279.]  DETERMINING   TANNIN.  771 

that  the  boiling  is  continued  each  time  for  at  least  15  minutes, 
because  woods  are  more  difficult  to  extract. 

In  the  case  of  extracts,  the  tanning-matter  content  of  which 
is,  as  a  rule,  approximately  known,  it  is  quite  easy  to  determine 
the  quantity  to  be  dissolved  in  one  litre  of  water  in  order  to  yield 
a  liquid  of  the  concentration  named. 

If  the  liquid  extracts  are  clear,  or  if  they  become  clear  on 
standing,  they  may  be  used  at  once  for  the  determination;  if 
otherwise,  a  sufficient  quantity  must  be  passed  through  a  dry 
filter.  If  the  turbid  extract  is  used,  somewhat  higher  results  are 
obtained,  and  these  I  consider  inaccurate  because  the  suspended 
organic  matters  also  use  up  some  potassium  permanganate.* 

If  the  liquid  extracts  also  contain  pectinous  substances,  these 
must  first  be  separated  if  correct  results  are  to  be  obtained,  because, 
as  JULIUS  LOWE  f  first  showed,  these  are  also  precipitated  by  the 
preparations  which  precipitate  tannin  (particularly  hide  powder, 
and  also  prepared  bone  and  horn  cartilage).  To  effect  this  pur- 
pose, hence,  according  to  LOWE,  evaporate  the  liquid  extract, 
e.g.,  of  the  oak  bark,  wThich  always  contains  pectinous  substances, 
with  the  addition  of  a  drop  of  acetic  acid,  to  dryness  on  a  water- 
bath,  extract  the  residue  with  strong  alcohol  (which  dissolves  the 
tannin  but  leaves  the  pectinous  substances),  evaporate  the  alcoholic 
solution  on  the  water-bath  until  all  the  alcohol  has  been  completely 
driven  off,  and  then  take  up  the  residue  with  water. 

2.  Determine    the   effective   value   of  the   potassium-perman- 
ganate solution  by  means  of  iron  or  oxalic  acid  (see  pp.  313  and 
316,  Vol.  I). 

3.  Measure  off  20  c.c.  of  the  indigo  solution,  add  1  litre  of  water, 
place  the  beaker  containing  the  liquid  in  a  white  porcelain  dish, 
and  then  run  in  (best  from  a  burette  provided  with  a  glass  cock) 
the  permanganate  solution  drop  by  drop  in  a  period  of  about  four 

*  In  experiments  carried  out  in  my  laboratory,  the  following  results,  as 
examples,  were  obtained:  With  an  oak-bark  extract,  using  a  filtered  solu- 
tion, 26-04,  as  against  27-52  per  cent,  with  an  unfiltered  solution  of  oak 
tannin.  With  an  extract  containing  tannin,  the  filtered  solution  gave  12-53 
while  the  unfiltered  solution  gave  13-66  per  cent,  tannin. 

f  Zeitschr.  /.  analyt.  Chem.,  iv,  368. 


772  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  279. 

minutes,  and  with  constant  stirring.  The  deep-blue  solution 
gradually  changes  to  dark-green,  then  light-green,  and  then  yellow- 
ish-green, the  last  greenish  tint  disappearing  with  the  addition 
of  the  next  drop  of  permanganate  solution.  In  order  to  sharply 
recognize  the  end  reaction,  it  is  advisable  to  add  the  permanganate 
solution  towards  the  end  very  slowly  in  single  drops.  If  the  change 
from  the  yellowish-green  color  is  not  sharp,  the  indigo-carmine 
was  not  sufficiently  pure,  and  especially  not  free  from  indigo-red. 
In  suqh  a  case  the  solution  cannot  be  used  for  accurate  determina- 
tions. The  concentration  of  the  indigo  solution  is  correct  if  20  c.c. 
of  it  require  about  an  equal  quantity  of  permanganate  solution; 
if  much  more  or  less  is  required,  the  indigo  solution  must  be  corre- 
spondingly diluted,  or  strengthened  by  the  addition  of  more  indigo- 
carmine,  and  then  again  standardized  against  the  permanganate 
solution.  The  solution  that  has  become  yellow  is  reserved  for 
comparison. 

4.  To  1  litre  of  water  add  20  c.c.  of  the  indigo  solution  and 
10  c.c.  of  the  tannin  extract,  and  then  run  in  permanganate  solu- 
tion, timing  the  addition  so  that  about  four  minutes  are  required 
to  run  in  the  total  quantity,  and  until  the  liquid  exhibits  a  pure 
yellow  color  exactly  like  that  obtained  by  standardizing  the  indigo 
solution  against  permanganate  solution  in  3.     If  in  this  experiment 
considerably  more  than  30  c.c.  permanganate  solution  have  been 
used,  the  quantity  of  tannin  extract  taken  was  too  large.     In  this 
case  repeat  the  experiment  with  a  correspondingly  smaller  quantity, 
and  ascertain  the  quantity  of  permanganate  solution  corresponding 
with  the  total  tannin  and  non-tannin,   by   deducting  from  the 
total  the  permanganate  solution  required  for  the  indigo. 

5.  Introduce  5  grm.  of  the  extracted  bone,  or  horn  cartilage, 
into  a  flask,  and  moisten  the  substance  with  exactly  50  c.c.  water, 
then  add  50  c.c.  of  the  liquid  containing  the  tannin,  stopper,  and 
allow  to  stand  for  twenty-four  hours,  frequently  shaking;    then 
filter  off  a  little  of  the  liquid  in  order  to  make  certain  that  all  the 
tannin  has  been  precipitated.     This  is  effected  by  concentrating  the 
filtered  liquid  by  evaporation,  and  adding  a  clear  solution  of  glue 
or  gelatin  saturated  with  sodium  chloride;  if  a  precipitate  forms, 


§  279.]  DETERMINING   TANNIN.  773 

add  to  the  contents  of  the  flask  a  further  quantity  of  extracted 
bone  or  horn  cartilage,  and  continue  the  digestion  until  the  object 
is  attained.  When  all  the  tannin  is  precipitated,  filter,  measure 
off  40  c.c.,  corresponding  with  20  c.c.  of  the  liquid  containing 
tannin,  add  20  c.c.  of  the  indigo  solution  and  1  litre  water,  and 
then  permanganate  solution  as  above,  until  the  liquid  has  a  pure, 
yellow  color.  In  this  manner  ascertain  the  quantity  of  perman- 
ganate used  up  by  the  non-tannins  in  20  c.c.,  and  by  halving  that 
required  for  10  c.c.  of  the  extract;  and  from  the  difference  ascertain 
the  permanganate  corresponding  with  the  tannin. 

An  example  will  make  this  clear 

10  grm.  chestnut  wood  gave  1000  c.c.  extract. 

100  c.c.  permanganate  solution  corresponded  with  0-1819 
crystallized  oxalic  acid. 

20  c.c.  indigo  solution  required  21  c.c.  permanganate  solution. 

20  c.c.  indigo  solution  plus  10  c.c.  chestnut-wood  extract  re- 
quired 32  c.c.  permanganate  solution.  On  deducting  from  this 
the  21  c.c.  corresponding  with  the  indigo  solution,  there  remained 
11  c.c.  for  the  tannin  and  non-tannins. 

5  grm.  extracted  bones  plus  50  c.c.  water  plus  50  c.c.  chestnut- 
wood  extract  yielded  a  filtrate  free  from  tannin;  and  40  c.c.  of  the 
filtrate  (  =  20  c.c.  of  the  extract)  plus  20  c.c.  indigo  solution  required 
22-6  c.c.  permanganate  solution,  hence  the  quantity  of  perman- 
ganate used  up  by  the  non-tannins  in  20  c.c.  of  the  extract  is 
22-6—21  =  1-6  c.c.,  and  consequently  that  in  10  c.c.  would  be 
0-8  c.c. 

On  now  deducting  this  0-8  c.c.  from  the  11  c.c.  obtained  above, 
there  remains  10-2  c.c.  permanganate  solution  for  the  tannin  in 
10  c.c.  of  the  extract. 

III.    CALCULATION. 

NEUBAUER'S  experiments  have  shown  that  63-024  grm.  crys- 
tallized oxalic  acid  (hence,  also  55-9  grm.  ferrous  iron),  and 
41-57  grm.  tannin  decompose  equal  quantities  of  permanganate 
solution,  and  are,  hence,  equivalent  in  this  respect.*  If  the  sub- 

*  I    must   mention    here    that    the    proportion   here   stated    has    been 


774  DETERMINATION    OF    COMMERCIAL   VALUES.  [§   279. 

stances  contained  the  same  kind  of  tanning  matter  as  nut  galls, 
i.e.,  gallotannic  acid,  the  tannin  may  be  readily  calculated  and 
expressed  in  per  cents,  from  the  figures  obtained  in  n,  i.e.,  from 
the  quantity  of  permanganate  solution  required  to  oxidize  the 
tanning  matter.  As,  however,  the  various  tanning  matters  do 
not  as  a  rule  contain  gallotannic  acid,  but  other  tannins,  which 
are  practically  still  unknown  in  a  pure  state,  and  of  which  it  is 
not  known  in  what  proportions  they  decompose  potassium  per- 
manganate, it  is  therefore  by  a  sort  of  tacit  understanding  that 
notwithstanding  this,  the  tannin  content  of  certain  tanning  sub- 
stances is  calculated  from  the  above  proportion  by  the  perman- 
ganate used.  For  instance,  according  to  this  practice,  12-24 
per  cent,  of  tannin  is  found  in  the  chestnut  wood  in  the  example 
cited  in  n,  according  to  the  following  calculation: 

100  c.c.  permanganate  solution  correspond  to  0-1819  grin, 
oxalic  acid,  and  hence,  according  to  the  proportion  63  •  024  :  41  •  57, 
also  0- 12  grm.  tannin.  1  c.c.  corresponds  therefore  to  0-0012  grm. 
tannin.  To  oxidize  the  tannin  in  10  c.c.  of  the  chestnut-wood 
extract  there  would  thus  be  required  10-2  c.c.  permanganate  solu- 
tion, which  hence  corresponds  with  10-2X0-0012  grm.  =  0-01224 
grm.  tannin.  But,  if  10  c.c.  of  chestnut-wood  extract  contain 
0-01224  grm.  tannin,  then  1000  c.c.  would  contain  1-224  grm.;  and 
this  quantity  being  obtained  from  10  grm.  chestnut  wood,  100 
grm.  would  of  course  contain  12-24  grm.  tannin. 

I  must  repeat  that  this,  and  every  analogous  calculation,  has  no 
scientific  basis,  and  that  the  result  based  on  it  and  expressing  the 

confirmed  by  ULBRICHT  (Annalen  der  Oenologie,  in,  63),  and  by  OSER  (Sitz- 
ungsber.  der  mathem.-naturwissenschaftl.  Classe  der  k.  Akademie  in  Wien, 
LXXII,  186);  but  on  the  other  hand,  COTTNCLER  and  SCHRODER  (Ber.  d. 
deutsch.  chem.  Gesettsch.  zu  Berlin,  xv,  1373;  Zeitschr.  /.  analyt.  Chem., 
274)  have  called  it  in  question;  they  found  the  proportion  to  be  63-024  : 
34-25.  [This  discrepancy  has  been  shown  by  SCHRODER  to  be  due  to  the 
different  manner  in  which  the  permanganate  was  added  in  titration,  NEU- 
BAUER  employing  the  "drop  method,"  while  COUNCLER  and  SCHRODER 
added  the  solution  in  successive  quantities  of  1  c.c.  with  a  short  interval 
between  each  addition.  This  modification  seriously  affects  the  volume  of 
the  standard  solution  consumed  (ALLEN,  Commercial  Organ.  Anal.,  in,  part  1, 
p.  76,  P.  BLAKISTON'S  SON  &  Co.,  1900).] 


§  280.]  DETERMINING   TANNIN.  775 

tannin  present  in  per  cents,  means  in  fact  no  more  than  that  the 
tannin  in  100  grm.  of  the  chestnut  wood  in  question  reduces  as 
much  permanganate  as  do  12-24  grm.  tannin,  presupposing  that 
the  calculation  is  based  on  the  proportion  of  63-024  of  oxalic  acid 
to  41-57  of  tannin. 

As  NEUBAUER  and  others  have  done  for  gallotannic  acid,  so 
has  OSER  *  sought  to  determine  in  what  proportion  quercitannic 
acid  is  equivalent  to  oxalic  acid  as  compared  with  permanganate. 
He  found  that  63  •  024  crystallized  oxalic  acid  and  62  •  32  querci- 
tannic acid  decolorize  equal  quantities  of  permanganate,  but  he 
does  not  consider  the  last  figure  to  be  in  any  way  reliable.  SIMAND, 
as  the  result  of  preliminary  experiments,  obtained  the  proportion 
63-024:60-11. 

No  comparisons  are  necessary  to  show  what  differences  must 
arise  when,  on  determining  the  tannin  in  a  tanning  substance, 
e.g.,  chestnut  wood,  NEUBAUER'S  ratio,  63-024:41-57,  or  that  of 
COUNCLER  and  SCHRODER,  63-024:34-25,  or  those  obtained  for 
quercitannic  acid,  63  •  024 : 62  •  32  or  63  •  024 :  60  •  11,  are  taken  as  basis 
for  the  calculation;  it  is  therefore  necessary  not  only  to  state  the 
result,  but  also  the  proportion  between  oxalic  acid  and  tannin  used 
in  the  calculation. 

B.    K  HAMMER'S  Method.-\ 
§280. 

This  method,  worked  out  in  my  laboratory  in  1860,  affords  at 
least  with  tannin  solutions,  and  with  careful  manipulation,  per- 
fectly reliable  and  accurate  results;  it  is  simple  to  perform,  and 
adapted  for  both  scientific  and  technical  purposes.  Compare  also 
FR.  GAUHE,J  W.  HALLWACHS,§  TH.  SALZER,||  FR.  KATHREINER,*[ 
and  PROCTER  and  HEWITT.**  NEUBAUER  ft  used  this  method  for 

*  Sitzungsber.  der  mathemat.-naturwissenschaftl.  Classe  der  k.  Akademie  in 
Wien,  LXXII,  186. 

f  Journ.  f.  prakt.  Chem.,  LXXXI,  159. 

J  Zeitschr.  f.  analyt.  Chem.,  in,  128. 

§  Ibid.,  v,  231.  1  Ibid.,  vii,  70.  ^  Ibid.,  xvm,  113. 

**  Ibid.,  xvm,  115.  ff  Ibid.,  x,  2. 


776  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  280. 

determining  the  tannin  in  the  solution  by  the  aid  of  which  he  ascer- 
tained the  equivalent  proportion  existing  between  oxalic  acid  and 
tannin  with  reference  to  permanganate  solution. 

In  the  case  of  solutions  of  other  tanning  substances,  the  objec- 
tion against  the  method  may  be  made  that  it  is  not  known  whether 
the  relations  between  the  content  and  the  specific  gravity  of  solu- 
tions of  other  tanning  substances  correspond  with  those  found  for 
tannin  solution — an  objection  which  in  all  probability  is  not  of 
great  weight,  but  which  can  be  completely  met  only  by  experimen- 
tally determining  these  relationships  for  solutions  of  other  tanning 
substances. 

In  solutions  of  tanning  substances  containing  also  pectinous 
matters,  HAMMER'S  original  method  must,  as  JUL.  LOWE  *  showed, 
be  modified  in  order  to  show  correct  results,  as  will  be  shown  below. 

a.  Principle. — On  determining  the  specific  gravity  of  a  tannin 
solution    containing   also   other   dissolved   substances,   and    then 
removing  the  tannin  alone,  but  in  such  a  manner  that  the  solution 
is  not  thereby  diluted  or  otherwise  changed,  and  on  finally  deter- 
mining the  specific   gravity   again,   the   decrease  in  the  specific 
gravity  must  be  proportional  to  the  quantity  of  tannin  that  was. 
present.     There  is  hence  needed  but  an  exact  table  giving  the  re- 
lationships between  the  content  and  the  specific  gravities  of  tannin 
solutions  of  varying  degrees  of  concentration,  in  order  to  be  able 
immediately  to  ascertain  the  tannin  content  of  the  solution  from 
the  difference  found. 

b.  Requisites. — To  determine  the  specific  gravity  there  is  re- 
quired either  a  pyknometer  (p.  765  this  volume),  or  a  fine  hydrom- 
eter indicating  either  the  specific  gravities  from  1-0000  to  1-0201, 
or  the  percentages   of  tannin   corresponding  with  these  specific 
gravities  for  pure  aqueous  solutions  of  tannin  (see  table  below) . 

To  remove  the  tannin  from  its  solutions,  HAMMER  recommended 
finely  comminuted  hide  powder,  the  so-called  "blosse,"  made  from 
hide  prepared  for  tanning.  The  prepared  hide  is  first  exhausted 
by  washing  with  water,  then  stretched  on  a  board,  dried  at  a  gentle 
heat,  and  reduced  by  means  of  a  rough  file  to  a  coarse  powder, 

*  Zeitschr.  f.  analyt.  Chem.,  iv,  368. 


§  280.]  DETERMINING   TANNIN.  777 

which  is  then  preserved  in  well-stoppered  flasks.  Instead  of  the 
hide  powder,  the  preparations  described  on  pp.  769  and  770  this 
volume  can  be  used — and  in  fact  with  better  results — i.e.,  the 
glue-yielding  tissue  of  the  bones,  or  the  horn  cartilage,  as  these  give 
up  less  soluble  matter  to  water  than  hide  powder  does  (compare 
foot-note,  p.  769).  4  parts  of  hide  powder,  prepared  bone,  or  horn 
cartilage  suffice  to  remove  1  part  of  tannin  from  a  fluid.  In  using 
it,  a  weighed  quantity  of  the  preparation  is  soaked  in  water  and 
then  expressed  in  order  that  the  adhering  water  may  not  noticeably 
dilute  the  solution  with  which  the  preparation  is  to  be  brought  into 
contact.  If  it  is  desired  to  entirely  eliminate  the  slight  source  of 
error  occasioned  by  this  water,  the  expressed  preparation  may 
be  again  weighed  in  order  to  ascertain  the  quantity  of  water  taken 
up,  and  which  may  be  subsequently  taken  into  account.*  The 
relations  between  the  tannin  content  and  specific  gravity  are 
shown  in  the  table  on  p.  778,  which,  as  heretofore,  must  serve  also 
for  solutions  of  other  tanning  matters  until  tables  for  these  are 
specially  prepared. 

c.  Procedure. — Care  must  be  taken  that  the  tannin  to  be  deter- 
mined is  obtained  in  a  clear  and  not  too  dilute  solution.  Hence 
first  boil  barks  or  the  like,  in  comminuted  form-,  with  water,  and 
then  completely  exhaust  them  in  a  percolator ;  triturate  inspissated 
vegetable  juices  with  water  in  a  mortar,  filter  through  linen,  and 
thoroughly  wash  the  residue.  From  1  part  of  the  substance  pre- 
pare about  10  parts  of  solution.  If,  after  complete  exhaustion  of 
the  substance,  the  solution  is  too  dilute,  it  must  be  concentrated 
by  evaporation.  Care  must  be  taken  to  obtain  from  about  200  to 
500  c.c.  of  solution  of  a  suitable  degree  of  concentration.  If  the 
extract  contains  pectinous  substances,  these  must  first  be  removed; 

*  TH.  SALZER  (Zeitschr.  f.  analyt.  Chem.,  vii,  71)  obtained  results  that 
did  not  appreciably  vary  on  treating  the  same  tannin  solution  once  with 
hide  powder  dried  at  100°,  and  again  with  the  hide  powder  moistened  and 
gently  pressed.  By  employing  hide  powder  dried  at  100°,  and  carefully 
washing  it  after  it  had  taken  up  the  tannin,  collecting  on  a  double  filter, 
drying  at  100°,  and  again  weighing,  he  obtained  from  the  increase  in  weight 
a  (satisfactorily  concordant)  means  of  controlling  the  value  obtained  by 
taking  the  specific  gravity. 


778 


DETERMINATION    OF    COMMERCIAL   VALUES.          [§  280. 


for  this  purpose  use  JUL.  LOWE'S  method,  described  on  p.  771  this 
volume. 


Percentage 
of 
Tannin. 

Specific 
Gravity 
at  15°. 

Percentage 
of 
Tannin. 

Specific 
Gravity 
at  15°. 

Percentage 
of 
Tannin. 

Specific 
Gravity 
at  15°. 

0-0 

1-0000 

1-7 

1-0068 

3-4 

1-0136 

0-1 

1-0004 

1-8 

1-0072 

3-5 

1-0140 

0-2 

1-0008 

1-9 

1-0076 

3-6 

1-0144 

0-3 

1-0012 

2-0 

•0080 

3-7 

1-0148 

0-4 

1-0016 

2-1 

-0084 

3-8 

1-0152 

0-5 

1-0020 

2-2 

•0088 

3-9 

1-0156 

0-6 

1-0024 

2-3 

•0092 

4-0 

1-0160 

0-7 

1-0028 

2-4 

•0096 

4-1 

1-0164 

0-8 

1-0032 

2-5 

-0100 

4-2 

1-0168 

0-9 

1-0036 

2-6 

•0104 

4-3 

•      1-0172 

1-0 

•0040 

2-7 

•0108 

4-4 

1-0176 

1-1 

-0044 

2-8 

•0112 

4-5 

1-0180 

1-2 

-0048 

2-9 

•0116 

4-6 

1-0184 

1-3 

-0052 

3-0 

•0120 

4-7 

1-0188 

1-4 

•0056 

3-1 

•0124 

4-8 

1-0192 

1-5 

-0060 

3-2 

-0128 

4-9 

1-0196 

1-6 

•0064 

3-3 

-0132 

5-0 

1-0201 

Now  weigh  the  prepared  tannin  solution.  To  simplify  the  cal- 
culation, it  is  convenient  to  make  up  the  weight  of  the  liquid  to  a 
round  number  of  grammes  by  adding  water;  then  mix  uniformly 
and  determine  the  specific  gravity  by  a  pyknometer  or  hydrom- 
eter. If  the  latter  is  used,  care  must  be  taken  that  the  cylinder 
is  either  dry  or  has  been  rinsed  off  with  a  small  quantity  of  the 
liquid  to  be  tested ;  further,  that  no  air-bubbles  adhere  to  the  float ; 
and  that  when  reading  off  the  eye  is  brought  to  the  level  with  the 
lower  border  of  the  meniscus  of  the  liquid. 

Now  weigh  off  in  a  dry  flask,  or  in  one  rinsed  out  with  the 
tannin-containing  liquid,  somewhat  more  of  the  tannin  solution 
than  is  required  to  fill  the  pyknometer  or  the  cylinder  used  with  the 
hydrometer,  and  add  4  times  the  quantity  of  hide  powder,  pre- 
pared bone,  or  horn  cartilage  required  for  the  tannin  found  as 
present  from  the  specific  gravity  of  the  liquid,  cork  the  flask,  vig- 
orously shake  for  some  time,  and  then  set  aside  for  24  hours,  with 
occasional  shaking.*  The  weighing  of  the  precipitant  and  the 


*  According  to  HAMMER  the  precipitation  of  the  tannin  is  already  com- 
plete after  shaking  a  short  time ;  the  experience  gained  in  using  the  modified 


§  280.]  DETERMINING    TANNIN.  779 

liquid  to  be  precipitated  need  but  be  approximately  made.  Now 
filter  the  liquid,  freed  from  its  tannin,  through  a  cloth  into  the 
cylinder  of  the  hydrometer,  or  the  pyknometer,  and  again  deter- 
mine the  specific  gravity. 

If  the  hydrometer  was  graduated  to  show  tannin  per  cents.,  the 
difference  between  the  two  readings  will  give  directly  the  tannin 
content  of  the  solution  examined;  if,  on  the  other  hand,  the  hy- 
drometer gives  but  the  specific  gravity,  or  if  this  has  been  ascer- 
tained by  means  of  the  pyknometer,  add  1  to  the  difference  between 
the  two  specific  gravities,  and  from  the  number  so  obtained  find 
the  corresponding  tannin  percentage  from  the  table.  This  being 
known,  the  weight  of  the  tannin  in  the  entire  quantity  of  the  solu- 
tion, i.e.,  in  the  quantity  of  the  substance  examined,  may  be  found 
by  a  simple  calculation. 

d.  Example. — 500  grm.  solution  were  obtained  from  40  grm. 
oak  bark.  At  15°  the  hydrometer  showed  the  liquid  to  contain 
apparently  1  •  7  per  cent,  of  tannin,  with  a  specific  gravity  of  1  •  0068. 
200  grm.  of  the  liquid  were  now  weighed  off,  this  quantity  appar- 
ently- containing  3  •  4  grm.  tannin  (1  •  7  per  cent.) ;  to  it  4  times  its 
quantity  or  13  •  6  grm.  of  hide  powder  were  added  after  having  been 
soaked  and  then  expressed.  After  filtration,  the  hydrometer 
showed  the  specific  gravity  of  the  liquid  to  be  1  •  0032,  correspond- 
ing to  a  tannin  content  of  0-8  per  cent.  The  difference  between 
the  two  determinations,  1-7  and  0-8,  is  0-9,  hence  the  solution 
contains  exactly  0-9  per  cent,  tannin.  But  if  100  grm.  contained 
0-9  grm.,  then  the  500  grm.  contained  4-5  grm.  tannin;  and  as  this 
was  obtained  from  40  grm.  oak  bark,  it  follows  that  the  latter  con- 
tained 11-25  per  cent.  Like  results  are  of  course  obtained  when 
the  calculations  are  based  upon  the  difference  between  the  specific 
gravities.  This  difference  amounted  to  1-0068- 1-0032  =  0-0036; 
on  adding  1,  we  get  1-0036,  and  this,  from  the  table,  which  see, 
corresponds  to  0  •  9  per  cent. 

LOWENTHAL  method,  however,  makes  a  more  prolonged  action  appear 
advisable. 


780  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  28L 

C. — Gravimetric  Modification  of  HAMMER'S  Method. 
§  281. 

As  may  be  readily  seen,  tannin  may  be  also  gravimetrically 
determined  by  using  HAMMER'S  principle.  This  modification  was 
first  proposed  by  A.  MUNTZ  and  RAMSPACHER,*  and  more  recently 
by  SiMAND.f  The  latter  employed  it  as  a  means  of  controlling  or 
verifying  the  relations  which  tannin  and  quercitannic  acid,  and 
oxalic  acid  or  ferrous  iron  in  solution,  respectively  bore  to  potas- 
sium permanganate. 

To  carry  out  the  method,  first  prepare  the  extracts  as  in  HAM- 
MER'S method;  and  they  must  also,  like  those  of  the  latter,  be  free 
from  pectinous  substances.  Evaporate  a  suitable  quantity  (SIMANI> 
employs  100  c.c.)  in  a  weighed  platinum  dish,  dry  the  residue  at 
100°  to  constant  weight,  weigh,  incinerate,  deduct  the  mineral 
constituents  from  the  residue,  and  thus  ascertain  the  total  quan- 
tity of  dissolved  organic  substances. 

Further,  add  to  a  like  quantity  of  the  tannin-containing  extract 
the  required  quantity  of  horn  cartilage  (vide  supra),  and  allow  to  act 
for  24  hours  in  order  to  precipitate  all  the  tannin.  At  the  end  of 
this  time,  filter,  wash  thoroughly,  evaporate  the  filtrate  as  above, 
dry  at  100°,  incinerate,  deduct  the  mineral  constituents  from  the 
total  weight  of  the  residue, '  and  thus  ascertain  the  weight  of  the 
substances  not  removed  by  the  horn  cartilage  (non-tannins). 
Lastly,  on  deducting  the  latter  from  the  total  tannin  and  non- 
tannins  first  obtained,  the  difference  will  give  the  weight  of  the 
tannin. 

D. — Other  Methods  of  Determining  Tannin. 

As  it  is  not  the  purpose  of  this  work  to  detail  all  the  numerous 
methods  proposed  or  employed  formerly,  as  well  as  in  recent  times, 
I  would  refer  regarding  them  to  the  Zeitschrift  fur  analytische 
Chemie,  I,  103,  104;  n,  137,  287,  419;  in,  484;  v,  1,  455,  456;  x, 

*  Compt.  rend.,  LXXIX,  380;  Zeitschr.  f.  analyt.  Chem.,  xiu,  462. 
j*  DINGLER'S  polyt.  Journ.,  CCXLVI,  41;   Zeitschr.  f.  analyt.  Chem.,  xxn, 
598. 


§  281.]  DETERMINING    TANNIN.  781 

1;  xin,  243;  xiv,  204;  xv,  112;  xvi,  123;  xvin,  112;  and  xxi, 
415,  552. 

Critical,  or  at  least  partly  critical,  investigations  of  the  methods 
of  determining  tannin  have  been  made,  and  the  results  published, 
by  FR.  GAUHE  (Zeitschr.  f.  ancdyt.  Chem.,  in,  122);  HALLWACHS 
(ibiti.,  v,  231);  TH.  SALZER  (ibid.,  vn,  70);  C.  O.  CECH  (ibid., 
vii,  130);  PH.  BUCHNER  (ibid.,  vn,  139);  NEUBAUER  (ibid., 
x,  1);  GUNTHER  (ibid.,  x,  354);  KATHREINER  (ibid.,  xvni,  113); 
and  others. 

[At  a  meeting  of  the  American  Association  of  Official  Agricul- 
tural Chemists,  held  hi  Washington,  U.  S.  A.,  on  November  16, 
1900,  a  paper  was  read  by  the  referee  of  the  Association,  Mr.  OMA 
CARR,  giving  the  following  particulars  of  experiments  which  had 
been  carried  out  with  a  view  to  the  improvement  of  the  official 
method  of  the  association  for  the  analysis  of  tanning  materials.* 

Soluble  Solids. — The  conclusions  drawn  from  experiments  as 
to  the  best  method  of  determining  the  soluble  solids  are  (1)  that 
if  the  filtration  is  performed  without  the  addition  of  an  "assistant," 
the  insoluble  matters  are  not  entirely  removed;  (2)  that  the 
absorption  of  the  tannin  by  the  filter-paper  is  largely  dependent 
upon  the  length  of  time  the  solution  is  hi  contact  with  the  paper; 

(3)  that  acetic  acid  modifies  the  basic  nature  of  the  filter-paper; 

(4)  that  it  is  possible  to  secure  concordant  results  by  the  addition 
of  lead  acetate  and  acetic  acid,  afterwards  filtering  through  paper; 

(5)  that  as  the  method  stands  it  gives  low  figures  for  oak  wood, 
and  high  for  quebracho,  and  this  will  hold  good  hi  comparison 
with  any  materials  so  differing. 

Hide  Powder. — The  Vienna  powder  generally  used  because 
of  its  close  adherence  to  the  limits  of  insolubility  and  absorption 
adopted  by  the  association,  has  recently  shown  such  a  wide  depar- 
ture from  these  limits  as  to  fall  wholly  without  the  range  of  allow- 
able variation;  it  has  also  been  noticed  that  many  of  the  samples 
of  Vienna  hide  powder  recently  received  contained  small  quantities 
of  acid. 

*  Journ.  Soc.  Chem.  Ind.,  1901,  p.  286;  Leather  Manufacturer,  Dec.  1900, 
241-248. 


782  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  281. 

It  will  be  seen  that  inasmuch  as  the  moisture  content  of  the 
wet  pressed  hide  is  variable  with  the  physical  condition  thereof, 
a  definite  statement  of  the  dry  hide  present  in  the  wet  cake  must 
be  made;  the  results  are  concordant  for  any  definite  quantity  of 
powder,  but  the  fineness  of  some  powders  permits  great  loss  in 
squeezing,  and  the  actual  dry  powder  present  in  the  solution  is 
thereby  variable. 

Volume  of  Solutions  for  Drying. — Owing  to  the  sensitiveness 
of  tanning  materials  to  heat  and  oxidation  whilst  drying,  it  is 
believed  that  the  use  of  volumes  yielding  0  •  4  to  0  •  5  grm.  of  residue 
would  give  more  concordant  results.  The  experience  of  the 
referee  is  that  residues  of  0-4  grm.  may  be  dried  to  nearly  constant 
weight  on  the  steam-bath  in  five  hours,  afterwards  drying  in  an  air- 
or  water-oven  for  half  an  hour;  it  is  therefore  to  be  recommended 
to  substitute  50  c.c.  wherever  100  c.c.  are  stipulated  in  the  official 
method. 

Fairly  concordant  results  were  obtained  by  eight  different 
members  of  the  association  making  analyses  of  the  same  samples 
of  oak-wood  and  quebracho  extract,  the  analyses  being  done  by 
the  official  method  of  the  association.  The  quebracho  is  a  severe 
trial  on  the  accuracy  of  the  method  owing  to  the  large  amount  of 
tanning  matter  present  and  the  extreme  fineness  of  the  insoluble 
matter;  variations  in  the  amount  of  non-tanning  matters  may 
be  largely  attributed  to  variations  in  the  character  of  the  hide 
powder  used. 

It  was  eventually  resolved  that  the  following  be  the  amended 
method  of  the  association: 

1.  Preparation  of  Sample. — Barks,  woods,  leaves,  dry  extracts, 
and  similar  tanning  materials  should  be  ground  to  such  a  degree 
of  fineness  that  they  can  be  thoroughly  extracted.     Fluid  extracts 
must  be  heated  to  a  temperature  of  50°  C.,  well  shaken  and  allowed 
to  cool  to  room  temperature. 

2.  Quantity   of  Material. — In  the   case   of  barks   and   similar 
materials,  use  such  quantity  as  will  give  about  0-8  grm.  of  total 
solids  per  100  c.c.  of  the  solution,  and  extract  in  SOXHLET  or  similar 
apparatus  at  steam  heat  for  non-starchy  materials.     For  canaigre 


§  281.]  DETERMINING   TANNIN.  783 

and  substances  containing  like  amounts  of  starch,  use  a  tempera- 
ture of  50°  to  55°  C.,  until  near  completion,  finishing  the  extraction 
at  steam  heat.  In  the  case  of  extracts,  weigh  such  quantity  as 
will  leave  a  residue  of  0-8  grm.  on  evaporation  of  100  c.c.  of  the 
solution,  dissolve  in  800  c.c.  of  water  at  a  temperature  of  80°  C., 
allow  to  stand  12  hours  and  make  up  the  quantity  to  1  litre. 

3.  Moisture. — Place  2  grm.,  if  it  be  an  extract,  in  a  flat-bot- 
tomed dish  not  less  than  6  cm.  hi  diameter,  add  25  c.c.  of  water, 
warm  slowly  until  dissolved  and  continue  the  evaporation  until 
dry. 

Ah1  evaporations  called  for  after  evaporation  to  dryness  on  the 
water-bath,  shall  be  done  by  one  of  the  following  three  methods, 
the  soluble  solids  and  non-tanning  residues  being  dried  under  as 
nearly  identical  conditions  as  possible. 

(a)  For  24  hours  at  a  temperature  of  100°  C. 

(6)  For  8  hours  at  100°  to  110°  C.  in  air-oven. 

(c)  To  constant  weight  in  vacuo  at  70°  C. 

4.  Total   Solids. — Shake   the   solution,    and   without   filtering 
immediately  remove  50  c.c.  with  a  pipette,  evaporate  in  a  weighed 
dish,  and  dry ;  the  dishes  should  be  flat-bottomed  and  not  less  than 
6  cm.  in  diameter. 

5.  Soluble  Solids. — Filtration  shall  take  place  through  double- 
pleated  filter-paper,  the  first  150  c.c.  passing  through  shall  be  re- 
jected, and  the  50  c.c.  next  passing  through  shall  be  collected, 
evaporated,  and  dried.     When  a  clear  filtrate  may  not  otherwise 
be  obtained,  the  use  of  10  grm.  of  barytes  previously  washed  in  a 
portion  of  the  solution  is  permissible.     Evaporation  during  filtra- 
tion must  be  guarded  'against. 

5a.  Optional  Method. — (a)  To  100  c.c.  of  the  solution  add  10  c.c. 
of  a  solution  of  lead  acetate,  4  grm.  per  litre,  adding  the  reagent 
drop  by  drop  from  a  burette  and  stirring  meanwhile.  Now  add 
10  c.c.  of  a  solution  of  acetic  acid,  36  grm.  of  glacial  acid  per  litre, 
stirring.  Throw  on  double-pleated  filter,  until  clear  reject,  and 
evaporate  and  dry  50  c.c. 

(b)  On  another  portion  of  100  c.c.  repeat  the  foregoing,  except 
that  20  c.c.  of  lead-acetate  solution  shall  be  used. 


784  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  281. 

Residue  from  (a)  shall  be  multiplied  by  1-2,  and  from  (6)  by 
1-3,  to  bring  back  to  the  original  100  c.c.  Add  to  the  corrected 
weight  of  the  residue  from  (a)  the  difference  between  (a)  and  (b), 
and  calculate  the  found  residue  to  soluble  solids.  This  corrects  for 
dilution  and  removal  by  lead. 

6.  Non-tanning  Matters. — Prepare  20  grm.  of  hide  powder  by 
washing  in  a  No.  7  beaker  with  from  800  to  1,000  c.c.  of  water, 
stir  well  and  let  stand  one  hour,  filter  the  magma  through  linen, 
squeeze  thoroughly  by  hand,  remove  as  much  moisture  as  possible 
by  means  of  a  press,  weigh  the  pressed  hide,  and  take  approximately 
one-fourth  for  moisture  determination.     Weigh  this  portion  care- 
fully and  dry  to  constant  weight.     Weigh  the  remaining  three- 
quarters,  which  must  contain  between  12  and  13  grm.  of  dry  hide, 
add  to  200  c.c.  of  the  solution  and  shake  10  minutes.     Throw  on  a 
funnel  with  cotton  plug  in  stem,  return  until  clear,  evaporate  50  c.c. 
and  dry.     The  weight  of  this  residue  must  be  corrected  for  the 
moisture  contained  in  the  wet  pressed  hide.     The  shaking  must  be 
done  in  some  form  of  mechanical  shaker.     The  machine  used  by 
druggists,  and  known  as  the  milk-shake,  is  recommended. 

7.  Tanning  Matters. — The  amount  of  these  is  shown  by  the 
difference  between  the  soluble  solids  and  the  non-tannins. 

8.  Testing    the  Hide  Powder. — (a)  Shake  10  grm.  of  powder 
with  250  c.c.  of  water  for  five  minutes,  strain  through  linen,  and 
squeeze  the  magma  thoroughly  by  hand;    repeat  this  operation 
three  times,  pass  the  last  filtrate  through  paper  until  clear,  evapo- 
rate 50  c.c.  and  dry;  if  this  residue  amounts  to  more  than  5  mgrm., 
the  powder  must  be  rejected. 

(6)  Prepare  a  solution  of  pure  gallotannic  acid  by  dissolving 
5  grm.  in  1,000  c.c.  of  water.  Determine  the  total  solids  by  evapo- 
rating and  drying  50  c.c.  of  this  solution.  Treat  200  c.c.  of  this 
solution  with  hide  powder,  exactly  as  in  paragraph  6.  The  powder 
must  absorb  at  least  95  per  cent,  of  the  total  solids.  The  gallotannic 
acid  used  must  be  completely  soluble  in  water,  acetone,  alcohol, 
and  acetic  ether,  and  shall  not  contain  more  than  1  per  cent,  of 
substances  not  removed  by  digesting  with  yellow  mercuric  oxide 
on  the  steam-bath  for  two  hours. 


§  282.]  DETERMINATION   OF   ANTHRACENE.  785 

(c)  Any  analysis  made  with  a  powder  which  does  not  fulfil  the 
conditions  of  the  preceding  paragraphs  shall  not  be  reported  as  by 
this  method. 

9.  Testing  the  Non-tanning  Filtrate. — (a)  For  tannin.     Test  a 
small  portion  of  the  clear  non-tanning  filtrate  with  a  few  drops  of 
a  1-per  cent,  solution  of  NELSON'S  gelatin,     A  cloudiness  indicates 
the  presence  of  tannin,  in  which  case  repeat  6,  using  25  instead  of 
20  grm.  of  powder. 

(6)  For  soluble  hide.  To  a  small  portion  of  the  clear  non- 
tannin  filtrate  add  a  few  drops  of  the  filtered  tanning  solution. 
A  cloudiness  indicates  the  presence  of  soluble  hide,  hi  which  case 
repeat  6,  giving  the  powder  a  more  thorough  washing. 

10.  Temperature  of  Solutions. — The  temperature  of  solutions 
shall  be  between  16°  and  20°  C.  when  measured  and  filtered. 

All  dryings  shall  be  in  flat-bottomed  dishes  not  less  than  6  cm. 
in  diameter. 

SCHLEICHER  and  SCHULL'S  filters  No.  590,  15  cm.,  shall  be  used 
for  all  nitrations. — TRANSLATOR.] 

IV.  DETERMINATION  OF  ANTHRACENE. 

§282. 

Since  the  production  of  alizarin  from  anthracene  has  now 
become  an  exceedingly  large  industry,  the  determination  of  anthra- 
cene in  crude  anthracene  has  become  a  frequently  occurring  prob- 
lem in  chemical  laboratories.  The  method  first  worked  out  by  E. 
LUCK  *  in  the  laboratory  of  MEISTER,  Lucius,  and  BRUNING,  of 
Hochst,  and  published  by  him  in  1873,  and  based  upon  the  con- 
version of  anthracene  into  anthraquinone,  has  gradually  devel- 
oped into  that  published  by  MEISTER,  Lucius,  and  BRUNING  in 
1876,f  and  now  generally  employed.  I  consider  it  proper  to  here 
describe  the  method,  and  to  supplement  the  description  with  such 
details  as  to  modifications  as  the  experience  gained  in  my  laboratory 
has  shown  to  be  of  value. 

*  Zeitschr.  f.  analyt.  Chem.,  xii,  347;  and  xin,  251. 
f  Ibid.,  xvi,  61. 


786  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  282. 

1.  Above  all  it  is  of  most  importance  that  the  sample  be  homo- 
geneous, and  that  care  be  taken  in  preparing  the  sample  that  this 
suffers  no  change  by  the  evaporation  of  adhering  volatile  hydro- 
carbons.    To  effect  this,  empty  the  crude  anthracene  into  a  dish, 
mix  it  quickly,  using  a  spatula  or  piece  of  cardboard,  and  crushing 
any  large  lumps,  and  then  transfer  it  to  a  glass-stoppered  flask. 
The  sample  to  be  analyzed  must  be  weighed  in  a  closed  tube,  which 
must  be  reweighed  after  the  anthracene  has  been  emptied  out. 
About  1  grm.  (0-97  —  1-03  grm.)  is  required  for  each  analysis. 

2.  Introduce  the  weighed  anthracene  into  a  flask  of  about  500  c.c. 
capacity,  and  cover  it  with  45  c.c.  glacial  acetic  acid.     The  flask 
should  be  provided  with  a  twice-perforated  stopper,  one  hole  bear- 
ing a  funnel  tube  fitted  with  a  glass  cock  and  terminating  below 
in  a  narrow  opening,  while  the  other  aperture  is  fitted  with  a  glass 
tube  bent  at  an  obtuse  angle  and  connected  with  a  reflux  con- 
denser.    Now  heat  the  contents  of  the  flask  to  boiling,  and  keep  it 
boiling  while  introducing  through  the  funnel  tube  a  solution  of  15 
grm.  chromic  acid  *  in  10  c.c.  glacial  acetic  acid  and  10  c.c.  water, 
allowing  the  solution  to  drop  in  slowly  so  that  the  operation  will 
require  two  hours  for  completion.     When  all  the  chromic  acid  has 
been  added,  keep  the  contents  of  the  flask  boiling  for  another  two 
hours. 

3.  Allow  the  flask  to  stand  for  12  hours,  then  add  400  c.c.  cold 
water  to  its  contents,  and  allow  to  stand  for  3  hours  longer.     Now 
collect  the  precipitated  anthraquinone  on  a  filter,  wash  it  first  with 
cold  water  until  the  washings  are  no  longer  acid,  then  with  about 
200   c.c.  boiling  diluted  1-per  cent,  caustic-potassa  solution,  and 
finally  with  pure,  hot  water  until  the  washings  are  no  longer  alkaline. 

4.  Now  rinse  the  anthraquinone  by  means  of  a  fine  but  strong 
stream  of  water  into  a  platinum  dish  the  weight  of  which  is  approx- 
imately known,  spreading  open  the  filter  on  a  glass  plate  in  order 
to  enable  the  anthraquinone  to  be  more  readily  removed;    then 
evaporate  on  a  water-bath,  dry  at  100°,  weigh  the  still  impure 
anthraquinone  approximately,  cover  it  with  ten  times  its  weight 

*  This  must  be  prepared  according  to  FRITZSCHE'S  method,  using  pure 
sulphuric  acid. 


§  283.]  INORGANIC   CONSTITUENTS   OF    PLANTS.  787 

of  fuming  sulphuric  acid  of  68°  Be".  =  1-86  sp.  gr.,  and  heat  for 
10  minutes  in  the  water-oven  (p.  58,  Fig.  31,  Vol.  I),  the  water  in 
which  must  be  maintained  briskly  boiling. 

5.  Pour  the  anthraquinone  solution  into  a   shallow  porcelain 
dish,  and  allow  it,  and  also  the  platinum  dish  in  which  small  por- 
tions of  the  solution  have  been  retained,  to  stand  in    a   humid 
place  for  12  hours  in  order  to  attract  moisture.     At  the  end  of  this 
time  rinse  out  the  platinum  dish  with  200  c.c.  cold  water  into  the 
porcelain  dish,  filter  off  the  anthraquinone,  wash  it  first  with  cold 
water  until  the  washings  are  no  longer  acid,  then  with  about  200  c.c . 
boiling  1-per  cent,  caustic-pot assa  solution,  and  lastly  with  hot, 
water  until  the  washings  are  no  longer  alkaline. 

6.  Now  rinse  the  washed  anthraquinone  into  a  platinum  dish, 
evaporate  on  a  water-bath,  and  dry  the  residue  at  100°  to  constant 
weight;   then  carefully  heat  the  dish  so  that  the  anthraquinone 
completely  volatilizes,  but  without  taking  fire,  and  again  weigh 
the  dish  with  the  residual  ash  and  carbon.     The  difference  between 
the  weighings  gives  the  weight  of  the  anthraquinone,  and  this 
multiplied   by  0-856   gives  the  anthracene.     [Anthracene,  C14Hlt 
=  178  •  08 ;  anthraquinone,  C14H8O2 = 208  •  064.] 

III.  DETERMINATION    OF    THE    INORGANIC    CONSTIT- 
UENTS OF  PLANTS  * 

§283. 

Since  the  researches  in  agricultural  chemistry  have  established 
the  fact  that  every  plant  requires  for  its  development  certain 

*  As  the  determination  of  the  inorganic  constituents  of  animal  substances 
is  less  frequently  undertaken  than  the  determination  of  those  of  plants, 
since  they  are  required  almost  entirely  for  scientific  rather  than  technical 
purposes,  1  have  omitted  a  detailed  description  in  the  text.  I  would  merely 
point  out,  howeveJ,  that,  in  general,  the  same  methods  of  procedure  may 
be  adopted  as  given  in  ihe  text.  According  to  H.  ROSE,  the  substances  which 
fuse  are  first  heated,  in  order  to  incinerate  them,  in  a  platinum  dish,  with 
stirring,  until  they  have  lost  their  fluidity,  and  the  greater  part  of  the  organic 
matter  is  decomposed.  The  almost  completely  carbonized  residue  is  next 
transferred  to  a  platinum  crucible  (at  this  stage  even  a  clay  crucible  may 
be  employed  without  disadvantage)  which  is  well  covered,  and  then  heated 


788  INORGANIC    CONSTITUENTS    OF  PLANTS.  [§  283. 

inorganic  constituents,  a  strong  desire  has  arisen  to  learn  what 
inorganic  constituents  are  required  for  the  individual  plants,  more 
particularly  for  cultivated  plants  and  weeds,  as  these  enable  con- 
clusions to  be  formed  regarding  the  constituents  of  the  soil.  This 
object  it  was  first  sought  to  reach  by  analyzing  the  ash  obtained 
by  incinerating  the  entire  plant  or  particular  parts  of  it,  e.g., 
the  seeds.  As  it  has  been  found,  however,  that  the  object  is  not 
fully  accomplished  by  this  means,  because  during  the  incineration 
of  the  plant  several  of  the  inorganic  constituents  must  be  lost, 
while  others  may  be  lost,  the  ash  analysis,  in  order  to  fully  answer 
the  question,  must  be  supplemented  by  separate  determinations 
of  the  individual  elements,  as  the  methods  otherwise  employed  have 
so  far  not  sufficed  to  accomplish  the  object.* 

to  dull  redness.  Burn  the  charcoal  so  obtained  with  the  aid  of  spongy 
platinum.  STRECKER'S  method  (described  in  the  text)  of  incinerating  with 
the  addition  of  baryta,  is  also  very  well  adapted  for  animal  substances. 
The  incineration  may  be  particularly  well  effected  according  to  SLATER 
(Chem.  Gaz.,  1855,  53)  by  mixing  the  substance  with  pure,  dry,  finely  pow- 
dered barium  dioxide  and  igniting.  STRECKER  calls  attention  in  his  paper 
(Annal.  d.  Chem.  u.  Pharm.,  LXXIII,  370)  to  the  fact  that  the  ashes  of  animal 
substances  frequently  contain  considerable  quantities  of  cyanates.  These 
are  most  simply  decomposed  by  moistening  the  ash  with  water  and  then 
gradually  heating  to  redness.  As  a  rule,  only  a  single  moistening  is  necessary 
in  order  to  convert  the  cyanates  into  carbonates.  In  order  to  determine 
the  chlorine,  incinerate  the  animal  substance  with  sodium  carbonate,  using 
1-5  to  2-5  grm.  for  every  50  grm.  of  the  organic  substance  (BEHAGHEL  VON 
ADLERSKRON,  Zeitschr.  f.  analyt.  Chem.,  XH,  405).  Finally,  I  would  point 
out  that  in  order  to  accurately  determine  the  total  phosphorus  and  sulphur, 
those  methods  must  be  employed  which  are  adapted  for  the  determination 
of  phosphorus  and  sulphur  in  organic  substances,  and  which  are  de- 
scribed in  §§  188  and  189.  Special  details  regarding  the  analysis  of  animal 
substances  are  given  by  F.  VERDEIL  in  his  paper  on  the  analysis  of  the  ash 
of  blood  of  man  and  many  animals  (Annal.  d.  Chem.  u.  Pharm^,  LXIX,  89; 
Pharm.  Centralbl.,  1849,  198;  LIEBIG  and  KOPP,  Jahresber.,  1849,  598);  and 
also  in  that  of  FR.  KELLER  on  the  ash  of  meat  bouillon  and  meat  (Annal.  d. 
Chem.  u.  Pharm.,  LXX,  91;  Pharm.  Centralbl. f  1849,  581;  LIEBIG  and  KOPP, 
Jahresber.,  1849,  599). 

*  CAILLAT  states  that  on  treating  herbaceous  plants  (clover,  lucern, 
sanfoin)  with  diluted  nitric  acid,  he  has  succeeded  in  extracting  the  in- 
organic constituents  so  completely  that  the  easily  combustible  residual  mass 
from  10  grm.  of  vegetable  matter  yielded  but  18  to  22  mgrms.  of  ash  consisting 
of  silica  and  ferric  oxide.  This  treatment,  he  states  further,  yields  a  larger 


§  283.]  ASH    ANALYSES.  789 

In  the  following  chapter  the  Ash  Analysis  will  be  given  under 
A,  while  under  B  will  be  detailed  the  Supplementary  Determina- 
tions, and  under  C  the  Arrangement  of  the  Results. 

A.  ASH  ANALYSES. 

As,  according  to  the  researches  heretofore  made,  the  ashes 
of  plants  contain  but  a  limited  number  of  acids  and  bases,  methods 
which  are  generally  applicable  may  be  devised  for  their  analysis; 
as  these  offer  many  peculiarities,  and  are  frequently  employed, 
only  those  will  be  here  described  which  appear  to  me  to  be  the 
simplest  and  best.  A  comprehensive  critique  of  the  numerous 
widely  differing  methods  proposed  cannot  be  given  here,  as  it 
is  beyond  the  scope  of  this  work. 

The  substances  which  are  generally  found  in  larger  quantities 
in  plant  ashes  are  as  follows : 

Bases:  Potassium,  sodium,  calcium,  magnesium,  iron  (as 
Fe2O3),  and  manganese  (as  Mn3O4). 

Adds,  or  Substances  Capable  of  Replacing  Them:  Silicic  acid, 
phosphoric  acid,  sulphuric  acid,  carbon  dioxide,  and  chlorine. 

Besides  these  there  are  sometimes  found  oxides  of  lithium, 
rubidium,  strontium,  barium,  and  copper;  fluorine;  occasionally 
alumina  (e.g.,  in  the  ashes  of  the  Lycopodiacece,  in  comparatively 
large  quantities);  iodine,  bromine,  cyanides,  and  cyanates  (only 
in  the  ash  of  highly  nitrogenous  substances);  boric  acid, sulphides, 
and  also  traces  of  zinc  oxide  or  of  other  oxides  of  the  heavy  metals. 
Of  the  substances  here  mentioned,  most  are  unquestionably  original 
constituents  of  the  plants;  many  again  may  have  been  present  as 
such,  or  they  may  have  been  formed  during  incineration ;  lastly 

quantity  o(  inorganic  constituents,  more  particularly  sulphuric  acid,  than 
can  be  obtained  by  incinerating  the  plant  (Compt.  rend.,  xxxix,  137; 
Jahresber.  von  LIEBIG  und  KOPP,  1849,  601).  RIVOT,  BEUDANT,  and  DAGUIN 
(Compt.  rend.,  1853,  835;  Journ.  f.  prakt.  Chem.,  LXI,  135)  prefer  destroying 
the  organic  matter  by  treatment  with  potassa  lye  and  passing  in  chlorine. 
W.  KXOP'S  experiments  may  also  be  mentioned  here;  he  sought  to  ascer- 
tain the  mineral  substances  required  for  the  plant  nutrition  by  allowing 
plants  to  grow  in  solutions  containing  known  quantities  of  inorganic  sub- 
stances and  subsequently  determining  the  quantities  left  in  solution. 


790  INORGANIC    CONSTITUENTS   OF   PLANTS.  [§  284. 

some  certainly  owe  their  origin  to  that  destructive  process.  Thus 
the  sulphates,  and  by  exception  even  the  carbonates,  found  in  the 
ash  may  have  been  original  constituents  of  the  plants,  but  they 
may  also  have  been  formed  by  the  destruction  of  salts  of  organic 
acids  and  by  the  combustion  of  the  unoxidized  sulphur  present  in 
every  plant ;  thus  the  metallic  sulphides  are  formed  by  the  action  of 
the  carbon  on  sulphates  with  an  insufficient  air  supply,  the  cyanides 
of  the  metals  result  from  heating  nitrogenous  carbon  with  alkali 
carbonates,  while  the  cyanates  result  from  the  oxidation  of  the 
cyanides,  etc. 

The  variety  of  these  constituents,  and  the  fact  that  some  of 
them  are  as  a  rule  present  only  in  very  small  quantities,  make  it 
a  by  no  means  easy  task  to  devise  methods  that  will  be  generally 
applicable,  the  more  so  as  the  method  sought  must  unite  accuracy 
with  some  degree  of  despatch. 

I  will  first  treat  of  the  preparation  of  the  ash  for  the  purpose  of 
analysis,  and  then  of  the  analysis  itself. 

I.   PREPARATION   OF   THE   ASH. 

§284. 

In  preparing  the  ash  the  following  conditions  must  be  fulfilled : 

1.  The  plants  or  parts  of  plants  to  be  incinerated  must  be  dry, 
suitably  comminuted  if  necessary,  and  free  from  all  adhering  im- 
purities. 

2.  The  ash  must  be  as  free  from  unconsumed  particles  as  possible. 

3.  During  the  process  of  incineration,  loss  of  essential  constit- 
uents must  be  avoided  so  far  as  possible. 

To  fulfil  the  first  condition,  the  plants  or  parts  of  the  plants 
must  therefore  be  carefully  selected,  cleaned,  and,  if  necessary, 
cut  up  and  dried.  It  is  not  always  possible  to  remove  adhering 
sand  or  clay  by  simple  rubbing  or  brushing,  more  particularly 
from  small  seeds.  For  cleaning  the  latter,  H.  ROSE  gives  the  follow- 
ing directions:  Treat  the  seeds  in  a  beaker  with  not  too  large  a 
quantity  of  water,  stir  well  for  a  moment  with  a  glass  rod,  and 
then  transfer  to  a  coarse  sieve  in  order  to  allow  the  fine  sand  to 


§  284.]  INORGANIC  CONSTITUENTS   OF   PLANTS.  791 

pass  through  while  retaining  the  seeds.  Repeat  this  operation 
several  times,  taking  care,  however,  never  to  leave  the  seeds  long 
in  contact  with  water,  otherwise  soluble  salts  may  be  extracted 
from  them.  Then  transfer  the  seeds  to  a  linen  cloth,  and  rub 
them  between  its  folds,  whereby  the  adhering  fine  sand  is  removed. 
Seeds  cleaned  in  this  manner  are  almost  entirely  free  from  foreign 
admixtures.  Then  dry  them  so  as  to  be  ready  for  incineration. 
The  jumping  of  the  seeds  during  heating  may  be  prevented  by 
first  crushing  them. 

When  cutting  plants,  it  is  of  course  necessary  to  employ  a 
perfectly  clean  knife  or  pair  of  scissors;  and  when  drying,  care 
must  be  taken  to  protect  the  plant  parts  from  dust  and  from  loss 
of  any  sap. 

To  fulfil  the  second  and  third  conditions,  the  main  thing  to  be 
borne  in  mind  is  that  the  incineration  must  be  effected  at  the 
lowest  possible  temperature  (at  a  dull  red  heat) ;  and  with  neither 
too  plentiful  nor  too  little  a  supply  of  air.  With  too  strong  a 
current  of  air  particles  of  the  ash  may  be  readily  carried  away, 
while  if  insufficient,  the  incineration  takes  too  long,  and  reductions 
take  place  more  easily.  If  the  ignition  is  too  strong,  not  only  do 
all  the  chlorides,  carbonates,  and  phosphates  of  the  alkalies  fuse 
and  greatly  impede  the  combustion  by  enveloping  the  carbon,  but 
the  alkali  chlorides  and  carbonates  *  may  be  easily  volatilized  by 
the  heat;  and  even  phosphoric  acid  may  be  lost  because,  as  ERD- 
MANN  first  showed,  acid  phosphates  of  the  alkalies  when  ignited 
with  carbon,  are  converted  into  neutral  salts,  with  reduction  and 
volatilization  of  a  part  of  the  phosphorus.  A  loss  of  chlorine, 
too,  cannot  be  avoided  by  careful  incineration,  as  the  acid  products 
of  the  dry  distillation  of  the  organic  substances  expel  hydrochloric 
acid — compare  H.  RosE,f  R.  WEBER,!  and  BEHAGHEL  VON  AD- 
LERSKRON.§  Although  loss  of  chlorine  and  phosphoric  acid  may 

*  Comp.  LANDOLT,  Zeitschr.  f.  analyt.  Chem.,  vn,  20;  A.  VOGEL,  iUd.9 
vii,  149. 

f  POGGENDORFF'S  Annal.,  LXXX,  113. 

J  Ibid.,  LXXXI,  407. 

§  Zeitschr.  /.  analyt.  Chem.,  xn,  405. 


792  PREPARATION    OF   THE  ASH.  [§  284. 

be  perfectly  prevented  by  proper  methods  of  incineration,  and  if 
necessary,  by  an  admixture  of  carbonate  of  sodium,  barium  or 
calcium  to  the  substance  to  be  incinerated,  this  is  not  the  case  with 
carbon  dioxide.  The  determination  of  carbon  dioxide  in  the  ash 
will  therefore  never  afford  any  certain  conclusions  regarding  the 
constituents  of  the  vegetable,  as  it  is  incorrect  to  suppose  that 
the  presence  of  carbonates  in  the  ash  of  a  plant,  which  itself  con- 
tains no  carbonates,  may  be  regarded  as  pointing  to  the  presence 
of  salts  of  organic  acids  in  the  plant,  since  alkali  carbonates  are 
readily  formed  by  the  action  of  nitrates  on  carbon,  or  by  the  action 
of  the  acid  products  of  the  dry  distillation  of  organic  substances 
on  alkali  chlorides  and  subsequent  decomposition  of  the  alkali 
compound  so  formed;  furthermore,  as  STEECKER  has  shown, 
alkali  carbonates  are  formed  when  orthophosphoric  acid  is  ignited 
with  a  large  excess  of  sugar  or  sugar-charcoal,  while  at  the  same  time 
alkali  pyrophosphates  are  formed.  Considering  not  only  this  fact, 
but  that  further  the  reverse  action  takes  place,  i.e.,  alkali  pyro- 
phosphates, when  strongly  ignited  with  carbonates,  are  converted 
into  orthophosphates,  it  follows  that  the  presence  of  orthophos- 
phates  or  pyrophosphates  in  an  ash  may  also  depend  upon  the 
manner  in  which  the  latter  has  been  prepared. 

The  conclusions  which  may  be  drawn  from  the  presence  of 
sulphuric  acid  in  an  ash  are  also  very  inaccurate,  even  when  the 
incineration  is  effected  with  the  addition  of  an  alkaline  earth,  as 
plants  contain,  in  the  first  place,  sulphuric  acid  in  the  form  of 
sulphates,  and,  secondly,  as  sulphur  organically  combined,  par- 
ticularly in  the  proteids.  If  the  incineration  is  properly  performed, 
the  whole  of  the  sulphates  originally  present  may,  it  is  true,  be 
obtained,  but  certainly  in  many  cases,  the  quantity  will  be  increased 
by  such  other  sulphates  as  were  formed  during  the  incineration. 
The  sulphuric-acid  content  of  an  ash  can,  therefore,  never  serve 
to  afford  a  conclusion  even  as  to  the  approximate  quantity  of 
sulphur  present  in  the  plant.* 

I  now  proceed  to  a  description  of  the  methods  which  may  be 
chosen  for  effecting  the  incineration. 

*  Compare  MAYER,  Annal.  d.  Chem.  u.  Pharm.,  ci,  136  and  154. 


§  284.]  PREPARATION    OF  THE    ASH.  793 

1.  Incineration  in  a  Muffle  or  Crucible. 

Incineration  in  a  muffle,  which  was  first  recommended  by 
ERDMANN,*  and  later  by  STRECKER,!  has  almost  entirely  super- 
seded the  older  method,  in  which  the  substance  was  burned  in 
obliquely  fixed  Hessian  crucibles. 

The  muffles  employed  are  made  of  the  same  material  as  Hessian 
crucibles,  and  are  about  25  cm.  long,  17  cm.  wide,  and  12  cm. 
high;  these  are  inside  measurements.  The  muffles  are  placed  in 
furnaces;  they  have  no  draught  chimney,  and  the  openings  are 
loosely  closed  with  perforated  covers.  The  air  circulation  so 
obtained  suffices  for  the  complete  combustion  of  the  carbonized 
substance. 

a.  First  dry  about  100  grm.  of  the  substance  to  be  incinerated, 
at  100°  or  110°.  Succulent  roots  or  fleshy  fruits  should  be  cut 
up  and  laid  on  glass  plates  for  this  purpose.  Weigh  the  dried 
substance,  then  place  it  in  a  shallow  platinum  or  porcelain  dish 
(better  still  in  a  shallow  platinum  or  porcelain  capsule  just  fitting 
into  the  muffle),  insert  it  in  the  muffle,  and  heat  the  latter  gradually. 
As  soon  as  pyroligneous  products  are  no  longer  evolved,  slightly 
increase  the  heat,  but  not  beyond  a  very  faint  red  heat  not  visible 
by  daylight.  At  this  temperature,  which  is  insufficient  to  fuse 
either  sodium  chloride  or  sodium  pyrophosphate,  the  carbon 
burns  off  with  feeble  incandescence,  and  twelve  hours  suffice  to 
obtain  sufficient  carbon-free  ash  for  analysis.  Substances  which 
are  not  adapted  for  this  mode  of  incineration  should  first  be  car- 
bonized in  a  large,  covered  platinum  or  even  Hessian  crucible, 
at  a  low  red  heat,  and  the  carbonized  mass  then  burned  in  the 
muffle.  As  a  rule,  it  is  inadvisable  to  stir  the  mass  during  incinera- 
tion, because  this  reduces  the  porosity  of  the  mass.  This  method, 
according  to  STRECKER,  occasions  no  loss  of  sodium  chloride  by 
volatilization. 

When  the  combustion  is  completed,  reconvert  any  alkalies  or 
alkaline  earths  formed  from  the  carbonates  by  loss  of  carbon 

*  Annul,  d.  Chem.  u.  Pharm.,  LIV,  353. 
f  Ibid.,  LXXIII,  366. 


794  INORGANIC    CONSTITUENTS    OF    PLANTS.  [§   284. 

dioxide,  so  far  as  possible,  into  neutral,  anhydrous  carbonates, 
weigh  the  ash  obtained,  triturate  it,  mix,  and  then  transfer  it 
to  a  well-closed  flask. 

The  conversion  of  the  alkalies  or  alkaline  earths  into  carbonates 
may  be  effected:  (a)  by  moistening  the  ash,  placing  under  a 
tubulated  bell-jar,  passing  carbon  dioxide  through  the  tubulure, 
and  allowing  to  stand  for  some  time,  repeating  the  operation  if 
necessary,  after  stirring  the  ash;  or  (/9)  by  repeatedly  evaporating 
the  ash  on  the  water-bath,  with  carbonic-acid  water  or  a  solution 
of  ammonium  carbonate.  Finally  dry,  and  heat  moderately  until 
all  the  water  has  been  expelled.  In  this  manner  alkalies  and  lime 
(also  baryta,  in  the  case  of  an  ash  prepared  with  barium  hydroxide 
as  in  4,  see  below),  are  converted  into  neutral  carbonates;  mag- 
nesia, however,  is  not,  as  when  it  is  present  as  such  in  the  ash,  it 
will  also  be  obtained  as  such,  or  at  least  partly  as  such,  in  the  ash 
treated  with  carbon  dioxide. 

6.  If  the  incineration  is  to  be  carried  out  on  the  small  scale, 
an  obliquely  fixed  platinum  crucible  heated  by  a  gas-  or  alcohol-lamp 
is  used.  The  crucible  should  be  fitted  with  a  slightly  arched  cover 
of  burned  clay,  or  a  disk  of  asbestos  cardboard,  fitting  as  closely 
as  possible  at  three  fourths  of  the  height  into  the  circular  opening 
of  the  crucible.  A  suitably  inclined  position  may  be  given  the 
apparatus  by  using  a  tripod  with  one  short  leg.  If  the  crucible 
is  then  heated  from  below  the  entrance  of  air  is  not  interfered 
with  by  the  burning  gases,  and  the  incineration  proceeds  just  as  in 
a  muffle  (J.  LOWE,*  G.  LUNGE  f).  As  regards  the  further  treat- 
ment of  the  ash,  compare  a. 

c.  In  the  case  of  vegetables  the  ash  of  which  is  rich  in  alkali 
salts,  particularly  chlorides,  and  which  is  hence  readily  fusible, 
it  is,  as  a  rule,  preferable  to  first  carbonize  the  substance  in  a  crucible 
by  prolonged  heating  at  the  lowest  temperature  possible,  then  to 
treat  with  water  to  extract  all  the  soluble  salts,  dry  the  residue, 
and  then  to  incinerate  in  a  muffle,  platinum  dish,  or  platinum 

*  Zeitschr.  f.  analyt.  Chem.,  xx,  223. 

f  Taschenbuch  fur  die  Soda-,  etc.,  Fabrikation,  Berlin,  F.  SPRINGER,  1883, 
p.  83. 


§  284.]  PREPARATION  OF   THE    ASH.  795 

crucible.  After  treating  the  ash  of  the  insoluble  portion  with 
carbonic-acid  water  or  ammonium  carbonate,  and  weighing  (see. 
above,  a),  dilute  the  solution  so  as  to  obtain  as  many  tenth-,  half-, 
or  whole-cubic  centimetres  as  there  are  milligrammes  of  ash  of  the 
insoluble  portion,  and  later,  in  the  analysis,  add  a  corresponding 
number  of  cubic  centimetres  of  the  solution  to  the  weighed  quanti- 
ties of  the  ash.  I  have  frequently  employed  this  method  with  de- 
cided success,  and  first  in  the  analysis  of  the  ash  of  the  ox-eye  daisy.* 
The  total  quantity  of  ash  is  ascertained  by  evaporating  to  dryness 
a  measured  quantity  of  the  solution  with  the  addition  of  carbonic- 
acid  water  or  a  solution  of  ammonium  carbonate,  and  weighing 
the  moderately  heated,  dry  residue.  Then  calculate  this  part 
to  the  whole,  and  add  the  result  (representing  the  weight  of  the 
residue  afforded  by  the  entire  solution)  to  the  weight  of  the  ash  of 
the  insoluble  portion. 

2.  Incineration  in  a  Dish,  with  the  Aid  of  an  Artificial 
Air-current  (F.  SCHULZE).! 

a.  The  organic  substance,  dried  at  100°  and  weighed,  carbonize 
in  a  crucible  at  a  low  red  heat,  transfer  the  carbon  to  a  shallow 
platinum  dish,  lay  on  the  latter  a  triangle  of  platinum  wire,  and  on 
the  triangle  place  an  ordinary  lamp  chimney  or  Argand  lamp 
chimney  (or  even  a  sufficiently  wide  retort  neck) ;  the  chimney 
may  also  be  clamped  in  a  retort  stand  and  thus  held  over  the  dish. 
The  increased  air-current  caused  by  the  chimney,  and  which  may 
be  regulated  by  employing  a  longer  or  shorter  chimney,  and  placing 
it  lower  or  higher,  suffices  to  effect  the  incineration,  even  of  cereal 
grains  at  an  astonishingly  low  temperature. J  When  the  incinera- 
tion is  complete,  weigh  the  ash,  and  proceed  as  in  1. 

6.  For  incinerating  vegetables  rich  in  alkali  salts,  the  method 
described  in  1,  c,  is  recommended. 

*  Journ.  f.  prakt,  Chem.,  LXX,  85. 
f  Communicated  to  the  author  by  letter 

J  F.  SCHULZE  employs  this  method  also  for  incinerating  filters,  placing 
the  crucible  containing  the  filter  into  the  dish. 


796  INORGANIC   CONSTITUENTS   OF   PLANTS.  [§  284. 

3.  Incineration  with  the  Aid  of  an  Artificial 
Air-current  (HLASIWETZ)  .* 

This  method  requires  a  silver,  platinum,  or  porcelain  tube 
shaped  like  a  tobacco  pipe.  For  difficultly  combustible  carbon  it 
should  be  cylindrical,  21  cm.  long,  4-5  cm.  wide,  and  tapering  to  a 
point  at  the  lower  end.  A  small  platinum  plate  provided  with  6 
to  8  perforations  prevents  any  carbon  or  ash  from  falling  out.  For 
readily  combustible  carbons,  the  tube  is  given  a  conical  or  crucible- 
like  form.  The  pipe  is  fitted  air-tight  into  one  tubulure  of  a  two- 
ne3ked  WOULFF  bottle  which  is  connected  in  the  usual  manner  with 
a  second  and  a  third,  and  the  latter  with  a  very  large  aspirator  (a 
capacious  barrel)  or  a  water-pump.  On  allowing  water  to  flow 
from  the  barrel,  or  on  effecting  suction  with  the  pump,  the  air  enters 
through  the  pipe  and  passes  through  the  water  with  which  the 
second  and  third  bottles  are  not  quite  half  filled.  To  conduct  the 
process,  carbonize  the  suitably  comminuted  organic  substance  in 
a  covered  porcelain  crucible;  as  soon  as  the  gases  cease  to  burn, 
transfer  the  feebly  glowing  carbon  to  the  pipe  by  means  of  a  funnel, 
and  immediately  allow  the  water  to  run  from  the  barrel,  or  employ 
moderate  suction.  The  aspiration  must  be  so  regulated  that  the 
combustion  proceeds  regularly,  but  at  not  too  high  a  temperature. 
From  time  to  time  gather  the  mass  together  by  means  of  a  plati- 
num wire ;  finally  heat  the  ash  for  a  short  time  in  a  platinum  dish 
in  order  to  consume  the  last  particles  of  carbon.  In  the  water  of 
the  WOULFF  bottles  will  be  found  traces  of  fixed  salts,  particularly 
chlorides;  also  carbon  dioxide  and  ammonia.  If  the  salts  are 
weighable,  determine  them. 

4.  Incineration  in  a  Muffle  with  the  Addition  of  Baryta 

(STRECKER).| 

Dry  the  organic  substance  at  100°,  and  slightly  carbonize  it  in 
a  platinum  or  porcelain  dish  over  the  lamp.  Moisten  the  carbon 
with  a  concentrated  solution  of  pure  barium  hydroxide,  employing 

*  Annal.  d.  Chem.  u.  Pharm.,  xcvn,  244 
f  Ibid.,  LXXIII,  366. 


§  284.]  PREPARATION    OF  THE  ASH.  797 

such  a  quantity  that  the  ash  left  on  incineration  may  contain  about 
half  its  weight  of  baryta.  Dry  the  moistened  carbon  again,  and 
burn  it  in  the  muffle  at  the  lowest  temperature  possible.  By  this 
treatment  the  ash  does  not  fuse,  but  remains  voluminous  and  loose, 
thus  allowing  complete  combustion  of  the  carbon.  The  residue 
must  still  contain  a  considerable  excess  of  baryta.  If  this  is  not 
the  case,  a  loss  of  phosphorus  may  be  apprehended,  at  least  in 
some  incinerations;  it  is  advisable  in  such  cases,  therefore,  to  in- 
cinerate a  fresh  portion  with  a  large  excess  of  baryta.  The  residue 
is  then  finely  powdered  and  intimately  mixed. 

As  E.  VON  RAUMER,*  on  incinerating  maize  grains  according 
to  the  method  just  described,  observed  that  the  ash  contained 
pyrophosphates,  he  recommended,  in  order  to  avoid  this  happen- 
ing when  incinerating  cereals,  to  soak  these  with  baryta  water,  then 
to  dry  and  incinerate.  The  ash  of  maize  so  treated  contained  only 
orthophosphates . 

If  the  quantity  of  ash  is  to  be  determined  in  the  baryta-contain- 
ing ash,  measured  quantities  of  baryta  water  of  known  strength 
must  be  added,  and  the  ash  treated  as  in  1,  a,  so  as  to  convert  into 
carbonates  the  alkalies  and  alkaline  earths  resulting  from  the  loss 
of  carbon  dioxide.  Finally  it  must  be  noted  that  baryta-contain- 
ing ash,  as  a  rule  (i.e.,  when  a  very  large  excess  of  baryta  has  not 
been  added),  no  longer  contains  all  the  chlorine  originally  present  in 
the  substance  incinerated.  The  quantities  of  ash  obtained  will 
hence  usually  be  too  low,  and  therefore  an  accurate  determination 
of  the  chlorine  in  the  organic  substance  should  be  made  in  a  sepa- 
rate portion  (see  below,  p.  810,  BUNGED  BEHAGHEL  VON  ADLERS- 
KRON)  4 

5.  Incineration  with  the  Aid  of  Spongy  Platinum  (H.  ROSE). 

Carbonize  about  100  grm.  of  the  substance  dried  at  100°,  in  a 
platinum  or  clay  crucible  at  a  dark-red  heat,  finely  triturate  the 
carbonized  mass  in  a  porcelain  mortar,  mix  it  intimately  with  20 

*  Zeitschr.  f.  analyt.  Chem.,  xx,  375. 
f  Zeitschr.  f.  Biologie,  ix,  part  1. 
j  Zeitschr.  f.  analyt.  Chem.,  xii,  405. 


798  INORGANIC   CONSTITUENTS   OF    PLANTS.  [§  285. 

to  30  grm.  spongy  platinum,  transfer  the  mixture  in  portions  to  a 
shallow,  thin,  platinum  dish,  and  heat  over  a  lamp  with  double 
draught.  After  a  short  time,  and  before  the  contents  begin  to 
ignite,  every  particle  of  carbon  begins  to  glimmer,  and  the  surface 
of  the  black  mixture  becomes  covered  with  a  gray  layer.  By  dili- 
gent, careful  stirring  with  a  small  platinum  spatula,  renew  the  sur- 
face and  promote  the  combustion.  So  long  as  the  mass  still  con- 
tains unconsumed  carbon,  the  glimmering  continues;  as  soon, 
however,  as  all  the  carbon  is  completely  burned,  all  visible  in- 
candescence ceases,  even  though  the  mass  is  still  more  strongly 
heated.  When  all  the  successive  portions  added  are  incinerated, 
mix  uniformly,  convert  any  oxides  that  may  have  formed  into 
carbonates  (see  above,  1,  a,  p.  793),  and  weigh.  On  deducting 
the  weight  of  the  spongy  platinum  added,  the  weight  of  the  ash 
is  obtained.  A  loss  of  chlorine  occurs  also  in  this  method  of 
incineration  (compare  p.  791). 

6.  Other  Methods  of  Incineration, 

The  processes  described  under  1  to  5  do  not  by  any  means 
exhaust  all  the  methods  of  incineration  proposed  or  employed. 
Thus  GRAGER*  and  AL.  MuLLERf  add  ferric  oxide  when  incin- 
erating, while  BECHAMP,t  for  the  incineration  of  difficultly  combus- 
tible vegetable  or  animal  substances,  e.g.,  beer  yeast,  recommends 
the  addition  of  bismuth  nitrate.  I  consider  it  sufficient  to  here 
confine  myself  to  a  mere  mention  of  these  particular  methods  of 
incineration. 

H.  ANALYSIS   OF  THE  ASH. 

§285. 

After  having  described  the  most  advantageous  methods  of 
preparing  the  plant-ash,  I  would  now  point  out  that  in  by  far  the 
majority  of  cases  the  methods  1  and  2,  if  properly  carried  out,  par- 
ticularly 1  c  or  2  b  in  suitable  cases,  are  perfectly  satisfactory. 

*  Jahresberich  von  KOPP  und  WILL,  1859,  693. 

•j-  Journ.  /.  prakt.  Chem.,  LXXX,  118. 

J  Compt.  rend.,  LXXIII,  337;  Zeitschr.  f.  analyt.  Chem.,  xi,  332. 


§  285.]  ANALYSIS   OF  THE  ASH.  799 

I  make  this  statement  in  order  to  explain  why,  in  the  following, 
reference  is  made  exclusively  to  the  analysis  of  pure  ash  (free  from 
barium  and  platinum).  In  such  cases  where  methods  4  or  5  are 
used,  the  modifications  required  and  which  are  described  below, 
are  but  slight,  and  readily  suggest  themselves. 

According  to  their  main  constituents,  the  ashes  may  be  classi- 
fied as  follows : 

a.  Ashes  in  which  carbonates  of  the  alkalies  and  alkaline  earths 
predominate.  Such  ashes  are  afforded  by  woods,  herbaceous 
plants,  etc. 

ft.  Ashes  in  which  phosphates  of  the  alkalies  and  alkaline  earths 
predominate.  To  this  class  belong  the  ashes  of  almost  all  seeds. 

7-.  Ashes  in  which  silica  predominates.  These  are  yielded  by 
the  stalks  of  the  Graminece,  Equisetacece,  etc. 

Although  it  is  clear  that  this  classification  cannot  be  quite 
strict,  and  that  numerous  lapses  from  one  group  to  another  occur, 
it  must  nevertheless  be  retained  if  the  analytical  methods  about 
to  be  described  are  to  be  used,  since  the  general  mode  of  procedure 
must  be  modified  according  as  the  ash  belongs  to  the  first,  second, 
or  third  class. 

a.  Qualitative  Analysis. 

As  the  constituents  which  usually  occur  in  ashes  are  in  general 
known,  it  would  be  superfluous  to  make  a  complete  qualitative 
analysis  of  every  ash.  It  is  only  necessary  to  make  a  few  pre- 
liminary tests  to  ascertain  the  presence  or  absence  of  more  rarely 
occurring  constituents,  and  also  to  which  of  the  above-mentioned 
classes  the  ash  belongs.  These  tests  are  as  follows: 

1.  Test  the  reaction  of  the  ash. 

2.  Test  whether  the  ash  is  completely  decomposed  on  warming 
with   concentrated   hydrochloric   acid.     If   the   ash   effervesces    on 
treatment  with  the  strong  acid,  it  may  be  regarded  as  a  proof  that 
the  ash  can  be  decomposed.     As  a  rule  it  is  only  the  ashes  of  the 
stalks  of  the  Graminece,  etc.,  rich  hi  silica,  which  cannot  be  com- 
pletely decomposed. 

3.  On  adding  an  alkali  acetate  to  the  hydrochloric-acid  solution 


800  INORGANIC   CONSTITUENTS   OF   PLANTS.  [§  286. 

of  an  ash,  after  separating  the  silica  and  removing  the  greater  part 
of  the  free  acid,  or  on  neutralizing  the  solution  with  ammonia 
and  then  adding  free  acetate  acid,  a  yellowish-white,  gelatinous 
precipitate  of  ferric  phosphate  separates  in  the  case  of  almost  all 
ashes.  It  is  now  necessary  to  ascertain  whether,  in  addition  to 
the  phosphoric  acid  found  in  this  precipitate,  there  is  a  further  quan- 
tity left  in  the  ash.  To  decide  this  question,  filter  off  the  precipitate 
thus  obtained,  and  add  an  excess  of  ammonia  to  the  filtrate.  If 
no  precipitate  forms,  or  if  a  brownish-red  precipitate  (of  ferric 
hydroxide)  forms,  the  ash  contains  no  more  phosphoric  acid;  if, 
however,  a  white  precipitate  (calcium  phosphate  and  ammonium- 
magnesium  phosphate)  forms,  it  is  certain  that  the  ash  contains 
more  phosphoric  acid  than  the  ferric  oxide  present  in  it  can  com- 
bine with,  and  the  ash  must  consequently  be  placed  in  the  second 
class. 

4.  Test  the  ash  for  manganese,  by  mixing  a  small  quantity  with 
sodium  carbonate  and  exposing  on  platinum  foil  to  the   outer 
flame  of  the  blowpipe  (see  "Qualitative  Analysis,"  14th  Germ,  ed., 
p.  140). 

5.  Test  whether  hydrogen  sulphide  is  evolved  on  treating  the 
ash  with  hydrochloric  acid. 

6.  Test    for    lithium,    rubidium,    strontium,    barium,    copper, 
aluminium,   iodine,  bromine,  fluorine,  and  the  other  substances 
mentioned  as  occasionally  occurring  in  very  minute  quantities, 
if  it  is  considered  of  interest  to  ascertain  if  traces  of  these  are 
present  (see  " Qualitative  Analysis,"  14th  Germ,  ed.,  p.  398). 

b.  Quantitative  Analysis. 

(v.  Ashes  in  which  Carbonates  of  the  Alkalies  or  Alkaline  Earths 

Predominate,  and  in  which  All  the  Phosphoric  Acid  may  be 

Assumed  to  be  Combined  with  Ferric  Oxide. 

§286. 

The  constituents  are  determined  in  two  separate  portions  of 
the  ash,  which  we  will  designate  as  AA  and  BB. 


§  286.]       DETERMINATION   OF   VARIOUS   CONSTITUENTS.  801 

In  BB  the  carbon  dioxide  *  and  chlorine  are  determined. 

In  AA  all  the  other  constituents  are  determined. 

If  the  ash,  however,  contains  sulphides,  three  separate  portions 
must  be  taken,  one  for  carbon  dioxide  and  hydrogen  sulphide, 
the  second  for  chlorine,  and  the  third  for  the  remaining  constit- 
uents. 

AA. 

1     DETERMINATION   OF  SILICA,   CARBON,   AND   SAND. 

Cover  4  or  5  grm.  of  the  ash  with  some  water  in  a  porcelain 
dish,  and  gradually  add  hydrochloric  acid.  If  the  ash  is  rich  in 
carbonates,  cover  the  dish  with  an  inverted  funnel  in  the  stem  of 
which  is  inserted  a  small  funnel  through  which  the  acid  is  added. 
In  this  manner  all  loss  from  spirting  may  be  avoided.  Now  heat 
gently,  and  as  soon  as  all  the  carbon  dioxide  has  been  driven  off, 
rinse  off  the  funnels  into  the  dish.  When  no  more  undecomposed 
ash  is  visible  besides  the  readily  distinguishable  carbonaceous 
particles  (and  which  are  almost  always  present),  evaporate  to 
dryness  in  a  water-bath,  frequently  stirring  towards  the  end, 
and  crushing  all  the  lumps,  any  sand  present  being  easily  recog- 
nized by  the  grating  sound. 

When  cold,  moisten  the  dry  mass  with  concentrated  hydro- 
chloric acid,  and  after  half  an  hour,  heat  with  a  moderate  quantity 
of  water  on  the  water-bath;  then  dilute  further,  filter  the  acid 
liquid  through  a  stout  filter  dried  at  110°  and  weighed. 

On  the  filter  will  be  found  the  silica,  mixed  with  carbon  and 
sand  if  these  are  present.  If  the  residue  consists  only  of  silica 
and  carbon,  wash  it  well,f  dry  at  110°,  weigh,  incinerate,  and 
thus  determine  the  silica,  the  difference  being  carbon.  Whether 
the  silica  is  pure  or  not  may  be  ascertained  by  heating  it  with 
hydrofluoric  and  sulphuric  acids.  If  the  residue,  however,  consists 
of  silica,  carbon,  and  sand,  transfer  it,  after  washing  and  drying, 

*  The  determination  of  this,  although  it  is  of  no  great  significance  (see 
p.  792  this  volume),  is  yet  necessary,  in  order  to  complete  the  analysis  and 
thus  afford  a  certain  control  of  its  accuracy. 

j*  As  any  considerable  quantity  of  carbon  can  be  washed  only  with  diffi- 
culty, ashes  rich  in  carbon  are  not  adapted  for  accurate  analyses. 


802  INORGANIC   CONSTITUENTS   OF    PLANTS.  [§  286. 

to  a  platinum  dish,  without,  however,  injuring  the  filter.     (If  the 
powder  is  perfectly  dry,  this  may  be  readily  accomplished,  only  a 
few  particles  of  carbon  adhering  to  the  paper,  usually  just  sufficient 
to  color  this  slightly.)     Now  boil  the  powder  for  half  an  hour  with: 
pure  (silica-free),  diluted  caustic-soda  solution  (or  with  a  concen-' 
trated  sodium-carbonate  solution),  whereby  the  silica  is  gradually/ 
dissolved  without  any  of  the  sand  or  carbon  present  being  attacked. 
Now  filter  through  the  original  filter-paper,  wash  the  undissolved 
residue  thoroughly,  and  dry  it  with  the  filter  at  110°  until  it  ceases 
to  lose  weight.    On  deducting  the  weight  of  the  filter,  the  remainder 
is  calculated  as  carbon  and  sand. 

The  filtrate  supersaturated  with  hydrochloric  acid  gives,  accord- 
ing to  §  140,  II,  a,  the  quantity  of  silica. 

2.    DETERMINATION    OF    ALL    THE     REMAINING    CONSTITUENTS 
EXCEPTING    CHLORINE   AND    CARBON    DIOXIDE. 

Mix  the  hydrochloric-acid  solution  filtered  off  from  the  silica, 
carbon,  and  sand  with  the  washings,  and  divide  the  whole,  either 
by  weight  or  measure,  into  three,  or  more  conveniently,  four 
parts,  in  order  that  should  a  determination  miscarry,  the  last  por- 
tion may  be  utilized  for  a  new  determination.  The  division  is 
most  simply  effected  by  filtering  the  liquid  into  a  200-c.c.  flask 
or  cylinder,  adding  first  the  washings,  then  sufficient  pure  water 
to  fill  up  to  the  mark,  shaking  and  then  pipetting  off  three 
portions  of  50  c.c.  each.  These  three  portions  we  will  designate  as 
aa,  bb,  and  cc.  In  aa  we  determine  the  ferric  phosphate,  any  free 
ferric  oxide  and  manganous  oxide,  the  alkaline  earths,  and  also 
alumina  should  this  happen  to  be  present.  In  bb  the  sulphuric 
acid  is  determined,  and  in  cc.  the  alkalies. 

aa.  Determination  of  the  Ferric  Phosphate,  etc.,  and  the  :, 

Alkaline  Earths. 

Cautiously  add  ammonia  to  the  liquid  until  the  resulting  precip- 
itate just  no  longer  redissolves,  then  add  ammonium  acetate  and 
sufficient  acetic  acid  to  decided  acidity.  The  persistent  yellowish- 
white  precipitate,  which  separates  best  on  gently  warming,  consists  , 


§  286.]       DETERMINATION    OF   VARIOUS  CONSTITUENTS.  803 

of  ferric  phosphate;  it  should  be  filtered  off  without  loss  of  time. 
If  the  quantity  of  the  precipitate  is  small,  and  the  ash  contains  no 
determinable  quantities  of  manganese  and  alumina,  and  if  the 
filtrate  is  not  red,  wash  the  precipitate  with  hot  water  containing 
some  ammonium  nitrate,  ignite,  weigh,  and  calculate  the  residue 
as  Fe2(PO4)2  (comp.  Vol.  I,  p.  227).  If,  however,  under  conditions 
similar  to  those  noted,  the  precipitate  is  larger,  wash  it  three  or 
four  times,  then  dissolve  in  the  smallest  quantity  of  hydrochloric 
acid  possible,  add  ammonia  until  a  permanent  precipitate  just 
begins  to  form,  then  add  ammonium  acetate  and  a  little  acetic 
acid.  After  gently  warming,  filter,  wash  as  above,  dry,  ignite, 
and  calculate  this  residue  also  as  Fe2(PO4)2. 

If  any  of  the  above  conditions  do  not  exist,  the  precipitate 
(whether  that  collected  directly  or  whether  first  collected,  washed, 
dissolved  in  hydrochloric  acid,  and  reprecipitated  by  ammonium 
acetate)  cannot  be  weighed  directly  and  calculated  as  Fe2(PO4)2, 
as  in  this  case  it  may  contain  manganous  oxide  and  alumina,  or,  if 
the  filtrate  was  red,  basic  ferric  phosphate.  If  only  the  latter  is 
present,  ignite  and  weigh  the  precipitate,  dissolve  in  hydrochloric 
acid,  determine  the  iron  in  the  solution  according  to  Vol.  I,  p.  460, 
g,  /?,  and  from  the  difference  ascertain  the  phosphoric  acid  that  was 
combined  with  it. 

If,  however,  the  precipitate  contains  also  manganese,  and  per- 
haps alumina  too,  dissolve  it  in  hydrochloric  acid,  separate  the  iron 
and  manganese  according  to  Vol.  I,  p.  460,  g,  ft  (separating  these 
according  to  Vol.  I,  p.  644  [82]),  evaporate  the  filtrate  hi  a  platinum 
dish  with  an  excess  of  pure  sodium  carbonate  until  ammonia  is  no 
longer  evolved,  then  add  some  potassium  nitrate,  evaporate  to 
dryness  and  heat  until  the  mass  melts ;  then  soften  the  melt  with 
water,  transfer  it  to  a  small  beaker,  add  hydrochloric  acid,  warm, 
filter,  and  add  ammonia  until  alkaline.  If  no  precipitate  forms, 
alumina  is  absent.  In  this  case  evaporate  repeatedly  with  nitric 
acid  on  the  water-bath,  and  determine  the  phosphoric  acid  by  the 
molybdenum  method  (Vol.  I,  p.  446,  /?).  If,  on  the  other  hand,  the 
ammonia  throws  down  a  precipitate,  add  nitric  acid  until  it  is  dis- 
solved, evaporate  repeatedly  with  nitric  acid,  determine  the  phos- 


804  INORGANIC   CONSTITUENTS    OF   PLANTS.  [§  286. 

phoric  acid  by  the  molybdenum  method,  precipitate  the  molybde- 
num from  the  nitrate  by  means  of  hydrogen  sulphide,  filter,  and  in 
the  filtrate  determine  the  alumina  according  to  Vol.  I,  p.  278,  a. 

If  the  hydrochloric-acid  solution  of  the  fused  mass  gives  a  pre- 
cipitate with  ammonia,  it  contains  aluminium ;  and  if  it  is  desired 
to  avoid  the  inconvenient  molybdenum  separation,  determine  the 
aluminium  in  the  hydrochloric-acid  solution  of  the  melt  as  alumin- 
um phosphate  by  adding  to  the  solution  some  sodium  phosphate, 
then  ammonia,  and  finally  acetic  acid  in  excess.  Collect  the  pre- 
cipitate thus  obtained,  wash,  dry,  ignite,  and  weigh  as  A12(P04)2. 

To  determine  the  phosphoric  acid  use  the  last  50  c.c.  of  the 
solution  filtered  off  from  the  silica,  etc.,  and  proceed  according  to 
p.  807,  a,  this  volume. 

In  the  filtrate  from  the  ferric  phosphate,  and  rendered  acid  by 
acetic  acid,  determine  the  calcium  and  magnesium,  and  also  the 
rest  of  the  iron  and  manganese*  if  these  are  present.  For  this  pur- 
pose precipitate  the  iron,  if  necessary,  with  ammonia,  or  the  iron 
and  manganese  (which  are  to  be  separated  as  in  Vol.  I,  p.  644  [82]) 
with  ammonia  and  ammonium  sulphide,  and  determine  the  cal- 
cium and  magnesium  according  to  Vol.  I,  p.  619  [36],  after  decom- 
posing the  excess  of  ammonium  sulphide  in  the  filtrate  by  evapo- 
rating with  hydrochloric  acid  and  filtering. 

bb.  Determining  the  Sulphuric  Acid. 

Precipitate  the  liquid,  bb,  with  barium  chloride,  and  determine 
the  precipitate  according  to  Vol.  I,  p.  434,  1.  If  the  solution  con- 
tains a  large  excess  of  hydrochloric  acid,  partially  neutralize  this 
first  with  ammonia. 

cc.  Determining  the  Alkalies. 

Add  as  much  barium  chloride  to  the  liquid  bb  as  will  just  suffice 
to  precipitate  the  sulphuric  acid,  then  evaporate  off  on  the  water- 
bath  the  greater  part  of  the  free  acid,  dilute,  add  a  few  drops  ferric- 

*  I  have  made  no  reference  in  the  text  to  the  very  rare  event  of  this 
liquid  still  containing  aluminium.  Should  this  be  present,  precipitate  it 
by  means  of  ammonia  or  ammonium  sulphide,  and  then  separate  the  alu- 
minium from  the  iron  or  manganese  according  to  §  160. 


§  286.]       DETERMINATION    OF    VARIOUS    CONSTITUENTS.  805 

chloride  solution,  then  pure  milk-of-lime  in  slight  excess,  heat  for 
some  time  on  the  water-bath,  and  filter.  In  this  manner  all  the 
sulphuric  acid,  phosphoric  acid,  iron,  manganese,  and  magnesium 
are  removed.  Wash  the  precipitate  until  the  last  washings  cease 
to  give  a  turbidity  with  silver-nitrate  solution  acidulated  with 
nitric  acid ;  then  precipitate  the  excess  of  calcium  in  the  filtrate  by 
adding  ammonium  carbonate  mixed  with  ammonia,  allow  to  settle, 
filter,  evaporate  to  dryness  in  a  platinum  dish  and  ignite  ;  dissolve 
reprecipitate  with  ammonium  carbonate  and  ammonia,  if  necessary 
repeating  the  precipitation  a  third  time  (in  fact  until  the  solution 
of  the  gently  ignited  residue  is  no  longer  rendered  turbid  by  am- 
monium carbonate  and  ammonia) ;  then  evaporate,  ignite  gently, 
weigh  the  residual  alkali  chlorides,  and  separate  potassium  and 
sodium,  if  both  are  present,  according  to  Vol.  I,  p.  599  [i]. 

N.B.  If  the  quantity  of  ash  is  small,  the  filtrate  from  the 
silica  may  be  divided  into  two  parts,  and  the  sulphuric  acid  and 
alkalies  determined  in  one,  first  precipitating  the  sulphuric  acid 
with  barium  chloride,  avoiding  any  appreciable  excess,  however, 
then  filtering  and  proceeding  as  in  cc. 

BB. 

DETERMINATION    OF    THE  CARBONIC  ACID,  CHLORINE,  AND   ANY  SUL- 
PHUR THAT  MAY  BE  PRESENT  AS  METALLIC  SULPHIDES. 

1.  When  the  qualitative  tests  have  shown  metallic  sulphides  to  be 
absent  from  the  ash. — Treat  a  second  portion  of  the  ash  according 
to  Vol.  I,  p.  490,  bb,  or  p.  493,  in  order  to  determine  the  carbonic 
acid.     Filter  the  contents  of  the  small  flask  in  which  the  solution 
is  effected  by  means  of    diluted  nitric  acid,  and  precipitate  the 
chlorine  with  silver  solution  according  to  Vol.  I,  p.  521,  a. 

2.  When  the  qualitative  tests  have  shown  metallic  sulphides  to  be 
present  in  the  ash. — Treat  a  second  portion  of  the  ash  with  hydro- 
chloric acid  in  order  to  determine  the  hydrogen  sulphide  (and  thus 
the  sulphur  present  in  combination  with  metals)  and  the  carbon 
dioxide  evolved,  according  to  p.  365,  d,  this  volume.     In  order  that 
the  hydrogen-sulphide  determination  may  be  accurate  it  is  advis- 


806  INORGANIC    CONSTITUENTS    OF    PLANTS.  [§  287. 

able  to  conduct  the  operation  in  an  atmosphere  of  hydrogen  (p.  519, 
a,  this  volume).  To  determine  the  chlorine,  boil  a  third  portion  of 
the  ash  with  water,  filter,  and  mix  the  filtrate  with  a  solution  of 
silver  nitrate  in  excess;  treat  the  portion  of  the  ash  insoluble  in 
water  with  cold,  diluted  nitric  acid,  filter,  and  use  this  filtrate  for 
acidulating  the  aqueous  filtrate  which  was  precipitated  with 
silver  nitrate.  Allow  the  whole  to  settle  in  a  place  secluded  from 
light,  filter  off  the  precipitate  consisting  of  silver  chloride  and 
silver  sulphide,  wash  it,  treat  with  ammonia  to  dissolve  the  silver 
chloride,  filter,  then  acidulate  the  filtrate  with  nitric  acid,  and 
determine  the  now  pure  silver  chloride  according  to  Vol.  I,  p.  521,  a. 
N.B.  Should  the  quantity  of  ash  be  very  small,  all  the  con- 
stituents, if  no  sulphides  are  present,  may  be  determined  in  one  por- 
tion. In  this  case  ascertain  first  the  carbon  dioxide  as  in  BB,  1, 
then  filter  through  a  weighed  filter,  determine  the  chlorine  in  the 
filtrate,  and  precipitate  the  excess  of  silver  with  hydrochloric  acid; 
spread  the  first  filter  on  a  glass  plate,  and  rinse  off  its  contents  into 
the  second  filtrate,  and  then  proceed  as  in  AA.  Carbon,  sand,  and 
silica  are  subsequently  again  collected  on  the  filter  which  mean- 
while has  been  rinsed  off  and  dried. 

/?.  Ashes  Decomposable  by  Hydrochloric  Acid,  and  in  which  a 

Further  Quantity  of  Phosphoric  Acid  is  Present  Above 

that  Combined  with  Iron. 

§287. 

Take  two  portions  of  ash,*  a  larger  one,  AA  and  a  smaller,  BB. 
In  BB  determine  the  carbon  dioxide  and  chlorine  as  in  §  286.  In 
A  A  determine  the  other  constituents.  If  the  quantity  of  ash  at 
hand  is  very  small,  determine  all  the  constituents  in  one  portion 
(see§286,BB,"N.B."). 

Treat  AA  with  hydrochloric  acid  and  separate  silica,  carbon, 
and  sand,  as  in  §  286.  Make  up  the  hydrochloric-acid  solution  to 

*  Should  such  ashes  contain  metallic  sulphides,  by  exception,  three  por- 
tions would  be  required,  and  the  analysis,  with  reference  to  the  determina- 
tion of  the  chlorine,  carbon  dioxide,  and  hydrogen  sulphide,  carried  out 
according  to  the  methods  described  on  p.  805,  2,  this  volume. 


§  287.J       DETERMINATION    OF   VARIOUS    CONSTITUENTS.  807 

300  c.c.,  and  divide  it  into  two  portions,  one,  aa,  of  100  c.c.,  and 
the  other,  bb,  of  200  c.c. 

In  aa  first  determine  the  sulphuric  acid  by  adding  barium 
chloride  in  the  least  possible  excess  and  filtering.  Then  add 
ferric-chloride  solution  until  the  liquid  appears  yellow,  expel 
almost  all  the  free  acid  hi  the  solution  by  evaporating  on  the 
water-bath,  dilute,  and  add  pure  milk-of-lime  until  the  liquid  is 
strongly  alkaline;  heat  almost  to  boiling,  filter,  wash  until  the 
washings  cease  to  react  for  chlorine,  remove  the  calcium  and 
barium  from  the  filtrate  with  ammonium  carbonate,  and  proceed 
to  determine  the  alkalies  according  to  §  286. 

To  bb  add  first  ammonia  in  slight  excess,  then  immediately 
acetic  acid  until  the  alkaline-earth  phosphates  as  first  precipitated 
are  redissolved.  The  precipitate,  which  usually  consists  chiefly 
of  ferric  phosphate,  but  which  may  also  contain  manganous  oxide, 
in  rare  cases  alumina,  too,  and  if  the  quantity  is  considerable,  also 
small  quantities  of  alkaline-earth  phosphates,  treat  as  detailed 
on  p.  802,  aa,  this  volume.  Divide  the  filtrate  into  two  portions, 
a  and  {3;  in  a  determine  the  phosphoric  acid,  and  in  [3  the  calcium 
and  magnesium. 

a.  To  determine  the  phosphoric  acid,  evaporate  the  liquid 
repeatedly  with  nitric  acid  on  the  water-bath,  almost  to  dryness, 
take  up  the  residue  with  nitric  acid,  and  determine  the  phosphoric 
acid  by  the  molybdenum  method  (Vol.  I,  p.  446,  /?).  I  would 
remark  here  that  after  dissolving  the  ammonium  phosphomolyb- 
date  in  ammonia  and  neutralizing  the  greater  part  of  the  ammonia 
with  hydrochloric  acid,  it  is  advisable  to  add  a  definite  quantity 
of  ammonia  (4  to  6  c.c.),  then  to  add  the  magnesia  mixture,  drop 
by  drop,  and  lastly  to  add  a  still  further  quantity  of  ammonia  until 
the  latter  forms  one-fourth  of  the  whole.  By  this  mode  of  deter- 
mining the  phosphoric  acid,  accurate  results  are  obtained  with 
certainty,  whether  the  ash  contains  ortho-  or  pyrophosphates. 

/?.  To  determine  the  calcium  and  magnesium  in  /?  proceed 
according  to  Vol.  I,  p.  621  [37].  If  the  ash  contains  a  determinable 
quantity  of  manganese,  this  must  be  removed  from  the  portion  fi 
in  which  the  calcium  and  magnesium  are  to  be  determined,  other- 


808  INORGANIC    CONSTITUENTS   OF    PLANTS.  [§  288. 

wise  it  would  be  thrown  down  partly  with  one,  partly  with  the 
other.  Hence  treat  /?,  acidulated  with  acetic  acid,  and  still  .con- 
taining alkali  acetate,  first  with  chlorine  or  bromine,  at  a  tem- 
perature of  50°  to  60°,  collect  the  hydrated  manganese  dioxide, 
wash  it,  dissolve  in  hydrochloric  acid,  and  precipitate  and  deter- 
mine the  manganese  as  sulphide;  evaporate  the  filtrate  which  still 
contains  portions  of  the  alkaline  earths  (Vol.  I,  p.  635,  a)  with 
hydrochloric  acid,  filter,  add  the  filtrate  to  the  filtrate  from  the 
hydrated  manganese  dioxide,  and  in  the  united  filtrates  determine 
the  calcium  and  magnesium  as  above  detailed. 

Of  the  great  variety  of  methods  which  may  be  chosen  for  /?, 
if  this  contains  no  manganese,  I  will  only  mention  the  following: 
After  separating  the  ferric  phosphate,  precipitate  first  the  calcium 
from  the  acetic-acid  solution  by  means  of  ammonium  oxalate 
(Vol.  I,  p.  621  [37]).  Divide  the  filtrate  into  two  equal  parts, 
and  in  one  determine  the  magnesia  by  adding  ammonia  and  sodium- 
ammonium  phosphate;  in  the  other  determine  the  phosphoric 
acid  by  evaporating  with  the  addition  of  nitric  acid,  and  then 
adding  ammonia  and  solution  of  magnesium  chloride  containing 
some  ammonium  chloride. 

7*.  Ashes  not  Decomposed  by  Hydrochloric  Acid. 

§288. 

Carbonic  acid  is  seldom  found  in  such  ashes;  when  it  is,  how- 
ever, determine  it  as  in  §  286.  This  is  also  true  of  chlorine.  So 
far  as  the  determination  of  the  other  constituents  is  concerned, 
the  ash  must  first  be  decomposed.  The  decomposition  may  be 
effected  in  various  ways. 

1.  It  may  be  effected,  as  WILL  and  I  first  proposed,  by  evapo- 
rating the  ash  to  dryness  with  pure  soda  lye  in  a  platinum  or  silver 
dish.  (Experiments  have  shown  that  by  this  treatment  the  sili- 
cates in  the  ash  are  completely  decomposed,  while  any  admixed 
sand  is  not  affected,  or  at  least,  but  very  slightly.  The  heat  must 
not  be  raised  towards  the  end  of  the  process  to  a  point  sufficient 
to  fuse  the  mass.)  Cover  the  residue  then  with  diluted  hydrochloric 


§  288.]        DETERMINATION   OF   VARIOUS    CONSTITUENTS.  809 

acid,  evaporate,  treat  again  with  hydrochloric  acid,  and  proceed 
with  the  insoluble  residue  (of  silica,  carbon,  and  sand),  as  above, 
§  286,  AA,  1;  the  solution,  however,  treat  as  in  §  286,  AA,  2,  or 
in  §  287,  AA.  It  is,  of  course,  evident  that  the  alkalies  cannot 
be  determined  in  the  latter,  but  must  be  determined  in  a  separate 
portion  of  the  ash  after  this  has  been  decomposed  by  fusion  with 
barium  hydroxide  or  treatment  with  hydrofluoric  acid. 

2.  WAY  and  OGSTON  *  mix  the  (sand-free)  ash  with  an  equal 
weight  barium  nitrate,  and  introduce  the  mixture  in  small  portions 
into  a  large  platinum  crucible.  By  this  treatment  the  ash  is 
rendered  readily  decomposable  by  hydrochloric  acid,  and,  should  it 
have  contained  carbon,  also  perfectly  white.  Separate  the  silica 
as  in  §  286,  AA,  1,  and  also  determine  and  allow  for  any  barium 
sulphate  that  may  be  present.  In  a  portion  of  the  hydrochloric- 
acid  solution  determine  the  alkalies  (according  to  §  286,  AA,  2,  cc); 
the  balance  is  precipitated  with  a  slight  excess  of  sulphuric 
acid.  (The  quantity  of  barium  nitrate  used  being  known,  the 
quantity  of  any  calcium  sulphate  present  is  calculated  from  the 
excess  over  the  weight  of  the  barium  sulphate  obtained.)  The 
nitrate  is  divided  into  two  portions,  the  ferric  phosphate,  calcium, 
and  magnesium  being  determined  in  one  (§  287),  and  the  phos- 
phoric acid  in  the  other,  as  in  §  134,  d,  a. 


Regarding  other  methods  of  analysis  of  plant  ashes  or  other 
ashes,  I  would  refer  to  the  works  of  E.  REICHARDT,!  R.  W.  BuNSEN,J 
J.  KONIG,§  and  R.  ULBRICHT,  (Analysis  of  the  Ash  of  Must  and 
Wine  ||). 

*  Journ.  of  the  Royal  Agricult.  Soc.  of  England,  vin,  Part  I;  Jahresber. 
von  LIEBIG  und  KOPP,  1849,  600. 

f  Archiv.  der  Pharm  [2],  cxxxn,  88;    Jahresber.  von  H.  WILL,  1867,  831. 

%  AnnaL  d.  Onologie,  i,  3;  Zeitschr.  f.  analyt.  Chem.,  ix,  283. 

§  Landwirthschaftl.  Versuchsstationen,  x,  396;  Zeitschr.  /.  analyt.  Chem., 
ix,  288. 

||  Landwrthschaftlichl.  Versuchsstationen,  xxv,  399. 


810  INORGANIC    CONSTITUENTS    OF    PLANTS.  [§   289. 

B.  SUPPLEMENTARY  DETERMINATIONS  OF  CERTAIN  OTHER 
INORGANIC  SUBSTANCES  IN  PLANTS. 

§289. 

From  what  has  been  stated  in  §  284,  it  follows  that,  although 
by  the  analysis  of  the  plant  ash  or  portion  of  a  plant,  the  composition 
of  the  ash,  which  in  itself  is  interesting  to  know,  may  be  ascer- 
tained, yet  the  analysis  affords  no  knowledge  of  the  quantities  of 
those  elements  which  are  lost  to  a  greater  or  less  extent  during 
incineration,  e.g.,  chlorine,  sulphur,  and  in  many  cases,  phosphorus. 

If  therefore  the  quantities  of  these  elements  present  in  the 
plant  or  plant  portions  are  also  to  be  ascertained,  the  following 
supplementary  determinations  must  also  be  made: 

1.    DETERMINATION   OF   THE   CHLORINE. 

This  is  effected  thus:  Moisten  about  10  grm.  of  the  commi- 
nuted plant  or  plant  portion  with  a  solution  of  about  1  grm.  sodium 
carbonate  and  dry.  Then  incinerate  in  a  platinum  dish  at  a 
moderate,  long-continued  heat,  whereby  if  the  incipient  red  heat 
is  not  exceeded,  no  loss  of  alkali  chloride  will  occur.  As  soon  as 
the  particles  of  carbon  cease  to  glimmer,  moisten  the  ash  (still 
containing  carbon)  with  water,  triturate,  exhaust  with  boiling 
water,  filter,  wash  the  filter,  and  add  it  to  the  remainder  of  the  ash 
in  the  platinum  dish ;  now  dry,  incinerate,  completely  Ureat  the 
ash  with  cold,  diluted  nitric  acid,  filter  into  the  aqueous  solution, 
add  a  further  quantity  of  nitric  acid,  if  necessary,  until  present  in 
excess,  and  then  determine  in  the  solution  the  chlorine  as  silver 
chloride,  according  to  Vol.  I,  p.  521,  a  (BEHAGHEL  VON  ADLERS- 
KRON  *).  Another  method  of  determining  chlorine  is  described 
below  under  3. 

2.   DETERMINATION   OF  THE  SULPHUR. 

This  may,  if  desired,  be  combined  with  that  of  phosphorus. 
*  Zeitschr.  /.  analyt.  Chem.,  xu,  395. 


§  289.]  SUPPLEMENTARY   DETERMINATIONS.  811 

a.  W.  KNOP  and  R.  ARENDT'S  Method.* 

Cover  the  comminuted  plant  portion  (about  4  to  5  gnu.)  with 
very  concentrated  nitric  acid,  evaporate  to  dryness  on  the  water- 
bath,  moisten  again  with  nitric  acid,  evaporate  once  more  but 
not  quite  to  dryness,  add  first  some  water,  then  2  or  3  grm.  pure 
anhydrous  sodium  carbonate  (which  must  suffice,  however,  to 
neutralize  all  the  free  acid),  and  dry,  finally,  with  stirring.  Now 
moisten  with  water,  whereby  the  mass  readily  separates  from 
the  dish,  add  first  a  further  quantity  of  water  so  that  the  whole 
acquires  a  thin,  mushy  consistency,  then  20  to  25  grm.  of  ground, 
anhydrous,,  sodium  carbonate,  mix  intimately,  dry  completely, 
triturate  to  a  fine  powder,  and  clean  out  the  dish,  which  has 
become  damp  from  the  steam,  with  sodium  carbonate.  Next 
heat  the  powder,  in  portions,  if  necessary,  in  a  silver  or  platinum 
crucible  over  an  alcohol  lamp,  until  the  mass,  which  must  not  be 
allowed  to  melt,  has  become  perfectly  white.  If  this  cannot  be 
accomplished,  triturate  the  substance  once  more,  mix  with  a  few 
centigrammes  of  potassium  nitrate,  and  heat  anew. 

Finally  treat  the  mass  with  water,  supersaturate  with 
hydrochloric  acid,  separate  the  silica,  precipitate  the  sulphuric 
acid  in  the  moderately  acid  liquid  by  adding  barium  chloride, 
and  from  the  impure  barium  sulphate  (which  is  to  be  purified 
as  in  Vol.  I,  p.  434)  calculate  the  sulphur.  If  the  phosphoric  acid 
is  to  be  determined  in  the  filtrate,  this  is  effected,  according  to 
KNOP,  by  means  of  the  uranium  method  (Vol.  I,  p.  451)  after 
reduction  of  the  small  quantity  of  ferric  chloride  present  with 
uranous  chloride. 

6.  Any  of  the  methods  suitable  for  determining  sulphur  and 
phosphorus  in  organic  substances,  and  detailed  in  §§  188  and  189, 
may  be  employed,  and  preferably  LIEBIG'S  (§  188,  1).  Take 
up  the  melt  with  water,  supersaturate  the  solution  with  hydro- 
chloric acid,  separate  the  silica,  and  in  the  filtrate  precipitate 
the  sulphuric  acid  with  barium  chloride.  If  the  phosphoric  acid 

*  Compare  R.  ARENDT,  "Das  Wachsthum  der  Faserpflanzen "  (personal 
communication  from  D.  G.  BRUGELMANN). 


812  INORGANIC   CONSTITUENTS   OF   PLANTS.  [§  289. 

is  also  to  be  determined,  this  may  be  done  not  only  as  described 
in  a,  but  also  by  nearly  neutralizing  with  sodium  carbonate  the 
nitrate  from  the  barium  sulphate,  then  adding  first  some 
ferric  chloride,  and  then  a  slight  excess  of  barium  carbonate. 
Filter  after  settling,  wash  the  precipitate  containing  all  the  phos- 
phoric acid,  dissolve  it  in  nitric  acid,  and  determine  the  phos- 
phoric acid  by  the  molybdenum  method  (Vol.  I,  p.  446,  /?). 

3.    DETERMINATION    OF    THE     SULPHURIC    ACID,     AND     IF     DESIRED, 
ALSO   THE   CHLORINE,    IN   PLANTS. 

If  the  question  has  also  to  be  decided  as  to  what  portion  of 
the  sulphur  found  in  2  is  present  in  the  plant  as  sulphuric  acid, 
exhaust  the  plant  with  cold  water  acidulated  with  nitric  acid,  as 
already  recommended  by  CAILLAT  (comp.  p.  788,  foot-note,  this  vol- 
ume). E.  WOLFF  *  recommends  for  this  purpose  the  employment  of 
a  glass  tube  about  60  cm.  long  and  1-5  to  2  cm.  diameter,  drawn 
out  at  one  end.  Connect  the  drawn-out,  open  end  with  a  glass  tube 
by  means  of  a  small  rubber  tube  provided  with  a  pinchcock. 
Introduce  a  plug  of  cotton  wool  boiled  in  very  dilute  nitric  acid 
into  the  narrow  part  of  the  tube,  and  over  it  place  about  10  grm. 
of  the  finely  divided  vegetable  substance.  Close  the  pinchcock, 
and  fill  the  apparatus  with  a  mixture  of  20  parts  water  and  1  part 
nitric  acid  of  1-2  sp.  gr.;  after  several  hours,  allow  some  of  the 
liquid  to  run  off,  so  that  a  new  stratum  of  the  acid  may  come  into 
contact  with  the  substance  to  be  extracted,  fill  the  tube  again, 
and  repeat  the  operation  until  a  sample  of  the  liquid  drawn  off 
gives  but  a  faint  opalescence  with  silver  solution.  If  only  the 
sulphuric  acid  is  to  be  determined  in  the  liquid,  evaporate  this, 
best  on  a  water-bath,  to  a  small  bulk,  dilute  it  with  water,  pre- 
cipitate with  barium  chloride,  and  purify  the  barium  sulphate 
according  to  Vol.  I,  p.  434.  If,  however,  the  chlorine  is  also  to  be 
determined,  precipitate  first  with  silver  nitrate,  filter  off  the  silver 
chloride  (containing  organic  matter),  remove  the  excess  of  silver 

*  His  "Anleitung  zur  chem.  Untersuch.  landwirthschaftlich  wichtiger  Stoffe," 
3d   edit-    167 


§  290.]  ARRANGEMENT   OF  THE   RESULTS.  813 

from  the  filtrate  with  hydrochloric  acid,  evaporate  the  filtrate 
until  nearly  all  the  free  acid  has  been  expelled,  then  dilute,  and 
determine  the  sulphuric  acid  as  above.  Wash  the  silver  chloride 
containing  the  organic  matter,  dissolve  in  ammonia,  add  sodium 
carbonate,  evaporate  the  solution,  and  heat  the  residue  just  to 
incipient  fusion;  then  treat  with  water,  acidulate  the  solution  with 
nitric  acid,  precipitate  the  silver  solution,  and  determine  the  now 
pure  silver  chloride  according  to  Vol.  I,  p.  521,  a.  The  determina- 
tion of  the  sulphuric  acid  and  chlorine  made  as  just  detailed  do 
not,  however,  usually  give  satisfactory  results,  because  the  plant 
tissues  can  only  with  difficulty  be  completely  exhausted  with 
cold  water  acidulated  with  nitric  acid. 

C.  ARRANGEMENT  OF  THE  RESULTS. 
§290. 

If  it  is  but  a  question  of  presenting  the  results  of  ash  analyses, 
it  is  usually  advisable  to  state  the  percentages  of  the  bases  and 
acids  separately,  as  the  manner  in  which  the  bases  and  acids  are 
combined  cannot  always  be  accurately  deduced.  In  the  case  of 
chlorine,  an  equivalent  quantity  of  oxygen  must  be  deducted. 
It  is  usually  preferred  to  put  down  chlorine  as  sodium  (or  potas- 
sium) chloride,  calculating  the  alkali  in  the  chloride  into  oxide, 
and  deducting  this  from  the  total  soda  or  potassa.  Any  man- 
ganese contained  in  ashes  containing  carbonates  of  the  alkaline 
earths,  is  present  as  manganic  oxide,  Mn2O3  (see  Vol.  I,  p.  636), 
or  as  mangano-manganic  oxide  (Mn3O4). 

If  the  results  are  given  in  this  way,  i.e.,  as  they  are  directly 
obtained,  they  cannot  be  compared  with  those  of  other  analyses, 
as  among  the  constituents  put  down  there  are,  or  may  be,  some 
which  are  immaterial,  e.g.,  carbon  and  sand.  In  order  to 
obtain  comparable  results,  therefore,  the  influence  of  these 
immaterial  constituents  must  be  eliminated.  This  is  effected  by 
crossing  out  the  carbon  and  sand,  and  calculating  the  essential 
constituents  into  parts  per  100.  The  carbon  dioxide,  on  the  other 
hand,  although  not  derived  from  the  inorganic  constituents  of 


814  INORGANIC   CONSTITUENTS   OF   PLANTS.  [§  290. 

the  plant,  must  be  put  down  if  the  ash  is  to  be  characterized  as 
such  (e.g.,  wood-ash,  which  is  employed  as  a  manure,  or  as  a  source 
of  potash). 

In  order  to  decide  the  question  as  to  what  inorganic  substances 
a  plant  withdraws  from  the  soil,  a  mere  statement  of  the  ash 
constituents  does  not  suffice,  as  has  already  been  shown  (p.  788  this 
volume);  the  results  of  the  supplementary  determinations  must, 
rather,  be  also  included,  and  the  whole  calculated  into  parts  per 
100  of  the  dried  plant. 

The  supplementary  determinations  give  the  quantity  of 
chlorine,  sulphur,  and  also  the  phosphorus ;  the  other  constituents, 
however,  are  ascertained  from  the  ash  analysis.  In  this  state- 
ment of  results  the  carbon  dioxide  is  omitted. 

In  order  to  calculate  the  ash  constituents  into  percentages  of 
plant  substance,  it  was  customary  formerly  to  calculate  the  total 
weight  of  ash  from  that  afforded  by  a  portion  of  the  carefully 
dried  and  cautiously  incinerated  vegetable  substance,  and  then  to 
incinerate  a  larger,  unweighed,  and  less  carefully  dried  quantity, 
and  to  analyze  the  ash  so  obtained.  From  this  a  very  simple 
calculation  afforded  the  percentages  of  the  several  constituents 
in  the  plant.  For  instance,  wheat  yielded  3  per  cent,  of  ash, 
and  this  was  found  to  contain  50  per  cent,  phosphoric  acid;  hence 
100  parts  of  wheat  contained  1  •  5  per  cent,  phosphoric  acid. 

It  will  be  seen  at  a  glance  that  this  method  is  very  convenient; 
but  it  must  be  noted  that  it  does  not  give  sufficiently  exact  results 
in  all  cases,  as  the  total  quantity  of  the  ash,  for  the  reasons  stated 
in  §  284,  is  not  constant,  but  is  variable  within  certain  limits, 
dependent  upon  the  duration,  intensity,  and  mode  of  heating.  As 
the  operator  can  never,  therefore,  be  certain  that  the  small  portion 
obtained  in  the  determination  of  the  total  ash  accurately  corre- 
sponds in  quantity  and  composition  with  the  larger  portion  which 
is  to  serve  for  the  analysis,  it  is  at  all  events  preferable  to  determine 
on  the  one  hand  the  total  quantity  of  the  substance  to  be  incin- 
erated, and  on  the  other  the  total  quantity  of  the  ash  obtained  and 
intended  for  analysis,  as  already  above  recommended. 

If  this  is  not  desired,  the  object  in  view  may  also  be  effected  with 


§  291.]  ANALYSIS    OF   SOILS.  815 

accuracy  by  first  incinerating  a  large,  unweighed  quantity  of  the 
vegetable  substance,  analyzing  the  ash,  and  thus  determining  the 
relative  proportions  of  the  constituents.  On  now  incinerating  a 
smaller  weighed  quantity  of  the  vegetable  dried  at  100°,  and  deter- 
mining in  the  ash  one  of  the  constituents  the  quantity  of  which  can 
suffer  no  change  because  of  the  mode  of  incineration  (e.g.,  lime),  we 
may  then,  knowing  the  relative  quantity  of  it  present  in  the  plant, 
as  well  as  the  proportions  in  which  it  and  the  other  constituents 
are  present,  readily  calculate  the  percentages  in  which  the  other 
constituents  are  present  in  the  plant. 

IV.  ANALYSIS  OF    SOILS. 
§291. 

The  fertility  of  a  soil  depends,  apart  from  climatic  conditions, 
upon  its  chemical  as  well  as  physical  nature.  The  chemical  nature 
is  dependent  not  only  upon  the  character  and  relative  proportions 
of  the  constituents,  but  also  upon  the  solubility  and  forms  of  com- 
bination of  the  constituents. 

Hence  if  an  analysis  is  to  afford  a  conclusion  as  to  the  fertility, 
of  a  soil,  it  must  take  into  account  all  the  above  points,  so  far  as 
possible.  I  say  so  far  as  possible  advisedly,  as  it  is  impossible,  in 
a  laboratory,  to  secure  the  action  of  solvents  in  the  same  manner 
in  which  they  operate  in  nature ;  and  so,  too,  the  chemico-physical 
examination  scarcely  affords  sufficient  conclusions  regarding  the 
various  ways  in  which  the  constituents  are  combined  in  the  soil. 
These  variations  may  be  seen,  for  instance,  from  the  fact  that  a 
still  perfectly  uncultivated  soil,  although  containing  all  the  sub- 
stances necessary  to  support  a  particular  plant,  is  still  unable  to 
support  it  while  capable  of  supporting  other  plants  requiring  an 
equal  or  even  greater  supply  of  material.  The  combination  of  the 
substances  is,  therefore,  the  resistance  the  soil  offers  against  yield- 
ing certain  constituents  to  plants,  a  resistance  which  is  overcome 
by  some  plants,  but  not  by  others;  and  which  experiments  have 
shown  to  decrease  with  cultivation  of  the  soil.* 

*  Comp.  v.  LIEBIG,  Die  Chemie  in  ihrer  Anwendung  auf  Agricultur  und 
Physiologic,  n,  p.  65  et  seq. 


816  COLLECTING   THE   SAMPLE.  [§  292. 

In  the  following,  bearing  in  mind  the  scope  of  this  work,  I  will 
fully  describe  the  mechanical  and  chemical  analysis,  but  as  regards 
the  investigation  of  the  most  important  physical  properties  of  soils, 
I  shall  have  to'  refer  to  works  on  agricultural  chemistry  and  to  the 
many  papers  devoted  to  this  subject.* 

A.  COLLECTING  THE  SAMPLE. 
§292. 

The  surface  soil  may  be  considered  to  be  the  upper  layer  which 
is  turned  up  by  the  plough  to  the  depth  of  30  cm. ;  the  subsoil  is 
the  layer  some  60  cm.  deep  next  below  the  surface  soil.  If  surface 
soil  or  subsoil  is  to  be  taken  from  any  particular  spot,  dig  a  hole 
about  30  to  50  cm.  square  and  with  perpendicular  sides  and  as 
nearly  level  bottom  as  possible,  and  cut  from  one  of  the  side  walls 
a  vertical  slice  of  uniform  thickness,  as  a  sample.  The  sample  of  the 
subsoil  should  be  taken  in  like  manner.  If  the  earth  to  be  exam- 
ined is  to  represent  the  average  composition  of  a  field,  take  samples 

*  More  or  less  comprehensive  information  regarding  the  investigation 
of  the  physical  characteristics  of  soils  is  given  by  the  older  writers,  SCHUBLER 
(Grundsdtze  der  Agriculturchemie,  u)  and  FR.  SCHULZE  (Journ.  f.  prakt.  Chem., 
XLVII,  241);  and  from  among  later  writers,  Dr.  EMIL  WOLFF'S  paper  on 
soil  analysis,  reported  by  the  members  of  the  commission  (Dr.  BRETSCHNEI- 
DER,  Dr.  GROUVEN,  Dr.  KNOP,  Dr.  PETERS,  Dr.  STOHMANN,  and  Dr.  ZOLLER) 
appointed  at  the  meeting  of  the  German  Agricultural  Chemists,  in  May,  1863 
(Landwirthschaftl.  Versuchsstationen,  1864,  vi;  Zeitschr.  f.  analyt.  Chem,, 
in,  85);  also  E.  WOLFF'S  Anleitung  zur  chemischen  Untersuchung  land- 
wirthschaftl.  wichtiger  Stoffe,  3d  ed.  (Berlin,  WIEGAND,  HEMPEL,  and  PAREY, 
1875) ;  also  E.  HEIDEN,  Denkschrift  zur  Feier  des  25  jahrigen  Bestehens  der 
agriculturchemischen  Versuchsstation  Pommritz  (Hannover,  PH.  COHEN,  1883, 
p.  152  et  seq.).  Special  reference  regarding  the  absorption  power  of  soils, 
and  the  methods  of  determining  it,  is  given  in  the  papers  by  v.  LIEBIG  (Annal. 
d.  Chem.  u.  Pharm.,  cv,  113);  A.  SALOMON  (Landw.  Versuchsstat.,  ix,  351); 
R.  BIEDERMANN  (ibid.,  xi,  1);  CL.  TREUTLER  (ibid.,  xiv,  301);  W.  KNOP 
(Zeitschr.  f.  analyt.  Chem.,  xm,  101;  xiv,  241;  xv,  171);  W.  PILLITZ  (ibid., 
xiv,  55  and  282);  A.  LISSAUER  (Landwirth.  Versuchsstat.,  xix,  11);  VAN 
BEMMELEN  (ibid.,  xxi,  135;  and  xxm,  265);  KONIG  (ibid.,  xxvi,  400); 
and  concerning  the  retention  of  water  by  the  soil,  in  the  papers  of  F.  SEEL- 
HEIM  (Zeitschr.  f.  analyt.  Chem.,  xix,  387);  H.  FLECK  (DiNGL.  polytech. 
Journ.,  ccxxxvm,  93);  ARMSBY  (Landwirthsch.  Versuchsstat.,  xxi,  397); 
and  HEIDEN  (ibid.,  xxvi,  407). 


§   293.]  MECHANICAL   ANALYSIS.  817 

in  like  manner  from  several  places  and  mix  uniformly.  Allow  the 
samples  to  become  thoroughly  air  dry.  In  summer  this  is  attained 
by  exposing  the  earth  in  a  shallow  box  in  a  dry  room ;  in  winter  by 
drying  the  earth  slowly  in  a  drying  closet  at  a  temperature  of 
30°  to  50°. 

About  5  kilos  are  required  for  a  complete  analysis. 

B.  MECHANICAL  ANALYSIS. 
§293. 

1.  Weigh  the  entire  quantity  of  air-dried  earth,  then  pick  out 
the  stones  and  brush  and  weigh  them. 

2.  Now  place  the  earth  in  a  tin  sieve  with  holes  3  mm.  in  diam- 
eter, and  sift  out  everything  that  will  pass  through.     Break  up  any 
residual  lumps  in  a  mortar,  with  moderate  pressure,  and  preferably 
with  a  wooden  pestle;  then  sift  again  and  preserve  the  sifted  earth. 
Now  place  the  sieve  in  a  dish,  add  sufficient  water  *  to  cover  the 
contents,  allow  to  stand  for  a  considerable  time,  and  then  wash, 
either  with  the  hand  or  with  a  brush,  until  all  the  clay  has  been 
removed  from  the  stones.     Lastly,  rinse  off  the  latter  with  a  little 
water,  transfer  to  a  dish,  dry  at  125°,  and  weigh.     The  weighed 
matter  is  gravel.     On  igniting  the  dried  gravel  hi  air,  the  loss  hi 
weight  will  represent  the  organic  matter  incident  to  the  gravel, 
provided  this  consists  of  such  stones  and  fragments  of  rocks  as  lose 
no  water,  carbon  dioxide,  or  volatile  constituents.     The  contents 
of  the  dish,  containing  all  the  earth  washed  from  the  gravel,  are 
allowed  to  dry  slowly,  towards  the  end  at  30°  to  50°;  then  mix  the 
residue  uniformly  with  the  dry,  sifted  earth,  spread  out  in  as  thin 
a  layer  as  possible,  and  allow  to  stand  for  several  days  in  a  vapor- 
and  dust-free  place  at  a  moderate  temperature;   the  air-dried  fine 
earth  (thus  designated  by  E.  WOLFF)  is  then  preserved  in  well-stop- 
pered flasks. 

I  must  here  remark  that  a  definition  as  to  what  constitutes 
"fine  earth,"  and  which,  of  course,  cannot  be  determined  scien- 

*  Distilled  water  must  be  used  in  all  these  operations;   see  note,  p.  820 
this  volume. 


818  ANALYSIS   OF   SOILS.  [§  293. 

tifically,  but  only  by  agreement,  has  so  far  not  been  agreed  upon. 
While,  for  instance,  according  to  E.  WOLFF'S  suggestion,  which  has 
been  adopted  by  many  other  agricultural  chemists,  the  term  ''fine 
earth"  is  given  to  that  portion  passing  through  a  sieve  with  holes 
3  mm.  in  diameter,  others  select  2  mm.,  and  not  a  few  even  still 
finer  sieves,  in  order  to  obtain  "fine  earth";  thus  HEIDEN  (Denk- 
schrift,  p.  119)  and  GRANDEAU  *  take  1  mm.;  E.  DIETRICH,! 
0-66  mm.;  A.  MULLERJ  and  also  KNOP,§  0-2  to  0-3  mm.  As  may 
be  readily  seen,  a  comparison  of  analyses  of  "fine  earth"  which  is 
not  further  characterized,  may  lead  to  quite  erroneous  conclusions, 
as  analyses  are  comparable  only  when  made  with  "fine  earth" 
prepared  in  a  uniform  manner. 

In  the  following  the  term  "  fine  earth  "  will  be  applied  to  the 
preparation  conforming  to  E.  WOLFF'S  definition,  but  the  methods 
of  analysis  are,  of  course,  applicable  to  all  other  kinds  of  "fine 
earth." 

3.  Many  very  different  methods  have  been  proposed  and  em- 
ployed for  the  further  mechanical  separation  of  air-dried  fine  -°arth. 
Many  agricultural  chemists  recommend  elutriation  and  subse- 
quent separation  of  the  residual  sand  into  portions  of  different 
degrees  of  fineness  by  passing  through  sieves  of  various  sizes. 
Others  sift  first  and  elutriate  only  the  finest  sifted  portion.  For 
sifting,  however,  sieves  of  varying  fineness  are  recommended, 
and  for  elutriation  some  prefer  so-called  flushing  apparatus,  and 
others  sedimentation  apparatus.  It  may,  hence,  be  readily  seen 
that  the  results  obtained  by  different  methods  cannot  exactly 
concur.  Although  the  comparison  of  results  is  thus  already 
made  difficult,  it  is  rendered  still  more  so  by  the  fact  that  the 
names  given  to  the  sand  of  different  degrees  of  fineness  vary,  e.g., 
"fine  gravel,"  "coarser  sand,"  "finer  sand,"  "argillaceous  sand," 

*  His  Handb.  f.  agriculturchem.  Analysen,  German  edit.,  by  HENNEBERG 
(Berlin,  WIEGAND,  HEMPEL,  and  PAREY,  1879,  p.  103). 

f  Zeitschr.  /.  analyt.  Chem.,  v,  298. 

J  Ibid.,  v,  443. 

§  According  to  A.  MAYER  the  largest  particles  of  KNOP'S  "fine  earth" 
are  0-3  mm.  in  diameter  (BOCKMANN'S,  chem.  techn.  Untersuchung.,  Berlin 
J.  SPRINGER,  1884,  n,  664). 


§  294.]  MECHANICAL  ANALYSIS.  819 

or  "finer  gravel/'  "pearl  sand/'  "coarse  sand,"  "fine  sand/'  or 
"coarse  gravel/7  "medium  gravel,"  "fine  gravel,"  "coarse  sand/1 
"fine  sand,"  etc. 

But  even  the  causes  here  enumerated  as  affording  non-con- 
cordant results  in  the  mechanical  separation  of  the  constituents 
of  a  "  fine  earth,"  and  whereby  the  clay  found  is  too  high,  and  fre- 
quently much  too  high,  are  by  no  means  exhausted.  The  most 
common  source  of  error  in  the  usual  methods  is  rather  that,  in  all 
the  elutriations  made  in  the  ordinary  manner,  the  clay  contained 
in  the  soil  is  not  obtained  pure,  but  mixed  with  fine  sand,  and  under 
certain  circumstances  with  finely  divided  calcium  carbonate 

(SCHLOSING,*  GRANDEAU,f   F.   SESTINI,J    and  N.   PELLEGRINI  §). 

It  is  not  my  purpose  to  here  detail  all  the  methods  proposed 
for  the  mechanical  analysis;  it  will  suffice  to  describe  the  following: 

a.  One  of  the  best  purely  mechanical  methods,  that  by  E. 
WOLFF  ||  and  somewhat  modified  by  W.  KNOP. 

6.  SCHLOSING'S  method,  which  combines  mechanical  separa- 
tion with  chemical  treatment,  and  which,  so  far  as  my  experience 
goes,  is  the  only  one  that  correctly  gives  the  quantity  of  clay 
present  in  the  soil. 

a.  Purely  Mechanical  Method. 
§294. 

Of  the  many  methods,  I  give  here  only  E.  WOLFF'S  modifica- 
tion of  KNOP'S  process  because,  with  very  simple  apparatus,  it 
gives  as  good  results  as  can  be  expected  from  a  purely  mechanical 
analysis.  Regarding  the  other  methods,  I  must  refer  to  the  original 
treatises  and  books  mentioned  in  the  foot-note.l" 

*  Compt.  rend.,  LXXVIII,  1276.  t  His  Handbuch.,  p.  104. 

J  Landwirthschajil.  Versuchsstat.,  xxv,  47.         §  Ibid.,  xxv,  48. 

||  His  Anleitung  zur  chem.  Untersuchung  landwirthschaftlich  wichtiger 
Stoffe,  3d  edit.,  p.  9. 

IF  Of  the  apparatus  for  elutriation  belonging  to  the  flushing  apparatus, 
those  of  SCHULZE  and  SCHONE  have  already  been  mentioned  on  pp.  414  and 
415  this  volume.  Others  belonging  to  this  category  are  described  by  NOBEL 
(comp.  E.  WOLFF'S  treatise  in  Zeitschr.  f.  analyt.  Chem.,  in,  90,  and  in  Land- 
irirthschaftl.  Versuchsstat.,  vin,  408);  E.  DIETRICH  (Zeitschr.  f.  analyt. 
Chem.,  v,  295);  and  AL.  MULLER  (ibid.,  xvi,  83).  Slight  modifications  of 


820  ANALYSIS    OF   SOILS.  [§  294. 

Boil  50  grm.  of  the  air-dried  fine  earth  with  distilled  water 
for  a  long  time,  transfer  to  a  brass  sieve  perforated  with  holes  1  mm. 
in  diameter,  and  set  in  a  basin  of  water  so  that  the  contents 
of  the  sieve  are  covered  with  water;  then  operate  as  above  de- 
tailed, in  order  to  separate  the  portion  of  more  than  1  mm.  in 
diameter  from  the  smaller.  In  the  same  manner  proceed  with 
the  latter  portion,  using  successively  sieves  with  holes  0-5  mm. 
and  0-25  mm.  in  diameter.  The  residues  remaining  in  the  sieves 
are  treated  as  above  described  for  gravel.  If  many  analyses  of 
earths  are  to  be  made,  it  is  advisable  to  use  an  apparatus  consisting 
of  sieves  of  various  degrees  of  fineness  fitted  into  each  other  so 
as  to  form  one  system,  which  is  suspended  in  a  wide,  deep  glass 
cylinder  filled  with  water.  The  sieves,  the  contents  of  which  are 
kept  in  motion  by  revolving  brushes,  then  work  simultaneously, 
and  the  operation  is  considerably  facilitated. 

The  further  separation  of  the  portion  passing  through  the 
finest  sieve  into  fine  sand  and  finest  elutriable  portions  (called 
"  dust "  by  E.  WOLFF)  is  effected  by  an  elutriation  flask  holding 
fully  a  litre,  and  about  20  cm.  high ;  in  the  neck  of  the  flask  there 
is  fitted  a  perforated  stopper  bearing  a  siphon,  the  short  end  of 
which  reaches  to  the  bottom  of  the  flask,  and  is  bent  upwards  at 
the  lower  end.  Introduce  the  portion  that  has  passed  through 
the  finest  sieve  into  the  flask,  fill  this  to  a  height  of  about  18  cm. 
with  distilled  water,*  shake  thoroughly,  and  allow  to  stand  for  a 
definite  time;  now  insert  the  siphon  and  draw  off  the  turbid  fluid 
from  the  sediment,  fill  again  with  water  and  repeat  the  operations. 
WOLFF  recommends  that,  after  the  first  shaking,  the  flask  should 

SCHONE'S  apparatus  are  recommended  by  E.  HEIDEN  (Denkschrift,  p.  121), 
and  by  C.  HOLTHOF  (Zeitschr.  /.  analyt.  Chem.,  xxv,  34).  Furthermore, 
sedimentation  apparatus  have  been  constructed  by  KNOP  (see  his  Bonitirung 
der  Ackererde,  2d  edit.,  p.  50  et  seq.} ;  J.  KUHN  (BOCKMANN'S  chem.  techn. 
Untersuchungen,  Berlin,  J.  SPRINGER,  u,  665);  and  R.  DEETZ  (Zeitschr.  /. 
analyt.  Chem.,  xv,  428). 

*  Elutriation  cannot  be  carried  out  with  spring-water,  because  the  slightest 
traces  of  lime,  magnesia,  and  alkali  salts  coagulate  the  clay  to  a  certain 
extent,  and  precipitate  it  with  the  sand  (SCHLOSING;  GRANDEAU,  loc.  cit., 
p.  105). 


§  294.]  MECHANICAL   ANALYSIS.  821 

be  allowed  to  stand  for  one  hour ;  then  for  half  an  hour,  one-quarter 
of  an  hour,  and  finally  only  five  minutes,  repeating  the  operation 
thrice  for  each  settling.  Lastly,  rinse  the  fine  sand  into  a  dish 
and  treat  it  like  the  other  sands. 

To  obtain  and  determine  the  finest  elutriated  portions  warm 
the  united,  turbid  washings  in  large  dishes  until  they  have  be- 
come perfectly  clear,  then  siphon  off  the  clear  liquid  above  sediment 
so  far  as  possible,  rinse  into  a  porcelain  dish  and  dry,  after  which 
transfer  the  residue  to  a  platinum  or  porcelain  crucible,  dry  at 
125°,  weigh,  ignite  in  air,  and  then  weigh  again. 

In  order  to  facilitate  the  deposition  of  the  finest  elutriable 
portions,  A.  MULLER*  recommends  adding  ammonia  soap,  while 
FR.  SCHULZE  recommends  ammonium  carbonate.  According 
to  E.  LAUFER,|  however,  neither  affords  satisfactory  results, 
although  he  finds  that  the  warming  greatly  hastens  deposition. 
Compare,  however,  A.  MULLER' s  J  criticism  of  this. 

On  adding  together  the  component  portions  of  the  air-dried 
fine  earth,  and  calculating  them  into  percentages,  they  do  not 
give  100,  but  less ;  the  difference  is  equivalent  to  the  moisture  con- 
tained in  the  fine  earth.  The  results  found  can  be  controlled  or 
checked  by  the  direct  method  of  determining  moisture  given  in 
§  296,  1.  If  the  direct  determination  of  the  finest  elutriable  por- 
tion has  been  omitted,  while  the  direct  determination  of  the  moisture 
has  been  carried  out  at  125°,  the  quantity  of  the  former  in  per 
cents  is  ascertained  by  deducting  the  sum  of  the  sand  dried  at 
125°  and  the  moisture  from  100. 

As  the  moisture  content  of  different  fine  earths  may  vary 
greatly,  it  is  advisable,  for  the  purpose  of  comparison,  to  refer 
the  figures  obtained  to  the  substance  dried  at  125°.  The  results 
of  the  purely  mechanical  analysis  may  be  thus  conveniently  stated 
as  follows: 

100  parts  of  the  fine  earth  dried  at  125°  contain  (for  example) 

*  Zeitschr.  f.  analyt.  Chem.,  v,  243. 

•)•  Landwirthschajil.  Versuchsstat.,  xvm,  61 ;  Zeitschr.  f.  analyt.  Chem.% 
xiv,  398. 

I  Landwirthschaftl  Versuchsstat.,  xxiv,  65. 


822  ANALYSIS   OF   SOILS.  [§  294. 


Non-com-  Combustible 
bustible     or  volatile 
matter.          matter. 


7'51  -i  Sand  of  1  to  3  mm.  diameter  ...............     6-91 

(  Organic  substances,  etc.,  belonging  thereto  ........         0-60 

30-96  JSand  9f  °*5  to  1<0  mm-  diameter  ...........   30-05 

(  Organic  substances,  etc.,  belonging  thereto.  .......         0-01 


Sand  of  0-15=  0-5  mm.  diameter  .......  _____   31-61 

1-10 


00.71  i  Sand  of  0-15=  0-5  mm.  diameter  ....... 

I  Organic  substances,  etc.,  belonging  thereto 
..  _  ™  j  Sand  of  less  than  0  •  25  mm.  diameter  .........   16-77 

'1  Organic  substances,  etc.,  belonging  thereto  ........         0-87 

11  19  •!  Finest  particles  ...........................   10-36 

(  Organic  substances,  etc.,  belonging  thereto  ........         0-82 

100-00  95-70        4-30 

7-16  Gravel  associated  with  100  parts  of  the  fine  earth  dried  at  125°. 
2-  10  Stones          "  "      "       "     "    "      "       "        "     "      " 

5  -03  Moisture  belonging  to     "       "      "     "     "        "        "     "      " 
(in  air-dried  condition). 

The  loss  in  weight  which  the  soil,  dried  at  125°,  undergoes  on 
ignition  in  air,  cannot  be  considered  merely  as  caused  by  the  com- 
bustion of  organic  matter,  since  the  clay,  dried  at  125°,  gives  up 
water  on  ignition,  calcareous  sand  loses  carbonic  acid,  etc.  The 
carbonic  acid  evolved  may  in  great  part  be  restored  to  the  residue 
by  moistening  this  with  a  solution  of  ammonium  carbonate,  dry- 
ing, repeating  this  treatment  several  times,  and  lastly  very  gently 
igniting.  Compare  §  296,  2.  The  figures  so  obatined  for  organic 
matter  are,  however,  only  of  approximate  value,  being  very  near 
the  truth  with  many  soils,  but  in  others  widely  divergent,  as  may 
be  seen  from  many  analyses  of  soils,  e.g.,  those  by  G.  LOGES.* 

[  F.  POQUILLON  |  gives  a  method  whereby  an  estimation  of  clay 
in  soils  may  be  made  in  two  or  three  days  at  the  most.  It  is  based 
on  the  fact  that  if,  instead  of  mixing  the  earth  with  distilled  water, 
a  dilute  solution  of  ammonium  chloride  is  used,  the  clay  is  held  in 
suspension  while  it  is  at  the  same  time  coagulated,  thus  enabling 
the  sand  to  deposit  almost  immediately. 

Ten  grm.  of  the  soil  are  placed  in  a  small  porcelain  crucible  and 
rubbed  round  the  sides  with  the  first  finger  while  adding  water 
drop  by  drop,  until  about  25  c.c.  have  been  added.  This  mixture 
is  transferred  to  a  beaker  of  150  c.c.  capacity,  and  about  100  to 

*  Landwirthschaftl  Versuchsstat.,  xxvm,  238. 
f  Chem.  News,  LXXXI,  219. 


§  294.]  MECHANICAL     ANALYSIS.  823 

120  c.c.  of  a  solution  of  ammonium  chloride,  1  grm.  per  litre,  are 
added.  After  well  stirring  with  a  glass  rod,  it  is  allowed  to  settle 
for  five  minutes,  and  the  liquid  decanted  into  a  litre  beaker.  On 
this  residue  100  to  125  c.c.  more  of  the  ammonium-chloride  solution 
are  poured;  stir  well  again,  allow  to  stand  for  five  minutes,  and 
decant  into  the  litre  beaker.  This  operation  is  repeated  until 
the  wash-waters  are  quite  clear;  this  will  require  six  or  eight 
washings  for  the  most  argillaceous  soils.  The  residue  is  treated 
with  hydrochloric  acid  diluted  with  water,  washed  with  distilled 
water,,  and  dried;  its  weight  gives  the  total  sand. 

The  thick  liquid  remaining  in  the  litre  beaker  is  treated  with 
a  few  drops  of  hydrochloric  acid,  to  decompose  the  calcareous  matter 
and  complete  the  coagulation  of  the  clay.  It  is  then  allowed  to 
stand  until  the  supernatant  liquid  is  clear;  this  requires  two  or 
three  hours.  The  clay  which  deposits  is  collected  on  a  weighed 
filter,  washed  with  distilled  water,  dried,  and  weighed. 

POQUILLOX  claims  for  this  method  the  following  advantages 
over  the  older  ones: 

1.  Instead  of  making  two  washings  on  the  filter,  one  to  remove 
the  lime  and  chalky  matter  and  the  other  to  free  the  clay  from 
the  ammonium  chloride,  a  single  washing  enables  us  to  get  rid  of 
both  the  lime  and  chloride  at  the  same  time. 

.2.  Instead  of  obtaining  the  clay  in  suspension  in  4  or  5  litres  of 
water,  it  is  now  found  in  750  to  1,000  c.c.;  this  is  in  one-fifth  or 
in  one-sixth  of  the  volume. 

3.  Instead  of  getting  the  clay  on  the  filter  after  five  or  six  days, 
this  stage  is  reached  after  about  three  hours. 

4.  The  clay  obtained  by  this  process  is  washed  more  rapidly 
than  that  obtained  by  the  old  method.     (The  author  states  that 
he  has  never  taken  more  than  a  day  and  a  half  to  effect  the  same 
amount  of  washing  that  used  to  require  three  or  four  days  by  the 
old  method.) — TRANSLATOR.] 


824  ANALYSIS    OF    SOILS.  [§   295. 

b.  SCHLOSING'S  Method* 

§295. 

This  method  has  for  its  object  the  determination  of  the  fol- 
lowing constituents  of  fine  earth: 

1.  Sand  insoluble  in  acids. 

2.  Clay. 

3.  Humus  substances. 

4.  Calcium   carbonate. 

5.  Moisture. 

Stir  10  grm.  of  air-dried  fine  earth  in  a  porcelain  dish  to  a 
stiff  paste  by  spirting  in  a  small  quantity  of  distilled  water;  then 
add  more  water,  and  knead  between  the  fingers  so  as  to  uniformly 
and  thoroughly  mix  the  soil.  Now  add  more  distilled  water,  and 
then  pour  the  turbid  liquid  into  a  beaker  of  about  250  to  300  c.c. 
capacity,  and  until  the  whole  mass  of  soil  has  been  separated 
and  elutriated.  The  quantity  of  water  taken  should  be  so  ad- 
justed that  not  more  than  200  to  250  c.c.  of  fluid  are  obtained. 
Now  add  hydrochloric  acid  by  drops,  until  the  calcium  carbonate 
is  completely  dissolved,  whereby  the  calcium  humate  is  at  the 
same  time  decomposed;  in  the  ase  of  soils  rich  in  calcium  assist 
the  action  by  gently  warming.  When  the  liquid  has  become 
clear,  separate  the  solution  from  the  precipitate  by  decantation 
and  filtration,  and  lastly  thoroughly  wash  the  residue  collected 
on  the  filter.  The  calcium  may  be  directly  determined  in  the 
liquid,  if  desired,  according  to  the  method  described  below 
(§  298,  a). 

Now  wash  back  the  contents  of  the  filter  into  the  beaker  pre- 
viously used,  by  the  aid  of  small  quantities  of  water,  add  0-5 
grm.  caustic  potassa  or  2  to  3  c.c.  ammonia,  and  allow  to  act  for 
four  to  five  hours  with  frequent  stirring,  thereby  effecting  the  solu- 
tion of  the  humus  substances  adhering  to  the  clay.  Next  nearly 
fill  the  beaker  with  distilled  water,  stir  thoroughly,  allow  to  stand 
twenty-four  hours,  f  siphon  off  the  liquid  above  the  sandy  sediment 

*  Compt.  rend.,  LXXVIII,  1276;   GRANDEAU'S  Handbuch,  p.  105. 
f  According  to  SESTINI  (Landwirthschaftl.  Versuchsstat.,  xxv,  47),  twelve 
hours  suffice. 


§  296.]  ANALYSIS    OF   SOILS.  825 

into  a  flask  of  about  1  •  5  litres  capacity,  replace  the  water  siphoned 
off  by  distilled  water,  stir  again,  and  once  more  allow  to  stand 
twenty-four  hours,  repeating  this  operation  six  times,*  until  the 
supernatant  liquid  appears  perfectly  clear.  The  1-5-litre  flask 
now  contains  the  total  clay  and  humus  substances,  the  latter  in 
alkaline  solution,  while  the  beaker  contains  the  sand,  which  may 
be  separated  into  various  fractions  as  in  §  294. 

To  the  liquid  containing  the  clay  add  5  to  10  grm.  potassium 
chloride,  in  order  to  facilitate  the  deposition  of  the  clay,  allow  the 
liquid  to  be  ome  perfectly  clear,  siphon  off  so  far  as  possible,  and 
decant  through  a  filter ;  finally  bring  the  total  clay  onto  the  filter, 
wash  it  with  distilled  water  until  the  last  quantity  added  no  longer 
runs  through  the  filter,  which  is  the  case  when  the  clay  no  longer 
contains  potassium  chloride.  Now  siphon  off  the  clear  water  from 
the  clay,  which  adheres  strongly  to  the  filter-paper,  spread  the 
latter  on  blotting-paper  until  the  clay  may  be  removed,  then 
introduce  the  latter  into  a  weighed  platinum  dish,  dry  it  at  150°, 
and  weigh.  Should  any  particles  still  adhere  to  the  filter-paper, 
incinerate  this  and  add  the  residue  to  the  main  bulk  of  the  clay. 

To  the  colored  liquid  separated  from  the  clay  add  acetic  acid 
to  distinct  acidity,  boil  until  the  carbon  dioxide  has  been  ex- 
pelled, precipitate  with  lead  acetate  until  the  supernatant  liquid 
appears  colorless,  allow  to  settle,  then  decant,  filter,  wash,  dry 
somewhat,  remove  the  precipitate  from  the  filter-paper,  dry  at 
100°,  and  weigh.  Now  cautiously  heat  it  in  air,  oxidize  any 
reduced  lead  with  ammonium  nitrate,  weigh  the  residue,  deduct  its 
weight  from  that  of  the  lead  humate,  and  calculate  the  difference 
as  humus  substances. 

Finally,  to  determine  the  moisture,  dry  a  separate  sample  of 
the  air-dried  fine  earth  at  150°  to  constant  weight. 

C.   CHEMICAL  ANALYSIS. 

§296. 

If  the  soil  were  treated  as  a  whole,  the  object  of  the  analysis 
being  merely  to  determine  the  quantities  of  potassium,  calcium, 

*  SESTINI  considers  twelve  repetitions  to  be  necessary. 


826  CHEMICAL  ANALYSIS.  [§  296. 

phosphoric  acid,  silica,  alumina,  etc.,  present  in  it,  the  results 
could  be  rapidly  obtained,  but  they  would  afford  no  conclusions 
regarding  the  solubilities  of  which  the  individual  constituents 
were  capable.  If,  on  the  other  hand,  we  treat  a  soil  successively 
with  various  solvents,  e.g.,  first  water,  then  with  water  containing 
carbon  dioxide  and  ammonium  salts,  then  with  a  cold  hydrochloric 
acid,  then  boiling  hydrochloric  acid,  and  lastly  with  concentrated 
sulphuric  acid,  certain  conclusions  are  afforded  regarding  the 
relative  solubilities  of  the  soil  constituents,  but  the  analysis  in 
this  case  becomes  extremely  complicated  and  requires  the  expen- 
diture of  an  extraordinary  amount  of  time  and  labor.  When, 
moreover,  it  must  be  remembired  in  addition  that  the  power  of 
the  soil  to  retain  some  substances  more  firmly  than  others,  hinders 
the  complete  extraction  of  the  substances  soluble  in  a  given  weak 
solvent,  there  must  necessarily  exist  some  uncertainty  regarding 
the  manner  in  which  the  chemical  analysis  of  a  soil  may  be  best 
effected. 

It  is  quite  certain  that  analyses  of  soils  cannot  be  compared 
when  they  are  carried  out  with  quite  different  solvents,  and  that 
chemists  must  agree  to  employ  certain  definite  solvents  if  the 
analyses  are  to  have  any  value.  Unfortunately,  however,  our 
knowledge  does  not  yet  suffice  to  enable  us  to  decide  with  certainty 
the  question  as  to  what  analytical  treatment  will  afford  the  most 
practical  statement  of  results,  i.e.,  the  form  which,  viewed  in 
connection  with  the  agricultural  experiments  made  upon  the 
same  soil,  will  lead  to  the  clearest  and  most  certain  conclusions; 
and  it  is  hence  evident  that  the  views  of  chemists  differ  regard- 
ing the  choice  of  the  solvents  to  be  employed. 

As  none  of  the  many  methods  proposed  for  treating  soils  with 
solvents  have  been  generally  adopted,  or  can  be  considered  as 
having  been  generally  agreed  upon,  I  will  detail  the  method  of 
analysis  described  in  the  first  edition  of  this  work,  and  which 
appeared  to  me  then  most  suitable;  and  this  method,  though 
naturally  improved  by  reason  of  the  experience  gained  since  then, 
still  appears  to  be  the  best  adapted  for  practical  purposes. 

If,  for  some  special  purpose,  the  investigation  is  to  be  still 


§  297.]  ANALYSIS    OF   SOILS.  827 

further  extended,  and  the  behavior  of  the  soil  towards  the  solvents 
(e.g.,  water  containing  carbonic  acid  or  ammonium  salts)  ascer- 
tained, this  may  be  done  without  further  directions,  as  the  prepa- 
ration of  such  extracts,  and  the  determination  of  the  dissolved 
constituents  in  them,  is  in  general  carried  out  in  the  manner 
described  for  the  aqueous  extract. 

1.    DETERMINATION   OF   THE  MOISTURE. 

Weigh  off  about  3  to  5  grm.  of  the  air-dried  fine  earth  in  a 
platinum  crucible  or  dish,  dry  at  125°  to  constant  weight,  and 
determine  the  loss  of  weight. 

2.    DETERMINATION   OF   THE    CHEMICALLY-COMBINED   WATER. 

Ignite  the  soil  (dried  at  125°)  with  access  of  air,  first  over  a 
lamp,  finally  with  the  blow-pipe,  to  constant  weight.  A  loss  of 
weight  results  from  the  expulsion  of  the  chemically-combined 
water,  carbon  dioxide,  nitric  acid,  ammonium  c  mpounds,  and 
combustible  organic  matter,  humus-like  and  otherwise;  on  the 
other  hand,  an  increase  in  weight  may  occur  under  certain  cir- 
cumstances, from  the  absorption  of  oxygen  by  ferrous  and 
manganous  compounds  or  metallic  sul  hides.  The  water  of  com- 
bination, therefore,  can  be  ascertained  from  the  loss  in  weight  on 
ignition  in  air  only  when  all  the  other  substances  present  which 
may  effect  an  increase  or  loss  in  weight,  have  been  determined. 
Even  then,  the  quantity  found  can  be  only  approximate,  because 
many  of  the  factors  which  influence  the  resul  cannot  be  deter- 
mined accurately. 

3.   DETERMINATION   OF  THE  SUBSTANCES  SOLUBLE  IN  WATER.* 

§297. 

For  the  separation  of  the  aqueous  extract,  one  of  the  following 
methods  may  be  chosen : 

a.  Weigh  off  as  much  fine  soil  as  will  be  equivalent  to  1000  grm. 
soil  dried  at  125°,  introduce  it  into  a  flask  of  about  6  litres  capacity, 

*  Compare  the  note  in  my  Anleitung  zur  qualitativen  chemischen  Analyse 
15th  edit.,  p.  435. 


828  CHEMICAL  ANALYSIS.  [§  297. 

add  sufficient  distilled  water  *  to  make  5000  c.c.,  including  that 
contained  in  the  weighed  soil  and  removable  at  125°,  and  mark  the 
level  of  the  water  in  the  flask  by  a  strip  of  gummed  paper  or  the 
like.f  Allow  the  water  to  remain  in  contact  with  the  soil  for  three 
days,  frequently  shaking  or  rolling  the  flask,  then  allow  to  settle, 
and  siphon  off  the  clear  liquid  into  another  flask;  allow  to  stand 
again  for  two  days,  siphon  off,  and  filter  if  necessary.  1000  c.c.  of 
the  liquid  thus  obtained  contain  the  soluble  constituents  of  200  grm. 
soil  dried  at  125°,  and  amounting,  on  an  average,  to  0- 1  to  0: 15  grm. 

/?.  FR.  SCHULZE'S  method.  For  this  method  of  extraction  there 
is  required  a  three-necked  WOULFF'S  flask  of  about  2  litres  capacity, 
and  with  a  tubulure  fitted  in  one  side  near  the  bottom.  Into  the 
middle  neck  there  is  fitted  air-tight  a  wide  glass  cylinder,  open 
above,  and  narrowed  below.  After  placing  a  loose  plug  of  sponge 
in  the  narrowed  part  of  the  tube,  covering  this  with  sifted,  clean 
gravel,  and  this  in  turn  with  sufficient  washed,  fine  sand  so  that  a 
small  part  of  the  wider  tube  may  be  filled  with  it,  fill  the  cylinder 
with  as  much  air-dried  fine  earth  as  will  represent  1000  grm.  of  the 
earth  after  being  dried  at  125°. 

One  of  the  other  two  necks  is  connected  with  the  tube  of  an  air- 
pump;  the  other,  as  well  as  the  tubulure  at  the  side,  is  closed. 
Moisten  the  earth  with  water,  add  more  from  time  to  time,  and 
allow  to  stand  for  24  hours ;  then  exhaust  the  air  in  the  flask,  thus 
causing  the  water  laden  with  the  soluble  portions  of  the  earth  to 
run  off  rapidly.  When  the  flask  is  nearly  filled,  open  the  third 
tubulure,  and  allow  the  liquid  to  run  off  through  the  lower  tubu- 

*  E.  WOLFF  recommends  to  saturate  one-fourth  of  the  water  with  car- 
bon dioxide. 

•j-  This  mark  is  required  only  when,  after  emptying  out  the  first  extract, 
it  is  desired  to  make  a  second,  third,  etc.,  with  an  equal  volume  of  water, 
in  order  to  determine  their  constituents  also,  and  which  some  agricultural 
chemists  consider  of  value  (compare  E.  WOLFF'S  Anleitung  zur  chemischen 
Untersuchung  landwirthschaftlich  wichtiger  Stoffe,  3d  edit.,  p.  25).  Complete 
exhaustion  of  a  soil  cannot  be  effected  even  by  repeated  extraction  with 
water,  partly  on  account  of  its  power  of  absorbing  many  substances,  and 
partly  because  of  the  slow  but  continuous  decomposition  of  the  organic 
substances  contained  in  it  (compare  A.  COSSA,  Zeitschr.  /.  analyt.  Chem., 
v,  166). 


§  297.]  ANALYSIS    OF   SOILS.  829 

lure.*  The  aqueous  extract  so  obtained  is  perfectly  clear.  As  a 
rule  it  is  sufficient  to  continue  the  extraction  until  5  litres  of  extract 
are  obtained.  By  proceeding  thus,  the  extract  obtained  in  /?  has 
the  same  degree  of  concentration  as  that  obtained  in  a. 

The  aqueous  extract  usually  contains  the  following  substances, 
which  may  be  determined,  if  necessary,  and  if  the  quantities  present 
are  not  too  small:  Potassium,  sodium,  ammonium,  calcium,  mag- 
nesium, ferric  and  perhaps  also  ferrous  iron,  sulphuric  acid,  phos- 
phoric acid,  nitric  acid,  chlorine,  silica,  at  times  carbon  dioxide,  and 
humus  substances.  To  determine  these  it  is  best  to  proceed  as 
follows : 

a.  Evaporate  2000  c.c.  of  the  solution  in  a  platinum  dish,  dry 
the  residue  at  125°,  and  weigh.  Note  the  weight  as  total  con- 
stituents soluble  in  water.  Then  gently  ignite  the  residue  for  a 
long  time  with  access  of  air,  moisten  with  a  concentrated  solution 
of  ammonium  carbonate,  evaporate,  gently  ignite,  ,and  weigh. 
The  loss  of  weight  arises  from  the  combustion  of  the  organic  sub- 
stances and  the  expulsion  of  the  nitric  acid  and  ammonium  com- 
pounds; on  deducting  the  weight  of  the  two  latter  from  the  total 
loss  in  weight,  the  difference  gives  the  humus  substances. 

Treat  the  residue  with  water  and  some  hydrochloric  acid  in  a 
porcelain  dish,  add  some  nitric  acid,  evaporate  to  dryness,  take  up 
again  with  hydrochloric  acid  and  water,  and  filter.  Silica  remains 
in  the  filter,  sometimes  mixed  with  a  little  carbon,  which  may  be 
burned  off  by  igniting .f  Thy  hydrochloric-acid  solution  divide 
into  two  parts,  a  and  /?. 

a.  To  this  first  add  ammonia  until  alkaline,  then  acetic  acid  in 
slight  excess,  then  a  few  drops  diluted  ferric-chloride  solution  to 
color  the  solution  red,  heat  to  boiling,  and  filter.  Dissolve  the 
precipitate,  after  washing,  in  hydrochloric  acid,  evaporate  the  solu- 
tion with  nitric  acid,  and  determine  the  phosphoric  add  by  the 
molybdenum  method  (p.  807  this  volume).  In  the  filtrate  from 

*  If  the  lower  tubulure  is  lacking,  empty  the  flask  by  means  of  a  siphon. 

t  If  the  aqueous  extract  was  not  quite  clear,  the  silica  thus  obtained 
contains  admixed  clay,  and  must  be  separated  from  the  latter  by  boiling 
with  a  solution  of  sodium  carbonate  (compare  p.  406,  6,  this  volume). 


830  DETERMINATION    OF  COMMERCIAL   VALUES.          [§  297. 

the  basic  ferric  phosphate  precipitate  the  calcium  with  ammonium 
oxalate,  and  in  the  filtrate  from  this  precipitate  the  magnesium 
with  ammonium  phosphate  (Vol.  I,  p.  621  [37]). 

/?,  To  this  also  add  first  ammonia  until  alkaline,  then  acetic 
acid  in  slight  excess,  heat  to  boiling  if  the  liquid  appears  reddish, 
and  filter.  The  precipitate  contains  all  the  iron.  To  determine 
this,  wash,  dissolve  in  hydrochloric  acid,  add  tartaric  acid,  ammo- 
nia, and  ammonium  sulphide,  allow  to  settle,  filter,  convert  the 
ferric  sulphide  into  ferric  oxide,  and  weigh  as  such  (Vol.  I,  p.  323, 6). 
(Should  the  iron  precipitate  also  contain  alumina,  it  must  be 
treated  as  detailed  on  p.  803  this  volume.) 

In  the  filtrate  from  the  ferric  phosphate  precipitate  the  sul- 
phuric acid  by  a  little  barium  chloride,  evaporate  the  filtrate  to 
dryness,  remove  the  ammonium  salts  by  igniting,  add  water,  pre- 
cipitate the  magnesia  by  adding  a  very  small  quantity  of  milk-of- 
lime,  and  proceed  to  determine  the  potassium  and  sodium  accord- 
ing to  p.  249  this  volume.  Should  the  composition  of  the  portion 
soluble  in  water  give  rise  to  the  fear  that  sulphuric  acid  may  be 
driven  off  or  reduced  on  igniting  the  residue,  the  sulphuric  acid 
must  be  determined  in  a  separate  portion  of  the  aqueous  solution 
according  to  §  205,  2. 

6.  Evaporate  1000  c.c.  of  the  solution  to  dryness  in  not  too  large 
a  dish,  and  determine  any  carbonates,  and  hence  combined  car- 
bonic acid  that  may  be  present,  by  means  of  decinormal  nitric  acid 
and  decinormal  soda  lye  (which  must  be  free  from  metallic  chlo- 
rides), according  to  p.  334,  3,  this  volume,  using  an  indicator  free 
from  chlorine  compounds  (e.g.,  a  little  phenolphtalein — p.  311 
this  volume).  Then  add  a  little  pure  sodium  carbonate,  evaporate 
to  dryness,  gently  ignite,  treat  the  residue  with  water,  filter,  acidu- 
late with  nitric  acid,  and  determine  the  chlorine  by  precipitation 
with  silver  nitrate  (Vol.  I,  p.  521,  a). 

c.  Nitric  acid  (and  also  any  nitrous  acid  present),  and  ammonia, 
if  this  is  present  in  determinable  quantity  in  the  aqueous  solution, 
are  determined  in  other  portions  of  the  solution  by  the  methods 
used  in  the  analysis  of  natural  waters  (pp.  186  and  211  this  vol- 
ume). The  nitric  acid  may  of  course  be  determined  by  any  of  the 


§  298.]  ANALYSIS   OF   SOILS.  831 

methods  described  in  §  149,  especially  those  which  may  be  carried 
out  in  the  presence  of  organic  substances,  and  which  yield  suffi- 
ciently accurate  results  even  when  determining  very  small  quan- 
tities of  nitric  acid.  Other  methods  of  determining  nitric  acid  will 
be  found  described  under  the  Analysis  of  Manures. 

4.    DETERMINATION  OF  THE  SUBSTANCES  SOLUBLE  IN 

HYDROCHLORIC  ACID.* 

§298. 

Weigh  off  as  much  air-dried  fine  earth  as  will  be  equivalent 
to  100  grm.  of  soil  dried  at  125°,  cover  it  with  50  c.c.  water  in  a 
400-  to  500-c.c.  flask,  mix  uniformly,  heat  on  the  water-bath,  and 
then  add  hydrochloric  acid,  sp.  gr.  1  •  149,  corresponding  with  30- 
per  cent.  HC1,  hi  portions  of  2  c.c.  each,  gradually  and  with  shak- 
ing, until  the  last  addition  ceases  to  cause  foaming  from  the  evolu- 
tion of  escaping  carbon  dioxide.f  To  the  solution  so  obtained  (water 
and  hydrochloric  acid),  add  an  equal  volume  of  hydrochloric  acid 
of  the  strength  mentioned  above,  heat  on  a  water-bath  for  five 
hours  with  frequent  shaking,  then  transfer  the  contents  to  a  weighed 
porcelain  dish,  and  rinse  out  with  water,  add  10  c.c.  nitric  acid, 
sp.  gr.  1-2,  and  evaporate  to  dryness  on  the  water-bath.  Then 
add  50  c.c.  hydrochloric  acid  of  sp.  gr.  1  •  1,  corresponding  to  20- 
per  cent.  HC1,  allow  to  stand  for  one  hour,  then  heat  for  one  hour 
on  the  water-bath,  add  about  200  c.c.  water,  and  separate  the 
solution  from  the  insoluble  portion  by  decanting  through  a  filter 
and  thoroughly  washing  the  residue.  Collect  the  solution  in  a 
marked  litre  flask.  If  it  is  seen  that  the  filtrate  together  with 
the  washings  measure  more  than  1  litre,  collect  the  last  washings 
separately,  concentrate  them  by  evaporating,  and  then  transfer 
them  to  the  litre  flask,  the  contents  of  which,  after  the  whole  is 
made  up  to  the  mark,  are  uniformly  mixed  by  shaking. 

*  The  following  inorganic  substances  pass  into  solution  in  hydrochloric 
acid :  Oxides  and  hydroxides ;  bases  of  the  carbonates ;  phosphates,  sulphates, 
bases  of  the  silicates  decomposable  by  hydrochloric  acid,  and  a  small  quantity 
of  the  silicic  acid  from  these. 

f  Should  the  mass  froth  so  that  a  running-over  is  feared,  a  few  drops  of 
alcohol  will  settle  the  foam. 


832  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  298. 

Spread  the  filter  out  on  a  glass  plate,  wash  its  contents  into 
the  dish  containing  the  bulk  of  the  insoluble  matter,  evaporate  to 
dryness  on  the  water-bath,  weigh  the  dish  together  with  its  con- 
tents, and  thus  ascertain  the  relative  weights  of  the  undissolved 
residue  and  the  fine  earth  originally  weighed  out.  Then  mix  it 
thoroughly  by  triturating,  transfer  the  uniformly  mixed  powder 
to  a  glass-stoppered  bottle,  and  proceed  with  it  as  in  5;  the  hydro- 
chloric-acid solution,  made  up  to  1  litre,  however,  treat  as  fol- 
lows :  * 

a.  300  c.c.,  corresponding  to  30  grm.  of  the  fine  earth  dried  at 
125°,  are  used  for  the  determination  of  the  ferric  iron,f  alumina, 
manganese,  calcium,  and  magnesium,  proceeding  according  to 
one  of  the  methods  detailed  in  §  161,  usually  that  described  in 
§  161,  2.  As  the  presence  of  phosphoric  and  silicic  acids  renders 
necessary  a  few  slight  modifications,  and  as,  moreover,  a  few 
additions  must  be  made  in  view  of  the  manganese  determination, 
I  will  again  give  here  a  short  sketch  of  the  process.  Remove  the 
too  great  an  excess  of  acid  by  evaporation,  nearly  neutralize  with 
sodium  carbonate,  and  precipitate  with  sodium  acetate,  as  in 
Vol.  I,  p.  647  [85].  Dissolve  the  washed  precipitate  in  hydro- 
chloric acid,  filter,  and  determine  any  residual  undissolved  silica. 
Divide  the  filtrate  into  two  parts,  after  it  has  been  united  with 
the  hydrochloric-acid  solution  from  the  secondary  alumina  pre- 
cipitation, and  which  will  be  presently  treated  of;  in  one  of  these 
parts  determine  the  iron  either  gravimetrically  (Vol.  I,  p.  642, 
[77]),  or  volumetrically  (Vol.  I,  p.  327,  6,  a),  and  in  the  other  part 
the  ferric  oxide  and  alumina,  together  with  the  phosphoric  acid 
and  some  silica,  by  precipitating  with  ammonia,  igniting,  and 
weighing  the  precipitate.  Fuse  the  latter  with  potassium  di- 

*  Regarding  an  essentially  different  method  of  treating  the  hydrochloric- 
acid  solution,  see  P.  LATSCHINOW,  Zeitschr.  /.  analyt.  Chem,  vu,  211. 

f  If  the  earth  contains  also  ferrous  iron,  a  separate  portion  of  the  soil 
must  be  extracted  with  diluted  hydrochloric  acid  in  a  current  of  carbon 
dioxide  with  the  aid  of  heat,  and  the  ferrous  iron  determined  in  the  solution 
according  to  Vol.  I,  p.  319,  b.  On  deducting  the  ferrous  iron  found  from 
the  total  iron  obtained  above,  after  calculating  to  equal  quantities  of  soil, 
the  difference  will  give  the  ferric  iron  present  in  the  soil. 


§  298.]  ANALYSIS    OF   SOILS.  833 

sulphate,  treat  with  hydrochloric  acid  and  water,  and  thus  ascer- 
tain the  small  quantity  of  silica  present.  On  deducting  this,  also 
the  phosphoric  acid  found  in  6,  and  also  the  ferric  oxide,  from  the 
weight  of  the  precipitate  thrown  down  by  the  ammonia,  the  alumina 
is  obtained. 

Acidulate  with  hydrochloric  acid  the  nitrate  from  the  pre- 
cipitate thrown  down  by  sodium  acetate,  and  add  ammonia  until 
just  alkaline,  thereby  usually  obtaining  a  further  slight  precipitate 
of  alumina,  which  collect,  wash,  and  dissolve  in  hydrochloric  acid 
(if  it  had  still  contained  manganese  it  would  have  been  necessary 
to  once  more  precipitate,  avoiding  any  appreciable  excess  of 
ammonia).  Add  the  hydrochloric-acid  solution  of  the  alumina 
to  the  hydrochloric-acid  solution  of  the  precipitate  thrown  down 
by  uie  sodium  acetate,  as  detailed  above. 

From  the  solution  which  remained  clear  on  the  addition  of 
ammonia,  or  which  was  filtered  from  the  alumina  precipitate, 
precipitate  the  manganese  with  ammonium  sulphide  (Vol.  I,  p.  295, 
a),  or  by  adding  bromine  and  ammonia,  the  latter  method  being 
preferable  in  the  case  of  small  quantities  of  manganese.  To 
-effect  this,  add  brominized  hydrochloric  acid  to  the  liquid  until 
it  appears  yellow,  then  add  ammonia  until  alkaline,  and  heat  to 
boiling.  The  resulting  brown  precipitate  of  hydrated  manganese 
dioxide  cannot  be  directly  ignited  and  weighed,  as  it  contains  alka- 
line earths.  It  should,  after  being  collected  and  washed,  be  dissolved 
in  a  little  hot  hydrochloric  acid,  the  solution  diluted,  then  pre- 
cipitated in  a  small  flask  with  ammonia  and  ammonium  sulphide, 
and  the  precipitated  manganous  sulphide  weighed.  The  liquid 
filtered  from  the  latter,  and  acidulated  with  hydrochloric  acid,  mix 
with  the  filtrate  from  the  hydrated  manganese  dioxide,  and  evapo- 
rate the  whole  to  dryness;  then  remove  the  ammonium  salts  by 
igniting,  and  in  the  residue  determine  the  calcium  and  magnesium 
according  to  Vol.  I,  p.  619.  If  the  manganese  has  been  previously 
precipitated  as  manganous  sulphide,  treat  the  filtrate  from  this, 
and  acidulate  with  hydrochloric  acid,  in  the  same  way. 

6.  300  c.c.  of  the  solution,  corresponding  to  30  grm.  of  the 
fine  earth  dried  at  125°,  are  used  for  the  determination  of  the 


834  DETERMINATION   OF   COMMERCIAL  VALUES.          [§  298. 

phosphoric  acid*  proceeding  as  detailed  on  p.  491,  10,  this 
volume. 

c.  300  c.c.  of  the  liquid  corresponding  to  30  gnn.  of  the  fine 
earth  dried  at  125°,  serve  for  the  determination  of  the  sulphuric 
acid  and  alkalies.  For  this  purpose  remove  the  greater  part  of 
the  free  acid  by  evaporating,  dilute,  and  precipitate  the  sulphuric 
acid  by  adding  a  slight  excess  of  barium-chloride  solution  to  the 
hot  liquid;  allow  to  stand  for  some  time,  filter,  ignite,  and  weigh 
the  barium  sulphate.  Should  this  appear  reddish  from  admixed 
ferric  oxide,  it  must,  in  order  to  obtain  accurate  results,  be  fused 
with  sodium  carbonate  and  the  sulphuric  acid  in  the  aqueous 
solution  of  the  melt  determined  as  in  Vol.  I,  p.  441,  6,  a. 

Precipitate  the  filtrate  from  the  barium  sulphate  with  am- 
monia and  ammonium  carbonate,  filter,  evaporate  to  dryness,  and 
remove  the  ammonium  salts  by  gently  igniting;  heat  the  residue 
with  water,  boil  with  a  little  milk-of-lime,  filter,  precipitate  with 
ammonia  and  ammonium  carbonate,  filter,  evaporate,  and  heat 
gently;  add  a  little  water,  precipitate  once  more  with  a  little 
ammonia  and  ammonium  carbonate,  evaporate,  heat,  weigh  the 
now  pure  alkali  chlorides,  and  separate  the  potassium  and  sodium 
by  means  of  platinum  chloride  (Vol.  I,  p.  599,  1,  a). 

In  the  case  of  soils  very  rich  in  humus,  this  method  does  not 
answer,  as  the  large  quantity  of  organic  matter  present  in  the 
solution,  and  which  has  beon  but  incompletely  decomposed  by 
evaporating  with  nitrohydrochloric  acid,  interferes  with  the  pre- 
cipitation of  the  hydrates  and  also  of  the  ferric  phosphate  and  alu- 
mina. The  organic  matter  may,  of  course,  be  removed  by  evapo- 
rating and  igniting,  but  in  this  case  the  iron  and  aluminium  are 
converted  into  the  very  inconvenient  condition  of  difficultly 
soluble  basic  salts.  In  such  a  case  it  is  best  to  proceed  as  follows: 

1.  300  c.c.  of  the  hydrochloric-acid  solution  serve  for  the 
determination  of  the  sulphuric  acid  and  alkalies;  any  notable 
deviation  from  the  method  described  above  in  c  is  unnecessary. 

*  Regarding  other  methods  of  determining  phosphoric  acid,  see  TH. 
SCHLOSING  (Zeitschr.f.  analyt.  Chem.,  vu,  473,  and  viu,  500) ;  and  W.  ScntiTZE 
(ibid.,  ix,  413). 


§  299.]  ANALYSIS   OF   SOILS.  835 

2.  Evaporate  600  c.c.  almost  to  dryness  in  a  platinum  dish, 
then  add  pure  potassa  lye  until  strongly  alkaline.  Evaporate  the 
whole  to  dryness  with  the  addition  of  a  little  sodium  carbonate  and 
potassium  nitrate,  and  ignite  to  destroy  the  organic  matter;  soften 
with  water,  and  decant  the  solution  into  a  flask ;  transfer  the  insoluble 
residue  to  a  glass  or  porcelain  dish,  and  warm  it  with  hydrochloric 
acid  until  dissolved,  unite  the  two  solutions,  and  make  up  to  600  c.c., 
and  in  300  c.c.  determine  the  constituents  mentioned  in  a,  and  in 
the  other  300  c.c.  determine  the  phosphoric  acid  according  to  the 
method  above  detailed. 

5.   EXAMINATION  OF   THE   PORTION   OF  SOIL  INSOLUBLE  IN 
HYDROCHLORIC   ACID.* 

§299. 

Dry  that  portion  of  the  fine  earth  insoluble  in  hydrochloric  acid 
on  the  water-bath,  weigh,  triturate,  and  uniformly  mix,  then  trans- 
fer to  a  dish,  mix  rapidly  once  more,  and  weigh  immediately  without 
delay  portions  of  5,  10,  and  15  grm.  each.  The  portions  are  best 
taken  from  the  mass  by  means  of  a  teaspoon.  It  must  always  be 
remembered  that  a  powder  like  the  one  in  question  is  very  prone  to 
lose  in  uniformity,  as  the  coarser  particles  tend  to  sink  to  the 
bottom,  leaving  the  finer  portion  at  the  surface. 

a.  Ignite  the  5-grm.  portion  with  access  of  air,  and  weigh  the 
residue.  After  calculating  from  the  part  to  the  whole,  the  total 
quantity  of  anhydrous  mineral  constituents  of  the  soil  insoluble  in 
hydrochloric  add,  is  ascertained. 

6.  Extract  the  10-grm.  portion  several  times  by  boiling  with  a 
concentrated  solution  of  sodium  carbonate,  and  proceed  to  deter- 
mine the  silica  thus  dissolved,  according  to  p.  406,  6,  this  volume. 
The  silica  found  here  may  be  either  that  separated  in  the  hydrated 
condition  from  the  decomposable  silicates  on  treating  the  earth 

*  Of  inorganic  substances,  this  contains  in  particular  the  silica  from  the 
silicates  decomposable  by  hydrochloric  acid,  the  silicates  not  decomposable 
by  hydrochloric  acid,  and  at  times  fragments  of  rock;  at  other  times  clay, 
together  with  the  hydrated  silica  often  admixed  with  it,  and  quartz  sand. 


836  DETERMINATION    OF   COMMERCIAL    VALUES.  [§  300. 

with  hydrochloric  acid,  or  that  mixed  with  the  clay  of  the  soil  as 
hydrate  (p.  420,  g,  this  volume). 

c.  Heat  the  15-grm.  portion  with  about  40  c.c.  concentrated, 
pure  sulphuric  acid  to  which  a  little  water  has  been  added,  for  10 
to  12  hours  in  a  platinum  dish,  and  so  that  the  excess  of  acid  is 
nearly  but  not  quite  driven  off.  When  cold,  moisten  with  concen- 
trated hydrochloric  acid,  allow  this  to  act  for  some  time  in  the 
warm,  add  water,  heat,  pass  through  a  filter,  and  repeat  the  opera- 
tion until  the  insoluble  residue  has  been  completely  and  thoroughly 
washed.  Spread  out  the  filter  on  a  glass  plate,  wash  the  adhering 
portion  of  the  residue  into  the  dish  containing  the  main  bulk,  evap- 
orate the  whole,  dry  at  100°,  weigh,  and  thus  ascertain  the  relation 
in  weight  to  that  portion  of  the  soil  insoluble  in  hydrochloric  acid, 
and  thereby  also  to  the  weighed  fine  earth;  then  mix  uniformly. 
Mix  the  filtrate  from  the  residue  with  the  washings  in  a  500-c.c. 
flask,  and  in  250  c.c.  determine  any  silica  that  may  have  passed 
into  solution,  together  with  the  alumina,  iron,  calcium,  and  mag- 
nesium, as  in  4,  a;  in  the  remaining  250  c.c.  determine  the  potas- 
sium and  sodium  as  in  4,  c.  It  must  here  be  noted  that  the  copious 
precipitate  of  barium  sulphate  obtained  on  precipitating  the  sul- 
phuric acid  with  barium  chloride,  must  be  ignited  after  being 
washed  and  dried,  then  extracted  by  boiling  with  diluted  hydro- 
chloric acid,  and  lastly  exhausted  with  water,  in  order  not  to  lose 
the  alkali  salts  carried  down  with  it.  The  solution  so  obtained 
is  united  with  the  filtrate  from  the  barium  sulphate. 

6.   EXAMINATION  OF  THE  RESIDUE  INSOLUBLE  IN  SULPHURIC  ACID. 

§300. 

a.  Boil  3  or  4  grm.  of  the  residue  repeatedly  with  a  solution  of 
sodium  carbonate,  and  determine  in  the  solution  the  dissolved 
silica  (p.  420,  g,  this  volume).  On  deducting  from  the  quantity 

*  By  treatment  with  sulphuric  acid,  the  clay  is  4ecomposed,  the  bases 
ccntained  therein  going  into  solution.  The  residue  thus  contains:  The 
silica  from  the  silicates  decomposed  by  hydrochloric  acid,  that  admixed 
as  hydrate  with  the  clay,  and  that  which  was  combined  with  bases  in  the 
clay,  as  well  as  the  silicates  not  decomposable  by  hydrochloric  or  sulphuric 
-acid  (fragments  of  rock),  and  also  quartz  sand. 


§  301.]  ANALYSIS    OF   SOILS.  837 

found  that  obtained  in  5,  6,  the  remainder  will  give  that  belonging 
to  the  clay  in  the  soil;  it  is  the  principal  constituent  of  the  clayey 
portion  of  the  soil,  which  resists  the  solvent  action  of  hydrochloric 
acid,  but  is  decomposed  by  sulphuric  acid. 

The  residue  remaining  after  extraction  by  boiling  with  sodium 
carbonate,  wash,  dry,  ignite,  and  weigh.  After  calculating  from  the 
part  to  the  whole,  the  result  will  give  the  soil  constituents  insoluble 
in  hydrochloric  acid  and  decomposable  by  sulphuric  acid. 

6.  Triturate  4  to  6  grm.  of  the  residue  insoluble  in  sulphuric  acid 
to  an  exceedingly  fine  powder  in  an  agate  mortar,  and  uniformly 
mix  the  powder.  Decompose  about  3  grm.  of  this  with  hydro- 
fluoric acid  (Vol.  I,  pp.  513  to  516),  and  then  determine  the  bases 
present.  If  the  silica  is  to  be  determined  not  only  by  difference, 
but  also  directly,  treat  0-5  grm.  of  the  fine  powder  as  in  Vol.  I, 
p.  511,  b,  a.  On  deducting  the  total  silica  thus  obtained  from  that 
found  in  6,  a,  the  silica  of  the  silicates  not  decomposable  by  sul- 
phuric acid,  and  present  as  quartz  sand,  is  ascertained. 

c.  As  by  b  only  the  total  silica  present  in  the  form  of  quartz 
and  that  combined  with  bases  is  obtained,  it  is  necessary,  in  order 
to  find  the  latter,  to  directly  determine  that  present  as  quartz. 
For  this  purpose  use  the  remainder  of  the  fine  powder  prepared  as  in 

6,  b.     The  methods  suitable  for  isolating  the  quartz  (heating  with 
phosphoric  acid,  or  with  sulphuric  acid  in  sealed  glass  tubes  *)  have 
already  been  detailed  under  the  analysis  of  clay  (p.  419  this  volume). 

7.  DETERMINATION  OF  THE  CARBON  CONTAINED  IN  THE  ORGANIC 

COMPOUNDS. 

§301. 

Carbon  is  present  in  the  soil  not  only  as  carbonic  acid,  but  also 
in  organic  substances,  and  in  fact,  chiefly  in  those  which,  through 
mouldering  and  decay,  have  become  converted  into  humus  (ulmin, 
humin,  ulmic  acid,  humic  acid,  geic  acid,  etc.).  It  may  suffice  to 
determine  the  total  carbon  present  in  the  organic  matter,  or  to 

*  Regarding  this  method,  compare  J.  HAZARD  (Zeitschr.  f.  analyt.  Chem., 
xxui,  158),  who  has  shown  that  by  this  treatment  a  great  deal,  but  by  no 
means  all,  of  the  silicates  is  decomposed. 


838  DETERMINATION    OF    COMMERCIAL   VALUES.  [§   301. 

make  supplementary  determinations  also  regarding  the  portion 
soluble  in  a  solution  of  sodium  carbonate  (humus  acids),  of  the 
portion  soluble  on  boiling  with  potassa  solution  (ulmin,  humin), 
and  lastly  of  the  waxy  and  resinous  substances  occasionally  present. 

a.  Determination  of  the  total  Organically  Combined  Carbon, 
a.  By  ultimate  analysis  in  the  dry  way. 

aa.  If  the  analysis  of  the  fine  earth  dried  at  125°  is  conducted 
as  detailed  on  p.  129,  this  volume,  §  191,  then,  from  the  carbonic 
acid  obtained,  that  present  in  the  form  of  carbonates  must  be 
deducted  (§  303,  a).  As  the  quantity  of  carbon  in  the  organic 
matter  is  thus  ascertained  from  the  difference  between  the  two 
determinations,  the  accuracy  of  the  result  is  impaired. 

bb.  R.  WARINGTON  and  W.  A.  PEAKE  *  recommend  to  first 
decompose  the  carbonates  present,  and  for  this  purpose  cover 
about  10  grm.  of  the  finely  powdered  soil  with  a  concentrated  solu- 
tion of  sulphurous  acid,  and  then  evaporate  the  whole  to  dryness. 
The  residue  is  then  transferred  to  a  platinum  boat,  and  the  organic 
matter  burnt  in  a  combustion  tube  with  the  aid  of  a  current  of 
oxygen  in  the  presence  of  cupric  oxide  (compare  p.  39,  this  vol- 
ume). For  the  absorption  of  the  nitrogen  oxides  and  aqueous 
vapors,  WARINGTON  and  PEAKE  employ  a  wash-bottle  containing 
concentrated  sulphuric  acid,  and  a  U-tube  filled  with  pieces  of 
pumice  stone  moistened  with  sulphuric  acid,  collecting  the  carbon 
dioxide  in  two  U-tubes  filled  with  caustic  soda  (or  soda-lime) . 

cc.  G.  LOGES  f  recommends  to  weigh  off  the  earth  to  be  ex- 
amined in  a  very  thin  glass  dish  (a  HOFFMEISTER  dish),  then  to 
add  to  it  diluted  phosphoric  acid  (in  the  case  of  sandy  soil  too 
large  an  excess  of  acid  must  not  be  employed) ,  and  then  to  evaporate 
the  whole  to  dryness  on  the  water-bath.  The  dish  and  its  con- 
tents are  then  ground,  mixed  with  powdered  cupric  oxide,  and 
introduced  into  a  combustion  tube  about  60  cm.  long,  open  at 
both  ends,  and  in  the  fore  part  of  which  is  placed  a  layer  of  granu- 

*  Berichte  der  deutsch.  chem.  Gesellsch.,  xm,  2096. 

t  Landwirthschaftl.  Versuchsstationen,  xxvin,  229  and  241 ;  Zeitschr.  /. 
analyt.  Chem.,  xxn,  619. 


$  301.]  ANALYSIS   OF   SOILS.  839 

lar  cupric  oxide  20  cm.  long  between  asbestos  plugs.  The  hinder 
end  of  the  combustion  tube  is  connected  with  two  wash-bottles, 
the  first  containing  potassa  solution,  and  the  second  baryta  water; 
the  fore  part  of  the  tube  is  connected  first  with  a  drying  cylinder 
the  upper  half  of  which  is  filled  with  cotton,  then  with  an  absorp- 
tion tube  for  retaining  baryta  water,  next  with  a  wash-bottle 
containing  baryta  water,  and  lastly  with  an  aspirator.  The 
drying  cylinder  containing  the  cotton  is  for  the  purpose  of  retaining 
any  water  and  oxygen  compound  of  nitrogen;  it  may  be  replaced 
t>y  a  copper  spiral  inserted  in  the  fore  part  of  the  tube.  The 
flask  of  baryta  water  interposed  between  the  absorption  tube  and 
the  aspirator  enables  the  operator  to  ascertain  whether  all  the 
carbon  dioxide  has  been  retained  by  the  former,  a  condition  which 
must  prevail  in  order  to  obtain  successful  results. 

The  operation  is  begun  by  heating  the  granular  cupric  oxide 
to  bright  redness,  while  a  current  of  air  is  drawn  through  the 
apparatus;  100  to  150  c.c.  of  baryta  water  (titrated  by  the  aid  of 
-an  oxalic-acid  solution  containing  10  grm.  per  litre)  are  then  intro- 
duced into  the  absorption  tube.  Next,  slowly  heat  the  combustion 
tube,  proceeding  from  the  fore  to  the  hinder  part  of  the  tube, 
while  a  quite  rapid  current  of  air  from  a  MARIOTTE  flask  is  con- 
stantly drawn  through  the  apparatus.  Lastly  determine  the  residual 
barium  hydroxide  in  25  or  50  c.c.  of  the  clear  baryta  water  after 
settling,  by  the  aid  of  oxalic  acid,  using  potassium  rosolate  as  an 
indicator;  this  gives  the  barium  precipitated  by  the  carbonic 
acid,  and  consequently  the  carbon  dioxide  and  the  carbon.* 

P.  By  oxidation  in  the  wet  way,  with  chromic  and  sulphuric 
acids,  in  the  manner  described  on  p.  510,  bb,  this  volume. 

•  This  method,  which  was  formerly  much  used,  I  call  attention 
to  here  simply  in  order  to  point  out  that  it  is  useless  in  soil  analysis. 
According  to  WARINGTON  and  PEAKE  (loc.  cit.)  only  80  to  90 
per  cent.,  and  according  to  G.  LOGES  (loc.  cit.)  only  64  to  96  per 
cent.,  of  the  carbon  present  is  thus  determined;  and  in  fact,  accord- 

*  Compare  the  determination  of  carbonic  acid  in  the  atmosphere  (§  336 
to  §  340). 


840  DETERMINATION    OF    COMMERCIAL   VALUES.  [§   301. 

ing  to  the  latter's  investigations,  because  many  of  the  organic 
substances  in  soils,  on  oxidation,  yield  acetic  acid,  which  resists 
further  oxidation  by  chromic  acid.* 

According  to  FR.  SCHULZE,  58  parts  of  carbon  represent  on  an 
average  100  parts  of  organic  matter  in  soil;  and  every  60  parts 
represent  100  parts  of  humus. 

b.  Determination  of  Humus. 

The  brown  or  black  substances  formed  as  a  result  of  the  action 
of  moisture  and  air  on  the  residual  plant  matter  in  the  soil,  and 
which  are  of  great  influence  on  the  character  and  fertility  of  the  soil, 
(although  opinions  have  been,  and  still  are,  held  regarding  their 
mode  of  action),  are  termed  humus  substances.  Attempts  have 
been  made  to  isolate  a  number  of  these,  and  to  characterize  them 
as  individual  chemical  compounds,  with  various  names,  e.g., 
ulmic  acid,  humic  acid,  ulmin.  humin,  etc. 

As  numerous,  however,  as  these  investigations  f  have  been, 
the  subject  cannot  be  considered  as  at  all  exhausted,  or  as  having 
led  to  any  definite  conclusion,  and  this  is  easily  understood  from 
the  fact  that  the  various  constituents  of  humus  very  closely 
resemble  each  other  in  properties,  and  that  neither  they  nor  their 
compounds  are  obtainable  in  a  crystalline  form.  Certain  facts, 
however,  have  been  established,  and,  being  of  importance  in  judg- 
ing of  the  character  of  soils,  they  must  be  here  considered. 
Among  these  is  the  fact  that  many  of  the  humus  constituents 
(humus  acids)  dissolve  in  boiling  solutions  of  alkali  carbonates 
— whether  due  to  the  humus  acids  being  present  in  the  free  state, 
or  whether  because  their  saline  compounds  are  decomposed  by 
alkali  carbonates — while  other  humus  constituents  are  not  dissolved 
although  they  do  dissolve  in  caustic  alkalies,  being  of  course  con- 
verted into  humus  acids  thereby. 

*  Compare  CROSS  and  BEVAN,  Zeitschr.  /.  analyt.  Chem.,  xxvi,  Part  I. 

f  See  the  collection  of  the  many  old  investigations  in  L.  GMELIN'S  Hand- 
buck  der  chemie,  4th  edit.,  by  K.  KRAUT,  vn,  1855;  OTTO,  in  SPRENGEL'S 
Bodenkunde,  p.  430;  FR.  SCHULZE,  Journ.  f.  prakt.  Chem.,  XLVII,  241;  W. 
DETMER,  Landwirthschaftl  Versuchsstat.,  xiv,  248;  GRANDEAU'S  Handbuch, 
pp.  108  and  112;  O.  PITSCH,  Landwirthschaftl.  Versuchsstat.,  xxvi,  1. 


§  301.]  ANALYSIS   OF   SOILS.  841 

a.  Determination   oj  the  humus   constituents    (humus   adds 
soluble  in  alkali  carbonates). 

Digest  from  10  to  100  grm.  of  the  air-dried  fine  earth  (accord- 
ing as  to  whether  the  qualitative  analysis  has  shown  much  or 
little  humus  acid  to  be  present)  with  a  solution  of  sodium  car- 
bonate (1  part  anhydrous  salt  to  10  parts  water)  on  the  water- 
bath  for  about  four  hours,  then  filter,  and  wash  with  boiling  water. 
In  order  to  determine  the  dissolved  humus  substances,  treat  the 
more  or  less  brown  filtrate  either  according  to  the  method  described 
on  p.  825  this  volume  (acidulating  with  acetic  acid,  boiling,  pre- 
cipitating with  lead  oxide,  etc.),  or,  acidulate  with  hydrochloric 
acid,  collect  the  brown  flocks  on  a  filter  dried  at  100°  and  weighed, 
wash  with  cold  water  until  the  washings  no  longer  have  an  acid 
reaction,  dry  at  100°,  weigh,  incinerate,  and  deduct  the  weight  of 
the  ash  from  the  weight  first  obtained,  calculating  the  difference 
as  humus  acids.  As  in  the  latter  method  the  filtrate  is  always 
colored,  the  first  method  is  to  be  preferred  in  the  case  of  light-brown 
solutions. 

/?.  Determination  of  the  humus  constituents  (humin,  etc.) 

insoluble  in  alkali  carbonates. 

Digest  the  residue  from  a  in  a  porcelain  dish  with  a  solution  of 
1  part  potassium  hydroxide  in  10  parts  water  on  the  water-bath 
for  several  hours,  replacing  the  water  as  it  evaporates;  then 
dilute,  decant  through  a  filter,  treat  the  residue  anew  with  caustic 
potassa  just  as  before,  dilute,  filter,  wash,  and  in  the  filtrate  deter- 
mine the  humus  acids  formed  from  the  humin,  etc.,  as  in  a.* 

*  FR.  SCHULZE  has  proposed  to  determine  the  humus  substances  ex- 
tractable  by  alkaline  solutions,  with  potassium  permanganate,  i.e.,  in  the 
same  way  organic  matter  in  water  is  determined  (see  p.  203  this  volume). 
SCHULZE,  to  effect  this  supplementary  determination,  boils  5  grm.  of  fine 
earth  with  100  c.c.  of  a  0-1-  to  1-per  cent,  potassa  solution  (E.  WOLFF  uses 
a  0-5-per  cent,  solution),  according  to  the  quantity  of  humus  in  the  soil; 
he  then  pours  the  mixture  on  a  filter  (instead  of  using  paper,  the  lower  part 
of  the  funnel  is  filled  with  well-ignited  finely  granular  sand),  washes,  makes 
up  the  filtrate  to  150  or  200  c.c.,  and  employs  a  few  c.c.  of  this  solution  for 
the  above-named  determination,  which,  naturally,  cannot  give  a  very  accu- 
rate result. 


842  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  302. 

c.  Determining  the  Waxy  and  Resinous  Substances. 

If  it  is  desired  to  more  closely  determine  these  substances, 
which  occur  in  appreciable  quantities  in  some  kind  of  soil 
(meadow,  marsh,  etc.),  dry  on  the  water-bath  a  quantity  of 
air-dried  earth  corresponding  to  100  grm.  fine  earth  dried  at 
125°,  then  boil  it  repeatedly  with  strong  alcohol,  transfer  the 
filtrates  to  a  flask,  and  distil  cff  half  the  alcohol;  then  allow  to 
<jool.  Any  wax  present  now  separates.  Collect  this  on  a 
weighed  filter,  wash  it  with  cold  alcohol,  and  determine  its  weight. 
Evaporate  the  filtrate,  finally  with  the  addition  of  water,  until  all 
the  alcohol  has  been  driven  off,  then  wash  the  separated  resin 
with  water,  dry,  and  weigh.  (If  the  total  quantity  of  wax  and 
resin  is  at  all  considerable,  it  must  be  deducted  from  the  weight 
of  the  humus  acid,  as  the  waxy  and  resinous  substances  have 
been  weighed  with  the  humus  substances.) 

S.   DETERMINING    THE    NITROGENOUS   CONSTITUENTS    OF    THE   SOIL. 

§302. 

Nitrogen  may  be  present  in  the  soil  combined  in  three  different 
ways,  e.g.,  as  nitric  acid  (or  nitrous  acid),  as  ammonia,  and  in 
organic  compounds.  It  is  not  enough  to  determine  the  nitrogen 
content  of  a  soil  in  order  to  know  the  character  of  the  latter,  but 
we  must  also  know  the  form  of  combination  in  which  it  occurs. 

a.  Determining  the  Nitric  Acid. 

As  nitrates  (also  nitrites)  are  not  retained  on  extracting  the 
soil  with  water,  the  total  quantity  of  these*present  will  be  found 
in  the  aqueous  extract,  in  which  they  have  already  been  deter- 
mined; see  §  297,  c. 

5.  Determining  the  Ammonia. 

As  the  soil  retains  ammonium  compounds  in  such  a  manner  that 
they  are  not  completely  extracted  by  water,  the  quantity  which 
may  be  found  in  the  extract,  even  if  determinate,  affords  no 
indication  of  the  total  quantity  present  in  the  soil.  The  quantity 


§  302.]  ANALYSIS   OF    SOILS.  843 

must  hence  be  ascertained  by  a  special  determination.  According 
to  the  investigations  of  KNOP  and  W.  WOLF,*  as  well  as  those  of 
A.  BAUMANN,!  ammonium  compounds  occur  in  soils  only  in  very 
small  quantities,  at  most  2  to  3  parts  ammonia  per  100,000  parts  of 
soil.  The  following  methods  have  been  recommended  for  the  deter- 
mination : 

a.  SCHLOSING'S  Method  (Vol.  I,  p.  255,  b). 

E.  WOLF  {  recommends  to  employ  50  grm.  of  air-dried  earth 
and  to  uniformly  moisten  with  40  c.c.  cold,  very  concentrated 
caustic  soda.  After  48  hours  all  the  ammonia  will  have  been 
expelled.  As,  however,  ammonia  is  continuously  evolved  by  the 
action  of  caustic  soda  on  soils  containing  humus,  even  though 
they  contain  no  ammonium  compounds,  the  method  is  inapplicable 
to  such  soils. § 

/?.  Distillation  with  Water  and  Calcined  Magnesium 
(Vol.  I,  p.  253,  3.,  a). 

E.  WOLF  (loc.  cit.)  proposes  distilling  100  grm.  of  air-dried  fine 
earth  with  500  c.c.  water  and  5  grm.  freshly  ignited  magnesia. 
GRANDEAU  ||  remarks  hereon  that  the  method  thus  carried  out 
cannot  afford  accurate  results,  because,  after  the  ammonia  present 
has  been  expelled,  other  nitrogenous  constituents  of  the  soil  will 
also  evolve  ammonia.  Very  accurate  results  can  be  obtained, 
according  to  him,  by  the  following  method,  also  proposed  by 
SCHLOSING,  in  which  the  ammonia  is  not  determined  by  direct  dis- 
tillation of  the  soil,  but  from  the  hydrochloric-acid  extract.  The 
method  is  carried  out  as  follows : 

aa.  Mix  1  volume  of  hydrochloric  acid  with  4  volumes  of  water, 

*  Chem.  Centralblatt,  1860,  540. 

f  Landwirthschaftliche  Versuchsstationen,  1886,  284. 

j  Anleitung  zur  chem.  Untersuchung  landurirthschaftl.  wichtiger  Staff et 
3d  edit.,  p.  47. 

§  Compare  also  earlier  statements,  particularly  A.  BAUMANN  (Ijand- 
vrirthschaftliche  Versuchsstationen,  1886,  255).  Whether  better  results  may 
be  obtained  with  milk-of-lime,  still  remains  to  be  investigated. 

||  His  Handbuch,  German  edit.,  p.  116. 


844  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  302. 

and  determine  any  possible  ammonia  content  in  the  diluted  acid 
according  to  cc. 

bb.  Introduce  a  quantity  of  air-dried  fine  earth  corresponding 
to  100  grm.  fine  earth  dried  at  125°  into  a  weighed  flask  of  from  1 
to  2  litres  capacity,  add,  but  without  warming,  50  c.c.  of  the  diluted 
acid  prepared  as  in  aa,  and  after  the  carbon  dioxide  has  been 
evolved,  add  another  50  c.c.,  and  if  necessary  a  still  further  quan- 
tity, until  the  hydrochloric  acid  is  unmistakably  present  in  excess. 
Now  add  ammonia-free  water  to  make  the  total  quantity  of  the 
liquid  400  c.c.,  mix  uniformly,  and  weigh  the  flask  with  its  contents; 
allow  to  stand  until  the  liquid  above  the  sediment  has  become 
clear,  carefully  draw  off  with  a  siphon  provided  with  a  pinchcock, 
and  determine  the  quantity  of  the  liquid  drawn  off  by  reweighing 
the  flask.  To  now  ascertain  what  proportion  of  the  whole  liquid 
has  been  removed,  filter  the  undissolved  residue,  wash  it,  dry  at 
125°,  and  deduct  its  weight  from  the  original  weight  of  the  total 
contents  of  the  flask.  In  the  liquid  siphoned  off  determine  the 
ammonia,  calculate  its  quantity  to  the  total  solution,  and  hence  to 
100  grm.  of  fine  earth  dried  at  125°. 

cc.  For  the  determination  of  the  ammonia  in  the  hydrochloric- 
acid  solution  the  apparatus  shown  in  Fig.  133  is  employed;  it 
differs  from  that  usually  used  for  distilling  ammonia,  in  that  the 
possibility  of  impurities  from  the  glass  constituents  passing  into 
the  ammoniacal  solution  to  be  titrated  is  excluded,  and  that  all 
the  ammonia  is  obtained  in  a  very  small  volume  of  liquid.  The 
hydrochloric-acid  extract  of  the  soil  is  introduced  into  the  retort, 
a,  with  sufficient  freshly  ignited  magnesia  to  have  this  present  in 
decided  excess.  The  condensing- tube,  S,  is  connected  with  the 
retort,  and  also  at  b  with  the  bent  platinum  tube,  c,  which  passes 
through  the  small  condenser,  P,  fed  from  the  reservoir,  R.  The 
lower  end  of  the  platinum  tube  dips  at  e  into  a  funnel-shaped  glass 
tube,  the  lower  end  of  which  extends  down  into  an  accurately 
measured  volume  of  very  dilute  titrated  sulphuric  acid,  each  c.c. 
of  which  contains  about  0-001  grm.  SO3,  and  which  is  contained  in 
the  flask,  B.  When  the  contents  of  the  retort,  a,  have  been  heated 
sufficiently  long  to  make  certain  that  all  the  ammonia  has  been 


§  302.] 


ANALYSIS   OF    SOILS. 


845 


driven  over  into  B,  titrate  the  excess  of  sulphuric  acid  by  lime 
water  which  has  been  previously  standardized  against  the  acid  by 


FIG.  133. 

the  aid  of  litmus  tincture  *  as  the  indicator.  A.  BAUMANN  t  recom- 
mends, particularly  when  using  glass  condensing  tubes,  to  de- 
termine the  ammonia  azotimetrically. 

f.  The  Azotimetric  Method. 

This  simple  method  of  determining  ammonia,  and  which  yields 
very  accurate  results,  was  originally  proposed  in  a  sufficiently  satis- 

*  In  order  to  secure  the  highest  degree  of  sensitiveness  SCHLOSING  recom- 
mends to  boil  a  very  concentrated  solution  of  litmus  in  distilled  water  with 
a  little  calcium  hydroxide,  allow  to  settle,  filter,  and  add  5  or  6  times  the 
volume  of  alcohol ;  filter  off  the  resulting  blue  precipitate,  wash  it  with  weak 
alcohol  a  few  times,  and  preserve  it  under  alcohol  in  stoppered  flasks.  To 
prepare  the  litmus  tincture  suspend  a  little  of  the  blue  precipitate  in 
water,  just  supersaturate  with  diluted  sulphuric  acid,  filter  off  the  calcium 
sulphate  formed,  boil  up  once  to  expel  carbon  dioxide,  and  then  accurately 
neutralize  with  potassa  or  soda  lye. 

t  Landwirthschajtl.  Versuchsstationen,  1886,  p.  255. 


846  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  302- 

factory  form  by  W.  KNOP,*  and  was  also  recommended  by  him  and  bjr 
W.  WOLF  f  for  the  determination  of  ammonia  in  soils.  The  method 
was  subsequently  repeatedly  examined,  modified,  and  improved,, 
particularly  by  E.  DIETRICH,!  W.  KNOP,§  P.  WAGNER, ||  and  F. 
SoxHLET.^f  It  depends  upon  the  known  action  of  an  excess  of  alkali 
hypobromite  on  ammonium  salts,  as  a  result  of  which  all  the  nitro- 
gen  of  the  ammonia  is  liberated ;  the  method,  however,  can  be  used 
for  the  determination  of  ammonia  in  soils  or  the  hydrochloric-acid 
solution  of  the  latter,  only  when  they  contain  no  other  nitrog- 
enous compounds  decomposable  by  alkali  hypobromite  with 
evolution  of  nitrogen,  e.g.,  urea,  and  are  not  rich  in  humus  (DIE- 
TRICH; A.  BAUMANN).  In  the  case  of  freshly  manured  soil,  humus, 
soils,  particularly  peaty  soil,  the  method  would  thus  give  inaccu- 
rate results.**  As  the  azotimetric  method  of  determining  ammonia 
in  manures  is  of  much  more  importance  than  in  the  analysis  of 
soils,  it  will  be  described  in  the  section  devoted  to  Manures  (§  322).. 

c.  Determination  of  Nitrogen  in  Organic  Compounds. 

a.  Determine  the  total  quantity  of  nitrogen  by  igniting  a 
portion  of  the  air-dried  soil  with  soda-lime  (82  to  05  this  volume) , 
and  deduct  therefrom  the  nitrogen  found  as  present  in  the  form  of 
nitric  acid  and  ammonia. 

If  the  soil  contains  but  a  very  small  quantity  of  organic  matter, 
mix  from  0-3  to  0-5  grm.  of  cane-sugar  with  the  sample  in  order 
to  obtain  also  the  nitrogen  of  the  nitric  acid  in  the  form  of  am- 
monia. E.  WOLFF  recommends  to  mix  the  sample  with  the  aqueous 
solution  of  the  sugar,  and  then  to  dry  it,  in  order  to  obtain  a  per- 
fectly thorough  mixture.  E.  SCHULZE  has  shown  (p.  84  this 
volume)  that  under  such  circumstances  small  quantities  of  nitrie 
acid  are  completely  converted  into  ammonia. 

*  Chem.  Centralbl.,  1860,  244. 
t  Ibid.,  1860,  257. 
J  Zeitschr.  f.  analyt.  Chem.,  v,  36. 
§  Ibid.,  ix,  225;  xiv,  248;  xxv,  301;  and  xxvi,  Part  I. 
||  Ibid.,  xm,  383;  and  xv,  250.  f  Ibid.,  xvi,  81. 

**  Compare  W.  KNOP  (Zeitschr.  f.  analyt.  Chem.,  ix,  225);  HUFNER  (ibid., 
X,  486);   PAGEL  (ibid.,  xv,  282);   A.  MORGEN    (ibid.,  xx,  37);   E.  SCHULZE: 
xi,  1);  and  A.  BAUMANN  (Landwirthschaftl.  Versuchsstat.,  1866,  281). 


§  303.]  ANALYSIS   OF   SOILS.  847 

ft.  Determine  the  total  nitrogen  present  in  the  organic  matter,, 
as  well  as  in  the  form  of  ammonia,  by  the  KJELDAHL  method, 
after  having  driven  off  any  nitric  acid  present  by  evaporating  with 
diluted  sulphuric  acid.  On  deducting  from  the  ammonia  thus 
obtained  that  found  in  the  soil  as  such,  the  ammonia  correspond- 
ing with  the  nitrogen  of  the  organic  matter  is  obtained.  See  also 
§  329,  r 

9.  SUPPLEMENTARY   DETERMINATIONS. 
§  303. 

a.  Determination  of  the  Carbon  Dioxide. 

In  a  sample  of  the  air-dried  fine  earth,  the  quantity  of  which 
should  be  larger  or  smaller  according  to  the  carbonic  acid  present, 
determine  the  carbon  dioxide  according  to  one  of  the  methods 
detailed  in  Vol.  I,  pp.  488  to  505;  any  carbonic  acid  absorbed  by 
the  sample  must  be  first  expelled,  however,  by  boiling  the  latter 
with  water. 

b.  Determination  of  the  Unoxidized  Sulphur. 
At  times  soils  contain  small  quantities  of  unoxidized  sulphur, 
the  greater  portion  being  present  in  the  form  of  sulphides 
(pyrites).  As  a  rule  it  may  be  readily  detected  by  determining 
the  sulphuric  acid  first  in  unignited  soil,  and  then  repeating  the 
determination  with  soil  after  ignition.  The  quantity  of  sulphuric 
acid  found  in  the  latter  determination  will  generally  be  greater 
than  in  the  first  (E.  WOLFF).  If  the  quantity  of  unoxidized 
sulphur  is  to  be  determined,  moisten  50  grm.  of  the  air-dried  fine 
earth  in  a  platinum  dish  with  a  concentrated  solution  of  pure 
potassium  nitrate;  add  a  little  pure  sodium  carbonate,  dry  and 
then  gradually  heat  to  redness.  The  oxidation  of  the  organic 
matter  is  complete  in  the  glimmering  mass.  When  cold,  soften 
the  mass  with  water,  heat  in  a  porcelain  dish  with  hydrochloric 
acid  and  a  little  nitric  acid,  filter,  separate  the  silica,  and  deter- 
mine the  sulphuric  acid ;  on  deducting  from  the  result  the  quantity 
found  in  §  298,  c,  the  difference  will  correspond  to  the  unoxidized 
sulphur  present  in  the  soil 


848  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  304. 

c.  Reaction  of  the  Soil. 

The  reaction  of  the  soil  should  also  be  stated.  In  order  to 
determine  this,  place  a  moderately  moist  lump  of  fresh  soil  on  a 
piece  of  sensitive  litmus-paper.  If  the  soil  is  acid,  observe  whether 
the  reddened  spots  on  the  paper  retain  their  color  or  lose  it; 
the  latter  will  be  the  case  if  the  acidity  is  due  to  free  carbonic  acid. 
d.  Further  Determinations. 

According  to  circumstances,  it  may  be  advisable  to  still  further 
extend  the  investigations;  e.g.,  to  determine  the  ferric  and 
aluminium  hydroxides  (A.  MULLER;*  W.  KNOpf);  to  determine 
the  quantity  and  nature  of  the  gases  absorbed  by  the  soil 
(BLUMTRITT  ;  J  REICH ARDT  §) ;  the  behavior  of  soil  when  moist, 
or  when  saturated  with  potassa  lye,  towards  the  atmospheric 
oxygen  (W.  WOLF;  FR.  SCHULZE||);  to  the  substances  passing 
into  the  ammoniacal  solution  with  the  humus,  in  SCHLOSING'S 
method  (§  295)  of  humus  determination  (Analysis  of  the  "Matiere 
Noire  "IF);  or  to  the  behavior  of  the  soil  in  the  dialyzer  (PETER- 
MAN  ;  **  SESTINI  ft)  •  Regarding  these  methods,  however,  I 
must  refer  to  the  original  sources. 

10.  STATEMENT  OF  THE  RESULTS. 

§304. 

The  results  of  the  chemical  examination  must  be  conveniently 
arranged  in  order  to  afford  a  clear  representation  of  the  composi- 
tion of  the  soil.  I  believe  that  the  following  scheme  is  best  adapted 
for  the  purpose.  The  numbers  given  have  been  selected  arbi- 
trarily, and  are  only  intended  to  illustrate  the  principles  of  the 
arrangement. 

*  Landwirthschaftl.  Versuchsstat.,  iv,  226;  Journ.  f.  prakt.  Chem.,  xcvm,  d. 
f  Landwirthschaftl.  Versuchsstat.,  vin,  41. 
J  Journ.  f.  prakt.  Chem.,  xcvm,  418. 
§  Ibid.,  xcvm,  458;  Zeitschr.  f.  analyt.  Chem.,  vn,  185. 
||  E.  WOLFF'S   Anleit.  zur   chem.   Untersuchung    landw.  wicht.  Stoffe,  3d 
edit.,  pp.  41  and  42. 

1"  GRANDEAU'S  Handbuch,  p.  113. 

**  Landwirthsch.  Versuchsstat.,  xv,  468. 

ft  Ibid.,  xxix,  459. 


§304.] 


ANALYSIS   OF   SOILS. 


849 


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850  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  305- 

V.  ANALYSIS  OF  MANURES. 

A.  GENERAL. 
§305. 

By  manures,  such  substances  are,  first,  to  be  understood,  as 
are  produced  in  agriculture,  and  consisting  chiefly  of  urine,  animal 
excrement,  and  stable  litter,  i.e.,  stable  manure;  and  secondly, 
such  as  are  purchased  by  the  farmer— artificial  manures.  The 
number  and  kind  of  the  latter  have,  in  the  course  of  time,  greatly 
increased,  on  account  of  the  joint  action  of  agricultural,  trade, 
and  technical  industries,  in  procuring  the  substanc  s  necessary 
for  plant  food,  particularly  phosphoric  acid,  potash,  and  nitrogen, 
from  the  most  varied  sources  and  in  the  most  manifold  combina- 
tions and  mixtures,  to  meet  the  various  requirements  demanded 
in  agriculture  and  vine-growing. 

While  the  chemical  examination  of  stable  manure  as  a  rule 
possesses  a  greater  scientific  interest,  the  analysis  of  artificial 
manures,  nevertheless,  is  of  exceedingly  great  practical  importance, 
because  their  very  variable  values  must  be  determined  by  a  chemical 
analysis  which  will  show  the  content  and  mode  of  combination 
of  the  effective  constituents. 

As  manure  manufacturers  and  dealers  now  guarantee  certain 
percentage  compositions,  and  the  farmer  is  now  enabled  to  have 
tests  made  at  the  agricultural  experimental  stations  and  com- 
mercial laboratories  as  to  whether  the  manures  are  up  to  the 
guarantee,  the  analysis  of  artificial  manures  is  a  matter  of  great 
importance  in  many  laboratories.  Many  chemists,  on  this  account, 
have  devoted  themselves  to  ascertaining  the  most  suitable  methods 
of  investigation,  and  in  fact  from  different  points  of  view  as  well. 
While  the  chief  aim  of  some  has  been  accuracy  of  results,  others 
sought  the  most  simple  and  speediest  methods;  and  frequently 
experimental  stations  and  manufacturers  united  in  order  to  regu- 


§  306. J  ANALYSIS   OF   MANURES.  851 

late  the  methods  of  analysis  with  a  view  to  securing  uniform 
results. 

I  will  endeavor,  hi  the  following,  to  take  note  of  all  these  differ- 
ent views,  so  far  as  possible,  and  I  believe  that  the  manner  of  best 
affording  an  oversight  over  the  whole  section  will  be  to  begin  with 
the  simpler,  and  to  pass  on  to  the  more  complicated  manures,  com- 
mencing with  the  manures  the  value  of  which  depends  upon  a  single 
constituent,  and  to  take  up  hi  succession  those  hi  which  two  or  more 
constituents  are  to  be  determined.  Before  beginning,  however, 
a  few  remarks  must  be  made  regarding  the  manner  of  taking  sam- 
ples, because  the  most  accurate  analysis  will  have  no  value  if  the  sam- 
ple does  not  truly  represent  the  average  composition  of  the  manure. 

B.  SAMPLING.* 

§306. 

In  taking  the  sample,  the  following  precautions  must  be 
observed: 

1.  If  the  heap  consists  of  lumps,  e.g.,  in  the  case  of  phosphorite, 
a  correct  sample  can  be  obtained  only  on  comminuting  a  large 
quantity,  and  uniformly  mixing  the  mass  obtained. 

2.  If  the  material,  from  which  the  sample  is  to  be  taken,  con- 
sists of  fine  powder  mixed  with  lumps  or  coarse  pieces,  separate 
these  by  sifting,  comminute  the  lump  by  trituration,  grinding,  or 
cutting  up,  and  uniformly  mix  the  mass  so  obtained  with  the  sifted 
portion. 

3.  If  the  samples  are  taken  from  a  more  or  less  pulverulent 
material  stored  in  casks  or  sacks,  it  is  not  sufficient  to  take  portions 
from  the  upper  layers  and  to  mix  them,  because  the  layers  in  the 
casks  or  sacks  may  differ.     As,  however,  it  is  exceedingly  difficult 
to  uniformly  mix  the  contents  of  many  casks  and  sacks  together, 
use  is  made  hi  such  a  case  as  a  rule,  of  a  sampling  toolrf  i.e.,  a  hollow 

*  Regarding  the  influence  of  the  manner  of  sampling  manures  on  the 
analytical  results,  a  comprehensive  investigation  was  made  with  guano,  by 
BARRAL  and  DUVAL  (Zeitschr.  f.  analyt.  Chem.,  xv,  490). 

f  E.  SCHUMANN,  "Anleit.  zur  Untersuchung  der  Kduflichen  Dungemittel," 
etc.,  1876;  P.  WAGNER,  "Lehrbuch  der  Dungerfabrikation"  Brunswick:  FR. 
VIEWEG  UND  SOHN,  1877,  176. 


852  DETERMINATION    OF    COMMERCIAL   VALUES.         [§  306. 

cylinder  with  a  point,  b,  and  a  handle,  a,  as  shown  in  Fig.  134. 
The  sampling-tool  is  made  of  stout  sheet  iron,  is  about 
60  cm.  long,  and  about  3  cm.  in  diameter.  It  is  pushed 
into  the  cask  or  sack,  and  turned  once  around,  whereby 
it  is  filled  with  the  material;  it  is  then  slowly  withdrawn, 
the  contents  emptied,  and  the  operation  repeated  as 
often  as  may  be  considered  necessary  to  secure  an 
average  sample — in  any  case  until  at  least  1  or  2  kilos 
of  the  material  have  been  removed.  In  the  case  of 
many  manures,  a  sampler  with  a  sharpened  edge 
instead  of  a  point  is  preferable. 

4.  If  it  is  desired  to  take  a  small  sample  from  a 
relatively  large  quantity  of  a  more  or  less  pulverulent 
substance,  for  the  purpose  of  sending  away,  or  for  fur- 
ther examination,  mix  the  mass  uniformly  on  a  suitable 
surface  (a  table,  or,  on  a  cloth  spread  on  the  floor,  or 
the  like),  then  spread  out  in  a  circular  layer  of  uniform 
thickness,  and  remove  a  segment  or  two,  so  that  the 
G'  '  weight  of  the  sample  will  be  about  500  grm. 

5.  The   samples   intended   for   analysis   should   be  packed  or 
stored  in  tightly  stoppered  glass  bottles ;  in  the  case  of  manures 
that  are  not  acid,  tin  boxes  with  closely  fitting  lids  may  be  used. 

6.  In  the  laboratory  the  samples  must,  as  a  rule,  be  once  more 
broken  up.     If  a  determination  of  the  moisture  as  well  as  an  analy- 
sis of  the  dried  sample,  are  to  be  made,  a  larger  quantity  of  the 
material  must  be  taken  for  the  former,  and  either  as  it  is,  or  after 
rapidly  mixing  in  a  large  mortar,   according  to   circumstances. 
The  material  is  then,  either  as  it  is,  or  after  partially  drying,  passed 
through  a  sieve  of  1  to  1  •  5  mm.  mesh,  and  the  coarser  parts  crushed 
and  also  sifted,  the  whole  being  finally  uniformly  mixed.     Now 
remove  a  small  sample  with  a  spoon,  reduce  it  to  a  fine  powder,  dry 
it  at  the  same  temperature  at  which  the  water-determination  was 
made,  and  employ  this  for  the  analysis.     If,  however,  no  moisture 
determination  is  to  be  made,  and  if  the  material  is  to  be  examined 
in  the  dry  form  in  which  it  comes,  the  sample  must  be  rapidly  pre- 
pared and  as  uniform  as  possible,  avoiding  so  far  as  possible,  all 


§   307.]  ANALYSIS    OF    MANURES.  853 

circumstances  that  may  favor  a  change  in  its  hygroscopic  state; 
it  is  also  advisable,  in  this  case,  to  dissolve  a  large  weighed  sample, 
and  to  employ  aliquot  portions  of  the  solution  for  the  determin- 
ations. 

7.  Wet  samples  may,  under  certain  circumstances,  be  uni- 
formly mixed  and  prepared  for  analysis,  at  least  for  the  determina- 
tion of  certain  circumstances,  by  mixing  with  a  weighed  quantity 
of  freshly  burnt  gypsum.  If  the  quantities  taken  have  been  cor- 
rectly gauged,  a  mixture  will  be  obtained  which  may  be  comminuted, 
passed  through  a  sieve,  and  uniformly  mixed.  If  a  loss  of  ammonia 
is  feared,  the  gypsum  used  must  previously  be  triturated  with  from 
3  to  5  per  cent,  of  concentrated  sulphuric  acid.  It  is  of  course 
scarcely  necessary  to  point  out  that,  when  gypsum  is  used  for  the 
mixing,  its  weight  must  be  taken  into  consideration  when  meas- 
uring out  portions  of  the  substance  for  analysis. 

C.  ANALYSIS  OP  MANURES  THE  VALUE  OF  WHICH  DEPENDS 

ENTIRELY   OR  ALMOST   ENTIRELY  UPON  THEIR 

PHOSPHORIC-ACID  CONTENT. 

I.  THOSE  CONTAINING  THE  WHOLE  OF  THE  PHOSPHORIC  ACID  IN  THE 
FORM  OF  COMPOUNDS  INSOLUBLE  IN  WATER. 

§307. 

To  this  class  belong  the  calcined  bone  phosphates  (bone-ash, 
bone-black),  precipitated  calcium  phosphates,  lime,  basic  slag  or 
Thomas  slag,  mineral  phosphates  (apatite,  phosphorite,  coprolites, 
osteolites,  Navassa-,  Sombrero-,  Carolina-phosphates,  etc),  and 
certain  kinds  of  guano  (Baker  guano,  Maracaibo  guano,  Jarvis 
guano,  etc.).  All  these  phosphates  contain  only  tribasic  phos- 
phoric acid  (orthophosphoric  acid),  chiefly  combined  with  calcium, 
and  in  fact  mostly  as  basic  calcium  orthophosphate,  tricalcium 
phosphate,  Ca^PO^;  many,  however,  such  as  the  cakes  or 
clinkers  of  the  Baker-  and  Jarvis-guano,*  and  occasionally  also  the 
precipitated  calcium  phosphate,  contain  so-called  neutral  calcium 
orthophosphate,  dicalcium  phosphate,  C£UjH2(PO4)2.  In  the  former 

*  C.  GILBERT,  Zeitschr.  f.  analyt.  Chem.,  xn,  1. 


854  DETERMINATION    OF    COMMERCIAL    VALUES.         [§  308. 

the  orthophosphate  contained  remains  unchanged  on  ignition,  but 
in  the  latter  it  is  converted  into  pyrophosphate, 


1.    DETERMINATION    OF  THE   MOISTURE. 

Dry  3  to  5  grm.  to  constant  weight.  So  far  as  the  temperature 
is  concerned,  100°  is  the  most  convenient,  hence  it  is  most  frequently 
used,  although  drying  at  110°  is  more  effective,  and  is  therefore  as 


FIG.  135. 

a  rule  preferable.  In  the  case  of  bone-black,  such  a  high  tempera- 
ture is  absolutely  necessary.  The  weighing  and  drying  are  most 
conveniently  effected  in  a  light  weighing-flask  provided  with  a 
hollow  stopper,  as  shown  in  Fig.  135. 

2.    DETERMINATION    OF    PHOSPHORIC   ACID. 

Of  the  many  possible  methods  of  determining  phosphoric  acid, 
the  gravimetric  molybdenum  method  has  proved  to  be  the  most 
reliable  under  all  circumstances  for  the  phosphates  here  under 
consideration.*  Besides  this  one,  the  method  recently  proposed 
by  C.  GLASER  f  is  also  described. 

a.  Dissolving  the  Substance. 
§308. 

a.  If  the  phosphate  to  be  examined  is  free,  or  almost  free, 
from  organic  substances,  readily  soluble  in  acids,  and  quite  or 
almost  free  from  readily  decomposable  silicates,  e.g.,  precipitated 

*  Z&itschr.  f.  analyt.  Chem.,  xxi,  289.  f  Ibid.,  xxiv,  178. 


§  308.]  ANALYSIS    OF   MANURES.  855 

calcium  phosphate,  and  if  in  the  form  of  a  uniform,  fine  powder, 
dissolve  0-4  to  0-5  grm.  in  warm  diluted  nitric  acid,  dilute  some- 
what, and  filter.  If,  however,  the  substance  is  not  quite  uniform 
and  in  powder,  dissolve  hi  the  manner  described  4  to  5  grm.  and 
make  up  to  500  c.c.,  or  8  to  10  grm.  to  1000  c.c.,  and  use  50  c.c. 
of  the  solution. 

^.  If  the  substance  to  be  examined  is  free  or  almost  free  from 
organic  matter,  more  difficultly  soluble  in  acids,  or  richer  in  de- 
composable silicates,  e.g.,  phosphorite,  or  Thomas  slag,  digest 
0-4  to  0-5  grm.  with  8  c.c.  fuming  hydrochloric  acid  for  an  hour  on 
the  water-bath,  evaporate  to  dryness,  moisten  the  residue  with 
5  c.c.  hydrochloric  acid,  add  a  little  water,  and  filter  off  the  residue 
(sand  and  silica),  the  quantity  of  which  is  usually  slight  in  the  case 
of  phosphorite,  but  quite  considerable  with  Thomas  slag.  Once 
more  evaporate  the  solution  almost  to  dryness,  add  10  c.c.  nitric 
acid  of  1-2  sp.  gr.,  evaporate  again  almost  to  dryness,  add  once 
more  10  c.c.  nitric  acid,  again  evaporate  almost  to  dryness,  add  5 
c.c.  nitric  acid  and  a  little  water,  and  transfer  all  to  a  beaker. 
If  the  substance  is  not  in  fine  powder,  and  not  uniform,  it  is  in  this 
case  also  advisable  to  make  a  solution  using  4  to  5  or  8  to  10  grm. 
and  making  up  the  volume  to  500  or  1000  c.c.  respectively,  taking 
50  c.c.  of  the  solution  for  the  analysis.  If  the  residue  insoluble 
hi  hydrochloric  acid  is  considerable,  it  is  necessary  to  take  the 
precaution  to  treat  it  as  described  in  ;-,  and  to  unite  the  nitric- 
acid  solution  so  obtained  with  the  main  solution,  or  to  test  it  sepa- 
rately for  phosphoric  acid. 

Y.  If  the  substance  to  be  examined  is  richer  in  organic  matter, 
or  only  completely  dissolved  with  difficulty  by  hydrochloric  acid, 
or  should  a  pyrophosphate  have  been  formed  in  it  by  ignition, 
fuse  0-4  or  0-5  grm.  of  the  substance  with  3  or  4  parts  of  sodium 
carbonate,  and  if  organic  matter  is  present,  1  part  of  potassium 
nitrate,  in  a  platinum  crucible,  soften  the  mass  with  water,  transfer 
to  a  beaker,  dilute,  cover  the  beaker  with  a  watch-glass,  and 
add  hydrochloric  acid  gradually,  until  it  is  present  in  considerable 
excess;  then  rinse  off  the  watch-glass,  transfer  the  solution  to  a 
porcelain  dish,  evaporate  to  dryness  on  the  water-bath,  add  10  c.c. 


856  DETERMINATION    OF   COMMERCIAL   VALUES.         [§  309. 

hydrochloric  acid  and  a  little  water,  heat,  and  filter;  evaporate  the 
nitrate  almost  to  dryness,  add  20  c.c.  nitric  acid  of  1-2  sp.  gr.,, 
and  evaporate  almost  to  dryness;  again  add  20  c.c.  nitric  acid, 
evaporate  almost  to  dryness,  add  5  c.c.  nitric  acid,  and  wash  into 
a  beaker  with  water.  In  using  this  method,  it  is  advisable,  even 
if  it  entails  more  trouble,  to  reduce  the  substance  to  a  fine,  homo- 
geneous powder,  because  the  fusion  of  a  much  larger  sample  for 
the  preparation  of  500  or  1000  c.c.  of  solutions  is  attended  by 
considerable  difficulty. 

d.  In  the  case  of  bone-black  it  is  best  to  first  boil  about  10  grm. 
with  about  50  c.c.  of  water,  and  then  to  gradually  add  about 
40  c.c.  nitric  acid  of  1-2  sp.  gr.,  continue  the  heating  for  an  hour,, 
dilute,  filter  into  a  litre  flask,  and  wash,  until  the  washings  are 
no  longer  acid.  Then  dry  the  contents  of  the  filter,  and  burn 
the  carbon.  If  there  is  any  residue,  warm  it  with  nitric  acid, 
dilute,  filter  into  the  main  solution,  make  up  the  whole  to  1000 
c.c.,  and  use  50  c.c.  for  analysis. 

6.  The  determination. 

a.  Molybdenum  Method* 

§309. 

aa.  To  the  nitric-acid  solution,  about  50  c.c.  in  volume, 
obtained  according  to  one  of  the  methods  described  in  §  308, 
and  corresponding  to  0  •  4  to  0  •  5  grm.  phosphate  (hence  containing 
0-1  to  0-2  grm.  phosphoric  acid)  add  so  much  molybdenum  solu- 
tion f  that  about  50  parts  of  molybdic  acid  will  be  present  to  1 

*  Although  the  molybdenum  method  has  already  been  described  in  Vol.  I, 
p.  446,  I  repeat  it  here,  as  in  the  interim  the  method  has  undergone  notable 
improvements;  compare  particularly  ABESSER,  JANI  and  MARCKER  (Zeitschr. 
/.  analyt.  Chem.,  xn,  239),  and  PEITZSCH,  ROHN,  and  P.  WAGNER  (ibid., 
xix,  444). 

f  The  molybdenum  solution  (5-per  cent.)  is  prepared  by  dissolving  1  part 
molybdic  acid  in  4  parts  8-per  cent,  ammonia,  and  pouring  the  solution  into 
15  parts  nitric  acid  of  1-2  sp.  gr.  It  may  also  be  prepared  by  dissolving 
150  grm.  of  pure,  powdered  ammonium  molybdate  in  1  litre  of  water  with 
the  aid  of  heat,  and  pouring  the  solution  into  1  litre  of  nitric  acid  1-2  sp.  gr 
If  the  ammonium  molybdate  used  is  (NH4)2MoO4  the  solution  will  contain 


§  309.]  ANALYSIS    OF    MANURES.  857 

part  of  phosphoric  acid,  hence,  as  a  rule,  about  150  c.c.  of  the 
5-per  cent,  solution,  and  then  allow  the  whole  to  stand  for  from 
four  to  six  hours  at  a  temperature  of  about  50°.  To  a  clear  sample 
of  the  liquid  decanted  from  the  precipitate  add  an  equal  volume 
of  molybdenum  solution,  and  keep  the  mixture  at  a  temperature 
of  50°  for  an  hour  to  test  whether  the  precipitation  was  com- 
plete. If  this  was  not  the  case,  mo*e  molybdenum  solution  must 
be  added,  and  the  whole  kept  warm  for  several  hours.  Then 
decant  the  liquid  through  a  small  filter,  and  repeatedly  wash  the 
precipitate,  the  greater  part  of  which  is  retained  in  the  beaker,  with 
small,  consecutively  added  portions  of  a  liquid  prepared  by  mixing 
100  parts  of  the  molybdenum  solution,  20  parts  nitric  acid  of 
1-2  sp.  gr.,  and  80  parts  water,*  until  the  filtrate  no  longer  con- 
tains calcium,  and  the  last  drops  give  no  turbidity  with  strong 
alcohol  containing  a  little  diluted  sulphuric  acid. 

Now  dissolve  the  ammonium  phosphomolybdate  in  the  small- 
est possible  quantity  of  ammonia.  As  a  rule,  this  is  most  con- 
veniently effected  by  allowing  slightly  warmed  ammonia  f  to 
drop  through  the  filter  into  the  beaker  containing  part  of  the 
precipitate,  and  until  the  latter  has  just  dissolved.  Then  dilute  with 
a  little  water,  filter  through  the  same  filter-paper  into  a  smaller 
beaker  (of  about  20  c.c.  capacity),  and  wash  the  beaker  as  well  as 
the  filter  with  dilute  ammonia  (1  volume  ammonia  and  3  volumes 
water).  In  order  to  determine  more  accurately  the  excess  of 
ammonia,  add  to  the  solution  diluted  hydrochloric  acid  until  the 
greater  part  of  the  ammonia  has  been  neutralized  (the  precipitate 
formed  must  partly  redissolve  on  stirring),  and  add  6  to  8  c.c. 
of  undiluted  ammonia,  which  may  be  conveniently  employed  for 

5-5  per  cent,  of  MoO3;  if  the  molybdate  having  the  formula  (NH4)8Mo7O24 
+  4H2O  is  used,  the  solution  will  contain  6-1  per  cent.  MoO3.  Whichever 
way  the  solution  is  prepared,  allow  it  always  to  stand  several  hours  in  a 
moderately  warm  place,  then  decant,  if  necessary,  and  preserve  it  in  a  dark 
place. 

*  P.  WAGNER  dilutes  the  molybdenum  solution  for  the  washing,  in  the 
proportion  of  1  volume  of  molybdenum  solution  to  3  volumes  of  water. 

f  Both  MARCKER  and  P.  WAGNER  dilute  the  ammonia  with  3  volumes 
water. 


858  DETERMINATION  OF   COMMERCIAL    VALUES.          [§  309. 

again  washing  out  the  beaker  and  the  filter.  Allow  the  liquid 
in  the  smaller  beaker,  and  which  should  not  exceed  70  to  75 
c.c.,  to  become  perfectly  cold,  and  then  run  it  from  a  burette  or 
pipette,  drop  by  drop  and  with  constant  stirring,  15  to  20  c.c. 
magnesium-chloride  mixture,*  and  lastly  so  much  undiluted 
ammonia  that  the  total  quantity  present  will  constitute  about 
one-fourth  of  the  liquid,  hence,  as  a  rule,  about  20  c.c.  more.  The 
ammonium-magnesium  phosphate  will  be  thus  obtained  in  the 
form  of  a  distinctly  crystalline  precipitate.  After  about  four 
hours,  collect  it  on  a  filter,  bring  the  residue  in  the  beaker  with 
small  portions  of  the  filtrate,  completely  on  to  the  filter/  and  wash 
with  a  mixture  of  1  part  ammonia  and  3  parts  water,  until  the  last 
drops  no  longer  give  a  turbidity  with  acid  silver-nitrate  solution; 
then  dry  the  precipitate,  incinerate  the  filter-paper  by  itself,  ignite 
the  precipitate  at  the  last  for  one  or  two  minutes  with  the  blow- 
pipe, and  weigh.  As  a  precaution  it  is  necessary  (a)  to  test  the 
filtrate  with  magnesium  chloride  to  make  certain  that  all  the 
phosphoric  acid  has  been  precipitated;  and,  in  analyses  where 
the  greatest  accuracy  is  required  (6),  to  warm  the  magnesium 
pyrophosphate  with  hydrochloric  acid,  in  order  to  ascertain 
whether  any  silica  remains,  in  which  case  this  is  to  be  weighed,  and 
its  weight  deducted.  The  hydrochloric-acid  solution,  on  treat- 
ment with  hydrogen  sulphide,  must  give  no  precipitate  of  molyb- 
denum sulphide,  or  at  least  not  a  weighable  one.  If  this  should 
be  obtained,  the  result  would  be  too  high. 

The  molybdenum  method  has  been  repeatedly  and  greatly  modi- 
fied. Although  I  cannot  enter  into  a  discussion  of  all  these  modi- 
fications, I  will  nevertheless  call  attention  to  two  which  are  in  use 

*  This,  as  already  stated  in  Vol.  I,  p.  445,  is  in  every  respect  preferable 
to  the  magnesium-sulphate  mixture.  As  crystallized  magnesium  chloride 
is  now  readily  obtainable,  the  mixture  may  be  prepared  from  110  grm. 
crystallized  magnesium  chloride,  140  grm.  ammonium  chloride,  700  c.c. 
ammonia  (containing  8  per  cent.  NH3),  and  1300  c.c.  water.  After  sev- 
eral days  filter  the  solution,  if  necessary  (M  ARCKER).  To  precipitate  0  •  1  grm. 
phosphoric  acid  10  c.c.  of  the  magnesium-chloride  solution  are  taken,  con- 
taining about  double  the  quantity  of  magnesia  necessary  for  precipitating 
the  phosphoric  acid. 


§  309.J  ANALYSIS   OF   MANURES.  859 

in  many  experimental  stations,  and  of  which  bb  is  designed  to  econo- 
mize time,  and  cc  also  to  economize  molybdenum  solution. 

bb.  First  modification  by  P.  WAGNER  * ;  this  differs  from  aa 
only  in  some  slight  changes  in  the  procedure.  Add  100  to  150 
c.c.  of  the  molybdenum  solution  prepared  from  ammonium  molyb- 
date  (see  foot-note,  p.  856)  to  25  to  50  c.c.  of  the  phosphate  solution 
containing  from  0- 1  to  0-  15grm.  phosphoric  acid,  and  contained  in 
a  porcelain  dish.  Heat  the  mixture  on  the  water-bath  or  over  the 
direct  flame  to  80°,  with  frequent  stirring,  and  then  set  aside  for  an 
hour.  Then  filter,  wash  the  yellow  precipitate  (which  of  course  need 
not  be  entirely  rinsed  onto  the  filter)  with  diluted  molybdenum  solu- 
tion (see  foot-note,  p.  857),  place  the  porcelain  dish  under  the  filter, 
perforate  the  latter  with  a  platinum  wire,  and  rinse  the  precipitate 
with  2^-per  cent,  ammonia  into  the  dish,  washing  the  filter  copi- 
ously ;  then  dissolve  the  precipitate  by  stirring,  pour  the  liquid  into  a 
beaker,  rinse  with  2^-per  cent,  ammonia,  and  add  as  much  of  the 
latter  as  will  make  up  the  volume  to  100  c.c.,  and  then,  while  stir- 
ring, add  about  1~>  c.c.  magnesium-chloride  mixture,  allow  to  stand 
covered  for  two  hours,  and  then  proceed  as  in  aa. 

cc.  Second  modification  by  P.  Wagner  f ;  this  depends  upon  the 
fact  ascertained  by  GILBERT  J  and  E.  RICHTERS  §  that  in  the  pres- 
ence of  15  per  cent,  ammonium  nitrate,  about  half  the  usual  quantity 
of  molybdenum  solution  suffices  to  precipitate  all  the  phosphoric 
acid. 

To  25  or  50  c.c.  of  the  phosphate  solution  contained  in  a  beaker, 
and  containing  perhaps  0  •  1  to  0  •  2  grm.  phosphoric  acid,  add  so  much 
of  a  concentrated  ammonium-nitrate  solution  |  and  5  •  5-  or  6  •  1-per 
cent,  molybdenum  solution  (see  foot-note,  p.  856)  that  the  total  liquid 
will  contain  15  per  cent,  ammonium  nitrate,  and  at  least  50  c.c. 
molybdenum  solution  for  every  0-1  grm.  phosphoric  acid  present. 
Heat  the  contents  of  the  beaker  in  a  water-bath  to  80°  or  90°,  and 

*  Zeitschr.  /.  analyt.  Chem.,  xix,  444. 
t  Ibid.,  xxi,  289. 

J  Correspondenzblatt  d.  Vereins  analytischer  Chem.,  i,  Nov.  J78. 
§  DINGLER'S  polyt.  Jour.,  cxcix,  183;  Zeitschr.  f.  analyt.  Chem.,  x,  469 
II  750  grm.  ammonium  nitrate  dissolved  in  sufficient  water  to  measure 
1  litre. 


860  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  310. 

then  set  aside  for  about  an  hour.  Then  filter,  and  wash  the  precipi- 
tate with  a  diluted,  acidulated  solution  of  ammonium  nitrate.* 
Next  dissolve  the  precipitate  as  in  bb  with  2^-per  cent,  ammonia, 
add  a  further  quantity  of  the  latter  so  that  the  volume  of  the  liquid 
will  be  about  75  c.c.,  and  then  while  stirring,  drop  in  10  c.c.  mag- 
nesium-chloride mixture  for  every  0  •  1  grm.  phosphoric  acid  present,, 
and  proceed  further  as  in  bb. 

/?.    C.  GLASER'S  Method. 
§310. 

I  have  no  personal  knowledge  of  this  method,  which  was  first 
proposed  by  C.  GLASER.f  As,  however,  according  to  GLASER,  it 
has  constantly  given  good  results,  I  give  a  description  of  it  here. 
The  method  is  based  upon  the  fact  that  phosphoric  acid  in  the 
presence  of  calcium  salts,  etc.,  and  ammonium  citrate,  is  at  once 
and  completely  precipitated  by  magnesia  mixture,  if  sufficient  sul- 
phuric acid  is  present  to  convert  all  the  calcium  salts  into  sulphates, 
and  provided  no  more  ammonium  citrate  is  used  than  is  necessary 
to  keep  the  calcium  salts  dissolved  in  alkaline  solution.  The  method 
is  carried  out  as  follows : 

Add  ammonia  to  the  acid  liquid  containing  the  calcium  phosphate 
until  a  turbidity  just  forms,  then  cautiously  add,  best  by  means  of  a 
dropping-tube  or  small  pipette,  as  much  of  a  50-per  cent,  citric- 
acid  solution  as  will  suffice  to  clear  the  liquid  again.  If  the  solution 
is  now  alkaline,  it  is  ready  for  precipitation.  Should  it,  however, 
still  have  an  alkaline  reaction,  add  ammonia  and  citric  acid  by 
turns  until  the  desired  point  is  reached,  i.e.,  until  after  the  addition 
of  the  last  drop  of  citric  acid,  the  perfectly  clear  liquid  is  still  dis- 
tinctly alkaline.  The  point  may  be  easily  hit,  after  some  practice, 
with  3  or  at  most  4  c.c.  of  citric-acid  solution.  To  the  cooled  liquid 
now  add,  drop  by  drop,  and  with  constant  stirring,  the  requisite 

*  150  grm.  ammonium  nitrate,  10  c.c.  nitric  acid,  and  sufficient  water  to 
measure  1  litre. 

t  Zeitschr.  /.  analyt.  Chem.,  xxiv,  178. 


§   310.]  ANALYSIS    OF    MANURES.  861 

quantity  of  magnesia  mixture,*  and  then  a  large  excess  of  ammonia. 
After  6  to  8,  or,  better,  12  hours,  filter,  wash  with  4-per  cent,  am- 
monia, dissolve  the  precipitate  on  the  filter  in  diluted  (about  15-per 
cent.)  sulphuric  acid,  and  reprecipitate  with  ammonia  and  a  little 
magnesia  mixture.  After  settling,  which  is  usually  complete  in 
one  hour,  collect  on  asbestos  contained  in  a  GOOCH  platinum  cru- 
cible, with  the  aid  of  the  pump,  wash  with  ammoniacal  water, 
then  ignite,  and  weigh  the  magnesium  pyrophosphate.t 


If  it  is  desired  to  determine  the  phosphoric  acid  in  any  of  the 
phosphates  enumerated  in  I  volumetrically  (by  the  uranium 
method) ,  more  particularly  in  the  case  of  phosphates  poor  in  ferric 
oxide,  solution  is  effected  as  in  §  308 ;  but  hydrochloric  may  be  used 
instead  of  nitric  acid.  In  this  case  remove  the  free  acid  so  far  as 
possible  by  evaporation,  finally  neutralize  with  potassa  or  soda  lye, 
and  then  proceed  according  to  §  313,  ftp. 

Should  the  phosphoric  acid  soluble  in  ammonium  citrate  be  de- 
termined in  one  of  the  phosphates  mentioned  in  I,  proceed  accord- 
ing to  §  315,  and  then  determine  that  still  remaining  in  the  insoluble 
residue.  On  deducting  this  quantity  from  the  total  phosphoric 
acid,  that  soluble  in  the  ammonium  citrate  is  ascertained. 

*  C.  GLASER  gives  the  following  directions  for  preparing  this :  Dissolve 
140  gnn.  magnesium  sulphate,  150  grm.  ammonium  sulphate,  and  30  grm. 
ammonium  chloride,  in  360  c.c.  16-per  cent,  ammonia  and  1650  c.c.  water, 
and  after  standing  for  several  days,  filter. 

f  The  three  test  analyses  detailed  by  C.  GLASER  appear  to  be  perfectly 
satisfactory;  in  my  opinion,  however,  there  remains  to  be  ascertained  whether 
in  these  cases  two  errors  have  not  compensated  each  other.  According  to 
observations  hitherto  made,  ammonium  citrate  may  hold  some  ammonium- 
magnesium  phosphate  in  solution  (as  is  known  of  tartaric  acid,  see  Vol.  I, 
p.  459,  e,  «),  while,  on  the  other  hand,  the  precipitate  will  contain  an  ad- 
mixture of  magnesium  sulphate  (compare  ROSE'S  Handbuch  der  analyt. 
Chem.,  6th  ed.,  by  FINKENER,  u,  513). 


862  DETERMINATION    OF   COMMERCIAL   VALUES.          [§  311. 

II.   MANURES  CONTAINING  PHOSPHORIC  ACID    PARTLY   IN    THE    FORM 
OF   WATER-SOLUBLE    COMPOUNDS. 

§311. 

Under  this  heading  are  comprised  the  products  obtained  on 
treating  the  phosphates  mentioned  in  I  with  sulphuric  acid,  i.e., 
superphosphates. 

These  contain  in  the  first  place,  besides  large  quantities  of  cal- 
cium sulphate  and  smaller  quantities  of  undecomposed  basic  cal- 
cium phosphate,  large  quantities  of  acid  calcium  phosphate,  and, 
under  some  circumstances,  also  free  phosphoric  acid.  The  phos- 
phoric acid  in  the  two  last  forms  is  soluble  in  water;  that  in  the 
other  forms  is  insoluble.  The  superphosphates  are  not,  however, 
unchangeable,  as  when  stored.  The  acid  calcium  phosphate, 
CaH4(PO4)2,  or  the  phosphoric  acid,  H3(PO4)  acts  upon  the  basic 
calcium  phosphate,  Ca3(PO4)2,  with  the  production  of  neutral  cal- 
cium phosphate,  Ca2H2(PO4)2.  As  this  is  insoluble  in  water,  the 
portion  of  the  phosphate  soluble  in  water  decreases,  while  the  por- 
tion insoluble  in  water  increases.  This  change  is  termed  "rever- 
sion of  the  superphosphate."  While  this  may  occur  in  super- 
phosphates prepared  by  the  action  of  sulphuric  acid  upon  almost 
pure  basic  calcium  phosphate,  it  occurs  to  a  much  greater  extent 
in  such  obtained  from  crude  phosphates  rich  in  ferric  oxide  or 
aluminium  silicate,  and  particularly  when  these  contain  also  cal- 
cium fluoride,  as  the  latter  evolves  hydrofluoric  acid  by  the  action  of 
the  sulphuric  acid  upon  it,  whereby  the  admixed  silicates  are  decom- 
posed. The  reversion  is  then  due  not  alone  to  the  reactions  already 
mentioned,  but  also  to  the  formation  of  insoluble  ferric  and  alu- 
minium phosphates. 

Phosphoric  acid  hence  has  a  different  agricultural  value  accord- 
ing to  the  condition  in  which  it  is  present,  whether  it  is  soluble  in 
water,  reverted,  or  undecomposed  (already  insoluble);  hence  in  a 
complete  analysis  of  superphosphates,  the  phosphoric  acid  present 
in  each  of  these  forms  must  be  separately  determined.  As,  how- 
ever, such  analyses  require  much  time  and  labor,  attempts  have 
been  made  to  determine  the  agricultural  value  more  simply.  To 


§  312.]  ANALYSIS   OF   MANURES.  863 

these  attempts  are  due  the  terms  "soluble  phosphoric  acid,"  and 
"citrate-soluble  phosphoric  acid."  In  the  following  all  these 
methods  of  determination  will  b  considered,  beginning  however, 
with  the  determination  of  the  moisture. 

1.  Determination  of  the  Moisture. 

This  is  effected  as  in  I,  1,  (p.  854,  this  volume),  and  as  a  rule  at 
^  00°.  As,  however,  the  large  quantity  of  calcium  sulphate  present 
yields  all  of  its  water  but  very  slowly  at  100°,  a  constant  weight  is 
obtained  only  after  prolonged  heating. 

.  2.  Determination  of  the  Phosphoric  Acid, 
a.  In  the  three  forms  in  which  it  may  occur  in  Superphosphates. 

a.  Determination  of  the  water-soluble  phosphoric  acid. 

§312. 
aa.  Preparation  of  the  Solution. 

act.  By  washing  on  the  filter*  Triturate  the  superphosphate 
with  a  little  water  in  such  a  manner  as  to  completely  break  down 
the  lumps,  but  not  to  reduce  the  coarser,  hard  pieces  to  fine  powder, 
then  rinse  onto  a  filter,  and  wash,  best  with  the  aid  of  the  water- 
pump,  with  cold  water,  until  the  washings  cease  to  have  an  acid 
reaction.  If  the  first  filtrate  becomes  turbid  on  mixing  with  the 
washings,  dissipate  the  turbidity  by  adding  a  little  nitric  acid; 
then  make  up  to  a  definite  volume,  and  mix.  In  the  case  of  finely 
powdered,  homogeneous  superphosphates,  prepare  250  c.c.  of  solu- 
tion from  about  5  grm.  of  the  substance;  with  less  uniform  prepa- 
rations, use  10  or  20  grm.,  and  make  500  or  1000  c.c.  of  solution. 

Pfi.  By  digestion  with  Water. — Although  the  method  described 
in  aa  must  be  considered  as  giving  the  most  accurate  results,!  yet, 
because  it  requires  more  time,  it  is  not  employed  in  the  German 
agricultural  experimental  stations;  these  have  agreed  upon  the 
following  method:! 

*  Compare  Zeitschr.  /.  analyt.  Chem.,  vn,  304,  and  XH,  276. 
t  Ibid.,  XH,  275. 
J  Ibid.,  xxi,  288. 


864  DETERMINATION   OF    COMMERCIAL   VALUES.          [§  313. 

Mix  20  grm.  of  the  superphosphate  with  water  in  a  mortar, 
lightly  crush  with  the  pestle  without  finely  triturating,  and  rinse 
into  a  litre  flask.  Then  immediately  fill  to  the  mark,  allow  to 
stand  for  two  hours,*  with  frequent  shaking  at  the  temperature 
of  the  room,  and  then  pass  through  a  dry  filter.  The  volume  of  the 
undissolved  residue  must  be  taken  into  account  in  the  subsequent 
calculation. 

bb.  Determining  the  Contents  of  the  Solution. 
§313. 

aa.  Gravimetric  Method. — Take  a  measured  volume  of  the  solu- 
tion prepared  according  to  §  312  aa  or  /?/?,  and  containing  0  •  1  to 
0-2  grm.  phosphoric  acid  and  determine  the  latter  according  to 
§309. 

pp.  Volumetric  Uranium  Method.^ — As  different  quantities  of 
uranium  solution  may  be  used  for  precipitating  one  and  the  same 
quantity  of  phosphoric  acid,  according  as  the  solution  of  the  latter 
contains  or  is  free  from  a  calcium  salt,  and  according  to  whether  an 
ammonium  salt  is  present  or  not,  it  must  be  considered  an  essential 
rule  that  the  phosphoric-acid  solution  which  is  to  serve  for  stand- 
ardizing the  uranium  solution,  must  be  as  nearly  as  possible  like 
the  one  to  be  tested.  Upon  this  basis  is  founded  the  following 
method  agreed  upon  by  the  German  agricultural  experimental 
stations,  which,  however,  is  considered  as  suitable  only  for  those 
superphosphates  that  contain  less  than  1  per  cent,  of  phosphoric 
acid  in  combination  with  iron  or  aluminium. J 

In  the  case  of  superphosphates  containing  not  appreciably  more 
than  20  per  cent,  of  water-soluble  phosphoric  acid,  add  50  c.c.  of 

*  The  duration  of  the  digestion,  in  the  case  of  certain  superphosphates, 
exerts  a  not  inappreciable  effect  on  the  result,  hence  the  period  of  digestion 
agreed  upon  must  not  be  arbitrarily  altered;  compare  ABESSER,  JANI,  and 
MARCKER,  Zeitschr.  f.  analyt.  Chem.,  xn,  275. 

f  As  the  uranium  method,  which  was  already  described  in  Vol.  1,  p.  453,  g, 
has  in  the  meantime  been  greatly  improved  (compare  particularly  ABESSER, 
JANI,  and  MARCKER,  Zeitschr.  /.  analyt.  Chem.,  xn,  254),  I  must  make  here 
further  additions  to  what  has  been  said  before. 

t  Zeitschr.  f.  analyt.  Chem.,  xxi,  288. 


§  313.]  ANALYSIS   OF   MANURES.  865 

an  acidulated  solution  of  ammonium  acetate  *  to  200  c.c.  of  the 
solution  prepared  according  to  §  312,  /?/?.  As  soon  as  the  resulting 
white  precipitate  of  ferric  phosphate  and  aluminium  phosphate  has 
settled,  pass  through  a  dry  filter,  remove  th  nitrate,  and  wash  the 
precipitate  thrice  with  hot  water,  then  ignite  and  weigh ;  calculate 
one-half  its  weight  as  phosphoric  acid  combined  with  iron  and 
aluminium.  When  superphosphates  contain  appreciably  more 
than  20  per  cent,  of  water-soluble  phosphoric  acid,  employ  only 
100  c.c.  of  the  solution,  and  add  100  c.c.  of  water  and  50  c.c.  of  the 
acidulated  ammonium-acetate  solution. 

The  uranium  solution  employed  is  made  from  uranium  nitrate  t 
the  titration  being  effected  by  using  50  c.c.  of  the  filtrate  from  the 
ferric  and  aluminium  phosphates  (but  not  diluted  with  the  wash- 
ings), and  consisting  of  40  c.c.  of  the  original  solution  and  10  c.c.  cf 
ammonium-acetate  solution  (see  Vol.  I,  p.  455).  The  end  reaction 
is  ascertained,  after  briskly  boiling  over  a  naked  flame  or  heating 
in  a  boiling  water-bath,  each  time,  by  adding  finely  powdered 
potassium  f errocyanide,  or  a  freshly  made  solution  of  it,  to  the  solu- 
tion on  a  white  porcelain  plate.  In  order  to  prevent  any  separation 
of  calcium  phosphate  from  the  solution,  it  is  advisable  to  add  the 
approximately  necessary  quantity  of  uranium  solution  in  the  cold, 
and  to  then  heat. 

The  effective  value  of  the  uranium  solution  is  ascertained  by  the 
i  id  of  an  iron-free  solution  of  a  superphosphate  containing  about 
16  per  cent,  of  phosphoric  acid,  or  a  solution  of  approximately 
equal  phosphoric-acid  strength  prepared  by  treating  pure  basic 
calcium  phosphate  with  a  corresponding  quantity  of  sulphuric  acid. 
When  standardizing  the  uranium  solution  the  same  proportion 
must  be  maintained  between  the  phosphoric-acid  solution  and  that 
of  the  ammonium  acetate,  as  in  the  analysis  of  the  superphosphate. 


*  100  grm.  pure  ammonium  acetate  and  100  c.c.  acetic  acid  of  sp.  gr. 
1  •  039  to  1  •  040,  with  sufficient  water  to  measure  1  litre. 

f  Dissolve  100  grm.  uranium  nitrate  in  2820  c.c.  water,  and  neutralize 
the  usually  small  quantity  of  free  nitric  acid  present  by  adding  10  grm. 
ammonium  acetate;  1  c.c.  of  the  solution  corresponds  to  about  0-005  phos- 
phoric acid. 


866  DETEEMINATION    OF    COMMERCIAL   VALUES.          [§  314. 

The  phosphoric-acid  content  of  the  titrating  solution  is  determined 
by  the  molybdenum  method. 

ff.  Acidimetric  Methods. 
§  314. 

The  acidimetric  methods  of  superphosphate  analysis  are  based 
upon  the  determination  of  the  acidity  by  a  standard  alkaline  solu- 
tion. Even  though  the  aqueous  solution  of  the  superphosphate 
contains  as  a  rule  only  acid  calcium  phosphate  together  with  cal- 
cium sulphate,  it  must  nevertheless  be  remembered  that  the  solu- 
tion may  also  contain  free  phosphoric  acid,  and  in  faultily  prepared 
substances,  free  sulphuric  acid  too.  As,  in  such  cases,  on  direct 
titration  with  soda-lye  correct  results  cannot  be  obtained,  the 
acidimetric  method  of  determining  the  value  of  superphosphates 
must  be  founded  on  another  basis.  The  first  method  proposed  for 
this  purpose  is  that  of  A.  MOLLENDA  ;  *  it  is  based  upon  the  precipi- 
tation of  the  calcium  in  the  solution  by  sodium  or  ammonium 
oxalate  at  the  boiling  temperature,  and  subsequent  titration  of  the 
solution  now  containing  acid  alkali  phosphate,  by  normal,  or,  better 
yet,  semi-normal,  soda-lye,  with  phenolphtalein  as  indicator.  The 
end  reaction  (a  violet  coloration)  appears  as  soon  as  the  acid  alkali 
phosphate  (e.g.,  monosodium  phosphate)  has  become  converted 
into  the  so-called  neutral  salt  (disodium  phosphate).  1  equivalent 
of  sodium  corresponds  to  1  equivalent  of  phosphoric  acid.  If  the 
superphosphate  contains  free  acid,  add  lime  water  or  sodium  car- 
bonate to  the  solution  until  a  slight  turbidity  forms  and  persists 
even  on  stirring,  whereby  the  free  sulphuric  acid  is  converted  into 
neutral  sulphate.  Then  precipitate  with  the  alkali  oxalate  and 
proceed  as  described.  It  is  better  to  ascertain  the  quantity  of 
lime  water  or  sodium  carbonate  required  for  this  purpose  by  a  sepa- 
rate experiment,  and  according  to  the  results  obtained  to  add  to 
the  solution  to  be  titrated  only  so  much  of  the  neutralizing  sub- 
stance that  the  solution  will  just  remain  clear.  It  is  unnecessary  to 
filter  off  the  calcium  oxalate.  The  liquid  to  which  the  excess  of 

*  Zeitschr.  /.  analyt.  Chem.,  xxn,  155. 


§  314.]  ANALYSIS   OF   MANURES.  867 

ammonium  oxalate  has  been  added  may  be  directly  titrated  with 
normal  soda  solution,  using  phenolphtalein  or  phenacetolin  as 
indicator.  The  test  analyses  given  by  MOLLENDA  are  satisfactory. 
See  also  R.  T.  THOMSON.* 

The  process  devised  by  A.  EMMERLING!  has  also  been  thor- 
oughly worked  out  and  adapted  as  well  for  ferruginous  super- 
phosphates. The  method  is  based  upon  the  two  following  experi- 
mentally established  facts: 

1.  Phosphoric  acid  is  almost  completely  precipitated  as  basic 
calcium  phosphate  on  adding  soda  lye  to  a  solution  of  superphos- 
phate to  which  an  excess  of  calcium  chloride  has  been  added;  the 
precipitation  is  perfectly  complete,  however,  only  when  the  mix- 
ture of  the  superphosphate  solution  and  calcium  chloride  is  allowed 
to  run  into  the  soda-lye,  because  in  that  case  the  liquid  is  alkaline 
during  precipitation.     On  adding  phenolphtalein  to  the  solution, 
the  end  reaction  appears  when  2  equivalents  of  Na-jO  have  been 
used  for  1  equivalent  of  phosphoric  anhydride. 

2.  On  adding  caustic  soda  to  a  solution  of  free  phosphoric  acid 
colored  with  methyl  orange,  the  color  changes  from  violet-red  to 
yellow  or  orange-yellow  when  all  the  phosphoric  acid  has  been  con- 
verted into  acid  sodium  phosphate  (monosodium  phosphate). 

For  carrying  out  the  method  the  following  are  required : 

1.  A  solution  of  caustic  soda,  1  c.c.  of  which  corresponds  with 
about  0-005  grm.  phosphoric  anhydride  (P2O5),  calculated  on  the 
proportion  of  2NaOH  :  P2O5.     When  standardizing  this  solution  by 
means  of  one-fifth-  or  one-tenth-normal  hydrochloric  acid,  the  same 
quantity  of  phenolphtalein  (2  c.c.)  should  be   added  as  is  used 
when  titrating  the  phosphoric  acid. 

2.  A  calcium-chloride  solution,  prepared  by  dissolving  200  grm. 
of  pure,  dry  calcium  chloride  in  one  litre  water.     The  alkaline 
solution  must  be  most  carefully  neutralized.     The  quantity  of 
normal  hydrochloric  acid  required  to  neutralize  100  c.c.  of  the 
solution  is  ascertained  by  titration,  and  the  remaining  900  c.c. 
are  then  correspondingly  neutralized. 


*  Zeitschr.  /.  analyt.  Chem.,  xxiv,  232. 

f  Landwirihschaftl.  Versuchsstationen,  1886,  429. 


868  DETERMINATION    OF    COMMERCIAL   VALUES.          [§   314. 

3.  A  solution  of  1  grm.  phenolphtalein  in  100  grm.  alcohol. 

4.  A  solution  of  methyl  orange  prepared  by  adding  small  quan- 
tities of  methyl  orange  to  water  until  the  solution  has  a  deep 
orange-yellow  color,  and  then  filtering. 

The  analysis  is  carried  out  as  follows:  Mix  200  c.c.  of  the  super- 
phosphate solution  (prepared  as  in  §  312)  with  50  c.c.  of  the  cal- 
cium-chlor-de  solution  and  allow  the  mixture  to  run  from  a  burette 
into  a  beaker  containing  a  measured  quantity  of  the  soda-lye  (which 
has  been  slightly  diluted  with  water,  and  to  which  2  c.c.  of  the 
phenolphtalein  solution  have  been  added),  until  the  red  color  en- 
tirely disappears.  In  the  case  of  superphosphates  of  mj.h  per- 
centage measure  off  20  c.c.;  with  superphosphates  containing  10 
to  15  per  cent.  P2O5  take  10  c.c.;  and  with  poorer  superphos- 
phates take  5  c.c.  The  addition  of  the  mixture  of  superphosphates 
with  calcium  chloride  is  made  rapidly  at  first  until  the  color  begins 
to  be  weak,  but  towards  the  end,  drop  by  drop  only.  The  end 
reaction  is  reached  when  every  trace  of  the  reddish  tint  has  van- 
ished, and  a  whitish,  yellowish,  or  faintly  brownish  color  has  devel- 
oped. When  stirring  the  liquid  while  the  mixture  is  being  dropped 
in,  the  formation  of  foam  should  be  avoided  as  much  as  possible, 
as  this  renders  difficult  the  recognition  of  the  color  change.  The 
experiment  must  be  repeated.  In  this  manner  there  is  found  the 
quantity  of  soda  required  to  neutralize  any  sulphuric  acid  present, 
or  that  required  to  convert  free  phosphoric  acid  into  acid  sodium 
phosphate. 

Now  measure  off  the  same  number  of  c.c.  of  the  superphosphate- 
calcium-chloride  solution  as  were  required  for  the  last  test,  or  the 
mean  of  the  two  tests,  then  dilute  with  a  little  water,  add  four 
to  six  drops  methyl-orange  solution  (i.e.,  a  sufficient  quantity  to 
afford  a  distinct  but  not  too  deep  violet-red  with  the  free  acid 
present),  and  then  run  in  from  a  burette  caustic-soda  lye  until  every 
trace  of  a  reddish  tint  has  disappeared  and  the  liquid  has  acquired 
a  yellow  or  orange-yellow  color.  This  test  also  must  be  repeated. 
On  deducting  from  the  soda  solution  used  in  the  titration  with 
phenolphtalein  the  quantity  required  in  the  methyl-orange  test, 
we  ascertain  the  number  of  c.c.  of  soda  solution  required  to  pre- 


§  315.]  ANALYSIS   OF   MANURES. 

cipitate  the  phosphoric  acid  as  basic  calcium  phosphate  (tricalcium 
phosphate) ;  on  now  multiplying  this  difference  by  the  quantity 
of  phosphoric  acid  corresponding  with  1  c.c.,  we  find  the  quantity 
of  phosphoric  acid  in  the  number  of  c.c.  of  superphosphate-calcium- 
chloride  mixture,  and  from  this  the  quantity  in  the  superphos- 
phate solution  according  to  the  proportion  250  :  200. 

The  many  test  analyses  given  by  EMMERLING  are  very  satis- 
factory, also  with  ferruginous  superphosphates;  the  differences, 
compared  with  those  afforded  by  the  uranium  method,  do  not  ex- 
ceed ±0-3  per  cent.  The  results  are  apt  to  fall  out  too  high, 
rather  than  too  low;  about  0-16  per  cent,  according  to  EMMERLING. 

/?.  Determination  of  the  "Reverted"  and  Unattached 
Phosphoric  Acid* 

§315 

The  "reverted"  phosphoric  acid  may  be  determined  both 
directly  and  indirectly.  Both  methods  are  based  upon  the  fact 
that  the  phosphoric-acid  compounds  formed  by  "reversion"  are 
soluble  in  a  solution  of  neutral  ammonium  citrate,  whereas  the 
unattacked  phosphates,  particularly  those  of  mineral  origin,  are 
practically  insoluble.  The  direct  method  is  inconvenient,  hence 
I  will  only  refer  to  the  treatise  mentioned  in  the  foot-note.  The 
indirect  method,  which  is  here  described,  is  far  more  convenient; 
it  at  the  same  time  gives  also  the  quantity  of  the  unattacked 
phosphates. 

Weigh  off  two  portions  of  2  grm.  each  of  the  superphosphate, 
and  extract  them  by  the  method  described  under  "Washing  on  the 
Filter"  (§  312).  In  the  residue  from  the  one  (a)  determine  the 
total  unattacked  and  " reverted"  phosphoric  acid  by  dissolving 
it  according  to  §  308,  and  determining  the  phosphoric  acid  accord- 
ing to  §  309.  Spread  the  filter  containing  the  second  residue  (6) 
on  a  glass  plate,  and  rinse  the  residue  completely  into  a  porcelain 
mortar  provided  with  a  lip,  using  for  the  purpose  a  solution  of 


*  Compare  FRESENIUS,  NEUBAUER,  and  LUCK,  Zeitschr.  f.  analyl.  Chem., 
x,  156. 


870  DETERMINATION    OF    COMMERCIAL    VALUES.          [§   316- 

neutral  ammonium  citrate,  sp.  gr.  1-09,  100  c.c.  of  which  have 
been  put  into  a  small  wash-bottle.  Allow  to  settle,  decant  the 
cloudy  supernatant  liquid  into  a  small  flask,  triturate  the  residue 
in  the  mortar  to  a  very  smooth  paste,  and  wash  this  with  the 
balance  of  the  ammonium-citrate  solution  into  the  small  flask. 
Allow  to  stand  for  half  an  hour  at  a  temperature  of  30°  to  40°, 
with  very  frequent  shaking,  and  then  filter.  Wash  the  residue  in 
the  filter  twice  or  thrice  with  a  mixture  of  equal  parts  water  and 
the  ammonium-citrate  solution  above  mentioned,  then  with 
water  alone,  then  dissolve  the  residue  according  to  §  308,  and  in 
the  solution  determine  the  unattacked  phosphoric  acid  according 
to  §  309.  On  deducting  the  quantity  found  from  that  found  in 
the  residue  a,  the  reverted  phosphoric  acid  is  ascertained. 

6.  Shortened  Methods  of  Determining  the  Values  of  Superphosphates. 

a.  Determination  of  "Soluble"  Phosphoric  Acid. 
§316. 

The  term  " soluble  phosphoric  acid,"  employed  to  denote  the 
value  of  superphosphates  (and  which  must  not  be  confounded  with 
the  term  <f  water-soluble  phosphoric  acid,"  or  with  the  term 
" citrate-soluble"  or  "assimilable  phosphoric  acid,"  which  will  be 
referred  to  below  under  6,  /?),  was  coined  by  P.  WAGNER,  who  also 
introduced  the  method  for  determining  the  "  soluble  phosphoric 
acid."  Both  the  term  and  the  method  have  been  recently  agreed 
upon  and  adopted  by  the  agricultural  experimental  stations  of 
Bonn,  Darm  tadt,  Speyer,  and  Wiesbaden,  and  in  the  manure 
factories  controlled  by  them,  in  order  to  assist  in  a  proper  valua- 
tion of  the  " reverted"  phosphoric  acid,  as  well  as  that  present  in 
the  precipitated  phosphates.*  The  method  is  based  upon  the 
fact  established  by  P.  WAGNER  in  precise  examinations  of 
manures,  that  100  parts  of  phosphoric  acid  contained  in  "  re- 
verted "  or  precipitated  phosphates  have,  on  an  average,  the  same 
agricultural  value  as  70  parts  of  phosphoric  acid  in  water-soluble 
phosphates;  together  with  his  assumption  that,  by  the  analytical 

*  Zeitschr.  /.  analyt.  Chem.,  xxv,  272. 


§  317.]  ANALYSIS   OF   MANUKES.  871 

method  to  be  described,  the  sum  of  the  phosphoric  acid  soluble  in 
water  and  that  of  the  equivalent  portions  of  water-soluble  precipi- 
tated or  " reverted"  phosphates  is  extracted  and  determined. 

The  method  of  determining  the  "soluble  phosphoric  acid'! 
is  as  follows:  Finely  triturate  5  grm.  of  the  superphosphate 
with  diluted  citrate  solution,*  and  rinse  into  a  500-c.c.  flask,  then 
fill  up  to  the  mark  with  diluted  citrate  solution.  Allow  the  mix- 
ture to  stand  for  eighteen  hours,  with  frequent  shaking,  at  the 
temperature  of  the  room,  and  then  filter.  To  50  c.c.  of  the  filtrate 
add  so  much  5-5  or  6-1  per  cent,  molybdenum  solution  (see 
foot-note,  p.  856  this  volume)  that  not  less  than  1  c.c.  of  it  will  be 
present  for  every  0-001  grm.  of  phosphoric  acid,  and  then  add 
concentrated  ammonium-nitrate  solution  (see  foot-note,  p.  859 
this  volume)  in  quantity  sufficient  to  constitute  one-fourth  of 
the  volume  of  the  entire  liquid.  After  heating  for  about  20 
minutes  in  a  water-bath  and  then  cooling,  filter,  wash  the  precipi- 
tate with  diluted  ammonium-nitrate  solution  (p.  860,  foot-note, 
this  volume),  pierce  the  filter,  and  then  wash  through  the  perforated 
filter  into  the  beaker  with  2-  -per  cent,  ammonia.  Wash  the 
filter  well  with  the  same  liquid,  and  into  the  cold  ammoniacal 
solution  drop  in  20  c.c.  magnesium-chloride  mixture  (p.  858,  foot- 
note, this  volume)  with  constant  stirring.  After  about  an  hour, 
collect  the  precipitate,  wash  with  2-per  cent/ammonia,  dry,  and 
then  ignite,  finally,  with  the  blowpipe. 

/?.  Determination  of  the  "  Citrate-soluble "  Phosphoric  Add. 

§317. 

While  the  recent  examinations  of  manures  by  P.  WAGNER 
have  shown  that  100  parts  of  phosphoric  acid  in  precipitated  or 
"reverted"  phosphates,  and  hence  soluble  in  ammonium  citrate, 
are  equivalent  to  70  parts  of  water-soluble  phosphoric  acid,  the 

*  Introduce  150  grm.  of  citric  acid  into  a  litre  flask,  dissolve  in  water, 
and  neutralize  with  ammonia.  Add  10  grm.  citric  acid  to  the  solution,  then 
fill  up  to  the  mark  with  water,  and  mix.  Of  this  concentrated  (and  perma- 
nent) solution,  mix  1  volume  with  4  volumes  to  make  the  diluted  (and  less 
permanent)  solution. 


872  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  317. 

earlier  investigations  of  manures  by  PETERMANN  and  by  other 
Belgian  and  French  agricultural  chemists  led  to  the  conclusion 
that  water-soluble  and  ammonium-citrate  soluble  phosphoric  acids 
were  equal  in  value.*  On  this  basis  is  founded  the  following 
method  by  PETERMANN  f  for  determining  the  value  of  superphos- 
phates, which  is  practised  in  Belgium  and  France,  and  the  object 
of  which  is  to  bring  simultaneously  into  solution,  by  the  aid  of 
ammonium  citrate,  both  the  water-soluble  and  reverted  phos- 
phoric acid  present  in  superphosphates — whence  the  abbreviated 
term  "  citrate-soluble  phosphoric  acid,"  which  is  also  occasionally 
designated  as  " assimilable  phosphoric  acid." 

The  ammonium-citrate  solution  employed  is  one  of  sp.  gr.  1-09, 
to  which  50  c.c.  of  ammonia  per  litre  has  been  added.  100  c.c. 
of  this  solution  are  put  into  a  small  wash-bottle,  and  with  it  2  grm. 
of  the  superphosphate  t  are  rinsed  into  a  porcelain  mortar,  tritu- 
rated, and  then  rinsed  with  the  remainder  of  the  ammonium-citrate 
solution  into  a  500-c.c.  flask,  wherein  the  mixture  is  digested 
for  an  hour  at  a  temperature  of  from  35°  to  38°,  with  frequent 
shaking.  Now  allow  to  cool,  fill  up  to  the  mark  with  water, 
shake,  pass  through  a  dry,  double  filter  (the  filtrate  is  at  first  fre- 
quently turbid,  but  soon  comes  through  clear),  and  precipitate 
100  c.c.  of  the  clear  filtrate  by  adding  60  c.c.  of  magnesium- 
chloride  mixture  (p.  858,  foot-note,  this  volume),  and  stirring 
constantly.  After  fifteen  hours,  collect  the  precipitated  am- 
monium-magnesium phosphate,  wash  with  2-5-per  cent,  am- 
monia, ignite,  and  weigh.  According  to  PETERMANN,  the  method 
does  not  give  absolutely  accurate  results,  but  differences  of  from 
0-2  to  0-4  per  cent,  as  compared  with  the  difference-method 
described  in  §315;  BRUNNER§  obtained  sufficiently  concordant 
results  in  parallel  analyses. 

*  Regarding  this  compare  GRANDEAU,  Handb.  f.  agriculturchen.  Analysen, 
p.  71;  BRUNNER,  Zeitschr.  f.  analyt.  Chem.,  xix,  141. 

f  Landwirthsch.  Versuchsstat.,  xxiv,  327;  Zeitschr.  /.  analyt.  Chem., 
xix,  142. 

"t  When  the  method  is  used  with  precipitated  phosphates  or  mixed  ma- 
nures, PETERMANN  uses  of  the  former  1  grm.  and  of  the  latter  5  grm. 

§  Zeitschr.  f.  analyt.  Chem.,  xix,  143. 


§  318.]  ANALYSIS   OF  MANURES.  873 

Appreciably  differing  from  these  conclusions  was  that  agreed  upon 
at  the  meelting  of  the  agricultural  chemists  at  Halle,  in  December, 
1881.  The  conclusion  then  arrived  at  was  to  the  effect  that  the 
methods  proposed  and  employed  for  determining  the  "citrate-solu- 
ble phosphoric  acid"  do  not  even  approximately  effect  their  object. 
Should  the  methods,  nevertheless,  be  employed  for  making  the  de- 
termination, it  was  agreed  upon  to  digest  5  grm.  of  unwashed  super- 
phosphate with  100  c.c.  of  PETERMANN'S  citrate  solution  in  a  250-c.c. 
flask  for  one  hour  at  40°,  then  to  fill  to  the  mark,  filter,  and  to  deter- 
mine the  phosphoric  acid  in  an  aliquot  portion  of  the  filtrate. 
When  communicating  the  result,  however,  the  deficiencies  of  the 
method  should  be  pointed  out;  *  see  also  Vol.  I,  p.  459,  e,  a. 

c.  Determination  of  the  total  Phosphoric  Add  in  Superphosphates. 

§318. 

Dissolve  5,  10,  or  20  grm.  of  the  superphosphate,  according  to 
the  homogeneity  of  the  latter,  in  nitric  acid  by  warming,  and  treat- 
ing any  difficultly  soluble  residue  with  hydrochloric  acid,  and  adding 
potassium  chlorate  in  order  to  decompose  any  organic  matter  pres- 
ent; then,  according  to  the  quantity  of  superphosphate  taken, 
make  up  the  liquid  to  250,  500,  or  1000  c.c.,  mix,  pass  through  a 
dry  filter,  and  in  a  portion  of  the  filtrate  containing  about  0  •  1  to  0  •  2 
grm.  phosphoric  acid,  determine  the  latter  according  to  §  309.  If 
hydrochloric  acid  or  potassium  chlorate  has  been  used  to  effect 
complete  solution,  the  portions  of  filtrate  pipetted  off  must  be 
repeatedly  evaporated  almost  to  dryness  with  nitric  acid,  the  residue 
heated  with  nitric  acid  and  water,  and  the  solution  then  filtered. 

D.  ANALYSIS    OF   MANURES    THE    VALUE    OF    WHICH   DEPENDS 
WHOLLY  OR  ALMOST  NEARLY  UPON  THEIR  POTASSIUM  CONTENT.  . 

§319. 

To  this  class  belong  potassium  chloride  and  potassium  sulphate, 
prepared  on  the  large  scale  from  the  waste  salt  of  the  Stassfurt  and 
other  rocksalt  beds,  and  which  reach  the  market  in  a  more  or  less 

*  Zeitschr.  f.  analyt.  Chem.,  xxi,  291. 


874  DETERMINATION   OF  COMMERCIAL  VALUES.          [§  319. 

pure  condition;  also  the  impure  salts,  the  "crude  potassium  sul- 
phate," obtained  from  the  mother  liquors,  and  containing  variable 
quantities  of  potassium  sulphate  and  potassium  chloride,  as  also 
the  minerals  from  which  the  potassium  salts  mentioned,  or  potas- 
sium double  salts,  are  prepared.  Such  minerals  are  carnallite 
(KCl-2MgCl2+12H2O),  containing  in  a  crude  state  about  16  per 
cent,  potassium  chloride  (with  about  20  to  25  per  cent,  sodium 
chloride,  15  to  20  per  cent,  kieserite,  and  2  to  4  per  cent,  mag- 
nesium chloride,  tachydrite,  etc.);  further,  kainite  (KCl[2MgSOJ 
+  6H2O),  which  as  crude  kainite,  contains  only  12  to  13  per  cent, 
potassium,  or  calculated  as  sulphate,  22  to  24  per  cent,  of  the  latter, 
besides  11  to  12  j>er  cent,  magnesium  sulphate,  12  to  15  per  cent, 
magnesium  chloride,  37  to  42  per  cent,  sodium  chloride,  about  2  per 
cent,  calcium  sulphate,  1  to  2  per  cent,  insoluble  residue,  and  about 
5  to  8  per  cent,  water.  Furthermore,  the  preparations  poor  in 
chlorine,  and  obtained  by  calcining  crude  kainite,  should  be 
mentioned;  these  come  into  the  market  as  " prepared  kainite," 
"crude  potassium-magnesium  sulphate,"  or  " potassium-mag- 
nesium sulphate  manures";  and  finally  the  "pure,  crystallized 
potassium-magnesium  sulphate"  obtained  from  kainite  by  treat- 
ment with  water,  and  containing  38  to  40  per  cent,  potassium 
sulphate. 

As  the  analysis  of  potassium  salts  has  already  been  thoroughly 
treated  of  in  §  225  (this  volume,  p.  341)  both  with  reference  to  the 
simple  determination  of  potassium  as  well  as  to  the  complete  analy- 
sis, I  will  only  refer  to  the  section  mentioned. 

For  the  potassium  determination  I  would  advise  taking  of  the 
aqueous  solution  of  the  salt  a  volume  that  will  yield  about  0  •  8  to  1  •  2 
grm.  potassium-platinic  chloride.  By  multiplying  the  weight  of 
the  potassium-platinic  chloride  dried  at  130°,  by  0  •  3056,  the  potas- 
sium chloride  is  obtained.  This  number  corresponds,  according 
to  WATT'S*  calculation,  with  BERZELIUS'  equivalent  of  platinum. 
On  multiplying  the  weight  of  the  double  platinum  salt  dried  at  130°, 
by  0  •  30697,  the  number  given  by  SEUBERT'S  f  equivalent,  the  result 

*  Zeitschr.  f.  analyt.  Chem.,  ix,  156. 
f  Annal.  d.  Chem.,  ccvn,  31. 


§  320.]  ANALYSIS   OF   MANURES.  875 

will  be  somewhat  too  high;  or  if  multiplied  by  0-3051,  the  num- 
ber obtained  when  using  ANDRE ws'  *  equivalent  for  platinum,  the 
result  will  be  too  low  for  potassium  chloride,  as  shown  by  investi- 
gations made  by  me.  f 

[When  the  calculations  are  based  upon  the  atomic  weights  used 
in  this  translation,  i.e.,  Pt=  194-  9;  K=39-ll;  01=35-45,  then  the 
factor  for  multiplying  the  potassium-platinic  chloride,  (KCl)2PtCl4, 
in  order  to  obtain  the  potassium  chloride,  is  0-30695. — TRANS- 
LATOR.] 

E.  ANALYSIS    OF    MANURES    THE    VALUE    OF    WHICH 

DEPENDS  SOLELY  OR  NEARLY  ALTOGETHER  UPON 

THE  NITROGEN  THEY  CONTAIN. 

In  this  class  belong  the  nitrates,  foremost  among  which  are 
Chili  saltpetre,  ammonium  salts,  and  such  nitrogenous  manures  of 
organic  origin  as  contain  so  little  of  other  manurial  substances 
(potassium,  phosphoric  acid),  that  the  value  of  the  latter  is  scarcely 
or  not  at  all,  taken  into  account,  e.g.,  dried  blood,  horn  meal,  etc. 
As  the  methods  of  determining  nitrogen  vary  according  to  the  form 
of  combination  in  which  it  occurs,  they  must  be  described  separately. 

I.  CHILI  SALTPETRE.  J 
§320. 

Although  pure  sodium  nitrate  contains  63-51  per  cent,  of  N2O5, 
or  16  •  5  per  cent,  of  nitrogen,  Chili  saltpetre,  as  it  contains  also  some 
sodium  chloride,  sodium  sulphate,  insoluble  residue,  water,  etc., 
can  be  guaranteed  by  the  dealer  to  contain  only  from  15  to  15-5  per 
cent,  nitrogen. 

Of  the  methods  detailed  in  §  149  (Vol.  I,  p.  571)  for  determining 
nitric  acid  in  Chili  saltpetre,  the  one  best  adapted  for  the  purpose 
is  that  of  REICH,  described  in  Vol.  I,  p.  572,  i.e.,  ignition  with  quartz 

*  Annal.  d.  Chem.  u.  Pharm.,  LXXXV,  255. 

f  Zeitschr.  f.  analyt.  Chem.,  xxi,  234. 

J  In  this  section  will  be  described  those  newer  methods  of  nitric-acid 
determination  which,  though  not  necessary  for  determining  the  value  of 
Chili  saltpetre,  are  nevertheless  to  be  borne  in  mind  as  of  use  in  mixed  ma- 
nures. 


876  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  320. 

sand,  as  it  is  rapid,  simple  and  yields  good  results.  It  may  also  be 
carried  out  in  the  manner  described  by  MARCKER  and  ABESSER,* 
a  modification  of  REICH'S  original  method  (loc.  cit.).  Mix  care- 
fully the  weighed  quantity  of  the  triturated  Chili  saltpetre  (about 
1  to  1  •  5  grm.)  with  about  seven  times  its  quantity  of  quartz  sand 
that  has  been  previously  extracted  with  hydrochloric  acid,  washed, 
and  ignited,  and  then  heat  the  mixture  in  a  crucible  for  four  hours, 
but  in  such  a  manner  that  only  about  one-third  of  the  crucible  is 
red-hot.  After  weighing,  make  certain  that  no  further  loss  of 
weight  follows  ignition  for  another  half-hour.  From  the  total 
loss  (nitric  acid  +  water)  found,  the  water  in  the  Chili  saltpetre 
must  be  deducted  in  order  to  ascertain  the  nitric-acid  content; 
this  may,  as  a  rule,  be  accomplished  by  drying  sharply  (at  about 
130°),  but  under  certain  circumstances,  e.g.,  when  adulterated 
with  kainite,  by  heating  even  to  fusion. 

Of  course,  other  methods  of  determining  the  nitric  acid  in 
Chili  saltpetre  may  be  employed.  Many  of  these  have  already 
been  described  in  §  149  (Vol.  I,  p.  571t),  and  others  are  of  more 
recent  date.  Although  REICH'S  method,  already  mentioned,  so 
far  as  simplicity  and  accuracy  are  concerned,  suffices  for  deter- 
mining the  value  of  Chili  saltpetre,  attention  must  be  called  to  other 
methods  which  are  largely  used  for  the  same  purpose,  as  well  as  to 
a  few  new  ones  for  use  in  the  analysis  of  mixed  manures. 

Instead  of  REICH'S  method,  that  of  PERSOZ  (Vol.  I,  p. 
572)  is  frequently  employed  for  determining  the  value  of  Chili 
saltpetre;  it  consists  in  heating  the  anhydrous  nitrate  with 
anhydrous  potassium  dichromate,  and  determining  the  nitric 
acid  from  the  loss  of  weight.  E.  PFEIFFER  J  recommends  the 
use  of  3  to  4  parts  of  potassium  dichromate  for  every  part 
of  Chili  saltpetre,  as  the  expulsion  of  the  nitric  acid  is 
thereby  facilitated,  and  also  advises  placing  a  triangle  of  thin 
platinum  wire  between  the  platinum  crucible  and  its  lid,  in  order 

*  Zeitschr.  f.  analyt.  Chem.,  xn,  281. 

f  J.  M.  EDER  (Zeitschr.  /.  analyt.  Chem.,  xvi,  267),  has  supplied  a  most 
praiseworthy  critique  of  most  of  the  methods  there  mentioned. 

%  Arch.  Pharm.  [3],  xui,  539;  Zeitschr.  /.  analyt.  Chem.,  xvui,  597. 


§  320.]  ANALYSIS   OF   MANURES.  877 

to  allow  space  for  the  vapors  to  escape.  The  temperature  must 
not  be  allowed  to  exceed  a  dark  red  heat;  and  the  operation  is 
over  when  the  mass  is  in  a  state  of  quiet  fusion.  If  green  particles 
of  chromic  oxide  are  observed  on  the  cooled  melt,  or  on  the  por- 
tions spirted  onto  the  lid,  the  experiment  must  be  rejected. 
Instead  of  potassium  dichromate,  some  recommend  using  a  mixture 
of  equal  parts  of  chromate  and  dichromate  of  potassium.*  A. 
WAGNER f  recommends  a  method  based  upon  a  new  principle;  it 
consists  in  fusing  together  the  nitrate  with  sodium  carbonate  and 
chromic  oxide  in  a  glass  tube  filled  with  carbon  dioxide,  lixiviating 
the  melt,  and  determining  in  the  filtrate  the  chromic  acid  formed, 
from  which  then  the  nitric  acid  may  then  be  calculated.  This  method 
also  gives  good  results,!  but  is  far  more  inconvenient  than  the 
method  of  REICH  or  PERSOZ.  The  nitric  oxide  evolved  may  be 
collected  for  the  purposes  of  control,  and  measured;  or,  as  in 
SCHLOSING'S  method  (Vol.  I,  p.  579),  converted  into  nitric  acid. 

All  the  methods  more  recently  recommended  for  determining 
the  nitric  acid  are  but  modifications  of  those  described  in  §  149,  or 
of  that  originally  devised  by  WALTER  CRUM  (p.  711  this  volume). 
Most  of  them  are  based  upon  the  conversion  of  nitric  acid  into 
nitric  oxide,  i.e.,  upon  the  same  principle  as  that  described  in 
Vol.  I,  p.  575,  d,  and  many  are  but  modifications  of  SCHLOSING'S 
method  (Vol.  I,  p.  579),  which  had  also  previously  been  modified 
in  various  ways  (Vol.  I,  p.  581,  and  this  volume,  p.  65). 

Above  all,  SCHLOSING§  himself  has  considerably  altered  his 
method,  and  has  imparted  to  it  a  high  degree  of  simplicity,  both 
in  regard  to  manipulation  and  calculation,  by  collecting  and 
measuring  over  water  the  nitric  oxide  obtained,  on  the  one  hand, 
by  the  action  of  a  known  volume  of  nitrate  on  ferrous  chloride, 
and  on  the  other  hand  from  the  unknown  quantity  of  nitric  acid  in 
the  substance  examined  under  identical  circumstances.  As  the 
first  experiment  gives  the  quantity  of  nitric  acid,  or  the  nitrogen 

*  P.  WAGNER,  Chemiker-Ztg.,  1883,  p.  1710. 

t  DINGLER'S  Polyt.  Journ.,  cc,  120,  and  cci,  420;  Zeitschr.  f,  analyt. 
Chem.,  xi,  91  and  314. 

t  Compare  also  EDER,  loc.  cit.,  p.  287. 

§  GRANDEAU'S  Handb.  d.  agriculturchem.  Analysen,  German  edit.,  p.  31. 


878  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  320. 

contained  therein,  corresponding  with  1  c.c.  of  nitric  oxide  under 
existing  conditions,  so  in  the  second  experiment  the  quantity  of  the 
unknown  nitric  acid  or  nitrogen  may  be  ascertained  from  the 
volume  of  nitric  oxide  obtained,  as  the  pressure,  degree  of  mois- 
ture, and  temperature  of  the  volume  of  gas  in  both  cases  are,  of 
course,  alike.  Even  the  other  usual  sources  of  error  inherent  in 
the  measurement  of  nitric  oxide  over  water  (the  slight  solubility  of 
nitric  oxide  in  water,  influence  of  the  oxygen  in  the  air  dissolved 
in  the  water)  are  hereby  excluded,  and  in  fact  the  more  completely 
the  greater  the  care  taken  that  the  volumes  of  nitric  oxide  obtained 
from  the  known  and  unknown  quantities  of  nitric  acid  are  approxi- 
mately equal,  or  that  they  do  not  differ  to  any  great  extent. 

SCHLOSING  has  devised,  and  recommends,  a  special  apparatus  for 
use  with  his  method,  and  especially  a  peculiarly  arranged  pneu- 
matic trough,  which  answers  every  requirement,  and  which  is  illus- 
trated in  GRANDEAU'S  Handbuch,  p.  34.  I  consider  it,  however, 
more  useful  to  here  describe  a  slightly  modified  form  of  the  appa- 
ratus devised  by  P.  WAGNER,*  and  shown  in  Fig.  136,  as  this  may 
be  readily  put  together  from  vessels  ordinarily  used  in  the  labora- 
tory. 

The  method  to  be  followed  in  determining  Chili  saltpetre  is  as 
follows : 

Introduce  40  c.c.  of  a  ferrous-chloride  solution  (containing 
about  200  grm.  iron  per  litre)  into  the  flask  a,  having  a  capacity  of 
from  250  to  300  c.c.,  then  add  40  c.c.  hydrochloric  acid  of  1  •  1  sp. 
gr.  Then  pour  a  few  c.c.  of  the  same  hydrochloric  acid  into  the 
funnel-tube  b  (provided  with  a  glass  cock)  the  finely  drawn  out  tip 
of  which  reaches  down  into  the  body  of  the  flask,  but  does  not  dip 
into  the  liquid.  Now  open  the  glass  cock  in  order  to  displace  the 
air  in  the  tube  by  the  acid,  but  promptly  close  before  the  last  of 
the  acid  has  run  through.  The  gas-delivery  tube,  c,  dips  into  the 
water  contained  in  a  glass  trough  about  24  cm.  wide  and  20  cm. 
deep,  and  into  which  cold  water  may  be  conducted  through  the 
opening  at  e,  in  order  to  expel  the  water,  warmed  and  contami- 
nated by  hydrochloric  acid  through  the  glass  tube  inserted  at  /. 

*  Chemiker-Ztg.,  1884,  651 ;  Zeitschr.  /.  analyt.  Chem.,  xxni,  559. 


320.] 


ANALYSIS   OF    MANURES. 


879 


In  the  trough  are  supported  four  or  more  measuring  cylinders 
graduated  in  0-  5  or  1  c.c.,  and  filled  with  water;  they  are  suspended 
from  a  wire  holder  having  rings  at  the  tops,  and  half -rings  at  the 
middle,  as  shown.  None  of  these  graduated  cylinders  should  be 


FIG.  136. 

placed  over  the  upturned  end  of  the  gas-delivery  tube,  c,  at  the 
beginning. 

Now  heat  the  contents  of  the  flask  a  to  boiling,  and  keep  it 
boiling  until  all  the  air  has  been  expelled,  which  may  be  readily 
ascertained  by  placing  a  test-tube  filled  with  water  over  the  end 
of  the  delivery-tube  c.  Then  support  one  of  the  measuring  tubes 
over  the  delivery-tube,  pour  10  c.c.  of  normal  nitrate  solution  con- 
taining exactly  33  grm.  pure  sodium  nitrate  per  litre,  into  the 


8*80  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  320. 

funnel-tube  b,  and  arrange  the  stop-cock  so  that  the  normal  solution 
will  slowly  drop  into  the  iron  solution,  which  must  be  kept  con- 
stantly boiling.  When  all  but  a  very  small  residue  has  passed 
fill  the  funnel  twice  with  hydrochloric  acid  of  1- 1  sp.  gr.,  and  allow 
this  also  to  drop  in  until  only  sufficient  acid  remains  to  fill  the 
tube.  When  this  is  accomplished,  the  first  operation  is  com- 
pleted. Now,  still  keeping  the  contents  of  a  boiling,  move  the 
graduated  tube  to  one  side  for  the  time  being,  and  replace  it  by  an- 
other. Pour  10  c.c.  of  the  Chili-saltpetre  solution  to  be  examined 
and  which,  too,  must  contain  33  grm.  per  litre,  into  the  funnel  6, 
and  proceed  with  the  process  just  as  before,  also  washing  out  the 
funnel  twice  with  hydrochloric  acid.  In  this  manner,  and  without 
exhausting  the  ferrous-chloride  solution,  six  or  seven  more  deter- 
minations may  be  made  and  also  a  final  control  determination 
with  the  normal  nitrate  solution,  as  well.  When  this,  too,  is  com- 
pleted, open  the  glass  cock  in  order  to  allow  air  to  enter  into  a, 
and  then  remove  the  heat. 

The  graduated  tube  c  ntaining  the  nitric  oxide  has  in  the  mean- 
time been  sunk  into  a  glass  cylinder  about  44  cm.  high  and  15  cm. 
wide  in  which  it  is  held  fast  by  brass  clips  fastened  to  the  edge  of 
the  cylinder.  The  water  displaced  on  sinking  the  tube  into  the 
cylinder  runs  off  through  a  side  tube.  When  certain  that  the  tem- 
perature of  all  the  tubes  and  their  contents  is  identical,  read  off 
the  volume  of  gas. 

If  the  process  has  been  carried  out  as  above  described,  the 
percentage  of  sodium  nitrate  in  Chili  saltpetre  may  be  calculated 
from  the  following  proportion:  The  nitric-oxide  gas  evolved  from 
0  •  33  grm.  pure  NaNO3  :  the  nitric-oxide  gas  evolved  from  0  •  33  grm. 
of  the  Chili  saltpetre  ::  100  :  x.  If,  however,  unlike  quantities  of 
pure  sodium  nitrate  and  of  the  substance  to  be  examined  have 
been  taken,  it  is  simplest  to  calculate  the  quantity  of  nitric  acid 
or  nitric  oxide  corresponding  to  1  c.c.  of  the  nitric  oxide  obtained 
from  the  former,  and  to  then  multiply  the  value  thus  found  by 
the  number  of  c.c.  of  nitric  oxide  yielded  by  the  unknown  quan- 
tity of  nitric  acid.  None  of  the  other  modifications  of  SCHLOS- 
ING'S  original  method  are  as  rapid  as  that  just  described.  I  will 


§  320.]  ANALYSIS    OF   MANURES.  881 

therefore  confine  myself  here  to  just  pointing  out  the  principles 
upon  which  they  are  based. 

C.  BOHMER  *  recommends  to  gravimetrically  determine  the 
nitric-oxide  gas  collected  in  a  LIEBIG'S  potash  bulb  filled  with  con- 
centrated chromic-acid  solution.  E.  WILDT  and  A.  SCHEIBE  |  re- 
convert the  nitric  oxide  into  nitric  acid,  and  determine  this  by 
titration,  using  for  the  purpose  an  apparatus  that  excludes  the  use 
of  a  mercurial  trough.  They  consider  their  method  preferable  to 
measuring  the  volume  of  nitric-oxide  gas,  more  particularly  when 
it  is  feared  that  the  nitric-oxide  gas  may  contain  an  admixture  of 
other  and  indifferent  gases,  as  may  happen  when  investigat- 
ing the  sap  of  plants.  WARINGTON  J  removes  the  air  from  the 
flask,  as  SCHLOSING  had  already  also  proposed,  by  means  of  a 
current  of  carbon  dioxide  passed  through  a  small  flask  containing 
a  little  water  and  placed  in  a  calcium-chloride  bath  heated  to  140°; 
the  nitric  oxide  is  collected  over  mercury,  treated  with  potassa 
lye,  and  finally  absorbed  by  a  saturated  ferrous-chloride  solution. 
He  recommends  his  method  particularly  for  the  accurate  deter- 
mination of  small  quantities  of  nitric  acid.  WILFARTH  §  converts 
the  nitric  oxide  into  nitric  acid  by  treatment  with  an  alkaline  solu- 
tion of  hydrogen  dioxide  of  known  strength,  and  then  determines 
the  nitric  acid  by  titration. 

Various  other  methods  proposed  have  also  been  based  up  n  the 
principle  mentioned  in  §  149,  e,  (Vol.  I,  p.  571),  e.g.,  conversion  of 
the  nitric  acid  into  ammonia,  and  will  be  but  briefly  mentioned 
here.  Such  are :  The  method  proposed  by  E.  PUGH,  and  modified 
by  O.  v.  DUMREICHER,||  in  which  a  hydrochloric-acid  solution  of 
stannous  chloride  is  used;  and  those  of  J.  WEST-KNIGHTS!"  and 
B.  KINXEAR,**  in  which  zinc  and  sulphuric  acid  are  employed. 

WALTER  CRUM'S  method  of  determining  nitric  acid,  and  the 

*  Zeitschr.  f.  analyt.  Chem.,  xxii,  20. 

f  Ibid.,  xxiii,  151. 

%  Ibid.,  xxiii,  547. 

§  Ibid.,  xxm,  587. 

||  Ibid.,  xx,  290. 

f  Ibid.,  xxu,  572. 

**  Ibid.,  xxv,  224. 


882  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  320. 

nitrometer  devised  by  LUNGE  for  carrying  out  the  method,  have 
already  been  minutely  described  in  §  271,  2  (p.  711  this  volume). 
According  to  WARINGTON'S  *  investigations,  the  method  is  particu- 
larly well  adapted  for  the  determination  of  small  quantities  of 
nitric  acid,  but  gives  too  low  results  if  large  quantities  of  organic 
substances  are  present;  this  opinion,  however,  is  not  in  accord 
with  LUNGE'S  f  experience.  SHEPHERD  J  has  recently  recommended 
using  the  nitrometer  for  determining  the  nitric  acid  in  manures. 
As  reference  will  have  to  be  made  to  these  paragraphs  when  treat- 
ing of  the  analysis  of  mixed  manures,  the  method  will  be  given  here 
in  detail. 

In  the  case  of  manures  containing  about  5  per  cent,  nitric  acid, 
take  not  more  than  0  •  2  grm.  of  the  substance ;  if  they  contain  less 
than  1  per  cent.,  take  from  2  to  3  grm.  The  extracts  are  prepared 
with  hot  water,  evaporated  to  a  small  volume,  and  introduced  into 
the  nitrometer.  It  is  unnecessary  to  remove  the  chlorine  by  treat- 
ment with  silver  sulphate.  The  volume  of  the  liquid  should  be  so 
small  that,  including  the  washings,  it  should  not  exceed  5  c.c.  Into 
the  perfectly  cooled  liquid  in  the  nitrometer  allow  double  its  volume 
of  pure,  concentrated  sulphuric  acid  to  cautiously  flow,  mix  the 
acid  with  the  aqueous  liquid  by  gently  shaking,  allow  any  carbon 
dioxide  evolved  to  escape  by  momentarily  opening  the  glass  cock,  if 
necessary,  and  then  shake  vigorously  in  order  to  evolve  the  nitric 
oxide.  The  reaction  is  completed  in  a  few  minutes.  Then  allow  to 
cool,  and  read  off  the  volume  of  the  gas.  If  comparative  parallel 
experiments  are  made  under  similar  conditions  with  nitre  solutions 
of  known  strength,  corrections  for  temperature  and  pressure  may 
be  disregarded,  the  calculation  being  then  made  as  in  SCHLOSING'S 
new  method. 

The  question  as  to  what  influence  organic  substances  exercise 
upon  the  result  requires  further  investigation. 

*  Zeitschr.  f.  analyt.  Chem.,  xix,  85. 
f  Ibid.,  xix,  208. 
.,  xxv,  270. 


§  321.]  ANALYSIS   OF   MANURES.  883 

II.  AMMONIUM  SALTS. 

The  determination  of  ammonia  in  ammonium  salts  is  as  a 
rule  effected  either  by  distillation  with  the  addition  of  calcined 
magnesia,  or  by  the  separation  and  measurement  of  the  nitrogen, 
according  to  the  method  to  which  KNOP  has  given  the  name 

"azotometry." 

a.  Distillation  Method. 

§321. 

This  method  has  already  been  described  hi  §  99,  3  (Vol.  I,  p.  253), 
and  in  regard  to  its  employment  for  the  determination  of  the  am- 
monia in  soils,  in  §  302,  b.  I  will  but  point  out  that  not  only 
with  mixed  manures,  but  also  with  the  ammonium  salts  prepared 
on  the  large  scale,  and  frequently  containing  ammonium  sulpho- 
cyanate,  the  distillation  must  always  be  carried  out  with  the 
addition  of  calcined  magnesia,  and  never  with  potassium  or  sodium 
hydroxide,  because  by  the  action  of  these  alkalies  the  nitrogen 
of  the  sulphocyanogen  is  also  converted  into  ammonia;  *  the  dis- 
tillation with  magnesia,  besides,  yields  accurate  results  also  when 
phosphates  are  present,!  and  any  explosive  ebullition  of  the  ammo- 
niacal  liquid  may  be  entirely  avoided  by  passing  steam  through  the 
liquid  instead  of  heating  the  latter  directly  (RuDORFF)4 

With  regard  to  the  receivers  for  holding  the  titrated  acid,  it  is 
of  course  unnecessary  to  adhere  strictly  to  the  form  described 
in  §  99,  3,  but  care  must  be  taken  that  the  ammoniacal  distillate 
does  not  come  into  contact  with  cork  or  rubber,  as  both  of  these 
retain  a  little  of  it.  KNUBLAUCH  §  highly  recommends  the  appa- 
ratus shown  in  Fig.  137  as  being  very  practical. 

a  is  the  distillation  flask,  having  a  capacity  of  from  200  to 
250  c.c.,  and  fitted  with  a  tube,  6,  connected  with  the  absorption 
apparatus,  e,  the  latter  having  the  form  of  a  flask  without  a  bottom, 
40  mm.  wide  below,  and  with  several  lips  formed  on  the  rim  in 

*  Comp.  ESILMAN,  Zeitschr.  f.  analyt.  Chem.,  xiv,  94. 
t  Comp.  MARCKER,  Ibid.,  x,  277. 
i  Ibid,,  xii,  440. 
§  Ibid.,  xxi,  161. 


884  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  321. 

order  to  better  distribute  the  bubbles  of  gas  evolved.  The  vessel 
e  is  suspended  in  the  glass  cylinder  c,  by  means  of  a  cork  slab,  d, 
fitted  around  the  neck,  and  in  such  a  manner  that  e  is  a  few  milli- 
metres above  the  bottom.  In  c  is  placed  the  measured  quantity 


FIG.  137. 

of  titrated  acid,  together  with  sufficient  water  to  cover  the  edge 
of  e  to  a  height  of  1  cm.  Finally,  the  cylinder  c  is  placed  in  an 
outer  vessel  g,  filled  with  water  for  the  purpose  of  cooling  and 
condensing.  After  the  contents  of  a  have  been  reduced  to  one- 
half  or  one-third  by  distillation,  and  all  the  ammonia  has  thus  been 
driven  off,  remove  the  stopper  from  e,  remove  c  from  the  cooler, 
and  when  quite  cold,  titrate  the  excess  of  acid,  without  removing 
e.  When  examining  ammonium  sulphate,  it  is  convenient  to 
dissolve  20  grm.  to  make  500  c.c.  of  solution,  and  to  take  25  c.c., 
corresponding  to  1  grm.,  for  the  distillation.  For  rinsing  the  walls 
of  a  about  10  c.c.  of  water  are  required.  If  20  c.c.  of  normal 
sulphuric  acid  have  been  taken,  then  about  6  c.c.  of  normal  soda 
will  be  required  to  neutralize  the  excess.  In  order  to  expel  the 
ammonia,  KNUBLAUCH  uses  a  little  solid  caustic  potassa,  which 
is  wrapped  in  filter-paper  and  introduced  into  the  contents  of  a; 
the  paper  floating  on  the  surface  of  the  liquid  facilitates  a  more 
quiet  boiling.  From  what  has  been  said  above,  however,  it  is 


§  322.]  ANALYSIS   OF   MANURES.  885 

evident  that  caustic  potassa  can  be  used  only  when  sulphocyan- 
ogen  and  other  nitrogenous  organic  substances  are  absent. 

According  to  THOMSON'S  *  investigations  the  best  indicators 
for  ammonia  titrations  are  litmus  (or  the  preparation  of  litmus 
mentioned  on  p.  845  this  volume),  methyl  orange,  or  phenacetolin; 
rosolic  acid  is  not  so  well  adapted,  while  phenolphtalein  is  unsuit- 
able. 

6.  Azotimetric  Method. 
§322. 

The  azotimetric  method,  to  which  reference  has  already  been 
made  on  p.  845,  this  volume,  is  based  upon  the  reaction  which 
takes  place  when  an  excess  of  an  alkali  hypobromite  acts  upon 
ammonia:  3NaBrO+2NH3  =  3NaBr+2N+3H2O.  All  the  nitro- 
gen of  the  ammonia  is  liberated,  and  can  be  measured.  I  here 
describe  the  method  in  its  most  complete  form  as  given  by  W. 
KXOP  (who  originated  it)  in  one  of  his  most  recent  publications.! 
The  apparatus  required  for  the  method  is  shown  in  Fig.  13S.J 
a,  the  decomposition  flask  in  which  the  sodium-hypobromite 
solution  is  allowed  to  act  upon  the  ammonium  salt,  is  from  10  to  11 
cm.  high,  5  cm.  diameter,  and  is  closed  by  a  hollow  glass  stopper 
which  is  prolonged  to  form  a  stout  glass  tube,  6,  8  to  9  cm.  long 
and  2  cm.  wide;  this  may  be  closed  above  by  means  of  a  glass  cock, 
the  latter  being  connected  above  with  a  strong  tapering  glass  tube 
sealed  on  to  the  upper  external  part  of  the  cock.  The  wide  tube  is 
tightly  packed  with  coarse  glass  beads  which  are  prevented  from 
falling  into  a  by  a  loose  ball  of  fine  platinum  wire.  The  vessel  a  is 
suspended  in  the  glass  cylinder  d  d  by  means  of  a  stout  metal  rod  c, 
the  ower  end  of  which  has  soldered  to  it  at  right  angles  a  metal 
plate  for  a  to  rest  upon,  and  provided  with  a  metallic  spring  clamp 

*  Zeitschr.  f.  analyt.  Chem.,  xxiv,  225. 

t  Ibid.,  xxv,  301. 

\  Regarding  other  apparatus  the  construction  of  which  differs  more  or 
less  from  the  one  shown,  see  P.  WAGNER,  Zeitschr.  f.  analyt.  Chem.,  xiu,  383, 
and  xv,  250:  SOXHLET,  ibid.,  xvi,  81;  GAWALOWSKI,  ibid.,  xvm,  244,  and 
xxiv,  61;  C.  MOHR,  ibid.,  xxm,  26;  and  MOSSALKI,  Bull,  de  la  Soc.  chim.  de 
Paris,  XL,  18. 


DETERMINATION    OF    COMMERCIAL   VALUES. 


[§  322. 


higher  up;  the  cylinder  d  d  is  50  cm.  high  and  18  cm.  in  diameter, 
and  is  filled  with  cold  water  for  cooling  purposes.  The  metal  rod 
may  be  raised  or  lowered  to  any  convenient  height,  and  secured  in 
place  by  a  screw,  as  shown.  If  this  is  removed,  the  support  for 


FIG.  138. 

the  decomposition  flask  still  hangs  from  the  metal  ring  on  the  edge 
of  d  d  on  two  stout,  steel  pins,  from  which  it  may  readily  be  removed 
and  on  which  it  may  as  easily  be  replaced. 

To  the  metal  ring  on  d  d  is  also  attached  by  means  of  a  screw 
the  metal  clamp  for  holding  the  U-tube  e,  one  limb  of  which  is 
graduated.  After  removing  the  screw,  and  taking  off  the  stop- 
cock /,  from  g,  as  well  as  removing  the  short  rubber  tube  connected 
with  the  ungraduated  limb  of  the  U-tube,  in  order  to  allow  the 


§  322.]  ANALYSIS    OF    MANURES.  887 

water  to  run  off,  the  U-tube  itself  can  be  taken  out  for  cleaning 
or  if  necessary,  for  renewing  the  rubber  tube.  The  graduated,  as 
well  as  the  plain,  and  somewhat  longer  limb  of  the  U-tube  (which 
should  extend  a  few  cm.  above  the  surface  of  the  water  in  d  d,  so 
that  the  U-tube  may  be  filled  with  distilled  water),  are  connected 
together  below  by  means  of  a  rubber  tube,  as  shown  in  the  illustra- 
tion. The  U-tube  may,  however,  also  be  made  in  one  piece,  in 
order  to  simplify  the  repairs  that  are  occasionally  necessary.  In 
order  to  connect  the  short  tube  projecting  from  the  side  of  the 
lower  end  of  the  non-graduated  limb,  with  the  glass  cock  /,  slip 
over  the  former  the  end  of  a  rubber  tube  20  cm.  long,  place  the 
U-tube  in  d  d,  draw  the  free  end  of  the  rubber  tube  by  means  of  a 
hook  through  the  tubulure  g,  and  slip  over  the  end  of  the  glass 
cock  which  has  first  been  inserted  into  a  perforated  cork  impreg- 
nated with  melted  paraffin ;  then  insert  the  cork  into  the  tubulure, 
g.  The  rubber  tube  h,  connecting  the  graduated  limb  of  the  U-tube 
with  the  vessel  a,  must  be  of  thick,  soft  material,  with  an  internal 
diameter  of  about  the  thickness  of  a  stout  knitting-needle.  It  must 
be  so  long,  that  a  may  be  removed  from  the  water  in  the  cooler  and 
placed  on  the  table  beside  d  d  without  stretching  the  tube  at  all. 
With  a  tube  of  such  length  no  change  in  its  volume  need  be  feared, 
and  the  shaking  and  reversing  of  a  outside  of  d  d  may  be  conve- 
niently effected. 

The  process  is  carried  out  as  follows : 

1.  Dissolve   15-2484*   grm.   of    pure,   anhydrous    ammonium 
chloride  in  water  to  measure  1000  c.c.     10  c.c.  of  this  solution  will 
contain  0-04  grm.  nitrogen. 

2.  Dissolve  20  grm.  of  the  ammonium  salt  to  be  examined 
if  ammonium  sulphate,  or  16  grm.  if  ammonium  chloride,  in  suffi- 
cient water  to  measure  1000  c.c. 

3.  After  loosening  the  screw  on  c,  lift  out  the  flask  a  together 
with  its  support,  place  a  alongside  the  azotometer  on  the  table, 
remove  the  stopper,  invert  it,  and  into  the  funnel-shaped  opening 
of  the  stopper,  the  glass  cock  being  open,  pour  as  much  brominized 

*  The  figures  in  the  German  text  are  15-2422;  recalculated  according  to 
the  values  used  in  the  translation  they  are  15-2484. — TRANSLATOR. 


888  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  322. 

soda  solution*  from  a  measured  quantity  of  50  c.c.  as  will  suffice 
to  thoroughly  wet  the  glass  beads,  then  pour  the  remainder  of  the 
50  c.c.  of  brominized  lye  into  a,  and  after  having  greased  the 
stopper  with  tallow,  insert  it  in  a  and  allow  to  stand  until  no  more 
lye  drips  from  the  beads ;  then,  by  means  of  a  pair  of  forceps,  place 
into  the  lye  a  glass  tube  of  suitable  width  and  length,  closed  at  one 
end,  and  containing  10  c.c.  of  the  ammonium-chloride  solution  of 
known  strength, f  again  insert  the  stopper,  and  connect  a,  the 
cock  of  b  being  open,  with  the  graduated  limb  of  the  U-tube  by 
means  of  the  rubber  tube ;  then  immerse  a  and  the  tube  in  the  cold 
water  in  d  d  by  suspending  the  support  on  the  two  metal  pins  already 
mentioned,  and  allow  to  stand  for  20  minutes,  taking  care  that  the 
level  of  the  water  is  at  the  same  height  in  both  limbs,  and  noting 
the  height.  A  small,  movable  plate  painted  one-half  white,  one- 
half  black,  serves  to  better  observe  the  level.  The  temperature 
of  the  water  in  c(d  should  not  differ  appreciably  from  that  of  the  sur- 
rounding air. 

Now  allow  about  30  c.c.  of  water  to  run  out  of  /,  remove  a 
from  the  water,  and  incline  it  slightly  so  that  a  little  of  the  am- 
monium-salt solution  may  run  out,  and  the  evolution  of  gas 
slowly  proceeds.  The  small  quantities  of  gaseous  ammonia 
carried  off  is  absorbed  and  decomposed  by  the  lye  adhering  to 
the  glass  beads.  The  further  mixture  of  the  two  liquids  is  effected 
in  the  same  way.  When  the  evolution  of  gas  finally  slackens, 
close  the  cock  on  b  and  shake  and  repeatedly  invert  a.  Then 
open  the  cock  on  b  again,  replace  a  and  the  tube  in-  the  cold  water, 
and  move  both  the  latter  up  and  down  to  mix  the  water;  next 
fix  its  lowest  possible  position,  allow  to  stand  for  20  minutes, 
allow  enough  water  to  run  off  through  until  the  water-level  in 
both  limbs  of  the  U-tube  is  at  the  same  height,  and  then  read 
off  the  number  of  c.c.  of  nitrogen  gas  evolved.  This  number, 

*  To  prepare  this  dissolve  100  grm.  caustic  soda  in  1250  c.c.  water,  cool 
strongly,  add  25  c.c.  bromine,  and  mix.  The  solution  must  be  protected 
from  the  action  of  light. 

t  P.  WAGNER  recommends  to  fuse  the  tube  containing  the  ammonium- 
salt  solution  to  the  bottom  of  the  decomposition  flask  (Zeitschr.  f.  analyt. 
Chem.,  xv,  250). 


§  322.]  ANALYSIS    OF    MANURES.  889 

about  32  c.c.,  corresponds  to  0-04  grm.  nitrogen  at  the  prevailing 
pressure,  and  the  temperature  of  the  water  used  for  cooling. 

4.  In  exactly  a  similar  manner  carry  out  the  experiment  with 
solution  No.  2,  and,  basing  the  calculation  upon  the  proportion 
between  the  volume  and  weight  of  nitrogen  found  in  3,  determine 
the  nitrogen  content  of  the  ammonium  salt  in  solution  No.  2. 
For  instance,  if  in  3,  we  had  obtained  33  c.c.,  whereas  in  No.  4  we 
obtained  30  c.c.,  of  nitrogen,  it  follows  that  in  the  10  c.c.  of  the 
solution  No.  2  the  weight  of  the  nitrogen  is 

33  c.c. :  0-04  grm.  N::  30  c.c.:  z;  and  z=0. 03636  grm. 

Should  experiment  4  have  yielded  a  volume  of  nitrogen  differing 
considerably  from  that  obtained  in  3,  repeat  the  experiment, 
using  a  correspondingly  larger  quantity  of  solution  No.  2. 

5.  When  a  long  series  of  such  tests  are  made  consecutively,  it 
is  advisable  to  check  the  relation  of  volume  to  weight  of  nitrogen 
found  in  3  by  making  another  determination,  using  10  c.c.  of 
solution  No.  1. 

6.  Instead  of  making  the  calculation  as  in  4,  and  which  is 
based  simply  upon  the  comparison  of  the  nitrogen  to  be  deter- 
mined with  a  known  volume  obtained  under  identical  conditions, 
the  volume  of  the  gas  may,  of  course,  be  measured,  and  its  weight 
calculated  from  the  volume.     In  this  case,  however,  it  is  evident 
that  regard  must  be  paid  to  pressure,  temperature,  and  hygro- 
scopicity,  as  well  as  to  the  circumstance  that  a  small  quantity 
of  nitrogen  remains  dissolved  in  the  decomposing  fluid,  this  quan- 
tity being  dependent  upon  the  temperature.     These  calculations 
may  be  avoided  by  making  use  of  the  following  tables  calculated 
by  E.  DIETRICH,*  and  given  on  pp.  890  to  892. 

7.  KNOP  uses  as  normal  liquid  an  aqueous  ammonium-chloride 
solution  containing  10  grm.  of  pure,  dry  ammonium  chloride  in 
2089-4  c.c.     Every  c.c.  of  this  solution  corresponds  to  1  c.c.  of  dry 
nitrogen  at  0°  and  760  mm.  pressure.     When  using  this  solution, 
the  experiment  will  also  give  the  relation  between  moist  nitrogen 
at  the  temperature  of  the  cooling  water  and  prevailing  barometric 
pressure,  and  dry  nitrogen  measured  at  0°  and  760  mm.  pressure. 

*  Zeitschr.  f.  analyt.  Chem.,  v,  38  to  40. 


890 


DETERMINATION    OF   COMMERCIAL   VALUES. 


[§  322. 


I.  Table  of  the  weight  in  milligrams  of  one  cubic  centimetre  of  Nitrogen  under 
pressures  of  720  to  770  mm.  mercury  and  at  temperatures  between  10° 
and  25°. 


mm. 


720 

722 

724 

726 

728 

730 

732 

H  10° 

1-13380 

1  -  13699 

1-14018 

1  •  14337 

1  •  14656 

1-14975 

1  •  15294 

4  11° 

1  -  12881 

1-13199 

1-13517 

1  •  13835 

1-14153 

1-14471 

1  •  14789 

&  12° 

1  •  12376 

1  -  12693 

1  -  13010 

1  •  13326 

1  •  13643 

1  -  13960 

-  14277 

H  13° 

1-11875 

•12191 

1  -  12506 

1  •  12822 

1-13138 

1  •  13454 

-13769 

9  14° 

1-11369 

•11684 

1-11999 

1-12313 

1-12628 

1  •  12942 

-  13257 

K  15° 

1  -  10859 

-11172 

1-11486 

1-11789 

1-12113 

1  -  12426 

-  12739 

2  16° 

1  -  10346 

•  10658 

1-10971 

1-11283 

1-11596 

1-  11908 

•  12220 

*  17° 

1-09828 

-10139 

1  •  10450 

1-10761 

1-11073 

1-11384 

•11695 

5  18° 

1-09304 

1-09614 

1-09924 

1  •  10234 

1  •  10544 

1  -  10854 

•11165 

K  19° 

1-08774 

1-09083 

1-09392 

1-09702 

-10011 

•  10320 

•  10629 

E  20° 

1-08246 

1-08554 

1-08862 

1-09170 

•09478 

•09786 

•  10094 

£  21° 

1-07708 

1-08015 

1-08322 

1-08629 

•08936 

1-09243 

•09550 

o  22° 

1-07166 

1-07472 

1-07778 

1-08084 

•08390 

•08696 

•09002 

fc  23° 

1-06616 

1-06921 

1-07226 

1-07531 

•07836 

•08141 

•08446 

S3  24° 

1-06061 

1-06365 

1-06669 

1-06973 

•07277 

•07581 

•07885 

H  25° 

1-05499 

1-05801 

1-06104 

1-06407 

•06710 

-07013 

-07316 

mm. 


734 

736 

738 

740 

742 

744 

B       10° 

1-15613 

1-15932 

1  •  16251 

1  -  16570 

1-16889 

1-17208 

4       H° 

1-15107 

1-15424 

1-15742 

1  -  16060 

1-16378 

1  -  16696 

&     12° 

1  -  14593 

1  -  14910 

1-15227 

1-15543 

1-15860 

1-16177 

13° 

1  -  14085 

1-14401 

1-14716 

1-15032 

1-15348 

1  -  15663 

14° 

1  •  13572 

1  •  13886 

1-14201 

1-14515 

1-14830 

1-15145 

a   15° 

1  -  13053 

1-13366 

1-13680 

1  •  13993 

1  •  14306 

1  •  14620 

16° 

1  •  12533 

1  -  12845 

1  -  13158 

1-13470 

1  •  13782 

1  •  14095 

fc     17° 

1  •  12006 

1-12317 

1-12629 

1  -  12940 

1  •  13251 

1  -  13562 

£     18° 

1-11475 

1-11785 

1-12095 

1  -  12405 

1-12715 

1  -  13025 

19° 

1-10938 

1-11248 

1-11557 

1-11866 

1-12175 

1  -  12484 

20° 

1  •  10402 

1-10710 

1-11018 

1-11327 

1-11635 

1-11943 

21° 

1-09857 

1-10165 

1  •  10472 

1  •  10779 

1-11086 

1-11393 

o     22° 

1-09308 

1-09614 

1-09921 

1  •  10227 

1-10533 

1  -  10839 

6     23° 

1-08751 

1-09056 

1-09361 

1-09666 

1-09971 

1-10276 

S     24° 

1-08189 

1-08493 

1-08796 

1-09100 

1-09404 

1-09708 

fi     25° 

1-07619 

1-07922 

1-08225 

1-08528 

1-08831 

1-09134 

322.] 


ANALYSIS   OF   MANURES. 


891 


I.  Table  of  the  weight  in  milligrams  of  one  cubic  centimetre  of  Nitrogen  under 
pressures  of  720  to  770  mm.  mercury  and  at  temperatures  between  10° 
and  25°. 


mm. 


746 

748 

750 

752 

754 

756 

758 

K  10° 

1  •  17527 

1-17846 

1-18165 

-18484 

1-18803 

•  19122 

•  19441 

<  11° 

1-17014 

1-17332 

1-17650 

•17168 

1  •  18286 

•18603 

•  18921 

£  12° 

1  •  16493 

1-16810 

1-17127 

•  17444 

•17760 

18077 

•18394 

H  13° 

1  •  15979 

1-16295 

1-16611 

•  16926 

•  17242 

-17558 

•17873 

9  14° 

•15459 

1-15774 

1-16088 

•16403 

•16718 

•17032 

•17347 

5  15° 

•  14933 

1-15247 

1-15560 

•15873 

•16187 

•16500 

•16814 

g  16° 

•  14407 

1-14720 

1  •  15032 

•15344 

•  15657 

•  15969 

•  16282 

S  17° 

•  13873 

1-14185 

1  •  14496 

•14807 

-15118 

•15429 

-  15741 

a  i8° 

•  13335 

1-13645 

1  •  13955 

•  14266 

-14576 

•  14886 

•15196 

H  19° 

•  12794 

1-13103 

1-13412 

1-13721 

•14030 

-14340 

•14649 

£  20° 

•  12251 

1-12559 

1-12867 

1-13175 

•13483 

1  •  13791 

-14099 

^  21° 

•11700 

1-12007 

1-12314 

1  -  12621 

•  12928 

1  -  13236 

•13543 

1  22° 

•11145 

1-11451 

1-11757 

1  •  12063 

•  123G9 

1-12675 

•  12982 

fa  23° 

•10581 

1  -  10886 

1-11191 

1-11496 

•11801 

1-12106 

•12411 

S  24° 

•10012 

1-10316 

1  -  10620 

1  -  10924 

•11228 

1-11532 

•11835 

H  25° 

•09437 

1-09740 

1  •  10043 

1  -  10346 

•  10649 

1-10952 

-11255 

mm. 


760 

762 

764 

766 

768 

770 

w     10° 

1-19760 

•20079 

1-20398 

1-20717 

•21036 

1-21355 

11° 

1  -  19239 

-  19557 

1  •  19875 

1-20193 

•20511 

1-20829 

&     12° 

1-18710 

-19027 

1  -  19344 

1  •  19660 

•19977 

1-20294 

13° 

1  -  18189 

-18505 

1-18820 

1  •  19136 

•  19452 

1  •  19768 

14° 

1-17661 

•  17976 

1  •  18291 

1-18605 

•18920 

1  •  19234 

15° 

1-17127 

•17440 

1-17754 

1-18067 

•18381 

1  -  18694 

16° 

1  -  16594 

•  16906 

1-17219 

•  17531 

•17844 

1-18156 

fc     17° 

1  -  16052 

•16363 

1  •  16674 

•  16985 

•  17297 

1-17608 

Q    18° 

1  •  15506 

•15816 

1  -  16026 

•  16436 

•  16746 

1-17056 

19° 

1  •  14958 

•15267 

1-15576 

-  15886 

•16195 

1  •  16504 

20° 

1  -  14408 

•14716 

1-15024 

-  15332 

-15640 

1  •  15948 

21° 

1  -  13850 

•  14157 

1  •  14464 

•  14771 

-15078 

1  •  15385 

o     22° 

1  •  13288 

•  13594 

1-13900 

•14206 

-14512 

1  •  14818 

fa     23° 

1-12716 

•  13021 

1  •  13326 

•  13631 

-  13936 

1  •  14241 

24° 

1-12139 

•12443 

1-12747 

1  •  13051 

1-13355 

1  •  13659 

S     25° 

1-11558 

1-11861 

1-12164 

1  •  12467 

1-12770 

1-13073 

892 


DETERMINATION   OF   COMMERCIAL   VALUES. 


[§  322. 


II.  Table  of  Absorption  of  Nitrogen  in  60  c.c.  of  the  decomposing  fluid  (50  c.c. 
of  brominized  lye  and  10  c.c.  water),  the  lye  having  a  sp.  gr.  of  1-1,  and 
such  strength  that  50  c.c.  corresponds  with  0-2  grm.  nitrogen,  in  the  evo- 
lution of  from  1  to  100  c.c.  of  gas. 


1 

1 

Absorbed. 

Evolved. 

Absorbed. 

Evolved. 

1 
< 

1 

1 

1 

Absorbed. 

1 

0-06 

21 

0-56 

41 

1-06 

61 

1-56 

81 

2-06 

2 

0-08 

22 

0-58 

42 

1-08 

62 

1-58 

82 

2-08 

3 

0-11 

23 

0-61 

43 

•  11 

63 

1-61 

83 

2-11 

4 

0-13 

24 

0-63 

44 

•13 

64 

1-63 

84 

2-13 

5 

0-16 

25 

0-66 

45 

•16 

65 

1-66 

85 

2-16 

6 

0-18 

26 

0-68 

46 

•18 

66 

1-68 

86 

2-18 

7 

0-21 

27 

0-71 

47 

•21 

67 

1-71 

87 

2-21 

8 

0-23 

28 

0-73 

48 

•23 

68 

1-73 

88 

2-23 

9 

0-26 

29 

0-76 

49 

•26 

69 

1-76 

89 

2-26 

10 

0-28 

30 

0-78 

50 

•28 

70 

1-78 

90 

2-28 

11 

0-31 

31 

0-81 

51 

•31 

71 

1-81 

91 

2-31 

12 

0-33 

32 

0-83 

52 

•33 

72 

1-83 

92 

2-33 

13 

0-36 

33 

0-86 

53 

•36 

73 

1-86 

93 

2-36 

14 

0-38 

34 

0-88 

54 

•38 

74 

1-88 

94 

2-38 

15 

0-41 

35 

0-91 

55 

•41 

75 

1-91 

95 

2-41 

16 

0-43 

36 

0-93 

56 

•43 

76 

1-93 

96 

2-43 

17 

0-46 

37 

0-96 

57 

•  46 

77 

1-96 

97 

2-46 

18 

0-48 

38 

0-98 

58 

•48 

78 

1-98 

98 

2-48 

19 

0-51 

39 

1-01 

59 

•51 

79 

2-01 

99 

2-51 

20 

0-53 

40 

1-03 

60 

•53 

80 

2-03 

100 

2-53 

In  §  302,  f,  the  description  of  the  azotimetric  method  for  de- 
termining the  ammonia  in  soils  is  referred  to  azotimetry  in  manure 
analysis.  It  is  hence  necessary  to  here  add  the  special  details 
required  when  employing  the  methol  in  the  analysis  of  soils. 
They  are  as  follows: 

1.  Instead  of  the  vessel  with  lead  cover  *  originally  used  by 
him,  KNOP  now  uses  f  as  the  decomposing  vessel  a  wide-necked 
flask,  divided  internally  by  a  vertical  glass  partition  into  two 
unequal  chambers.     This  replaces  the  vessel  a  in  Fig.  138  (p.  886 
this  volume),  but  is  provided  with  the  same  form  of  stopper  and 
glass  cock. 

2.  As  the  one  chamber  must  be  large  enough  to  hold  100  grm. 
of  soil  and  also  125  c.c.  of  liquid,  the  vessel  will  be  so  large  that  it 
cannot  be  immersed  with  the  U-tube  in  the  same  cooling  cylinder. 

*  Chem.  CentralbL,  1860,  251. 

t  Zeitschr.  /.  analyt.  Chem.,  xxv,  304. 


§  322.]  ANALYSIS   OF   MANURES.  893 

It  must  hence  be  cooled  in  a  separate  vessel,  taking  care  that  the 
temperature  at  the  beginning  and  end  remains  the  same. 

3.  Place  in  the  larger  chamber  a  quantity  of  fine  earth  repre- 
senting 100  grm.  of  soil  dried  at  125°,  mix  with  it  125  c.c.  of  a  sat- 
urated,  clear  borax  solution,*  place  25  c.c.  of  the  brominized 
lye  in  the  smaller  chamber  of   the  decomposition  vessel,  insert 
the  stopper  lightly,  connect  the  latter  with  the  U-tube,  and  sur- 
round both  it  and  the  decomposition  vessel  with  water  in  the 
cooling  vessels;    allow  to  stand  for  20  minutes,  taking  care  to 
adjust  the  water-levels  in  the  U-tube,  and  gradually  bring  the 
brominized  lye  in  contact  with  the  soil  by  moderately  shaking, 
the  cock  at  b  being  at  first  open,  and  then  closed.     This  suffices 
for   the    complete    decomposition    of    the    ammonia.    After   the 
decomposition  flask  has  regained  its  original  temperature,  measure 
the  evolved  nitrogen.     As  the  quantity  of  liquid  in  the  decom- 
position flask  is  not  very  small,  the  quantity  of  nitrogen  absorbed 
must,  in   accurate   experiments,   not  be  neglected.     DIETRICH,! 
however,  has  pointed  out  the  difficulty  of  determining  this  factor 
with  accuracy. 

4.  According  to  A.  BAUMANN  J  the  results  obtained  when  treat- 
ing the  soil  according  to  3,  are  incorrect.    He  proposes,  as  DIETRICH 
(loc.  tit.    had  already  done,  to  submit,  not  the  soil  itself,  but  its 
hydrochloric-acid  extract,  to  the  azotimetric  test.     According  to 
W.  KNOP  §  the  incorrect  results  obtained  by  othess  in  the  direct 
azotimetric  determination  of  soils  are  due  to  the  employment  of 
too  strongly  alkaline  brominized  lye.     To  avoid  the  error  caused 
by  this,  he  recommends  in  his  above-mentioned  latest  treatise  to 
prepare  the  decompo  ing  liquid  by  simply  pouring  on  to  the  soil 
mixed  with  borax  solution  a  solution  of  calcium  hypobromite  (200 
c.c   water,  calcium  hydroxid    in  excess,  and  15  c.c.  bromine),  or 
at  most  to  add  a  small  quantity  of  sodium  hydroxide. || 

*  The  object  of  the  borax  solution  is  to  avoid  the  errors  due  to  the  con- 
traction usually  observed  when  strongly  alkaline  liquids  are  shaken  with  soils. 
t  Zeitschr.  f.  analyt.  Chem.,  v,  44. 
\  Landwirthschaftl.  Versuchsstationen,  1886,  247. 
§  Zeitschr.  f.  analyi.  Chcm.,  xxvi,  Part  I. 
1|  As  the  treatises  of  A.  BAUMANN  and  W.  KNOP  came  into  my  hands  only 


894  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  323. 


III.  SUBSTANCES  CONTAINING  ORGANICALLY  COMBINED  NITROGEN. 

The  nitrogen  in  organic  combinations  can  be  determined  accord- 
ing to  the  methods  detailed  in  §§  183  to  188  (pp.  56  to  95  this 
volume).*  It  was  customary  until  lately  to  use  almost  exclu- 
sively PELIGOT'S  modification  of  VARRENTRAPP-WILL'S  method 
(§  187).  In  1883,  however,  J.  KJELDAHL  published  a  method  of 
determining  nitrogen,  based  upon  an  entirely  new  principle,  and 
this  method  has  rapidly  gained  such  wide  recognition  as  to  make 
it  appear  as  though  it  would  gradually  replace  the  VARRENTRAPP- 
WILL'S  method,  at  least  in  the  analysis  of  manures.! 

Before  proceeding  to  describe  the  KJELDAHL  method,  I  wish  to 
add  here  a  few  supplementary  points  to  the  description  given  on 
p.  94  this  volume,  regarding  the  mode  of  carrying  out  PELIGOT'S 
modification  of  the  VARRENTRAPP-WILL  process  on  the  manu- 
facturing scale. 

a.   Modified  VARRENTRAPP-WILL  Method. 
§323. 

1.  P.  WAGNER, J  as  well  as  THIBAULT,  recommend  igniting  with 
soda-lime  in  a  current  of  hydrogen  in  a  wrought-iron  tube  open  at 
both  ends  (Fig.  139).  This  tube  is  95  cm.  long,  and  17  cm.  wide; 
it  extends  17  cm.  beyond  the  fore  part  of  the  combustion-furnace, 

when  correcting  the  proofs  of  this  section,  I  could  only  detail  the  more  im- 
portant features  in  the  text;  I  would  therefore  strongly  advise  all  who  are 
occupied  with  the  determination  of  ammonia  in  soils  by  the  azotimetric 
method,  to  thoroughly  study  both  treatises. 

*  Since  §  185  was  written  a  whole  series  of  papers  has  appeared  regarding 
the  DUMAS  method  of  determining  nitrogen,  for  which  consult  Zeitschr.  f. 
analyt.  Chem.,  KREUSLER  (Landwirthschaftl.  Versuchsstationen,  xxxi,  207; 
Zeitschr.  f.  analyt.  Chem.,  xxiv,  438)  has  published  a  treatise  giving  all  the 
details  of  the  method,  as  well  as  a  modified  form  of  the  process  which  gives 
the  most  reliable  results. 

•j-  See  MARCKER,  or  HEFFTER,  HOLLRUNG,  and  MORGEN  (Chemiker-Ztg., 
vm,  432;  Zeitschr.  f.  analyt.  Chem.,  xxin,  553);  E.  SCHULZE  or  BOSSHARDT 
(Zeitschr.  f.  analyt.  Chem.,  xxiv,  199);  and  TH.  PFEIFFER  and  F.  LEHMAN 
(ibid.,  xxiv,  388). 

|  Chemiker-Ztg. ,  vm,  650;  Zeitschr.  f.  analyt.  Chem.,  xxm,  557. 


§  323.] 


ANALYSIS   OF   MANURES. 


895 


and  25  cm.  beyond  the  hinder  end,  and  it  rests  in  a  sheet-iron 
trough.  The  ends  are  closed  by  rubber  stoppers.  At  a  distance 
of  about  15  cm.  from  the  fore  end  of  the  tube  is  placed  a  12-cm. 
long  layer  of  soda-lime,  granulated,  but  net  caked,  and  retained  in 
place  between  an  asbestos  plug  in  front  and  a  roll  of  iron  wire  be- 
hind: this  will  suffice  for  about  100  combustions.  To  fill  the  tube, 
mix  the  substance  with  powdered  soda-lime  in  a  mortar,  and,  by 
aid  of  a  sheet-copper  scoop,  h,  transfer  the  mixture  to  a  tinned- 
iron  trough,  i,  31  cm.  long,  provided  with  a  turned-down  piece  of 


FIG.  139. 

tinned  iron  at  the  back.  In  order  to  collect  any  portions  which 
may  have  been  spilled,  place  the  tinned-iron  trough  in  a  sheet- 
copper  trough,  k,  3i  cm.  wide.  After  covering  the  contents  in  i 
with  the  soda-lime  which  has  been  used  for  rinsing  out  the  mortar, 
insert  the  trough  into  the  combustion-tube,  and  push  the  latter 
into  place  with  the  wire,  e,  which  is  left  in  with  it;  now  close  the 
tube  with  rubber  stoppers,  attach  the  receiver,  and  pass  a  slow  cur- 
rent of  hydrogen*  (which  must  be  maintained  throughout  the 
process)  through  the  apparatus.  Then  heat  first  the  soda-lime  to 
redness,  and  next  the  mixture  of  the  organic  substance  and  soda- 
lime,  gradually  proceeding  from  the  fore  to  the  hinder  end.  The 

*  Instead  of  hydrogen,  G.  LOGES  (Chemiker-Ztg.,  vin,  1741 ;  Zeitschr.  /. 
analyt.  Chem.,  xxiv,  449)  recommends  using  a  current  of  illuminating 
gas  freed  from  ammonia  by  passing  it  through  a  vertical  tube  filled  with 
glass  beads  moistened  with  diluted  sulphuric  acid  (1  part  concentrated 
sulphuric  acid  and  3  parts  water). 


DETERMINATION   OF    COMMERCIAL   VALUES.  [§  323. 

termination  of  the  combustion  may  be  recognized  on  shutting  off 
the  supply  of  hydrogen,  and  observing  whether  the  height  of  the 
acid  in  the  receiver  suffers  any  change.  If  it  does  not,  and  if  no 
more  gas  bubbles  are  evolved,  extinguish  the  burners,  change  the 
receiver,  and  as  soon  as  the  trough  and  wire  are  no  longer  red-hot, 
withdraw  them  by  means  of  the  hooked  wire,  n,  insert  a  freshly 
charged  trough  in  the  still  hot  tube,  and  proceed  with  a  new  com- 
bustion. 

P.  WAGNER  recommends  the  apparatus  g  f  as  a  receiver.  The 
acid  is  introduced  at  /,  which  is  partly  filled  with  glass-wool.  The 
escaping  hydrogen  is  thus  compelled  to  pass  through  the  glass-wool 
moistened  with  the  sulphuric  acid,  and  hence  gives  up  to  the  acid 
the  last  trace  of  ammonia.  P.  WAGNER  titrates  back  by  adding 
a  little  rosolic  acid  to  the  contents  of  g,  then  adding  titrated  soda- 
lye  until  a  red  color  develops,  then  transferring  the  liquid  to  a 
porcelain  dish,  pouring  back  again  into  the  receiver  through  /, 
thence  back  again  into  the  porcelain  dish,  and  finally  completing 
the  titration.  The  receiver  is  rinsed  out  a  second  and  a  third  time 
with  the  titrated  liquid,  finally  adding,  if  necessary,  more  soda-lye 
until  the  end-reaction  persists. 

Should  the  end-reaction  not  be  sufficiently  sharp  because  of  the 
coloration  of  the  acid  by  empyreumatic  products,  add  to. the 
titrated  liquid  a  few  drops  acid,  evaporate  to  dryness  on  the  water- 
bath,  rinse  the  residue  with  the  aid  of  10  c.c.  water  into  the  azo- 
tometer,  and  determine  the  nitrogen  (p.  885  this  volume).  P. 
WAGNER  points  out  that  when  employing  this  method,  the  acid 
very  seldom  exhibits  a  color,  and  that  the  method  will  give  trust- 
worthy results  even  with  such  substances  as  blood  meal  or  leather 
meal;*  the  results,  however,  can  be  obtained  by  combustion  in 
a  glass  tube  without  the  current  of  hydrogen,  but  only  with 
greater  difficulty. 

2.  If  it  is  impossible  to  effect  the  comminution  of  the  organic 

*  Compare  KREUSLER'S  investigations  (Landwirthschaftl.  Versuchsstationen, 
xxxi,  248 ;  Zeitschr.  /.  analyt.  Chem.,  xxiv,  446)  which  in  general  confirm  those 
of  WAGNER.  Since  §§186  and  187  were  written,  numerous  other  treatises 
have  been  written  regarding  combustions  with  soda-lime,  and  may  be  found 
in  the  Zeitschrift  fur  analytische  Chemie. 


§  324-]  ANALYSIS    OF    MANURES.  897 

substance  required  in  the  VARRENTRAPP-WILL  method,  or  at  least 
if  it  requires  a  long  time  to  effect  it,  treat  the  weighed  substance, 
e.g.,  horn  shavings,  wool,  or  the  like,  with  concentrated  sulphuric 
acid,  with  the  aid  of  heat,  if  necessary,  until  a  clear,  thickish  liquid 
results.  After  sufficient  action,  neutralize  the  excess  of  acid 
carefully  with  finely  powdered  calcium  carbonate,  and  then  mix  the 
dry  powder  so  obtained  with  soda-lime  (GRAXDEAU,*  KRAUCH  |). 
CRETE,  J  who  essentially  recommended  the  same  treatment,  neu- 
tralizes the  sulphuric  acid  with  soda-lime.  I  would  point  out  that, 
by  the  action  of  sulphuric  acid  on  nitrogenous  organic  substances 
on  heating,  ammonium  sulphate  may  be  formed  (compare  KJEL- 
DAHL'S method  below),  hence  in  such  cases  care  must  be  taken 
that  on  adding  the  soda-lime  no  loss  of  ammonia  occurs.  If  it  is 
advisable  to  use  a  large  quantity  of  the  substance  under  examina- 
tion in  order  to  obtain  a  correct  average  sample,  weigh  the  dry 
powder  obtained  after  the  treatment  with  sulphuric  acid  and 
calcium  carbonate,  and  take  an  aliquot  part  for  the  combustion 
with  the  soda-lime. 

6.  KJELDAHL'S  Method. § 
§324. 

KJELDAHL'S  method  is  based  upon  the  fact,  previously  unknown, 
that  the  nitrogen  of  nitrogenous  organic  substances  is  converted 
into  ammonia  on  heating  the  substances  for  some  time  with  a 
large  quantity  of  sulphuric  acid  at  a  temperature  approaching 
the  boiling-point  of  the  acid,  and  then  oxidizing  with  potassium 
permanganate  the  solution  so  obtained.  After  supersaturating 
with  soda-  or  potassa-lye,  the  ammonia  formed  can  be  distilled  off 
and  determined  by  the  usual  methods. 

*  His  Handbuch  /.  agriculturchem.  Analysen,  German  edit.,  p.  18. 

t  Chemiker-Ztg.,  v,  703. 

J  Zeitschr.  /.  analyt.  Chem.,  xvm,  486. 

§  Ibid.,  xxn,  366.  As  this  method  is  of  great  importance  for  the  de- 
termination of  nitrogen,  not  only  in  manures,  but  also  in  inorganic  sub- 
stances generally,  and  could  not  be  described  earlier  in  this  work,  I  give  it 
here  in  full  detail. 


898  DETERMINATION   OF   COMMERCIAL  VALUES.  [§  324. 

The  reactions  occurring  in  this  interesting  process  were  first 
investigated  by  DAFERT,*  and  are  stated  by  him  to  be  as  follows : 

1.  The  sulphuric   acid  abstracts  from  the  organic  substance 
the  elements  of  water,  with  the  formation  of  the  latter. 

2.  The  sulphurous  acid  produced  by  heating  the  sulphuric  acid 
with  the  resulting  carbonized  mass,  exerts  a  reducing  action  on  the 
nitrogenous  organic  matter. 

3.  The  powerful  oxidizing  action  of   the   potassium  perman- 
ganate converts  any  stable  nitrogenous  decomposition  products 
into  ammoniacal  compounds. 

The  reaction  described  under  2  is  the  general  and  principal  one; 
that  mentioned  under  3  can  be  considered  only  as  completing  it 
under  certain  circumstances. 

'According  to  ASBOTH,!  hydrogen  is  also  evolved  by  the  action 
of  sulphuric  acid  on  organic  substances  containing  hydrogen,  and 
this  latter  effects  the  conversion  of  the  nitrogen  into  ammonia. 
He  bases  this  opinion  upon  the  fact  that  the  whole  of  the  nitrogen 
is  obtained  as  ammonia  only  when  there  is  no  lack  of  substances 
containing  hydrogen  present. 

KJELDAHL'S  method  was  very  soon  and  repeatedly  tested,  after 
being  made  public,  and,  as  already  above  mentioned,  has  gained 
general  recognition  both  in  its  original  form  and  in  its  various 
modifications,  because  of  the  ease  and  rapidity  with  which  it  may 
be  carried  out.  from  its  extended  applicability,  on  account  of  the 
reliability  of  its  results,  as  well  as  on  account  of  its  inexpensiveness. 
The  method,  as  may  be  seen  from  what  has  already  been  stated, 
comprises  two  operations,  namely:  a. — Decomposition  of  the  or- 
ganic substance  and  conversion  of  the  nitrogen  into  ammonia ;  and 
6. — Determination  of  the  ammonia  in  the  solution  obtained  in  a. 

In  the  following  I  will  first  describe  the  method  in  its  original 
form,  and  will  then  describe  the  modifications  proposed  and  adopted. 

*  Zeitschr.  f.  analyt.  Chem.,  xxiv,  455. 

f  Chem.  CentralbL,  1886,  165;  Zeitschr.  f.  analyt.  Chem.,  xxv,  575. 


§  325.]  ANALYSIS    OF    MANUKES. 


a.     KJELDAHL'S  Original  Method. 
§325. 

If  the  substance  contains  from  1  to  2  per  cent,  nitrogen  weigh 
off  about  0  •  7  grm. ;  if  it  contains  about  5  per  cent,  weigh  off  0  •  25 
grm.*  The  substance  need  be  comminuted  only  to  such  an  extent 
as  to  enable  a  true  average  sample  to  be  obtained,  and  the  weighing 
may  be  effected  in  the  small  flask  in  which  solution  is  to  be  effected. 
The  flask  should  have  a  capacity  of  about  100  c.c.,  and  be  of  good, 
refractory  glass ;  its  neck  should  be  rather  long  and  narrow.  If  the 
substance  is  a  liquid,  take  a  quantity  of  it  containing  the  proper 
quantity  of  dry  matter,  and  evaporate  the  solvent  f  (if  no  loss  of 
ammonia  is  feared  thereby)  in  a  drying-closet,  or  on  the  water-bath 
in  a  current  of  air  freed  from  ammonia.  Now  introduce  into  the 
flask  10  c.c.  of  sulphuric  acid  to  which,  to  compensate  for  the  water 
it  contains,  a  little  fuming  sulphuric  acid,  or  preferably  phosphoric 
anhydride,|  is  added;  then  fix  the  flask  in  a  slanting  position  dur- 
ing the  reaction,  and  heat  on  a  wire  gauze  with  a  small  flame.  As 
during  the  course  of  the  operation  copious  fumes  of  sulphuric  and 
sulphurous  acids  are  evolved,  the  heating  should  be  done  under  a 
good  draught.  As  a  rule,  the  contents  of  the  flask  at  first  become 
black  and  tarry.  On  continued  heating  to  near  the  boiling-point 
of  the  acid,  when  the  liquid  lightly  " bumps"  from  time  to  time, 
a  brisk  reaction  sets  in  with  evolution  of  gas,  during  which  the  sub- 
stance is  completely  dissolved.  When  the  evolution  of  gas  slackens, 

*  When  the  substance  is  still  richer  in  nitrogen,  KJELDAHL  recommends 
instead  of  taking  a  smaller  quantity,  to  weigh  off  about  four  times  the  neces- 
sary quantity,  and  to  make  up  the  acid  solution  to  100  c.c.,  taking  then  25 
c.c.  for  the  determination  of  the  ammonia. 

t  Urine  should  not  be  evaporated,  PFLUGER  and  BORLAND  (Zeitschr.  /. 
analyt.  Chem.,  xxiv,  636). 

|  The  sulphuric  acid  or  mixture  of  acids  must  be  free  from  ammonia 
and  carefully  guarded  from  contamination  with  it.  For  the  sake  of  certainty 
treat  0-5  grm.  pure  sugar  with  10  c.c.  acid  exactly  as  detailed  in  the  text, 
oxidizing  with  potassium  permanganate,  and  then  distil  with  soda  or  potassa 
lye.  If  any  ammonia  is  hereby  obtained,  the  quantity  must  be  deducted 
from  the  result  obtained  in  determination  (see  the  calculation  of  the  analysis). 


900  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  325. 

the  condensed  vapors  of  sulphuric  acid  wash  the  sides  of  the  flask 
clean  again,  and  carry  back  into  the  liquid  the  carbonaceous  par- 
ticles that  have  been  spirted  up.  After  heating  for  about  two  hours 
continuously,  the  solution  appears  clear,  and  is  pale-brown.  It  is 
unnecessary,  however,  in  the  case  of  many  substances  (e.g.,  albu- 
minous substances  and  their  derivatives),  to  prolong  the  action 
for  so  long  a  time,  as  the  object  is  effected  by  heating  for  an  hour 
or  two,  and  even  though  the  mixture  is  still  black.  In  the  case  of 
substances,  however,  that  offer  greater  resistance  to  the  conversion 
of  their  nitrogen  into  ammonia,  it  is  best  to  prolong  the  heating 
until  incipient  decolorization,  which  is  most  easily  effected  with 
the  aid  of  phosphoric  anhydride. 

As  a  rule,  on  treatment  with  sulphuric  acid  or  a  mixture  of  this 
with  phosphoric  anhydride,  the  greater  part  of  the  nitrogen,  and 
with  many  substances,  e.g..  uric  acid,  gluten-proteids,  etc.,  even 
the  whole,  is  converted  into  ammonia ;  but  with  other  albuminoid 
substances  and  most  bodies  belonging  to  the  fatty  series  only  90 
to  95  per  cent,  is  converted  into  ammonia,  and  in  the  case  of  certain 
alkaloid  (quinine,  morphine)  only  25  to  40  per  cent,  of  nitrogen  is 
thus  converted. 

When  the  action  of  the  acid  is  at  an  end,  remove  the  flame,  and 
add  to  the  liquid  powdered  potassium  permanganate  in  small  por- 
tions, which  may  be  added  in  rapid  succession,  and  best  in  the  form 
of  a  continuous  shower  of  dust.*  The  reaction  is  very  brisk,  and 
is  accompanied  by  the  evolution  of  greenish  vapors  and  strong 
detonations;  frequently  small  flashes  of  flame  are  also  seen.  No 
loss  of  ammonia  occurs  during  the  operation. 

The  at  first  usually  dark  liquid  rapidly  becomes  paler  by  the 
action  of  the  permanganate,  then  colorless,  and  on  further  addition, 
dark-green,  or,  if  phosphoric  anhydride  has  also  been  used,  bluish- 
green  from  the  formation  of  manganic  salts.  When  these  colors 
appear  the  oxidation  is  complete;  then  allow  the  liquid  to  cool. 

*  For  producing  this  KJELDAHL  recommends  a  wide  glass  tube  with 
narrow  mouth-piece,  e.g.,  the  upper,  broken-off  part  of  a  condenser  tube, 
within  the  lower  part  of  which  a  small,  sufficiently  fine  piece  of  wire  gauze  is 
fixed:  on  gently  tapping  the  tube  filled  with  dry,  quite  finely  powdered 
potassium  permanganate,  this  falls  through  the  gauze. 


§  325.]  ANALYSIS   OF   MANURES.  901 

Next  dilute  the  cooled  acid  solution  by  pouring  it  into  the  dis- 
tilling flask  containing  water,  and  rinsing  out  well  with  water.  On 
adding  the  water  the  green  color  of  the  liquid  passes  into  brown. 
The  distilling  flask  should  have  a  capacity  of  about  750  c.c.,  and 
the  exit  tube  with  which  it  is  provided,  is  bent  obliquely  upwards, 
and  is  connected  with  a  condenser.  KJELDAHL  prefers  for  this  a 
spiral  tube  the  exit  end  of  which  is  connected  with  an  absorption 
apparatus.  The  latter  may  be  a  250-c.c.  ERLENMEYER  flask  fitted 
with  a  two-holed  rubber  stopper;  the  straight  lower  part  of  the 
condenser  passes  through  one  hole  to  about  the  centre  of  the 
flask,  without  dipping  into  the  acid,  while  in  the  other  hole  is  fitted 
a  glass  tube  bent  at  a  right  angle  and  open  to  the  air. 

Introduce  into  the  absorption  flask  30  c.c.  semi-decinormal 
sulphuric  acid,  remove  the  stopper  of  the  distilling  flask,  introduce 
a  few  zinc  turnings  in  order  to  prevent  ''bumping0  during  boiling, 
then  immediately  run  in  40  c.c.  soda-lye  of  1-3  sp.  gr.,  replace  the 
stopper  without  delay,  and  heat  the  now  alkaline  liquid  until  all  the 
ammonia  has  gone  over,  which  is,  as  a  rule,  the  case  when  about 
one-half  of  the  liquid  has  been  distilled  off.  * 

The  ammonia  in  the  receiver  can  now  be  determined  by  any 
suitable  method.  KJELDAHL  prefers  one  of  the  older  volumetric 
methods  now  but  little  used,  and  which  is  based  upon  the  fact  that, 
on  adding  an  acid  to  a  mixture  of  potassium  iodate  and  potassium 
iodide,  a  quantity  of  iodine  is  liberated  equivalent  to  that  of  the 
acid,  and  may  be  titrated  by  means  of  sodium  thiosulphate.  To 
carry  out  this  process,  dissolve  a  few  crystals  of  potassium  iodide 
in  the  still  acid  liquid  in  the  absorption  flask,  then  add  a  not  too 
small  quantity  of  well-made,  thin  starch  paste,  followed  by  a  few 
drops  of  a  4-per-cent.,  potassium-iodate  solution,  and  lastly  a 
titrated  solution  of  sodium  thiosulphate  (about  equal  to  the  semi- 
decinormal  acid)  until  decolorization.  As  such  a  dilute  solution 
of  sodium  thiosulphate  possesses  but  little  stability,  its  titre  must 
be  newly  determined  for  every  series  of  tests,  and  this  may  be  done 
by  means  of  iodine,  as  in  §  146,  or  as  above,  by  aid  of  a  titrated  acid. 

KJELDAHL  checks  his  results,  as  above  mentioned,  by  treating 
0-5  grm.  pure  sugar  exactly  in  the  manner  detailed,  employing 


902  DETERMINATION    OF    COMMERCIAL   VALUES.  [§  326. 

like  quantities  of  acids  and  other  reagents  in  order  to  eliminate  any 
errors  due  to  the  presence  of  nitrogen  in  the  reagents.  If  30  c.c. 
of  sodium-thiosulphate  solution  are  required  for  30  c.c.  of  semi- 
decinormal  sulphuric  acid,  but  only  29-8  c.c.  have  been  used  in  the 
control  experiment,  then  this  latter  figure  must  be  used  in  calcu- 
lating the  analysis. 

The  calculation  is  very  simple.  The  number  of  c.c.  of  semi- 
decinormal  sodium-thiosulphate  solution  corresponding  with  the 
neutralized  acid  is  multiplied  by  7  •  02  (half  the  equivalent  of  nitro- 
gen). The  number  so  obtained,  divided  by  the  number  of  centi- 
grammes of  substance  taken,  gives  the  percentage  content  of  nitro- 
gen. As  an  example,  KJELDAHL  gives  a  determination  of  nitrogen 
in  barley. 

0-645  grm.  of  barley  was  treated  as  above  described,  and  30  c.c. 
of  semi-decinormal  sulphuric  acid  were  taken.  The  relation  found 
between  this  and  the  semi-decinormal  sodium-thiosulphate  solu- 
tion in  the  control  test  was  found  to  be  30  :  29-8.  Titrating  back 
required  14-5  c.c.  of  the  thiosulphate  solution: 

IK  Q v 7  02 

29.8-14.5=15-3;  -    l^-^!  =  1 . 66  per  cent,  nitrogen. 
o4  •  o 

/?.  Modifications  of  KJELDAHL'S  Method. 
§326. 

As  may  be  seen  from  what  has  been  said  in  §  325,  KJELDAHL'S 
method  was  first  introduced  in  a  form  worked  out  with  the  greatest 
care,  and  the  test  analyses  given  by  KJELDAHL  also  leave  scarcely 
anything  to  be  desired  so  far  as  accuracy  is  concerned.  Notwith- 
standing this,  nearly  all  chemists  who  have  busied  themselves  with 
the  testing  and  employment  of  this  method — and  their  number  is 
large,  as  may  be  seen  by  reference  to  the  foot-note  * — have  em- 
ployed and  recommended  modifications : 

*  HEFFTER,  HOLLRUNG,  and  MORGEN  (Chemiker-Ztg.,  vni,  432;  Zeitschr. 
j.  analyt.  Chem.,  xxin,  553) ;  PETRI  and  TH  LEHMANN  (Zeitschr.  /.  physiolog. 
Chem.,  vin,  200;  Zeitschr.  f.  analyt.  Chem.,  xxin,  596) ;  E.  BOSSHARD  (Zeitschr. 
/.  analyt.  Chem.,  xxiv,  199);  E.  PFLUGER  and  K.  BORLAND  (Archiv.  /.  d. 


§  326.]  ANALYSIS   OF   MANUEES.  903 

Of  this  number,  many  are  but  slight  modifications.  WILFARTH'S 
modification,  however,  is  of  more  importance,  as  are  also  those  of 
v.  ASBOTH  and  JODLBAUER,  with  reference  to  the  determination 
of  nitrogen  in  nitrates. 

I  will  first  touch  upon  the  slighter  modifications,  then  upon 
WILFARTH'S,  and  lastly  upon  the  modifications  by  v.  ASBOTH  and 
JODLBAUER. 

As  nearly  all  of  the  chemists  cited  in  the  foot-note  titrate  the 
excess  of  acid  in  the  ammonia  determination  by  the  usual  acidi- 
metric  method  with  baryta  water  or  soda-lye,  using  litmus  or 
another  indicator,  and  without  commenting  upon  the  KJELDAHL 
method  of  separating  iodine  and  determining  this,  they  use  larger 
quantities  of  substance  (1  to  1-5  grm.),  larger  flasks  for  heating 
(150  to  250  c.c.  capacity),  and  20  c.c.  of  the  acid  mixture  instead 
of  10  c.c.  Regarding  this  last,  many  discard  the  fuming  sulphuric 
acid  (which  often  contains  nitric  acid)  and  as  an  acid  mixture 
employ  a  solution  of  200  grm.  phosphoric  anhydride  in  1  litre  of 
pure  concentrated  sulphuric  acid,  while  others  employ  a  mixture 
of  equal  volume  of  concentrated  and  fuming  sulphuric  acid, 
others  again  preferring  either  this  mixture  or  one  of  4  volumes  of 
concentrated  and  1  volume  of  fuming  sulphuric  acid  with  the  addi- 
tion of  100  grm.  of  phosphoric  anhydride  per  litre  of  mixture. 
BRUNNEMANN  and  SEYFERT  mix  the  substance  with  2  grm. 
phosphoric  anhydride,  then  heat  with  5  c.c.  of  a  mixture  of  4 
volumes  concentrated  and  1  volume  of  fuming  sulphuric  acid 

gesammte  Physiolog.,  xxxv,  454,  and  xxxvi,  102;  Zeitschr.  /.  analyt,  Chem., 
Kxrv,  299  and  635);  TH.  PFEIFFER  and  F.  LEHMANN  (Zeitschr.  f.  analyt. 
Chem.,  xxiv,  388);  KREUSLER  (ibid.,  xxiv,  393  and  453;  Landwirthschaftl. 
Versuchsstationen,  xxxi,  269)  ;  C.  ARNOLD  (Archiv.  der  Pharm.  [3],  xxin,  177; 
Zeitschr.  f.  analyt.  Chem.,  xxiv,  454;  Chem.  Centralbl,  1886,  p.  337).;  F.  W. 
DAFERT  (Zeitschr.  f.  analyt.  Chem.,  xxrv,  454);  H.  WILFARTH  (Chem.  Cen- 
tralbl. [3],  xvi,  17  and  113;  Zeitschr.  f.  analyt.  Chem.,  xxiv,  455);  BALCKE 
(Wochenschr.  f.  Brauerei,  I,  No.  11);  P.  KULISCH  (Zeitschr.  /.  analyt.  Chem,, 
xxv,  149) ;  RINDELL  and  HANNIN  (ibid.,  xxv,  155) ;  CZECZETKA  (Monats- 
hefte  f.  Chem.,  vi,  63:  Zeitschr.  f.  analyt.  Chem.,  xxv,  252);  A.  v.  ASBOTH 
(Chem.  Centralbl.,  1886,  p.  161) ;  ULSCH  (ibid.,  375) ;  M.  JODLBAUER  (ibid., 
433) ;  BRUNNEMANN  and  SEYFERT  (Chemiker-Ztg.,  vm,  1820) ;  R.  WARINGTON 
(Chem.  News,  LII,  162:  Zeitechr.  f.  analyt.  Chem.,  xxv,  427). 


904  DETERMINATION   OF    COMMERCIAL    VALUES.          [§  326. 

until  the  brisk  evolution  of  gas  slackens,  and  then  continue  the 
heating  after  a  further  quantity  of  15  c.c.  of  the  acid  mixture  has 
been  added. 

Other  changes  are  such  as  are  concerned  with  the  manner, 
intensity,  and  duration  of  heating;  all  agree,  however,  that  it  is 
safest  to  prolong  the  action  until  the  solution  acquires  the  color 
of  Rhine  wine,  or  appears  reddish  or  colorless.  HEFFTER,  HOLL- 
RUNG  and  MORGEN,  and  also  KREUSSLER,  have  described  special 
stoves  for  heating  a  number  of  flasks  at  the  same  time.  KREUSSLER 
places  on  the  flask  a  cylindrical  glass  vessel  open  above  and  below, 
in  order  to  lessen  the  evolution  of  acid  vapors.  ULSCH  employs 
glass  bulbs  with  stems. 

CZECZETKA  employs  for  oxidizing  purposes  a  solution  of  potas- 
sium permanganate  in  concentrated  sulphuric  acid  instead  of  the 
powdered  salt. 

A  500-  to  750-c.c.  flask  is  sufficient  for  the  distillation,  even 
when  larger  quantities  of  the  substance  and  20  c.c.  of  the  acid 
mixture  are  used.  The  quantity  of  liquid  to  be  distilled  should  be 
from  200  to  250  c.c.,  according  to  the  quantity  of  water  used  for 
dilution.  The  alkali  solution  (preferably  potassa  solution,  which 
is  less  likely  than  soda  to  cause  bumping  during  boiling)  is  added 
to  the  cold,  diluted  liquid,  and  it  is  best  to  add  it  first  in  quantity 
sufficient  to  nearly  neutralize  the  acid,  then  to  cool  the  liquid,  and 
then  to  add  a  further  quantity  of  the  alkali  solution  in  sufficient, 
but  not  too  great,  excess.  When  employing  zinc  turnings,  it  is 
especially  necessary  to  avoid  too  large  an  excess  of  alkali,  because 
if  the  evolution  of  hydrogen  becomes  too  violent,  it  is  difficult  to 
prevent  drops  of  alkali  solution  from  being  carried  over,  even 
when  employing  safety  apparatus,  of  which  many  have  been  pro- 
posed. If  the  lye  contains  nitric  acid,  the  nitrogen  of  this  is  con- 
verted into  ammonia  on  using  zinc.  In  order  to  prevent  bumping, 
it  has  been  recommended  to  pass  in  a  gentle  current  of  steam  or 
air.  The  form  of  the  distilling-flask  and  receiver  may  of  course 
be  variously  modified.  It  is  always  advisable  to  have  several 
bulbs,  which  are  to  be  partly  filled  with  fragments  of  glass,  blown 
on  the  tube  connecting  the  distillation-flask  with  the  condenser 


§  326.]  ANALYSIS   OF   MANURES.  905 

tube.  The  apparatus  shown  in  Fig.  81,  and  described  in  Vol.  I, 
p.  254,  is  excellently  adapted  for  the  purpose,  and  so  also  is  the  one, 
so  far  as  the  receiver  is  concerned,  described  on  p.  884  this  volume, 
Fig.  137. 

If,  as  recommended  by  most  of  the  chemists  above  cited,  a 
larger  quantity  of  substance  is  taken,  a  stronger  acid  than  the 
semi-decinormal  recommended  by  KJELDAHL  must  be  employed, 
in  fact  normal,  seminormal,  or  decinormal  acid. 

When  titrating  according  to  the  iodine  method  proposed  by 
KJELDAHL,  both  PFLUGER  and  BORLAND,  who  have  retained  and 
recommended  the  method,  point  out  that  the  last  small  quantities 
of  free  acid  require  some  time  to  decompose  the  mixture  of  potas- 
sium iodide  and  iodate,  particularly  in  the  case  of  very  dilute  solu- 
tions. Twenty-four  hours  are  required  for  complete  decomposition, 
but  at  the  end  of  one  or  two  hours  the  error  amounts  only  to  at 
most  0-1  to  0-2  c.c.  of  decinormal  sodium-thiosulphate  solution. 

When  titrating  the  excess  of  acid  by  the  usual  acidimetric 
methods,  many  prefer  baryta  water  to  potassa-  or  soda-lye.  The 
indicators  to  be  specially  recommended  are  SCHLOSING'S  prepara- 
tion of  litmus,*  p.  845  this  volume,  methyl  orange,  and  phenacet- 
olin  (THOMSON  f). 

WILFARTH'S  modification  is  based  upon  the  fact  that  the  addi- 
tion of  metallic  oxides  facilitates  the  action  of  the  acid  mixture  on 
the  organic  mixture;  the  most  suitable  have  been  found  to  be 
cupric  oxide,  and  particularly  mercuric  oxide  prepared  by  the  wet 
way  (when  prepared  by  the  dry  way  the  mercuric  oxide  is  apt  to 
contain  nitric  oxide).  WILFARTH'S  modification,  which  has  proved 
satisfactory  in  every  respect,  is  carried  out  as  follows :  Mix  1  grm. 
of  the  nitrogenous  substance  (if  poor  in  nitrogen  2  to  3  grm.  may 
be  taken)  with  20  c.c.  of  an  acid  mixture  consisting  of  3  volumes 
of  pure,  concentrated  sulphuric  acid  and  2  volumes  of  fuming  sul- 
phuric acid  and  with  the  addition  of  0  •  7  grm.  of  the  mercuric  oxide 
prepared  by  the  wet  way  (or  an  equivalent  quantity  of  mercuric 

*  Compare  RINDELL  and  HANNIN,  Zeitschr.  f.  analyt.  Chem.,  xxv,  155. 
t  Ibid.,  xxiv,  225. 


906  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  326. 

sulphate  or  metallic  mercury),  and  heat  in  a  flask,  which  should 
be  of  good  potash  glass,  on  a  wire  gauze  over  a  naked  flame,  gently 
at  first,  then  somewhat  more  strongly,  and  finally  to  gentle  boiling. 
On  continuing  the  heat  until  the  liquid  has  become  colorless,  the 
oxidization  with  potassium  permanganate  will  be  unnecessary; 
if  it  is  desired,  however,  to  save  time,  heat  only  until  the  liquid  has 
acquired  the  color  of  light  Rhine  wine,  and  then  oxidize  with  potas- 
sium permanganate.  After  it  has  been  diluted,  and  made  alkaline 
with  potassa-lye,  as  above  described,  add  a  quantity  of  solution 
of  sulphurated  potassa  (40  g-m.  sulphurated  potassa  per  litre) 
more  than  corresponding  to  the  mercury  used,  and  whereby  the 
mercury  is  precipitated  as  sulphide.  In  order  to  ascertain  the 
approximate  quantity  of  sulphurated-potassa  solution  required, 
dissolve  0  •  5  grm.  mercuric  oxide  in  diluted  sulphuric  acid  and  then 
find  out  how  much  of  the  sulphurated  potassa  solution  is  required 
to  completely  precipitate  it.  It  is  advisable  to  employ  a  con- 
siderable excess  of  the  sulphurated-potassa  solution,  in  order  to 
be  certain  of  the  complete  decomposition  of  the  mercuro-ammo- 
nium  compounds.  It  is  only  after  twice  or  thrice  the  requisite 
quantity  has  been  added  that  the  odor  of  hydrogen  sulphide  be- 
comes perceptible,  but  this  does  not  affect  the  accuracy  of  the 
results.  No  bumping  occurs  when  the  liquid  holds  mercuric  sul- 
phide in  suspension,  at  least  not  when  potassa-lye  is  used;  of  course, 
a  little  zinc  may  also  be  added. 

WILFARTH'S  method  has  also  been  modified;  thus  KULISCH 
recommends  an  acid  mixture  of  equal  volumes  of  concentrated  and 
fuming  sulphuric  acids  containing  100  grm.  phosphoric  anhy- 
dride per  litre.  He  obtained  absolutely  accurate  results  with  the 
substances  (wine  yeast  and  must  extract)  only  when  the  heating 
was  prolonged  until  the  liquid  became  colorless,  and  then  sub- 
sequently oxidized  with  potassium  permanganate.  KULISCH 
also  recommends  adding  a  small  quantity  of  metallic  mercury. 
ARNOLD  uses  0  •  5  grm.  cupric  sulphate  and  1  grm.  metallic  mercury, 
while  ULSCH  employs  0  •  05  grm.  cupric  oxide  and  5  drops  (but  no 
more)  of  a  platinic-chloride  solution  1  c.c.  of  which  contains  0-04 
grm.  platinum. 


§  326.]  ANALYSIS  OF   MANURES.  907 

If  the  nitrogen  is  present  in  the  form  of  nitric  acid,  neither  the 
original  KJELDAHL  method  nor  the  WILFARTH  modification  will 
yield  good  results.  The  object,  may,  however,  be  effected  by 
making  certain  additions;  \hus  according  to  v.  ASBUTH  (.oc.  dt.) 
fairly  good  results  are  obtained  by  adding  benzoic  acid.  He  recom- 
mends using  1  •  75  benzoic  acid  to  0  •  5  grm.  potassium  nitrate,  finally 
decomposing  the  difficultly  decomposab.e  benzoate  with  po.assium 
permanganate  and  subsequent  prolonged  heating.  If  the  nitrogen 
is  present  as  oxide,  or  in  he  form  of  cyanogen,  v.  ASBOTH  adds 

1  grm.  sugar;  as  the  metallic  addition,  he  employs  0-5  grm.  cupric 
sulphate.     The  distillation  is  effected  after  the  addition  of  a  solu- 
tion of  Rochelle  salt  in  soda-lye  (350  grm   sodium  pota  shim  tar- 
trate  and  300  grm.  sodium  hydroxide  dissolved  in  1  litre  water), 
in  order  to  keep  the  cupric  and  manganous  oxides  in  solution. 

According  to  JODLBAUER  (loc.  a';.)  the  addition  of  benzoic  acid 
when  nitrates  are  present  does  not  with  certainty  yield  sufficiently 
satisfactory  results,  but  they  are  satisfactory  on  treating  0-2  to  0-5 
grm.  potassium  nitrate  (or  a  corresponding  quantity  of  another 
nitrate)  with  20  c.c.  concentrated  sulphuric  acid  and  2  •  5  c.c.  phenol- 
sulphuric  acid  (obtained  by  dis  olving  50  grm.  phenol  in  concen- 
trated sulphuric  acid  to  make  100  c.c.),  with  the  addition  of  from 

2  to  3  grm.  zinc  dust  and  5  drops  of  a  platinic-chloride  solution, 
1  c.c.  of  which  contains  0-04  grm.  platinum.     After  heating  for 
about  four  hours,  the  liquid  is  colorless,  and  is  then  ready  for  further 
treatment  and  distillation.     When  a  mixture  of  sulphuric  acid  and 
phosphoric  anhydride  is  employed,  heating  for  two  hours  already 
suffices,  but  then  the  decomposing  flask  is  strongly  attacked,  and 
in  a  short  time  becomes  unserviceable. 

F.  ANALYSIS  OF  MANURES  CONTAINING  TWO  OR  MORE  MANURIAL 

SUBSTANCES. 

In  order  to  afford  some  data  for  a  choice  of  methods  suitable 
for  all  cases,  I  give  here  a  general  process  first,  applicable  not  only 
to  stable  manure,  but  also  to  nearly  all  kinds  of  manures,  and  will 
then  proceed  to  detail  the  methods  which  are  specially  adapted 
for  commercial  manures. 


908  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  327. 

I.  GENERAL  PROCESS. 

§327. 

The  manure  is  uniformly  mixed  by  chopping  and  grinding,  and 
the  several  portions  required  for  the  various  determinations  are  then 
successively  weighed  out.* 

1.    DETERMINATION  OF  WATER. 

Dry  10  grm.  at  110°,  and  determine  the  loss  of  weight  (§  29). 
(It  will  be  but  seldom  necessary  to  make  a  correction  for  the  ammo- 
nium carbonate  that  escapes  with  the  water,  f) 

2.    TOTAL   FIXED    CONSTITUENTS. 

Incinerate  a  weighed  portion  of  the  residue  obtained  in  1,  in  a 
platinum  dish  or  large,  obliquely  placed  platinum  crucible,  at  a 
gentle  heat  (pp.  794  and  795,  this  volume),  moisten  the  ash  with 
a  solution  of  ammonium  carbonate,  allow  to  dry,  gently  ignite, 
and  then  weigh. 

3.    CONSTITUENTS   BOTH    SOLUBLE   AND   INSOLUBLE   IN   WATER. 

Digest  10  grm.  of  the  fresh  manure  with  about  300  c.c.  water, 
collect  the  residue  on  a  weighed  filter  (§  50),  wash,  dry  at  110°,  and 
weigh.  The  total  weight  of  insoluble  constituents  is  thus  obtained, 
and  the  difference — after  deducting  the  water  as  found  in  1 — will 
give  the  weight  of  those  soluble  in  water.  Now  incinerate  the 
insoluble  residue,  treat  with  ammonium  carbonate  as  in  2,  weigh, 
and  thus  ascertain  the  total  weight  of  the  fixed  constituents  con- 
tained in  the  insoluble  portion,  and  from  the  difference,  the  total 
quantity  of  those  contained  in  the  soluble  part. 

4.    FIXED    CONSTITUENTS   SINGLY. 

Dry  a  larger  portion  of  the  manure,  and  treat  it  exactly  as  in 
one  of  the  methods  given  for  the  preparation  and  analysis  of  plant 
ashes. 

*  Accurate  directions  for  obtaining  a  correct  average  sample  of  stable 
manure  are  given  in  E.  WOLFF'S  Anleitung  zur  chem.  Untersuchung  land- 
wirthschaftl.  wichtiger  Stoffe  (Berlin:  WIEGAND,  HEMPEL,  and  PAREY,  3d 
edit.,  p.  115). 

f  Should  this  happen,  proceed  as  in  the  determination  of  water  in  guano 
(§  331,  1). 


§  328.]  ANALYSIS   OF  MANURES.  909 

5.    TOTAL    CARBON. 

Subject  a  portion  of  the  residue  obtained  in  1  to  elementary 
analysis;  as  manures  may  contain  chlorine  and  sulphur  com- 
pounds, it  is  best  to  make  the  combustion  with  lead  chromate 
V§  176).  On  account  of  the  nitrogen  content,  and  also  of  inor- 
ganic substances  present,  what  has  been  said  in  §§  183  and  191, 
respectively,  must  be  borne  in  mind.  If  the  dried  manure  con- 
tains carbonates,  the  carbonic  acid  must  be  determined  in  a  separate 
portion.  On  deducting  this  from  the  quantity  found  in  the  ele- 
mentary analysis,  the  difference  will  give  the  quantity  derived 
from  the  carbon  of  the  organic  matter.  The  method  given  on 
p.  510  this  volume  (oxidation  of  the  organic  matter  with  chromic 
acid  with  the  addition  of  sulphuric  acid)  may  also  occasionally  be 
employed  with  good  results,  particularly  if  no  chlorine  compounds 
are  present.*  When  carbonates  are  present,  the  properly  diluted 
sulphuric  acid  is  first  allowed  to  act  alone,  until  all  carbon  dioxide 
has  been  evolved,  before  adding  the  chromic  acid  and  connecting 
the  decomposing-flask  with  the  ab  orption  apparatus. 

6.    SULPHUR    COMPOUNDS. 

If  the  manures  contain  unoxidized  sulphur  (as,  for  instance,  is 
usually  the  case  with  manures  taken  from  the  sewers  of  towns), 
determine  the  total  sulphur  in  a  sample  by  the  method  detailed  for 
soil  analysis  (§  303,  6) ;  then  heat  a  second  portion  with  diluted 
hydrochloric  acid,  repeatedly  if  necessary,  filter,  determine  in  the 
filtrate  the  sulphuric  acid  which  is  present  as  such,  and  from  the 
difference  ascertain  the  unoxidized  sulphur  that  was  present. 

7.    TOTAL   NITROGEN. 

§328. 

If  the  manure,  as  is  frequently  the  case,  contains  the  nitrogen 
in  the  form  of  nitric  acid,  ammonia,  and  in  organic  combination, 
then  DUMAS'  method  (§185)  is  unquestionably  best  adapted 
for  obtaining  the  total  nitrogen  at  one  operation.  KJELDAHL'S 
method  (§§  324  to  326)  and  that  of  VARREXTRAPP-WILL  (§§  186 

*  Compare,  however,  in  this  connection  p.  839,  /3,  this  volume. 


910  DETERMINATION   OF   COMMERCIAL  VALUES.         [§  328. 

and  187),  on  the  other  hand,  cannot  be  used  in  their  original  form 
if  any  notable  quantity  nitric  acid  is  present,  but  the  modifications 
detailed  below  must  be  employed. 

a.  Preparatory  Treatment. 

If  the  manure  is  damp  and  not  homogeneous,  and  gives  off 
ammonia  on  drying,  moisten  a  weighed  quantity  (about  10  grm.) 
with  a  dilute  solution  of  oxalic  acid  so  that  the  whole  mass  is 
neutral  or  only  slightly  acid,  dry  at  about  50°,  weigh,  mix  uni- 
formly, and  employ  portions  of  the  dry  substance  so  obtained 
for  the  nitrogen  determination.  If  the  manure  is  of  a  similar 
character,  but  does  not  give  off  ammonia  on  drying,  treat  it  in  like 
manner,  but  without  adding  oxalic  acid.  If  the  manure,  on  the 
other  hand,  is  dry,  uniform,  and  in  fine  powder,  it  is,  of  course, 
fit  for  examination  without  further  preparation. 

6.  The  Process. 

a.  DUMAS'  Method. — The  only  objection  that  may  be  made 
against  this  method  (which  was  minutely  detailed  in  §  185,  and 
which  was  also  alluded  to  on  p.  894  this  volume),  is,  that  it  is  too 
complicated  for  the  examination  of  manures.  The  employment 
of  it  cannot,  however,  be  avoided  when  it  is  a  question  of  checking 
the  results  of  other  analyses.  Instead  of,  as  in  this  method,  driving 
the  nitrogen  into  the  measuring-cylinder  by  carbon  dioxide,  the 
SPRENGEL  mercury  pump  is  now  being  frequently  employed  with 
the  test  results.  Compare  with  this  the  work  of  FRANKLAND 
and  ARMSTRONG,*  'GiBBS,f  PFLUGER,J  JOHNSOHN  and  JENKINS,§ 
DABNEY,  Jr.,  and  VON  HERFF.|| 

ft.  JODLBAUER'S  Modification  of  KJELDAHL'S  Method  (p.  907, 
this  volume). — This  method,  as  already  mentioned,  also  gives 
accurate  results  when  the  nitrogen  is  present  in  the  form  of  nitric 
acid. 

*  Zeitschr.  f.  analyt.  Chem.,  vm,  489. 
f  Ibid.,  xi,  206. 
J  Ibid.,  xvin,  296. 
§  Ibid.,  xxi,  274. 
||  Ibid.,  xxv,  425. 


§  328.]  ANALYSIS    OF    MANURES.  911 

f.  VARRENTRAPP-WILL'S  Method  and  its  Modifications. — If 
the  quantity  of  nitrates  is  rather  small,  while  that  of  the  organic 
matter  is  sufficiently  large,  then  the  VARRENTRAPP-WILL  method 
in  its  original  form,  or  PELIGOT'S  modification  of  it  (§  187,  see 
also  p.  84,  this  volume)  is  satisfactory.  If,  however,  the  quantity 
of  nitric  acid  is  somewhat  larger,  then  such  modifications  must 
be  chosen  whereby  the  acid  will  be  fully  and  completely  reduced. 
Such  methods  have  been  repeatedly  proposed,  and  as  I  had  no 
occasion  to  describe  them  before  this,  I  will  detail  them  here, 
although  the  modified  methods  no  longer  possess  the  same  im- 
portance they  first  had,  because  of  the  introduction  of  the 
modified  KJELDAHL  method,  which  accomplished  the  object  more 
easily  and  surely. 

The  first  modification  of  the  VARRENTRAPP-WILL  method  to 
be  mentioned  is  that  of  E.  A.  CRETE;*  he  employed  a  mixture  of 
soda-lime  and  xanthogenates  for  converting  the  nitric  acid  into 
ammonia.  Later  on  RUFFLE  f  recommended  a  mixture  of  2 
equivalents  sodium  hydroxide,  1  equivalent  lime,  and  1  equivalent 
of  crystallized  sodium  thiosulphate.  He  used  an  iron  combustion 
tube,  closed  at  the  hinder  end,  and  charged  as  follows :  5  grm.  of  the 
above  mixture  were  placed  in  the  hinder  end,  followed  by  about 
30  grm.  of  the  mixture  triturated  with  from  1  to  1  •  5  grm.  of  the 
substance  to  be  analyzed,  the  latter  having  previously  been  uni- 
formly incorporated  with  1  grm.  of  a  mixture  of  equal  parts  of 
sublimed  sulphur  and  powdered  charcoal;  after  this  follows  more 
soda-lime  mixture,  then  about  18  grm.  pure  soda-lime,  and  lastly 
an  asbestos  plug  which  is  so  placed  as  to  still  leave  about  20  cm. 
of  the  tube  empty.  The  test-analyses  given  by  RUFFLE  are  satisfac- 
tory. In  the  analysis  of  artificial  manures  it  is  at  times  necessary 
to  effect  the  intimate  mixture  of  the  substance  with  sodium  thio- 
sulphate by  evaporating  it  with  a  solution  of  the  thiosulphate. 
A.  GUYARD  (H.  TAMM  J)  proposed  to  heat  to  redness  a  mixture 

*  Ber.  der  deutsch.  Chem.  Gesellsch.  zu  Berlin,  xi,  1557;  Zeitschr.  f.  analyt. 
Chem.,  xvin,  106. 

t  Joum.  Chem.  Soc.,  1881,  p.  87;  Zeitschr.  f.  analyt.  Chem.,  xxi,  412. 
\  Chem.  News,  XLV,  159;  Zeitschr.  f.  analyt.  Chem.,  xxi,  584. 


912  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  328. 

of  the  substance  with  soda-lime  and  dried  sodium  acetate. 
A.  GOLDBERG  *  recommends  a  mixture  of  100  parts  soda-lime, 
100  parts  stannous  sulphide,  and  20  parts  sulphur;  and  with  this 
he  obtained  approximate  (about  0-3  to  1  per  cent,  too  low)  results 
with  potassium  nitrate. 

Most  of  these  modifications  were  critically  tested  by  various 
experimenters,  and  with  very  varying  results.  First,  as  concerns 
RUFFLE'S  method,  CRISPO,!  PELLET,J  and  also  DABNEY,  Jr.,  and 
VON  HERFF§  obtained  good  results  with  it;  FASSBENDER,||  and 
also  ARNOLD, ^[  however,  who  effected  the  combustion  in  glass  tubes 
and  consequently  employed  anhydrous  sodium  thiosulphate, 
obtained  much  less  satisfactory  results.  SHEPHERD**  obtained 
approximately  accurate  results  with  guanos  containing  only 
small  quantities  of  nitre,  but  with  potassium  nitrate  the  results 
were  too  low.  J.  KONIG  ft  reported  that  the  method  gives  correct 
results  with  natural  Peruvian  guanos,  and  even  when  they  contain 
nitrates,  but  the  results  were  too  low  in  the  case  of  artificial  mix- 
tures of  guano  with  saltpetre ;  RUBE  JJ  also  obtained  good  results 
with  manures,  particularly  guano,  and  ascribes  the  unfavorable 
results  recorded  by  others  to  their  not  having  adhered  strictly  to 
RUFFLE'S  original  method,  but  to  having  made  changes  in  it. 

P.  WAGNER  §§  also  obtained  serviceable  results  with  guanos 
containing  potassium  nitrate,  by  employing  the  following  slightly 
modified  method,  in  which  mixtures  having  the  composition  here 
given  are  used:  1. — 100  parts  by  weight  powdered  soda-lime  and 
10  parts  by  weight  oxalic  acid.  2. — 100  grm.  calcined  gypsum 
mixed  with  6  c.c.  concentrated,  pure  sulphuric  acid  (preserved  in 

*  Zeitschr.  f.  analyt.  Chem.,  xxm,  244. 

f  Neue  Zeitschr.  f.  Rubenzuckerindustrie,  ix,  162;  Zeitschr.  f.  analyt. 
Chem.,  xxn,  434. 

|  Rev.  d.  ind.  chim.  ebagr.,  vi,  605;  Zeitschr.  f.  analyt.  Chem.,  xxn,  434. 
§  Amer.  Chem.  Journ.,  vi,  234:  Zeitschr.  f.  analyt.  Chem.,  xxv,  425. 
||  Repert.  d.  analyt.  Chem.,  n,  225;  Zeitschr.  f.  analyt.  Chem.,  xxn,  434. 
If  Arch.  d.  Pharm.  [3],  xx,  92;  Zeitschr.  f.  analyt.  Chem.,  xxn,  435. 
**  Chem.  News,  XLVII,  75;   Zeitschr.  f.  analyt.  Chem.,  xxn,  435. 
ft  Rep.  d.  analyt.  Chem.,  in,  1 ;  Zeitschr.  f.  analyt.  Chem.,  xxn,  436. 
jt  Zeitschr.  /.  analyt.  Chem.,  xxm,  43. 
§§  Chemiker-Ztg.,  vni,  651;  Zeitschr.  /.  analyt.  Chem.,  xxm,  559. 


§  328.]  ANALYSIS   OF   MANURES.  913 

well-stoppered  bottles).  3. — 100  parts  by  weight  of  sodium 
thiosulphate  dried  at  100°,  and  intimately  mixed  in  a  warmed 
mortar  with  100  parts  powdered  and  well-dried  soda-lime,  8  parts 
finely  powdered  charcoal,  and  8  parts  sublimed  sulphur,  all  by 
weight  (to  be  preserved  in  a  long-necked  bottle  closed  by  a  rubber 
stopper).  The  glass  tube  used  for  the  determination  is  40  cm. 
long,  8  mm.  wide,  and  with  one  end  sealed  and  rounded;  it  is 
charged  by  first  introducing  a  5-cm.  long  layer  of  the  mixture  No. 
1 ;  then  1  •  5  grm.  of  an  intimate  mixture  of  equal  parts  by  weight 
of  the  guano  to  be  examined  and  of  mixture  No.  2,  is  mixed  with 
about  20  grm.  of  mixture  No.  3,  and  introduced  without  de!ay  into 
the  tube,  after  which  the  latter  is-  filled  with  granulated  soda-lime, 
and  stoppered  with  an  asbestos  plug.  By  making  blank  com- 
bustions any  correction  that  may  be  necessary  to  make  is  ascer- 
tained. 

GRETE'S  method  afforded  J.  KONIG  (loc.  cit.)  results  like  those 
of  RUFFLE;  TAMM'S  method,  on  the  other  hand,  found  no  de- 
fender, although  C.  ARNOLD*  and  subsequently  HouzEAuf  also 
sought  to  combine  the  methods  of  RUFFLE  and  TAMM,  and  with 
success.  In  his  most  recent  publication  C.  ARNOLD  J  recommends 
igniting  0-5  grm.  of  the  substan  e  (or  cnly  0-3  grm.,  if  the  sub- 
stance contains  more  than  20  per  cent,  nitrogen)  with  a  mixture  of 
2  parts  anhydrous  sodium  thiosulphate  with  1  part  each  of  soda- 
lime  and  sodium  formate  (to  which  a  little  sugar  is  added  when 
analyzing  nitrates  of  the  heavy  metals).  The  glass  tube  contains 
at  the  hinder  end  5  cm.  of  the  mixture  just  described,  then  the 
mixture  containing  the  substance  (12  to  15  cm.),  next  a  layer  15 
to  20  cm.  long  of  the  finely  powdered  mixture,  and  lastly  5  to  10  cm. 
of  soda-lime.  The  heat  must  not  be  raised  during  combustion  to 
such  a  point  as  to  allow  the  mass  to  sinter  and  form  a  large  channel, 
but  must  nevertheless  be  sufficient  for  the  complete  combustion 
of  the  substance.  If  the  latter  is  not  the  case,  and  the  acid  in  the 
receiver  appears  dark  or  cloudy,  the  results  are  unreliable.  The 

*  Rep.  der  analyt.  Chem.,  n,  331 ;  Zeitschr.  f.  analyt.  Chem.,  xxn,  437. 

t  Compt.  rend.,  c,  1445;  Zeitschr.  f.  analyt.  Chem.,  xxv,  424. 

£  Rep.  der  analyt.  Chem.,  v,  41 ;  Zeitschr.  /.  analyt.  Chem.,  xxrv,  451. 


914  DETERMINATION    OF    COMMERCIAL    VALUES.  [§  329. 

results  obtained  by  ARNOLD  by  this  method,  in  the  analysis  of 
nitrates  and  nitro-compcunds  are  entirely  satisfactory. 

Lastly,  I  would  point  out  that  the  total  nitrogen  may  also  be 
ascertained  by  adding  together  that  existing  as  nitric  acid  (see  below 
under  8,  /?),  and  the  sum  of  the  quantities  present  as  ammonia  and 
in  the  organic  matter  (see  below,  8,  7-,  bb  or  cc). 

8.    NITROGEN  IN  ITS  DIFFERENT  FORMS  OF  COMBINATION. 

§329. 

a.  In  Ammoniacal  Compounds. 

The  ammonia  is  most  conveniently  determined  by  distilling  a 
weighed  sample  of  the  substance  with  water  and  calcined  magnesia 
(p.  253,  a,  Vol.  I,  and  p.  883  this  volume).  If  any  organic  matter 
is  present,  the  nitrogen  of  which  may  be  thereby  partly  converted 
into  ammonia,  it  is  preferable  to  employ  SCHLOSING'S  method, 
based  upon  the  action  of  milk-of-lime  in  the  cold  (Vol.  I,  p.  255,  6, 
and  p.  843  this  volume).  If  it  is  desired  to  determine  the  ammo- 
nia azotimetrically,  this  is  best  effected  in  the  hydrochloric-acid 
extract  of  the  manure  (compare  §  322,  azotimetric  determination 
of  ammonia  in  soils) . 

/?.  In  the  Form  of  Nitric  Acid. 

Thoroughly  extract  a  sample  of  the  manure  with  hot  water,  con- 
centrate the  solution  (first  neutralizing  if  it  is  acid)  by  evaporation, 
make  up  to  a  definite  volume,  and  in  a  measured  portion  determine 
the  nitric  acid,  and  hence  the  nitrogen  in  it,  most  conveniently  by 
P.  WAGNER'S  slight  modification  of  SCHLOSING'S  method  (p.  877 
this  volume). 

The  nitrometric  method  (p.  713  this  volume),  may  also  be  em- 
ployed with  good  results,  and  is  preferred  and  recommended  by 
many  analysts.*  In  this  case  evaporate  almost  to  dryness  the 
measured  quantity  of  the  aqueous  solution,  neutralized  if  neces- 
sary, add  a  little  sulphuric  acid  in  order  to  decompose  any  carbon- 

*  See  SHEPHERD  (Chem.  News,  XLVII,  76;  Zeitschr.  /.  analyt.  Chem., 
xxv,  270).  YARDLEY  (Chem.  News,  XLVII,  92;  Zeitschr.  f.  analyt.  Chem., 
xxv,  448). 


§  329.]  ANALYSIS  OF    MANURES.  915 

V 

ates  that  may  be  present,  expel  the  carbonic  acid  by  gently  warming, 
and  introduce  the  liquid  (which  should  measure  not  more  than  2  or 
3  c.c.)  into  the  nitrometer,  rinsing  the  funnel  of  the  latter  twice  with 
concentrated  sulphuric  acid.  SHEPHERD  (loc.  cit.)  introduces  the 
liquid,  which,  together  with  the  washings  should  not  exceed  5  c.c., 
at  once  into  the  nitrometer,  adds  to  the  cold  liquid  twice  its  volume 
of  concentrated  sulphuric  acid,  mixes  the  latter  with  the  aqueous 
liquid  by  gently  shaking,  opens  the  cock  momentarily  to  allow  any 
carbon  dioxide  evolved  \o  escape,  and  then  shakes  vigorously  to  dis- 
engage the  nitric  oxide. 

In  case  of  manures  which  have  an  acid  reaction,  all  direct 
evaporation  of  the  aqueous  extract  must,  of  course,  as  already 
mentioned,  be  avoided,  as  otherwise  there  may  be  a  loss  of  nitric 
acid.  To  directly  determine  this  nitrometrically,  extract  a  weighed, 
not  too  small,  sample  of  the  manure  with  warm  water  in  such  a 
manner  that  while  the  residue  is  exhausted,  the  solution  is  as  con- 
centrated as  possible,  then  make  the  latter  up  to  a  definite  volume, 
and  use  5  c.c.  for  the  nitrometric  determination.  (YARDLEY,  loc. 
cit.) 

Y.  In  Organic  Combination. 

aa.  Deduct  from  the  total  nitrogen  found  in  §  328  the  nitrogen 
of  the  ammonia  compounds  (a)  and  that  present  as  nitric  acid  (/?), 
and  thus  ascertain  from  the  difference  the  nitrogen  present  in  or- 
ganic combination. 

bb.  According  to  O.  REITMAIR,*  if  the  manure  contains  nitrates 
pour  3  c.c.  of  50-per-cent.  sulphuric  acid  f  over  about  1  grm.  of  the 
finely  powdered  sample  in  a  shallow  tin-foil  dish  about  60  mm.  in 
diameter  and  20  mm.  deep,  stir  with  a  very  short,  glass  rod,  and 
heat  in  a  drying  closet  for  3  to  4  hours  at  60°  to  80°,  then  for  1  hour 
at  120°  to  130°.  The  dish  will  now  contain  a  moist  mass  from  which 
all  the  nitric  acid  (but  no  other  nitrogen)  has  been  expelled.  The 

*  Rep.  dcr  analyt.  Chem.,  v,  262;  Zeitschr.  f.  analyt.  Chem.,  xxv,  583. 

t  The  employment  of  concentrated  sulphuric  acid  as  used  by  DREYFUS 
(Bull,  de  la  Societe  Chim.  de  Paris,  XL,  267;  Zeitschr.  f.  analyt.  Chem., 
xxiri,  246),  is  not  to  be  recommended,  because  if  organic  matter  is  present, 
a  part  of  the  nitrogen  of  the  nitric  acid  may  be  converted  into  ammonia. 


916  DETERMINATION    OF    COMMERCIAL    VALUES.          [§  330. 

nitrogen  in  this  mass  may  then  be  determined  either  by  the  KJEL- 
DAHL  or  the  VARRENTRAPP-WILL  method.  If  the  former  method 
is  used  transfer  the  dish  together  with  its  contents  into  the  decom- 
posing-flask ;  if  the  latter  method  is  employed,  add  to  the  con- 
tents of  the  dish  a  pulverulent  mixture  of  gypsum  and  marble,  stir 
well  together,  remove  the  mass  from  the  dish,  and  mix  it  with 
soda-lime  in  the  usual  manner.  The  tin-foil  dish,  sprinkled  with 
soda-lime,  and  bent  together,  is  also  introduced,  together  with 
the  glass  rod,  into  the  combustion  tubes.  . 

On  deducting  the  nitrogen  of  the  ammonia  (8,  a)  from  the  total 
nitrogen  determined  in  the  residue  obtained  by  one  or  other  of  the 
above  methods,  after  the  expulsion  of  the  nitric  acid,  the  difference 
gives  the  nitrogen  present  in  the  form  of  organic  matter. 

cc.  Heat  the  weighed  substance,  if  it  contains  nitrates,  with  a 
suitable  quantity  of  ferrous  sulphate  and  concentrated  hydrochloric 
acid,  thus  freeing  it  completely  from  nitric  acid,  then  dry  the 
residue,  and  determine  in  the  latter  the  total  nitrogen  present  in 
the  form  of  ammonia  and  organic  compounds,  by  KJELDAHL'S 
method  (R.  WARINGTON).*  The  calculation  is  made  as  in  7-,  bb. 

II.  ANALYSIS   OF    COMMERCIAL   MANURES. 

1.  BONE  PREPARATIONS. 

§  330. 

The  bones  of  vertebrate  animals  in  the  dry  state  contain  about 
70  per  cent,  of  inorganic  and  30  per  cent,  of  organic  matter.  The 
former  consists  of  basic  calcium  phosphate  and  small  quantities  of 
calcium  carbonate,  calcium  fluoride,  and  magnesium  phosphate; 
the  latter  consists  chiefly  of  cartilaginous  substances  and  fat.  The 
average  nitrogen  content  of  the  dry  bones  is  from  4  to  5  per  cent. ; 
the  phosphoric-acid  content  from  27  to  30  per  cent.;  and  the  fat 
about  10  per  cent.  On  boiling  with  water,  as  also  on  exposure  to 
air,  the  content  of  nitrogen  and  fat  decreases,  while  that  of  the 
phosphoric  acid  increases.  The  manurial  value  of  bones  depends 
upon  the  degree  of  comminution  of  the  latter  and  their  content  of 

*  Chem.  News,  LII,  162;  Zeitschr.  f.  analyt.  Chem  ,  xxv,  427. 


§  330.]  ANALYSIS    OF    COMMERCIAL    MANURES.  917 

nitrogen  and  phosphoric  acid.  The  presence  of  fat  is  rather  preju- 
dicial than  otherwise.  In  commerce  the  following  bone  prepara- 
tions are  met  with : 

a.  Bone-meal. 

Bone-meal  comes  into  commerce  in  three  forms — namely  as 
crude,  steamed,  and  fermented.  It  is  customary  to  guarantee  the 
crude  to  contain  from  2-5  to  4-5  per  cent,  nitrogen  and  18  to  21 
per  cent,  phosphoric  acid;  the  steamed,  from  3  to  4-5  per  cent, 
nitrogen  and  20  to  21  per  cent,  phosphoric  acid;  and  the  fermented, 
4  per  cent,  nitrogen  and  20  per  cent,  phosphoric  acid.  The  analy- 
sis is  usually  confined  only  to  the  determinations  a,  /?,  7-,  and  occa- 
sionally also  d. 

a.  Moisture. — Dry  about  5  grm.  of  the  substance  at  110°  in  a 
light,  wide-mouthed  flask  (Fig.  135i,  p.  854  this  volume)  and 
determine  the  loss  of  weight. 

/?.  Ash,  Sand,  and  Phosphoric  Add. — Heat  about  5  grm., 
gently  at  first,  but  gradually  more  strongly,  with  access  of  air, 
until  the  ash  has  become  white,  then  moisten  the  latter  with  ammo- 
nium carbonate,  dry,  gently  ignite,  and  weigh  the  ash.  Then 
gently  boil  this  for  some  time  with  15  to  20  c.c.  nitric  acid,  slightly 
diluted  with  water,  and  until  all  the  soluble  matter  has  dissolved, 
then  dilute,  and  filter  into  a  500-c.c.  flask ;  wash  the  insoluble  residue, 
dry,  ignite,  weigh,  and  calculate  it  as  sand.  When  cold,  dilute  the 
contents  of  the  flask  to  the  mark,  mix,  and  in  50  c.c.  of  the  mixture, 
containing  about  0-1  grm.  phosphoric  acid,  determine  the  acid 
according  to  §  309,  or  §  313,  /?/?.  If  it  is  desired  to  determine  in 
the  ash  the  other  substances  usually  present  (calcium,  magnesium, 
iron,  etc.),  treat  a  further  measured  portion  of  the  nitric-acid  solu- 
tion according  to  §  287. 

f.  Nitrogen. — As  the  nitrogen  in  bone-meal  is  present  only  in 
the  form  of  organic  matter,  it  is  sufficient  to  determine  it  in  about 
1  grm.  of  the  substance  by  combustion  with  soda-lime  (§  187  and 
§  323),  or  according  to  KJELDAHL  (§§  325  and  326).  With  either 
method  20  c.c.  of  seminormal  sulphuric  acid  are  required. 

d.  As.  in  determining   the   manurial  value  of  bone-meal,  the 


918  DETERMINATION    OF    COMMERCIAL   VALUES.          [§  330. 

degree  of  comminution  must  be  taken  into  account,  determine  this  by 
dividing  100  grm.  into  four  grades  of  fineness  by  the  aid  of  three 
sieves.  STOHMANN*  has  proposed  for  this  purpose  the  following 
sieves:  No.  I  has  11  meshes  to  the  square  millimetre;  No.  II  has  5; 
and  No.  Ill  has  2  •  5.  What  remains  on  sieve  No.  Ill  is  residue  IV. 
e.  If  the  fat  also  is  to  be  determined,  exhaust  the  residue  from 
a  (powdering  more  finely,  if  necessary)  with  carbon  disulphide  or 
ether  in  one  of  the  forms  of  extraction  apparatus  adapted  for  this 
purpose,f  evaporate  the  solvent  in  a  light,  wide-mouthed  flask, 
heat  the  residue  for  some  time  at  100°,  and  weigh  the  fat. 

£.  The  carbonic  acid  may  be  determined  by  one  of  the  methods 
described  in  §  139,  II. 

b.  Bone-black  (Animal  Charcoal). 

Bone-black  is  extensively  employed  in  the  manufacture  of  sugar 
for  decolorizing  and  removing  lime.  Recently  prepared,  it  con- 
sists of  a  mixture  of  bone  earth  with  7-  5  to  10-5  per  cent,  of  carbon, 
but  during  use  it  takes  up  lime,  coloring  matter,  pectinous  matter, 
etc.,  from  which  it  is  freed  during  the  process  of  revivifying  by 
treatment  with  acids,  fermentation,  washing,  and  ignition.  When 
it  is  finally  "  spent,"  it  is  taken  by  the  manure  manufacturers,  and 
is  then  usually  employed  in  the  manufacture  of  superphosphate. 
As  the  bone-black  is  greatly  altered  and  in  many  ways  contami- 
nated, the  quality  of  that  met  with  in  the  market  varies  greatly, 
and  can  only  be  determined  by  analysis.  Although  this  is  one 
reason  why  bone-black  is  so  frequently  analyzed,  yet  there  is 
another,  as  it  is  necessary  to  have  analyses  made  of  the  bone-black 
which  is  to  be  revivified  and  used  in  the  sugar  manufacture.  In 
order  to  ascertain  how  much  hydrochloric  acid  it  is  necessary  to 
employ  for  revivifying  the  bone-black,  the  quantity  of  calcium 
which  is  present  not  in  combination  with  phosphoric  acid  (and 

*  P.  WAGNER'S  Lehrbuch  der  Dungerfabnkation.  Brunswick,  FR.  VIEWEG 
und  SOHN,  187. 

f  Compare  Zeitschr.  /.  analyt.  Chem.,  xn,  179;  xiv,  82;  xvn,  174  and 
320;  xvm,  441;  xxi,  98;  xxn,  528;  xxiv,  48;  xxv,  396;  Rep.  der  analyt. 
Chem.,  1886,  p.  390. 


§  330.]  ANALYSIS   OF   COMMERCIAL   MANURES.  919 

usually  present  as  calcium  carbonate)  must  be  determined  in  each 
individual  case. 

In  the  following  paragraphs  I  give  a  complete  analysis  of  bone- 
black,  but  would  point  out  that  it  is,  as  a  rule,  sufficient  to  deter- 
mine the  phosphoric-acid  content  in  order  to  ascertain  its  manurial 
value. 

1.  Dry  about  5  grm.  of  the  substance  at  110°,  and  from  the  loss 
of  weight  determine  the  moisture. 

2.  Dissolve  about  5  grm.  in  the  flask  a,  shown  on  p.  365,  Fig. 
103  this  volume,  and  determine  the  carbonic  acid  according  to  the 
method  there  described.     If  only  the  phosphoric  acid  is  to  be 
determined  in  the  filtrate  by  the  molybdenum  method,  use  diluted 
nitric  acid  as  the  solvent,  but  otherwise  employ  diluted  hydro- 
chloric acid.    To  make  certain  that  everything  soluble  passes  into 
solution,  the  acid  must  be  allowed  to  act  for  15  to  20  minutes  at 
a  temperature  near  the  boiling-point. 

3.  Filter  the  solution  obtained  in  2,  through  a  filter  dried  and 
weighed  at  100°;  wash  the  residue,  dry  at  110°,  and  thus  ascertain 
the  sum  of  the  carbon,  any  insoluble  inorganic  substance  that  may 
be  present,  and  the  mineral  impurities  (sand  and  clay)  insoluble  in 
the  nitric  or  hydrochloric  acid.     Then  ignite  the  dried  filter  with 
access  of  air,  and  thus  obtain  the  sand  and  clay  as  a  residue,  the 
carbon  and  any  insoluble  organic  matter  being  ascertained  from 
the  difference. 

4.  The  filtrate  from  3  make  up  to  500  c.c.,  and  in  50  c.c.  deter- 
mine the  phosphoric  acid  as  in  §  330,  a.     In  other  portions  deter- 
mine the  other  constituents  (iron,  calcium,  magnesium,  alkalies, 
and  sulphuric  acid)  according  to  §  287. 

5.  Dissolve  another  weighed  portion  of  the  substance  in  diluted 
nitric  acid,  dilute,  and  in  the  filtrate  determine  any  hydrochloric 
acid  that  may  be  present. 

6.  To  determine  the  calcium  sulphide,  which  is  usually  present  in 
quantities  too  small  to  permit  of  its  exact  determination  with  the 
carbonic  acid  (see  2) .  it  is  best  to  heat  about  10  grm.  of  the  bone- 
black  with  diluted  hydrochloric  acid  in  a  current  of  hydrogen, 
pass  the  gas  containing  hydrogen  sulphide  through  brominized 


920  DETERMINATION   OF   COMMERCIAL   VALUES.          [§  330. 

hydrochloric  acid,  determine  the  sulphuric  acid  formed,  and  from 
this  calculate  the  calcium  sulphide  (see  p.  519  this  volume). 

7.  To  determine  the  calcium  carbonate,  or  the  carbonate  and 
the  free  lime,  SCHEIBLER'S  method,  described  on  p.  500,  g,  a,  Vol.  I,, 
is  usually  employed  in  the  factories.  The  bone-black  is  first  dried, 
and  reduced  to  as  fine  a  powder  as  possible.  The  quantity  taken 
should  be  so  chosen  as  not  to  contain  too  small  a  quantity  of  car- 
bonic acid ;  about  3  grm.  of  the  dried  bone-black  may  be  considered 
as  about  the  proper  quantity.  SCHEIBLER  has  given  his  apparatus 
a  no  mal  weight,  and  in  his  treatise  *  gives  tables  for  facilitating 
calculation.  If  a  bone-black  contains  calcium  hydroxide,  moisten 
the  weighed  portion  with  10  to  20  drops  of  an  ammonium-carbonate 
solution  in  a  porcelain  dish,  evaporate  to  dryness,  heat  the  residue 
somewhat  more  strongly  (but  nowhere  near  redness),  and  trans- 
fer the  contents  of  the  dish  without  loss  to  the  decomposing  flask. 

If  the  work  is  carefully  done,  the  results  are  very  concordant 
and  accurate;  and  many  analyses  can  be  made  in  a  short  time. 

c.  Bone-ash;  and 
d.  Precipitated  Calcium  Phosphate  from  Bones. 

These  owe  their  value  solely  to  their  phosphoric-acid  content, 
which  may  be  determined  according  to  §§  307  to  310,  or  also  §  313,  /9/?. 

e.  Superphosphates  prepared  from  Bone. 

If  these  are  prepared  from  bone-black  or  bone-ash,  only  the 
phosphoric  acid  in  its  various  conditions  of  solubility  need  be 
considered  in  determining  their  value;  if,  however,  they  are  pre- 
pared from  bone-meal,  then  the  nitrogen  also  must  be  determined. 

Regarding  the  determination  of  the  phosphoric  acid  see  §§311 
to  318;  the  nitrogen  is  determined  as  in  the  case  of  bone-meal 
(§330,a,r). 

*  Anleitung  zum  Gebrauch  des  Apparates  zur  Bestimmung  der  Kohlensauren 
Kalkerde  in  der  Knochenkohle,  etc.,  by  C.  SCHEIBLER,  printed  as  MS.,  6th 
edit.,  Berlin,  1874. 


§  331.]  ANALYSIS    OF   COMMERCIAL   MANURES.  921 

2.  GUANO  (PERUVIAN  GUANO). 

§331. 
a.  Crude  Guano. 

Guano,  the  more  or  less  modified  excrement  of  sea-birds,  occur- 
ring on  the  islands  and  coasts  whence  it  is  obtained,  is  of  exceed- 
ingly irregular  composition,  due  to  the  various  influences  to  which 
it  has  been  exposed  in  the  course  of  time,  hence  its  value,  which 
depends  upon  its  content  of  nitrogen  and  phosphoric  acid,  can 
be  ascertained  only  by  chemical  analysis.  The  good  guano  beds  of 
the  Chinchas  Islands,  which  for  a  long  time  supplied  all  the  de- 
mands, and  yielded  a  guano  containing  on  an  average  12  per  cent, 
nitrogen  and  12  •  3  per  cent,  phosphoric  acid,  are  now  almost  com- 
pletely denuded,  and  the  guano  beds  now  being  worked,  afford  a 
preparation  poorer  in  nitrogen,  but  richer  in  phosphoric  acid.* 

In  the  following  I  will  first  give  an  introduction  to  the  analysis 
of  guano,  such  as  is  usually  sufficient,  and  will  then  detail  the 
methods  which  are  to  be  employed  when  making  a  complete  analy- 
sis of  guano. 

1.  Determination  of  Moisture. 

As  guano,  on  heating,  not  only  gives  up  water,  but  may  also 
lose  ammonia,  the  latter  evolved  during  the  determination  may  be 
estimated  along  with  the  moisture. 

FRUHLIXG  and  SCHULZ  |  recommend  the  following  method  and 
apparatus  (Fig.  140;  for  this  purpose: 

Weigh  off  about  2  grm.  of  the  guano  in  a  porcelain  boat,  insert 
this  into  the  glass  tube  m  n  placed  in  a  water-bath,  connect  it  with 
the  bulb-tube  c  containing  10  c.c.  seminormal  sulphuric  acid,  and 
by  means  of  a  water-pump  or  aspirator  connected  at  d  draw  a  slow 
current  of  air  through  the  apparatus,  the  air  being  dried  and  freed 

*  Regarding  the  occurrence  of  guano  ii  various  parts  of  the  world,  see 
E.  HEIDEN,  "  Lehrbuch  der  Diingerlehre,"  2d  edit.  Hanover,  PHIL.  COHEN, 
1884,  u,  part  2,  p.  340. 

f  See  his  Anleitung  zur  Untersuchung  der  fur  die  Zueker-Industrie  in 
Betracht  Kommenden  Rohmaterialien,  etc.  Brunswick,  F.  VIEAVEG  und  SOHN, 
1876. 


922 


DETERMINATION    OF    COMMERCIAL   VALUES. 


[§  331. 


from  ammonia  by  means  of  the  tube  b  filled  with  pieces  of  pumice 
stone  moistened  with  concentrated  sulphuric  acid.*  When  the 
water  in  the  water-bath  has  been  maintained  boiling  for  about  an 
hour,  the  drying  is  complete.  The  loss  of  weight  of  the  boat  with 
the  guano  gives  the  moisture  together  with  the  ammonia  evolved; 
and  the  quantity  of  the  latter  can  be  determined  by  titrating  the 
contents  of  c  with  soda  lye  or  baryta  water,  the  difference  then 
giving  the  moisture. 


FIG.  140. 

2.  Determination  of  the  Nitrogen. 

Guano  contains  the  nitrogen  for  the  most  part  in  the  form  of 
ammonia  salts,  and  in  less  quantity  in  the  form  of  uric  acid  and 
other  organic  compounds,  and  in  smallest  quantity  in  the  form  of 
nitric  acid,  if  any  of  this  last  is  present.  Determine  the  total  nitro- 
gen, and  also  the  quantities  present  in  the  various  forms  of  combina- 
tion according  to  §§  328  and  329.  0-5  to  1  grm.  of  the  substance 
suffices  for  the  determination  of  the  total  nitrogen.  When  KJEL- 
DAHL'S  or  VARRENTRAPP-WILL'S  method  is  employed,  it  is  advis- 
able to  introduce  20  c.c.  of  seminormal  sulphuric  acid.  If  the 
combustion  is  made  with  soda-lime,  the  guano  is  best  mixed  with 
the  soda-lime  in  the  combustion  tube  itself  by  means  of  a  wire, 
because  on  triturating  together  guano  with  soda-lime  in  a  mortar, 
an  appreciable  quantity  of  ammonia  is  evolved  (see  p.  88  this 
volume). 

*  Compare  the  foot-note,  p.  930  this  volume. 


§  331.]  ANALYSIS   OF    COMMERCIAL    MANURES.  923 

3.  Determination  of  the  Phosphoric  Add. 

a.  Total  Phosphoric  Acid. — Heat  about  2  •  5  grm.  guano  with  from 
two  to  four  times  its  weight  of  a  mixture  of  2  parts  anhydrous 
sodium  carbonate  and  1  part  potassium  nitrate,  gently  at  first,  but 
gradually  increasing  the  heat,  until  the  contents  of  the  crucible 
have  become  white.  When  cold,  soften  the  mass  by  warming  with 
water,  rinse  into  the  beaker,  add  about  30  c.c.  nitric  acid  of  1-25 
sp.  gr.,  by  the  aid  of  which  any  portions  adhering  to  the  crucible 
are  also  to  be  removed;  then  warm  until  all  the  soluble  portion  has 
dissolved,  evaporate  to  dryness  to  remove  silica,  take  up  the  resi- 
due with  nitric  acid  and  water,  filter,  make  up  the  solution  to  250 
c.c.,  and  in  50  c.c.  determine  "the  phosphoric  acid  according  to 
§  309,  or  §  313,  /?/?. 

Instead  of  a  mixture  of  sodium  carbonate  and  potassium 
nitrate,  G.  GILBERT*  employs  a  mixture  of  2  parts  anhydrous 
sodium  carbonate  and  1  part  potassium  chlorate.  When  the  mass 
has  become  white,  the  contents  of  the  crucible  are  further  heated 
for  15  minutes  at  a  bright  red  heat;  when  cold,  the  fused  mass  is 
treated  as  above. 

6.  Phosphoric  Acid  "Soluble  in  Water,"  or  "Soluble"  as  defined 
in  §  316. — If  the  phosphoric  acid  soluble  in  water,  and  that  soluble 
in  an  ammonium-citrate  solution  containing  free  citric  acid  (§  316) 
are  to  be  determined,  treat  5  grm.  of  the  guano  with  the  solvent 
according  to  §  312  or  §  316  respectively,  wash  the  undissolved 
residue,  and  determine  the  phosphoric  acid  in  it  as  in  a,  using  how- 
ever, 100  c.c.  of  the  solution  which  was  made  up  to  250  c.c.,  the 
"water-soluble"  or  " soluble"  phosphoric  acid  being  found  from 
the  difference. 

4.  Total  Fixed  Constituents. 

Incinerate  about  5  grm.  of  the  guano  in  an  obliquely  fixed 
platinum  or  porcelain  crucible,  and  weigh  the  ash.  If  the  analysis 
of  a  guano  is  to  be  complete,  the  following  additional  determina- 
tions must  be  made: 

*  Zeitschr.  /.  analyt.  Chem.,  xn,  1. 


924  DETERMINATION    OF   COMMERCIAL    VALUES.          [§  331. 

5.  Fixed  Constituents  Singly. 

These  are  determined  in  the  manner  described  in  §§  287  and 
289. 

6.  Total  Carbon. 
Determine  this  according  to  §  327,  5. 

7.  Carbonic  Acid. 

Determine  this  by  one  of  the  methods  described  in  §  139,  II; 
the  most  accurate  results,  however,  are  obtained  by  the  method 
described  in  Vol.  I,  p.  493.  Genuine  guano  contains  but  a  very 
small  quantity  of  carbonates,  hence  if  a  guano  effervesces  strongly 
when  treated  with  diluted  hydrochloric  acid,  this  may  be  consid- 
ered conclusive  proof  that  it  has  been  adulterated  with  calcium 
carbonate. 

8.   Uric  Acid. 

If  it  is  desired  to  ascertain  the  quantity  of  uric  acid  in  a  guano  * 
containing  it,  digest  a  not  too  small,  weighed  quantity  of  the 
guano  with  water  containing  a  little  soda-lye,  for  several  hours  at 
a  gentle  heat,  then  filter,  wash,  concentrate  the  washings  by  evap- 
oration, add  this  to  the  nitrate,  and  acidulate  with  hydrochloric 
acid;  allow  to  stand  48  hours  at  the  lowest  available  temperature, 
and  collect  the  precipitated  uric  acid  on  a  small  filter  dried  at  100° 
and  weighed;  then  wash  with  the  smallest  possible  quantity  of  ice- 
cold  water  until  the  last  washings  no  longer  react  for  hydrochloric 
acid,  then  dry  at  100°,  and  weigh. 

9.  Oxalic  Acid. 

To  determine  the  oxalic  acid  in  guano  containing  ammonium 
oxalate,  boil  5  grm.  of  the  guano  with  20  grm.  sodium  carbonate 
and  about  200  c.c.  water,  make  up  the  fluid,  when  cold,  to  500  c.c., 
mix,  and  pass  through  a  dry  filter.  Acidulate  50  or  100  c.c.  of  the 
filtrate  with  acetic  acid  if  necessary,  and  determine  the  oxalic  acid 
according  to  §  137,  a. 

*  To  qualitatively  test  for  uric  acid,  pour  a  little  diluted  nitric  acid  over 
some  guano,  and  carefully  evaporate  to  dryness;  if  uric  acid  is  present,  the 
residue  will  have  a  yellow  or  yellowish-red  color,  changed  to  a  beautiful 
purple-red  by  a  trace  of  ammonia  (the  murexid  reaction). 


§  331.]  ANALYSIS    OF    COMMERCIAL   MANURES.  925 

10.  Constituents  Soluble  and  Insoluble  in  Water. 

Warm  10  grm.  guano  with  about  200  c.c.  water,  and  filter  with- 
out delay  through  a  weighed  filter;  wash  the  residue  with  hot  water 
until  the  washings  no  longer  have  a  yellowish  tinge  and  leave  no 
appreciable  residue  when  evaporated  on  platinum  foil,  then  dry, 
and  weigh.  On  deducting  the  sum  of  the  water  and  the  insoluble 
residue  from  the  weight  of  the  guano,  the  difference  will  give  the 
quantity  of  the  soluble  constituents.  Incinerate  the  insoluble 
portion,  weigh  the  ash,  and  deduct  its  weight  from  the  value  ascer- 
tained in  4 — the  difference  will  give  the  sum  of  the  fixed,  soluble 
salts.  With  very  good  grades  of  guano  the  residue  insoluble  in 
water  amounts  to  from  50  to  55  per  cent.,  but  in  the  inferior  grades, 
it  amounts  to  from  80  to  90  per  cent.  The  brown,  aqueous  solu- 
tion of  good,  genuine  guano  evolves  ammonia  on  evaporation,  has 
a  urinous  odor,  and  leaves  a  brown  saline  mass  consisting  chiefly  of 
sodium  and  potassium  sulphates,  ammonium  chloride,  and  oxalate, 
urate,  and  phosphate  of  ammonium.* 

b.  Decomposed  Guano. 

The  nitrogen,  and  also  the  phosphoric  acid,  are  determined  in 
this  just  as  in  crude  guano.  The  moisture,  and  the  phosphoric 

*  Although  the  determination  of  the  portions  soluble  and  insoluble  in 
water  is  not  without  value  in  judging  of  the  value  of  a  guano,  it  must  never- 
theless be  pointed  out,  that  the  quality  and  quantity  of  the  water-soluble 
constituents  are  by  no  means  constant,  or  characteristic  of  a  guano.  VON 
LIEBIG  (Annal.  d.  Chem.  u.  Pharm.,  cxix,  13),  has,  in  fact,  shown  that  the 
kind  of  salts  passing  into  solution  varies  according  to  whether  the  solution 
is  filtered  immediately,  or  only  after  some  time.  In  the  former  case,  the 
solution  will  contain  much  oxalate  and  little  phosphate  together  with  some 
ammonium  sulphate;  in  the  latter  case,  the  ammonium  oxalate  is  more 
or  less  completely  replaced  by  ammonium  phosphate,  the  oxalic  acid  on 
the  other  hand  remaining  behind  in  the  residue,  combined  with  calcium. 
The  cause  of  this  interesting  behavior  is  that  though  calcium  phosphate  in 
contact  with  ammonium  oxalate  and  water  scarcely  undergoes  any  change, 
yet  it  is  very  soon  converted  into  calcium  oxalate,  with  formation  of  ammo- 
nium phosphate,  if  ammonium  sulphate  (or  ammonium  chloride)  is  present 
also,  as  this  renders  the  calcium  phosphate  more  soluble.  The  dissolved  por- 
tion is  immediately  precipitated  by  oxalic  acid,  and  the  ammonium  sulphate 
is  thus  enabled  to  act  on  a  fresh  portion  of  calcium  phosphate. 


926  DETERMINATION   OF   COMMERCIAL   VALUES.  [§  332. 

acid  in  its  various  conditions  of  solubility,  however,  are  deter- 
mined in  the  manner  detailed  for  superphosphates  (§§  311  to  317 
inclusive). 

3.  FISH  GUANO,  "GRANAT"  GUANO,  HORN-MEAL,  TENDON- 
MEAL,  AND  FLESH-MEAL  MANURE. 

§332. 

The  manures  mentioned  above  owe  their  mamirial  value  to 
their  organically  combined  nitrogen,  and  also,  although  to  a  much 
less  degree,  to  their  phosphoric  acid.  Their  potassa  content  is 
usually  so  small  as  to  require  little  or  no  consideration.  The 
average  content*  of  fish  guano  is  from  7  to  9  per  cent,  nitrogen 
and  10  to  13-5  per  cent,  phosphoric  acid;  of  "granat"  guano, 
8  per  cent,  nitrogen  and  3  per  cent,  phosphoric  acid;  of  horn-meal, 
10  per  cent,  nitrogen  and  5  to  6  per  cent,  phosphoric  acid;  of 
tendon-meal,  9-7  per  cent,  nitrogen  and  6-3  per  cent,  phosphoric 
acid.  In  the  case  of  flesh-meal  manure  the  nitrogen  and  phos- 
phoric-acid contents  vary  between  rather  wide  limits. 

Determine  the  phosphoric  acid  and  also  the  nitrogen  by  the 
method  described- for  guano,  using  for  the  nitrogen  determination 
0-7  to  1  grm.  of  substance,  and  20  c.c.  of  the  seminormal  sulphuric 
acid  in  the  receiver.  Determine  the  moisture,  ash,  and  sand,  as 
described  for  bone-meal. 

4.  MIXED  MANURES. 
§333. 

As  it  is  of  great  importance  in  agriculture  to  employ  manures 
of  which  the  quantity  and  character  of  the  manurial  constituents 
are  accurately  known,  manure  manufacturers  prepare  mixed  man- 
ures of  most  varied  kind,  and  guarantee  the  quantity,  form  of 
combination,  and  solubility  of  the  important  constituents,  i.e., 
nitrogen,  phosphoric  acid,  and  potassium. 

*  See  Mittlere  Zusammensetzung  der  Dilngemittel,  by  E.  WOLFF  (M.ENZEL 
and  v.  LENGERKE'S  landwirthschaftliche  Kalender,  1875). 


§  333.]  ANALYSIS    OF    COMMERCIAL    MANURES.  927 

These  mixed  manures  may  be  divided  into  those  having  a  neu- 
tral or  alkaline  reaction,  and  those  having  an  acid  reaction.  To  the 
former  belong  especially  those  guanos  made  up  to  a  definite  com- 
position by  admixtures  of  ammonium  sulphate,  Chili  saltpetre, 
blood-meal,  etc.;  the  latter  comprises  mixtures  of  superphosphates 
with  ammonium  sulphate,  Chili  saltpetre,  potassium  salts,  etc. 

The  former  are  analyzed  by  the  methods  detailed  for  guano 
(§  331),  or,  if  they  contain  Chill  saltpetre,  the  nitrogen  is  deter- 
mined by  the  methods  detailed  in  §§  328  and  329. 

The  superphosphates  containing  nitrogen  and  potassium  are 
analyzed,  so  far  as  the  moisture  and  the  total  phosphoric  acid  as 
well  as  that  present  in  its  various  forms  of  solubility,  are  con- 
cerned, according  to  §§  311  to  318  inclusive;  the  nitrogen,  how- 
ever, both  total  and  in  its  various  forms  of  combination,  is  deter- 
mined accord'ng  to  §§  328  and  329.  The  potassium  is  determined 
as  follows: 

Heat  about  20  grm.  of  the  substance  with  about  200  c.c.  water 
to  boiling,  allow  to  settle,  decant  the  liquid  into  a  litre  flask,  and 
boil  the  residue  again  with  about  200  c.c.  water,  and  then  rinse  the 
whole  into  the  litre  flask;  allow  to  become  cold,  fill  up  to  the  mark 
with  water,  shake,  and  pass  through  a  dry  filter.  If  the  manure  is 
rich  in  potassium  salts,  employ  50  c.c.  of  the  filtrate  for  the  potas- 
sium determination,  but  i?  poor  in  potassium  salts,  make  the 
determination  in  100  c.c.  of  filtrate.  Add  100  to  200  c.c.  of  water, 
boil,  and  carefully  add  barium-chloride  solution,  avoiding  too  large 
an  excess,  so  long  as  a  precipitate  forms,  then  allow  to  settle,  and 
filter.  In  the  filtrate  then  determine  the  alkalies,  particularly  the 
potassium,  according  to  §  287.  If  only  the  potassium  is  to  be 
determined,  ascertain  the  approximate  weight  of  the  alkali  chlorides 
in  order  to  obtain  an  idea  as  to  the  quantity  of  platinic-chloride 
solution  required. 

In  cases  where  extreme  accuracy  is  required,  the  collected 
barium  sulphate  must  be  gently  ignited  and  boiled  with  diluted 
hydrochloric  acid,  the  filtrate  then  evaporated  to  dryness,  the 
residue  taken  up  with  water,  and  this  liquid  added  to  the  main 
solution. 


928  DETERMINATION    OF    COMMERCIAL   VALUES.  [§   333. 


VI.  ANALYSIS  OF  ATMOSPHERIC  AIR. 

In  the  analysis  of  atmospheric  air  we  usually  confine  our  atten- 
tion to  the  following  constituents:  Oxygen,  nitrogen,  carbonic 
acid,  and  aqueous  vapor.  It  is  only  in  exceptional  cases  that  the 
exceedingly  minute  quantities  of  ammonia  and  other  gases — many 
of  which  may  be  assumed  to  be  always  present  in  infinitesimal 
traces — are  also  determined. 

It  does  not  come  within  the  scope  of  the  present  work  to  de- 
scribe all  the  methods  which  have  been  employed  by  BRUNNER, 
BUNSEN,  DUMAS  and  BOUSSINGAULT,  REGNAULT  and  REISET, 
FRANKLAND  and  WARD,  MORLEY,  VON  JOLLY,  KREUSLER,  HEMPEL, 
and  others,  in  their  comprehensive  investigations  made  to  estab- 
lish the  relative  proportions  of  oxygen  and  nitrogen  in  atmospheric 
air.  I  have  nothing  to  add  to  them,  and  there  is  therefore  little 
object  in  giving  here  abstracts  of  the  original  papers.  A  com- 
pilation of  all  these,  and  especially  the  methods  employed  for  deter- 
mining the  oxygen  in  the  air,  has  been  published  by  KREUSLER,* 
who  has  also  given  all  the  references  in  his  admirable  work,  so  that 
in  this  connection  his  original  papers  may  be  consulted.  I  must 
add,  however,  that  in  the  interim,  HEMPEL  has  published  a  second 
paper,!  in  which  the  consensus  of  all  reliable  investigations, 
namely,  that  the  proportion  of  oxygen  in  atmospheric  air  varies 
but  between  narrow  limits,  is  also  confirmed. 

I  will  therefore  here  confine  myself  to  those  methods  which 
may  be  best  employed  in  testing  atmospheric  air  for  its  chief  con- 
stituent i  for  hygienic  or  technical  purposes,  and  will  omit  the 
description  of  the  methods  for  the  physical  examination  of  air, 
and  the  determination  of  its  content  of  ozone,  ammonia,  and 
other  gases  occurring  in  very  minute  quantities.! 

*  Landwirthschaftliche  Jahrbucher,  by  Dr.  H.  THIEL,  1885,  p.  305  et  seq. 

t  fierichte  der  deutschen  chem.  Gesellschaft,  xvm,  1800. 

J  C.  FLUGGE'S  Lehrbuch  der  hygienischen  Untersuchungs-Methoden  (Leipzig, 
VEIT  &  Co.,  1881)  gives  a  comprehensive  statement  of  the  relative  methods. 
A  special  introduction  to  the  bacterial  examination  of  air  is  given  by  F. 
HUEPPE,  in  Die  Methoden  der  Bakterienforschung,  3d  edit.,  Wiesbaden, 
C.  W.  KREIDEL,  1886. 


5  334.] 


ANALYSIS    OF   ATMOSPHERIC  AIR. 


929 


A.  DETERMINATION  OF   THE   WATER    AND    CARBONIC   ACID. 

I.  BRUNNER'S  Method. 
§334. 

In  this  method,  a  measured  volume  of  air  is  slowly  drawn,  by 
means  of  an  aspirator,  through  an  accurately  weighed  apparatus 
filled  with  substances  having  the  property  of  retaining  the  aqueous 
vapor  and  the  carbonic  acid,  and  estimating  these  two  constituents 
from  the  increased  weight  of  the  apparatus.  * 

Fig.  141  represents  the  arrangement  recommended  by  REG- 
;NAULT. 


FIG.  141. 

The  vessel  V  is  made  of  galvanized  iron,  or  of  sheet  zinc;  it 
holds  from  50  to  100  litres,  and  stands  upon  a  strong  tripod  in  a 
trough  large  enough  to  hold  the  whole  of  the  water  that  V  con- 
tains. At  a  a  brass  tube,  c,  with  stop-cock,  is  firmly  fixed  in  with 
cement.  Into  the  aperture  b,  which  serves  also  to  fill  the  appara- 
tus, a  thermometer  reaching  down  to  the  midddle  of  V  is  fixed  air- 
tight by  means  of  a  perforated  cork  impregnated  with  wax. 

*  There  are,  however,  more  accurate  and  far  more  rapid  methods  for 
determining  the  carbonic  acid. 


930  DETERMINING  WATER  AND   CARBONIC  ACID.         [§  334. 

The  efflux  tube,  r,  which  is  provided  with  a  cock,  is  bent  slightly 
upward,  to  guard  against  the  least  chance  of  air  entering  the  vessel 
from  below.  The  capacity  of  the  vessel  is  ascertained  by  filling  it 
completely  with  water,  and  then  accurately  measuring  the  contents 
in  graduated  vessels.  The  end  of  the  tube  c  is  connected  air-tight 
with  F,  by  means  of  a  caoutchouc  tube;  *  the  tubes  A  to  F  are 
similarly  connected  with  one  another.  A,  B,  E,  and  F  are  filled 
with  small  pieces  of  pumice  stone  f  moistened  with  pure  concen- 
trated sulphuric  acid;  C  and  D  with  moist,  slaked  lime.J  Finally 
A  is  connected  with  a  long  tube  leading  to  the  place  from  which 
the  air  intended  for  analysis  is  to  be  taken.  The  corks  of  the  tubes 
are  coated  with  sealing  wax.  The  tubes  A  and  B  are  intended  to 
withdraw  the  moisture  from  the  air;  they  are  weighed  together. 
C,  D,  and  E  are  also  weighed  joint ly.§  C  and  D  absorb  the  car- 

*As  the  walls  of  caoutchouc  tubes  are  to  a  certain  extent  permeable 
by  moist  air  (LASPEYRES,  DIBBITS),  and  absorb  carbon  dioxide  (MUNTZ  and 
AUBIN,  SPRING  and  ROLAND),  care  must  be  taken  that  the  ends  of  the  glass 
tubes  connected  by  the  rubber  tubing  are  ground  to  fit  closely,  and  are 
pressed  tightly  together. 

f  In  order  to  completely  free  the  pumice  from  chlorides,  moisten  it  with 
concentrated  sulphuric  acid,  and  heat  it  to  redness  in  a  Hessian  crucible. 

J  I  have  again  adopted  the  method  of  filling  the  tubes,  so  far  as  con- 
cerning the  lime,  as  in  BRUNNER'S  original  plan,  instead  of  filling  with  potassa 
lye  tubes  containing  pumice  stone,  because,  as  HLASIWETZ  (Chem.  Centralbl., 
1856,  p.  517)  has  shown,  potassa  lye  absorbs  not  only  carbonic  acid,  but  also 
oxygen,  a  fact  which  had  already  been  previously  pointed  out  by  H.  ROSE. 
The  object  may  also  be  attained  by  the  use  of  soda-lime.  Calcium  chloride 
is  to  be  rejected  for  absorbing  the  water,  as  it  fails  to  thorough^  dry  the  air, 
and  because,  as  HLASIWETZ  (loc.  cit.,  p.  517)  has  shown,  traces  of  chlorine 
corresponding  with  the  ozone  content  of  the  air  are  carried  off.  Nor  can 
concentrated  sulphuric  acid  be  recommended  in  very  accurate  investigations, 
because  it  retains  carbonic  acid,  although  but  a  very  small  quantity  (W.  B. 
and  R.  E.  ROGERS,  HLASIWETZ,  SPRING  and  ROLAND).  In  such  cases  it  is 
usually  best  to  use  phosphoric  anhydride,  which  dries  the  air  somewhat 
more  thoroughly  than  sulphuric  acid;  it  cannot,  however,  be  employed  in 
U-tubes,  but  in  straight  tubes  inclined  upwrards,  and  of  the  form  shown 
in  Fig.  12,  p.  15,  this  volume  (DIBBITS,  Zeitschr.  f.  analyt.  Chem.,  xv,  156; 
compare  also  A.  MITSCHERLICH,  p.  51  this  volume,  and  W.  E.  MORLEY,  Zeitschr. 
f.  analyt.  Chem.,  xxiv,  533). 

§  When  weighing  the  tubes,  care  must  be  taken  to  allow  them  to  attain, 
while  closed,  the  temperature  of  the  weighing-room.  They  are  then,  if 
necessary,  again  wiped  off,  and,  after  being  stoppered  (best  with  ground- 


§  334.]  ANALYSIS    OF    ATMOSPHERIC    AIR.  931 

bonic  acid ;  E  the  aqueous  vapor  which  may  have  been  withdrawn 
from  the  hydrate  of  lime  by  the  dry  air.  F  need  not  be  weighed; 
it  simply  serves  to  protect  E  against  the  entrance  of  aqueous  vapor 
from  V. 

The  aspirator  is  completely  filled  with  water;  c  is  then  con- 
nected with  F,  and  thus  with  the  entire  system  of  tubes;  the  cock 
r  is  opened  a  little,  just  sufficiently  to  cause  a  slow  efflux  of  water. 
As  the  height  of  the  column  of  water  in  F  is  continually  dimin- 
ishing, the  cock  must  from  time  to  time  be  opened  a  little  wider,, 
to  maintain  as  nearly  as  possible  a  uniform  flow  of  water.  When 
V  is  completely  emptied,  the  height  of  the  thermometer  and  that 
of  the  barometer  are  noted,  and  the  tubes  A  and  B,  and  C,  D,  and 
E  weighed  again. 

As  the  increase  of  weight  of  A  and  B  gives  the  amount  of 
water,  that  of  C,  D,  and  E  the  amount  of  carbonic  acid,  and  the 
capacity  of  V  *  the  volume  of  the  air  (freed  from  water  and  car- 
bonic acid)  which  has  passed  through  the  tubes,  the  calculation  is 
in  itself  very  simple ;  but  it  involves,  at  least  in  very  accurate  analy- 
ses, the  following  corrections:  .- 

a.  Reduction  of  the  air  in  V,  which  is  saturated  with  aqueous 
vapor,  to  dry  air;  since  the  air  which  penetrates  through  c  is  dry 
(see  §  198,  r). 

P.  Reduction  of  the  volume  of  dry  air  so  found  to  0°,  and  760 
mm.  (§  198,  a  and  ,9). 

When  these  calculations  have  been  made,  the  weight  of  the  air 
which  has  penetrated  into  V  is  readily  found  (1000  c.c.  of  dry  air 
at  0°  and  760  mm.  weigh  1-2932  grm.),  and  as  the  carbonic  acid 
and  water  have  also  been  weighed,  the  respective  quantities  of 
these  constituents  of  the  air  may  now  be  expressed  in  per  cents,  by 


glass  stoppers),  or  left  open,  hung  on  the  balance  beam,  and  weighed  after 
ten  minutes.  It  is  not  advisable  to  close  the  tubes  with  rubber  stoppers 
(DIBBITS,  loc.  cit.,  p.  160).  The  balance-case  must  be  kept  as  dry  as  possible 
by  keeping  in  it  large  quantities  of  calcium  chloride. 

*  Or  from  the  quantity  of  water  which  has  flown  from  V,  as  the  experi- 
ment may  be  altered  in  this  way,  that  a  portion  only  of  the  water  is  allowed 
to  run  out,  and  received  in  a  measuring-vessel. 


932  DETERMINING   WATER  AND   CARBONIC   ACID.        [§  335. 

weight,  or,  calculating  the  weights  into  volumes,  in  per  cents,  by 
measure. 

Considering  the  great  weight  and  size  of  the  absorption  appara- 
tus, in  comparison  with  the  increase  of  weight  by  the  process,  at 
least  25,000  c.c.  of  air  must  be  passed  through;  the  air  inside  the 
balance-case  must  be  kept  as  dry  as  possible  by  means  of  a  sufficient 
quantity  of  calcium  chloride,  and  the  apparatus  left  for  some  time 
in  the  balance-case  before  proceeding  to  weigh.  Neglect  of  these 
measures  would  lead  to  considerable  errors,  more  particularly  as 
regards  the  carbonic  acid,  the  quantity  of  which  in  atmospheric  air 
is,  on  an  average,  about  one-eighth  that  of  the  aqueous  vapor 
(comp.  HLASIWETZ,  loc.  cit.). 

II.  PETTERSSON'S  Method. 
§335. 

Water  and  carbonic  acid  in  small  quantities  of  air  can  be  deter- 
mined far  more  rapidly,  and  yet  very  accurately,  by  the  recently 
published  method  of  O.  PETTERSSON  *  which  is  carried 
out  by  the  aid  of  the  apparatus  illustrated  in  Fig.  144. 

A  is  a  100-c.c.  pipette,  the  lower  portion  of  which 
is  graduated  in  millimetres  (Fig.  142).  For  this  a  table 
is  calculated  showing  the  amount  in  parts  of  a  cubic 
centimetre  corresponding  with  the  divisions  marked  on 
the  tube.  The  upper  part  of  the  pipette  communicates 
on  the  right  with  the  reservoir  B,  filled  with  glass-wool 
and  phosphoric  anhydride;  and  on  the  left  with  the 
reservoir  C,  filled  with  glass-wool,  and  thoroughly 
dried,  and  still  hot  soda-lime,  the  whole  being  con- 
nected by  a  system  of  narrow,  but  yet  not  capillary 
tubes  .f  The  whole  system  of  three  reservoirs  is 
immersed  in  a  vessel  filled  with  water,  in  which  a 
uniform,  but  of  course  not  constant,  temperature  is 
maintained  by  means  of  a  stirrer,  the  handles  of  which, 
r  r,  are  seen  at  the  top  of  Fig.  144,  the  plate  being 
shown  in  Fig.  143.  The  analysis  is  effected  by  meas-  IG'  142' 

*  Zeitschr.  /.  analyt.  Chem.,  xxv,  467. 

t  The  tubes  in  the  illustration,  Fig.  143,  are,  for  the  sake  of  clearness, 


§  335.] 


ANALYSIS   OF   ATMOSPHERIC  AIR. 
FIG.  143. 


933 


FIG.  144. 


934  DETERMINING    WATER   AND   CARBONIC   ACID.        [§   335. 

uring  the  sample  of  air  in  the  pipette  A,  and  passing  it  first 
into  the  drying  vessel  B,  and  then,  after  the  air  has  been 
dried,  bringing  it  back  to  A,  and  then  measuring  by  means  of 
the  graduated  tube  the  diminution  in  volume  caused  by  drying; 
the  carbonic  acid  in  the  air  to  be  examined  is  then  absorbed 
in  the  same  manner,  and  the .  diminution  again  measured  in  A. 
The  carrying  out  of  the  operation  hence  involves  two  distinct 
operations:  1. — The  transfer  and  retransfer  of  the  air  from  one 
vessel  to  another;  and  2. — The  leveling  of  the  mercury  in  the 
graduated  tube,  and  the  measuring  of  the  volume  of  air  inclosed 
in  A. 

In  carrying  out  the  analysis,  first  fill  both  B  and  A  with  the  air 
to  be  examined;  that  in  B  being  first  dried,  while  that  in  A  is  left 
unchanged.  For  this  purpose  completely  fill  A  with  mercury,  by 
means  of  a  mercury  reservoir  connected  with  the  cock  X  by  a  rubber 
tube  wound*  with  thin,  flexible  copper  wire,  the  reservoir  being 
suspended  by  a  cord  whereby  it  may  be  raised  or  lowered  at  con- 
venience; then  empty  A  again  by  sinking  the  mercury  reservoir, 
while  the  cocks  7-,  d,  and  /?  are  closed,  and  the  lower  end  of  the  tube 
p  containing  phosphoric  anhydride  is  in  connection  by  means  of  a 
suitable  glass  tube  with  the  space  containing  the  air  to  be  analyzed. 
The  dried  air  then  enters  through  p  and  the  cock  n  into  B,  entering 
through  a  short,  pointed  tube  over  the  end  of  which  a  small  bell- 
jar  is  inverted.  The  air  previously  contained  in  B  is  hereby 
expelled,  and  after  repeating  the  operation  a  number  of  times  by 
suitably  opening  and  closing  the  cocks  e,  and  f,  is  completely  re- 
placed by  the  air  to  be  examined. 

When  B  has  been  filled  in  this  manner,  close  //,  and  proceed  to 
fill  A  with  the  air  to  be  examined.  For  this  purpose,  open  the 
cock  r,  while  d  and  e  are  closed,  fill  A  with  mercury,  and,  if  the  air 
to  be  tested  is  other  than  that  of  the  room  in  which  the  apparatus 
is  contained,  connect  the  upper  outlet  of  A  with  the  glass  tube 
leading  to  the  space  occupied  by  the  air  to  be  examined,  the  tube 

drawn  wider  than  they  should  be,  but  the  other  parts  of  the  apparatus  are 
correctly  proportioned,  so  far  as  possible.  The  inner  diameter  of  the  tubes 
and  cocks  should,  nevertheless,  not  be  narrower  than  1  mm. 


§  335.]  ANALYSIS    OF    ATMOSPHERIC   AIR.  935 

having  previously  been  filled  with  this  air  by  suction,  and  then 
allow  the  mercury  to  run  out  to  about  the  zero  point  on  the  scale. 
Then  close  the  cock  A  and  regulate  the  height  of  the  mercury  by  the 
screw  /  which  is  made  to  compress  by  means  of  a  brass  plate  the 
rubber  tube  connecting  the  graduated  tube  with  the  cock  X,  until 
the  mercury  stands  exactly  at  zero,  which  may  be  ascertained  by 
means  of  a  lens.  As  the  rubber  tube  compressed  by  the  screw  / 
must  at  tunes  resist  considerable  pressure,  one  should  be  selected 
having  stout  walls,  and,  after  it  has  been  fixed  in  position  it  should 
be  covered  with  a  strong  piece  of  silk,  stitched  on. 

A  being  thus  filled  with  the  air  to  be  examined,  open  d,  e,  ct,  and 
ft,  so  that  the  pressure  will  be  equal  throughout  the  apparatus,and 
set  the  stirrer  in  motion  so  that  all  parts  of  the  apparatus  will 
acquire  the  same  temperature.  The  small  drop  constituting  the 
liquid  seal  x  in  the  differential  manometer,  and  which  occupies  only 
about  3  to  4  mm.  of  the  manometer  tube,  and  consisting  preferably 
of  concentrated  sulphuric  acid  colored  with  indigo  blue,*  auto- 
matically comes  to  rest  at  one  of  the  marks  on  the  small  scale. 
This  must  be  accurately  observed  by  means  of  a  lens,  and  noted, 
as  in  each  of  the  succeeding  operations  the  drop  must  be  brought 
back  to  exactly  the  same  point  before  reading  off  the  volume.  The 
horizontal  part  of  the  manometer  tube  is  slightly  depressed  at  the 
centre  so  that  the  drop  naturally  assumes  a  central  position.  After 
all  the  differences  of  temperature  and  pressure  have  been  adjusted, 
close  7-,  §,  and  /?,  but  leave  e  open.  Now  open  A,  raise  the  mercury 
reservoir  so  that  A  will  be  gradually  filled  and  the  air  in  it  driven 
into  B.  As  the  dry  air  already  in  B  cannot  escape,  the  pressure 
in  it  of  course  increases  considerably,  hence  the  mercury  reservoir 
must  be  raised  to  a  height  of  about  130  cm.  in  order  to  bring  the 
level  of  the  mercury  from  the  zero  mark  on  the  scale  tube  up  to  the 
T-shaped  branch  of  the  narrow  connecting  tube  above  the  pipette 
A,  and  so  completely  drive  the  contents  of  A  into  B. 

After  about  10  to  20  minutes,  the  last  traces  of  moisture  origin- 
ally in  A,  and  now  compressed  in  B,  are  absorbed.  Then  allow  the 

*An  index  still  more  sensitive  than  the  sulphuric  acid  is  a  petroleum 
of  high  boiling-point. 


936  DETERMINING   WATER  AND    CARBONIC   ACID.       [§  335- 

air  to  return  again  from  B  to  A  by  gradually  lowering  the  mercury^ 
reservoir,  so  that  the  air  in  A  is  at  about  its  original  pressure,  set 
the  stirrer  in  motion  in  order  to  make  the  temperature  uniform 
throughout  the  apparatus,  then  very  cautiously  open  /?,  whereupon 
the  small  index  moves  either  to  the  right  or  left,  according  as  the 
mercury  in  the  graduated  tube  has  been  placed  too  high  or  too 
low;  now  close  A,  turn  the  screw  /  until  x  has  about  resumed  its 
original  position,  open  a  cautiously,  and  bring  the  index  to  its  old 
position  by  turning  the  screw  /;  now  wait  a  few  minutes  to  see  that 
the  index  remains  stationary,  and  as  soon  as  this  is  the  case,  read 
off  the  height  of  the  mercury  in  the  graduated  tube.  The  difference 
found  corresponds  with  the  moisture  that  the  air  in  A  had  contained. 
If  there  is  any  doubt  as  to  whether  the  absorption  of  the  moisture 
was  complete  in  B,  the  air  may  be  driven  once  more  from  A  into 

B,  and  the  reading  repeated. 

When  the  determination  of  the  moisture  is  finished,  drive  the 
air  in  a  similar  manner  from  A  into  C,  in  order  to  allow  the  carbon 
dioxide  to  be  absorbed.  For  this  purpose  the  cocks  7-,  s  and  a 
must  be  closed,  while  d  is  open.  The  absorption  of  the  carbon 
dioxide  is,  as  a  rule,  complete  in  ten  minutes,  so  that  on  repeating 
the  operation,  no  further  decrease  in  volume  is  observed  in  the 
graduated  tube.  If,  as  directed,  C  has  been  filled  with  sharply 
dried  and  still  hot  soda-lime,  the  air  freed  from  the  carbonic  acid 
will  be  (at  least  in  cases  where  the  air  contains  the  usual  propor- 
tion of  carbonic  acid)  so  dry  that  the  diminution  in  volume  may 
be  read  off  at  once.  Should  there  be  any  fear  that  the  air  in  C 
has  again  taken  up  moisture,  it  must  be  dried  again  in  B,  and  the 
diminution  in  volume  then  read  off. 

As  is  evident,  variations  in  the  pressure  of  the  external  air 
cannot  affect  the  measurements,  because  the  cocks  7-  and  //  are 
closed  during  the  process  of  absorption.  The  temperature  through- 
out the  apparatus,  although  uniformly  maintained,  nevertheless  is 
not  constant,  hence  the  internal  pressure  naturally  varies.  As, 
however,  the  alteration  in  volume  of  the  glass  vessels  A,  B,  and 

C,  as  well  as  of  the  air  contained  in  them,  is   proportional,  the 
effects  of  the  variations  of  temperature  are  automatically  neu- 


§  335.]  ANALYSIS   OF   ATMOSPHERIC   AIR.  937 

tralized,  and  the  determinations,  on  reference  to  the  calibrating 
tables,  give  the  percentage  by  volume  of  water  and  carbonic  acid, 
and  sufficiently  accurate  at  least  for  ordinary  analyses.  When 
it  becomes  a  question  of  the  highest  degree  of  accuracy,  care  must 
be  taken  that  the  temperature  within  the  system  does  not  vary 
at  all,  or  does  so  only  by  not  more  than  0  •  1° ;  *  for,  if  the  varia- 
tion amounts  to  a  whole  degree,  it  will  be  found  that,  in  conse- 
quence of  the  unequal  expansion  of  the  phosphoric  anhydride  in 
B  and  the  soda-lime  in  C,  the  compensation  is  only  approximate, 
and  never  complete. 

If,  as  described,  first  the  moisture  and  then  the  carbonic  acid  is 
determined  hi  one  and  the  same  volume  of  air,  then,  as  the  mercury- 
level  at  the  close  of  the  moisture  determination  will  usually  be 
in  the  wider  part  of  the  graduated  tube,  the  diminution  in  volume 
corresponding  with  the  carbonic  acid  will  always  be  read  off  in 
this  part.  If  it  is  desired  to  read  off  in  the  narrow  part,  so  as  to 
insure  greater  accuracy,  open  the  cock  /z,  after  determining  the 
moisture,  and  admit  so  much  dry  air  through  p  and  B  to  that 
already  in  A  that  the  mercury-level  again  stands  at  the  zero-mark 
of  the  graduated  tube,  then  open  for  a  couple  of  seconds  the  cocks 
ft  s,  a,  and  /?,  so  that  the  air  in  C  is  also  reduced  to  the  atmospheric 
pressure,  next  close  7-,  a,  and  e,  and  //,  drive  the  dry  air  in  A  into 
C,  and  in  ten  minutes  or  so,  when  the  carbonic  acid  has  been 
absorbed,  read  off  the  diminution  hi  volume  thus  caused  in  the 
narrower  part  of  the  graduated  tube. 

The  method  described  is,  according  to  PETTERSSOX'S  experi- 
ments, accurate  to  about  0  •  002  per  cent.  If  an  accuracy  of  about 
0-05  per  cent,  suffices,  as  in  hygienic  examinations  of  the  air  hi 
rooms  for  carbonic  acid,  and  the  hygrometric  determinations  of 
atmospheric  moisture,  PETTERSSON  recommends  a  much  smaller  ap- 
paratus, readily  transportable  in  a  wooden  case,  and  the  pipette 
A  of  which  holds  only  18  c.c.  When  using  this  instrument,  the 
water  absorption  is  effected  in  an  ORSAT  tube  filled  with  concen- 

*  This  must  be  accomplished  by  keeping  the  temperature  of  the  room 
approximately  constant,  but  not  by  raising  or  lowering  the  temperature  of 
the  water  reservoir  by  adding  hot  or  cold  water. 


938  DETERMINATION    OF    CARBONIC    ACID.  [§  336. 

trated  sulphuric  acid;  the  carbonic  acid,  however,  is  absorbed  by 
means  of  dry  soda-lime. 

The  graduated  tube,  in  the  small  apparatus,  also  has  a  wider 
and  a  narrower  part,  but  the  wider  part  is  below,  and  serves  for  the 
determination  of  the  moisture,  while  the  carbonic  acid  is  deter- 
mined in  the  narrower,  upper  part  of  the  tube. 

The  PETTERSSON  apparatus  must  naturally  be  very  carefully 
operated.  Those  used  by  PETTERSSON  in  his  investigations  were 
made  by  FRANZ  MULLER,  of  Bonn. 

B.  DETERMINATION  OF  THE  CARBONIC  ACID  ALONE. 

I.  PETTENKOFER'S  Original  Method* 

§336. 

a.  Principle  and  Requisites. — In  PETTENKOFER'S  method  a 
known  volume  of  air  is  made  to  act  upon  a  definite  quantity  of 
standard  baryta  water  (standardized  by  oxalic-acid  solution),  in  such 
manner  that  the  carbonic  acid  is  completely  combined  with  the 
baryta.  The  baryta  water  is  then  poured  out  into  a  cylinder  and 
allowed  to  deposit  with  exclusion  of  air,  an  aliquot  part  of  the 
clear  fluid  is  then  removed,  and  the  baryta  remaining  in  solution 
is  determined.  Calculating  from  the  part  to  the  whole,  the  differ- 
ence between  the  oxalic  acid  required  for  a  certain  quantity  of 
baryta  water  before  and  after  the  action  of  the  air  represents  the 
barium  carbonate  formed,  and  consequently  the  carbonic  acid 
present. 

Two  kinds  of  baryta  water  are  used:  one  contains  21  grm. 
and  the  other  7  grm.  crystallized  barium  hydroxide f  in  the  litre; 


*  Abhandl.  der  naturwissensch.  u.  techn.  Commission  der  k.  bayer.  Akad. 
der  Wiss.,  n,  1;  Annal.  der  Chem.  u.  Pharm.,  n,  Supplementband,  p.  1. 

f  The  barium  hydroxide  must  be  entirely  free  from  caustic  potassa,  and 
soda,  the  smallest  quantities  of  which  render  the  volumetric  estimation  in 
the  presence  of  barium  carbonate  impossible,  since  the  normal  alkali  oxalates 
decompose  the  alkali-earth  carbonates.  When  a  trace  even  of  barium  car- 
bonate is  suspended  in  the  fluid — and  this  is  always  the  case  when  a  baryta 
water  which  has  been  used  for  the  absorption  of  carbonic  acid  is  not  filtered — 
the  reaction  continues  alkaline  if  the  smallest  trace  of  potassa  or  soda  is 
present,  because  the  alkali  oxalate  formed  immediately  enters  into  reaction 


§  336.]  ANALYSIS   OP    ATMOSPHERIC    AIR.  939 

these  serve  for  the  determination  of  larger  and  smaller  quantities 
of  carbonic  acid  respectively.  1  c.c.  of  the  stronger  corresponds 
to  about  3  mgrm.  carbonic  acid,  of  the  weaker  1  c.c.  corresponds 
to  about  1  mgrm.  The  baryta  solutions  should  be  kept  in  the 
bottles  described  and  figured  on  p.  496  this  volume.  The  tubes 
b  and  c  contain  pumice  stone  impregnated  with  potassa  lye;  the 
bottle  d  may  be  omitted. 

The  oxalic-acid  solution  which  serves  for  standardizing  the 
baryta  water  contains  2-8647  grm.  per  litre  of  cryst.  oxalic  acid, 
which  must  be  neither  effloresced  nor  moist;*  1  c.c.  corresponds  to 
1  mgrm.  CO2.  The  baryta  water  is  standardized  as  follows: 
Transfer  30  c.c.  of  it  to  a  flask,  and  then  run  in  the  oxalic  acid 
from  a  MOHR'S  burette  with  an  ERDMAXX  float;  shake  the  fluid 
from  time  to  time,  closing  the  mouth  of  the  flask  with  the  thumb. 
The  vanishing  point  of  the  alkaline  reaction  is  ascertained  with 
delicate  turmeric-paper  .f  As  soon  as  a  drop  of  the  acid  solution 
placed  on  the  paper  does  not  give  a  brown  ring,  the  end  is  attained. 
If  you  were  obliged,  in  the  first  experiment,  to  take  out  too  many 
drops  for  testing  with  turmeric-paper,  consider  the  result  as  only 
approximate,  and  make  a  second  experiment,  adding  at  once  the 
whole  quantity  of  oxalic  acid  to  within  1  or  0-5  c.c.  and  then  be- 
ginning to  test  wdth  paper.  A  third  experiment  would  be  found  to 
agree  with  the  second  to  0-1  c.c.  The  reaction  is  so  sensitive 


with  the  barium  carbonate.  A  fresh  addition  of  oxalic  acid  converts 
the  alkali  carbonate  again  into  oxalate,  and  the  fluid  is  for  a  moment 
neutral,  till,  on  shaking  with  air,  the  carbonic  acid  escapes,  and  any 
barium  carbonate  still  present  converts  the  alkali  oxalate  again  into  car- 
bonate. To  test  a  baryta  water  for  caustic  alkali,  determine  the  alkalinity 
of  a  perfectly  clear  portion,  and  then  of  a  portion  that  has  been  mixed  with  a 
little  pure  precipitated  barium  carbonate.  If  you  use  more  oxalic  acid  in  the 
second  than  in  the  first  experiment,  caustic  alkali  is  present,  and  some  barium 
chloride  must  be  added  to  the  baryta  water  before  it  can  be  used. 

*  It  may  be  obtained  perfectly  pure  by  decomposing  lead  oxalate  with 
diluted  sulphuric  acid.  Other  methods  for  preparing  it  are  given  on  p.  300 
this  volume.  As  regards  the  drying,  see  Vol.  I,  p.  144. 

f  Prepared  with  lime-free  Swedish  filter-paper  and  tincture  of  turmeric. 
The  alcohol  used  in  making  the  latter  must  be  free  from  acid.  Dry  the 
paper  in  a  dark  room,  and  keep  it  protected  from  the  light.  It  should  have 
a  lemon-yellow  color. 


940  DETERMINATION    OF    CARBONIC   ACID.  [§  336» 

that  all  foreign  alkaline  matter,  particles  of  ash,  tobacco  smoke  r 
etc.,  must  be  carefully  guarded  against. 

b.  The  Actual  Analysis. — This  may  be  effected  in  two  different 
ways. 

a.  Take  a  perfectly  dry  bottle,  of  about  6  litres  capacity,  with 
well-fitting  ground-glass  stopper,  and  accurately  determine  the 
capacity;  fill  the  bottle,  by  means  of  a  pair  of  bellows,  with  the 
air  to  be  analyzed;  add  45  c.c.  of  the  dilute  standard  baryta  water, 
and  cause  the  baryta  water  to  spread  over  the  inner  surface  of  the 
bottle  by  turning  the  latter  about,  but  without  much  shaking.  In 
the  course  of  about  half  an  hour  the  whole  of  the  carbonic  acid  is 
absorbed.  Pour  the  turbid  baryta  water  into  a  cylinder,  close 
securely,  and  allow  to  deposit;  then  take  out,  by  means  of  a  pipette, 
30  c.c.  of  the  clear  supernatant  fluid,  run  in  standard  oxalic  acid, 
multiply  the  volume  used  by  1-5  (as  only  30  c.c.  of  the  original 
45  are  employed  in  this  experiment),  and  deduct  the  product  from 
the  c.c.  of  oxalic  acid  used  for  45  c.c.  of  the  fresh  baryta  water; 
the  difference  represents  the  quantity  of  baryta  converted  into 
carbonate,  and .  consequently  the  amount  of  the  carbonic  acid. 
If  the  air  is  unusually  rich  in  carbonic  acid,  the  concentrated 
baryta  water  is  employed. 

/?.  Pass  the  air  through  a  tube  or  through  two  tubes  contain- 
ing measured  quantities  of  standard  baryta  water  and  finish  the 
experiment  as  in  a.  For  passing  a  definite  quantity  of  air  we 
should  generally  employ  an  aspirator  (p.  929  this  volume) ;  PETTEN- 
KOFER  in  his  experiments  with  the  aspiration  apparatus  forced  the 
air  by  means  of  small  mercurial  pumps  first  through  the  tubes,  and 
then  through  an  apparatus  for  measuring  the  gas.  The  form  and 
arrangement  of  the  tubes  is  illustrated  by  Fig.  145.  Two  such 
tubes  were  used;  the  first  was  1  metre,  the  second  0-3  metres  long; 
they  were  filled  with  baryta  water — the  former  with  the  stronger 
solution,  the  latter  with  the  weaker.  The  tubes  are  held  in  a  brass 
holder  lined  with  rubber  and  cork,  and,  by  means  of  pointers,  levels, 
and  leveling  screws,  can  be  fixed  at  any  desired  inclination.  The 
inclination  should  be  such  that  the  single  bubbles  of  air  which  enter 
through  the  short  limbs  of  the  tubes,  and  are  carried  beyond  the 


§  337.]  ANALYSIS    OF    ATMOSPHERIC   AIR.  941 

bend  of  the  tube  by  a  narrow,  flexible  tube,  move  on  with  the 
necessary  rapidity  without  uniting.  The  motion  of  the  gas  bubbles 
keeps  up  a  constant  mixing  of  the  baryta  water.  On  exhausting 
the  air  with  an  aspirator,  a  water  manometer  will  be  necessary 


Fig.  14& 

to  ascertain  the  true  volume  of  air.  The  pressure,  reduced  to 
mercurial  pressure,  must  be  deducted  from  the  prevailing  baro- 
metric pressure. 

II.  Modifications  of  PETTENKOFER'S  Method. 

1.  Such  as  refer  to  Method  a. 

§337. 

As  in  the  filling  of  a  6-litre  flask  by  means  of  a  bellows,  the 
object  can  be  accomplished  with  certainty  only  after  prolonged 
blowing,  and  as  the  unavoidable  noise  is  sometimes  (in  churches, 
schools,  theatres,  etc.)  very  disturbing,  KL.  SONDEN  *  recommends 
the  following  apparatus  for  filling  the  flask  with  the  air  to  be 
examined;  the  apparatus,  however,  can  be  used  only  in  com- 
paratively large  spaces,  as  in  small  ones  the  carbonic  acid  result- 
ing from  the  combustion  of  the  photogen  exerts  an  appreciable 
influence : 

b,  in  Fig.  146,  is  a  tin  cylinder  inclosing  a  photogen  lamp  a,  the 
lamp-glass,  c,  of  which  extends  for  a  distance  of  75  cm.  into  the 
chimney.  At  e  the  tin  cylinder  6  sets  in  a  foot-plate,  by  which 
it  is  closed  below.  The  tin  side-tube  d  carries  a  rubber  ring  at  its 
upper  end,  the  opening  of  which  corresponds  with  that  in  the 

*  Arbeiten  frdn  Stockholms  Helsovdrdsndmds  Laboratorium.  Stock- 
holm, pub.  by  K.  L.  BECKMANN,  1886,  p.  14. 


942 


DETERMINATION    OF    CARBONIC   ACID. 


[§  338. 


bottom  of  the  flask  g,  and  prevents  the  admission  of  the  air  from 
the  side.  On  lighting  the  lamp,  there  is  set  up  a  current  of  air  in 
the  direction  shown  by  the  arrows,  by  which  a  6-litre  flask  may 
be  filled  with  fresh  air  in  less  than  a  minute  and  a  half.  On  allow- 
ing the  lamp  to  burn  for  five  minutes,  the  object  is  accomplished 


TIG.  146. 

with  still  greater  certainty.    The  neck  of  the  flask  g  and  the  open- 
ing in  its  bottom  are  then  closed  with  rubber  stoppers. 

2.  Modifications  of  the  Method  described  in  /3. 

§338. 

W.  SPRING  and  L.  ROLAND,  who  have  made  exhaustive  inves- 
tigations regarding  the  determinations  of  carbonic  acid  in  air* 

*  Recherches  sur  ks  proportions  d'acide  carbonigue  contenues  dans  I'air. 
Brussels:  F.  HAYEZ,  1885. 


§  338.1 


ANALYSIS    OF    ATMOSPHERIC   AIR. 


943 


have  modified  PETTENKOFER'S  absorption  tubes,  in  the  manner 
shown  in  Fig.  147. 


FIG.  147. 

As  will  be  seen,  the  tubes  R  and  r  can  be  closed  by  glass  cocks. 
They  are  1  •  1  metres  long,  14  mm.  internal  diameter,  and  are  fixed 
at  a  slight  inclination,  so  that  it  takes  from  12  to  15  seconds  for  an 
air  bubble  entering  at  B  or  b'  to  pass  through  one  of  the  tubes  filled 
with  baryta  water.  E  and  Er  are  graduations  giving  the  capacity 
of  the  tubes  in  cubic  centimetres;  the  graduations  serve  for  the 
purpose  of  indicating  the  degree  of  evaporation  which  the  baryta 
water  undergoes  from  the  passage  of  the  air  through  it.  It  may  be 
remarked  here  that  the  lower  tube  only  serves  at  first  as  a  check 
for  ascertaining  whether  all  the  carbonic  acid  has  been  absorbed 
in  the  upper  tube.  According  to  the  investigations  of  SPRING 
and  ROLAND  it  is  found  that  when  operating  according  to  the 
directions  given,  and  only  about  1000  litres  of  air  are  passed  through 
the  tubes,  no  turbidity  occurs  in  the  second  tube;  but  when  about 
30,000  litres  of  air  have  passed  through,  a  decided  precipitate  of 
barium  carbonate  is  observed  also  in  the  second  tube.  The  tube 
T  leads  to  the  space  the  air  of  which  is  to  be  investigated;*  S, 

*  If  it  is  desired  to  introduce  the  air  in  a  dried  condition  into  the  tubes, 


944  DETERMINATION    OF    CARBONIC   ACID.  [§  338. 

however,  leads  to  an  aspirator  having  a  capacity  of  about  115 
litres,  and  the  general  arrangement  of  which  is  about  like  that 
described  on  p.  929  this  volume.  The  exit  tube  is  of  glass,  and 
dips  into  a  water  tank  provided  with  an  overflow  spout.  The 
height  of  the  water  in  the  tube  affords  an  indication  as  to  the  degree 
of  rarefaction  of  the  air  in  the  apparatus  at  the  end  of  the  opera- 
tion. The  water  manometer,  M,  serves  as  a  control;  and  a  ther- 
mometer inserted  into  the  aspirator  shows  the  temperature  of  the 
.air  in  it. 

The  tubes  are  filled  with  baryta  water  saturated  at  a  compara- 
tively low  temperature,  so  that  during  the  experiment  its  tempera- 
ture is  increased  rather  than  diminished,  a  separation  of  barium- 
hydroxide  crystals  being  thereby  with  certainty  avoided.  The 
baryta  water  is  prepared  by  dissolving  crystals  of  baryta  in  water 
by  the  aid  of  heat,  and  allowing  the  unfiltered  solution  to  become 
«old.  As  the  baryta  crystals  always  contain  a  little  barium 
carbonate,  the  operator  is  certain  also  of  obtaining  a  baryta  water 
saturated  with  barium  carbonate. 

To  start  with,  the  tubes  are  first  rinsed  out  with  hydrochloric 
acid,  then  with  water,  and  lastly  several  times  with  some  of  the 
baryta  water  to  be  employed.  Then,  with  the  cocks  all  closed, 
they  are  allowed  to  drain  thoroughly,  being  fixed  vertically  for  this 
purpose  with  the  cocks  at  the  top.  Now  introduce  into  each  tube  by 
means  of  a  pipette  125  c.c.  of  the  titrated  baryta  water,  fix  the 
tubes  perpendicularly  with  the  cocks  below,  read  off  the  height  of 
the  liquids  on  the  graduations  E  and  E',  and  then  fix  the  tubes  in 
the  positions  shown  in  Fig.  147;  assemble  the  apparatus,  open 
the  cocks  R  and  r,  and  then  also  the  exit  cock  of  the  aspirator, 
and  in  such  a  manner  that  it  will  take  12  to  15  seconds  for  every 
air-bubble  to  pass  through  one  tube;  at  this  speed,  it  will  require 
from  10  to  12  hours  to  empty  the  aspirator.  Now  measure  the 
height  of  the  water  in  the  exit-tube  of  the  aspirator  and  also  that 
in  the  manometer,  M,  and  divide  the  number  of  millimetres  by 

concentrated  sulphuric  acid  cannot  be  recommended  for  drying  purposes 
(SPRING  and  ROLAND,  loc.  cit.,  p.  64) ;  a  tube  filled  with  phosphoric  anhydride 
is  best  adapted  for  the  purpose;  see  foot-note,  p.  930  this  volume. 


§  339.]  ANALYSIS   OF   ATMOSPHERIC   AIR.  945 

13-5  in  order  to  calculate  the  water-pressure  into  mercuria  pres- 
sure, read  off  the  barometric  pressure,  and  the  temperature  of  the 
air  within  the  aspirator,  and  using  these  figures,  calculate  the 
volume  of  the  air  drawn  through  the  tubes,  reduced  to  0°  and 
760  mm.  pressure  and  hi  the  dry  condition  (compare  §  198). 
From  this  volume  the  weight  of  the  air  can  be  ascertained  by 
multiplying  the  number  of  litres  by  1  •  2932. 

Before  proceeding  to  determine  the  caustic  baryta  remaining 
in  the  tubes  B  B' ,  or  in  both  tubes,  place  the  tubes  again  vertically, 
with  the  cocks  below,  and  if  necessary,  open  the  latter  cautiously 
in  order  to  remove  any  slight  quantity  of  ah-  remaining  hi  t,  and 
then  read  off  the  height  of  the  liquid  on  the  graduations  E  and  Er , 
in  this  manner  ascertaining  the  loss  in  volume  sustained  by  the 
125  c.c.  of  baryta  water  by  evaporation;  this  loss  must  be  taken 
into  account  in  making  the  calculations. 

The  contents  of  the  tubes  may  be  treated  either  hi  the  manner 
directed  by  PETTENKOFER,  i.e.,  by  allowing  the  baryta  water 
rendered  turbid  by  suspended  barium  carbonate  to  settle  hi  a 
closed  flask,  or  the  barium  carbonate  may  be  filtered  off.  If  the 
latter  method  be  chosen,  the  fact  observed  by  A.  MULLER  (Vol.  I, 
p.  486),  that  filter-paper  retains  barium  hydroxide,  must  be  taken 
into  consideration.  The  papers  employed  must,  therefore,  always 
be  alike,  and  the  quantity  of  baryta  retained  on  passing  through 
them  125  c.c.  baryta  water  of  the  same  strength  as  that  used  in 
the  experiment,  must  be  determined,  and  the  proper  correction 
made.  SPRING  and  ROLAND  preferred  the  latter  method. 

3.  Modifications  in  the  Manner  of  Titrating  the  Baryta  Water. 

§339. 

Whereas  PETTENKOFER  recommends  oxalic  acid,  with  curcuma- 
paper  as  indicator,  for  titrating  baryta  water,  SPRING  and  ROLAND 
(loc.  cit.,  p.  51)  prefer  to  use  hydrochloric  acid,  using  litmus  tincture 
as  the  indicator;  they  also  point  out  (loc.  cit.,  p.  71  et  seq.)  that 
glass  vessels,  if  not  previously  rinsed  out  with  baryta  water,  con- 
vert determinable  quantities  of  baryta  into  an  insoluble  com- 
pound, wherefore  they  first  rinse  out  with  baryta  water  both  the 


946  DETERMINATION  OF   CARBONIC   ACID.  [§  340, 

absorption  tubes  and  the  measuring  pipette,  and  let  them  drain 
before  using  them.  REISET  gives  sulphuric  acid  the  preference. 
KL.  SONDEN  also  uses  the  latter,  diluted  so  that  1  c.c.  corresponds 
with  1  mgrm.  of  carbonic  acid.  In  order  to  exclude  so  far  as 
possible  the  influence  of  atmospheric  carbonic  acid  on  the  baryta 
water,  he  recommends  *  to  take  up  the  50  c.c.  to  be  titrated  with 
a  pipette  provided  with  a  protecting  soda-lime  tube.  The  con- 
tents are  emptied  into  a  flask,  some  phenolphtalein  added,  and 
then  sulphuric  acid  until  they  are  colorless  (see  p.  311  this  volume). 
Now  measure  off  into  another  flask  a  quantity  of  acid  exactly 
equal  to  that  just  employed,  add  phenolphtalein,  and  then  add 
50  c.c.  of  the  baryta  water  in  such  a  way  that  the  point  of  the 
pipette  is  below  the  surface  of  the  acid.  To  the  liquid,  which  is 
now  red,  very  cautiously  add  sulphuric  acid  until  the  color  just 
vanishes,  the  acid  used  being  then  considered  as  the  correct 
quantity.  It  will  be  seen  that  by  this  mode  of  operating  the 
atmospheric  air  remains  in  contact  but  a  few  moments  with  the 
liquid  still  slightly  alkaline  from  baryta.  Employing  this  method, 
SONDEN  obtained  the  figures  published  by  him  in  the  Zeitschr.  f. 
analyt.  Chem.,  xxv,  478,  and  which  were  compared  with  those 
obtained  by  PETTERSSON'S  method. 

III.  Method  proposed  by  FR.  MOHR,  and  tested  by  HLASIWETZ  and 

H.V.GlLM.t 

§  340. 

This,  like  PETTENKOFER'S  method,  consists  in  drawing  a  large 
quantity  of  air,  at  least  60  litres,  through  a  long,  slightly  inclined 
tube  containing  pieces  of  glass  and  clear  baryta  water,  collecting 
the  barium  carbonate  formed  with  exclusion  of  air,  and  washing  the 
tubes,  as  well  as  the  precipitate  on  the  filter,  first  with  distilled 
water  saturated  with  barium  carbonate,  and  then  with  pure, 
boiled  water.  Lastly,  the  barium  carbonate  still  in  the  tube,  and 
also  that  remaining  on  the  filter,  is  dissolved  by  diluted  hydro- 
chloric acid,  the  solution  evaporated  to  dryness,  the  residue  gently 

*  Personal  communication.  f  Chem.  CentralbL,  1857,  760. 


§  340.]  ANALYSIS    OF   ATMOSPHERIC    AIR.  947 

ignited,  and  the  chlorine  in  the  barium  chloride  formed  deter- 
mined as  in  §  141,  6,  a,  calculating  1  equivalent  of  carbonic  acid 
for  2  equivalents  of  chlorine.  As  may  be  readily  seen,  the  barium 
content  of  the  hydrochloric-acid  solution  may  also  be  determined 
by  precipitating  with  sulphuric  acid.  For  filtering  the  barium 
carbonate,  v.  GILM  employed  a  double  funnel  (Fig.  148) ;  the  inner 
cork  has,  besides  the  perforation  through  which  the  neck  of  the 
funnel  passes,  a  lateral  slit,  which  establishes  a 
communication  between  the  air  in  the  outer  fun- 
nel and  the  air  in  the  bottle. 

As,  with  the  absorption  apparatus  arranged 
as  described,  the  air  has  to  force  its  way  through 
a  column  of  fluid,  the  manometer  is  required  to 
determine  the  actual  volume  of  the  air;  the 
height  indicated  by  this  instrument  being  de- 
ducted from  the  barometric  pressure  observed 
during  the  process. 

FR.  MOHR*  now  recommends  as  the  absorb-  FIG.  148. 

ent  fluid  a  solution  of  barium  hydroxide  in  pot- 
ash. This  is  prepared  by  dissolving  crystals  of  barium  hydroxide 
in  weak  solution  of  potassa  with  the  aid  of  heat,  and  filtering  off 
the  barium  carbonate,  which  invariably  forms  in  small  quantity. 
The  clear  filtrate  is  accordingly  saturated  with  barium  carbonate. 
MOHR  now  leaves  out  the  fragments  of  glass. 

This  method  afforded  v.  GILM  very  concordant  results.  Nev- 
ertheless, it  involves  one  source  of  error  apart  from  the  unavoidable 
effect  of  the  action  of  the  atmospheric  air  during  filtration.  If 
clear  baryta  water  is  passed  through  paper  with  the  most  careful 
possible  exclusion  of  air,  and  the  filter  is  washed  till  the  washings 
are  free  from  baryta,  and  dilute  hydrochloric  acid  is  then  poured 
upon  the  filter,  and  the  filtrate  thus  obtained  is  evaporated,  a  small 
quantity  of  barium  chloride  will  be  left,  showing  that  a  little  baryta 
was  kept  back  by  the  paper.  AL.  MuLLERf  has  already  called 
attention  to  the  capacity  of  filter-paper  for  retaining  baryta;  and 

*  Lehrbuch  der  Titrirmethode,  5th  ed.,  F.  VIEWEG  und  SOHN,  p.  526. 
f  Journ.  /.  prakt.  Chem.,  LXXXIII,  384. 


948  DETERMINING    OXYGEN   AND   NITROGEN.  [§  341. 

the  proper  correction  must  also  be  made  for  the  baryta  rendered 
insoluble  by  the  surface  of  the  glass  vessel  (see  §  339) . 

C.  DETERMINATION  OF  THE  OXYGEN  AND  NITROGEN. 

§341. 

As  already  mentioned,  the  methods  for  the  exact  determination 
of  the  oxygen,  and  also  of  the  nitrogen,  in  atmosphere,  to  which 
reference  has  been  made  on  p.  928  this  volume,  will  not  be  treated 
of  here.  Those  who  desire*  to  investigate  this  subject,  must  not 
only  become  familiar  with  the  original  treatises,  but  must  also  have 
become  experienced  in  gas  analysis,  for  which  the  works  of  R. 
BUNSEN,*  W.  HEMPEL,f  and  CL.  WINKLER,}  especially,  will  be 
found  to  be  of  great  assistance. 

n     fw 

6* 


FIG.  149. 

The  method  I  shall  give  is  that  proposed  by  v.  LIEBIG;§  it  is 
useful  when  it  is  required  to  determine  the  quantity  of  oxygen  in 
air  in  a  more  or  less  confined  space,  within  0  •  1  or  0  •  2  per  cent,  of 

*  Gasometrische  Methoden,  by  ROB.  BUNSEN,  2d  edit.,  F.  VIEWEG  und  SOHN, 
Brunswick,  1877. 

f  WALTHER  HEMPEL,  Neue  Methoden  zur  Analyse  der  Gase,  F.  VIEWEG  und 
SOHN,  Brunswick,  1880. 

J  CLEMENS  WINKLER,  Lehrbuch  der  technischen  Gasanalyse,  J.  G.  ENGEL- 
,  Freiberg,  1885. 

§  Annal.  d.  Chem.  u.  Pharm.,  LXXVII,  107. 


§   341  .J  ANALYSIS    OF    ATMOSPHERIC    AIR.  949 

the  volume,  in  a  short  time  and  without  the  aid  of  complicated 
apparatus.  LIEBIG'S  method  is  based  upon  the  observation  made 
by  CHEVREUL  and  DOBEREINER,  that  pyrogallic  acid,  in  alkaline 
solutions,  has  a  powerful  tendency  to  absorb  oxygen. 

1.  A  strong  measuring  tube,  holding  30  c.c.  and  divided  into- 
0-2  or  0-1  c.c.,  is  filled  to  J  with  the  air  intended  for  analysis. 
The  remaining  part  of   the  tube  is  filled  with  mercury,  and  the 
tube  is  inverted  over  that  fluid  in  a  tall  cylinder,  widened  at  the 
top  (Fig.  149). 

2.  The  volume  of  air  confined  is  measured  (§  12).     If  it  is 
intended  to  determine  the  carbonic  acid — which  can  be  done  with; 
sufficient  accuracy  only  if  the  quantity  of  the  acid  amounts  to* 
several  per  cents. — the  air  is  dried  by  the  introduction  of  a  ball  of  cal- 
cium chloride  (§  16)  before  measuring.     If  it  is  not  intended  to 
determine  the  carbonic  acid  this  operation  is  omitted.     A  quantity 
of  solution  of  potassa  of  1-4  sp.  gr.  (1  part  of  dry  potas- 
sium hydroxide  to  2  parts  of  water),*  amounting  to  from 

•^  to  -g^j-  of  the  volume  of  the  air,  is  then  introduced  into 
the  measuring  tube  by  means  of  a  pipette  with  the  point 
bent  upwards  (Fig.  150),  and  spread  over  the  entire  inner 
surface  of  the  tube  by  shaking  the  latter  (see  p.  61  this 
volume) ;  when  no  further  diminution  of  volume  takes  FIG.  150. 
place,  the  decrease  is  read  off.  If  the  air  has  been  dried 
previously  with  calcium  chloride,  the  diminution  of  the  volume 
expresses  exactly  the  amount  of  carbonic  acid  contained  in  the  air; 
but  if  it  has  not  been  dried  with  calcium  chloride,  the  diminution 
in  the  volume  cannot  afford  correct  information  as  to  the  amount 
of  the  carbonic  acid,  since  the  strong  solution  of  potassa  absorbs 
aqueous  vapor. 

3.  When  the  carbonic  acid  has  been  removed,  a  solution  of 
pyrogallic  acid,  containing  1  grm.  of  the  acid  in  5  or  6   c.c.  of 
water,  is  introduced  into  the  same  measuring  tube  by  means  of 
another  pipette,  similar  to  the  one  used  in  2  (Fig.  150) ;  the  quan- 
tity of  pyrogallic  acid  employed  should  be  half  the  volume  of  the 

*  These  are  the  quantities  and  the  concentrations  of  potassa  and  pvro- 
gallic-acid  solutions  recommended  by  LIEBIG;  they  may,  of  course,  be  also 
varied  somewhat ;  see  6. 


950  DETERMINING    OXYGEN   AND  NITROGEN.  [§  341. 

solution  of  potassa  used  in  2.  The  mixed  fluid  (the  pyrogallic  acid 
and  solution  of  potassa)  is  spread  over  the  inner  surface  of  the 
tube  by  shaking  the  latter,  and,  when  no  further  diminution  of 
volume  is  observed,  the  residuary  nitrogen  is  measured. 

4.  The  solution  of  pyrogallic  acid  mixing  with  the  solution  of 
potassa  of  course  dilutes  it,  causing  thus  an  error  from  the  diminu- 
tion of  its  tension;    but  this  error  is  so  trifling  that   it   has   no 
appreciable  influence  upon  the  results ;  it  may,  besides,  be  readily 
corrected,  by  introducing  into  the  tube,  after  the  absorption  of  the 
oxygen,  a  small  piece  of  hydrate  of  potassa  corresponding  to  the 
amount  of  water  in  the  solution  of  the  pyrogallic  acid. 

5.  There  is  another  source  of   error  in  this  method:  viz.,  on 
account  of  a  portion  of  the  fluid  always  adhering  to  the  inner  sur- 
face of  the  tube,  the  volume  of  the  gas  cannot  be  read  off  with 
absolute  accuracy.     In  comparative  analyses,  the  influence  of  this 
defect  upon  the  results  may  be  almost  entirely  neutralized,  by 
taking  nearly  equal  volumes  of  air  in  the  several  analyses.* 

6.  The  volume  of  nitrogen  will  finally,  under  certain  circum- 
stances, be  found  to  be  a  little  too  high,  because,  as  CALVERT,  CLOEZ, 
and  BOUSSINGAULT  have  shown,  a  little   carbon  monoxide  may 
be  formed  by  the  action  of  the  potassa  lye  on  the  pyrogallic  acid, 
and  remain  unabsorbed  together  with  the  nitrogen.     I  have  pur- 
posely said  may  be  formed,  as,  according  to  W.  HEMPEL,!  this 
does  not  occur,  for  example,  on  mixing  one  volume  of  a  25-per 
cent,  pyrogallic-acid  solution  with  six  volumes  of  about  60-per  cent, 
potassa  solution. 

7.  Notwithstanding  these  sources  of  error,  the  results  obtained 
by  this  method  are  very  accurate  and  constant.    In  eleven  analyses 
which  v.  LIEBIG  reports,  the  greatest  difference  in  the  amount  of 
oxygen  found  was  between  20-75  and  21-03.     The  numbers  given 
express  the  actual  and  uncorrected  results. 

*As  already  stated  on  p.  266  this  volume,  BUNSEN  (Gasometrischen 
Methoden,  2d  edit.,  p.  94)  employs  for  the  absorption  of  oxygen  a  papier- 
m§ch6  ball  saturated  with  a  concentrated  alkaline  solution  of  potassium 
pyrogallate,  which  he  introduces  into  the  gaseous  mixture  attached  to  a 
platinum  wire.  By  adopting  this  proceeding  the  source  of  error  mentioned 
in  5  is  avoided.  See  also  RUSSELL,  Journ.  Chem.  Soc.,  1868,  pp.  130,  131. 

f  Berichte  der  deulsch.  chem.  Gescllsch.,  xvm,  278. 


PART  III. 
EXERCISES    FOR    PRACTICE. 


EXEECISES  FOE  PRACTICE. 

IN  the  following  pages  I  have  given  60  exercises  which  appear 
to  me  to  be  specially  well  adapted  for  teaching  the  theory  and 
practice  of  quantitative  chemical  analysis.  They  are  almost 
identical  with  those  that,  for  many  years,  have  been  given  in  my 
laboratory,  hence  I  can  with  confidence  state  that  they  can  all  be 
easily  carried  out,  and  that  the  order  in  which  they  are  arranged 
has  been  found  practical.  A  glance  through  this  section  will  show 
that  a  few  volumetric  methods  have  been  inserted  among  the 
gravimetric  methods.  By  this  change  the  monotony  of  the  gravi- 
metric operations  has  been  varied  in  a  useful  manner,  while  the 
hurried  manner  of  working  into  which  beginners  are  easily  led  by 
continuous  operations  in  volumetric  methods,  is  effectively  ob- 
viated, while  at  the  same  time  the  knowledge  is  properly  awakened 
to  the  fact  that  hi  the  realm  of  analysis  very  different  me'aecte 
lead  to  the  same  result,  and  the  mind  is  stimulated  to  make 
comparisons  of  the  various  methods  and  to  critically  judge  them. 

The  principal  point  kept  in  view  in  the  selection  of  these  exer- 
cises has  been  that  most  of  them,  and  more  particularly  the  first, 
should  permit  an  exact  control  of  the  results.  This  is  of  the 
utmost  importance  for  students,  since  a  well-grounded  self- 
reliance  is  among  the  most  indispensable  requisites  for  a  successful 
pursuit  of  quantitative  investigations,  and  this  is  only  to  be  attained 
by  ascertaining  for  one's  seif  how  near  the  results  found  approach 
the  truth. 

Now  a  rigorously  accurate  control  is  practicable  only  in  the 
analysis  of  pure  salts  of  known  composition,  or  of  mixtures  com- 
posed of  definite  proportions  of  pure  bodies.  When  the  student 
has  acquired,  in  the  analysis  of  such  substances,  the  necessary  self- 

953 


954  EXERCISES   FOR   PRACTICE. 

reliance,  he  may  proceed  to  the  analysis  of  minerals  or  products 
of  industry  in  which  such  rigorous  control  is  unattainable. 

The  second  point  kept  in  view  in  the  selection  of  these  exer- 
cises has  been  to  make  them  comprise  both  the  more  important 
analytical  methods  and  the  most  important  bodies,  so  as  to  afford 
the  student  the  opportunity  of  acquiring  a  thorough  knowledge 
of  every  branch  of  quantitative  analysis. 

Bearing  this  in  mind,  it  will  be  naturally  found  that  I  have 
not  always  employed  the  simplest  methods. 

Organic  analysis  offers  less  variety  than  the  analysis  of  inor- 
ganic substances;  the  exercises  relating  to  the  former  branch  are 
therefore  less  numerous  than  those  relating  to  the  latter. 

I  would  advise  the  student  to  analyze  the  same  substance 
repeatedly,  until  the  results  are  quite  satisfactory.  [It  is  a  good 
habit  always  to  carry  on  together  duplicate  analyses.  It  requires 
but  little  more  time  to  make  two  analyses  than  to  make  one,  and 
the  operator's  experience  is  thus  very  economically  doubled.] 

It  is  by  no  means  necessary  for  the  student  to  go  through  the 
whole  of  these  examples ;  the  time  which  he  may  require  to  attain 
proficiency  in  analysis  depends,  of  course,  upon  his  own  abilities. 
One  may  be  a  good  analyst  without  having  tried  every  method  or 
determined  every  body.  A  few  substances  well  analyzed  yield 
more  profit  than  can  be  obtained  from  going  over  many  processes 
in  a  superficial  manner. 

Finally,  the  student  is  warned  against  prematurely  attempting 
to  discover  new  methods;  he  should  wait  until  he  has  attained  a 
good  degree  of  proficiency  in  general  chemistry,  and  more  particu- 
larly in  practical  analysis. 


IRON.  955 


EXERCISES. 

A.    SIMPLE    DETERMINATIONS    IN     THE    GRAVIMETRIC    WAY, 

INTENDED  TO  PERFECT  THE  STUDENT  IN  THE  PRACTICE 

OF  THE  MORE  COMMON  ANALYTICAL  OPERATIONS. 

1.  IRON. 

Procure  10  to  15  grm.  of  fine  bright  pianoforte  wire,  cut  it  into 
lengths  of  about  0-3 grm.  and  keep  it  free  from  rust  in  a  dry  bottle. 

Weigh,  on  a  watch-glass,  for  each  estimation,  about  0-3  grm. 
of  wire,  and  dissolve  in  hydrochloric  acid,  with  addition  of  nitric 
acid.  The  acids  are  diluted  with  a  little  water. 

The  solution  is  effected  by  heating  in  a  moderate-sized  beaker 
covered  with  a  watch-glass.  When  complete  solution  has  ensued, 
and  the  color  of  the  fluid  shows  that  all  the  iron  is  dissolved  as 
ferric  chloride  (if  this  is  not  the  case  some  more  nitric  acid  must 
be  added),  rinse  the  watch-glass,  dilute  the  fluid  to  about  200  or 
300  c.c.,  heat  to  incipient  ebullition,  add  ammonia  in  moderate 
excess,  and  filter  through  a  filter  exhausted  with  hydrochloric  acid, 
etc.  (Comp.  §  113,  1,  a). 

As  the  ferric  oxide  generally  contains  a  small  quantity  of  silica 
partially  arising  from  the  silicon  in  the  wire,  partially  taken  up 
from  the  glass  vessels,  after  it  is  weighed,  digest  with  fuming 
hydrochloric  acid,  with  the  addition  of  a  few  drops  stannous 
chloride,  dilute,  collect  the  silica  on  a  small  filter,  ignite  and  weigh. 
The  weight  is  the  silica + the  ashes  of  both  filters.  The  residue 
should  be  white;  if  it  is  red,  it  indicates  that  some  of  the  ferric 
oxide  has  remained  undissolved. 

The  best  method  of  writing  down  the  records  of  an  analysis  is 
here  given,  once  and  for  all;  and  a  rather  complicated  example 
is  here  selected  as  being  all  the  better  for  the  purpose. 

Watch-glass + iron 10-3192 

"         empty ,       9-9750 


Iron 0-3442 


956  EXERCISES   FOR   PRACTICE. 

Crucible + ferric  oxide + silica + filter  ash 17  •  0703 

"    empty 16-5761 

0-4942 

Ash  of  large  filter.^. 0-0008 

Ferric  oxide+silica 0  •  4934 

Crucible  +  silica  +  ashes  of  both  filters 16  •  5809 

"    empty 16-5761 


0-QQ48 
Ashes  of  the  filters  .  0  •  0014 


Silica 0-0034 

0-4934-0-0034=0-4900  ferric  oxide = 0-343  iron 
which  gives  99  •  65  per  cent. 

2.  LEAD  ACETATE. 

Determination  of  Lead. — Triturate  the  dry  and  non-effloresced 
crystals*  in  a  porcelain  mortar,  and  press  the  powder  between 
sheets  of  blotting  paper  until  fresh  sheets  are  no  longer  moistened 
by  it. 

a.  Weigh  about  1  grm.,  dissolve  in  100  c.c.  of  water,  with  addi- 
tion of  a  few  drops  of  acetic  acid,  and  proceed  exactly  as  directed 
§  116,  1,  a. 

b.  Weigh  about  1  grm.,  dissolve  in  50  c.c.  of  water  with  the 
addition  of  a  few  drops  acetic  acid  and  proceed  exactly  as  directed 
§  116,  3,  a,  a. 

PbO 222-92  58-82 

(C2H3O)20 102-048  26-92 

3H2O 54-048  14-26 


379-016  100-00 


*  Obtained  by  dissolving  the  pulverized  commercial  salt  in  hot  water 
nearly  to  saturation,  filtering,  adding  a  drop  or  two  of  acetic  acid  to  the 
solution,  and  slowly  evaporating  to  crystallization. 


ARSENOUS   OXIDE.  957 

• 

3.  ARSENOUS  OXIDE. 

Dissolve  about  0-2  grm.  pure  arsenous  oxide  in  small  lumps  in 
a  flask  of  about  500  c.c.  capacity,  in  some  solution  of  soda;  by 
digesting  on  the  water-bath ;  dilute  with  a  little  water,  add  hydro- 
chloric acid  in  excess,  and  then  nearly  fill  the  flask  with  clear  water. 
Pass  in  hydrogen  sulphide  without  access  of  air  and  without  warm- 
ing, until  present  in  excess;  then  proceed  in  all  other  respects  ex- 
actly as  directed  §  127,  4,  a.  A  pair  of  watch-glasses  should  be 
used  in  drying  the  filter. 

Asa 150  75-76 

O3 48  24-24 

198  100-00 

4.  POTASH  ALUM. 

Determination  of  Aluminium. — Press  pure  triturated  potash 
alum  between  sheets  of  blotting-paper;  weigh  off  about  2  grm., 
dissolve  in  water,  and  determine  aluminium  as  directed  in  §  105,  a. 

K20 94-22  9-93 

A12O3 102-2  10-77 

4SO3 320-28  33-74 

24H20 432-384  4556 

949-084  100-00 

5.  POTASSIUM  BICHROMATE. 

Determination  of  the  Chromic  Acid — a.  Fuse  pure,  potassium 
dichromate  at  a  gentle  heat,  weigh  off  about  0-4  to' 0-6  grm.,  dis- 
solve in  water  in  a  porcelain  dish,  and  reduce  with  hydrochloric 
acid  and  alcohol;  expel  the  latter  by  heating  on  the  water-bath, 
dilute  the  residue  with  about  200  c.c.  water  and  proceed  to  deter- 
mine the  chromic  acid  exactly  as  detailed  in  §  130, 1,  a,  a. 

b.  Weigh  off  again  about  0-2  grm.,  dissolve  in  water,  and 
precipitate  the  solution  (the  volume  of  which  should  be  about 
100  c.c.)  with  mercurous  nitrate  (§  130,  I,  a,  /?).  The  precipita- 


958  EXERCISES   FOR   PRACTICE. 

tion  is  best  effected  at  the  boiling  temperature,  and  the  washing 
with  hot  water  to  which  a  little  mercurous  nitrate  has  been  added » 

K20 94-22  32-01 

2Cr(X. ,  .   200-20  67-99 


294-42  100-00 


6.  SODIUM  CHLORIDE. 

Preparation. — Sodium  chloride  is  far  less  soluble  in  hydro- 
chloric acid  than  in  water.  On  account  of  this  property  the  crude 
produce — common  salt — may  be  purified  from  the  magnesium 
chloride  and  calcium  sulphate  which  it  contains  as  follows:  To 
100  c.c.  of  a  saturated  solution  add  very  gradually  an  equal  vol- 
ume of  pure  concentrated  hydrochloric  acid  Drain  the  mass  of 
fine  crystals  which  separates  on  a  funnel,  the  throat  of  which  is 
loosely  closed  with  filter-paper.  Wash  with  a  small  volume  of 
pure  dilute  hydrochloric  acid,  and  at  last,  in  order  to  test  the  purity 
of  the  product,  allow  5  or  6  c.c.  of  distilled  water  to  pass  through. 
Collect  the  water  that  runs  through  in  a  test-tube  separately,  and  add 
to  it  barium  chloride.  If  no  turbidity  results,  the  sodium  chloride 
is  free  from  sulphates  and  may  be  assumed  to  be  pure  enough  for 
analysis.  Remove  it  from  the  funnel  and  dry  it  in  a  porcelain 
dish.  If  not  free  from  sulphates,  the  product  may  be  subjected  to 
a  repetition  of  the  process.  This,  however,  will  rarely  be  neces- 
sary.* 

A  portion  f  of  the  salt  thus  obtained  is  heated  in  a  covered  cru- 
cible until  it  ceases  to  decrepitate,  but  not  to  fusion,  and  preserved 
in  a  weighing-tube  (like  a  small  test-tube,  but  not  flared  at  the 
mouth)  which  is  to  be  closed  with  a  soft,  well-fitting,  and  smooth 
cork. 

*  When  large  quantities  of  pure  sodium  chloride  are  required,  it  is  more 
economical  to  prepare  it  from  a  solution  of  common  salt  by  saturating  the 
solution  with  HC1  gas. 

f  Pure  sodium  chloride  is  needed  in  other  analyses,  and  the  chief  part 
of  what  is  thus  prepared  should  be  carefully  bottled  and  reserved  for  future 


ESTIMATION   OF   CHLORINE.  959 

6  a.  ESTIMATION  OF  CHLORINE. 

Heat  pure  sodium  chloride  in  a  platinum  crucible  until  anhy- 
drous (compare  p.  522,  Vol.  I),  dissolve  about  0  •  4  grm.  of  it  in  about 
150  c.c.  of  water,  and  determine  the  chlorine  according  to  §  141,1,  a . 

Na 23-05  39-40 

Cl 35-45  60-60 

58-50  100-00 

The  procedure  next  detailed  may  also  be  profitably  followed: 

1.  Weighing  out  ihe  substanc  — The  tube  containing  the  pre- 
pared salt  is  wiped,  if  need  be,  free  from  dust.    The  cork  is  taken 
out,  and  by  means  of  a  bit  of  thin  paper,  or  a  clean  linen  handkerchief, 
any  particles  of  salt  adhering  to  the  cork,  and  to  the  inside  of  the 
tube  as  far  as  the  cork  reaches,  are  removed.     The  cork  is  replaced 
and  the  whole  is  weighed  (see  §§9  and  10),  the  weight  being  imme- 
diately recorded  in  the  note-book     A  clean  beaker  or  assay-flask, 
of  about  200  c.c.  capacity,  being  ready,  the  weighing-tube  is  held 
over  it  and  the  cork  carefully  removed.     A  portion  of  substance  is 
allowed  to  fall  in  the  vessel,  and,  the  cork  being  replaced,  the  tube 
is  again  counterpoised.     If  two  to  three  decigrammes  have  been 
emptied,  the  operator  is  ready  to  proceed.     If  less,  more  should  be 
transferred  from  the  tube  to  the  vessel      If  more,  or  much  more, 
it  is 'better  to  begin  anew,  by  weighing  off  another  portion  into 
another  beaker  or  flask.     In  this  manner  weigh  off  two  portions  in 
separate  vessels,  so  as  to  carry  together  duplicate  analyses.     Now 
affix  a  piece  of  gummed  paper  to  each  vessel,  and  label  them  to 
correspond  with  their  designation  in  the  note-book. 

2.  Solution  and  precipitation. — Dissolve  the  weighed  portions, 
each  in  about  100  c.c.  of  cold  distilled  water,  add  a  few  drops  of 
pure  nitric  acid,  and,  lastly,  clear  solution  of  silver  nitrate  *   until 
further  addition  no  longer  produces  a  precipitate. 

Agitate  the  mixture  well,  but  with  care  to  avoid  loss.  This  can 
be  done  by  shaking,  if  a  flask  is  used,  or  by  stirring  with  a  glass 
rod,  if  a  beaker  be  employed. 

*  Solution  of  a  silver  coin  in  nitric  acid  answers  for  this  purpose  as  well  as 
pure  nitrate,  provided  it  be  clear  and  contain  but  little  free  acid. 


960  EXERCISES   FOR   PRACTICE. 

Set  the  vessel  aside  in  a  dark  place,  covered  with  paper  or  a 
watch-glass  to  exclude  dust,  and  let  stand  for  about  12  hours,  or 
until  the  precipitate  has  subsided  and  the  liquid  above  it  is  perfectly 
clear,  then  add  a  drop  of  silver  nitrate  to  make  sure  that  the  pre- 
cipitation is  complete  (if  not  complete,  add  more  solution  of  silver, 
and  let  stand  again  for  some  hours) . 

3.  Filtration. — A  filter  is  placed  in  a  funnel  at  least  \  inch 
deeper  than  itself,  and  moistened  with  water,  at  the  stme  time 
being  carefully  pressed  down  so  that  its  edges  touch  the  glass  at  all 
points.  The  funnel  being  supported  on  a  stand,  a  clean  beaker  or 
flask  is  put  beneath  it,  and  the  operator  proceeds  to  pour  the  liquid 
— on  whose  surface  some  particles  of  silver  chloride  usually  float — 
into  the  filter,  leaving  the  bulk  of  the  precipitate  undisturbed.  To 
do  this  without  loss  the  following  precautions  may  be  regarded:  a. 
Touch  the  edge  or  lip  of  the  vessel  with  a  very  slight  coat  of  tallow  (a 
small  bit  of  which  is  kept  at  hand  under  the  edge  of  the  work- 
table,  and  is  applied  with  the  finger).  6.  Pour  lowly  over  the 
greased  place,  along  a  glass  rod*  held  nearly  vertical,  so  directing 
the  stream  that  it  shall  strike  against  the  ide,  not  into  the  vertex 
of  the  filter,  c.  When  the  filter  is  filled  to  within  \  inch  of  the 
top  discontinue  the  pouring,  bringing  the  rod  into  the  vessel  con- 
taining the  precipitate,  after  it  has  drained  so  that  nothing  will  fall 
from  it. 

The  vessel  containing  the  precipitate,  as  well  as  that  which 
receives  the  filtrate,  and  likewise  the  funnel,  should  be  kept  covered 
as  much  as  possible  in  all  cases  when  nicety  is  required,  to  prevent 
access  of  dust,  insects,  etc.f 

The  filtration  of  silver  chloride  should  be  conducted  without 
exposing  it  to  strong  light,  whereby  it  is  blackened,  with  loss  of 
chlorine. 

*  The  pouring-rod  may  be  simply  straight,  and  an  inch  longer  than  the 
diagonal  of  the  vessel,  or  when  it  is  desirable  not  to  disturb  a  precipitate,  it 
may  be  3  to  4  inches  long  and  bent  siphon  fashion  so  as  to  hang  on  the  edge 
of  a  beaker  or  flask.  In  either  case  its  end  should  be  rounded  by  fusion, 
and  those  portions  along  which  the  liquid  flows  must  not  be  handled. 

f  The  most  convenient  covers  are  large  watch-glasses,  but  square  plates 
of  glass,  or  even  cards,  will  generally  answer. 


ESTIMATION   OF   CHLORINE.  961 

4.  When  all,  or  nearly  all,  the  liquid  has  passed  the  filter, 
there  remains  to  wash  and  to  transfer  the  precipitate. 

These  operations  may  be  carried  on  as  follows:  pour  about  100 
€.c.  of  cold  distilled  water  upon  the  precipitate,  which  mostly 
remains  in  the  vessel  where  it  was  formed,  and  agitate  vigorously, 
in  order  to  break  up  and  divide  the  lumpy  silver  chloride,  and  bring 
every  part  of  it  perfectly  in  contact  with  the  water.* 

The  water  and  precipitate  are  now  poured  together  upon  the 
filter,  with  the  precautions  before  detailed.  The  last  portions  of  the 
precipitate  are  removed  from  the  beaker  or  flask  by  repeated  rins- 
ings, in  which  a  wash-bottle  (Figs.  58  to  61,  p.  99,  Vol.  I)  may  be 
conveniently  employed. 

Any  portions  of  precipitate  that  adhere  to  the  sides  of  the  ves- 
sel too  strongly  to  be  removed  by  a  stream  from  the  wash-bottle 
must  be  rubbed  off.  For  this  purpose  a  feather  is  employed.! 

The  dish  being  wiped  clean,  externally,  a  little  water  is  put  in  it, 
-and,  it  being  held  up  to  the  light,  its  whole  interior  surface  is  gently 
rubbed  with  the  feather,  then  rinsed,  rubbed  again  and  rinsed,  so 
long  as .  careful  inspection  discovers  any  portions  of  adhering  pre- 
cipitate; finally,  the  feather  is  rinsed  in  a  stream  of  water,  the 
rinsings  in  each  case  being  poured  upon  the  filter. 

The  washing  is  now  continued  by  help  of  the  wash-bottle.  A 
jet  of  cold  water  is  directed,  first,  upon  the  interior  of  the  funnel, 
just  above  the  filter,  then  upon  the  edge  of  the  filter  itself.  If 
thrown  immediately"  against  the  paper,  this  is  liable  to  be  perfo- 
rated. The  stream  of  water  is  carried  around  the  edge  of  the  filter 
until  the  latter  is  nearly  full,  and  the  liquid  is  then  allowed  to  dram 
off.  This  process  is  repeated  until  a  portion  of  the  wash-water, 
collected  to  the  depth  of  an  inch  in  a  test-tube  containing  a  drop 

*  When  in  a  beaker,  the  agitation  must  be  made  with  great  caution,  by 
means  of  a  glass  stirring-rod:  when  in  a  narrow-mouthed  flanged  flask,  this 
may  be  tightly  closed  by  a  perfectly  smooth  cork  (softened  for  the  purpose 
by  squeezing)  and  then  shaken  violently. 

f  It  is  made  from  a  goose-quill,  by  cutting  off  the  extreme  tip  for  an  inch 
or  so,  and  smoothly  trimming  away  the  beard,  except  a  portion  of  one-half 
inch  in  length  on  the  inside  of  the  curve.  The  tubular  part  may  be  removed 
or  not,  to  suit  the  depth  of  the  dish  which  is  to  be  washed. 


962  EXERCISES   FOR   PRACTICE. 

of  hydrochloric  acid,  gives  no  turbidity  of  silver  chloride.  When 
this  is  accomplished,  the  precipitate  is  washed  down  into  the  ver- 
tex of  the  filter.  The  funnel  is  then  closely  covered  with  paper, 
labelled,  allowed  to  drain  thoroughly,  and  set  away  in  a  warm 
place  for  drying. 

5.  Drying  the  filter. — In  public  laboratories  a  heated  closet  is 
usually  provided  for  drying  filters.     Its  temperature  should  not 
exceed  100°  C.     In  default  of  such  special  arrangement,  the  dry- 
ing may  be  effected  over  the  register  of  a  hot-air  furnace,  or  over  a 
common  stove  or  kitchen  range. 

The  funnel  may  also  be  supported  on  a  retort-stand  over  a  sheet 
of  iron,  which  is  heated  beneath  by  a  lamp,  or  may  be  placed  at 
once  in  the  water-bath.  See  §  50. 

6.  When  the  precipitate  is  perfectly  dry  we  proceed  to  ignite 
it  for  weighing. 

A  small  porcelain  crucible  (platinum  must  not  be  used)  is 
cleaned,  gently  ignited,  and  when  cool  (after  15  to  28  minutes) 
weighed. 

The  work-table  being  clean,  two  small  sheets  of  fine  and  smooth 
writing  or  glazed  paper  are  opened  and  laid  down  side  by  side. 
The  filter  is  removed  from  the  funnel  and  carefully  inverted  upon 
one  of  the  papers.  The  precipitate  is  loosened  from  the  filter  by 
squeezing  and  rubbing  gently  between  the  fingers,  and  when  it  has 
mostly  separated  the  filter  is  lifted,  reversed,  and  any  portions  of 
silver  chloride  still  adhering  are  loosened  by  rubbing  its  sides 
together.  What  is  thus  detached  is  poured  or  shaken  out  on  the 
paper.  . 

The  filter  is  now  spread  out  as  a  half -circle  upon  the  other  sheet 
of  paper,  and,  beginning  with  the  straight  edge,  is  folded  up  into 
a  narrow  flattened  roll,  the  two  ends  of  which  are  then  brought 
together.  In  this  way  those  central  portions  of  the  filter  to 
which  particles  of  precipitate  adhere  are  thoroughly  enveloped  by 
the  exterior  parts,  so  that  in  the  subsequent  burning  nothing  can 
easily  escape. 

The  crucible  being  placed  on  the  glazed  paper,  the  filter  is 
taken  by  the  two  free  ends  in  a  clean  pincers  or  tongs,  put  to  the 


ESTIMATION    OF   CHLORINE.  963 

flame  of  a  lamp  to  set  it  on  fire,  and  then  held  over  the  crucible 
until  it  is  completely  charred.  It  is  then  dropped  into  the  crucible 
and  moistened  with  two  or  three  drops  of  nitric  acid.  The  cruci- 
ble is  covered  and  placed  over  a  low  flame  until  its  contents  are  dry ; 
it  is  then  heated  somewhat  more  strongly,  whereby  the  carbon  is 
nearly  or  entirely  consumed. 

The  crucible  being  allowed  to  cool,  one  more  drop  of  nitric 
acid,  and  afterwards  a  drop  of  hydrochloric  acid,  is  added  to  the 
residue,  and  it  is  heated  cautiously,  without  the  cover,  until  fumes 
cease  to  escape.  This  treatment  with  nitric  acid  serves  to  Destroy 
carbon  and  convert  any  reduced  silver  to  nitrate,  which  the  hydro- 
chloric acid  in  turn  transforms  into  chloride.  When  the  crucible 
is  cool,  it  is  placed  again  on  the  paper,  and  the  precipitate  is  poured 
into  it  from  the  other  sheet,  the  last  particle  being  detached  by 
cautious  tapping  with  the  fingers  underneath,  or  by  the  use  of  a 
clean  camel's-hair  pencil. 

The  crucible  is  now  put  over  a  low  flame  and  heated  cautiously 
until  the  silver  chloride  begins  to  fuse  on  the  edges.  It  is  then 
covered  and  let  cool.  When  cold  it  is  weighed  Read  §  115  1, 
and  the  references  there  made 

7.  Record  and  ca  culati  n  o "  results. — The  amount  of  silver 
chloride  is  learned  by  subtracting  from  the  total  the  joint  weight 
of  the  crucible  and  filter-ash.  The  quantity  of  chlorine  is  obtained 
by  multiplying  the  amount  of  silver  chloride  by  the  decimal  0-2473. 
In  order  to  compare  results  they  are  reduced  to  per  cent,  statements 
by  the  following  proportion: 

Substance  :  chlorine  in  substance  ::  100  :  chlorine  in  100;  i.e., 
per  cent. 


The  record  may  be  made  as  follows:  It  is  well  to  work  out  the  calcula- 
tions in  full  in  the  weight-book,  as  in  case  of  mistake  the  data  are  at  hand 
for  revision. 

No.  1.  No.  2. 

NaCl  and  tube 6*615  6-180 

«       «      «    —substance 6-180  5-765 

Substance 0-435  0-415, 


964  EXERCISES  FOR  PRACTICE. 

Crucible,  AgCl,  and  ash 15  •  3630  14  •  3270 

Cr- 14-298    )149QQ-  13-309    > 

Ash..  0-0015  f14'2"5  0-0015  f13'3105 


AgCl 1-0635  1-0165 

0-2473  0-2473 

31905  30495 

74445  71155 

42540  40660 

21270  20330 


a ." =0-26300355  0-25138045 

0-435)26-300355(60-46        0-415)25-138045(60-57 
2610  2490 

2003  2380 

1740  2075 

2635  3054 

2610  2905 

Found.        Calculated. 
No.  1.       No.  2. 

Chlorine 60-46  60-57  60-62 

[We  have  here  employed  the  simplest  arithmetical  calculation.  It  is 
well  to  duplicate  the  calculation  with  help  of  the  tables  given  in  the  Appendix. 

The  first  determination  given  above  is  not  only  fair  for  this  method,  but 
answers  all  ordinary  purposes.  The  second  is  very  good,  though  with  care 
still  closer  accordance  with  theory  can  be  easily  attained.] 

B.  COMPLETE  ANALYSIS  OF  SALTS  IN  THE  GRAVIMETRIC  WAY- 
CALCULATION    OF    THE    FORMULA    FROM    THE     RESULTS 
OBTAINED  (§§  202,  203). 

7.  CALCIUM  CARBONATE.* 

Heat  pure  calcium  carbonate  in  powder  (no  matter  whether 
Iceland  spar  or  the  artificially  prepared  substance),  gently  in  a 
platinum  crucible. 

a.  Determination  of  Calcium. — Dissolve  in  a  covered  beaker 
about  1  grm.  in  dilute  hydrochloric  acid  with  the  addition  of  some 
water,  heat  gently  until  the  carbonic  acid  is  completely  expelled, 
dilute  if  necessary  to  about  300  c.c.,  and  determine  calcium  as 
directed  (§  103,  2,  b,  a). 

To  control,  convert  the  calcium  carbonate  into  calcium  sul- 

*Ca<S>CO. 


CUPRIC   SULPHATE.  965 

phate,  and  weigh  it  as  such.  For  this  purpose  transfer  it  to  a 
weighed  platinum  dish,  dissolve  it  in  very  dilute  hydrochloric  acid 
while  keeping  the  dish  covered  with  a  watch-glass,  which  is  after- 
wards rinsed,  and  then  proceed  as  in  §  103,  1,  b. 

b.  Determination  of  Carbonic  Add. — Determine  in  about  0-8 
grm.  the  carbonic  acid  as  in  §  139,  II,  c. 

CaO 56-1  56-04 

CO2.  . 44-0  43-96 

100-1  100-00 

8.  CUPRIC  Sui  PHATE.* 

A  complete  analysis  of  this  should  be  made.  Triturate  the  pure 
crystals  f  in  a  porcelain  mortar>  and  press  between  blotting-paper. 

a.  Weigh  an  empty  bulb-tube,  then  half  fill  the  bulb  with  the 
copper  sulphate,  J  weigh  again,  place  it  in  an  air-bath  having 
openings  in  its  sides  (Vol.  I,  p.  64,  Fig.  38),  and  proceed  as  directed 
in  §  29,  employing  a  current  of  dry  air.  When  no  more  water 
escapes  at  120°  to  140°,  and  repeated  weighing  of  the  bulb-tube 
gives  constant  results,  the  loss  in  weight  gives  the  quantity  of  water 
of  crystallization  present  in  the  salt.  Instead  of  the  bulb-tube 
an  ordinary  wide  tube  may  also  be  employed,  the  copper  sulphate 
being  placed  in  a  boat  and  the  latter  inserted  into  the  tube  and 
heated  as  described.  In  order  to  guard  against  the  reabsorption  of 
water  by  the  dehydrated  copper  sulphate  during  the  weighing, 
insert  the  boat  in  a  small  tube  closed  by  a  glass  or  even  a  cork 
stopper,  which  is  weighed  along  "with  it  both  before  and  after  the 
heating,  a  wire  being  twisted  around  the  tube  near  the  stopper  and 

*Cu<Q<SO2+5H2O. 

t  [Boil  a  solution  of  commercial  blue  vitriol  with  a  little  pure  lead  di- 
oxide to  oxidize  the  iron,  then  with  a  little  barium  carbonate  to  precipitate 
it,  filter  and  crystallize. — H.  WURTZ,  Am.  Journ.  [2],  xxvi,  367.] 

%  This  is  effected  by  pushing  down  into  one  end  of  the  tube  to  the  bulb  a 
glass  rod  around  which  paper  has  been  rolled,  and  then  filling  in  the  salt 
through  the  other  tube.  Then  restore  the  bulb-tube  again  to  a  horizontal 
position  and  tap  it  gently,  finally  withdrawing  the  glass  rod,  and,  if  neces- 
sary, cleaning  the  tubes  with  a  feather. 


966  EXERCISES   FOR   PRACTICE. 

so  bent  that  the  ends  of  the  wire  serve  as  feet;  this  will  prevent  the 
tube  f  i  om  rotating  on  its  axis  and  spilling  the  contents  of  the  boat. 
Care  must  be  taken  that  the  thermometer  is  inserted  to  a  proper 
depth  in  the  air-bath,  so  that  it  may  correctly  indicate  the  actual 
temperature  of  the  copper  sulphate. 

b.  Determining  the  Water  Halhydration. — Continue  the  experi- 
ment, raising  the  temperature  to  250°  or  260°.      The   additional 
loss  of  weight  gives  the  quantity  of  the  more  strongly  combined 
water  of  halhydration.     In  order  to  raise  the  temperature  suffi- 
ciently high,  it  will  be  necessary  to  employ  two  gas  burners  if  the 
gas  pressure  is  too  low. 

c.  Dissolve   another  portion   of  the   copper  sulphate   (about 
1-5  grm.)  in  about  200  c.c.  water,  and  determine  the  sulphuric 
acid  according  to  §  132,  I,  1. 

d.  Dissolve  about  1-5  grm.  in  about  200  c.c.  water,  and  deter- 
mine the  copper  oxide  as  in  §  119, 1,  a,  by  means  of  potassa  solution. 

CuO 79-60  31-87 

SO8 80-07  32-06 

H2O 18-016  7-21 

4H20 72-064  28-86 

249-75          100-00 

9.  CRYSTALLIZED  HYDROGEN  SODIUM  PHOSPHATE.* 

a.  Determination   of   the    Water   of    Crystallization. — Weigh    a 
platinum  crucible  with  about  4  grm.  of  quartz  sand  which  has 
been  freshly  ignited  with  access  of  air,  then  add  1  grm.  of  the 
finely  powdered  sodium  phosphate  which  has  been  dried  by  press- 
ing between  blotting-paper,  and  then  heat  to  100°  until  its  weight 
is  constant;  the  loss  of  weight  gives  the  water  of  crystallization. 

b.  Determination  of  the  Water  of  Constitution. — Ignite  the  resi- 
due obtained  in  a. 

c.  Determination  of  Phosphoric  Acid. 

a.  Treat  1  to  1-5  grm.  of  the  salts  dissolved   in   about 
200  c.c.  of  water  as  directed  in  §  134,  b,  a. 

*HO  \ 

NaO-^PO+12HO2. 
•       NaOX 


SILVER    CHLORIDE.  967 

/?.  Treat  about  0-5  grm.  of  the  salt  dissolved  in  40  to  50  c.c. 
of  water,  as  directed  in  §  134,  b,  /?.     Compare  also  §  309, 
a,  aa. 

I  recommend  the  student  to  perform  the  determination  by  each 
of  these  methods,  as  they  are  both  hi  common  use  in  the  analytical 
laboratory. 

d.  Determination  of  Sodium.  —  Dissolve  about  1-5  grm.  of  the 
sodium  phosphate  in  about  150  c.c.  water,  and  treat  as  in  §  135, 
d,  /?.     After  the  excess  of  silver  has  been  separated  by  hydrochloric 
acid,  evaporate  the  liquid  repeatedly  with  hydrochloric  acid  to 
dryness  in  order  to  expel  all  nitric  acid.     Then  dissolve  the  residue 
in  a  little  water,  transfer  the  solution  to  a  platinum  dish,  and 
weigh  the  sodium  chloride  in  this;  compare  §  98,  3. 

If  the  weighing  has  taken  a  rather  long  time,  the  sodium  chloride 
easily  takes  up  a  little  water,  and  the  weight  will  be  slightly  too 
high.     It  is  hence  advisable  to  heat  again  after  weighing,  allow 
to  cool  in  the  desiccator,  place  the  weights  from  the  first  weighing 
in  one  pan  of  the  balance  and  the  dish  containing  the  sodium 
chloride  in  the  other,  and  to  then  complete  the  weighing  rapidly, 
thus  obtaining  the  correct  result. 

P2O5  .................  142-00  19-82 

..124-10  17-31 


H2O  .......  .  ..........   18-016  2-52 

24H2O  ................  432-384          60-35 

716-50          100-00 

10.  SILVER  CHLORIDE. 

Ignite  about  2  grm.  of  pure  fused  silver  chloride  in  a  stream  of 
pure  dry  hydrogen*  till  complete  decomposition  is  effected,  and 
weigh  the  silver  obtained.  The  ignition  may  be  performed  in  a 
light  bulb  tube,  or  in  a  porcelain  boat  in  a  glass  tube,  or  in  a  porce- 
lain crucible  with  perforated  cover  (§  115,  4,  a). 

*  To  thoroughly  purify  and  dry  the  hydrogen  evolved  from  zinc  and  di- 
luted sulphuric  acid,  conduct  it  through  three  flasks,  the  first  of  which  con- 
tains a  solution  of  potassium  permanganate  acidulated  with  sulphuric  acid, 
the  second  potassa-  or  soda-lye,  and  the  last  pure  concentrated  sulphuric  acid- 


968  EXERCISES   FOR    PRACTICE. 

The  chlorine  is  estimated  by  difference. 

Ag 107-92  75-27 

01.  .  35-45  24-73 


143-37          100-00 

11.  MERCURIC  SULPHIDE  (CINNABAR). 

Reduce  to  a  fine  powder,  and  dry  at  100°,  most  conveniently 
in  a  pair  of  watch-glasses. 

a.  Determination  of  Sulphur. — Treat  about  0-5  grm.;  as  directed 
in  §  148,  II,  A,  2,  a,  /?  (Vol.  I,  p.  568).  The  operation  should  be 
conducted  in  the  open  air,  or  under  a  good  draught  cupboard. 
Transfer  the  cinnabar  to  a  small  flask,  add  from  an  equal  to  double 
the  volume  of  potassium  chlorate,  and  then  sufficient  water  to 
dissolve  the  greater  part  of  the  chlorate. 

When  this  is  done,  add  gradually,  and  with  constant  shaking, 
about  25  c.c.  diluted  hydrochloric  acid,  allow  to  stand  12  to  24 
hours,  and  lastly  heat  gently  on  the  water-bath,  thus  effecting 
complete  solution  without  any  separation  of  sulphur.  Before 
precipitating  the  sulphuric  acid  formed  with  barium  chloride 
(§  132,  I,  1),  neutralize  the  greater  part  of  the  hydrochloric  acid 
with  ammonia,  and  dilute  the  liquid  to  about  200  c.c. 

6.  Determination  of  Mercury.- — Dissolve  about  0-5  grm.  as  be- 
fore, dilute,  and  allow  to  stand  in  a  moderately  warm  place  until 
the  smell  of  chlorine  has  nearly  gone  off;  filter  if  necessary,  add 
ammonia  in  excess,  heat  gently  for  some  time,  add  hydrochloric 
acid  until  the  white  precipitate  of  amido-mercuric  chloride  is  re- 
dissolved,  and  from  the  solution,  which  now  no  longer  smells  of 
chlorine  and  measures  about  400  c.c.,  precipitate  the  mercury  as- 
sulphide  by  means  of  hydrogen  sulphide,  as  directed  in  §  118,  3. 

Hg 200-00  86-18 

S..  .  32-07  13-82 


•  232-07  100-00 


CRYSTALLIZED    CALCIUM    SULPHATE. 


12.  CRYSTALLIZED  CALCIUM  SULPHATE.* 

Select  clean  and  pure  crystals  of  selenite,  triturate  to  a  coarse 
powder,  and  dry,  if  necessary,  in  the  exsiccator  (§  27)  . 

a.  Determination  of  Water.  —  Heat  1  to  2  grm.  in  a  platinum  or 
porcelain  crucible  to  low  redness,  and  determine  the  loss  of  weight. 
Compare  §  35,  a,  a,  and  §  73,  a. 

b.  Determination  of  Sulphuric  Acid  and  Calcium.  —  Treat  about 
1  grm.  as  in  §  132,  II,  b,  a  (Vol.  I,  p.  441).     In  order  to  conveniently 
remove  the  melt  from  the  platinum  crucible,  first  allow  to  become 
perfectly  cold,  then  heat  without  the  lid  and  until  the  edge  of  the 
mass  begins  to  melt,  allow  to  cool  again,  and  pour  sufficient  water 
into  the  crucible  to  completely  cover  the  mass,  and  warm  slightly* 
The  cake  will  then  at  once  become  loose  (STOCKMANN). 

CaO  ........................   56-10  32-58 

SO3  .........................  80-07  46-50 

2H2O..  .   36-032  20-92 


172-202  10-000 

C.  SEPARATION  OF  TWO  BASIC  OR  TWO  ACID  RADICALS 

FROM  EACH  OTHER,  AND  DETERMINATIONS  IN  THE 

VOLUMETRIC  WAY. 

13.  SEPARATION  OF  IRON  FROM  MANGANESE. 

Dissolve  hi  hydrochloric  acid  about  0-2  grm.  fine  pianoforte 
wire,  and  about  the  same  quantity  of  ignited  mangano-manganic 
oxide  (prepared  as  directed  §  109,  1,  a) ;  heat  with  a  little  nitric 
acid,  and,  after  diluting  the  solution  to  about  500  c.c.,  separate  the 
two  metals  by  means  of  sodium  acetate  as  in  §  160,  3,  a  [82]. 
Concentrate  the  filtrate  and  washings  to  about  200  c.c.,  precipi- 
tate the  manganese  with  ammonium  carbonate,  and  weigh  it  as 
mangano-manganic  oxide  (TAMM'S  method,  §  160,  2,  b  [Si].  In  the 
filtrate  concentrated  by  evaporation,  determine  with  bromine  and 
ammonia  any  small  quantities  of  manganese  that  may  still  be 
present  (p.  833  this  volume).  Any  slight  precipitate  obtained 

*Ca<Q>SO3+2H2O. 


970  EXERCISES   FOR    PRACTICE. 

thus  may  be  at  once  ignited,  and  weighed  as  mangano-manganic 
oxide. 

14.  VOLUMETRIC  DETERMINATION  OF  IRON  BY  SOLUTION  OF 
POTASSIUM  PERMANGANATE. 

a.  Standardizing  the  Solution  of  Potassium  Permanganate. — By 
metallic  iron  (fine  piano  wire),  1  grm.  of  which  should  be  dissolved 
in  dilute  sulphuric  acid  (§  112,  2,  a,  Vol.  I,  p.  312). 

I  would  point  out  that  it  is  better  to  allow  only  boiled  distilled 
water  to  reascend  into  the  flask  a,  and  not  the  water  used  as  a  seal, 
which  often  contains  hydrocarbons. 

b.  Determining  the  Percentage  Content  of  Oxalic  Acid. — Weigh  off 
1  or  2  grm.  of  pure  oxalic  acid,  press  between  blotting-paper,  dis- 
solve in  water,  dilute  to  250  c.c.,  and  titrate  50  c.c.  according  to 
§  112,  2,  a,  a,  cc.  (Vol.  I,  p.  316). 

c.  Determination  of  Ferrous  Iron  in  Ammonium  Ferrous  Sul- 
phate.— Dissolve  12  grm.  of  the  pressed  salt  in  water  with  the  addi- 
tion of  a  little  diluted  sulphuric  acid,  dilute  to  500  c.c.,  and  in  por- 
tions of  50  c.c.  determine  the  iron: 

a.  In  the  solution  of  the  salt  acidulated  with  sulphuric  acid 
(Vol.  I,  p.  318,/?). 

/?.  In  the  solution  acidulated  with  hydrochloric  acid,  i.e.,  after 
the  addition  of  about  30  c.c.  hydrochloric  acid  of  sp.  gr.  1  •  12  (Vol.  I, 

p.3i9,r). 

7-.  In  the  solution  acidulated  with  hydrochloric  acid  as  in  /?, 
with  the  addition  of  20  c.c.  of  a  solution  of  manganous  sulphate 
containing  200  grm.  per  litre.  By  this  addition  the  disturbing 
influence  of  the  hydrochloric  acid  is  counteracted  (F.  KESSLER;  CL. 
ZIMMERMANN)  . 

d.  In  the  solution  acidulated  with  hydrochloric  acid  as  in  /?, 
with  the  addition  of  10  to  20  c.c.  of  a  cold,  saturated  solution  of 
lead  chloride  (N.  W.  THOMAS). 

FeO 71-900  18-33 

(NH4)20 52-144  13-29 

2SO3 160-140  40-82 

6H20 108-096  27-56 

392-280     100-00 


DETERMINATION    OF    IRON   WITH    STANNOUS    CHLORIDE.    971 

15.  VOLUMETRIC  DETERMINATION  OF  IRON  WITH  STANNOUS 

CHLORIDE. 

Warm  about  5  grm.  of  the  finely  powdered  brown  hematite 
(dried  at  100°  and  moderately  ignited)  with  strong  hydrochloric 
acid  until  the  ferric  oxide  has  completely  dissolved,  add,  if  neces- 
sary, a  little  potassium  chlorate,  then  heat  until  all  the  free  chlorine 
has  been  expelled,  dilute,  filter,  make  up  the  solution  to  250  c.c.  or 
500  c.c.,  and  mix  by  shaking.  In  50  or  100  c.c.  of  the  solution 
determine  the  iron  by  means  of  stannous  chloride  according  to 
§  113,  3,  6,  a  (Vol.  I,  p.  327). 

16.  DETERMINATION  OF  NITRIC  ACID  IN  POTASSIUM  NITRATE. 
Heat  pure  potassium  nitrate,  but  not  to  fusion,  and  transfer 

it  to  a  dry,  well-stoppered  tube. 

Determine  the  nitric  acid  in  0-2  to  0-3  grm.  as  hi  §  149,  II,  d,  ft 

(Vol.  I,  p.  577). 

K,O 94-24  46-57 

N2O5 108-08       53-43 

202-30      100-00 

17.  SEPARATION  OF  MAGNESIUM  FROM  SODIUM. 

Dissolve  about  0-2  grm.  pure  recently  ignited  magnesia  (which 
is  easily  obtained  by  igniting  pure  magnesium  oxalate,  but  which, 
for  the  sake  of  safety,  should  be  washed  with  boiling  water  and 
after  drying,  again  ignited)  and  about  0-3  grm.  pure  well-dried 
sodium  chloride  in  dilute  hydrochloric  acid  (avoiding  a  large  excess), 
and  separate  by  ammonium-phosphate  methods  described  in  §  153, 
/?,  4  (Vol.  I,  p.  612). 

As  it  is  important  that  the  ammonium  phosphate  should  be 
added  only  in  slight  excess,  a  solution  of  known  strength  should 
be  employed,  and  the  quantity  added  calculated.  From  the  filtrate 
remove  the  phosphoric  acid  by  means  of  ferric  chloride  (Vol.  I, 
p.  612,  6,  a). 


972  EXERCISES  FOR  PRACTICE. 

18.  SEPARATION  OF  POTASSIUM  FROM  SODIUM. 
Triturate  crystallized  sodium-potassium  tartrate  (Rochelle  salt), 
press  between  blotting-paper,  weigh  off  about  1-5  grm.,  heat  in  a 
platinum  crucible,  gently  at  first,  then  for  some  time  to  gentle 
ignition.  The  carbonaceous  residue  is  completely  extracted  with 
water,  and  the  residue,  after  being  collected  and  washed,  is  care- 
fully ignited,  and  again  extracted  with  water.  The  united  alka- 
line filtrates  are  then  acidulated  with  hydrochloric  acid,  the  acid 
fluid  is  evaporated  in  a  weighed  platinum  dish,  and  the  chlorides 
are  weighed  together  (§  97,  3).  Then  separate  them  by  platinic 
chloride  (§  152,  a,  and  this  volume,  pp.  345  and  874) ;  then  weigh 
the  potassium-platinic  chloride,  and  calculate  the  sodium  from 
the  difference. 

K20 94-22 

Na20 62-10 

C8H8O10 264-064 

8H2O.' 144-128 


564-512  100-00 

19.  VOLUMETRIC   DETERMINATION   OF  CHLORINE   IN    CHLORIDES, 

AND  THE  INDIRECT  DETERMINATION  OF  THE  POTASSA 

AND  SODA  IN  ROCHELLE  SALT. 

a.  Preparation  and  examination  of  the  solution  of  silver  nitrate 
(§141, 1,  6,  a,  Vol.  I,  p.  522). 

b.  Indirect   determination   of   the   sodium   and   potassium   in 
Rochelle  salt,  by  volumetric  estimation  of  the  chlorine  in  the  alkali 
chlorides  prepared  as  in  No.   18.      For  calculation  see  §  200,  af 
this  volume,  p.  166. 

20.  ACIDIMETRY. 

a.  Preparation  of  normal  hydrochloric  acid  and  soda-lye  (§  215, 
I,  p.  293,  this  volume). 

b.  Testing  the  correctness  of  the  normal  hydrochloric  acid  with 
pure  sodium  carbonate,  and  with  Iceland  spar  (§  215,  II,  p.  301, 
this  volume). 


ACIDIMETRY.  973 

c.  Preparation  of  normal  sulphuric  acid  by  means  of  normal 
soda  solution,  known  to  be  correct. 

d.  Determination  of  the  strength  of  a  diluted  sulphuric  acid 
by  its  specific  gravity:  a,  By  means  of  the  pyknometer  (§  209,  a, 
p.  242,  or  §  278,  p.  765,  this  volume;   or  6,    By  the    araeometer ; 
or  c,    By  MOHR'S    balance  (Zeitschr.  f.   analyt.    Chem.,  ix,  233). 
For  the  calculation  see  §  214, I,  a,  p.  285  this  volume. 

e.  Determination  of  the  strength  of  the  same  diluted  sulphuric 
acid  by  normal  soda  solution  (§  215,  III,  a,  p.  302,  this  volume), 
using  various  indicators  (§  215,  6,  pp.   309  to  312,  this  volume). 
Compare  also  THOMSON  (Zeitsch.  f.  analyt.  Chem.,  xxiv,  222). 

/.  Determination  of  the  strength  of  a  vinegar  (§  215,  III,  a 
and  6,  3,  pp.  302  and  303,  this  vol.).  In  the  case  of  colorless  or  only 
slightly  colored  vinegar,  phenolphtalein  is  to  be  particularly 
recommended. 

g.  Determination  of  the  total  tartaric  acid  in  potassium  bitar- 
trate,  according  to  the  method  of  GOLDENBERG,  GEROMONT  &  Co. 
(Zeitschr.  f.  analyt.  Chem.,  xxn,  270). 

Heat  to  boiling  exactly  3  grm.  of  the  finely  powdered  substance 
with  30  to  40  c.c.  water  and  2  to  2-5  grm.  potassium  carbonate 
for  10  to  20  minutes,  with  frequent  stirring;  when  somewhat  cooled, 
transfer  the  liquid  (which  now  contains  all  the  tartaric  acid  in  the 
form  of  neutral  potassium  tartratg)  to  a  100-c.c.  flask  or  cylinder, 
allow  to  become  perfectly  cold,  fill  up  the  flask  or  cylinder  to  the 
mark,  and  shake ;  after  standing  a  while,  filter  through  a  dry  filter- 
paper  into  a  dry  flask.  Then  evaporate  50  c.c.  of  the  filtrate  down 
to  10  c.c.,  add  2  c.c.  glacial  acetic  acid  to  convert  all  the  neutral 
tartrate  into  potassium  bitartrate,  add  100  to  120  c.c.  of  95-per 
cent,  (at  least)  alcohol,  stir  vigorously,  and  after  allowing  to  stand 
for  a  while,  filter.  Wash  the  residue  with  95-per  cent,  alcohol  until 
the  washings,  when  diluted  with  water,  no  longer  have  an  acid  re- 
action. Now  retransfer  the  still  moist  precipitate  with  the  filter 
to  the  porcelain  dish,  and  heat  to  boiling  with  water,  under  con- 
stant stirring.  Titrate  this  liquid  with  normal  soda  solution,  using 
litmus  tincture  or  phenolphtalein  as  indicator.  The  number  of 
c.c.  used,  when  multiplied  by  10,  gives  at  once  the  percentage  of 


974  EXERCISES    FOR    PRACTICE. 

tartaric  acid  in  the  substance  examined,  as  it  relates  to  1.5  grmv 
i.e.,  the  quantity  corresponding  to  yf^-  equivalent  of  tartaric  acid, 
which,  in  the  form  of  potassium  bitartrate,  requires  10  c.c.  of  nor- 
mal soda  solution.  If  the  tartar  is  so  impure  that  the  precipitated 
potassium  bitartrate  is  not  white,  the  titration  must  be  effected  by 
the  aid  of  a  sensitive,  pale-red  litmus-paper  (p.  305, 3,  this  volume). 
Further,  when  this  is  the  case,  it  is  necessary,  in  order  to  obtain 
perfectly  accurate  results,  to  standardize  the  soda  solution  also 
against  chemically  pure  potassium  bitartrate  dried  at  100°,  using 
the  same  litmus-paper,  because  the  standard  thus  obtained  differs 
somewhat  from  that  obtained  by  normal  acid,  or  even  potassium 
bitartrate,  when  litmus  tincture  is  employed. 

h.  Determination  of  the  potassium  bitartrate  in  crude  tartar. 

The  following  method  may  be  used  instead  of  or  in  addition  to 
the  method  detailed  in  g,  i.e.,  the  determination  of  pure  potassium 
bitartrate  in  crude  tartar  or  in  beer-yeast  may  be  effected  by  F. 
KLEIN'S  *  method. 

First  determine  the  approximate  acidity  of  the  triturated, 
uniformly  mixed  substance  (p.  305,  3,  this  volume),  and  from  this 
ascertain  the  approximate  quantity  of  the  potassium  bitartrate. 
Then  weigh  off  so  much  as  will  contain  about  1  •  8  to  2  •  2  grin,  potas- 
sium bitartrate,  boil  repeatedly  (about  five  times)  with  water, 
decanting  each  time  through  a  filter;  finally  bring  the  residue 
on  to  the  filter  and  wash  it  with  boiling  water  until  the  washings 
cease  to  redden  litmus-paper  in  the  least  degree.  Now  evaporate 
the  mixed  washings  to  40  c.c.,  add  5  grm.  potassium  c  loride,  and 
stir  vigorously  for  15  minutes  with  a  gla  s  rod.  To  separate  the 
now  completely  deposited  potassium  bitartrate  from  the  liquid 
there  is  required  a  solution  made  by  dissolving  5  grm.  finely  pow- 
dered, pure  potassium  bitartrate  in  200  c.c.  distilled  water  in  a 
250-c.c.  flask,  and,  after  shaking,  adding  25  grm.  potassium  chloride, 
filling  the  flask  up  to  the  mark,  setting  aside  for  several  hours,  with 
frequent  shaking,  and  then  filtering. 

A  filter  is  now  moistened  with  this  solution  and  the  potassium- 

*  Zeitschr.  f.  analyt.  Chem.,  xxiv,  383. 


ALKALIMETRY.  975 

bitartrate  precipitate  brought  onto  it.  After  it  has  completely 
drained,  wash  it  by  dropping  onto  it  the  solution  just  described, 
using  altogether  about  15  c.c.,  then  allow  to  again  drain  thoroughly, 
retransfer  the  precipitate  together  with  the  filter  to  the  dish,  heat 
with  water,  and  titrate  the  potassium  bitartrate  with  seminormal 
soda  solution.*  KLEIN  recommends  phenolphtalein  as  indicator. 
If  the  impure  nature  of  the  precipitated  potassium  bitartrate 
necessitates  the  use  of  litmus  paper  for  titrating,  then  the  semi- 
normal  soda  solution  must  be  standardized  by  the  aid  of  the  same 
paper  against  pure,  potassium  bitartrate  dried  at  100°  (see  at  end 

of  g). 

21.  ALKALIMETRY. 

a.  Preparation  of  the  normal  acid  after  DESCROIZILLES  and 
GAY-LUSSAC  (§  219). 

b.  Valuation  of  commercial  potash  afte    expulsion  o   the  water 
by  gentle  ignition  (§  224,  III,  1,  p.  340  this  volume). 

a.  After  MOHR  (§  220). 

/?.  After  DESCROIZILLES  and  GAY-LUSSAC  (§  220). 

22.  DETERMINATION  OF  AMMONIUM. 

Treat  about  0-8  grm.  pure  (unsublimed),  and  dried  ammonium 
chloride  as  directed  (§  99,  3,  a,  Vol.  I,  p.  253). 

NH4 18-072        33-77        NH3 17-064          30-59 

Cl.  .         .35-45          66-23        HC1..         ..36-458          69-41 


53-522       100-00  53-522         100-00 

23.  SEPARATION  OP  IODINE  FROM  CHLORINE. 

Dissolve  about  0-8  grm.  pure  potassium  iodide  dried  at  180° 
(§  65.  6),  and  about  2  to  3  grm.  pure,  anhydrous  sodium  chloride, 
in  water  to  make  250  c.c.,  and  determine  the  iodine  and  chlorine: 

a.  In  50  c.c.  according  to  §  169,  2,  b  [263], 

For  calculation,  see  §  200,  c. 

6.  In  10  c.c.  according  to  §  169,  2,  c  [264]. 

*  As  the  40  c.e.  of  filtrate  contain  a  small  quantity  of  tartar,  a  correction 
must  be  made;  in  fact,  according  to  my  experience,  0-2  c.c.  of  seminormal 
alkali  should  be  allowed  for  40  c.c.  of  the  filtrate. 


976  EXERCISES    FOR    PRACTICE 


D.  ANALYSIS  OF  ALLOYS,  MINERALS,  INDUSTRIAL  PRODUCTS, 
ETC.,  IN  THE  GRAVIMETRIC  AND  VOLUMETRIC  WAY. 

24.  ANALYSIS  OF  BRASS. 

Brass  consists  of  from  25  to  35  per  cent,  of  zinc  and  from  75  to 
65  per  cent,  of  copper.  It  also  contains  usually  small  quantities  of 
tin  and  lead,  and  occasionally  traces  of  iron.  The  analysis  is  car- 
ried out  as  follows: 

a.  According  to  §  264,  first  method  (p.  655  this  volume). 

6.  Partly  by  electrolysis. 

a.  As  a  preliminary  test;  dissolve  about  2  grm.  pure,  pressed 
copper  sulphate  in  wat  r  to  make  250  c.c.,  and  in  50  c.c.  determine 
the  copper  by  electrolysis.  For  this  purpose  add  20  c.c.  nitric  acid 
of  1-2  sp.  gr.  and  130  c.c.  water  (p.  620  this  volume),  and  precipi- 
tate the  copper  by  the  lectric  current  (p.  621  this  volume). 

ft.  Dissolve  about  1  •  5  grm.  brass  in  nitric  acid,  separate  any  tin 
and  lead  as  in  a,  make  up  the  solutio  i  freed  from  these  to  250  c.c., 
and  in  50  c.c.  after  the  addition  of  20  c.c.  nitric  acid  of  1-2  sp.  gr., 
and  130  c.c.  water,  precipitat  the  copper  as  on  p.  502  this  volume. 
Without  interrupting  the  current,  draw  off  first  the  solution,  then 
the  washings,  into  a  flask,  by  means  of  a  suitable  aspirator,*  con- 
centrate the  whole  by  evaporating  down  to  about  100  c.c.,  and 
precipitate  the  zinc  as  in  a. 

25.  DETERMINATION  OF  SILVER  IN  SILVER  COIN. 

Dissolve  a  silver  coin  (say  a  dime)  in  16  to  20  c.c.  nitric  acid 
of  1  •  2  sp.  gr.  with  the  addition  of  a  little  water,  heat  until  all  nitrous 
acid  is  expelled,  dilute  to  100  c.c.,  and  in  50  c.c.  determine  the  silver 
volumetrically  by  VOLHARD'S  method  (p.  570  this  volume). 

26.  ANALYSIS  OF  SOFT  SOLDER  (TiN  AND  LEAD). 
According  to  §  267,  C,  II,  first  method  (p.  683  this  vol.). 

*  Compare,  for  example,  H.  FRESENIUS  and  F.  BERGMANN,  Zeitschr.  j. 
analyt.  Chem.,  xix,  316. 


See  §  235. 


ANALYSIS    OF   FELSPAR.  977 

27.  ANALYSIS  OF  A  DOLOMITE. 
28.  ANALYSIS  OF  FELSPAR. 


a.  Decomposition  by  sodium  carbonate  (§  140,  II,  b,  a) ;  re- 
moval of  the  silicic  acid  which  is  weighed  and  then  volatilized 
by  hydrofluoric  acid  (Vol.  I,  p.  5 11,  second  paragraph)  in  order  to 
ascertain  whether  the  silica  contains  any  alumina;  precipitation 
of  the  aluminium  with  the  small  quantity  of  iron  as  hydroxides 
by  ammonia  (hi  platinum  or  Berlin  porcelain,  not  hi  glass  vessels) 
as  in  §  161, 4  [i  15] ;  separation  of  barium,  if  present,  from  the  filtrate 
with  dilute  sulphuric  acid,  and  then  of  calcium  with  ammonium 
oxalate,  as  in  §  154  6  [36].  Finally,  solution  of  the  weighed  alu- 
mina in  concentrated  hydrochloric  acid,  separation  and  weighing  of 
traces  of  silica  if  present;  evaporation  with  sulphuric  acid  and 
volumetric  determination  of  iron,  generally  present  in  small  quan- 
tities as  in  §  160,  2  [97]. 

6.  Decompose  with  hydrofluoric  acid,  preferably  by  AL. 
MITSCHERLICH'S  method  (Vol.  I,  pp.  514  and  515).  Evaporate  with 
the  addition  of  a  little  sulphuric  acid  until  no  more  hydrochloric 
acid  is  evolved,  then  gradually  heat  more  strongly  until  the  greater 
part  of  the  free  sulphuric  acid  is  also  expelled  shake  up  the  res- 
idue with  water,  heat,  add  barium  chloride  cautiously  so  long  as 
a  precipitate  forms,  and  when  cold,  but  without  previous  filtration, 
add  ammonium  carbonate  and  ammonia.  Allow  to  settle  in  the 
cold,  filter,  evaporate  the  filtrate  to  dryness,  ignite  the  residue  in 
order  to  expel  the  ammonium  salts,  dissolve  in  water,  remove  any 
magnesium  and  any  small  quantities  of  barium  and  calcium 
that  may  be  present,  according  to  p.  418,  e,  this  vol.,  and  lastly 
determine  the  potassium  according  to  §  97,  3.  If  sodium  is  also 
present,  the  alkalies  should  be  separated  as  in  §  152  [i].  If  ex- 
ceedingly great  accuracy  is  desired,  the  small  quantity  of  potas- 
sium salt  precipitated  with  the  barium  sulphate  must  also  be 
taken  into  account,  see  p.  927  this  volume. 

c.  Decomposition  by  SMITH'S  method  (Vol.  I,  p.  519). 


978  EXERCISES    FOR    PRACTICE. 

29.  ANALYSIS  OF  ZINC  BLENDE. 
a.  Complete  Analysis. 

Proceed  to  determine  the  sulphur,  as  well  as  to  dissolve  and 
separate  any  lead  and  other  metals  of  the  fifth  or  sixth  groups 
that  may  be  present,  according  to  §  241,  first  method  (p.  431  this 
vol.),  after  which  proceed  as  follows:  Heat  the  filtrate  in  order 
to  expel  the  hydrogen  sulphide,  add  nitric  acid,  and  continue  the 
heat  in  order  to  convert  the  ferrous  into  ferric  iron,  allow  to  cool, 
and  add  an  excess  of  ammonia.  Then  filter,  wash,  dissolve  the 
precipitate  in  hydrochloric  acid,  and  precipitate  the  ferric  oxide 
and  any  aluminium  present,  as  basic  salt,  as  in  §  160,  3,  a  [82]. 
Concentrate  by  evaporation  the  filtrate  thus  obtained,  add  a  slight 
excess  of  ammonia  in  order  to  precipitate  any  slight  residual  alu- 
minium and  iron,  filter  if  necessary,  and  if  the  quantity  of  precipi- 
tate is  considerable,  repeat  the  solution  and  reprecipitation  of  the 
latter  with  hydrochloric  acid  and  ammonia.  Dissolve  the  precipi- 
tate in  hydrochloric  acid,  add  the  solution  to  the  hydrochloric-acid 
solution  of  the  main  precipitate  of  ferric  oxide,  precipitate  the 
mixed  solution  with  ammonia,  wash  the  precipitate,  then  dry  and 
weigh  it.  Then  dissolve  it  in  concentrated  hydrochloric  acid,  deter- 
mine any  residual  silica,  and  deduct  this  from  the  weight  found. 
If  the  solution  thus  obtained  contains  also  aluminium,  separate  the 
ferric  oxide  and  alumina  as  in  §  160,  2  [77]. 

Acidulate  with  acetic  acid  the  united  ammoniacal  filtrates  con- 
taining the  whole  of  the  zinc,  add  ammonium  acetate,  and  pre- 
cipitate with  hydrogen  sulphide  with  the  aid  of  heat;  then  thor- 
oughly wash  the  zinc  sulphide  first  by  decantation,  and  then  on 
the  filter,  with  hot  water  containing  a  little  ammonium  nitrate, 
and  determine  it  according  to  §  108,  2.  The  filtrate  from  the  zinc 
sulphide  concentrate  down  to  a  small  volume,  add  bromine,  then 
ammonia,  and  heat.  If  a  precipitate  of  hydrated  manganese  di- 
oxide forms,  filter  this  off,  wash  it  dry,  ignite,  and  weigh  as  mangano- 
manganic  oxide.  As  at  times  the  zinc  sulphide  carries  down  with 
it  small  quantities  of  manganese  sulphide,  it  is  necessary,  as  a  pre- 
caution, to  dissolve  the  weighed  zinc  sulphide  in  hydrochloric  acid,. 


ANALYSIS   OF    GALENA.  979 

with  the  addition  of  some  nitric  acid,  then  to  add  bromine  followed 
by  ammonia  to  the  solution,  and  to  then  ascertain  whether,  on 
digestion  at  a  gentle  heat,  any  flocks  of  hydrated  manganese 
dioxide  separate;  if  this  occurs,  the  manganese  so  precipitated 
should  be  determined  as  above,  and  the  quantity  taken  into  account 
in  the  calculation. 

6.  Volumetric  Determination  of  the  Zinc  according  to  §  242. 
30.  ANALYSIS  OF  GALENA. 

a.  Determination  of  the  sulphur,  lead,  iron,  etc.,  according  to 
§  259,  A,  1  (p.  574  this  volume). 

6.  Determination  of  the  silver  in  galena,  according  to  §  259, 
A,  3,  b  (p.  578  this  volume). 

31.  VALUATION  OF  CHLORINATED  LIME. 

According  to  §  233,  p.  376  this  volume. 

a.  By  PENOT'S  method  (p.   379  this  volume). 

b.  lodometrically  (p.  382  this  volume) .     The  preparation  of  the 
solutions  required  for  this,  and  the  method  of  determining  the 
liberated  iodine,  are  described  in  §  146. 

In  order  to  obtain  concordant  results  with  both  methods,  all 
the  preparations  must  first  be  properly  made,  so  that  the  exam- 
ination of  the  same  " chlorinated-lime  milk"  can  be  carried  out  in 
the  shortest  tune  by  the  methods  a  and  b. 

32.  VALUATION  OF  MANGANESE  (§  247). 

a.  After  FRESENIUS  and  WILL  (p.  458  this  volume). 

b.  After  BUNSEN  (p.  465  this  volume). 

c.  By  means  of  iron  (p.  466  this  volume). 

33.  DETERMINATION  OF  SULPHUR  IN  PYRITES. 

a.  Determination  hi  the  dry  way  (§  256,  II,  1,   p.  561  this 
volume) . 

b.  Determination  in  the  wet  way  (§  256,  II,  2,  6,  p.  564  this 
volume). 


980  EXERCISES  FOR  PRACTICE. 

34.  DETERMINATION  OF  ARSENIC  IN  AN  IRON  OCHRE  OR  IN  AN 
OCHREOUS  SEDIMENT  FROM  A  FERRUGINOUS  WATER. 

Digest  about  10  to  20  grm.  with  about  50  to  100  c.c.  pure  fum- 
ing hydrochloric  acid,  and  treat  the  solution  according  to  §  268, 
p.  691  this  volume.  If  the  receive;  is  connected  with  the  con- 
denser so  as  to  be  air-tight,  as  shown  in  Fig.  81,  Vol.  I,  p.  254, 
a  little  water  placed  in  the  receiver,  and  in  the  P  ELI  GOT  tube 
connected  with  it,  the  hydrochloric-acid  solution  mixed  with  the 
excess  of  ferrous-chloride  solution  may  be  distilled  at  once,  i.e., 
without  previously  diluting  it  with  water,  thus  attaining  the  pur- 
pose much  more  rapidly. 

35.  ANALYSIS  OF  GUNPOWDER. 
According  to  §  227. 

36.  DETERMINATION  OF  CHROMIUM  IN  CHROME  IRON  ORE. 
According  to  §  239,  I,  a,  b  or  c  and  II  b,  /?.     When  titrating 
the  excess  of  ferrous  oxide  with  potassium  permanganate,  care 
must  be  taken  to  add  manganese  sulphate  (see  Exercise  14,  c). 

37.  DETERMINATION  OF  MANGANESE  IN  A  MANGANESE  ORE. 
According  to  §  250. 

38.  ANALYSIS  OF  A  CLAY  OR  A  SOIL. 

a.  Mechanical   analysis,  according  to   §  238,  I,  or  §  293,  re- 
spectively. 

b.  Chemical  analysis,  according  to  §  238,  II,  or  §  296,  respec- 
tively. 

39.  DETERMINATION  OF  NICKEL  AND  COBALT  IN  AN  ORE. 
According  to  §  251,  first  method. 

40.  DETERMINATION    IN    PIG    IRON    OF    CHEMICALLY-COMBINED 
CARBON,  GRAPHITE,   SULPHUR,   PHOSPHORUS,   SILICON,  AND 

ANY  OTHER  CONSTITUENTS  WHICH  MAY  BE  PRESENT. 
According  to  §  255. 


ANALYSIS    OF   SPRING-   OR   MINERAL  WATER.  981 

41.  ANALYSIS  OF  A  SPRING  WATER  OR  A  MINERAL  WATER. 
According  to  §  205  or  §  206,  et  seq.,  respectively. 

42.  ANALYSIS  OF  A  PLANT  ASH. 
According  to  §§  283  to  290. 

43.  DETERMINATION  OF  THE  SUGAR  IN  FRUIT,  HONEY,  MILK,  OR 

THE  LIKE. 

According  to  §§  274  to  277. 

44.  DETERMINATION  OF  ANTHRACENE  IN  A  CRUDE  ANTHRACENE. 
According  to  §  282. 

45.  DETERMINATION  OF  ALCOHOL  IN  WINE   OR    OTHER  LIQUID 

CONTAINING  ALCOHOL. 
According  to  §  278. 

46.  DETERMINATION  OF  TANNIC  ACID  IN  TANNING  MATERIALS.. 
According  to  §  279. 

E.  DETERMINATION  OF  THE  SOLUBILITY  OF  SALTS. 

47.  DETERMINATION  OF  THE  DEGREE  OF  SOLUBILITY  OF 
COMMON  SALT. 

a.  At  boiling  heat. — Dissolve  perfectly  pure  pulverized  sodium 
chloride  in  distilled  water,  in  a  flask,  heat  to  boiling,  and  keep  in 
ebullition  until  part  of  the  dissolved  salt  separates.     Filter  the 
fluid  now  with  the  greatest  expedition,  through  a  funnel  surrounded 
with  boiling  water  and  covered  with  a  glass  plate,  into  an  accurately 
tared  capacious  measuring  flask.     As  soon  as  about  100  c.c.  of 
fluid  have  passed  into  the  flask,  insert  the  cork,  allow  to  cool,  and 
weigh.     Fill  the  flask  now  up  to  the  mark  with  water,  and  deter- 
mine the  salt  in  an  aliquot  portion  of  the  fluid,  by  evaporating  in  a 
platinum  dish  (best  with  addition  of  some  ammonium  chloride, 
which  will,  in  some  measure,  prevent  decrepitation) ;  or  by  deter- 
mining the  chlorine  (§  141). 

b.  At  14°. — Allow  the  boiling  saturated  solution  to  cool  down 


982  EXERCISES   FOR   PRACTICE. 

to  this  temperature  with  frequent  shaking,  and  then  proceed  as 
in  a. 

100  parts  of  water  dissolve  at  109-7°. .  .  .40-35  of  sodium  chloride. 
100      "     "     "          "        "     14° 35-87  "      *• 

48.  DETERMINATION  OF  THE  DEGREE  OF  SOLUBILITY  OF 
CALCIUM  SULPHATE. 

a.  At  100°. 

6.  At  12°. 

Digest  pure  pulverized  calcium  sulphate  for  some  time  with 
water,  in  the  last  stage  of  the  process  at  40°  to  50°  (at  which  tempera- 
ture sulphate  of  lime  is  most  soluble) ;  shake  the  mixture  frequently 
during  the  process.  Decant  the  clear  solution,  together  with  a 
little  of  the  precipitate,  into  two  flasks,  and  boil  the  fluid  in  one  of 
them  for  some  time;  allow  that  in  the  other  to  cool  down  to  12°, 
with  frequent  skaking,  and  let  it  stand  for  some  time  at  that  tem- 
perature. Then  filter  both  solutions,  weigh  the  filtrates,  and  deter- 
mine the  amount  of  calcium  sulphate  respectively  contained  in 
them,  by  evaporating  and  igniting  the  residues. 

100  parts  of  water  dissolve  at  100° 0-217  of  anhydrous  calcium  sulphate 

100     "      "     "  "       "     12° 0-233  "         "  "  " 

Compare  MARIGNAC,  Zeitschr.  /.  analyt.  Chem.,  xm,  57. 


F.  DETERMINATION  OF  THE  SOLUBILITY  OF  GASES  IN  LIQUIDS; 
AND  ANALYSIS  OF  GASEOUS  MIXTURES. 

49.  DETERMINATION    OF    THE    ABSORPTION-COEFFICIENT    OF 
SULPHUROUS  ACID. 

See  Ann.  d.  Chem.  u.  Pharm..  xcv,  1;  also  §  131,  2. 

50.  ANALYSIS  OF  ATMOSPHERIC  AIR. 

Determination  of  the  carbonic  acid  (§  336  to  §  339),  and  oxygen 
tt  341). 


ANALYSIS   OF  TARTARIC   ACID.  983 

G.     ORGANIC     ANALYSIS,     AND     DETERMINATIONS     OF     THE 

EQUIVALENTS  OF  ORGANIC  COMPOUNDS;   ALSO  ANALYSES 

IN  WHICH  ORGANIC  ANALYSIS  HAS  TO  BE  EMPLOYED. 

51.  ANALYSIS  OF  TARTARIC  ACID. 
Select  clean  and  white  crystals.     Powder  and  dry  at  100°. 

a.  Burn  with  cupric  oxide,  by  LIEBIG'S  method  (§  174). 

b.  Burn  with  cupric  oxide,  by  BUN  SEN'S  method  (§  175). 

c.  Burn  in  oxygen  (§  178). 

C4 48-000  31-99 

H0 6-048  4-03 

0«.  .  96-000  63-98 


150-048  100-00 

-52.  DETERMINATION  OF  THE  NITROGEN  IN  CRYSTALLIZED  POTAS- 
SIUM FERROCYANIDE. 

Triturate  the  perfectly  pure  crystals,  press  hi  blotting-paper, 
if  necessary,  and  preserve  in  a  closed  tube  Determine  the  nitro- 
gen: 

a.  By  VARRENTRAPP- WILL'S  method  (§  186). 

b.  By  PELIGOT'S  modification  of  VARRENTRAPP-WILL'S  method 
(§  187). 

c.  By  WILFARTH'S  modification  of  KJELDAHL'S  process  (§  326). 

4>3.  ANALYSIS  OF  URIC  ACID  (or  any  other  pure  organic  compound 

of  carbon,  hydrogen  oxygen,  and  nitrogen). 
Dry  pure  uric  acid  at  100° 

a.  Determine  the  carbon  and  hydrogen  according  to  §  183. 

b.  Determine  the  nitrogen : 
a.  According  to   §  187. 

t8.  By  KJELDAHL'S  process,  WILFARTH'S  modification  (§  326). 
f.  By  DUMAS'  method  (§  185). 

C5 60-00 

N4 56-16 

H4 4-032 

O8 48-00 

168-192    100-00 


984  EXERCISES   FOR   PRACTICE. 

54.  ANALYSIS  OF  ETHER. 

The  portion  employed  must  have  been  recently  rectified  and 

rendered  anhydrous  by  digestion    with   fused  calcium   chloride. 
Process  §  180. 

C4 48-00  64-79 

Hlo 10-08  13-61 

O. .                                                16-00  21-60 


74-08  100-00 

55.  ANALYSIS  OF  A  HARD  COAL. 

According  to  §  272,  B,  p.  721  this  volume. 
The  determination  is  best  effected  by  WILFARTH'S  modification 
of  KJELDAHL'S  method  (§  326). 

56.  ANALYSIS  OF  A  BONE  MEAL. 
According  to  §  330,  a. 

57.  ANALYSIS  OF  A  MANURE  MIXTURE  IN  WHICH  THE  NITROGEN 

IS  PRESENT  IN  THE  FORM  OF  AMMONIA,  NlTRIC  ACID,  AND 

IN  ORGANIC  COMBINATION,  AND  THE  PHOSPHORIC  ACID 

IS  PRESENT  IN  DIFFERENT  DEGREES  OF  SOLUBILITY. 

According  to  §  333. 

58.  ANALYSIS  OF  BENZOIC  ACID,  AND  DETERMINATION  OF 
ITS  EQUIVALENT. 

a.  The  silver  in  silver  benzoate  is  determined  as  directed  in  §  115, 
1  or  4. 

b.  The  carbon  and  hydrogen  in  benzoic  acid  dried  at  100°,  are 
determined  by  any  suitable  method.     Calculation,  §  203,  2. 

59.  ANALYSIS  OF  AN  ORGANIC  BASE,  AND  DETERMINATION 

OF  ITS  EQUIVALENT. 

Analysis  of  the  base  and  its  platinum  double  salt.     Calculation, 
§  203,  3. 

60.  DETERMINATION  OF  THE  DENSITY  OF  CAMPHOR  VAPOR. 
Method  described  in  §  194.     Calculation,  §  204. 


ANALYTICAL   EXPERIMENTS.  985 


ANALYTICAL  EXPERIMENTS. 

1.  ACTION  OF  WATER  UPON  GLASS  AND  PORCELAIN  VESSELS,  IN 
THE  PROCESS  OF  EVAPORATION  (to  §  41). 

A  large  bottle  was  filled  with  water  cautiously  distilled  from  a  copper  boiler 
with  a  tin  condensing  tube.  All  the  experiments  hi  1  were  made  with  this 
water. 

a.  300  c.c.,  cautiously  evaporated  in  a  platinum  dish,  left  a  residue  weigh- 
ing, after  ignition,  0-0005  grai.  =0-0017  per  1000. 

6.  600  c.c.  were  evaporated,  boiling,  nearly  to  dryness,  in  a  wide  flask  of 
Bohemian  glass;  the  residue  was  transferred  to  a  platinum  dish,  and  the 
flask  rinsed  with  100  c.c.  distilled  water,  which  was  added  to  the  residue  in  the 
dish ;  the  fluid  in  the  latter  was  then  evaporated  to  dryness,  and  the  residue 
ignited. 

The  residue  weighed 0-0104  grm. 

Deducting  from  this  the  quantity  of  fixed  matter  origi- 
nally contained  in  the  distilled  water,  viz 0-0012      " 

There  remains  substance  taken  up  from  the  glass 0-0092     " 

=0-0153  per  1000. 

In  three  other  experiments,  made  hi  the  same  manner,  300  c.c.  left,  in  two 
0 •  0049  grm.,  in  the  third  0 •  0037  grm. ;  which,  calculated,  for  600  c.c.,  gives  an 

average  of 0-0090  grm. 

And  after  a  deduction  of 0-0012      " 

0-0078     " 
=0-013  per  1000. 

We  may  therefore  assume  that  1  litre  of  water  dissolves,  when  boiled  down 
to  a  small  bulk  in  glass  vessels,  about  14  milligrammes  of  the  constituents  of 
the  glass. 

c.  600  c.c.  were  evaporated  nearly  to  dryness  in  a  dish  of  Berlin  porcelain 
and  in  all  other  respects  treated  as  in  6. 

The  residue  weighed 0  •  0015  grm. 

Deducting  from  this  the  quantity  of  fixed  matter  con- 
tamed  in  the  distilled  water,  viz 0-0012      " 


There  remains  substance  taken  up  from  the  porcelain. . .   0-0003      " 
=0-0005  per  1000. 

2.  ACTION  OF  HYDROCHLORIC  ACID  UPON  GLASS  AND  PORCELAIN  VESSELS, 
IN  THE  PROCESS  OF  EVAPORATION  (to  §  41). 

The  distilled  water  used  in  1  was  mixed  with  -fa  of  pure  hydrochloric  acid. 

a.  300  grm.,  evaporated  in  a  platinum  dish,  left  0-002  grm.  residue. 

&.  300  grm.,  evaporated  first  in  Bohemian  glass  nearly  to  dryness,  then  in  a 
platinum  dish,  left  0  •  0019  residue ;  the  dilute  hydrochloric  acid,  therefore,  had 
not  attacked  the  glass. 


EXERCISES   FOR    PRACTICE. 

c.  300  grm..  evaporated  in  Berlin  porcelain,  etc.,  left  0-0036  grm.,  accord- 
ingly after  deducting  0-002,  0-0016  =  0-0053  per  1000. 

d.  In  a  second  experiment  made  in  the  same  manner  as  in  c.,  the  residue 
amounted  to  0-0034,  accordingly  after  deducting  0-002,  0-0014=0-0047  per 
1000. 

Hydrochloric  acid,  therefore,  attacks  glass  much  less  than  water,  whilst 
porcelain  is  about  equally  affected  by  water  and  dilute  hydrochloric  acid.  This 
shows  that  the  action  of  water  upon  glass  consists  in  the  formation  of  soluble 
basic  silicates.  Porcelain  is  attacked  much  more  by  water  containing  hydro- 
chloric acid  than  by  pure  water. 

3.  ACTION  OF  SOLUTION  OF  AMMONIUM  CHLORIDE  UPON  GLASS  AND 
PORCELAIN  VESSELS,  IN  THE  PROCESS  OF  EVAPORATION  (to  §  41). 

In  the  distilled  water  from  1,  T^  of  ammonium  chloride  was  dissolved,  and 
the  solution  filtered. 

a.  300  c.c.,  evaporated  in  a  platinum  dish,  left  0-006  grm.  fixed  residue. 

6.  300  c.c.,  evaporated  first  nearly  to  dryness  in  ^Bohemian  glass,  then  to 
dryness  in  a  platinum  dish,  left  0-0179  grm. ;  deducting  from  this  0  •  006  grm., 
there  remains  substance  taken  up  from  the  glass,  0-0119  =0-0397  per  1000. 

c.  300  c.c.,  treated  in  the  same  manner  in  Berlin  porcelain,  left  0-0178, 
deducting  from  this  0-006,  there  remains  0-0118=0-0393  per  1000. 

Solution  of  ammonium  chloride,  therefore,  strongly  attacks  both  glass  and 
porcelain  in  the  process  of  evaporation. 

4.  ACTION  OF  SOLUTION  OF  SODIUM  CARBONATE  UPON  GLASS  AND 
PORCELAIN  VESSELS  (to  §  41). 

In  the  distilled  water  from  1,  TV  of  pure  crystallized  sodium  carbonate  was 
dissolved. 

a.  300  c.c.,  supersaturated  with  hydrochloric  acid  and  evaporated  to  dry- 
ness  in  a  platinum  dish,  etc.,  gave  0-0026  grm.  silica  =0-0087  per  1000. 

6.  300  c.c.  were  gently  boiled  for  three  hours  in  a  glass  vessel,  the  evaporat- 
ing water  being  replaced  from  time  to  time ;  the  tolerably  concentrated  liquid 
was  then  treated  as  in  a;  it  left  a  residue  weighing  0-1376  grm.;  deducting 
from  this  the  0  •  0026  grm.  left  in  a,  there  remains  0-135  grm.  =0  •  450  per  1000. 

c.  300  c.c.,  treated  in  the  same  manner  as  in  b,  in  a  porcelain  vessel,  left 
0-0099;  deducting  from  this  0-0026  grm.,  there  remains  0-0073=0-0243 
per  1000. 

Which  shows  that  boiling  solution  of  sodium  carbonate  attack^  glass  very 
strongly,  and  porcelain  also  in  a  very  marked  manner. 

5.  WATER  DISTILLED  FROM  GLASS  VESSELS  (to  §  56,  1). 

42-41  grm.  of  water  distilled  with  extreme  caution  from  a  tall  flask  with  a 
LIEBIG'S  condenser,  left  upon  evaporation  in  a  platinum  dish,  a  residue  weigh- 
ing, after  ignition,  0-0018  grm.,  consequently  ^kw 


ANALYTICAL    EXPERIMENTS.  987 

6.  POTASSIUM  SULPHATE  AND  ALCOHOL  (to  §  68,  a). 

a.  Ignited  pure  potassium  sulphate  was  digested  cold  with  absolute  alco- 
hol, for  several  days,  with  frequent  shaking;  the  fluid  was  filtered  off,  the 
filtrate  diluted  with  water,  and  then  mixed  with  barium  chloride.  It  re- 
mained perfectly  clear  upon  the  addition  of  this  reagent,  but  after  the  lapse 
of  a  considerable  time  it  began  to  exhibit  slight  opalescence.  Upon  evapora- 
tion to  dryness,  there  remained  a  very  trifling  residue,  which  gave,  how- 
ever, distinct  indications  of  the  presence  of  sulphuric  acid. 

6.  The  same  salt  treated  in  the  same  manner,  with  addition  of  some  pure 
concentrated  sulphuric  acid,  gave  a  filtrate  which,  upon  evaporation  in  a  plati- 
num dish,  left  a  clearly  perceptible  fixed  residue  of  potassium  sulphate. 

7.  DEPORTMENT  OF  POTASSIUM  CHLORIDE  IN  THE  AIR  AND  AT  A 
HIGH  TEMPERATURE  (to  §  68,  c). 

0-9727  grm.  of  pure,  ignited  (not  fused)  pure  potassium  chloride,  heated 
for  10  minutes  to  dull  redness  in  an  open  platinum  dish,  lost  0-0007  grm. ;  the 
salt  was  then  kept  for  10  minutes  longer  at  the  same  temperature,  when  no 
further  diminution  of  weight  was  observed.  Heated  to  bright  redness  and 
semi-fusion,  the  salt  suffered  a  further  loss  of  weight  to  the  extent  of  0-0009 
grm.  Ignited  intensely  and  to  perfect  fusion,  it  lost  0-0034  grm.  more. 

Eighteen  hours'  exposure  to  the  air  produced  not  the  slightest  increase  of 
weight. 

8.  SOLUBILITY  OF  POTASSIUM  PLATINIC  CHLORIDE  IN  ALCOHOL  (to  §  68,  d). 
a.  In  absence  of  free  Hydrochloric  Acid. 

a.  An  excess  of  perfectly  pure,  recently  precipitated  potassium  platinic 
chloride  was  digested  for  6  days  at  15  to  20°,  with  alcohol  of  97  •  5  per  cent.,  in  a 
stoppered  bottle,  with  frequent  shaking.  72  •  5  grm.  of  the  perfectly  colorless 
filtrate  left  upon  evaporation  in  a  platinum  dish  a  residue  which,  dried  at  100°, 
weighed  0  •  006  grm. ;  1  part  of  the  salt  requires  therefore  12083  parts  of  alcohol 
of  97  •  5  per  cent,  for  solution. 

{3.  The  same  experiment  was  made  with  alcohol  of  76  per  cent.  The  fil- 
trate might  be  said  to  be  colorless ;  upon  evaporation,  slight  blackening  ensued, 
on  which  account  the  residue  was  determined  as  platinum.  75  •  5  grm.  yielded 
0  •  008  grm.  platinum,  corresponding  to  0  •  02  grm.  of  the  salt.  One  part  of  the 
salt  dissolves  accordingly  in  3775  parts  of  alcohol  of  76  per  cent. 

f.  The  same  experiment  was  made  with  alcohol  of  55  per  cent.  The  fil- 
trate was  distinctly  yellowish.  63-2  grm.  left  0-0241  grm.  platinum,  cor- 
responding to  0  •  06  grm.  of  the  salt.  One  part  of  the  salt  dissolves  accordingly 
in  1053  parts  of  alcohol  of  55  per  cent. 

b.  In  presence  of  free  Hydrochloric  Acid. 

Recently  precipitated  potassium  platinic  chloride  was  digested  cold  with 
alcohol  of  76  per  cent.,  to  which  some  hydrochloric  acid  had  been  added.  The 
solution  was  yellowish;  67  grm.  left  0-0146  grm.  platinum,  which  corresponds 
to  0-0365  grm.  of  the  salt.  One  part  of  the  salt  dissolves  accordingly  in 
3185  parts  of  alcohol  mixed  with  hydrochloric  acid. 


EXERCISES    FOR    PRACTICE. 


9.  SODIUM  SULPHATE  AND  ALCOHOL  (to  §  69,  a). 

Experiments  made  with  pure  anhydrous  sodium  sulphate,  in  the  manner 
described  in  6,  showed  that  this  salt  comports  itself  both  with  pure  alcohol, 
and  with  alcohol  containing  sulphuric  acid,  exactly  like  potassium  sulphate. 

10.  DEPORTMENT  OF  IGNITED  SODIUM  SULPHATE  IN  THE  AIR  (to  §  69,  a). 

2  •  5169  grm.  anhydrous  sodium  sulphate  were  exposed,  in  a  watch-glass,  to 
the  open  air  on  a  hot  summer  day.  The  first  few  minutes  passed  without  any 
increase  of  weight,  but  after  the  lapse  of  5  hours  there  was  an  increase  of 
0-0061  grm. 

11.  EXPERIMENTS  WITH  SODIUM  NITRATE  (to  §  69,  6). 

a.  4*5479  grm.  of  pure  fused  sodium  nitrate  on  being  exposed  to  the  air 
(in  April,  in  fine  weather)  for  24  hours,  increased  in  weight  0  •  0006  grm. 

6.  4  •  5479  grm.  of  pure  sodium  nitrate  were  dissolved  in  water,  in  a  plati- 
num dish,  and  pure  nitric  acid  added  to  the  solution;  the  mixture  was  then 
evaporated  to  dryness  on  the  water-bath,  and  the  residue  cautiously  heated 
until  the  mass  at  the,  bottom  of  the  dish  began  to  fuse.  The  contents  of  the 
dish  when  cooled  weighed  4-5503  grm.,  and  after  being  heated  again  to  com- 
plete fusion,  4  •  5474  grm. 

12.  DEPORTMENT  OF  SODIUM  CHLORIDE  IN  THE  AIR  (to  §  69,  c). 
4-3281  grm.  of  chemically  pure,  moderately  ignited  (not  fused)  sodium 
chloride,  which  had  been  cooled  under  a  bell-glass  over  sulphuric  acid,  ac- 
quired during  45  minutes'  exposure  to  the  (somewhat  moist)  air  an  increase  of 
weight  of  0-0009  grm. 

13.  DEPORTMENT  OF  SODIUM  CHLORIDE  UPON  IGNITION  BY  ITSELF 

AND  WITH  AMMONIUM  CHLORIDE  (to  §  69,  c). 

4.3281  grm.  chemically  pure,  ignited  sodium  chloride  were  dissolved  in 
water,  in  a  moderate-sized  platinum  dish,  and  pure  ammonium  chloride  was 
added  to  the  solution,  which  was  then  evaporated  and  the  residue  gently 
heated  until  the  evolution  of  ammonium  chloride  fumes  had  apparently 
ceased.  The  residue  weighed  4  •  3334  grm.  It  was  then  very  gently  ignited 
for  about  2  minutes,  and  after  this  re-weighed,  when  the  weight  was  found  to 
be  4-3314  grm.  A  few  minutes'  ignition  at  red  heat  reduced  the  weight  to 
4-3275  grm.,  and  2  minutes'  further  ignition  at  a  bright  red  heat  (upon  which 
occasion  white  fumes  were  seen  to  escape),  to  4  •  3249  grm. 

14.  DEPORTMENT  OP  SODIUM  CARBONATE  IN  THE  AIR  AND  ON  IGNITION 

(to  §  69,  d). 

2-1061  grm.  of  moderately  ignited  chemically  pure  soduim  carbonate  were 
exposed  to  the  air  in  an  open  platinum  dish  in  July  in  bad  weather;  after  10 
minutes  the  weight  was  2  •  1078,  after  1  hour,  2-1113,  after  5  hours,  2  •  1257. 

1-4212  grm.  of  moderately  ignited  chemically  pure  sodium  carbonate  were 
ignited  for  5  minutes  in  a  covered  platinum  crucible,  but  so  that  no  fusion 
took  place,  and  the  weight  was  unaltered.  Heated  more  strongly  for  5 


ANALYTICAL   EXPERIMENTS.  989 

minutes  it  partially  fused,  and  then  weighed   1-4202.     After  being  kept 
fusing  for  5  minutes,  it  weighed  1  •  4135. 

15.  DEPORTMENT  OF  AMMONIUM    CHLORIDE    UPON    EVAPORATION 
AND  DRYING  (to  §  70,  a). 

0-5625  grm.  pure  and  perfectly  dry  ammonium  chloride  was  dissolved  in 
water  in  a  platinum  dish,  evaporated  to  dryness  in  the  water-bath,  and  com- 
pletely dried ;  the  weight  was  now  found  to  be  0  •  5622  grm.  (ratio  100 :  99  •  94). 
It  was  again  heated  for  15  minutes  in  the  water-bath,  and  afterwards  re- 
weighed,  when  the  weight  was  found  to  be  0-5612  grm.  (ratio  100:99-77). 
Exposed  once  more  for  15  minutes  to  the  same  temperature,  the  residue 
weighed  0-5608  grm.  (ratio  100  :  99-69). 

16.  SOLUBILITY  OF  AMMONIUM  PLATINIC  CHLORIDE  IN  ALCOHOL  (to  §  70, 6). 
a.  In  absence  of  free  Hydrochloric  Acid. 

a.  An  excess  of  perfectly  pure,  recently  precipitated  ammonium  platinic 
chloride  was  digested  for  6  days,  at  15  to  20°,  with  alcohol  of  97  •  5  per  cent.,  in 
a  stoppered  bottle,  with  frequent  agitation. 

74-3  grm.  of  the  perfectly  colorless  filtrate  left,  upon  evaporation  and 
ignition  in  a  platinum  dish,  0-0012  grm.  platinum,  corresponding  to  0-0028 
of  the  salt.  One  part  of  the  salt  requires  accordingly  26535  parts  of  alcohol 
of  97  •  5  per  cent. 

/?.  The  same  experiment  was  made  with  alcohol  of  76  per  cent.  The 
filtrate  was  distinctly  yellowish. 

81.75  grm.  left.  0-0257  platinum,  which  corresponds  to  0-0584  grm.  of  the 
salt,  One  part  of  the  salt  dissolves  accordingly  in  1406  parts  of  alcohol  of 
76  per  cent. 

f.  The  same  experiment  was  made  with  alcohol  of  55  per  cent.  The 
nitrate  was  distinctly  yellow.  Slight  blackening  ensued  upon  evaporation, 
and  56-5  grm.  left  0-0364  platinum,  which  corresponds  to  0-08272  grm.  of 
the  salt.  Consequently,  1  part  of  the  salt  dissolves  in  665  parts  of  alcohol  of 
55  per  cent. 

6.  In  presence  of  Hydrochloric  Acid. 

The  experiment  described  in  /?  was  repeated  with  this  modification,  that 
some  hydrochloric  acid  was  added  to  the  alcohol.  76  •  5  grm.  left  0  •  0501  grm. 
of  platinum,  which  corresponds  to  0-1139  grm.  of  the  salt.  672  parts  of  the 
acidified  alcohol  had  therefore  dissolved  1  part  of  the  salt. 

17.  SOLUBILITY  OF  BARIUM  CARBONATE  IN  WATER  (to  §  71,  b). 
a.  In  Cold  Water. — Perfectly  pure,  recently  precipitated  BaCO3  was  di- 
gested for  5  days  with  water  of  16  to  20°,  with  frequent  shaking.  The  mix- 
ture was  filtered,  and  a  portion  of  the  filtrate  tested  with  sulphuric  acid, 
another  portion  with  ammonia ;  the  former  reagent  immediately  produced 
turbidity  in  the  fluid,  the  latter  only  after  the  lapse  of  a  considerable  time. 
84-82  grm.  of  the  solution  left,  upon  evaporation,  0-006  BaCO3.  One  part 
of  that  salt  dissolves  consequently  in  14137  parts  of  cold  water. 


990  EXERCISES  FOR   PRACTICE. 

6.  In  Hot  Water. — The  same  barium  carbonate  being  boiled  for  10  minutes 
•with  pure  distilled  water,  gave  a  filtrate  manifesting  the  same  reactions  as 
that  prepared  with  cold  water,  and  remaining  pertectly  clear  upon  cooling. 
84-82  grm.  of  the  hot  solution  leit,  upon  evaporation,  0-0055  grm.  of  barium 
carbonate.  One  part  of  that  salt  dissolves  therefore  in  15421  parts  of  boiling 
water. 

18.  SOLUBILITY  OF  BARIUM  CARBONATE  IN  WATER  CONTAINING  AMMONIA 
AND  AMMONIUM  CARBONATE  (to  §  71,  6). 

A  solution  of  chemically  pure  barium  chloride  was  mixed  with  ammonia 
and  ammonium  carbonate  in  excess,  gently  heated  and  allowed  to  stand  at 
rest  for  12  hours;  the  fluid  was  then  filtered  off;  the  filtrate  remained  per- 
fectly clear  upon  addition  of  sulphuric  acid;  but  alter  a  lapse  of  a  very  con- 
siderable time,  a  hardly  perceptible  precipitate  separated.  84-82  grm.  of 
the  filtrate  left,  upon  evaporation  in  a  small  platinum  dish,  and  subsequent 
gentle  ignition,  0  •  0006  grm.  One  part  of  the  salt  had  consequently  dissolved 
in  141000  parts  of  the  fluid. 

19.  SOLUBILITY  OF  BARIUM  SILICO-FLUORIDE  IN  WATER  (to  §  71,  c). 

a.  Recently  precipitated,  thoroughly  washed  barium  silico-fluoride  was 
digested  for  4  days  in  cold  water,  with  frequent  shaking;  the  fluid  was  then 
filtered  off,  and  a  portion  of  the  filtrate  tested  with  dilute  sulphuric  acid,* 
another  portion  with  solution  of  calcium  sulphate;  both  reagents  produced 
turbidity — the  former  immediately,  the  latter  after  one  or  two  seconds — pre- 
cipitates separated  from  both  portions  after  the  lapse  of  some  time.  84-82 
grm.  of  the  filtrate  left  a  residue  which,  after  being  thoroughly  dried,  weighed 
0-0223  grm.  One  part  of  the  salt  had  consequently  required  3802  parts  of 
cold  water  for  its  solution. 

6.  A  portion  of  another  sample  of  recently  precipitated  barium  silico-fluo- 
ride was  heated  with  water  to  boiling,  and  the  solution  allowed  to  cool  (upon 
which  a  portion  of  the  dissolved  salt  separated).  The  cold  fluid  was  left  for 
a  considerable  time  longer  in  contact  with  the  undissolved  salt,  and  was  then 
filtered  off.  The  filtrate  showed  the  same  deportment  with  solution  of  sul- 
phate of  lime  as  that  of  a.  84  •  82  grm.  of  it  left  0  •  025  grm.  One  part  of  the 
salt  had  accordingly  dissolved  in  3392  parts  of  water. 

20.  SOLUBILITY  OF  BARIUM  SILICO-FLUORIDE  IN  WATER  ACIDIFIED  WITH 
HYDROCHLORIC  ACID  (to  §  71,  c). 

a.  Recently  precipitated  pure  barium  silico-fluoride  was  digested  with  fre- 
quent agitation  for  3  weeks  with  cold  water  acidified  with  hydrochloric  acid. 
The  filtrate  gave  with  sulphuric  acid  a  rather  copious  precipitate.  84  •  82  grm. 
left  0-1155  grm.  of  thoroughly  dried  residue,  which,  calculated  as  barium 
silico-fluoride,  gives  733  parts  of  fluid  to  1  part  of  that  of  salt. 

6.  Recently  precipitated  pure  barium  silico-fluoride  was  mixed  with  water 
very  slightly  acidified  with  hydrochloric  acid,  and  the  mixture  heated  to  boil- 
ing. Cooled  to  12°,  84-82  grm.  of  the  filtrate  left  a  residue  of  0-1322  grm., 
Which  gives  640  parts  of  fluid  to  1  part  of  the  salt. 


ANALYTICAL   EXPERIMENTS.  991 

N.B.  The  solution  of  barium  silico-fluoride  in  hydrochloric  acid  is  not 
effected  without  decomposition;  at  least,  the  residue  contained,  even  after 
ignition,  a  rather  large  proportion  of  barium  chloride. 

21.  SOLUBILITY  OF  STRONTIUM  SULPHATE  IN  WATER  (to  §  72.  a), 

a.  In  Water  of  14°. 

84-82  grm.  of  a  solution  prepared  by  4  days'  d/gestion  of  recently  pre- 
cipitated strontium  sulphate  with  water  at  the  common  temperature,  left 
0-0123  grm.  of  strontium  sulphate.  One  part  of  strontium  sulphate  dissolves 
consequently  in  6895  parts  of  water. 

b.  In  Water  of  100°. 

84  •  82  grm.  of  a  solution  prepared  by  boiling  recently  precipitated  strontium 
sulphate  several  hours  with  water,  left  0-0088  grm.  Consequently  1  part  of 
strontium  sulphate  dissolves  hi  9638  parts  of  boiling  water. 

22.  SOLUBILITY  OF  STRONTIUM  SULPHATE  IN  WATER  CONTAINING 

HYDROCHLORIC  ACID  AND  SULPHURIC  ACID  (to  §  72,  a). 

a.  84-82  grm.  of  a  solution  prepared  by  3  days'  digestion,  left  0-0077  grm. 
SrS04. 

b.  42  •  41  grm.  of  a  solution  prepared  by  4  days'  digestion,  left  0  •  0036  grm. 

c.  Pure  strontium  carbonate  was  dissolved  in  an  excess  of  hydrochloric 
acid,  and  the  solution  precipitated  with  an  excess  of  sulphuric  acid  and  then 
allowed  to  stand  in  the  cold  for  a  fortnight.     84  •  82  grm.  of  the  filtrate  left 
0-0066  grm. 

In  a.  1  part  of  SrSO4  required  11016  parts. 

b.  1     "     "      "  "         11780     " 

c.  1     "     "      "  "         12791     " 

Mean 11862  parts. 

23.  SOLUBILITY  OF  STRONTIUM  SULPHATE  IN  DILUTE  NITRIC  Acn>, 

HYDROCHLORIC  ACID,  AND  ACETIC  ACID  (to  §  72,  a). 

a.  Recently  precipitated  pure  strontium  sulphate  was  digested  for  2  days 
in  the  cold  with  nitric  acid  of  4  •  8  per  cent.     1 50  grm.  of  the  filtrate  left  0  •  3451 
grm.     One  part  of  the  salt  required  accordingly  435  parts  of  the  dilute  acid 
for  its  solution;  in  another  experiment  1  part  of  the  salt  was  found  to  require 
429  parts  of  the  dilute  acid.     Mean,  432  parts. 

b.  The  same  salt  was  digested  for  2  days  in  the  cold  with  hydrochloric 
acid  of  8  •  5  per  cent.     100  grm.  left  0  •  21 1 5,  and  in  another  experiment,  0-2104 
grm.     One  part  of  the  salt  requires,  accoicdngly,  in  the  mean,  474  parts  of 
hydrochloric  acid  of  8  •  5  per  cent,  for  its  solution. 

c.  The  same  salt  was  digested  for  2  days  in  the  cold  with  acetic  acid  of  15-6 
per  cent.  C2H4O.,.     100  grm.  left  0-0126,  and  in  another  experiment,  0-0129 
grm.     One  part  of  the  salt  requires,  accordingly,  in  the  mean,  7843  parts  of 
acetic  acid  of  15-6  per  cent. 


992  EXERCISES    FOR    PRACTICE. 

24.  SOLUBILITY  OF  STRONTIUM  CARBONATE  IN  COLD  WATER  (to  §  72,  6). 

Recently  precipitated,  thoroughly  washed  strontium  carbonate  was  digest- 
ed several  days  with  cold  distilled  water,  with  frequent  shaking.  84  •  82  grm. 
of  the  nitrate  left,  upon  evaporation,  a  residue  weighing,  after  ignition,  0  •  0047 
grm.  One  part  of  strontium  carbonate  requires  therefore  18045  parts  of 
water  for  its  solution. 

25.  SOLUBILITY  OF  STRONTIUM  CARBONATE  IN  WATER  CONTAINING 

AMMONIA  AND  AMMONIUM  CARBONATE  (to  §  72,  6). 

Recently  precipitated,  thoroughly  washed  strontium  carbonate  was  di- 
gested for  4  weeks  with  cold  water  containing  ammonia  and  ammonium  car- 
bonate, with  frequent  shaking.  84.82  grm.  of  the  filtrate  left  0-0015  grm. 
SrCO3.  Consequently,  1  part  of  the  salt  requires  56545  parts  of  this  fluid  for 
its  solution. 

If  solution  of  strontium  chloride  is  precipitated  with  ammonium  carbonate 
and  ammonia  as  directed  §  102,  2,  a,  sulphuric  acid  produces  no  turbidity  in 
the  filtrate,  after  addition  of  alcohol. 

26.  SOLUBILITY  OF  CaCO3  IN  WATER  CONTAINING  AMMONIA  AND 

AMMONIUM  CARBONATE  (to  §  73,  6). 

Pure  dilute  solution  of  calcium  chloride  was  precipitated  with  ammonium 
carbonate  and  ammonia,  allowed  to  stand  24  hours,  and  then  filtered.  84  •  82 
grm.  left  0-0013  grm.  CaCO3.  One  part  requires  consequently  65246  parts. 

26,  a.  SOLUBILITY  OF  CALCIUM  CARBONATE  IN  COLD  AND  IN  BOILING 

WATER  (to  §  73,  6). 

a.  A  solution  prepared  by  boiling  as  in  26,  6,  was  digested  in  the  cold  for  4 
weeks,  with  frequent  agitation,  with  the  undissolved  precipitate.  84  •  82  grm. 
left  0-0080  CaCO3.  One  part  therefore  required  10601  parts. 

6.  Recently  precipitated  calcium  carbonate  was  boiled  for  some  time  with 
distilled  water.  42-41  grm.  of  the  filtrate  left,  upon  evaporation  and  gentle 
ignition  of  the  residue,  0  •  0048  CaCO3.  One  part  requires  consequently  8834 
parts  of  boiling  water. 

27.  DEPORTMENT  OF  CALCIUM  CARBONATE  UPON  IGNITION  IN  A  PLATINUM 

CRUCIBLE  (to  §  73,  6). 

0  •  7955  grm.  of  perfectly  dry  calcium  carbonate  was-exposed,  in  a  small  and 
thin  platinum  crucible,  to  the  gradually  increased  and  finally  most  intense 
heat  of  a  good  BERZELIUS'  lamp.  The  crucible  was  open  and  placed  obliquely. 
After  the  first  15  minutes  the  mass  weighed  0  •  6482 ;  after  half  an  hour  0  •  6256 ; 
after  one  hour  0-5927,  which  latter  weight  remained  unaltered  after  15 
minutes'  additional  heating.  This  corresponds  to  74-5  per  cent.,  whilst  the 
proportion  of  CaO  in  the  carbonate  is  calculated  at  56  per  cent. ;  there  re- 
mained therefore  evidently  still  a  considerable  amount  of  the  carbonic  acid. 

28.  COMPOSITION  OF  CALCIUM  OXALATE  DRIED  AT  100°  (to  §  73,  c). 
0-8510  grm.  of  thoroughly  dry  pure  calcium  carbonate  was  dissolved  in 
hydrochloric  acid ;  the  solution  was  precipitated  with  ammonium  oxalate  and 


ANALYTICAL    EXPERIMENTS.  993 

ammonia,  and  the  precipitate  collected  upon  a  weighed  filter  and  dried  at  100°, 
until  the  weight  remained  constant.  The  calcium  oxalate  so  produced 
weighed  1-2461  grm.  Calculating  this  as  CaC2O4-f- H2O,  the  amount  found 
contained  0-4772  CaO,  which  corresponds  to  56-07  per  cent,  in  the  calcium 
carbonate ;  the  calculated  proportion  of  CaO  in  the  latter  is  56  per  cent. 

29.  DEPORTMENT  OF  FRESHLY  IGNITED  CAUSTIC  LIME  ON  EXPOSURE 
TO  AIR  (to  §  73,  d). 

0-5599  grm.  of  caustic  lime,  obtained  by  igniting  calcium  oxalate  in  a 
covered  platinum  crucible  over  the  blow-pipe,  after  standing  in  the  scale  pan 
1  minute  weighed  0-5599  grm.;  after  2  minutes,  0-5605;  after  6  minutes, 
0-5609;  after  17  minutes,  0-5625.  The  platinum  crucible  containing  the 
caustic  lime,  was  left  for  15  minutes  in  the  desiccator  before  making  the  first 
weighing. 

30.  DEPORTMENT  OF  MAGNESIUM  SULPHATE  IN  THE  AIR  AND  UPON 
IGNITION  (to  §  74,  a). 

0-8135  grm.  of  perfectly  pure  anhydrous  MgSO4  in  a  covered  platinum 
crucible  acquired,  on  a  fine  and  warm  day  in  June,  in  half  an  hour,  an  increase 
of  weight  of  0  •  004  grm.,  and  in  the  course  of  12  hours,  of  0 •  067  grm.  The  salt 
could  not  be  accurately  weighed  in  the  open  crucible,  owing  to  continual 
increase  of  weight. 

0-8135  grm.,  exposed  for  some  time  to  a  very  moderate  red  heat,  suffered 
no  diminution  of  weight ;  but  after  5  minutes'  exposure  to  an  intense  red  heat, 
the  substance  was  found  to  have  lost  0-0075  grm.,  and  the  residue  gave  no 
longer  a  clear  solution  with  water.  About  0  •  2  grm.  of  pure  magnesium  sul- 
phate exposed  in  a  small  platinum  crucible,  for  15  to  20  minutes,  to  the  heat 
of  a  powerful  blast  gas  lamp,  gave,  with  dilute  hydrochloric  acid,  a  solution 
in  which  barium  chloride  failed  to  produce  the  least  turbidity. 

31.  SOLUBILITY  OF  AMMONIUM  MAGNESIUM  PHOSPHATE  IN  PURE 
WATER  (to  §  74,  6). 

a.  Recently  precipitated  ammonium  magnesium  phosphate  was  thoroughly 
•washed  with  water,  then  digested  for  24  hours  with  water  of  about  15°,  with 
frequent  shaking. 

84-42  grm.  of  the  filtrate  left 0-0047  grm. 

of  magnesium  pyrophosphate. 

b.  The  same  precipitate  was  digested  in  the  same  manner 
for  72  hours. 

84-42  grm.  of  the  filtrate  left 0-0043     " 

Mean 0-0045     " 

which  corresponds  to  0  •  00552  grm.  of  the  anhydrous  double  salt.  One  part  of 
that  salt  dissolves  therefore  in  15293  parts  of  pure  water. 

The  cold  saturated  solution  gave,  with  ammonia,  after  the  lapse  of  a  short 
time,  a  distinctly  perceptible  crystalline  precipitate;  on  the  addition  of 
sodium  phosphate,  it  remianed  perfectly  clear,  and  even  after  the  lapse  of 


994  EXERCISES   FOR    PRACTICE. 

2  days  no  precipitate  had  formed;  ammonium  sodium  phosphate  produced 
a  precipitate  as  large  as  that  caused  by  ammonia. 

31,  a.  SOLUBILITY  OF  AMMONIUM  MAGNESIUM  PHOSPHATE  IN  WATER 

CONTAINING  AMMONIA  (to  §  74,  6). 

a.  Pure  ammonium  magnesium  phosphate  was  dissolved  in  the  least  pos- 
sible amount  of  nitric  acid;  a  large  quantity  of  water  was  added  to  the  solu- 
tion, then  ammonia  in  excess.  The  mixture  was  allowed  to  stand  at  rest  for 
24  hours,  then  filtered;  its  temperature  was  14°.  84-42  grm.  left  0-0015 
magnesium  pyrophosphate,  which  corresponds  to  0-00184  of  the  anhydrous 
double  salt.  Consequently  1  part  of  the  latter  requires  45880  parts  of  ammo- 
niated  water  for  its  solution. 

6.  Pure  ammonium  magnesium  phosphate  was  digested  for  4  weeks  with 
ammoniacal  water,  with  frequent  shaking;  the  fluid  (temperature  14°)  was 
then  filtered  off;  126-63  grm.  left  0-0024  magnesium  pyrophosphate,  which 
corresponds  to  0-00296  of  the  double  salt.  One  part  of  it  therefore  dissolves 
in  42780  parts  of  ammoniacal  water.  Taking  the  mean  of  a  and  6,  1  part  of 
the  double  salt  requires  44330  parts  of  ammoniacal  water  for  its  solution. 

31,  6.  ANOTHER  EXPERIMENT  ON  THE  SAME  SUBJECT  (to  §  74,  6). 
Recently  precipitated  ammonium  magnesium  phosphate,  most  carefully 
washed  with  water  containing  ammonia,  was  dissolved  in  water  acidified  with 
hydrochloric  acid,  ammonia  added  in  excess,  and  allowed  to  stand  in  the  cold 
for  24  hours.  169-64  grm.  of  the  filtrate  left  0-0031  magnesium  pyrophos- 
phate, corresponding  to  0-0038  of  anhydrous  ammonium  magnesium  phos- 
phate. One  part  of  the  double  salt  required  therefore  44600  parts  of  the 
fluid. 

31,  c.  SOLUBILITY  OF  AMMONIUM  MAGNESIUM  PHOSPHATE  IN  WATER 

CONTAINING  AMMONIUM  CHLORIDE  (to  §  74,  6). 

Recently  precipitated,  thoroughly  washed  ammonium  magnesium  phos- 
phate was  digested  in  the  cold  with  a  solution  of  1  part  of  ammonium  chloride 
in  5  parts  of  water.  18-4945  grm.  of  the  filtrate  left  0-002  magnesium  pyro- 
phosphate, which  corresponds  to  0-00245  of  the  double  salt.  One  part  of 
the  salt  dissolves  therefore  in  7548  parts  of  the  fluid. 

31,  d.  SOLUBILITY  OF  AMMONIUM  MAGNESIUM  PHOSPHATE  IN  WATER 

CONTAINING  AMMONIA  AND  AMMONIUM  CHLORIDE  (to  §  74,  6). 

Recently  precipitated,  thoroughly  washed  ammonium  magnesium  phos- 
phate was  digested  in  the  cold  with  a  solution  of  1  part  of  ammonium  chloride 
in  7  parts  of  ammoniacal  water.  23-1283  grm.  of  the  filtrate  left  0-0012 
magnesium  pyrophosphate,  which  corresponds  to  0-00148  of  the  double  salt. 
One  part  of  the  double  salt  requires  consequently  15627  parts  of  the  fluid  for 
its  solution. 

32.  DEPORTMENT  OF  ACID  SOLUTIONS  OF  MAGNESIUM  PYROPHOSPHATE 

WITH  AMMONIA  (to  §  74,  c). 

0-3985  grm.  magnesium  pyrophosphate  was  treated  for  several  hours,  at 
a  high  temperature,  with  concentrated  sulphuric  acid.  This  exercised  no 


ANALYTICAL    EXPERIMENTS.  995 

perceptible  action.  It  was  only  after  the  addition  of  some  water  that  the 
salt  dissolved.  The  fluid,  heated  for  some  time,  gave,  upon  addition  of  ammo- 
nia in  excess,  a  crystalline  precipitate,  which  was  filtered  off  after  18  hours; 
•  the  quantity  of  magnesium  pyrophosphate  obtained  was  0-3805  grm.,  that 
is,  95-48  per  cent.  Sodium  phosphate  produced  in  the  filtrate  a  trifling 
precipitate,  which  gave  0-0150  grm.  of  magnesium  pyrophosphate,  that  is, 
3-76  per  cent. 

0-3565  grm.  magnesium  pyrophosphate  was  dissolved  in  3  grm.  nitric 
acid,  of  1-2  sp.  gr. ;  the  solution  was  heated,  diluted,  and  precipitated  with 
ammonia:  the  quantity  of  magnesium  pyrophosphate  obtained  amounted  to 
0-3485  grm.,  that  is,  98-42  per  cent.;  0-4975  grm.  was  treated  in  the  same 
manner  with  7  •  6  grm.  of  the  same  nitric  acid :  the  quantity  re-obtained  was 
0 •  4935  grm.,  that  is,  99  •  19  per  cent. 

0-786  grm.,  treated  in  the  same  manner  with  16-2  grm.  of  nitric  acid,  gave 
0-7765  grm.,  that  is,  98-79  per  cent. 

The  result  of  these  experiments  may  be  tabulated  thus : 


Retained.  Loss. 

1:9  98-42  percent.  1-58 

1:15  99-19         "  0-81 

1:20  98-79         "  1-21 

33.  SOLUBILITY  OF  PURE  MAGNESIA  IN  WATER  (to  §  74,  d). 
a.  In  Cold  Water. 

Perfectly  pure  well-crystallized  magnesium  sulphate  was  dissolved  in 
water,  and  the  solution  precipitated  with  ammonium  carbonate  and  caustic 
ammonia;  the  precipitate  was  thoroughly  washed — in  spite  of  which  it  still 
retained  a  perceptible  trace  of  sulphuric  acid — then  dissolved  in  pure  nitric 
acid,  an  excess  of  acid  being  carefully  avoided.  The  solution  was  then  re- 
precipitated  with  ammonium  carbonate  and  caustic  ammonia,  and  the  pre- 
cipitate thoroughly  washed.  The  so-prepared  perfectly  pure  magnesium 
carbonate  was  ignited  in  a  platinum  crucible  until  the  weight  remained  con- 
stant. The  residuary  pure  magnesia  was  then  digested  in  the  cold  for  24  hours 
with  distilled  water,  with  frequent  shaking.  The  distilled  water  used  was 
perfectly  free  from  chlorine,  and  left  no  fixed  residue  upon  evaporation. 

a.  84-82  grm.  of  the  filtrate,  cautiously  evaporated  in  a  platinum  dish, 
left  a  residue  weighing,  after  ignition,  0-0015  grm.  One  part  of  the  pure 

magnesia  dissolved  therefore  in 56546 

parts  of  cold  water. 

The  digestion  was  continued  for  48  hours  longer,  when 

0.  84  •  82  grm.  left  0-0016  grm.     One  part  required  there- 
fore    53012 

f.  84-82  grm.  left  0-0015  grm.     One  part  required 56546 

Average 55368 

The  solution  of  magnesia  prepared  in  the  cold  way  has  a  feeble  yet  distinct 
alkaline  reaction,  which  is  most  easily  perceived  upon  the  addition  of  very 


996  EXERCISES  FOR  PRACTICE. 

faintly  reddened  tincture  of  litmus;  the  alkaline  reaction  of  the  solution  is 
perfectly  manifest  also  with  slightly  reddened  litmus  paper,  or  with  turmeric- 
or  dahlia-paper,  if  these  test-papers  are  left  for  some  time  in  contact  with  the 
solution. 

Alkali  carbonates  fail  to  render  the  solution  turbid,  even  upon  boiling. 

Sodium  phosphate  also  fails  to  impair  the  clearness  of  the  solution,  but  if 
the  fluid  is  mixed  with  a  little  ammonia  and  shaken,  it  speedily  becomes  tur- 
bid, and  deposits  after  some  time  a  perceptible  precipitate  of  ammonium 
magnesium  phosphate. 

b.  In  Hot  Water. 

Upon  boiling  pure  magnesia  with  water,  a  solution  is  obtained  which  con- 
ports  itself  in  every  respect  like  the  cold-prepared  solution  of  magnesia.  A 
hot-prepared  solution  of  magnesia  does  not  become  turbid  upon  cooling,  nor 
does  a  cold-prepared  solution  upon  boiling.  84  •  82  grm.  of  hot-prepared  solu- 
tion of  magnesia  left  0-0016  grm.  MgO. 

34.  SOLUBILITY  OF  PURE  MAGNESIA  IN  SOLUTIONS  OF  POATSSIUM  CHLORIDE 
AND  SODIUM  CHLORIDE  (to  §  74,  d). 

Three  flasks  of  equal  size  were  charged  as  follows: 

1.  With  1  grm.  pure  potassium  chloride,  200  c.c.  water  and  some  perfectly 
pure  magnesia. 

2.  With  1  grm.  pure  sodium  chloride,  200  c.c.  water  and  some  pure  mag- 
nesia. 

3.  With  200  c.c.  water  and  some  pure  magnesia. 

The  contents  of  the  three  flasks  were  kept  boiling  for  forty  minutes,  then 
filtered,  and  the  clear  filtrates  mixed  with  equal  quantities  of  a  mixture  of 
sodium  phosphate,  ammonium  chloride  and  ammonia.  After  twelve  hours 
a  very  slight  precipitation  was  visible  in  3,  and  a  considerably  larger  precipi- 
tation had  taken  place  in  1  and  2. 

35.  PRECIPITATION  OF  ALUMINIUM  BY  AMMONIA,  ETC.  (to  §  75,  a). 

a.  Ammonia  produces  in  neutral  solutions  of  aluminium  salts  or  of  alum, 
as  is  well  known,  a  gelatinous  precipitate  of  aluminum  hydroxide.  Upon  fur- 
ther addition  of  ammonia  in  considerable  excess,  the  precipitate  redissolves 
gradually,  but  not  completely. 

6.  If  a  drop  of  a  dilute  solution  of  alum  is  added  to  a  large  quantity  of 
ammonia,  and  the  mixture  shaken,  the  solution  appears  almost  perfectly 
clear;  however,  after  standing  at  rest  for  some  time,  slight  flakes  separate. 

c.  If  a  solution  of  alumina,  mixed  with  a  large  amount  of  ammonia,  is 
filtered,  and 

a.  The  filtrate  boiled  for  a  considerable  time,  flocks  of  aluminium  hydrox- 
ide separate  gradually  in  proportion  as  the  excess  of  ammonia  escapes. 

/?.  The  filtrate  mixed  with  solution  of  ammonium  chloride,  a  very  percep- 
tible flocculent  precipitate  of  aluminium  hydroxide  separates  immediately; 
the  whole  of  the  aluminium  present  in  the  solution  will  thus  separate  if  the 
ammonium  chloride  be  added  in  sufficient  quantity. 


ANALYTICAL    EXPERIMENTS.  997 

7-.  The  filtrate  mixed  with  ammonium  sesquicarbonate,  the  same  reaction 
takes  place  as  in  /?. 

o.  The  filtrate  mixed  with  solution  of  sodium  chloride  or  of  potassium 
chloride,  no  precipitate  separates,  but,  after  several  days'  standing,  slight 
flakes  of  aluminium  hydroxide  subside,  owing  to  the  loss  of  ammonia  by 
evaporation. 

d.  If  a  neutral  solution  of  alumina  is  precipitated  with  ammonium  car- 
bonate, or  if  a  solution  strongly  acidified  with  hydrochloric  or  nitric  acid  is 
precipitated  with  pure  ammonia,  or  if  to  a  neutral  solution  a  sufficient  amount 
of  ammonium  chloride  is  added  besides  the  ammonia;  even  a  considerable 
excess  of  the  precipitants  will  fail  to  redissolve  the  precipitated  aluminium 
hydroxide,  as  appears  from  the  continued  perfect  clearness  of  the  filtrates  upon 
protracted  boiling  and  evaporation. 

36.  PRECIPITATION  OF  ALUMINIUM  BY  AMMONIUM  SULPHIDE  (to  §  75,  a). 
(Experiments  made  by  J.  FUCHS,  formerly  Assistant  in  my  Laboratory.} 

a.  50  c.c.  of  a  solution  of  pure  ammonium-alum,  which  contained  0-3939 
A12O3  were  mixed  with  50  c.c.  water  and  10  c.c.  solution  of  ammonium  sul- 
phide, and  filtered  after  ten  minutes.     The  ignited  precipitate  weighed  0  •  3825 
grm. 

b.  The  same  experiment  was  repeated  with  100  c.c.  water;  the  precipitate 
weighed  0-3759  grm. 

c.  The  same  experiment  was  repeated  with  200  c.c.  water;  the  precipitate 
weighed  0-3642  grm. 

37.  PRECIPITATION  OF  CHROMIUM  BY  AMMONIA  (to  §  76,  a). 

Solutions  of  chromic  chloride  and  of  chrome-alum  (concentrated  and 
dilute,  neutral  and  acidified  with  hydrochloric  acid)  were  mixed  with  ammo- 
nia in  excess.  All  the  filtrates  drawn  off  immediately  after  precipitation 
appeared  red,  but  when  filtered  after  ebullition,  they  all  appeared  colorless, 
if  the  ebullition  had  been  sufficiently  protracted. 

38.  SOLUBILITY  OF  THE  BASIC  ZINC  CARBONATE  IN  WATER  (to  §  77,  a). 

Perfectly  pure,  recently  (hot)  precipitated  basic  zinc  carbonate  was  gently 
heated  with  distilled  water,  and  subsequently  digested  cold  for  many  weeks, 
with  frequent  shaking.  The  clear  solution  gave  no  precipitate  with  ammo- 
nium sulphide,  not  even  after  long  standing. 

84-82  grm.  left  0-0014  grm.  zinc  oxide,  which  corresponds  to  0-0019  basic 
zinc  carbonate  (74  per  cent,  of  ZnO  being  assumed  in  this  salt).  One  part  of 
the  basic  carbonate  requires  therefore  44642  parts  of  water  for  solution. 

39.  DEPORTMENT  OF  ZINC  SULPHIDE  ON  WASHING  (to  §  77,  c). 
In  these  experiments,  as  also  in  40  and  41,  the  sulphide  of  the  metal  was 
precipitated  from  a  solution  of  the  neutral  salt,  containing  ammonium  chlo- 
ride, by  adding  to  it  yellow  ammonium  sulphide  and  allowing  it  to  remain 
in  a  closed  vessel  for  twenty-four  hours;  first  the  clear  liquid  and  then  the 
precipitate  was  poured  on  to  6  filters  of  equal  size,  so  that  the  quantity  of 


998  EXERCISES   FOR    PRACTICE. 

the  metallic  sulphide  on  each  filter  was  about  the  same.  The  washing 
was  at  once  commenced  and  continued,  without  interruption,  the  following 
liquids  being  used:  I.  Pure  water;  II.  Water  containing  sulphuretted 
hydrogen;  III.  Water  containing  sulphide  of  ammonium;  IV.  Water  con- 
taining chloride  of  ammonium,  afterwards  pure  water;  V.  Water  con- 
taining sulphuretted  hydrogen  and  chloride  of  ammonium,  afterwards  water 
containing  sulphuretted  hydrogen;  and  VI.  Water  containing  sulphide  of 
ammonium  and  chloride  of  ammonium,  afterwards  water  containing  sul- 
phide of  ammonium. 

The  nitrates  were  at  first  colorless  and  clear.  On  washing,  the  first  three 
filtrates  ran  through  turbid,  the  turbidity  was  strongest  in  II,  and  weakest  in 
III ;  the  last  three  remained  quite  clear.  On  adding  ammonium  sulphide 
no  change  took  place;  the  turbidity  of  the  first  three  was  not  increased,  the 
clearness  of  the  last  three  was  not  impaired.  Ammonium  chloride  there- 
fore decidedly  exercises  a  favorable  action,  and  the  water  containing  it  may 
be  displaced  by  water  containing  ammonium  sulphide. 

40.  DEPORTMENT  OF  MANGANESE  SULPHIDE  ON  WASHING  (to  §  78,  e). 

The  filtrates,  as  in  39,  \rere  at  first  clear  and  colorless.  But  after  the 
washing  had  been  continued  some  time,  I  appeared  colorless,  slightly  opales- 
cent; II,  whitish  and  turbid;  III,  yellowish  and  turbid;  IV,  colorless, 
slightly  turbid;  V,  slightly  yellowish,  nearly  clear;  VI,  clear,  yellowish.  To 
obtain  a  filtrate  that  remains  clear,  therefore,  the  wash- water  must  at  first 
contain  ammonium  cliloride.  Addition  of  ammonium  sulphide  also  cannot 
be  dispensed  with,  as  all  the  filtrates  obtained  without  this  addition  gave 
distinct  precipitates  of  manganese  sulphide  when  the  reagent  was  subse- 
quently added  to  them. 

41.  DEPORTMENT  OF  NICKEL  SULPHIDE  (ALSO  OF  COBALT  SULPHIDE 

AND  FERROUS  SULPHIDE)  ON  WASHING  (to  §  79,  e). 

In  the  experiments  with  nickel  sulphide  the  clear  filtrates  were  put  aside/ 
and  then  the  washing  was  proceeded  with.  The  washings  of  the  first  three  ran 
through  turbid,  of  the  last  three  clear.  When  the  washing  was  finished,  I 
was  colorless  and  clear;  II,  blackish  and  clear;  III,  dirty  yellow  and  clear; 
IV,  colorless  and  clear;  V,  slightly  opalescent;  VI,  slightly  brownish  and 
opalescent.  On  addition  of  ammonium  sulphide,  I  became  brown;  II  re- 
mained unaltered;  III  remained  unaltered;  IV  became  black  and  opaque; 
V  became  brown  and  clear;  VI  became  pure  yellow  and  clear. 

Cobalt  sulphide  and  ferrous  sulphide  behaved  in  an  exactly  similar  manner. 
It  is  plain  that  these  sulphides  oxidize  more  rapidly  when  the  wash-water 
contains  ammonium  chloride,  unless  ammonium  sulphide  is  also  present. 
Hence  it  is  necessary  to  wash  with  a  fluid  containing  ammonium  sulphide; 
and  the  addition  of  ammonium  chloride  at  first  is  much  to  be  recommended, 
as  this  diminishes  the  likelihood  of  our  obtaining  a  muddy  filtrate. 


ANALYTICAL   EXPERIMENTS.  999 


41,  a.  DEPORTMENT  OF  COBALTOUS  HYDROXIDE  PRECIPITATED  BY 
ALKALIES  (to  §  80,  a). 

A  solution  of  cobaltous  chloride  was  precipitated  boiling  with  solution  of 
soda,  and  the  precipitate  washed  with  boiling  water  until  the  filtrate  gave  no 
longer  the  least  indication  of  presence  of  chlorine.  The  dried  and  ignited 
residue,  heated  with  water,  manifested  no  alkaline  reaction.  It  was  reduced 
by  ignition  in  hydrogen  gas,  and  the  metallic  cobalt  digested  hot  with  water. 
The  decanted  water  manifested  no  alkaline  reaction,  even  after  considerable 
concentration;  but  the  metallic  cobalt,  brought  into  contact,  moist,  with 
turmeric-paper,  imparted  to  the  latter  a  strong  brown  color. 

42.  SOLUBILITY  OF  LEAD  CARBONATE  (to  §  83,  a). 
a.  In  pure  Water. 

Recently  precipitated  and  thoroughly  washed  pure  lead  carbonate  was 
digested  for  eight  days  with  water  at  the  common  temperature,  with  frequent 
shaking.  84-42  grm.  of  the  filtrate  were  evaporated,  with  addition  of  some 
pure  sulphuric  acid;  the  residuary  lead  sulphate  weighed  0-0019  grm.,  which 
corresponds  to  0-00167  lead  carbonate.  One  part  of  the  latter  salt  dissolves 
therefore  in  50551  parts  of  water.  The  solution,  mixed  with  hydrogen 
sulphide  water,  remaining  perfectly  colorless,  not  the  least  tint  being  de- 
tected in  it,  even  upon  looking  through  it  from  the  top  of  the  test-cylinder. 

b.  In  Water  containing  a  little  Ammonium  Acetate  and  also  Ammonium 

Carbonate  and  Ammonia. 

X  highly  dilute  solution  of  pure  lead  acetate  was  mixed  with  ammonium 
carbonate  and  ammonia  in  excess,  and  the  mixture  gently  heated  and  then 
allowed  to  stand  at  rest  for  several  days.  84-42  grm.  of  the  filtrate  left, 
upon  evaporation  with  a  little  sulphuric  acid,  0-0041  grm.  lead  sulphate, 
which  corresponds  to  0-0036  of  the  carbonate.  One  part  of  the  latter  salt 
requires  accordingly  23450  parts  of  the  above  fluid  for  solution.  The  solu- 
tion was  mixed  with  hydrogen  sulphide  water;  when  looking  through  the 
fluid  from  the  top  of  the  test-cylinder,  a  distinct  coloration  was  visible;  but 
when  looking  through  the  cylinder  laterally,  this  coloration  was  hardly 
perceptible.  Traces  of  lead  sulphide  separated  after  the  lapse  of  some  tune. 

c.  In  Water  containing  a  large  proportion  of  Ammonium  Nitrate,  together 

with  Ammonium  Carbonate  and  Caustic  Ammonia. 

A  highly  dilute  solution  of  lead  acetate  was  mixed  with  nitric  acid,  then 
with  ammonium  carbonate  and  ammonia  in  excess;  the  mixture  was  gently 
heated,  and  allowed  to  stand  at  rest  for  eight  days.  The  filtrate,  mixed  with 
hydrogen  sulphide,  exhibited  a  very  distinct  brownish  color  upon  looking 
through  it  from  the  top  of  the  cylinder;  but  this  color  appeared  very  slight 
only  when  looking  through  the  cylinder  laterally.  The  amount  of  lead 
dissolved  was  unquestionably  more  considerable  than  in  b 


1000  EXERCISES   FOR   PRACTICE. 

43.  SOLUBILITY  OF  LEAD  OXALATE  (to  §  83,  6). 

A  dilute  solution  of  lead  acetate  was  precipitated  with  ammonium  oxalate 
and  ammonia,  the  mixture  allowed  to  stand  at  rest  for  some  time,  and  then 
filtered.  The  filtrate,  mixed  with  hydrogen  sulphide,  comported  itself 
exactly  like  the  nitrate  of  No.  42f  b,  i.e.,  the  liquid  appeared  faintly  brown 
on  looking  through  it  from  the  top  of  the  cylinder,  while,  when  viewed  later- 
ally, the  color  was  scarcely  perceptible.  The  same  deportment  was  observed 
in  another  similar  experiment,  in  which  ammonium  nitrate  had  been  added 
to  the  solution. 

44.  SOLUBILITY  OF  LEAD  SULPHATE  IN  PURE  WATER  (to  §  83,  d). 

Thoroughlyjwashed  and  still  moist  lead  sulphate  was  digested  for  five  days 
with  water,  at  10  to  15°,  with  frequent  shaking.  84-42  firm,  of  the  filtrate 
(filtered  off  at  11°)  left  0-0037  grm.  lead  sulphate.  Consequently  1  part  of 
this  salt  requires  22816  parts  of  pure  water  at  11°  for  solution. 

The  solution,  mixed  with  hydrogen  sulphide,  exhibited  a  distinct  brown 
color  when  viewed  from  the  top  of  the  cylinder,  but  this  color  appeared  very 
slight  upon  looking  through  the  cylinder  laterally. 

45.  SOLUBILITY  OF  LEAD  SULPHATE  IN  WATER  CONTAINING  SULPHURIC 

ACID  (to  §83,  rf). 

A  highly  dilute  solution  of  lead  acetate  was  mixed  with  an  excess  of  dilute 
pure  sulphuric  acid ;  the  mixture  was  very  gently  heated,  and  the  precipitate 
allowed  several  days  to  subside.  80-31  grm.  of  the  filtrate  left  0-0022  grm. 
lead  sulphate.  One  part  of  this  salt  dissolves  therefore  in  36504  parts  of 
water  containing  sulphuric  acid.  The  solution,  mixed  with  hydrogen  sul- 
phide appeared  colorless  to  the  eye  looking  through  the  cylinder  laterally, 
and  very  little  darker  when  viewed  from  the  top  of  the  cylinder. 

46.  SOLUBILITY  OF  LEAD  SULPHATE  IN  WATER  CONTAINING  AMMONIUM 

SALTS  AND  FREE  SULPHURIC  ACID  (to  §  83,  d}. 

A  highly  dilute  solution  of  lead  acetate  was  mixed  with  a  tolerably  large 
amount  of  ammonium  nitrate,  and  sulphuric  acid  in  excess  added.  After 
several  days'  standing,  the  mixture  was  filtered.  The  filtrate  was  nearly 
indifferent  to  hydrogen-sulphide  water;  viewed  from  the  top  of  the  cylinder, 
it  looked  hardly  perceptibly  darker  than  pure  water. 

47.  DEPORTMENT  OF  LEAD  SULPHATE  UPON  IGNITION  (to  §  83,  d). 

Speaking  of  the  determination  of  the  atomic  weight  of  sulphur,  ERDMANN 
and  MARCHAND  *  state  that  lead  sulphate  loses  some  sulphuric  acid  upon 
ignition.  In  order  to  inform  myself  of  the  extent  of  this  loss,  and  to  ascertain 
how  far  it  might  impair  the  accuracy  of  the  method  of  determining  lead  as  a 
sulphate,  I  heated  2-2151  grm.  of  absolutely  pure  PbSO4  to  the  most  intense 
redness,  over  a  spirit-lamp  with  double  draught.  I  could  not  perceive  the 

*  Journ.  fur  Prakt.  Chem.,  xxxi,  385. 


ANALYTICAL    EXPERIMENTS.  1001 

slightest  decrease  of  weight;  at  all  events,  the  loss  did  not  amount  to  0-0001 
grm. 

48.  DEPORTMENT  OP  LEAD  SULPHIDE  ON  DRYING  AT  100°  (to  §  83,  /). 

Lead  sulphide  was  precipitated  from  a  solution  of  pure  lead  acetate  with 
hydrogen  sulphide,  and  when  dry,  kept  for  a  considerable  time  at  100°  and 
weighed  occasionally.  The  following  numbers  represent  the  results  of  the 
several  weighings: 

L  0-8154.       II.  0-8164.       III.  0-8313.       IV.  0-8460.       V.  0-864. 

49.  DEPORTMENT  OF  METALLIC  MERCURY  AT  THE  COMMON  TEMPERATURE 
AND  UPON  EBULLITION  WITH  WATER  (to  §  84,  a). 

To  ascertain  in  what  manner  loss  of  metallic  mercury  occurs  upon  drying, 
and  likewise  upon  boiling  with  water,  and  to  determine  which  is  the  best 
method  of  drying,  I  made  the  following  experiments : 

I  treated  6-4418  grm.  of  perfectly  pure  mercury  in  a  watch-glass,  with 
distilled  water,  removed  the  water  again  as  far  as  practicable  (by  decanta- 
tion  and  finally  by  means  of  blotting-paper),  and  weighed.  I  now  had 
6-4412  grm.  After  several  hours'  exposure  to  the  air,  the  mercury  was 
reduced  to  6  •  441 1.  I  placed  these  6  •  441 1  grm.  under  a  bell-jar  over  sulphuric 
acid,  the  temperature  being  about  17°.  After  the  lapse  of  twenty-four  hours 
the  weight  had  not  altered  in  the  least.  I  introduced  the  6-4411  grm.  mer- 
cury into  a  flask,  treated  it  with  a  copious  quantity  of  distilled  water,  and 
boiled  for  fifteen  minutes  violently.  I  then  placed  the  mercury  again  upon 
the  watch-glass,  dried  it  most  carefully  with  blotting-paper,  and  weighed. 

The  weight  was  now  6  •  4402  grm.  Finding  that  a  trace  of  mercury  had 
adhered  to  the  paper,  I  repeated  the  same  experiment  with  the  6  •  4402  grm. 
After  fifteen  minutes'  boiling  with  water,  the  mercury  had  again  lost  0  •  0004 
grm.  The  remaining  6-4398  grm.  were  exposed  to  the  air  for  six  days  (in 
summer,  during  very  hot  weather),  after  which  they  were  found  to  have  lost 
only  0-0005  grm. 

49.  a.  DEPORTMENT  OF  MERCURIC  SULPHIDE  WITH  SOLUTION  OF  POTASSA, 

AMMONIUM  SULPHIDE,  ETC.  (to  §  84,  c). 

a.  If  recently  precipitated  pure  mercuric  sulphide  is  boiled  with  pure 
solution  of  potassa,  not  a  trace  of  it  dissolves  in  that  fluid;  hydrochloric 
acid  produces  no  precipitate,  nor  even  the  least  coloration,  in  the  filtrate. 

6.  If  mercuric  sulphide  is  boiled  with  solution  of  potassa,  with  addition 
of  some  hydrogen-sulphide  water,  ammonium  sulphide,  or  sulphur,  com- 
plete solution  is  effected. 

c.  If  freshly  precipitated  mercuric  sulphide  is  digested  in  the  cold  with 
yellowish  or  very  yellow  ammonium  sulphide,   slight  but  distinctly  per- 
ceptible traces  are  dissolved,  while  in  the  case  of  hot  digestion  scarcely  any 
traces  of  mercury  can  be  detected  in  the  solution.* 

d.  Thoroughly  washed  mercuric  sulphide,  moistened  with  water,  suffers 

*  Comp.  my  experiments  in  the  Zeitschrift  f.  Anal.  Chem.,  m,  140. 


1002  EXERCISES    FOR    PRACTICE. 

no  alteration  upon  exposure  to  the  air;  at  least,  the  fluid  which  I  obtained 
by  washing  mercuric  sulphide  which  had  been  thus  exposed  for  twenty-four 
hours,  did  not  manifest  acid  reaction,  nor  did  it  contain  mercury  or  sulphuric 
acid. 

50.  DEPORTMENT  OF  CUPRIC  OXIDE  UPON  IGNITION  (to  §  85,  6). 

Pure  cupric  oxide  (prepared  from  cupric  nitrate)  was  ignited  in  a  platinum 
crucible,  then  cooled  under  a  bell-jar  over  sulphuric  acid,  and  finally  weighed. 
The  weight  was  3  •  542  grm.  The  oxide  was  then  most  intensely  ignited  for 
five  minutes  over  a  BERZELIUS'  lamp,  and  weighed  as  before,  when  the  weight 
was  found  unaltered ;  the  oxide  was  then  once  more  ignited  for  five  minutes, 
but  with  the  same  result. 

51.  DEPORTMENT  OF  THE  CUPRIC  OXIDE  IN  AIR  (to  §  85,  6). 

A  platinum  crucible  containing  4  •  3921  grm.  of  gently  ignited  cupric  oxide 
(prepared  from  the  nitrate)  stood  for  ten  minutes,  covered  with  the  lid,  in  a 
warm  room  (in  winter) ;  the  weight  of  the  oxide  was  found  to  have  increased 
to  4  •  3939  grm. 

The  oxide  was  then  intensely  ignited  over  a  spirit-lamp;  after  ten  min- 
utes standing  in  the  covered  crucible,  the  weight  had  not  perceptibly  in- 
creased ;  after  twenty-four  hours'  it  had  increased  by  0  •  0036  grm. 

52.  DEPORTMENT  OF  BISMUTH  SULPHIDE  UPON  DRYING  AT  100°  (to  §  86,  g). 

0  •  4558  grm.  of  bismuth  sulphide  prepared  in  the  wet  way  were  placed  in 
the  desiccator  on  a  watch-glass,  and  allowed  to  stand  at  the  common  tem- 
perature. After  three  hours  the  weight  was  0  •  4270,  after  six  hours  0  •  4258, 
after  two  days  the  same. 

0-3602  grm.  of  the  bismuth  sulphide  so  dried  was  put  into  a  water-bath, 
in  fifteen  minutes  it  weighed  0  •  3596,  half  an  hour  afterwards  0  •  3599,  in  half 
an  hour  more  0-3603,  in  two  hours  0-3626.  In  a  second  experiment  the 
drying  was  kept  up  for  four  days,  and  a  continual  increase  of  weight  was 
observed. 

0  •  5081  grm.  of  bismuth  sulphide  dried  in  the  desiccator  was  heated  in  a 
boat  in  a  stream  of  carbonic  acid.  After  gentle  ignition  the  weight  was 
0-5002,  after  repeated  heating  0-4992.  The  bismuth  sulphide  was  visibly 
volatilized  on  ignition  in  the  current  of  carbonic  acid.  • 

53.  DEPORTMENT  OF  CADMIUM  SULPHIDE  WITH  AMMONIA,  ETC.  (to  §  87,  c). 

Recently  precipitated  pure  cadmium  sulphide  was  diffused  through  water, 
and  the  following  experiments  were  made  with  the  mixture: 

a.  A  portion  was  digested  cold  with  ammonia  in  excess,  and  filtered. 
The  filtrate  remained  perfectly  clear  upon  addition  of  hydrochloric  acid. 

b.  Another  portion  was  digested  hot  with  excess  of  ammonia,  and  filtered. 
This  filtrate  likewise  remained  perfectly  clear  upon  addition  of  hydrochloric 
aeid. 

c.  Another  portion  was  digested  for  some  time  with  solution  of  potassium 


ANALYTICAL   EXPERIMENTS.  1003 

cyanide,  and  filtered.  This  filtrate  also  remained  perfectly  clear  upon  addi- 
tion of  hydrochloric  acid. 

d.  Another  portion  was  digested  with  ammonium  hydrosulphide,  and 
filtered.  The  turbidity  which  hydrochloric  acid  imparted  to  this  filtrate 
was  pure  white. 

(A  remark  made  by  WACKENRODER,  in  BUCHNER'S  Repertor.  d.  Pharm., 
XL vi,  226,  induced  me  to  make  these  experiments.) 

54.  DEPORTMENT  OF  PRECIPITATED  ANTIMONOUS  SULPHIDE  ON  DRYING 

(to  §  90,  a). 

0-4457  grm.  of  the  substance  dried  at  100°  lost,  when  heated  to  blacken- 
ing in  a  stream  of  carbonic  acid,  0-0011  water. 

0  •  2899  grm.  of  pure  precipitated  antimonous  sulphide  dried  in  the  desic- 
cator lost,  when  dried  at  100°,  0-0007. 

0- 1932  grm.  of  the  substance  dried  at  100°  gave  up  0-0012,  when  heated 
to  blackening  in  a  stream  of  carbonic  acid,  and  after  stronger  heating,  during 
which  fumes  of  antimony  sulphide  began  to  escape,  the  total  loss  amounted 
to  0  •  0022  grm. 

0-1670  grm.  of  the  substance  dried  at  100°  lost  0-0005  grm.  on  being 
heated  to  blackening  in  a  stream  of  carbonic  acid. 

55.  DETERMINATION  OF  AMMONIA,  as  in  §  99,  3. 

The  accuracy  of  this  method  of  estimating  ammonia  is  now  so  well  estab- 
lished that  any  observations  on  the  subject  are  rendered  unnecessary. 

55,  a.  AMOUNT  OF  WATER  IN  HYDRATED  SILICA  (to  §  93,  9). 
(Experiments  made  by  my  assistant,  Mr,  LIPPERT.) 

A  dilute  solution  of  soluble  glass  was  slowly  dropped  into  hydrochloric 
acid,  so  long  as  the  precipitate  continued  to  dissolve  rapidly,  then  the  clear 
fluid  was  heated  in  the  water-bath,  till  it  set  to  a  transparent  jelly.  This 
jelly  was  dried  so  far  as  possible  with  blotting-paper,  diffused  in  water,  and 
washed  by  decantation  till  the  fluid  altogether  ceased  to  give  the  chlorine 
reaction.  It  was  then  transferred  to  a  filter,  and  the  latter  spread  on  blotting- 
paper  and  exposed  till  a  crumbly  mass  was  left  from  the  spontaneous  evapo- 
ration of  water.  One  half  (I)  was  dried  for  eight  weeks  in  the  desiccator 
over  sulphuric  acid,  with  occasional  trituration,  the  other  half  (II)  was  dried 
under  similar  circumstances,  but  in  a  vacuum.  Both  were  transferred  to 
closed  tubes  and  these  were  kept  in  the  desiccator. 

The  weighing  of  the  substance  dried  at  100°  was  effected  between  watch- 
glasses.  For  the  purpose  of  igniting  the  residue,  it  was  allowed  to  satiate  itself 
with  aqueous  vapor  by  exposure  to  the  air,  otherwise  a  considerable  quantity 
of  the  substance  would  have  been  lost,  then  water  was  dropped  upon  it  in  the 
watch-glass,  then  it  was  rinsed  into  a  platinum  crucible,  dried  in  a  water-bath, 
and  ignited,  at  first  cautiously,  towards  the  end  intensely. 


1004  EXERCISES   FOR    PRACTICE. 

The  substance  I  contained 

Expt.  1.  Expt.  2. 

Water,  escaping  at  or  below  100° 4  •  19  )  2 

above  100° 4-76  J 

Silica..  91-05  90-72 


100-00  100-00 

Consequently  the  hydrate  dried  at  100°  consists  of  4  •  97  water  and  95  •  03  silica. 
In  the  substance  dried  in  the  desiccator  the  oxygen  of  the  total  water  :  the 
oxygen  of  the  silica  (SiO2),  according  to  the  first  experiment  :  :  1  :  6-1,  accord- 
ing to  the  second  experiment  :  :  1  : 5  •  86.  And  in  the  substance  dried  at 
100°  the  oxygen  of  the  water  :  the  oxygen  of  the  silica : :  1  : 11  •  5. 
The  substance  II  contained 

Expt.  1.    Expt.  2.        Expt.  3. 


Water,  escaping  at  or  below  100°.  .       4-75        4-71) 
at  above  100°.  ...       5-26         5  •  21  ) 
Silica..  89-99       90-08  90-05 


100-00     100-00         100-00 

Consequently  the  hydrate  dried  at  100°  consists  on  the  average  of  5-49  water 
and  94  •  51  silica.  In  the  substance  dried  in  a  vacuum  over  sulphuric  acid  the 
oxygen  of  the  total  water  :  the  oxygen  of  the  silica — on  an  average::  1 :  5-41. 
And  in  the  substance  dried  at  100°  the  oxygen  of  the  water  :  the  oxygen  of  the 
silica::  1:10-43. 

56.  DETERMINATION  OF  BARIUM  BY  PRECIPITATION  WITH  AMMONIUM 
CARBONATE  (to  §  101,  2,  a). 

0-7553  grm.  pure  ignited  barium  chloride  precipitated  after  §  101,  2,  a, 
gave  0  •  7142  BaCO3,  which  corresponds  to  0  •  554719  BaO  =  73-44  per  cent.  (100 
parts  of  BaCl2  ought  to  have  given  73  •  59  parts).  The  result  accordingly  was 
99-79  instead  of  100. 

57.  DETERMINATION  OF  BARIUM  IN  ORGANIC  SALTS  (to  §  101,  2,  6). 
0-686  grm.  barium  racemate   (Ba2C8H8O12+5Aq.)   treated  according  to 
§101,  2,  b,  gave  0-408  barium  carbonate = 0-3169  BaO  =  46 -20  per  cent, 
(calculated  46-38  per  cent.);  i.e.,  99-61  instead  of  100. 

58.  DETERMINATION  OF  STRONTIUM  AS  STRONTIUM  SULPHATE 
(to  §  102,  1,  a). 

a.  An  aqueous  solution  of  1  •  2398  grm.  SrCl2  was  precipitated  with  sul- 
phuric acid  in  excess,  and  the  precipitated  strontium  sulphate  washed  with 
water.     It  weighed  1-4113,  which  corresponds  to  0-795408  SrO=64-15  per 
cent,  (calculated  65-38  per  cent.) ;  i.e.,  98-12  instead  of  100. 

b.  1  •  1510  grm.  SrCo3  was  dissolved  in  excess  of  hydrochloric  acid,  the  solu- 
tion diluted,  and  then  precipitated  with  sulphuric  acid ;  the  precipitated  SrSO4 
was  washed  with  water;   it  weighed  1-4024  =  0-79039  SrO  =  68-68  per  cent, 
(calculated  70-07  per  cent.) ;  i.e.,  98-02  instead  of  100. 


ANALYTICAL   EXPERIMENTS  1005 

59.  DETERMINATION  OF  STRONTIUM  AS  SULPHATE,  WITH  CORRECTION 
(to  §  102,  1,  a). 

The  filtrate  obtained  in  No.  58,  b,  weighed  190-84  grm.  According  to 
experiment  No.  22,  11862  parts  of  water  containing  sulphuric  acid  dissolve 
1  part  of  strontium  sulphate;  therefore,  190-84  grm.  dissolve  0-0161.  The 
washings  weighed  63-61  grm.  According  to  experiment  No.  21,  6895  parts 
of  water  dissolve  1  part  of  SrSO4;  therefore,  63-61  grm.  dissolve  0.0161  grm. 

Adding  0-0161  and  0-0092  to  the  1-4024  actually  obtained,  we  find  the 
total  amount  =  1  •  4277  grm.,  which  corresponds  to  0-80465  SrO  =  69  91  per 
cent,  in  SrCO3  (calculated  70-07  per  cent.) ;  i.e.,  99-77  instead  of  100. 

60.  DETERMINATION  OF  STRONTIUM  AS  STRONTIUM  CARBONATE 
(to  §  102,  2). 

1-3104  grm.  strontium  chloride,  precipitated  according  to  §  102,  2,  gave 
1  -  2204  SrCO3,  containing  0  •  8551831  SrO =65-26  per  cent,  (calculated  65  •  38) ; 
i.e.,  99-82  instead  of  100. 

61.  DETERMINATION  OF  CALCIUM  AS  CALCIUM  SULPHATE  BY  PRECIPITATION 

(to  §  103,  1,  a). 

In  the  four  following  experiments,  Nos.  61  to  64,  pure  air-dried  calcium 
carbonate  was  used,  in  a  portion  of  which  the  amount  of  anhydrous  car- 
bonate had  been  determined  by  very  cautious  heating.  0-7647  grm.  left 
0-7581  grm.,  which  weight  remained  unaltered  upon  further  (extremely 
gentle)  ignition;  the  air-dried  carbonate  contained  accordingly  55-516  per  cent, 
of  lime. 

1-186  gnn.  of  "the  air-dried  calcium  carbonate"  was  dissolved  in  hydro- 
chloric acid,  and  the  solution  precipitated  with  sulphuric  acid  and  alcohol, 
after  §  103,  1,  a.  Obtained  1  •  5949  grm.  CaSO4,  containing  0  •  65598  CaO,  i.e., 
55-31  per  cent,  (calculated  55-51),  which  gives  99-64  instead  of  100. 

62.  DETERMINATION  OF  CALCIUM  AS  CaCO,,,  BY  PRECIPITATION  WITH 
AMMONIUM  CARBONATE  AND  WASHING  WITH  PURE  WATER  (to  §  103,  2,  a). 

A  hydrochloric  acid  solution  of  1-1437  grm.  of  "the  air-dried  calcium  car- 
bonate" gave  upon  precipitation  as  directed,  1  •  1243  grm.  anhydrous  calcium 
carbonate,  corresponding  to  0  •  629608  CaO  =  55-05  per  cent,  (calculated  55  •  51 
per  cent),  which  gives  99-17  instead  of  100. 

63    DETERMINATION  OF  CALCIUM  AS  CaCO3,  BY  PRECIPITATION  WITH 
AMMONIUM  OXALATE  FROM  ALKALINE  SOLUTION  (to  §  103,  2,  6,  a). 

1  •  1734  grm.  of  "the  air-dried  calcium  carbonate"  dissolved  in  hydrochloric 
acid,  and  treated  as  directed  §  103,  2,  6,  a,  gave  1  •  1632  grm.  CaCO3  (reaction 
not  alkaline),  containing  0  •  651392  of  CaO  =  55  •  513  per  cent,  calculated  55  •  516 
per  cent.),  which  gives  99-99  instead  of  100. 


1006  EXERCISES    FOR    PRACTICE. 

63,  a.  DETERMINATION  OF  CALCIUM  AS  OXALATE  (to  §  103,  2,  6,  d). 
0-857  grm.  of  "the  air-dried  calcium  carbonate"  were  dissolved  in  hydro- 
chloric acid;  the  solution  was  precipitated  with  ammonium  oxalate  and 
ammonia,  the  precipitate  washed,  and  then  dried  at  100°,  until  the  weight 
remained  constant.  The  precipitate  (CaC2O4+H2O)  weighed  1-2461  grm. 
containing  0-477879  CaO  =  55-76  per  cent,  (calculated  55-516  per  cent), 
which  gives  100-45  instead  of  100. 

64.  DETERMINATION  OF  CALCIUM  AS  CaCO3  BY  PRECIPITATION  AS 

CALCIUM  OXALATE  FROM  ACID  SOLUTION  (to  §  103,  2,  6,  /?). 
0-857  grm.  of  "the  air-dried  calcium  carbonate"  dissolved  in  hydrochloric 
acid  and  precipitated  from  this  solution  according  to  the  directions  of  §  103, 
2,  6,  /?,  gave  0-8476  calcium  carbonate  (which  did  not  manifest  alkaline 
reaction,  and  the  weight  of  which  did  not  vary  in  the  least  upon  evaporation 
with  ammonium  carbonate),  containing  0-474656  CaO  =  55-39  per  cent, 
(calculated  55-51),  which  gives  99-78  instead  of  100. 

64,  a.  DETERMINATION  OF  MAGNESIUM  AS  Mg2P2O7  (to  §  104,  2). 

a.  A  solution  of  1  -  0587  grm.  pure  anhydrous  magnesium  sulphate  in 
water,  precipitated  according  to  §  104,  2,  gave  0-9834  magnesium  pyro- 
phosphate,  containing  0-35438  MgO  =  33-476  per  cent,  (calculated  33-33 
per  cent.),  which  gives  lO'0-43  instead  of  100. 

6.  0-9672  MgSO4  gave  0-8974  Mg2P2O7  =  33-43  per  cent,  of  MgO  (calcu- 
lated 33-33),  which  gives  100-30  instead  of  100. 

65.  VOLUMETRIC  DETERMINATION  OF  CALCIUM  PRECIPITATED  AS  OXALATE 

(to  §  103,  3,  a  and  6). 

Six  portions,  of  10  c.c.  e,ach,  were  taken  of  a  solution  of  pure  calcium 
chloride,  in  2  portions  the  calcium  was  determined  in  the  gravimetric  way 
(by  precipitation  with  ammonium  oxalate,  and  weighing  as  CaCO3) ;  in  two 
by  the  alkalimetric  method  (§  103,  3,  a),  and  in  two  by  precipitation  with 
ammonium  oxalate,  and  estimation  of  the  oxalic  acid  in  the  precipitate  by 
solution  of  potassium  permanganate.  The  following  were  the  results  ob- 
tained : 

a.  In  the  gravimetric        6.  By  the  alkalimetric       c.  By  solution  of  potas- 

way.  method.  sium  permanganate. 

0-5617CaCO3  0-5614  0-5613 

0-5620      "  0-5620  0-5620 

66.  PRECIPITATION  OF  ZINC  ACETATE  BY  HYDROGEN  SULPHIDE  (to  §  108,  6). 

a.  A  solution  of  pure  zinc  acetate  was  treated  with  the  gas  in  excess, 
allowed  to  stand  at  rest  for  some  time,  and  then  filtered.  The  filtrate  was 
mixed  with  ammonia.  It  remained  perfectly  clear  at  first,  and  even  after 
long  standing  a  few  hardly  visible  flocks  only  had  separated. 

6.  A  solution  of  zinc  acetate  to  which  a  tolerably  large  amount  of  acetic 


ANALYTICAL   EXPERIMENTS.  1007 

acid  had  been  added  previously  to  the  precipitation  with  hydrogen  sulphide, 
showed  exactly  the  same  deportment. 

67.  DETERMINATION  OF  IRON  AS  SULPHIDE  (to  §  113,  2). 

10  c.c.  of  a  pure  solution  of  ferric  chloride  was  precipitated  with  ammonia; 
obtained  0  •  1453  Fe,O3  =  0  - 10171  Fe. 

10  c.c.  was  precipitated  with  ammonia  and  ammonium  sulphide,  and 
treated  after  §  113,  2,  obtained  0-1596  FeS  =  0-10157  Fe. 

10  c.c.  again  yielded  0-1605  FeS  =  0-1021  Fe. 

68.  DETERMINATION  OF  LEAD  AS  CHROMATE  (to  §  116,  4). 

1-0083  grm.  pure  lead  nitrate  were  treated  according  to  §  116,  4.  The 
precipitate  was  collected  on  a  weighed  filter,  and  dried  at  100°,  obtained 
0-9871  grm.  =0-67833  PbO.  This  gives  67-3  per  cent.  Calculation  67-4. 

0-9814  lead  nitrate  again  yielded  0-9625  chromate  =  67  -  4  per  cent. 

68,  a.  DETERMINATION  OF  MERCURY  IN  THE  METALLIC  STATE,  IN  THE 

WET  WAY,  BY  MEANS  OF  STANNOUS  CHLORIDE  (to  §  118,  1,  6). 
2-01  grm.  mercuric  chloride  ^gave  1-465  grm.  metallic  mercury  =  72-88 
per  cent,  (calculated  73-83  per  cent.),  which  gives  98-71  instead  of  100 
(SCHAFFNER).  The  loss  is  not  inherent  in  the  method,  i.e.,  it  does  not  arise 
from  mercury  evaporating  during  the  ebullition  and  desiccation,  but  its 
origin  lies  in  the  fact  that  one  usually  does  not  allow  sufficient  time  for 
the  mercury  to  settle  quite  completely,  and  in  general  is  not  careful  enough 
in  decanting,  and  drying  with  paper,  etc. 

69.  DETERMINATION  OF  COPPER  BY  PRECIPITATION  WITH  ZINC  IN  A 
PLATINUM  DISH  (to  §  119,  2,  a). 

30-882  grm.  pure  cupric  sulphate  were  dissolved  in  water  to  250  c.c.; 
10  c.c.  of  the  solution  contained  accordingly  0-31387  grm.  metallic  copper. 

a.  10  c.c.  precipitated  with  zinc  in  a  platinum  dish,  gave  0-3140  =  100-06 
per  cent. 

6.  In  a  second  experiment  10  c.c.  gave  0-3138  =  100  per  cent. 

70.  DEPORTMENT  OF  COPPER  PRECIPITATED  BY  ZINC,  WHEN  IGNITED  IN 

HYDROGEN  (Vol.  I,  p.  374,  foot-note). 

A  dilute  solution  of  copper  sulphate,  acidified  with  hydrochloric  acid, 
was  precipitated  with  zinc  in  a  platinum  crucible,  and  the  precipitate  washed 
with  water,  then  with  alcohol,  and  dried  at  100°;  0-7961  grm.  of  this  was 
ignited  for  a  quarter  of  an  hour  in  hydrogen.  It  then  weighed  0  •  7952  grm. 

71.  DETERMINATION  OF  COPPER  AS  CUPROUS  SULPHOCYANATE 

(to  §  119,  3,  6). 

0-5965  grm.  of  pure  cupric  sulphate  was  dissolved  in  a  little  water,  and 
after  addition  of  an  excess  of  sulphurous  acid,  precipitated  with  potassium 
sulphocyanate.  The  well-washed  precipitate,  dried  at  100°,  weighed  0-2893, 


1008  EXERCISES    FOR   PRACTICE. 

corresponding  to  0-1892  CuO  =  31-72  per  cent.     As  cupric  sulphate  contains 
31-83  per  cent.,  this  gives  99-66  instead  of  100. 

72.  DETERMINATION  OF  COPPER  BY  DE  HAEN'S  METHOD  (to  §  119,  4,  a). 

Four  10  c.c.'s  of  a  solution  of  cupric  sulphate,  each  10  c.c.  containing 
0-0254  grm.  Cu,  were  severally  mixed  with  potassium  iodide,  then  with 
50  c.c.  of  a  solution  of  sulphurous  acid  (50  c.c.  corresponding  to  12-94  c.c. 
iodine  solution).  After  addition  of  starch  paste,  iodine  solution  was  added 
until  the  fluid  appeared  blue. 
This  required, 

In  a,  4-09 
6,3-95 

c,  4-06 

d,  3-95 

As  100  c.c.  of  iodine  solution  contained  0-58043  grm.  iodine,  this  gives 
For  a,  0-0256  Cu  instead  of  0-0254 
"    6,0-0260  "        "       " 
"    c,  0-0257  "        "       "        " 
"    d,  0-0260  "        "       "        " 

Another  experiment,  made  with  100  c.c.  of  the  same  solution  of  cupric 
sulphate,  gave  0-2606  instead  of  0-254  of  copper.  Ammonium  nitrate 
having  been  added  to  10  c.c.  of  the  solution  of  cupric  sulphate,  then  some 
dilute  hydrochloric  acid,  3-4  and  3-5  c.c.  of  iodine  solution  were  required 
instead  of  4  c.c. — a  proof  that  considerably  more  iodine  had  separated  than 
corresponded  to  the  copper. 

73.  ACTION  OF  POTASSIUM-CYANIDE  SOLUTION  ON  AMMONIACAL 
SOLUTION  OF  CUPRIC  OXIDE  (to  §  119,  4,  6). 

a.  Each  of  three  10  c.c.  solutions  of  copper  sulphate,  containing  0-1 
grm.  of  copper  sulphate,  was  mixed  with  increasing  quantities  of  solution 
of  ammonia,  and  sufficient  water  to  equalize  the  degree  of  concentration  in 
the  three  portions;  solution  of  potassium  cyanide  was  then  added,  drop  by 
drop,  until  the  blue  color  had  disappeared.  This  required  the  following 
quantities : 
Copper-sulphate  Solution.  Ammonia.  Water.  Potassium-cyanide  Solution. 

10  c.c.  4  c.c.  12  c.c.  6-7     c.c. 

10  c.c.  8  c.c.  8  c.c.  6-85  c.c. 

10  c.c.  16  c.c.  0  c.c.  7-1     c.c. 

Neutral  ammonium  salts  also  exert  some  influence,  as  shown  by  the  fol- 
lowing experiments,  which  were  made  the  next  day  with  the  same  solutions : 

Copper-sulphate    Ammonia  Wafoi  Potassium-cyanide 

Solution.  Solution. 

6-7  c.c. 
0)        7-4  c.c. 

7-0  c.c. 
7-3  c.c. 


10  c.c. 

2  c.c. 

14  c.c. 

10  c.c. 

2  c.c. 

14  c.c.  Solution  NH4C1  ( 

10  c.c. 

6  c.c. 

(  10  c.c.  H2O 
1     4  c.c.  HSO<  (1  :  5) 

10  c.c. 

2  c.c 

(    8  c.c.  NH<NO3(1  : 
(    6  c.c.  H2O 

10) 

ANALYTICAL   EXPERIMENTS.  1009 

6.  Each  of  several  10  c.c.  of  a  copper-sulphate  solution  containing  0-1  grm. 
CuSO4  was  mixed  with  10  c.c.  of  a  solution  of  ammonium  sesquicarbonate 
(1  :  10),  and,  after  the  addition  of  water  to  some,  and  of  solution  of  neutral 
ammonium  salts  to  the  others,  potassium-cyanide  solution  was  added  at 
60°  until  the  disappearance  of  the  blue  color. 
There  were  used : 

Copper-  Ammonium-  Potassium- 

sulphate  carbonate  Water,  etc.  cyanide 

Solution.  Solution.  Solution. 

10  c.c.  10  c.c.  10  c.c.  !TT'!A'A 

(  II,  16 -6 

10  c.c.  10  c.c.  10  c.c.  (NHJ^O.a  :  10) 

10c.c.  10  c.c.  10  c.c.  (XH4)2N03(1  :  10)        |   J'  J™ 

10  c.c.  10  c.c.  10  c.c.  NH4C1(1  : 10)  j    *'  ]7'] 

\  -LAj  J.  /  •  A, 

The  addition  of  2  drops  of  1  :  20  potassium-ferrocyanide  solution,  as  recom- 
mended by  FLECK,  does  not  assist  much  in  hitting  the  end-reaction,  as  the 
solution,  which  has  a  red  color  towards  the  end,  naturally  becomes  pale-yellow 
on  the  further  addition  of  potassium  cyanide,  and  becomes  fully  decolorized 
only  after  adding  more  cyanide,  and  on  having  stood  for  some  time. 

74.  PRECIPITATION  OF  BISMUTH  NITRATE  BY  AMMONIUM  CARBONATE 
(to  §  120,  1,  a). 

If  a  solution  of  bismuth  nitrate,  no  matter  whether  containing  much  or 
little  free  nitric  acid,  is  mixed  with  water,  precipitated  with  ammonium 
carbonate  and  ammonia,  and  filtered  without  applying  heat,  the  filtrate 
acquires,  upon  addition  of  hydrogen-sulphide  water,  a  blackish-brown  color. 
But  if  the  mixture  before  filtering  is  heated  for  a  short  time  nearly  to  boiling, 
hydrogen  sulphide  fails  to  impart  this  color  to  the  filtrate,  or,  at  all  events, 
the  change  of  color  is  hardly  visible  to  the  eye  looking  through  the  full  test- 
tube  from  the  top. 

75.  DETERMINATION  OF  ANTIMONY  AS  SULPHIDE  (to  §  125,  1). 
0-559  grm.  of  pure  air-dried  tartar  emetic,  treated  according  to  §  125,  1, 
gave  0-2902  grm.  antimonous  sulphide  dried  at  100°=  0-2492  grm.  or  44-58 
per  cent,  of  antimonous  oxide.  Heated  to  blackening  in  a  current  of  car- 
bonic acid,  the  precipitate  lost  0  •  0079  grm.  (reckoned  from  a  part  to  the  whole) 
leaving  accordingly  0-2823  grm.  of  anhydrous  antimonous  sulphide,  which 
corresponds  to  0-24245  grm.,  or  43-37  per  cent,  of  antimonous  oxide.  As 
the  tartar  emetic  contains  43-70  per  cent,  of  antimonous  oxide,  the  process 
gives,  if  the  precipitate  is  dried  at  100°,  102-01;  if  heated  to  blackening, 
99 -22  instead  of  100. 

76.  VOLUMETRIC  DETERMINATION  OF  ANTIMONY  (to  §  125,  3,  a). 
5-0822  grm.  of  chemically  pure  tartar  emetic  were  dissolved  and  made  up 
to  250  c.c. 

Four  portions  of  this  solution,  of  10  c.c.  each,  were  severally  mixed  with 


1010  EXERCISES   FOR    PRACTICE. 

different  quantities  of  a  cold  saturated  solution  of  pure  sodium  bicarbonate* 
and  with  different  quantities  of  water;  after  the  addition  of  2  c.c.  of  starch 
paste  to  each  portion,  iodine  solution  (100  c.c.  =  0-53064  of  iodine,  corres- 
ponding with  0  •  30501  of  antimony  trioxide)  was  dropped  in  until  the  starch- 
iodide  reaction  made  its  appearance. 

1.  10  c.c.  of  the  tartar-emetic  solution +  5  c.c.  of  solution  of.  NaHCO3, 
required  29-9  c.c.  of  the  iodine  solution  to  impart  to  the  liquid  a  reddish 
color,  which  did  not  instantly  disappear  upon  shaking;  and  30-1  c.c.  to  pro- 
duce a  distinct  blue  tint;  after  some  time,  the  latter  also  disappeared. 

2.  10  c.c.  of  the  tartar-emetic  solution +  10  c.c.  of  solution  of  NaHCO3. 
After  the  addition  of  29-2  c.c.  of  the  iodine  solution,  the  liquid  just  began  to 
exhibit  a  red  tint,  which  immediately  disappeared;   29-4  c.c.  produced  a  dis- 
tinct blue  coloration,  which  disappeared  only  after  fifteen  minutes. 

3.  10  c.c.  of  the  tartar-emetic  solution +20  c.c.  of  solution  of  NaHCOg. 
After  the  addition  of  29-2  c.c.  of  the  iodine  solution,  the  liquid  just  began  to 
exhibit  a  red  tint;  29-5  c.c.  produced  a  distinct  blue  tint,  which  disappeared 
only  after  fifteen  minutes. 

4.  10  c.c.  of  tartar-emetic  solution  +20  c.c.  of  solution  of  NaHCO  +100 
c.c.  of  water.     With  29-2  c.c.,  first  reddish  coloration,  with  29-5  distinctly 
blue. 

The  results  of  the  last  three  experiments,  therefore,  agreed  quite  well,  and 
as  29-5  c.c.  of  iodine  solution  corresponds  with  0-08998  of  antimony  trioxide, 
which  are  contained  in  0  •  20329  of  tartrate  of  antimony  and  potassa,  the  two 
last  experiments  give  44-26  per  cent,  of  antimony  trioxide,  in  tartar  emetic; 
the  formula  requires  43-70.  If  the  first  reddening  of  the  liquid,  which  re- 
mains visible  for  a  short  time  after  stirring,  is  considered  as  the  final  reaction, 
only  29-2  c.c.  of  the  iodine  solution  was  required,  which  gives  43-81  of  anti- 
mony trioxide  in  tartar  emetic. 

77.  ACTION  OF  IODINE  SOLUTION  ON  SOLUTION  OF  SODIUM  CARBONATE 

(to  §  125,  3,  a). 

A  solution  of  pure  sodium  carbonate,  perfectly  free  from  reducing  sub- 
stances, *  and  containing  5  grm.  of  anhydrous  salt  in  100  c.c.,  was  used;  the 
iodine  solution  contained  0-53064  grm.  of  iodine  in  100  c.c.,  and  the  tem- 
perature was  19  •  5°.     The  quantity  of  thin  starch  paste  added  in  each  experi- 
ment was  2  c.c.     Two  stages  of  the  reaction  were  distinguished : 
a.  The  point  at  which  the  liquid  exhibited  the  first  faint  blue  tint. 
6.  The  point  at  which  the  liquid  presented  the  same  blue  color  as  a  mix- 
ture of  30  c.c.  of  water  with  2  c.c.  of  starch  paste,  and  1  drop  of  iodine  solution, 
c.c.  Na2CO3.  c.c.  Water.  c.c.  Iodine. 

a.  b. 

1.  20  0  0-2  0-4 

2.  20  60  0-55  0-8 

3.  20  120  0-8  1=2 
4-                 20                        280                        1-7                          2-2 

*  This  is  best  prepared  from  thoroughly  washed  sodium  bicarbonate;  a  drop  of  a 
dilute  solution  of  potassium  permanganate  imparted  to  20  c.c.  of  it  a  red  tint,  which  did 
not  disappear  on  adding  dilute  sulphuric  acid  in  excess. 


ANALYTICAL   EXPERIMENTS.  1011 

Deducting  in  1, 1  drop,  in  2,  2  drops,  in  3,  0-1  c.c.,  in  4,  0-2  c.c.,  of  iodine- 
solution,  these  being  the  quantities  severally  required  to  impart  a  blue  tint  to 
the  pure  water  mixed  with  starch  paste,  the  results  of  this  series  of  experi- 
ments clearly  show  that  the  same  quantity  of  sodium  carbonate  will  prevent 
a  larger  amount  of  iodine  from  forming  iodide  of  starch,  the  more  consider- 
able the  volume  of  water  present. 

78.  ACTION  OF  IODINE  SOLUTION  ON  SOLUTION  OP  SODIUM  BICARBONATE 
(to  §  125,  3,  a). 

The  experiments  were  made  with  a  cold  saturated  solution  of  sodium 
bicarbonate,  free  from  the  monocarbonate,  and  from  reducing  substances; 
the  other  conditions  were  the  same  as  in  No.  77. 

c.c.  NaHCO3.       c.c.  Water.  c.c.  Iodine. 

a.  b. 

1.  20  0  Idrop. 

2.  20  60  Idrop  0-05  c.c. 

3.  20  120  0-05  c.c.  0-10  c.c. 

4.  20  280  0-10  c.c.  0-25  c.c. 

The  results  of  this  series  of  experiments  clearly  show  that  sodium  bicar- 
bonate exercises  no  influence  o.i  the  iodide  of  starch  reaction. 

79.  ESTIMATION  OF  ARSENOUS  ACID  BY  IODINE  SOLUTION  (to  §  127,  5,  a,  1). 

2-5  grm.  of  pure  arsenous  acid  were  dissolved  in  a  solution  of  pure  sodium 
carbonate,  hydrochloric  acid  added  to  the  dilute  solution  in  very  slight  excess, 
and  the  whole  made  up  to  250  c.c. ;  the  temperature  was  20°,  and  the  iodine 
solution  contained  0-53064  grm.  of  iodine  in  100  c.c. 

1.  10  c.c.  of  this  solution +  20  c.c.  of  a  solution  of  sodium  bicarbonate 
saturated  at  20°,+ 2  c.c.  starch  paste,  required  49-05  c.c.  of  the  iodine  solution 
to  impart  a  reddish  tint  to  the  liquid,  which  after  a  short  time  disappeared; 
and  49-25  c.c.  to  produce  a  distinct  blue  coloration. 

2.  Same  conditions  as  in  1,  but  with  addition  of  250  c.c.  of  water;   first 
appearance  of  a  light  bluish  tint  at  49- 1  c.c.,  and  a  distinct  blue  at  49-25  c.c. 
of  the  iodine  solution. 

3.  Same  conditions  as  in  1,  but  substituting  for  the  20  c.c.  of  solution  of 
sodium  bicarbonate,  10  c.c.  of  a  solution  of  perfectly  pure  sodium  carbonate 
(1 :  20),  prepared  from  thoroughly  washed  bicarbonate.     First  i  eddish  tint 
at  49-25  c.c.,  and  a  distinct  blue  coloration  at  49-32  c.c.  of  iodine  solution. 

4.  Same  conditions  as  in  3,  with  20  c.c.  of  solution  of  sodium  carbonate 
instead  of  10  c.c.     Distinct  blue  color  at  49  •  27  c.c. 

5.  Same  as  in  4,+  250  c.c.  of  water.     Distinct  blue  color  at  49  -3  c.c. 

6.  Same   as  in  5,  but  with  50  c.c.  of  solution  of  carbonate  of  sodium 
instead  of  20  c.c.     Distinct  blue  color  with  49-46  c.c.  of  the  iodine  solution. 

These  results  agree  well  together.  49  c.c.  of  iodine  solution  was  clearly 
sufficient  to  convert  the  arsenous  into  arsenic  acid,  corresponding  with  0-1014 
grm.  of  arsenous  acid,  while  the  10  c.c.  of  solution  used  contained  0-100  grm. 


1012  EXERCISES   FOR   PRACTICE. 

80.  DETERMINATION  OP  PHOSPHORIC  ACID  AS  MAGNESIUM 
PYROPHOSPHATE  (to  §  134,  6,  a). 

1-9159  and  2-0860  grm.  pure  crystallized  disodium  hydrogen  phosphate, 
treated  as  directed  §  134,  6,  a,  gave  0-5941  and  0-6494  grm.  of  magnesium 
pyrosphosphate  respectively.  These  give  19-83  and  19-91  per  cent,  of  P2O6 
in  disodium  hydrogen  phosphate,  instead  of  19  •  83  per  cent. 

81.  DETERMINATION  OF  PHOSPHORIC  ACID  AS  URANYL  PYROPHOSPHATE 

(to  §  134,  c). 

30  c.c.  of  a  solution  of  pure  disodium  hydrogen  phosphate,  treated  with 
magnesium  sulphate,  ammonium  chloride,  and  ammonia,  as  directed  §  134,  b, 
a,  gave  0-3269  grm.  of  magnesium  pyrophosphate.  10  c.c.  contained  accord- 
ingly 0-06982  grm.  of  phosphoric  anhydride. 

10  c.c.  of  the  same  solution  were  then  precipitated  with  uranyl  acetate  as 
directed  §  134,  c.  The  ignited  precipitate  was  treated  with  a  little  nitric  acid, 
then  again  ignited;  after  cooling,  it  weighed  0-3478  grm.  corresponding  to 
0-06954  grm.  of  phosphoric  anhydride. 

82.  DETERMINATION  OF  FREE  HYDROGEN  SULPHIDE  BY  MEANS  OF 
SOLUTION  OF  IODINE  (to  §  148,  I,  a). 

The  experiments  were  made  to  settle  the  following  questions : 

a.  Does  the  quantity  of  iodine  required  remain  the  same  for  solutions  of 
hydrogen  sulphide  of  different  degrees  of  dilution? 

b.  Does  the  equation  H2S+I2=2HI+S  really  represent  the  decomposi- 
tion which  takes  place? 

The  hydrogen-sulphide  water  was  contained  in  a  flask  closed  by  a  doubly 
perforated  cork ;  into  one  aperture  a  siphon  with  pinchcock  was  fitted,  to  draw 
off  the  fluid;  into  the  other  aperture  a  short  open  tube,  which  did  not  dip  into 
the  fluid. 

Question   a. 

a.  About  30  c.c.  of  iodine  solution  were  introduced  into  a  flask,  which  was 
then  tared;  hydrogen- sulphide  water  was  added  until  the  yellow  color  had 
just  disappeared.  The  flask  was  then  closed,  weighed,  starch  paste  added, 
and  then  solution  of  iodine  until  the  fluid  appeared  blue. 

70-2  grm.  H2S  water  requred  23-4  c.c.   iodine  solution,  100  accord- 
ingly 33-33  c.c. 

68-4  grm.  required  22-7  c.c.  iodine  solution,  100  accordingly  33-20  c.c. 
P.  Same  process ;  but  the  fluid  was  diluted  with  water  free  from  air. 

61-5  grm.  H2S  water-f-200  grm.  water  required  20-7  c.c.  iodine  solu- 
tion, 100  accordingly  33-65  c.c. 

52-4  grm.4-400  grm.  water  required  17-7  c.c.  iodine  solution,  100  ac- 
cordingly 33-77. 

The  iodine  solution  contained  0-00498  iodine  in  1  c.c.  Considering  that 
addition  of  a  larger  volume  of  water  necessarily  involves  a  slight  increase  in 
the  quantity  of  iodine  solution,  these  results  may  be  considered  sufficiently 
corresponding. 


ANALYTICAL   EXPERIMENTS.  1013 

Question  b. 

According  to  a,  100  grm.  of  the  H..S  water  contained  0-02215  grm.  H^, 
assuming  the  proportion  to  be  100  :  33  •  2. 

173-6  grm.  of  the  same  water  were,  immediately  after  the  experiments 
in  a,  drawn  off  into  a  hydrochloric  acid  solution  of  arsenous  acid;  after  24 
hours,  the  arsenous  sulphide  was  filtered  off,  dried  at  100°,  and  weighed. 
0-0920  grm.  were  obtained,  which  corresponds  to  0-03814  HjS,  or  a  per- 
centage of  0-02197. 

The  second  question  also  is  therefore  answered  in  the  affirmative. 

83.  SOLUTION  OF  MAGNESIUM  CHLORIDE  DISSOLVES  CALCIUM  OXALATE 
(to  §  154,  6). 

If  some  calcium  chloride  is  added  to  a  solution  of  magnesium  chloride,  then 
a  little  ammonium  oxalate,  no  precipitate  is  formed  at  first;  but  upon  slightly 
increasing  the  quantity  of  ammonium  oxalate,  a  trifling  precipitate  gradually 
separates  after  some  time. 

If  an  excess  of  ammonium  oxalate  is  added,  the  whole  of  the  calcium  is 
thrown  down,  but  the  precipitate  contains  also  magnesium  oxalate.  This 
shows  that  to  effect  the  separation  of  the  two  bases  by  ammonium  oxalate, 
the  reagent  must  be  added  in  excess;  whilst,  on  the  other  hand,  in  the  pres- 
ence of  much  magnesium,  the  operator  must  expect  to  precipitate  some  of  the 
magnesium,  as  the  following  experiments  (No.  84)  clearly  show. 

84.  SEPARATION  OF  CALCIUM  FROM  MAGNESIUM  (to  §  154,  6). 

The  fluids  employed  in  the  following  experiments  were,  a  solution  of  cal- 
cium chloride,  10  c.c.  of  which  corresponded  to  0-5618  CaCO3;  a  solution  of 
magnesium  chloride,  containing  0-250  MgO  in  10  c.c  ;  a  solution  of  ammo- 
nium chloride  (1:8);  solution  of  ammonia,  containing  10  per  cent.  XH3; 
solution  of  ammonium  oxalate  (1  : 24) ;  acetic  acid,  containing  30  per  cent. 
C2H40, 

The  precipitation  was  effected  at  the  common  temperature;   the  precipi- 
tate of  calcium  oxalate  was  filtered  off  after  20  hours, 
a.  Influence  of  the  degree  of  dilution. 

a.  10   c.c.    MgCLj,  10  c.c.  CaCl2,  10  c.c.  NH4C1,  4  drops  NH4OH, 

50  c.c.  water,  20  c.c.  (NH4)2C2O4.     Result,  0-5705  CaCO3. 
ft.  Same  as  a,  with  150  c.c.  water  instead  of  50  c.c.     Result,  0-5670 

CaCO3. 
6.  Influence  of  excess  of  ammonia. 

Same  as  a,  /?  + 10  c.c.  XH4OH.     Result,  0 •  5614  grm.  CaCOs. 

c.  Influence  of  excess  of  ammonium  chloride. 

Same  as  a,  /?  +  40  c.c.  NH4C1.     Result,  0-5652  grm. 

d.  Influence  of  excess  of  ammonia  and  ammonium  choride. 

Same  as  a,  ft  +  30  c.c.  NH4C1+ 10  c.c.  NH4OH.     Result,  0  •  5613  grm. 

e.  Influence  of  free  acetic  acid. 

Same  as  a,  /?,  only  with  6  drops  C^O^  instead  of  the  4  drops 
XH4OH.     Result,  0-5594  gnn. 


1014  EXERCISES    FOR   PRACTICE. 

/.  Influence  of  excess  of  ammonium  oxalate  in  feebly  alkaline  solution. 

Same  as  a,  /?  +  20  c.c.  (NH4)2C2O4.     Result,  0  •  5644  grm.  CaCO3. 
g.  Influence  of  excess  of  ammonium  oxalate  in  strongly  alkaline  solution. 
Same  as  a,  ft+ 10  c.c.  NH4OH+  20  c.c.  (NH4)2C2O4.     Result,  0  •  5644. 
h.  Influence  of  excess  of  ammonium  oxalate  in  presence  of  much  NH4C1 

and  NH4OH. 
Same  as  a,   /?  + 10  NH4OH+  30  NH4C1+20   (NH4)2C2O4.      Result, 

0  •  5709  grm. 
i.  Influence  of  excess  of  ammonium  oxalate  in  solution  slightly  acidified 

with  C2H4O2. 
Same  as  a,  ft  -  4  drops  NH4OH+  6  drops  C2H4O2+  20  c.c.  (NH4)2C2O4. 

Result,  0-5661  grm. 

Consequently,  when  a  notable  amount  of  magnesium  is  present  there  is 
always  a  chance  of  magnesium  oxalate,  or  ammonium  magnesium  oxalate 
precipitating  along  with  the  calcium  oxalate. 

Another  series  of  experiments  in  which  a  solution  of  magnesium  oxalate  in 
hydrochloric  acid  was  mixed  with  ammonia  under  varying  circumstances, 
proved  also  that,  in  presence  of  a  notable  quantity  of  magnesium,  mag_ 
nesium  oxalate,  or  magnesium  ammonium  oxalate,  will  always  separate 
after  standing  for  some  time,  no  matter  whether  in  a  cold  or  a  warm  place. 

In  a  third  series  of  experiments,  the  separation  was  effected  by  double  pre- 
cipitation, in  accordance  with  §  154  [36].  The  same  solutions  were  emploj^ed 
as  in  the  first  series,  with  the  exception  of  the  magnesium  chloride,  for  which 
a  solution  was  substituted  containing  0-2182  grm.  MgO,  in  10  c.c. 

10  c.c.  CaCl2  +  30  c.c.  MgCl2  +  20  c.c.  NH4C1  +  300  c.c.  water, +6  drops 
ammonia,  +  a  sufficient  excess  of  ammonium  oxalate.  Results,  in  two  experi- 
ments, 0-5621  and  0  •  5652,  mean  0  •  5636,  instead  of  0  •  5618  CaCO3 ;  also  0  •  6660 
and  0-6489  MgO,  mean  0-6574,  instead  of  0-6546. 

85.  SENSITIVENESS  OF  VARIOUS  METALLIC  SOLUTIONS  TOWARDS 
HYDROGEN  SULPHIDE  (to  §  208,  8,   p.  229  this  volume.) 

Five  portions,  of  500  c.c.  each,  were  taken,  of  a  highly  dilute  aqueous 
solution  of  hydrogen  sulphide  containing  0-003  H2S  in  1000  parts. 

There  was  added — 

a.  CuCl2  gave  a  blackish  coloration. 

6.  As2O3  dissolved  in  hydrochloric  acid  gave  a  precipitate  only  after 
12  hours;  the  liquid  had  not  quite  cleared  then. 

c.  CdCl2  gave  a  beautiful  flocculent  precipitate  after  1  hour. 

d.  Ag^O3.     The  solution  appeared  blackish;    it  required  12  hours  for 
the  precipitate  to  subside  completely. 

e.  HgCy2.     The   solution  appeared  blackish;    it  required   12  hours  for 
the  precipitate  to  subside. 

86.  DETERMINATION  OF  HYDROGEN  SULPHIDE  BY  SOLUTION  OF 

CADMIUM  (to  §  208,  8,  p.  229  this  volume). 

230-3  grm.  of  the  same  hydrogen -sulphide  water  which  has  served  for 
the  experiments  in  No.  82,  and  containing  in  100  grm.  0-02215  of  H2S,  was 


ANALYTICAL    EXPERIMENTS.  1015 

mixed  with  solution  of  cadmium  in  excess,  filtered  after  24  hours,  and  the 
precipitate  washed,  dried  at  100°,  and  weighed.  Result,  0-2395.  If  the 
precipitate  had  consisted  of  pure  cadmium  sulphide,  it  would  have  given, 
by  calculation,  0-0247  per  cent.  H2S,  consequently  too  much.  A  portion 
of  it  was  therefore  deflagrated  with  sodium  carbonate  and  potassium  nitrate, 
and  the  residue  tested  for  chlorine ;  a  distinct  reaction  was  observed. 

87.  DETERMINATION  OF  CARBONIC  ACID  IN  SELTZER  WATER 
(to  §  209,  5,  p.  251  this  volume). 

The  total  carborflc  acid  in  the  mineral  water  of  Xiederselters  was  deter- 
mined exactly  as  described  in  this  volume,  p.  251,  5.  The  following  were 
the  results: 

1.  Water  from  the  top  of  the  shaft  (collected  with  a  plunging  siphon  and 
transferred  to  bottles  provided  with  calcium  hydroxide  and  calcium  chloride). 

221-331  water  yielded  0-7640  CO2  =  3  -45184  per  thousand. 
221-246      "  "       0-7654    "    =3-45949    "          " 

2.  Water  from  the  bottom  of  the  shaft  (collected  with  the  apparatus  (Fig. 
84,  p.  226  of  this  volume). 

250  •  398  water  yielded  0  •  8654  CO2  =  3-45609  per  thousand. 
230-044     "  "       0-7952    "    =3-45673   "          " 

88.  CHLORIMETRICAL  EXPERIMENTS  (to  §  233,  et  seq.). 

10  grm.  chlorinated  lime  were  rubbed  up  wifh  water,  made  up  to  one 
litre,  and  the  following  experiments  made: 

a.  By  PEXOT'S  method  (§  233,  p.  379  this  volume);  obtained  2-35,  and 
23-5  per  cent. 

b.  By  means  of  iron  (modification  1,  p.  385  this  volume);  obtained  23-6 
per  cent. 

c.  By  BUXSEN'S  method  (p.  382  this  volume);   results,  23-6,  and  23-6 
per  cent. 

• 
88,  a.  SEPARATION  OF  IODINE  FROM  CHLORINE  BY  PISANI'S  METHOD. 

0-2338  grm.  potassium  iodide,  dissolved  in  water,  +£  c.c.  of  solution  of 
iodide  of  starch,  required  14  c.c.  of  decinormal  silver  solution  =  0  •  2322  grm. 
potassium  iodide. 

0-3025  grm.  potassium  iodide,  mixed  with  about  double  the  quantity  of 
sodium  chloride,  required  18-2  c.c.  silver  solution  =  0-3021  KI. 

0-2266  grm.  potassium  iodide,  mixed  with  about  100  times  as  much 
sodium  chloride,  required  13-7  c.c.  silver  solution =0-2272  KI. 

88,  b.  SEPARATION  OF  IODINE  FROM  BROMINE  BY  PISANI'S  METHOD. 

0-3198  grm.  potassium  iodide,  mixed  with  double  the  quantity  of  potas- 
sium bromide,  required  19-2  c.c.  of  decinormal  silver  solution  =  0-3187  KI. 


1016  EXERCISES  FOR  PRACTICE. 

89.  DRYING  OF  MANGANESE  (to  §  246,  I,  p.  457  this  volume) . 

Four  small  pans,  containing  each  8  grm.  of  manganese  of  53  per  cent., 
were  first  heated  in  the  water-bath.  After  3  hours,  I  had  lost  0  •  145 ;  after 
6  hours,  II  0-15;  after  9  hours,  III  0-15;  after  12  hours,  IV  0-15  grm.  I 
and  II,  having  been  left  standing,  loosely  covered,  in  the  room  for  12  hours, 
II  was  found  to  weigh  exactly  as  much  as  at  first;  I  wanted  only  0-01  grm. 
of  the  original  weight. 

The  four  pans  were  now  heated  for  2  hours  to  120°.  After  cooling,  they 
were  found  to  have  lost  each  0  •  180  of  the  original  weight.  I  and  II  having 
been  left  standing,  loosely  covered,  in  the  room  for  60  hours,  were  found  to 
have  again  acquired  their  original  weight  by  attracting  moisture.  Ill  and 
IV  were  heated  for  2  hours  to  150°.  The  loss  of  weight  in  both  cases  was 
0-215  grm.  Having  been  left  standing,  loosely  covered,  in  the  room  for 
72  hours,  both  were  found  to  weigh  0-05  less  than  at  first.  Assuming  the 
hygroscopic  moisture  expelled  to  be  reabsorbed  by  standing  in  the  air,  this 
shows  that  at  150°  a  little  chemically  combined  water  escapes  along  with 
the  moisture,  and  accordingly  that  the  temperature  must  not  exceed  120°. 

My  experiments  will  be  found  described  in  detail  in  DINGLER'S  polyt. 
Journ.,  cxxxv,  277  et  seq. 

90.  DEPORTMENT  OF  NICKEL  HYDROXIDE  TOWARDS  BOILING  WATER 
(to  foot-note,  p.  477  this  volume). 

A  solution  of  2  grm.  of  crystallized  nickel  sulphate,  to  which  2  to  3  grm. 
of  potassium  chloride  had  been  added,  was  poured  into  excess  of  dilute 
boiling  solution  of  potassa,  and  the  precipitate  of  nickel  hydroxide  washed 
with  boiling  distilled  water,  first  by  decantation  and  then  on  the  filter,  until 
the  washings  no  longer  gave  a  turbidity  with  silver  nitrate.  The  filtrate 
and  washings  were  then  removed,  and  the  precipitate  on  the  filter  again 
washed  with  boiling  distilled  water  until  1  litre  had  passed  through.  The 
filtrate  was  then  evaporated  to  dryness,  the  residue  treated  with  a  very 
small  quantity  of  hydrochloric  acid,  ammonia  added  in  excess,  and  the  whole 
filtered :  the  solution,  which  had  only  the  slightest  bluish  tinge,  was  acidified 
with  acetic  acid  and  precipitated  hot  by  hydrogen  sulphide.  A  very  small 
quantity  of  nickel  sulphide  was  thus  obtained,  which,  when  converted  into 
anhydrous  nickel  sulphate  weighed  0-0005  grm.,  corresponding  with  0-00024 
grm.  of  nickel  oxide. 

91.  DETERMINATION  OF  SILVER  IN  ARGENTIFEROUS  LEAD 
(to  p.  538  this  volume). 

a.  10  grm.  Of  lead  sulphide  and  0-3  grm.  of  silver  sulphide  were  treated 
as  directed  on  p.  577,  3,  a,  a,  and  the  silver  in  the  button  determined  as  on 
p.  583,  4,  a.     Obtained  a  button  of  8-093,  and  from  this  0-3458  grm.  of 
silver  chloride,  instead  of  0-347  grm. 

b.  5  grm.  of  lead  sulphide  and  0  -05  grm.  of  silver  sulphide  gave  a  button 
of  4-025  grm.  and  0-0562  grm.  of  silver  chloride,  instead  of  0-0578  grm. 

c.  10  grm.  of  lead  sulphide  and  0-01  grm.  of  silver  sulphide  gave  a  button 
of  7-7384  grm.  and  0-0106  grm.  of  silver  chloride,  instead  of  0-0115  grm. 


APPENDIX    I. 

OFFICIAL   METHODS   OF  ANALYSIS  ADOPTED  BY  THE 
ASSOCIATION  OF   OFFICIAL  AGRICULTURAL  CHEM- 
ISTS AT   ITS   MEETING,  NOVEMBER   11,  12, 
AND  14,  1898  * 

(Bulletin  No.  46,  Revised  Edition,  U.  S.  Dep't.  of  Agriculture.  Division  of  Chemistry,  1899.) 

I.— METHODS  FOR  THE  ANALYSIS  OF  FERTILIZERS. 
1.  PREPARATION  OF  SAMPLE. 

The  sample  should  be  well  intermixed,  finely  ground,  and  passed  through  a 
sieve  having  circular  perforations  1  mm.  in  diameter.  The  grinding  and  sift- 
ing should  be  performed  as  rapidly  as  possible,  to  avoid  loss  or  gain  of  mois- 
ture during  the  operation. 

2.  DETERMINATION  OF  MOISTURE. 

In  potash  salts,  sodium  nitrate,  and  ammonium  sulphate  heat  from  1  to  5 
grm.  at  130°  (circa)  until  the  weight  is  constant.  The  loss  in  weight  is  con- 
sidered as  moisture.  In  all  other  fertilizers  heat  2  grm.,  or  5  grm.  if  the  sam- 
ple be  very  coarse,  for  five  hours,  at  100°,  in  a  steam  bath. 

3.  DETERMINATION  OF  PHOSPHORIC  Aero. 

(a)    GRAVIMETRIC    METHOD. 

(1)  Preparation  of  Reagents. 

(a)  AMMONIUM-CITRATE  SOLUTION. — Dissolve  370  grm.  of  commercial  cit- 
ric acid  in  1500  c.c.  of  water;  nearly  neutralize  with  commercial  ammonia; 
cool;  add  ammonia  until  exactly  neutral  (testing  with  saturated  alcoholic 
solution  of  corallin),  and  dilute  to  volume  of  2  litres.  Determine  the  specific 
gravity,  which  should  be  1  -09  at  20°. 

Optional  Method. — To  370  grm.  of  commercial  citric  acid  add  commercial 
ammonia,  specific  gravity  0-96,  until  nearly  neutral;  reduce  the  specific 
gravity  to  nearly  1  •  09  and  make  exactly  neutral,  testing  as  follows :  Pre- 
pare a  solution  of  fused  calcium  chloride,  200  grm.  to  the  litre,  and  add  four 
volumes  of  strong  alcohol.  Make  the  mixture  exactly  neutral,  using  a  small 
amount  of  freshly  prepared  corallin  solution  as  preliminary  indicator,  and 
test  finally  by  withdrawing  a  portion,  diluting  with  an  equal  volume  of  water, 
and  testing  with  cochineal  solution;  50  c.c.  of  this  solution  will  precipitate 
the  citric  acid  from  10  c.c.  of  the  citrate  solution.  To  10  c.c.  of  the  nearly 


*  Edited  by  HARVEY  W.  WILET. 

1017 


1018  APPENDIX   I. 

neutral  citric  solution  add  50  c.c.  of  the  alcoholic  calcium-chloride  solution, 
stir  well,  filter  at  once  through  a  folded  filter,  dilute  with  an  equal  volume  of 
water,  and  test  the  reaction  with  neutral  solution  of  cochineal.  If  acid  or 
alkaline,  add  ammonia  or  citric  acid,  as  the  case  may  be,  mix,  and  test  again, 
as  before.  Repeat  this  process  until  a  neutral  reaction  is  obtained.  Add 
sufficient  water  to  make  the  specific  gravity  1  •  09  at  20°. 

(6)  MOLYBDIC  SOLUTION. — Dissolve  100  grm.  of  molybdic  acid  in  400  grm. 
or  417  c.c.  of  ammonia,  specific  gravity  0  •  96,  and  pour  the  solution  thus  ob- 
tained into  1500  grm.  or  1250  c.c.  of  nitric  acid,  specific  gravity  1-20.  Keep 
the  mixture  in  a  warm  place  for  several  days,  or  until  a  portion  heated  to  40° 
deposits  no  yellow  precipitate  of  ammonium  phosphomolybdate.  Decant 
the  solution  from  any  sediment  and  preserve  it  in  glass-stoppered  vessels. 

(c)  AMMONIUM-NITRATE  SOLUTION. —  Dissolve    200  grm.    of    commercial 
ammonium  nitrate  in  enough  water  to  make  the  volume  of  the  solution  2  litres. 

(d)  MAGNESIA  MIXTURE. — Dissolve  22  grm.  of  recently  ignited  calcined 
magnesia  in  dilute  hydrochloric  acid,  avoiding  an  excess  of  the  latter.     Add  a 
little  calcined  magnesia  in  excess,  and  boil  a  few  minutes  to  precipitate  iron, 
alumina,  and  phosphoric  acid;   filter;   add  280  grm.  of  ammonium  chloride, 
700  c.c.  of  ammonia  of  specific  gravity  0-96,  and  water  enough  to  make  the 
volume  2  litres.      Instead  of  the  solution  of  22  grm.  of  calcined  magnesia,  110 
grm.  of  crystallized  magnesium  chloride  (MgCl2-6H2O)  may  be  used. 

(e)  DILUTE  AMMONIA  FOR  WASHING. — This  solution  should  contain  2-5 
per  cent.  NH3. 

(/)  MAGNESIUM-NITRATE  SOLUTION. —  Dissolve  220  grm.  of  calcined  mag- 
nesia in  nitric  acid,  avoiding  an  excess  of  the  latter ;  then  add  a  little  calcined 
magnesia  in  excess;  boil;  filter  from  the  excess  of  magnesia,  ferric  oxide,  etc., 
and  dilute  with  water  to  2  litres. 

(2)  Total  Phosphoric  Acid. 

(a)  METHODS  OF  MAKING  SOLUTION. — Treat  2  grm.  of  the  sample  by  one 
of  the  methods  given  below.  After  solution,  cool,  dilute  to  200  or  250  c.c., 
and  pour  on  a  dry  filter. 

(at)  Ignite  and  dissolve  in  hydrochloric  acid. 

(a2)  Evaporate  with  5  c.c.  of  magnesium  nitrate,  ignite,  and  dis- 
solve in  hydrochloric  acid. 

(a3)  Boil  with  from  20  to  30  c.c.  of  strong  sulphuric  acid,  adding 
from  2  to  4  grm.  of  sodium-  or  potassium  nitrate  at*  the  beginning  of 
the  digestion  and  a  small  quantity  after  the  solution  has  become  nearly 
colorless,  or  adding  the  nitrate  in  small  portions  from  time  to  time. 
A  KJELDAHL  flask  marked  at  250  c.c.  is  recommended.  After  the 
solution  is  colorless,  add  150  c.c.  of  water  and  boil  for  a  few  minutes,  cool, 
and  make  up  to  mark. 

(a4)  Digest  with  strong  sulphuric  acid  and  such  other  reagents 
as  are  used  in  either  the  plain  or  modified  KJELDAHL  or  GUNNING 
method  for  estimating  nitrogen.  Do  not  add  any  potassium  perman- 
ganate, but  after  the  solution  has  become  colorless  add  about  100  c.c.  of 
water  and  boil  for  a  few  minutes,  cool,  and  make  up  to  a  convenient 


OFFICIAL    METHODS  OF   ANALYSIS.  1019 

volume;  2-5  grm.  of  substance  and  a  digestion  flask  marked  at  250 
c.c.  are  recommended. 

(aj  Dissolve  in  30  c.c.  of  concentrated  nitric  acid  and  a  small 
quantity  of  hydrochloric  acid,  and  boil  until  organic  matter  is  de- 
stroyed. 

(a«)  Add  30  c.c.  of  concentrated  hydrochloric  acid,  heat,  and  add 
cautiously  in  small  quantities  at  a  time,  about  0  •  5  grm.  of  finely  pul- 
verized potassium  chlorate,  to  destroy  organic  matter. 

(a7)  Dissolve  in  from  15  to  30  c.c.  of  strong  hydrochloric  acid  and 
from  3  to  10  c.c.  of  nitric  acid.  This  method  is  recommended  for 
fertilizers  containing  much  iron  or  aluminium  phosphate. 
(6)  DETERMINATION. — Take  an  aliquot  portion  of  the  solution  prepared 
above,  corresponding  to  0-25  grm.,  0-50  grm.,  or  1  grm.,  neutralize  with 
ammonia,  and  clear  with  a  few  drops  of  nitric  acid.  In  case  hydrochloric 
or  sulphuric  acid  has  been  used  as  solvent,  add  about  15  grm.  of  dry  ammo- 
nium nitrate  or  a  solution  containing  that  amount.  To  the  hot  solution  add 
50  c.c.  of  molybdic  solution  for  every  decigramme  of  P2O5  that  is  present. 
Digest  at  about  65°  for  an  hour,  filter,  and  wash  with  cold  water,  or  preferably 
ammonium-nitrate  solution.  Test  the  filtrate  for  phosphoric  acid  by  renewed 
digestion  and  addition  of  more  molybdic  solution.  Dissolve  the  precipitate 
on  the  filter  with  ammonia  and  hot  water,  and  wash  into  a  beaker  to  a  bulk 
of  not  more  than  100  c.c.  Nearly  neutralize  with  hydrochloric  acid,  cool, 
and  add  magnesia  mixture  from  a  burette;  add  slowly  (about  1  drop  per 
second),  stirring  vigorously.  After  fifteen  minutes  add  30  c.c.  of  ammonia 
solution  of  density  0-96.  Let  stand  for  some  time;  two  hours  is  usually 
enough.  Filter,  wash  with  2-5-per  cent.  XH3  until  practically  free  from 
chlorides,  ignite  to  whiteness  or  to  a  grayish  white,  and  weigh. 

(3)  Water-soluble  Phosphoric  Add. 

Place  2  grm.  of  the  sample  on  a  9  cm.  filter,  wash  with  successive  small 
portions  of  water,  allowing  each  portion  to  pass  through  before  adding  more, 
until  the  filtrate  measures  about  250  c.c.  If  the  filtrate  be  turbid,  add  a 
little  nitric  acid  Make  up  to  any  convenient  definite  volume;  mix  well 
with  an  aliquot  part,  and  proceed  as  under  total  phosphoric  acid. 

(4)  Citrate-insoluble  Phosphoric  Acid. 

(a)  IN  ACIDULATED  SAMPLES. — Heat  100  c.c.  of  strictly  neutral  ammo- 
nium citrate  solution  of  1-09  specific  gravity  to  65°  hi  a  flask  placed  in  a 
bath  of  warm  water,  keeping  the  flask  loosely  stoppered  to  prevent  evapo- 
ration. When  the  citrate  solution  in  the  flask  has  reached  65°,  drop  into 
it  the  filter  containing  the  washed  residue  from  the  water-soluble  phosphoric- 
acid  determination,  stopper  tightly  with  a  smooth  rubber,  and  shake  violently 
until  the  filter-paper  is  reduced  to  a  pulp.  Place  the  flask  in  the  bath  and 
maintain  it  at  such  a  temperature  that  the  contents  of  the  flask  will  stand 
at  exactly  65°.  Shake  the  flask  every  five  minutes.  At  the  expiration  of 
exactly  30  minutes  from  the  time  the  filter  and  residue  are  introduced, 
remove  the  flask  from  the  bath  and  immediately  filter  the  contents  as  rapidly 


1020  APPENDIX   I. 

as  possible.  Wash  thoroughly  with  water  at  65°.  Transfer  the  filter  and 
its  contents  to  a  crucible,  ignite  until  all  organic  matter  is  destroyed,  add 
from  10  to  15  c.c.  of  strong  hydrochloric  acid,  and  digest  until  all  phosphate 
is  dissolved;  or  return  the  filter  with  contents  to  the  digestion  flask,  add  from 
30  to  35  c.c.  strong  nitric  acid,  from  5  to  10  c.c.  strong  hydrochloric  acid, 
and  boil  until  all  phosphate  is  dissolved.  Dilute  the  solution  to  200  c.c. 
If  desired,  the  filter  and  its  contents  may  be  treated  according  to  methods 
(a2),  (a3),  or  (a4),  under  total  phosphoric  acid.  Mix  well;  filter  through  a 
dry  filter;  take  a  definite  portion  of  the  filtrate  and  proceed  as  under  total 
phosphoric  acid. 

(6)  IN  NON-ACIDULATED  SAMPLES. — In  case  a  determination  of  citrate- 
insoluble  phosphoric  acid  is  required  in  non-acidulated  samples  it  is  to  be 
made  by  treating  2  grm.  of  the  phosphatic  material,  without  previous  wash- 
ing with  water,  precisely  in  the  way  above  described,  except  that  in  case 
the  substance  contains  much  animal  matter  (bone,  fish,  etc.)  the  residue 
insoluble  in  ammonium  citrate  is  to  be  treated  by  one  of  the  processes  de- 
scribed under  total  phosphoric  acid  (a2),  («3),  or  (a4). 

(5)  Citrate-soluble  Phosphoric  Acid. 

The  sum  of  the  water-soluble  and  citrate-insoluble  subtracted  from  the 
total  gives  the  citrate-soluble  phosphoric  acid. 

(6)    OPTIONAL   VOLUMETRIC    METHOD. 

(1)  Preparation  of  Reagents. 

(a)  MOLYBDIC  SOLUTION. — To  100  c.c.  of  molybdic  solution,  prepared 
as  directed  on  p.  1018,  add  5  c.c  of  nitric  acid  (specific  gravity,  1-42).  This 
solution  should  be  filtered  each  time  before  using. 

(6)  POTASSIUM-NITRATE  OR  AMMONIUM-NITRATE  SOLUTION  FOR  WASH- 
ING.— Dissolve  3  grm.  of  the  salt  in  100  c.c.  of  water. 

(c)  NITRIC-ACID  SOLUTION  FOR  WASHING. — Dilute  100  c.c.  of  nitric  acid 
(specific  gravity,  1-42)  to  1  litre  with  water. 

(d)  STANDARD    POTASSIUM-HYDROXIDE    SOLUTION. — This    solution     con- 
tains 18-17106  grm.  of  potassium  hydroxide  to   the   litre.     It  is  prepared 
by  diluting  323-81   c.c.  of  normal  potassium  hydroxide,  which  has  been 
freed  from  carbonates  to  1  litre.     One  hundred  c.c.  of  the  solution  should 
neutralize  32-38  c.c.  of  normal  acid.     One  c.c.  is  equal  to  1  mgrm.  P2O3 
(1  per  cent.  P3O5  on  basis  of  0- 1  grm.  of  substance). 

(e}  STANDARD  NITRIC-ACID  SOLUTION. — The  strength  of  this  solution 
is  the  same  as,  or  one-half  that  of,  the  standard  alkali  solution,  and  is  deter- 
mined by  titrating  against  that  solution,  using  phenolphtalein  as  indicator. 

(/)  PHENOLPHTALEIN  SOLUTION. — One  grm.  of  phenolphtalein  is  dis- 
solved in  100  c.c.  of  alcohol. 

(2)  Total  Phosp  hone  A  cid. 

(a)  METHODS  OF  MAKING  SOLUTION. — Dissolve  according  to  methods 
(a,),  (at),  (ae),  or  (a7)  (p.  1018),  preferably  by  (as),  when  these  acids  are  a 
suitable  solvent,  and  dilute  to  200  c.c.  with  water. 


OFFICIAL   METHODS   OF    ANALYSIS.  1021 

(6)  DETERMINATION; 

(bj)  For  percentages  of  5  or  below  use  an  aliquot  corresponding 
to  0-4  grm.  substance;  for  percentages  between  5  and  20  use  an 
aliquot  corresponding  to  0-2  grm.  substance;  and  for  percentages 
above  20  use  an  aliquot  corresponding  to  0  •  1  grm.  substance.  Add 
from  5  to  10  c.c  of  nitric  acid,  depending  on  the  method  of  solution 
(or  the  equivalent  in  Ammonium  nitrate),  nearly  neutralize  with 
ammonia,  dilute  to  from  75  to  100  c.c.,  heat  in  water  bath  to  from 
60°  to  65°,  and  for  percentages  below  5  add  from  20  to  25  c.c.  of  freshly 
filtered  molybdic  solution.  For  percentages  between  5  and  20  add 
from  30  to  35  c.c  molybdic  solution ;  stir,  let  stand  about  15  minutes, 
filter  at  once,  wash  once  or  twice  with  water  by  decantation,  using 
from  25  to  30  c.c  each  time,  agitating  the  precipitate  thoroughly 
and  allowing  to  settle ;  transfer  to  filter  and  wash  five  or  six  times, 
using  enough  water  to  make  with  the  decantation  washings  about 
200  c.c.  Transfer  precipitate  and  filter,  to  beaker  or  precipitating 
vessel,  dissolve  in  small  excess  of  standard  alkali,  add  a  few  drops  of 
phenolphtalein  solution  and  titrate  with  standard  acid  (nitric). 

(3)   Water-soluble  Phosphoric  Acid. 

Dissolve  according  to  directions  given  under  (3)  p.  1019.  To  an  aliquot 
portion  of  the  solution  corresponding  to  0-2  or  0-4  grm.,  add  10  c.c.  of  con- 
centrated nitric  acid  and  then  ammonia  until  a  slight  permanent  precipi- 
tate is  formed,  dilute  to  60  c.c.,  and  proceed  as  under  (2),  (6^. 

(4)  Citrate-insoluble  Phosphoric  Acid. 

Make  the  solution  according  to  the  directions  given  under  (4),  p  1019,  and 
determine  the  phosphoric  acid  in  an  aliquot  portion  corresponding  to  0-4 
grm.,  as  directed  in  (2),  (&,). 

(5)  Citrate-soluble  Phosphoric  Acid. 

The  sum  of  the  water-soluble  and  citrate-insoluble  subtracted  from  the 
total  gives  the  citrate-soluble  phosphoric  acid. 

4.  DETERMINATION  OF  NITROGEN. 

(a)    K.TELDAHL    METHOD. 

[Not  applicable  in  the  presence  of  nitrates.] 

(1)  Preparation  of  Reagents. 

(a)  STANDARD  ACID  SOLUTION. 

(at)  Standard  Hydrochloric  Acid,  the  absolute  strength  of  which 
has  been  determined  by  precipitating  with  silver  nitrate  and  weighing 
the  silver  chloride  as  follows: 

To  any  convenient  quantity  of  the  acid  to  be  standardized,  add 
solution  of  silver  nitrate  in  slight  excess,  and  2  c.c.  pure  nitric  acid, 
specific  gravity,  1-2.  Heat  to  boiling  point,  with  constant  stirring, 
and  keep  at  this  temperature  for  some  minutes  without  allowing 


1022  APPENDIX   I. 

violent  ebullition,  until  the  precipitate  assumes  the  granular  form. 
Allow  to  cool  somewhat,  and  then  filter  through  asbestos.  Wash 
the  precipitate  by  decantation,  with  200  c.c.  of  very  hot  water,  to 
which  have  been  added  8  c.c.  of  nitric  acid  and  2  c.c.  of  dilute  solu-' 
tion  of  silver  nitrate  containing  1  grm.  of  the  salt  in  100  c.c.  of  water. 
The  washing  by  decantation  is  performed  by  adding  the  hot  mixture 
in  small  quantities  at  a  time,  beating  up  the  precipitate  well  with  a 
thin  glass  rod  after  each  addition.  The  pump  is  kept  in  action  all  the 
time ;  but  to  keep  out  dust  during  the  washing,  the  cover  is  removed 
from  the  crucible  only  when  the  fluid  is  to  be  added. 

Put  the  capsule  and  precipitate  aside,  return  the  washings  once 
through  the  asbestos  so  as  to  obtain  them  quite  clear,  and  set  aside 
to  recover  excess  of  silver.  Rinse  the  receiver  and  complete  the 
washings  of  the  precipitate  with  about  200  c.c.  of  cold  water.  Half 
of  this  is  used  to  wash  by  decantation  and  the  remainder  to  transfer  the 
precipitate  to  the  crucible.  Finish  washing  in  the  crucible,  the  lumps 
of  silver  chloride  being  broken  down  with  the  glass  rod.  Remove 
the  second  filtrate  from  the  receiver  and  pass  about  20  c.c.  of  98-per 
cent,  alcohol  through  the  precipitate.  Dry  at  from  140°  to  150°. 

(a2)  Standard  Sulphuric  Acid,  the  absolute  strength  of  which  has 
been  determined  by  precipitation  with  barium  chloride. 

For  ordinary  work  half  normal  acid  is  recommended,  i.e.,  acid 
containing  24-5185  grm.  sulphuric  acid  to  the  litre.  For  work  in 
determining  very  small  amounts  of  nitrogen,  one-tenth  normal  acid 
is  recommended.  In  titrating  mineral  acids  against  ammonia  solu- 
tions, use  cochineal  as  indicator. 

(6)  STANDARD  ALKALI  SOLUTION. — The  strength  of  this  solution,  rela- 
tive to  the  acid,  must  be  accurately  determined.  One-tenth  normal  ammonia 
solution,  i.e.,  containing  1-7051  grm.  of  ammonia  to  the  litre,  is  recommended. 

(c)  SULPHURIC  ACID. — The  sulphuric,  acid  used  should  have  a  specific 
gravity  of  1-84  and  be  free  from  nitrates,  and  also  from  ammonium  sulphate. 

(d)  METALLIC  MERCURY   OR  MERCURIC   OXIDE. — If  mercuric   oxide  be 
used,  it  should  be  prepared  in  the  wet  way,  but  not  from  mercuric  nitrate. 

(e)  POTASSIUM  PERMANGANATE. — This  reagent  is  used  in  a  finely  pul- 
verized state. 

(/)  GRANULATED  ZINC,  PUMICE  STONE,  OR  ZINC  DUST. — One  of  these 
reagents  is  added  to  the  contents  of  the  distillation  flasks,  when  found  neces- 
sary, in  order  to  prevent  bumping.  When  zinc  dust  is  used,  0-5  grm.  will 
be  found  sufficient. 

(gr)  POTASSIUM-SULPHIDE  SOLUTION. — A  solution  of  40  grm.  of  commer- 
cial potassium  sulphide  in  one  litre  of  water. 

(h)  SODIUM-HYDROXIDE  SOLUTION. — A  saturated  solution  of  sodium 
hydroxide  free  from  nitrates. 

(i)  INDICATOR. — A  solution  of  cochineal  is  prepared  by  digesting  and 
frequently  agitating  3  grm.  of  pulverized  cochineal  in  a  mixture  of  50  c.c. 
of  strong  alcohol  and  200  c.c.  of  distilled  water  for  a  day  or  two  at  ordinary 
temperature j.  The  filtered  solution  is  employed  as  indicator. 


OFFICIAL    METHODS    OF   ANALYSIS.  1023 

(2)  Apparatus. 

(a)  KJELDAHL  DIGESTION  FLASKS. — These  are  pear-shape,  round-bottom 
flasks,  made  of  hard,  moderately  thick,  well-annealed  glass,  having  a  total 
capacity  of  about  250  c.c.  They  are  22  cm.  long,  and  have  a  maximum 
diameter  of  6  cm., tapering  gradually  to  a  long  neck,  which  is  2  cm.  in  diam- 
eter at  the  narrowest  part  and  flared  a  little  at  the  edge. 

(6)  DISTILLATION  FLASKS. — For  distillation,  a  flask  of  ordinary  shape, 
of  about  550  c.c.  capacity,  may  be  used.  It  is  fitted  with  a  rubber  stopper, 
and  with  a  bulb  tube  above  to  prevent  the  possibility  of  sodium  hydrate 
being  carried  over  mechanically  during  distillation.  The  bulbs  may  be 
about  3  cm.  in  diameter,  the  tubes  being  of  the  same  diameter  as  the  con- 
denser and  cut  off  obliquely  at  the  lower  end,  which  is  fastened  to  the  con- 
denser by  a  rubber  tube. 

(c)  KJELDAHL  FLASKS  FOR  BOTH  DIGESTION  AND  DISTILLATION. — These 
are  pear-shape,  round-bottom  flasks,  having  a  total  capacity  of  about  550  c.c. 
made  of  hard,  moderately  thick,  and  well-annealed  glass.  When  used  for 
distillation,  the  flasks  are  fitted  with  rubber  stoppers  and  bulb  tubes,  as  given 
under  distillation  flasks. 

(3)  Determination. 

(a)  THE  DIGESTION. — From  0-7  to  3-5  grm.  of  'the  substance  to  be  ana- 
lyzed, according  to  its  proportion  of  nitrogen,  are  brought  into  a  digestion 
flask  with  approximately  0-7  grm.  of  mercuric  oxide,  or  its  equivalent  in 
metallic  mercury,  and  20  c.c.  of  sulphuric  acid.  The  flask  is  placed  hi  an 
inclined  position,  and  heated  below  the  boiling-point  of  the  acid  for  from  5 
to  15  minutes,  or  until  frothing  has  ceased.  If  the  mixture  froths  badly,  a 
small  piece  of  paraffin  may  be  added  to  prevent  it.  The  heat  is  then  raised 
until  the  acid  boils  briskly.  No  further  attention  is  required  till  the  contents 
of  the  flask  have  become  a  clear  liquid,  which  is  colorless,  or  at  least  has  only 
a  very  pale  straw  color.  The  flask  is  then  removed  from  the  flame,  held 
upright,  and,  while  still  hot,  potassium  permanganate  is  dropped  in  carefully 
and  in  small  quantities  at  a  time,  till,  after  shaking,  the  liquid  remains  of  a 
green  or  purple  color. 

(6)  THE  DISTILLATION. — After  cooling,  the  contents  of  the  flask  are  trans- 
ferred to  the  distilling  flask  with  about  200  c.c.  of  water,  a  few  pieces  of  granu- 
lated zinc,  pumice  stone,  or  0-5  grm.  of  zinc  dust  when  found  necessary  to 
keep  the  contents  of  the  flask  from  bumping,  and  25  c.c.  of  potassium  sul- 
phide solution,  are  added,  with  shaking.  Next  add  50  c.c.  of  the  soda  solu- 
tion, or  sufficient  to  make  the  reaction  strongly  alkaline,  pouring  it  down 
the  side  of  the  flask  so  that  it  does  not  mix  at  once  with  the  acid  solution. 
Connect  the  flask  with  the  condenser,  mix  the  contents  by  shaking,  and  distill 
until  all  ammonia  has  passed  over  into  the  standard  acid.  The  first  150  c.c. 
of  the  distillate  will  generally  contain  all  the  ammonia.  This  operation 
usually  requires  from  forty  minutes  to  one  hour  and  a  half.  The  distillate  is 
then  titrated  with  standard  alkali. 

The  use  of  mercuric  oxide  in  this  operation  greatly  shortens  the  time 


1024  APPENDIX   I. 

necessary  for  digestion,  which  is  rarely  over  an  hour  and  a  half  in  case  of  sub- 
stances most  difficult  to  oxidize,  and  is  more  commonly  less  than  an  hour. 
In  most  instances  the  use  of  potassium  permanganate  is  quite  unnecessary, 
but  it  is  believed  that  in  exceptional  cases  it  is  required  for  complete  ,oxida-r 
tion,  and  in  view  of  the  uncertainty  it  is  always  used.  The  potassium  sul- 
phide removes  all  the  mercury  from  the  solution,  and  so  prevents  the 
formation  of  mercur-ammonium  compounds  which  are  not  completely 
decomposed  by  the  sodium  hydroxide.  The  addition  of  zinc  gives  rise  to  an 
evolution  of  hydrogen  and  prevents  violent  bumping.  Previous  to  use  the 
reagents  should  be  tested  by  a  blank  experiment  with  sugar,  which  will 
partially  reduce  any  nitrates  that  are  present,  which  might  otherwise 
escape  notice. 

(6)    GUNNING   METHOD. 

[Not  applicable  in  the  presence  of  nitrates.] 

(1)  Preparation  of  Reagents. 

(a)  POTASSIUM  SULPHATE. — This  reagent  should  be  pulverized  before 
using. 

The  other  standard  solutions  and  reagents  used  are  the  same  as  those 
described  under  KJELDAHL  method  (pp.  1021  and  1022). 

(2)  Apparatus. 

The  apparatus  used  is  the  same  as  that  described  in  the  KJELDAHL  method 
(p.  1022). 

(3)  Determination. 

In  a  digestion  flask  holding  from  250  to  500  c.c.,  place  from  0- 7  to  3  •  5  grm. 
of  the  substance  to  be  analyzed,  according  to  its  proportion  of  nitrogen. 
Then  add  10  grm.  of  powdered  potassium  sulphate  and  from  15  to  25  c.c. 
(ordinarily  about  20  c.c.)  of  concentrated  sulphuric  acid.  Conduct  the 
digestion  as  in  the  KJELDAHL  process,  starting  with  a  temperature  below 
boiling-point  and  increasing  the  heat  gradually  until  frothing  ceases.  Di- 
gest until  the  mixture  is  colorless  or  nearly  so.  Do  not  add  either  potassium 
permanganate  or  potassium  sulphide.  Dilute,  neutralize,  and  distill  as  in 
the  KJELDAHL  method.  In  neutralizing,  it  is  convenient  to  add  a  few  drops 
of  phenolphtalein  indicator,  by  which  one  can  tell  when  the  acid  is  com- 
pletely neutralized,  remembering  that  the  pink  color,  which  indicates  an 
alkaline  reaction,  is  destroyed  by  a  considerable  excess  of  strong  fixed  alkali. 
The  distillation  and  titration  are  conducted  as  in  the  KJELDAHL  method. 

(c)    KJELDAHL  METHOD  MODIFIED  TO  INCLUDE  THE  NITROGEN  OF  NITRATES. 

(1)  'Preparation  of  Reagents. 

Besides  the  reagents  given  under  the  KJELDAHL  method,  there  will  be 
needed — 

(a)  ZINC  DUST. — This  should  be  an  impalpable  powder;  granulated  zinc 
or  zinc  filings  will  not  answer. 

(6)  SODIUM  THIOSULPHATE. 

(c)  COMMERCIAL  SALICYLIC  ACID. 


OFFICIAL   METHODS   OF   ANALYSIS.  1025 

(2)  Apparatus. 

The  apparatus  used  is  the  same  as  in  the  KJELDAHL  method  ((a),  (2)). 
(3)  Determination. 

Place  from  0  •  7  to  3  •  5  grm.  of  the  substance  to  be  analyzed  into  a  KJELDAHL 
digestion  flask,  add  30  c.c.  of  sulphuric  acid  containing  1  grm.  of  salicylic  acid 
and  shake  until  thoroughly  mixed,  then  add  5  grm.  of  crystallized  sodium 
thiosulphate ;  or  add  to  the  substance  30  c.c.  of  sulphuric  acid  containing 
2  grm.  of  salicylic  acid,  then  add  gradually  2  grm.  of  zinc  dust,  shaking  the 
contents  of  the  flask  at  the  same  time.  Finally,  place  the  flask  on  the  stand 
for  holding  the  digestion  flasks,  where  it  is  heated  over  a  low  flame  until  all 
danger  from  frothing  has  passed.  The  heat  is  then  raised  until  the  acid 
boils  briskly  and  the  boiling  continued  until  white  fumes  no  longer  escape 
from  the  flask.  This  requires  about  five  or  ten  minutes.  Add  approxi- 
mately 0-7  grm.  of  mercuric  oxide  or  its  equivalent  in  metallic  mercury, 
and  continue  the  boiling  until  the  liquid  in  the  flask  is  colorless  or  nearly 
so.  In  case  the  contents  of  the  flask  are  likely  to  become  solid  before  this 
point  is  reached,  add  10  c.c.  more  of  sulphuric  acid.  Complete  the  oxidation 
with  a  little  potassium  permanganate  in  the  usual  xway,  and  proceed  with 
the  distillation  as  described  in  the  KJELDAHL  method.  The  reagents  should 
be  tested  by  blank  experiments. 

(d)    GUNNING  METHOD   MODIFIED  TO  INCLUDE   THE  NITROGEN  OF  NITRATES. 

(1)  Preparation  of  Reagents. 

Besides  the  reagents  given  under  the  Gunning  method,  there  will  be 
needed — 

(a)  SODIUM  THIOSULPHATE. 

(6)  COMMERCIAL  SALICYLIC  ACID. 

(2)  Apparatus. 

The  apparatus  used  is  the  same  as  that  given  under  the  KJELDAHL  method 
((a),  (2)). 

(3}  Determination. 

In  a  digestion  flask  holding  from  250  to  500  c.c.  place  from  0-7  to  3-5 
grm.  of  the  substance  to  be  analyzed,  according  to  the  amount  of  nitrogen 
present.  Add  from  30  to  35  c.c.  of  salicylic-acid  mixture,  namely,  30  c.c. 
sulphuric  acid  to  1  grm.  of  salicylic  acid,  shake  until  thoroughly  mixed, 
and  allow  to  stand  from  five  to  ten  minutes,  with  frequent  shaking;  then  add 
5  grm.  of  sodium  thiosulphate  and  10  grm.  of  potassium  sulphate.  Heat 
very  gently  until  frothing  ceases,  then  heat  strongly  until  nearly  colorless. 
Dilute,  neutralize,  and  distill  as  in  the  GUNNING  method. 

(e)     ABSOLUTE     OR     CUPRIC-OXIDE     METHOD. 
[Applicable  to  all  nitrogen  determinations.] 

(1)  Preparation  of  Reagents. 

(a)  Coarse  cupric  oxide. — To  be  ignited  and  cooled  before  using. 
(6)  Fine  cupric  oxide.—  Prepared  by  grinding  ordinary  cupric  oxide. 


1026  APPENDIX   I. 

(c)  Metallic  copper. — Granulated  copper,  or  fine  copper  gauze,  heated  and 
cooled  in  a  current  of  hydrogen. 

(d)  Sodium  bicarbonate,  free  from  organic  matter. 

(e)  Caustic  potash  solution. — A  supersaturated  solution  of  caustic  potash 
in  hot  water. 

(2)  Apparatus. 

(a)  Combustion-tube  of  best  hard  Bohemian  glass,  about  66  cm.  long  and 
12-7  mm.  internal  diameter. 

(6)  Azotometer  of  at  least  100  c.c.  capacity,  accurately  calibrated. 

(c)  Sprengel  mercury  air-pump. 

(d)  Small  paper  scoop,  made  from  stiff  writing  paper. 

(3)   Determination. 

Use  from  1  to  2  grm.  of  ordinary  commercial  fertilizers.  In  the  case  of 
highly  nitrogenized  substances  the  amount  to  be  used  must  be  regulated 
by  the  amount  of  nitrogen  estimated  to  be  present.  Fill  the  tube  as  fol- 
lows: (1)  About  5  cm.  of  coarse  cupric  oxide.  (2)  Place  on  the  small  paper 
scoop  enough  of  the  fine  cupric  oxide  to  fill,  after  having  been  mixed  with 
the  substance  to  be  analyzed,  about  10  cm.  of  the  tube;  pour  on  this  the 
substance,  rinsing  the  watch  glass  with  a  little  of  the  fine  oxide,  and  mix 
thoroughly  with  a  spatula ;  pour  into  the  tube,  rinsing  the  scoop  with  a  little 
fine  oxide.  (3)  About  30  cm.  of  coarse  cupric  oxide.  (4)  About  7  cm.  of 
metallic  copper.  (5)  About  6  cm.  of  coarse  cupric  oxide.  (6)  A  small 
plug  of  asbestos.  (7)  From  0-8  to  1  grm.  of  sodium  bicarbonate.  (8)  A 
large,  loose  plug  of  asbestos.  Place  the  tube  in  the  furnace,  leaving  about 
2-5  cm.  of  it  projecting;  connect  with  the  pump  by  a  rubber  stopper  smeared 
with  glycerol,  taking  care  to  make  the  connection  perfectly  tight. 

Exhaust  the  air  from  the  tube  by  means  of  the  pump.  When  a  vacuum 
has  been  obtained,  allow  the  flow  of  mercury  to  continue ;  light  the  gas  under 
that  part  of  the  tube  containing  the  metallic  copper,  the  anterior  layer  of 
cupric  oxide  (see  (5)  above),  and  the  sodium  bicarbonate.  As  soon  as  the 
vacuum  is  destroyed  and  the  apparatus  filled  with  carbon  dioxide,  shut 
off  the  flow  of  mercury,  and  at  once  introduce  the  delivery-tube  of  the  pump 
into  the  receiving  arm  of  the  azotometer  just  below  the  surface  of  the  mer- 
cury seal,  so  that  the  escaping  bubbles  will  pass  into  the  air  and  not  into  the 
tube,  thus  avoiding  the  useless  saturation  of  the  caustic-potash  solution. 

When  the  flow  of  carbon  dioxide  has  very  nearly  or  completely  ceased,  pass 
the  delivery-tube  down  into  the  receiving  arm,  so  that  the  bubbles  will  escape 
into  the  azotometer.  Light  the  gas  under  the  30  cm.  layer  of  oxide,  heat 
gently  for  a  few  moments  to  drive  out  any  moisture  that  may  be  present, 
and  bring  to  a  red  heat.  Heat  gradually  the  mixture  of  substance  and 
oxide,  lighting  one  jet  at  a  time.  Avoid  a  too  rapid  evolution  of  bubbles, 
which  should  be  allowed  to  escape  at  the  rate  of  about  one  per  second,  or  a 
little  faster. 

WTien  the  jets  under  the  mixture  have  all  been  turned  on,  light  the  gas 
under  the  layer  of  oxide  at  the  end  of  the  tube.  When  the  evolution  of  gas 
has  ceased,  turn  out  all  the  lights  except  those  under  the  metallic  copper 


OFFICIAL   METHODS    OF    ANALYSIS,  1027 

and  anterior  layer  of  oxide,  and  allow  to  cool  for  a  few  moments.  Exhaust 
with  the  pump  and  remove  the  azotometer  before  the  flow  of  mercury  is 
stopped.  Break  the  connection  of  the  tube  with  the  pump,  stop  the  flow  of 
mercury,  and  extinguish  the  lights.  Allow  the  azotometer  to  stand  for  at 
least  an  hour,  or  cool  with  a  stream  of  water  until  a  permanent  volume  and 
temperature  have  been  reached. 

Adjust  accurately  the  level  of  the  potassium-hydroxide  solution  in  the 
bulb  to  that  in  the  azotometer;  note  the  volume  of  gas,  temperature,  and 
height  of  barometer;  make  calculation  as  usual,  or  read  results  from  tables. 

(/)    RUFFLE   METHOD. 

(1)  Preparation  of  Reagents. 

(a)  Standard  solutions  and  indicator  the  same  as  for  the  KJELDAHL  method 
(p.  1021). 

(6)  A  mixture  of  equal  parts  by  weight  of  fine  slaked  lime  and  finely 
powdered  sodium  thiosulphate  dried  at  100°. 

(c)  A  mixture  of  equal  parts  by  weight  of  finely  powdered  granulated 
sugar  and  flowers  of  sulphur. 

(d)  Granulated   soda-lime,    as   described   under   the    soda-lime  method 
(p.  1028). 

(2)  Apparatus. 

(a)  Combustion-tubes  of  hard  Bohemian  glass,  70  cm.  long  and  1-3  cm. 
in  dameter. 

(6)  Bulbed  U-tubes  or  WILL'S  bulbs,  as  described  under  the  soda-lime 
method. 

(3)  Determination. 

Clean  the  U-tube  and  introduce  10  c.c.  of  standard  acid. 

Fill  the  tube  as  follows:  (1)  A  loosely  fitting  plug  of  asbestos,  previously 
ignited,  and  then  from  2-5  to  3-5  cm.  of  the  thiosulphate  mixture.  (2)  The 
weighed  portion  of  the  substance  to  be  analyzed  is  intimately  mixed  with 
from  5  to  10  grm.  of  the  sugar  and  sulphur  mixture.  (3)  Pour  on  a  piece 
of  glazed  paper  or  in  a  porcelain  mortar  a  sufficient  quantity  of  thiosulphate 
mixture  to  fill  about  25  cm.  of  tube:  then  add  the  substance  to  be  analyzed, 
as  previously  prepared,  mix  carefully,  and  pour  into  the  tube :  shake  down  the 
contents  of  the  tube:  rinse  off  the  paper  or  mortar  with  a  small  quantity 
of  the  thiosulphate  mixture:  then  fill  up  with  soda-lime  to  within  5  cm.  of 
the  end.  (4)  Place  another  plug  of  ignited  asbestos  at  the  end  of  the  tube 
and  close  with  a  cork  (5)  Hold  the  tube  in  a  horizontal  position  and  tap  on 
the  table  until  there  is  a  gas  channel  all  along  the  top.  Make  connections 
with  the  U-tube  containing  the  acid;  aspirate  and  see  that  the  apparatus 
is  tight. 

The  Combustion. — Place  the  prepared  combustion-tube  in  the  furnace, 
letting  the  open  end  project  a  little,  so  as  not  to  burn  the  cork.  Commence 
by  heating  the  soda-lime  portion  until  it  is  brought  to  a  full  red  heat.  Then 
turn  on  slowly  jet  after  jet  toward  the  farther  end  of  the  tube,  so  that  the 
bubbles  come  off  two  or  three  a  second.  When  the  whole  tube  is  red-hot 


1028  APPENDIX    I. 

the  evolution  of  the  gas  has  ceased  and  the  liquid  in  the  U-tube  begins  to 
recede  toward  the  furnace,  attach  the  aspirator  to  the  other  limb  of  the 
U-tube,  break  off  the  end  of  the  combustion-tube,  and  draw  a  current  of  air 
through  for  a  few  minutes.  Detach  the  U-tube  and  wash  its  contents  into 
a  beaker  or  porcelain  dish,  add  a  few  drops  of  the  cochineal  solution,  and 
titrate. 

(0)    SODA-LIME    METHOD. 

[Not  applicable  in  the  presence  of  nitrates.] 

(1)  Preparation  of  Reagents. 

(a)  STANDARD  SOLUTIONS  AND  INDICATOR. — Those  mentioned  under 
the  KJELDAHL  method  (a),  (6),  (i),  pp.  1021  and  1022)  may  be  used. 

(6)  SODA-LIME. — Excellent  soda-lime  may  be  easily  and  quickly  prepared 
by  adding  2-5  parts  of  quicklime  to  1  part  by  weight  of  commercial  caustic 
soda  (such  soda  as  is  used  in  the  KJELDAHL  method)  dissolved  in  a  sufficient 
amount  of  water  to  slake  the  lime.  The  mixture  is  then  dried  and  heated 
in  an  iron  pot  to  incipient  fusion,  and  when  cold  is  ground  and  sifted.  Two 
sizes  of  granules  are  required  in  this  method — 

(6t)  Fine  enough  to  pass  through  a  2-5  mm.  sieve. 

(62)  Fine  enough  to  pass  through  a  1-25  mm.  sieve. 

(c)  SODIUM  CARBONATE  AND  LIME  OR  SLAKED  LIME. — Instead  of  soda- 
lime,  JOHNSON'S  mixture  of  sodium  carbonate  and  lime  or  slaked  lime  may 
be  used. 

Slaked  lime  may  be  granulated  by  mixing  it  with  a  little  wrater  to  form  a 
thick  mass,  which  is  dried  in  the  water  oven  until  hard  and  brittle.  It  is 
then  ground  and  sifted  as  above.  Slaked  lime  is  much  easier  to  work  with 
than  soda-lime  and  gives  excellent  results,  though  it  is  probable  that  more 
of  it  should  be  used  in  proportion  to  the  substance  to  be  analyzed  than  in 
the  case  with  soda-lime. 

(2)  Apparatus. 

(a)  ASBESTOS. — The  asbestos  used  should  be  ignited  and  kept  in  a  glass- 
stoppered  bottle. 

(6)  COMBUSTION-TUBES. — These  are  about  40  cm.  long  and  of  12  mm. 
internal  diameter,  drawn  out  to  a  point  and  closed  at  one  end. 

(c)  U-TUBES. — Large-bulb  U-tubes  with  glass  stopcocks,  or  WILL'S 
tubes  with  four  bulbs. 

(3)  Determination. 

The  substance  to  be  analyzed  should  be  powdered  finely  enough  to  pass 
through  a  sieve  of  1  mm.  mesh;  0-7  or  1-4  giro.,  according  to  the  amount  of 
nitrogen  present,  are  used  for  the  determination.  Into  the  closed  end  of 
the  combustion-tube  put  a  small  loose  plug  of  asbestos,  and  upon  it  about 
4  cm.  of  fine  soda-lime.  In  a  porcelain  dish  or  mortar  mix  the  substance 
to  be  analyzed,  thoroughly  but  quickly,  with  enough  fine  soda-lime  to  fill 
about  16  cm.  of  the  tube,  or  about  40  times  as  much  soda-lime  as  substance 
and  put  the  mixture  into  the  combustion-tube  as  quickly  as  possible  by 
means  of  a  wide-neck  funnel,  rinsing  out  the  dish  and  funnel  with  a  little 
more  fine  soda-lime,  which  is  to  be  put  in  on  top  of  the  mixture.  Fill  the 


OFFICIAL   METHODS    OF  ANALYSIS.  1029 

rest  of  the  tube  to  about  5  cm.  from  the  end  with  granulated  soda-lime,  making 
it  as  compact  as  possible  by  tapping  the  tube  gently  while  held  in  a  nearly 
upright  position  during  the  filling.  The  layer  of  granulated  soda-lime  should 
not  be  less  than  12  cm.  long.  Lastly,  put  in  a  plug  of  asbestos  about  2  cm. 
long,  pressed  rather  tightly,  and  wipe  out  the  end  of  the  tube  to  free  it  from 
adhering  particles. 

Connect  the  tube  by  means  of  a  well-fitting  rubber  stopper  or  cork  with 
the  U-tube  or  WILL'S  bulbs,  containing  10  c.c.  of  standard  acid,  and  adjust 
it  in  the  combustion  furnace  so  that  the  end  projects  about  4  cm.  from  the 
furnace,  supporting  the  U-tube  or  WILL'S  bulbs  suitably.  Heat  the  portion 
of  the  tube  containing  the  granulated  soda-lime  to  a  moderate  redness,  and 
when  this  is  attained  extend  the  heat  gradually  through  the  portion  con- 
taining the  substance,  so  as  to  keep  up  a  moderate  and  regular  flow  of 
gases  through  the  bulb,  maintaining  the  heat  of  the  first  part  until  the 
whole  tube  is  heated  uniformly  to  the  same  degree.  Keep  up  the  heat 
until  gases  have  ceased  bubbling  through  the  acids  in  the  bulbs,  and  the 
mixture  of  substance  and  soda-lime  has  become  white,  or  nearly  so,  which 
shows  that  the  combustion  is  finished.  The  combustion  should  occupy 
about  three-quarters  of  an  hour,  or  not  more  than  one  hour.  Remove  the 
heat,  and  when  the  tube  has  cooled  below  redness  break  off  the  closed  tip 
and  aspirate  air  slowly  through  the  apparatus  for  two  or  three  minutes, 
to  bring  all  the  ammonia  into  the  acid.  Disconnect,  wash  the  acid  into  a 
beaker  or  flask,  and  titrate  with  the  standard  alkali. 

During  the  combustion  the  end  of  the  tube  projecting  from  the  furnace 
must  be  kept  heated  sufficiently  to  prevent  the  condensation  of  moisture,  yet 
not  enough  to  char  the  stopper.  The  heat  may  be  regulated  by  a  shield  of 
tin  slipped  over  the  projecting  end  of  the  combustion  tube. 

It  is  found  very  advantageous  to  attach  a  BUNSEN  valve  to  the  exit  tube, 
allowing  the  evolved  gasses  to  pass  out  freely,  but  preventing  a  violent 
(l sucking  back"  in  case  of  a  sudden  condensation  of  steam  in  the  bulbs. 

(/O    MAGNESIUM    OXIDE    METHOD. 
[Applicable  only  to  the  determination  of  ammonia.] 

From  0-7 -to  3-5  grm.  of  the  substance  to  be  analyzed,  according  to  the 
proportion  of  ammonia  present,  are  brought  into  a  distillation  flask  (2),  (c) 
(p.  1023),  with  about  200  c.c.  of  water  and  5  grm.  or  more  of  magnesium  oxide 
free  from  carbon  dioxide.  The  flask  is  then  connected  with  a  condenser, 
and  100  c.c.  of  the  liquid  distilled  into  standard  acid.  The  residual  acid 
is  titrated  as  in  the  KJELDAHL  method,  page  1023. 

(l)    ULSCH    METHOD,    MODIFIED    BY    STREET.* 
[Applicable  to  all  nitric  and  ammoniacal  nitrogen  determinations.] 
Place  1  grm.  of  the  sample  in  a  half -litre  flat-bottomed  flask.     Add  about 
30  c.c.  of  water,  1  grm.  of  reduced  iron,  and  10  c.c.  of  a  mixture  of  strong 

*  Methods  (t)  and  (?)  are  not  official,  but  the  association  directed  that  they  be  printed 
immediately  after  the  official  methods. 


1030  APPENDIX   I. 

sulphuric  acid  with  an  equal  volume  of  water;  shake  well  and  allow  to  stand 
for  a  short  time.  This  will  remove  the  danger  of  an  explosion  caused  by 
the  otherwise  violent  action  which  takes  place.  Close  the  neck  of  the  flask 
with  a  rubber  stopper  through  which  passes  a  dropping-bulb  filled  with  water. 
The  flask  having  thus  been  stoppered,  place  it  on  a  slab  to  which  a  moderate 
heat  is  applied.  Heat  the  solution  slowly,  boil  it  for  five  minutes,  and  cool. 
Add  about  100  c.c.  of  water,  a  little  paraffin,  and  from  7  to  10  grm.  of  mag- 
nesium oxide.  The  flask  is  then  connected  with  a  condenser,  such  as  is  used 
in  the  KJELDAHL  method,  and  the  mixture  boiled  for  forty  minutes,  the 
ammonia  being  collected  in  a  known  amount  of  standard  acid.  When  mag- 
nesia is  used,  assurance  must  be  had  that  it  is  strongly  in  excess,  and  forty 
minutes  are  necessary  for  the  complete  distillation  of  the  ammonia.  The 
contents  of  the  receiver  are  titrated  as  in  the  KJELDAHL  method,  page  1023. 

(f)    ZINC-IRON    METHOD. 
[Applicable  to  the  determination  of  nitric  and  ammoniacal  nitrogen.] 

Ten  grm.  of  the  sample  are  dissolved  in  500  c.c.  of  water.  Of  this  solu- 
tion 25  c.c.,  corresponding  to  one-half  grm.,  are  placed  in  a  distillation  flask 
of  about  400  c.c.  capacity,  120  c.c.  of  water  added,  also  about  5  grm.  of  well 
washed  and  dried  zinc  dust  and  an  equal  weight  of  reduced  iron.  To  the 
solution  are  added  80  c.c.  of  sodium  hydrate  of  32°  B.  The  flask  is  then  con- 
nected with  the  condensing  apparatus  and  the  distillation  carried  on  syn- 
chronously with  the  reduction,  the  ammonia  being  collected  in  carefully  stand- 
ardized acid.  The  distillation  is  continued  for  one  or  two  hours,  or  until 
100  c.c.  have  been  distilled.  The  resulting  distillate  is  titrated  as  in  the 
KJELDAHL  method,  page  1023. 

5.  DETERMINATION  OF  POTASH, 
(a)  LINDO-GLADDING  METHOD. 
(1)  Preparation  of  Reagents. 

(a)  Ammonium  -  chloride  Solution. — Dissolve  100  grm.  of  ammonium 
chloride  in  500  c.c.  of  water,  add  from  5  to  10  grm.  of  pulverized  potassium- 
platinic  chloride,  and  shake  at  intervals  for  six  or  eight  hours.  The  mix- 
ture is  allowed  to  settle  over  night  and  filtered,  and  the  residue  is  ready  for 
the  preparation  of  a  fresh  supply. 

(6)  Platinum  Solution. — The  platinum  solution  used  contains  1  grm.  of 
metallic  platinum  (2  •  1  grm.  of  H2PtCl0)  in  every  10  c.c. 

(2)  Methods  of  Making  Solution. 

(a)  With  Potash  Salts  and  Mixed  Fertilizers. — Boil  10  grm.  of  the  sample 
with  300  c.c.  of  water  thirty  minutes.  In  the  case  of  mixed  fertilizers,  add 
to  the  hot  solution  a  slight  excess  of  ammonia  and  then  sufficient  powdered 
ammonium  oxalate  to  precipitate  all  the  lime  present.  Cool,  dilute  to  500  c.c., 
mix  and  pass  through  a  dry  filter.  In  case  of  ch'oride  and  sulphate  of  potash, 
sulphate  of  potash  and  magnesia  and  kainit,  dissolve  and  dilute  to  500  c.c. 
without  the  addition  of  ammonium  and  ammonium  oxalate. 


OFFICIAL    METHODS   OF   ANALYSIS.  1031 

(6)  With  Organic  Compounds. — When  it  is  desired  to  determine  the  total 
amount  of  potash  in  organic  substances,  such  as  cottonseed  meal,  tobacco 
stems,  etc.,  saturate  10  grm.  with  strong  sulphuric  acid,  and  ignite  in  a  muffle 
at  a  low  red  heat  to  destroy  organic  matter.  Add  a  little  strong  hydrochloric 
acid,  warm  slightly  in  order  to  loosen  the  mass  from  the  dish,  and  proceed 
as  directed  under  (3)  (a). 

(3)  Determination. 

(a)  In  Mixed  Fertilizers. — Evaporate  50  c.c.  of  the  solution  made  accord- 
ing to  (2),  corresponding  to  1  grm.  of  the  sample,  nearly  to  dryness,  add  1  c.c- 
of  diluted  sulphuric  acid  (1  to  1),  evaporate  to  dryness  and  ignite  to  white, 
ness.  As  all  the  potash  is  in  form  of  sulphate,  no  loss  need  be  apprehended 
by  volatilization  of  potash,  and  a  full  red  heat  must  be  maintained  until  the 
residue  is  perfectly  white.  Dissolve  the  residue  in  hot  water,  using  at  least 
20  c.c.  for  each  dgrm.  of  KjO,  add  a  few  drops  of  hydrochloric  acid  and  plati- 
num solution  in  excess.  Evaporate  on  a  water  bath  to  a  thick  paste  and 
treat  the  residue  with  80-per  cent,  alcohol,  sp.  gr.  0-8645,  avoiding  the  absorp- 
tion of  ammonia.  Wash  the  precipitate  thoroughly  with  80-per  cent,  alcohol 
both  by  decantation  and  on  the  filter,  continuing  the  washing  after  the 
filtrate  is  colorless.  Wash  finally  with  10  c.c.  of  the  ammonium-chloride 
solution  (1)  (a)  to  remove  impurities  from  the  precipitate  and  repeat  this 
washing  five  or  six  times.  Wash  again  thoroughly  with  80-per  cent,  alcohol 
and  dry  the  precipitate  for  thirty  minutes  at  100°.  The  precipitate  should 
be  perfectly  soluble  in  water. 

(6)  Chloride  of  Potash. — Dilute  25  c.c.  of  the  solution,  prepared  accord 
ing  to  (2)  (a),  with  25  c.c.  of  water,  acidify  with  a  few  drops  of  hydrochloric 
acid,  add  10  c.c.  of  platinum  solution  and  evaporate  to  a  thick  paste.     Treat 
the  residue  as  under  (3)  (a). 

(c)  Sulphate  of  Potash,   Sulphate  of  Potash  and  Magnesia,  and  Kainit. — • 
Dilute  25  c.c.  of  the  solution,  prepared  according  to  (2)  (a),  with  25  c.c.  of 
water,  acidify  with  a  few  drops  of  hydrochloric  acid  and  add  15  c.c.  of  plati- 
num solution.     Evaporate  the  mixture  and  proceed  as  directed  under  (3)  (a), 
except  that  25  c.c.  portions  of  ammonium-chloride  solution  should  be  used. 

(d)  Water-soluble  Potash  in  Wood  Ashes    and  Cotton-hull  Ashes. — Use 
above  method  making  tjie  solution  according  to  (2)   (a),  and  pay  special 
attention  to  the  last  senterice  of  (3)  (a). 

(6)    OPTIONAL    METHOD.* 

(1)  Preparation  of  Reagent. 

Platinum  Solution. — The  platinum  solution  used  is  the  same  as  that  de- 
scribed under  the  LINDO-GLADDING  method. 

(2)  Method  of  Making  Solution. 

The  solution  is  prepared  as  directed  under  the  LINDO-GLADDING  method, 
omitting  in  all  cases  the  addition  of  ammonia  and  ammonium  oxalate. 

*  The  LINDO-GLADDING  method  is  preferable  in  the  presence  of  soluble  sulphates. 


1032  APPENDIX   I. 

(3)  Determination. 

Dilute  25  c.c.  of  the  solution  made  as  directed  under  (2),  (50  c.c.,  if  less 
than  10  per  cent,  of  potassium  oxide  be  present)  to  150  c.c.,  heat  to  100°, 
and  add,  drop  by  drop  with  constant  stirring,  a  slight  excess  of  barium-chloride 
solution.  Without  filtering,  add  in  the  same  manner  barium  hydrate  in 
slight  excess.  Filter  while  hot  and  wash  until  the  precipitate  is  free  from 
chloride.  Add  to  the  filtrate  1  c.c.  of  strong  ammonium  hydrate,  and  then 
a  saturated  solution  of  ammonium  carbonate  until  the  excess  of  barium  is 
precipitated.  Heat  and  add,  in  fine  powder,  0-5  grm.  of  pure  oxalic  acid 
or  0-75  grm.  of  ammonium  oxalate.  Filter  and  wash  free  from  chlorides, 
evaporate  the  filtrate  to  dryness  in  a  platinum  dish,  and  ignite  carefully 
over  the  free  flame,  below  a  red  heat,  until  all  volatile  matter  is  driven  off. 
Digest  the  residue  with  hot  water,  filter  through  a  small  filter  and  dilute  the 
filtrate,  if  necessary,  so  that  for  each  dgrm.  of  K2O  there  will  be  at  least  20  c.c- 
of  liquid.  Acidify  with  a  few  drops  of  hydrochloric  acid  and  add  platinum 
solution  in  excess.  Evaporate  on  a  water  bath  to  a  thick  sirup  and  treat 
the  residue  with  80-per  cent,  alcohol  (specific  gravity  0-8645).  Wash  the 
precipitate  thoroughly  with  80-per  cent,  alcohol  both  by  decantation  and 
after  collecting  on  a  Gooch  or  other  form  of  filter.  Dry  for  thirty  minutes 
at  100°  and  weigh. 

It  is  desirable,  if  there  be  an  appearance  of  foreign  matter  in  the  double 
salt,  that  it  should  be  washed  according  to  the  previous  method  with  several 
portions  of  the  ammonium  chloride  solution  of  10  c.c.  each. 

(c)    FACTORS. 

For  the  conversion  of  potassium  platinichloride  to  KC1,  use  the  factor 
0-3069;  to  K2SO4,  0-3587,  and  to  K.O,  0-1939. 


II.  METHODS  FOR  THE  ANALYSIS  OF  FOODS. 
1.  PREPARATION   OF  SAMPLE. 

The  substance  is  to  be  ground  and  passed  through  a  sieve  with  circular 
holes  1  mm.  in  diameter 

2.  DETERMINATION  OF  MOISTURE. 

Dry  from  2  to  3  grm.  of  the  substance  for  five  hours,  at  the  temperature 
of  boiling  water,  in  a  current  of  dry  hydrogen  or  in  vacuo.  If  the  substance 
be  held  in  a  glass  vessel,  the  latter  should  not  be  in  contact  with  the  boiling 
water 

3.  DETERMINATION   OF   ASH. 

Char  from  2  to  3  grm.  of  the  substance  and  burn  to  whiteness  at  the  lowest 
possible  red  heat.  If  a  white  ash  cannot  be  obtained  in  this  manner,  exhaust 
the  charred  mass  with  water:  collect  the  insoluble  residue  on  a  filter,  burn, 
add  this  ash  to  the  residue  from  the  evaporation  of  the  aqueous  extract,  and 
heat  the  whole  to  a  low  redness  till  the  ash  is  white  or  nearly  so. 


OFFICIAL   METHODS    OF   ANALYSIS.  1033 

4.  DETERMINATION  OF  ETHER  EXTRACT, 
(a)  PREPARATION  OF  ANHYDROUS  ETHER, 

To  prepare  the  anhydrous  alcohol-free  ether  required  for  the  estima- 
tion of  fat,  wash  any  of  the  commercial  brands  of  ether  with  two  or  three 
successive  portions  of  distilled  water,  and  add  solid  caustic  soda  or  potash 
until  most  of  the  water  has  been  extracted  from  the  ether.  Carefully  cleaned 
metallic  sodium,  cut  into  small  pieces,  is  added  until  there  is  no  further 
evolution  of  hydrogen  gas.  The  ether  thus  dehydrated  must  be  kept  over 
metallic  sodium,  and  should  be  only  lightly  stoppered  in  order  to  allow  any 
accumulating  hydrogen  gas  to  escape.  If  may  be  drawn  off  with  a  pipette  as 
required. 

(&)    DETERMINATION 

(1)  Direct  Method. 

Extract  from  2  to  3  gnn.  of  the  substance  dried  as  for  the  determination 
of  the  moisture,  with  anhydrous  alcohol-free  ether  for  sixteen  hours.  Dry  the 
extract  to  constant  weight. 

(2)  Indirect  Method. 

Determine  moisture  as  above,  extract  the  dried  substance  for  sixteen 
hours  as  directed,  dry  again,  and  regard  loss  of  weight  as  ether  extract. 

5.  DETERMINATION  OF  CRUDE  PROTEIN. 

Determine  nitrogen  as  directed  for  nitrogen  in  fertilizers  and  multiply 
the  result  by  6-25. 

6.  DETERMINATION  OF  ALBUMINOID  NITROGEN  BY  STUTZER'S  METHOD. 

(a)    PREPARATION    OF    REAGENTS. 

Prepare  cupric  hydrate  as  follows:  Dissolve  100  grm.  of  pure  cupric  sul- 
phate in  5  litres  of  water,  add  25  c.c.  of  glycerin,  and  then  dilute  solution  of 
sodium  hydrate  until  the  liquid  is  alkaline;  filter;  rub  the  precipitate  up 
with  water  containing  5  c.c.  of  glycerin  per  litre,  and  wash  by  decantation 
or  filtration  until  the  washings  are  no  longer  alkaline.  Rub  the  precipitate 
up  again  in  a  mortar  with  water  containing  10  per  cent  of  glycerin,  thus  pre- 
paring a  uniform  gelatinous  mass  that  can  be  measured  out  with  a  pipette. 
Determine  the  quantity  of  cupric  hydrate  per  cubic  centimeter  of  this 
mixture 

(6)    DETERMINATION. 

Place  0-7  grm.  of  the  substance  in  a  beaker,  add  100  c.c.  of  water,  heat 
to  boiling,  or,  in  the  case  of  substances  rich  in  starch,  heat  on  the  water 
bath  ten  minutes:  add  a  quantity  of  cupric-hydrate  mixture  containing 
about  0-5  grm.  of  the  hydrate;  stir  thoroughly,  filter  when  cold,  wash  with 
cold  water,  and,  without  removing  the  precipitate  from  the  filter,  determine 
nitrogen  according  to  one  of  the  methods  given  for  the  determination  of 
nitrogen  in  fertilizers  (pp.  1022  e'  seq.},  adding  sufficient  potassium-sulphide 
solution  to  completely  precipitate  all  copper  and  mercury.  The  filter-papers 
used  must  be  practically  free  from  nitrogen.  If  the  substance  examined  con- 


1034  APPENDIX   I. 

sists  of  seed  of  any  kind,  or  residues  of  seeds,  such  as  oil  cake  or  anything 
else  rich  in  alkaline  phosphates,  add  a  few  cubic  centimeters  of  a  concen- 
trated solution  of  alum  just  before  adding  the  cupric  hydrate,  and  mix  well 
by  stirring.  This  serves  to  decompose  the  alkaline  phosphates.  If  this 
be  not  done,  cupric  phosphate  and  free  alkali  may  be  formed,  and  the  protein- 
copper  precipitate  may  be  partially  dissolved  in  the  alkaline  liquid. 

7.  DETERMINATION  OF  CRUDE  FIBER  AND  CARBOHYDRATES. 

For  these  methods,  see  Determination  of  Carbohydrates  in  Agricultural 
Products. 

8.  OFFICIAL   METHODS   FOR  THE   DETERMINATION   OF  CARBOHYDRATES  IN 

GRAINS  AND  BY-PRODUCT  CATTLE  FOODS. 

(a)  DETERMINATION  OF  REDUCING  SUGARS  (ESTIMATED  AS  DEXTROSE). 
Stir  3  grm.  of  the  sample  in  a  beaker  with  50  c.c.  of  water  for  an  hour. 
Filter  into  a  quarter-litre  flask,  wash,  and  make  up  to  mark.     Determine 
reducing  sugar  as  dextrose  according  to  method  (c),  page  1045.     If  the  solu- 
tion be  difficult  to  filter,  2  c.c.  of  alumina  cream  should  be  added. 

.  ..;•..  •     (6)   DETERMINATION  OF  SUCROSE. 

Determine  the  sucrose  in  50  c.c.  of  the  filtrate  obtained  above  according 
to  method  (c),  page  35.  Before  calculating  the  invert  sugar  obtained  as 
sucrose,  deduct  the  reducing  sugar  determined  as  dextrose  in  (a). 

(c)    DETERMINATION    OF    STARCH    IN    COMMERCIAL   STARCHES  AND  POTATOES.* 

Heat  the  insoluble  residue  obtained  under  (a)  for  two  and  a  half  hours 
with  200  c.c.  of  water  and  20  c.c.  of  hydrochloric  acid  (specific  gravity  1  •  125) 
in  a  flask  provided  with  a  reflux  condenser.  Cool,  and  neutralize  with  sodium 
carbonate.  Complete  the  volume  to  a  quarter  of  a  litre,  filter,  and  deter- 
mine the  dextrose  in  an  aliquot  portion  of  the  filtrate.  The  weight  of  dextrose 
obtained  multiplied  by  0  •  9  gives  the  weight  of  starch. 

(d)  DIASTASE  METHOD  FOR  STARCH. 

Extract  3  grm.  of  the  finely  powdered  substance  on  a  hardened  filter 
with  five  successive  portions  of  10  c.c.  of  ether,  wash  with  150  c.c.  of  10- 
per  cent,  alcohol,  and  then  with  a  little  strong  alcohol.  Place  the  residue 
in  a  beaker  with  50  c.c.  of  water,  immerse  the  beaker  in  a  boiling  water  bath 
and  stir  the  contents  constantly  until  all  of  the  starch  is  gelatinized;  cool 
to  55°  C. ;  add  from  20  to  40  c.c.  of  malt  extract  and  maintain  at  this  tem- 
perature until  a  microscopic  examination  of  the  residue  with  iodine  reveals 
no  starch.  Cool  and  make  up  directly  to  250  c.c. ;  filter.  Place  200  c.c.  of 
the  filtrate  in  a  flask  with  20  c.c.  of  25-per  cent  hydrochloric  acid  (specific 
gravity  1  •  125)  connect  with  a  reflux  condenser  and  heat  in  a  boiling  water- 
bath  for  two  and  a  half  hours;  neaily  neutralize  while  hot  with  sodium  car- 

*  NOTE  BY  EniTcm. — In  this  method  there  will  be  included  as  starch  the  pentosans 
and  other  carbohydrate  bodies  present  which  suffer  hydrolysis  and  conversion  into  re- 
ducing sugars  on  boiling  with  hydrochloric  acid. — H.  W.  WILEY. 


OFFICIAL    METHODS    OF   ANALYSIS.  1035 

bonate,  and  make  up  to  500  c.c.  Mix  the  solution  well,  pour  through  a  dry 
filter,  and  determine  the  dextrose  in  an  aliquot  part.  Convert  the  dextrose 
into  starch  by  the  factor  0-9. 

Preparation  of  Malt  Extract. — Digest  10  grm.  of  fresh,  finely  ground 
malt  over  night  at  ordinary  temperature,  with  200  c.c.  of  water,  and  filter. 
Determine  the  amount  of  dextrose  in  a  given  quantity  of  the  filtrate  after 
boiling  with  acid,  etc.,  as  in  the  starch  determination,  and  make  the  proper 
correction. 

(e)  PROVISIONAL  METHOD  FOR  THE  DETERMINATION  OF  PENTOSANS  BY 
MEANS  OF  PHLOROGLUCIN. 

Three  grm.  of  the  material  are  placed  in  a  flask,  together  with  100  c.c.  of  12- 
per  cent,  hydrochloric  acid  (specific  gravity  1-06)  and  several  pieces  of 
recently  heated  pumice  stone.  The  flask,  placed  upon  wire  gauzCj  is  con- 
nected with  a  condenser  and  heat  applied,  rather  gently  at  first,  using  a  gauze 
top  to  distribute  the  flame,  and  so  regulated  as  to  distill  over  30  c.c.  in  about 
ten  minutes.  The  30  c.c.  driven  over  are  replaced  by  a  like  quantity  of  the 
dilute  acid,  and  the  process  continued  so  long  as  the  distillate  gives  a  pro- 
nounced reaction  with  aniline  acetate  on  filter-paper.  To  the  completed 
distillate  is  gradually  addect  a  quantity  of  phloroglucin  (free  from  diresorcin) 
dissolved  in  12-per  cent,  hydrochloric  acid,  and  the  resulting  mixture  thor- 
oughly stirred.  The  amount  of  phloroglucin  used  should  be  about  double 
that  of  the  furfurol  expected.  The  solution  first  turns  yellow,  then  green; 
and  very  soon  an  amorphous  greenish  precipitate  appears,  which  grows 
rapidly  darker,  till  it  finally  becomes  almost  black.  The  solution  is  made 
up  to  500  c.c.  with  12-per  cent,  hydrochloric  acid,  and  allowed  to  stand  over 
night. 

The  amorphous  black  precipitate  is  filtered  into  a  tared  Gooch  through 
an  asbestos  felt,  washed  with  100  c.c.  of  water,  dried  to  constant  weight 
by  heating  from  three  to  four  hours  at  100°,  cooled  and  weighed,  the  in- 
crease in  weight  being  reckoned  as  phloroglucid.  To  calculate  the  furfurol 
from  the  phloroglucid,  use  the  following  formulae: 

Phloroglucid  (less  than  and  up  to  0 -2  grm.)  -=- 1  •  82  =  furfurol. 

Phloroglucid  (from  0-2  to  0-3  grm.)  -=-1- 895  =  furfurol. 

Phloroglucid  (from  0-3  to  0-4  grm.)  -4- 1  •  92  =  furfurol. 

Phloroglucid  (above  0-4  grm.) -r- 1  •  93  =  furfurol. 

To  calculate  the  furfurol  to  pentosan  or  pentose,  use  the  following  for- 
mulae: 

I.  (furfurol  0-Ol04)Xl-68  =  xylan. 
II.  (furfurol  0  •  0104)  X  2  •  07  =  araban. 

III.  (f urf urol  0  -0104)  X 1  •  88  =  pentosan. 

IV.  (furf urol  0-0104)  Xl- 91  -xylose. 

V.   (furfurol  0  •  01 04)  X  2  •  35  =  arabinose. 
VI.  (furfurol  0  •  0104)  X  2 • 13  =  pentose. 

Qualitative  Test  of  the  Purity  of  the  Phloroglucin. 

Dissolve  a  small  quantity  of  the  phloroglucin  in  a  few  drops  of  acetic 
anhydride,  heat  almost  to  boiling,  and  add  a  few  drops  of  concentrated  sul- 


1036  APPENDIX   I. 

phuric  acid.     A  violet  color  indicates  the  presence  of  diresorcin.     A  phloro- 
glucin  which  gives  more  than  a  faint  coloration  must  be  rejected. 

(/)  METHOD  FOR  ESTIMATING  GALACTAN. 

Extract  3  grm.  of  the  substance  on  a  hardened  filter  with  five  successive 
portions  of  10  c.c.  of  ether,  place  the  extracted  residue  in  a  beaker  about 
5-5  cm.  in  diameter  and  7  cm.  deep,  together  with  60  c.c.  of  nitric  acid  of  1  •  15 
specific  gravity,  and  evaporate  the  solution  to  exactly  one-third  its  volume 
on  a  water  bath  at  a  temperature  of  94°  to  96°.  After  standing  twenty-four 
hours,  add  10  c.c.  of  water  to  the  precipitate,  and  allow  it  to  stand  another 
twenty-four  hours.  The  mucic  acid  has  in  the  meantime  crystallized,  but  is 
mixed  with  considerable  material  only  partially  oxidized  by  the  nitric  acid. 
The  solution  is  therefore  filtered  through  filter  paper,  washed  with  30  c.c. 
of  water,  to  remove  as  much  of  the  nitric  acid  as  possible,  and  the  filter  and 
contents  replaced  in  the  beaker.  Thirty  c.c.  of  ammonium-carbonate  solu- 
tion, consisting  of  1  part  ammonium  carbonate,  19  parts  water,  and  1  part 
strong  ammonia  are  added,  and  the  mixture  heated  gently  on  a  water-bath 
for  fifteen  minutes.  The  ammonium  carbonate  takes  up  the  mucic  acid,  form- 
ing the  soluble  mucate  of  ammonia.  The  filtrate  is  evaporated  to  dryness 
over  a  water-bath,  5  c.c.  of  nitric  acid  of  1-15  specific  gravity  are  added, 
and  the  mixture  thoroughly  stirred  and  allowed  to  stand  for  thirty  minutes. 
The  nitric  acid  decomposes  the  ammonium  mucate,  precipitating  the  mucic 
acid,  which  is  collected  on  a  tared  filter  or  Gooch,  washed  with  from  10  to  15 
c.c.  of  water,  then  with  60  c.c.  of  alcohol,  and  a  number  of  times  with  ether, 
dried  at  100°  for  a  short  time,  and  weighed.  The  mucic  acid  multiplied 
by  1-33  gives  galactose,  and  this  product  multiplied  by  0-9  gives  galactan, 

(g)    DETERMINATION    OF   CRUDE    FIBER. 

Extract  2  grm.  of  the  substance  with  ordinary  ether  or  use  the  residue 
from  the  determination  of  the  ether  extract.  To  this  residue,  in  a  500-c.c.  flask 
add  200  c.c.  of  boiling  1-25-per  cent,  sulphuric  acid;  connect  the  flask  with  an 
inverted  condenser,  the  tube  of  which  passes  only  a  short  distance  beyond 
the  rubber  stopper  into  the  flask.  Boil  at  once,  and  continue  the  boiling 
for  thirty  minutes.  A  blast  of  air  conducted  into  the  flask  may  serve  to 
reduce  the  frothing  of  the  liquid.  Filter;  wash  with  boiling  water  till  the 
washings  are  no  longer  acid;  rinse  the  substance  back  into  the  same  flask 
with  200  c.c.  of  a  boiling  1-25-per  cent,  solution  of  sodium  hydroxide,  free, 
or  nearly  so,  from  sodium  carbonate;  boil  at  once,  and  continue  the  boiling 
for  thirty  minutes  in  the  same  manner  as  directed  above  for  the  treatment 
with  acid.  Filter  on  a  Gooch,  and  wash  with  boiling  water  till  the  washings 
are  neutral;  dry  at  110°;  weigh;  incinerate  completely.  The  loss  of  weight 
is  crude  fiber. 

The  filter  used  for  the  first  filtration  may  be  linen,  one  of  the  forms  of 
glass-wool  or  asbestos  filters,  or  any  other  form  that  secures  clear  and  reason- 
ably rapid  filtration.  The  solutions  of  sulphuric  acid  and  sodium  hydroxide 
are  to  be  made  up  of  the  specified  strength,  determined  accurately  by  titration 
and  not  merely  from  specific  gravity. 


OFFICIAL   METHODS   OF   ANALYSIS.  1037 


III.     METHODS  FOR  THE  DETERMINATION  OF  SOLUBLE  CAR- 
BOHYDRATES IN  AGRICULTURAL  PRODUCTS,  INCLUDING 
METHODS  FOR  THE  DETERMINATION  OF  WATER 
AND   ASH   IN  COMMERCIAL   AND  INDUSTRIAL 
SACCHARINE  PRODUCTS. 

1.  DETERMINATION  OF  WATER. 

(a)    BY   DRYING. 

(1)  IN  SUGARS. — Dry  from  2  to  5  gnu.  in  a  flat  dish  (nickel,  platinum, 
or  aluminium),  at  the  temperature  of  boiling  water,  for  ten  hours:   cool  in  a 
desiccator  and  weigh :  return  to  the  oven  and  dry  for  an  hour.     If  on  weigh- 
ing there  be  only  a  slight  change  of  weight,  the  process  may  be  considered 
finished;    otherwise  the  drying  must  be  continued  until  the  loss  of  water 
in  one  hour  is  not  great. 

(2)  IN  MASSECUITES,  MOLASSES,  HONEYS,  AND  OTHER  LIQUID  AND  SEMI- 
LIQUID  PRODUCTS  (PROVISIONAL  METHOD). — Prepare  pumice  stone  in  two 
grades  of  fineness.     One  of  these  should  pass  through  a  1-mm.  sieve,  while 
the  other  should  be  composed  of  particles  too  large  for  a  millimeter  sieve, 
but  sufficiently  small  to  pass  through  a  sieve  having  meshes  6  mm.  hi  diam- 
eter.     Make  the  determination  in  flat  metallic  dishes  or  in  shallow,  flat- 
bottomed  weighing  bottles.     Place  a  layer  of  the  fine  pumice  stone  3  mm.  in 
thickness  over  the  bottom  of  the  dish,  and  upon  this  place  a  layer  of  the 
coarse  pumice  stone  from  6  to  10  mm.  in  thickness.     Dry  the  dish  thus  pre- 
pared and  weigh.     Dilute  the  sample  with  a  weighed  portion  of  water  in 
such  a  manner  that  the  diluted  material  shall  contain  from  20  to  30  per  cent, 
of  dry  matter.     Weigh  into  the  dish,  prepared  as  described  above,  such  a 
quantity  of  the  diluted  sample  as  will  yield,  approximately,  1  grm.  of  dry 
matter.     Use  a  weighing  bottle  provided  with  a  cork  through  which  a  pipette 
passes  if  this  weighing  can  not  be  made  with  extreme  rapidity.     Place  the 
dish  in  a  water-oven  'and  dry  to  constant  weight  at  the  temperature  of  boil- 
ing water,  making  trial  weighings  at  intervals  of  two  hours.     In  case  of 
materials  containing  much  levulose  or  other  readily  decomposed  substances, 
conduct  the  drying  in  vacuo  at  a  lower  temperature.     In  the  case  of  very 
unstable  material,  the  temperature  can  safely  be  lowered  to  70°. 

(3)  PROVISIONAL  METHOD  FOR  DRYING  MOLASSES  WITH  QUARTZ  SAND. — 
In  a  flat-bottomed  dish  place  6  or  7  grm.  of  pure  quartz  sand  and  a  short  stir- 
ring rod.     Dry  thoroughly,  cool  in  a  desiccator,  and  weigh.     Then  add  3  or 
4  grm.  of  the  molasses,  mix  with  the  sand,  and  dry  at  the  temperature  of 
boiling  water  for  from  eight  to  ten  hours.     Stir  at  intervals  of  an  hour:  then 
cool  in  a  desiccator  and  weigh.      Stir,  heat  again  in  the  water-oven  for  an 
hour,  cool  and  weigh.     Repeat  heating  and  weighing  until  loss  of  water  hi 
one  hour  is  not  greater  than  3  mgrm. 

This  sample  may  be  used  for  the  determination  of  ash  by  the  ALBERTI- 
HEMPEL  method  (See  method  II  (d)  under  ' '  ash.") 

The  sand  used  should  be  pure  quartz.  It  should  be  digested  with  strong 
HC1,  washed,  dried,  and  ignited,  and  kept  In  a  stoppered  bottle. 


1038  APPENDIX   I. 

(6)    AREOMETRIC   METHODS.* 

(1)  DETERMINATION  OF  SPECIFIC  GRAVITY,  WATER,  AND  TOTAL  SOLIDS 
BY  MEANS  OF  A  SPINDLE. — The  density  of  juices,  sirups,  etc.,  is  most  con- 
veniently determined  by  means  of  BAUME'S  or  BRIX'S  hydrometer  or  areo- 
meter, preferably  with  the  latter,  as  the  graduations  of  the  scale  give  close 
approximations  to  the  percentages  of  total  solids.     The  BRIX  spindle  should 
be  graduated  to  tenths.     It  is  therefore  desirable,  for  accuracy,  that  the 
range  of  degrees  recorded  by  each  individual  spindle  be  as  limited  as  pos- 
sible, this  end  being  best  secured  by  the  employment  of  sets  consisting  of 
not  less  than  three  spindles.     The  solutions  should  be  as  nearly  as  possible 
of  the  same  temperature  as  the  air  at  the  time  of  reading,  and  if  the  variation 
from  the  temperature  of  the  graduation  of  the  spindle  amount  to  more  than 
1°,  compensation  must  be  made  by  reference  to  the  table  of  corrections  for 
temperature,   pages    1039  and    1040.     This   temperature   should   be    17-5°. 
Before  taking  the  density  of  a  juice,  it  should  be  allowed  to  stand  in  the 
cylinder  until  all  air-bubbles  have  escaped. 

In  case  the  sample  is  too  dense  to  determine  the  density  directly,  a  weighed 
portion  of  it  must  first  be  diluted  with  a  weighed  quantity  of  water,  or  a 
weighed  portion  must  be  dissolved  and  diluted  to  a  known  volume  with 
water.  In  the  first  instance  the  per  cent,  of  total  solids  is  calculated  by 
the  following  formula; 

~W  Sf 
Per  cent,  of  solids  in  the  undiluted  material  = •. 

w 

$  =  per  cent,  of  solids  in  the  diluted  material. 
W  =  weight  of  the  diluted  material. 
w  =  weight  of  the  sample  taken  for  dilution. 

When  the  dilution  is  made  to  a  definite  volume  the  following  formula  is 
to  be  used: 

Per  cent,  of  solids  in  the  undiluted  material  =          . 

F  =  volume  of  the  diluted  solution. 
D  =  specific  gravity  of  the  diluted  solution. 
S  =  per  cent,  of  solids  in  the  diluted  solution. 
W=  weight  of  the  sample  taken  for  dilution. 

(17-5°\ 
) ,   degrees    BRIX 
17  •  5  / 

(per  cent,  by  weight  of  sucrose)  and  degrees  BATJME,  is  given  below. 

(2)  DETERMINATION  OF  SPECIFIC  GRAVITY,  WATER,  AND  TOTAL  SOLIDS 
BY  MEANS  OF  A  PYCNOMETER. — When  a  more  accurate  determination  of  the 
per  cent,  of  solids  or  of  water  or  of  the  specific  gravity  is  desired,  the  deter- 
mination should  be  made  with  a  specific-gravity  bottle  or  pycnometer.     When 
of  too  high  density  for  a  direct  determination,  the  sample  may  be  diluted,  as 
described  under  (1). 

*  This  method  does  not  apply  to  low-grade  sugar  products. 


OFFICIAL    METHODS    OF   ANALYSIS. 


1039 


A  TABLE    FOR  THE   COMPARISON   OF  SPECIFIC    GRAVITIES,    DEGREES  BRIX  AND 

DEGREES   BAUME. 


Degree 
Brix  or 
Per  Cent, 
by 
Weight  of 
Sucrose. 

Specific 
Gravity. 

Degree 
Baume. 

Degree 
Brix  or 
Per  Cent, 
by 
Weight  of 
Sucrose. 

Specific 
Gravity. 

Degree 
Baume. 

Degree 
Brix  or 
Per  Cent 
by 
Weight  of 
Sucrose. 

Specific 
Gravity. 

Degree 
Baume. 

1.0 

.00388 

0.6 

33.0 

1  .  14423 

18.5 

65.0 

.31989 

35.6 

2.0 

.00779 

1.1 

34.0 

1.14915 

19.05 

66.0 

.32601 

36.1 

3.0 

.01173 

1.7 

35.0 

1.15411 

19.6 

67.0 

.33217 

36.6 

4.0 

.01570 

2.3 

36.0 

1.15911 

20.1 

68.0 

.33836 

37.1 

5.0 

.01970 

2.8 

37.0 

1  .  16413 

20.7 

69.0 

.34460 

37.6 

6.0 

.02373 

3.4 

38.0 

1  .  16920 

21.2 

70.0 

.35088 

38.1 

7.0 

.02779 

4.0 

39.0 

1  .  17430 

21.8 

71.0 

.35720 

38.6 

8.0 

.03187 

4.5 

40.0 

1  .  17943 

22.3 

72.0 

.36355 

39.1 

9.0 

.03599 

5.1 

41.0 

1.18460 

22.9 

73.0 

.36995 

39.6 

10.0 

.04014 

5.7 

42.0 

1  .  18981 

23.4 

74.0 

.37639 

40.1 

11.0 

.04431 

6.2 

43.0 

1  .  19505 

23.95 

75.0 

.38287 

40.6 

12.0 

.04852 

6.8 

44.0 

1.20033 

24.5 

76.0 

.38939 

41.1 

13.0 

.05276 

7.4 

45.0 

1  .  20565 

25.0 

77.0 

.39595 

41.6 

14.0 

.05703 

7.9 

46.0 

1.21100 

25.6 

78.0 

.40254 

42.1 

15.0 

.06133 

8.5 

47.0 

1  .  21639 

26.1 

79.0 

.40918 

42.6 

16.0 

.06566 

9.0 

48.0 

1.22182 

26.6 

80.0 

.41586 

43.1 

17.0 

.07002 

9.6 

49.0 

1.22728 

27.2 

81.0 

.42258 

43.6 

18.0 

.07441 

10.1 

50.0 

1  .  23278 

27.7 

82.0 

.42934 

44.1 

19.0 

.07884 

10.7 

51.0 

1.23832 

28.2 

83.0 

.43614 

44.6 

20.0 

.08329 

11.3 

52.0 

1.24390 

28.8 

84.0 

.44298 

45.1 

21.0 

.08778 

11.8 

53.0 

1  .  24951 

29.3 

85.0 

.44986 

45.5 

22.0 

.09231 

12.4 

54.0 

1  .  25517 

29.8 

86.0 

.45678 

46.0 

23.0 

.09686 

13.0 

55.0 

1  .  26086 

30.4 

87.0 

.46374 

46.5 

24.0 

.  10145 

13.5 

56.0 

1  .  26658 

30.9 

88.0 

.47074 

47.0 

25.0 

.10607 

14.1 

57.0 

1.27235 

31.4 

89.0 

.47778 

47.45 

26.0 

.11072 

14.6 

58.0 

1.27816 

31.9 

90.0 

.48486 

47.9 

27.0 

.11541 

15.2 

59.0 

1.28400 

32.5 

91.0 

.49199 

48.5 

28.0 

.12013 

15.7 

60.0 

1.28989 

33.0 

92.0 

.49915 

48.9 

29.0 

.12488 

16.3 

61.0 

1  .  29581 

33.5 

93.0 

.50635 

49.4 

30.0 

.12967 

16.8 

62.0 

1.30177 

34.0 

94.0 

.51359 

49.8 

31.0 

.  13449 

17.4 

63.0 

1  .  30777 

34.5 

95.0 

1.52087 

50.3 

32.0 

1  .  13934 

17.95 

64.0 

1.31381 

35.1 

When  the  number  expressing  the  specific  gravity  found  by  analysis  falls 
between  the  numbers  given  in  the  above  table,  the  exact  equivalent  in  de- 
grees BRIX  or  BAUME  is  found  by  a  simple  calculation. 

Example. — The  pycnometer  shows  the  specific  gravity  of  a  certain 
sirup  to  be  12-0909.  The  table  shows  that  the  corresponding  de- 
gree BRIX  is  between  45-0  and  46-0.  Subtracting  the  specific  gravity 
of  a  solution  of  45°  BRIX  from  the  corresponding  figure  for  46°,  we 
have  (expressing  the  specific  gravities  as  whole  numbers)  121,100  — 
120,565  =  535,  the  difference  in  specific  gravity  for  1°  BRIX  at  this 
point  in  the  table.  Subtracting  the  specific  gravity  corresponding 
to  45°  from  the  specific  gravity  found  by  analysis,  we  have  120,909  — 
120,565  =  344.  fff  =  0-64,  the  fraction  of  1°  BRIX  more  than  45°. 
The  degree  BRIX  corresponding  to  a  specific  gravity  of  1  •  20909  is 
therefore  45-64. 

If  the  spindle  reading  or  pycnometer  determination  be  made  at  any  other 
temperature  than  17-5°,  the  result  should  be  corrected  by  the  use  of  the 
following  table: 


1040 


APPENDIX   I. 


TABLE     FOR     CORRECTION    OF    THE    READINGS    OF    THE    BRIX    SPINDLE    WHEN 

THE   READING   IS   MADE   AT   OTHER   THAN   THE   STANDARD 

TEMPERATURE,    17-5°. 

[For  temperatures  below  17  -5°  the  correction  is  to  be  subtracted.] 
[For  temperatures  above  17  •  5°  the  correction  is  to  be  added.] 


Tem- 
pera- 
ture 

Degree  Brix  of  the  Solution. 

0 

5 

10 

15 

20 

25 

30 

35 

40 

50 

60 

70 

75 

0 

0.17 

0.30 

0.41 

0.52 

0.62 

0.72 

0.82 

0.92 

0.98 

1.11 

1.22 

1.25 

1.29 

5 

0.23 

0.30 

0.37 

0.44 

0.52 

0.59 

0.65 

0.72 

0.75 

0.80 

0.88 

0.91 

0.94 

10 

0.20 

0.26 

•j.29 

0.33 

0.36 

0.39 

0.42 

0.45 

0.48 

0.50 

0.54 

0.58 

0.61 

11 

0.18 

0.23 

0.26 

0.28 

0.31 

0.34 

0.36 

0.39 

0.41 

0.43 

0.47 

0.50 

0.53 

12 

0.16 

0.20 

0.22 

0.24 

0.26 

0.29 

0.31 

0.33 

0.34 

0.36 

0.40 

0.42 

0.46 

13 

0.14 

0.18 

0.19 

0.21 

0.22 

0.24 

0.26 

0.27 

0.28 

0.29 

0.33 

0.35 

0.39 

14 

0.12 

0.15 

0.16 

0.17 

0.18 

0.19 

0.21 

0.22 

0.22 

0.23 

0.26 

0.28 

0.32 

15 

0.09 

0.11 

0.12 

0.14 

0.14 

0.15 

0.16 

0.17 

0.16 

0.17 

0.19 

0.211   0.25 

16 

0.06 

0.07 

0.08 

0.09 

0.10 

0.10 

0.11 

0.12 

0.12 

0.12 

0.14 

0.16 

0.18 

17 

0  02 

0.02 

0.03 

0.03 

0.03 

0.04 

0.04 

0.04 

0.04 

0.04 

0.05 

0.05 

0.06 

18 

0.02 

0.03 

0.03 

0.03 

0.03 

0.03 

0.03 

0.03 

0.03 

0.03 

0.03 

0.03 

0.02 

19 

0.06 

0.08 

0.08 

0.09 

0.09 

0.10 

0.10 

0.10 

0.10 

0.10 

0.10 

0.08 

0.06 

20 

0.11 

0.14 

0.15 

0.17 

0.17 

0.18 

0.18 

0.18 

0.19 

0.19 

0.18 

0.15 

0.11 

21 

0.16 

0.20 

0.22 

0.24 

0.24 

0.25 

0.25 

0.25 

0.26 

0.26 

0.25 

0.22 

.18 

22 

0.21 

0.28 

0.29 

0.31 

0.31 

0.32 

0.32 

0.32 

0.33 

0  34 

0.32 

0.29 

0.25 

23 

0.27 

0.32 

0.35 

0.37 

0.38 

0.39 

0.39 

0.39 

0.40 

0.42 

0.39 

0.36 

0.33 

24 

0.32 

0.38 

0.41 

0.43 

0.44 

0.46 

0.46 

0.47 

0.47 

0.50 

0.46 

0.43 

0.40 

25 

0.37 

0.44 

0.47 

0.49 

0.51 

0.53 

0.54 

0.55 

0.55 

0.58 

0.54 

0.51 

0.48 

26 

0.43 

0.50 

0.54 

0.56 

0.58 

0.60 

0.61 

0.62 

0.52 

0.66 

0.62 

0.58 

0.55 

27 

0.49 

0.57 

0.61 

0.63 

0.65 

0.68 

0.68 

0.69 

0.70 

0.74 

0.70 

0.65 

0.62 

28 

0.56 

0.64 

0.68 

0.70 

0.72 

0.76 

0.76 

0.78 

0.78 

0.82 

0.78 

0.72 

0.70 

29 

0.63 

0.71 

0.75 

0.78 

0.79 

0.84 

0.84 

0.86 

0.86 

0.90 

0.86 

0.80 

0.78 

30 

0.70 

0.78 

0.82 

0.87 

0.87 

0.92 

0.92 

0.94 

,0.94 

0.98 

0.94 

0.88 

0.86 

35 

1.10 

1.17 

1.22 

1.24 

1.30 

1.32 

1.33 

1.35 

1.36 

1.39 

1.34 

1.27 

1.25 

40 

1.50 

1.61 

1.67 

1.71 

1.73 

1.79 

1.79 

1.80 

1.82 

1.83 

1.78 

1.69 

1.65 

50 

2.65 

2.71 

2.74 

2.78 

2.80 

2.80 

2.80 

2.80 

2.79 

2.70 

2.56 

2.51 

60 

3.87 

3.88 

3.88 

3.88 

3.88 

3.88 

3.88 

3.90 

3.82 

3.70 

3.43 

3.41 

70 

5.17 

5.18 

5.20 

5.14 

5.13 

5.10 

5.08 

5.06 

4.90 

•4.72 

4.47 

4.35 

80 

6.62 

6.59 

6.54 

6.46 

6.38 

6.30 

6.26 

6.03 

5.82 

5.50 

5.33 

90 

8.26 

8.16 

8.06 

7.97 

7.83 

7.71 

7.58 

7.30 

6.96 

6.58 

6.37 

100 

10.01 

9.87 

9.72 

9.56 

9.30 

9.21 

9.03 

8.64 

8.22 

7.76 

7.42 

Example. — A  sugar  solution  shows  a  reading  of  30  •  2°  BRIX  at  30°. 
To  find  the  necessary  correction  for  the  conversion  of  this  reading  to 
the  reading  which  would  have  been  obtained  if  the  observation  had  been 
made  at  17-5°,  find  the  vertical  column  in  the  table  headed  30°  BRIX, 
which  is  the  nearest  to  the  observed  reading.  Follow  down  this 
column  until  the  number  is  reached  which  is  opposite  to  the  tem- 
perature of  observation— in  this  case  30°.  The  number  found,  0-92, 
is  to  be  added  to  the  observed  reading,  making  it  31  •  12. 

2.  ASH. 
(«)  DETERMINATION  OF  ASH. 

(1)  Heat  from  5  to  10  grm.  of  the  material  (sugar,  molasses,  honey)  in  a 
platinum  dish  *  of  from  50  to  100  c.c.  capacity  at  100°  until  the  water  is  ex- 
pelled, and  then  slowly  over  a  flame  until  intumescence  ceases.  The  dish 


*  If  the  substance  contain  tin  or  any  other  metal  capable  of  uniting  with  platinum, 
a  dish  made  of  some  other  material  must  be  used. 


OFFICIAL    METHODS    OF   ANALYSIS.  1041 

is  then  placed  in  a  muffle  and  heated  at  low  redness  until  a  white  ash  is  ob- 
tained. 

For  soluble  ash  digest  the  ash,  obtained  as  above  with  water,  filter  through 
a  Gooch,  wash  with  hot  water,  and  dry  the  residue  at  100°. 

(2)  Use  50  mgrm.  of  zinc  oxide  to  25  grm.  of  molasses  or  50  grm.  of  sugar. 
Incorporate  thoroughly  by  adding  dilute  alcohol  and  mixing;  dry  and  ignite 
as  above.     Deduct  the  weight  of  zinc  oxide  used  from  the  weight  of  ash. 

(3)  Carbonize  the  mass  at  a  low  heat,  dissolve  the  soluble  salts  with  hot 
water,  burn  the  residual  mass  as  above,  add  the  solution  of  soluble  salts, 
and  evaporate  to  dryness  at  100°;  ignite  gently,  cool  in  a  desiccator,  and 
weigh. 

(4)  Saturate  the  sample  with  sulphuric  acid,  dry,  ignite  gently,  then  burn 
in  a  muffle  at  low  redness.     Deduct  one-tenth  of  the  weight  of  the  ash,  then 
calculate  the  per  cent. 

(5)  Thoroughly  mix  5  grm.  of  the  material  with  a  somewhat  larger  weight 
of  pure  quartz  sand  in  a  platinum  dish;  ignite  in  a  muffle  at  a  moderate  red 
heat. 

(6)  To  avoid  the  correction  of  one-tenth,  as  proposed  by  SCHEIBLER,  and 
one-fifth,  as  proposed  by  GIRARD  and  VIOLETTE,  when  sugars  are  burned 
with  sulphuric  acid,  BOYER  suggests  incineration  with  benzoic  acid  as  giving 
the  real  quantity  of  mineral  matter  without  correction. 

The  benzoic  acid  is  dissolved  in  90-per  cent,  alcohol,  25  grm.  of  the 
acid  to  100  c.c.  of  alcohol.  Five  grm.  of  the  sugar  are  weighed  in  a  capsule 
and  moistened  with  1  c.c.  of  water.  The  capsule  is  heated  slowly  in  order 
to  caramelize  the  sugar  without  carbonizing  it;  2  c.c.  of  the  benzoic-acid 
solution  are  next  added,  and  the  capsule  warmed  until  all  the  alcohol  is 
evaporated;  the  temperature  is  then  raised  until  the  sugar  is  converted  into 
carbon.  The  decomposing  benzoic  acid  produces  abundant  vapors,  which 
render  the  mass  extremely  porous,  especially  if  a  circular  motion  be  imparted 
to  the  capsule.  The  slow  heating  is  continued  until  all  the  benzoic  acid  is 
volatilized.  The  carbon  obtained  is  voluminous  and  of  a  brilliant  black 
color.  The  incineration  is  accomplished  in  a  muffle  at  a  low  red  heat.  The 
capsule  should  be  weighed  quickly  when  taken  from  the  desiccator,  in  order 
to  avoid  the  absorption  of  water  by  the  alkaline  carbonates.  Ammonium 
benzoate  may  be  employed  instead  of  benzoic  acid,  and  the  analyst  should  pre- 
viously assure  himself  that  neither  the  acid  nor  the  ammonium  salt  leaves 
a  residue  on  incineration.  In  addition  to  giving  the  mineral  matter  directly, 
this  method  permits  the  determination  of  its  composition  also — a  matter 
of  no  small  importance. 

(6)  QUANTITATIVE  ANALYSIS  OF  THE  ASH. 

Proceed  as  in  ash  analysis  (pp.  1096  to  1098). 

3.  DETERMINATION  OF  NITROGEN. 

Any  of  the  methods  adopted  by  the  association  for  the  estimation  of 
nitrogen  may  be  used  (p.  1021). 


1042  APPENDIX   I. 

4.  DETERMINATION  OF  REDUCING  SUGARS. 

(a)  PREPARATION  OF  REAGENTS  (SOXHLET'S  MODIFICATION  OF  FEHLING'S 

SOLUTION). 

(1)  34-639*  grm.  of  CuSO4-5H2O  are  dissolved  in  water  and  diluted  to 
500  c.c. 

(2)  173  grm.  of  Rochelle  salts  and  50  grm.  of  sodium  hydroxide,  dissolved 
in  water  and  diluted  to  500  c.c.     The  requisite  quantity  of  sodium  hydroxide 
is  best  obtained  by  using  100  c.c.  of  a  solution  containing  500  grm.  of  caustic 
soda  in  1  litre.     A  solution  of  this  strength  has  a  specific  gravity  of  1-393 
at   15°. 

(3)  Mix  equal  volumes  of  solutions  (1)  and  (2)  and  boil  immediately 
before  use.     The  mixture  is  the  mixed  copper  reagent  to  be  used  for  all  the 
methods  given  below  except  ALLIHN'S  method  for  dextrose,  for  which  a  special 
reagent  must  be  used. 

(6)  VOLUMETRIC  METHODS. 

(1)  Approximate  volumetric  method  for  rapid  work. 

Place  10  c.c.  of  the  mixed  copper  reagent  in  a  large  test  tube  and  add 
10  c.c.  of  distilled  water.  Heat  to  boiling,  and  gradually  add  small  por- 
tions of  the  solution  of  the  material  to  be  tested  until  the  copper  has  been 
completely  precipitated,  boiling  to  complete  the  reaction  after  each  addition. 
Two  minutes'  boiling  is  required  for  complete  precipitation  when  the  full 
amount  of  sugar  solution  has  been  added  in  one  portion.  When  the  end 
reaction  is  nearly  reached  and  the  amount  of  sugar  solution  to  be  added 
can  no  longer  be  judged  by  the  color  of  the  solution,  a  small  portion  of  the 
liquid  is  removed  by  means  of  KNORR'S  modification  of  WILEY'S  filtering 
tube  f  (any  other  rapid  means  of  filtration  may  be  used  that  removes  but  a 
small  portion  of  the  hot  liquid),  is  transferred  to  a  small  porcelain  crucible  or 
test  plate,  acidified  with  dilute  acetic  acid,  and  tested  for  copper  with  a 
dilute  solution  of  potassium  ferrocyanide.  The  sugar  solution  should  be  of 
such  a  strength  as  will  give  a  burette  reading  of  15  to  20  c.c.,  and  the 
number  of  successive  additions  should  be  as  small  as  possible. 

Since  the  factor  for  calculation  varies  with  the  minute  details  of  manipula- 
tion, every  operator  must  determine  a  factor  for  himself,  using  a  known 
solution  of  a  pure  sample  of  the  sugar  that  he  desires  to  determine  and  keeping 
the  conditions  the  same  as  those  used  for  the  determinations.  For  the 
standardization  of  a  solution  for  the  determination  of  invert  sugar  in  sugar- 
house  products,  dissolve  2-5  grm.  of  pure  sucrose  in  75  c.c.  of  water,  add 
5  c.c.  of  hydrochloric  acid  (specific  gravity  1  •  188  at  15°),  and  invert  according 
to  method  (6)  under  Optical  Methods  for  the  Determination  of  Sucrose 
by  Inversion  (p.  1050).  Neutralize  the  acid  with  sodium  .carbonate  and 
dilute  to  1  litre.  The  2-5  grm.  of  sucrose  become  2-6316  grm.  of  invert 

*  According  to  the  atomic  weights  used  in  this  book  the  figures  should  be  34' 669. — 
TRANSLATOR. 

t  Principles  and  Practice  of  Agricultural  Analysis,  in,  130,  131. 


OFFICIAL   METHODS   OF  ANALYSIS.  1043 

sugar.     The  weight  of  invert-sugar  equivalent  to  10  c.c.  of  the  copper  reagent 
is  calculated  as  follows: 

2-  6316 X  number  of  c.c.  of  the  standard  sugar  solution  used     y 
1000 

the  weight  of  invert-sugar  required  to  completely  precipitate    the  copper 
in  10  c.c.  of  the  reagent  under  the  conditions  used  for  the  titration.     For 
the  calculation  of  the  result  of  the  titration  of  an  unknown  solution: 
Let  X  =  the  factor  obtained  as  above; 

V  =  the  number  of  c.c.  of  unknown  sugar  solution  required  to  precipi- 
tate the  copper  from  10  c.c.  of  copper  solution; 
W  =  the  weight  of  the  material  under  examination  in  1  c.c.  of  the 
solution. 

Then  1QQ     =per  cent,  of  invert-sugar  in  the  sample. 
VW 

The  calculation  can  be  much  simplified  by  so  standardizing  the  copper 
reagent  that  50  mgrm.  of  invert-sugar  will  be  required  to  reduce  the  copper 
from  10  c.c.  of  the  copper  reagent.  The  various  tables  given  in  works  on 
sugar  analysis  then  become  applicable.  These  tables  are  arranged  for  a 
"glucose  normal  solution"  containing  5  grm.  of  the  material  to  be  exam- 
ined in  100  c.c.  When  the  weight  per  100  c.c.  is  more  or  less  than  5  grm. 
the  number  found  hi  the  table  is  increased  or  diminished  accordingly. 
(2)  SOXHLET'S  Method. 

A  preliminary  titration  is  made  to  determine  the  approximate  percentage 
of  reducing  sugar  in  the  material  under  examination.  A  solution  is  prepared 
which  contains  approximately  1  per  cent,  of  reducing  sugar.  Place  in  a 
beaker  100  c.c.  of  the  mixed  copper  reagent  and  approximately  the  amount 
of  the  sugar  solution  for  its  complete  reduction.  Boil  for  two  minutes. 
Filter  through  a  folded  filter  and  test  a  portion  of  the  filtrate  for  copper 
by  use  of  acetic  acid  and  potassium  ferrocyanide.  Repeat  the  test,  varying 
the  volume  of  sugar  solution,  until  two  successive  amounts  of  sugar  solution 
are  found  which  differ  by  0-1  c.c.,  one  giving  complete  reduction  and  the 
other  leaving  a  small  amount  of  copper  in  solution.  The  mean  of  these  two 
readings  is  taken  as  the  volume  of  the  solution  required  for  the  complete  pre- 
cipitation of  100  c.c.  of  the  copper  reagent. 

Under  these  conditions  100  c.c.  of  the  mixed  copper  reagent  require  0-475 
grm.  of  anhydrous  dextrose,  or  0*494  grm.  of  invert-sugar,  for  complete 
reduction.  The  percentage  is  calculated  by  the  following  formula: 

W  =  the  weight  of  the  sample  hi  1  c.c.  of  the  sugar  solution ; 
V  =  the  volume  of  the  sugar  solution  required  for  the  complete  reduction 
of  100  c.c.  of  the  copper  reagent. 

Then  1M*^475-per  cent,  of  dextrose, 

100X0-494 
or =y=p =  P61"  cent,  of  invert-sugar. 

(3)  Other  volumetric  methods.  (See  Principles  and  Practice  of  Agricultural 
Analysis.  Vol.  Ill,  pp.  121  et  seq.) 


1044 


APPENDIX   I. 


c)    GRAVIMETRIC   METHODS. 

(1)  Methods   of   Reducing    the    Copper   Solution. 

(a)  METHOD  FOR  MATERIALS  CONTAINING  1  PER  CENT.  OR  LESS  OF  INVERT- 
SUGAR  AND  A  HIGH  PERCENTAGE  OF  SUCROSE. — The  solution  of  the  material 
to  be  examined  is  so  prepared  as  to  contain  20  grm.  in  100  c.c.,  and  it  must 
be  freed  from  suspended  impurities  by  filtration  and  from  soluble  impurities 
by  lead  subacetate,  removing  the  excess  of  lead  by  means  of  sodium  carbon- 
ate. In  a  beaker  of  250  c.c.  capacity  place  50  c.c.  of  the  mixed  copper  re- 
agent and  50  c.c.  of  the  sugar  solution.  Heat  this  mixture  at  such  a  rate 
that  approximately  four  minutes  are  required  to  bring  it  to  the  boiling-point, 
and  boil  for  exactly  two  minutes.  Add  100  c.c.  of  cold,  recently  boiled,  dis- 
tilled water.  Filter  immediately  and  finish  the  determination  by  one  of 
the  methods  given  below  (p.  1048)  for  the  determination  of  the  copper  con- 
tained in  the  precipitate  of  cuprous  oxide  obtained  in  the  determination  of 
reducing  sugars. 

The  corresponding  percentage  of  invert-sugar  is  found  by  the  use  of  the 
following  table: 

HERTZFELD'S  TABLE  FOR  THE  DETERMINATION  OF  INVERT-SUGAR  IN 
MATERIALS  CONTAINING  1  PER  CENT.  OR  LESS  OF  INVERT-SUGAR 

AND  A  HIGH  PERCENTAGE  OF  SUCROSE. 


Copper 
Reduced  by 

Invert- 

Copper 
Reduced  by 

Invert- 

Copper 
Reduced  by 

Invert- 

10  Grammes  of 
Material., 

sugar. 

10  Grammes  of 
Material. 

sugar. 

10  Grammes  of 
Material. 

sugar. 

Milligrammes. 

Per  Cent. 

Milligrammes. 

Per  Cent. 

Milligrammes. 

Per  Cent. 

50 

0-05 

120 

0-40 

190 

0-79 

55 

0-07 

125 

0-43 

195 

0-82 

60 

0-09 

130 

0-45 

200 

0-85 

65 

0-11 

135 

0-48 

205 

0-88 

70 

0-14 

140 

0-51 

210 

0-90 

75 

0-16 

145 

0-53 

215 

0-93 

80 

0-19 

150 

0-56 

220 

0-96 

85 

0-21 

155 

0-59 

225 

0-99 

90 

0-24 

160 

0-62 

230 

1-02 

95 

0-27 

165 

0-65 

235 

1-05 

100 

0-30 

170 

0-68 

240 

1-07 

105 

0-32 

175 

0-71 

245 

1-10 

110 

0-35 

180 

0-74 

115 

0-38 

185 

0-76 

(6)  METHOD  FOR  MATERIALS  CONTAINING  MORE  THAN  1  PER  CENT.  OP 
INVERT-SUGAR. — Prepare  a  solution  of  the  material  to  be  examined  in  such 
a  manner  that  it  contains  20  grm.  in  100  c.c.  after  clarification  and  the  re- 
moval of  the  excess  of  lead.  Prepare  a  series  of  solutions  in  large  test-tubes 
by  adding  1,  2,  3,  4,  5,  etc.,  c.c.  of  this  solution  to  each  successively.  Add 
5  c.c.  of  the  mixed  copper  reagent  to  each,  heat  to  boiling,  boil  two  minutes, 


OFFICIAL   METHODS   OF   ANALYSIS. 


1045 


and  filter.  Note  the  volume  of  sugar  solution  which  gives  the  filtrate  light- 
est in  tint,  but  still  distinctly  blue.  Place  twenty  times  this  volume  of  the 
sugar  solution  in  a  100  c.c.  flask,  dilute  to  the  mark,  and  mix  well.  Use 
50  c.c.  of  the  solution  for  the  determination,  which  is  conducted  as  described 
under  (a).  For  the  calculation  of  the  result  use  the  folio  whig  formulas  and 
table  of  factors  of  MEISSL  and  HILLER: 

Let  Cu  =the  weight  of  copper  obtained; 
P  =  the  polarization  of  the  sample ; 
W  =  the  weight  of  the  sample  hi  the  50  c.c.  of  the  solution  used  for 

determination ; 

F  =  the  factor  obtained  from  the  table  for  conversion  of  copper  to 
in  vert-sugar; 

Cu 

-—  =  approximate  absolute  weight  of  invert-sugar  =  Z; 

i  no 
ZX-—  =  approximate  per  cent,  of  in  vert-  sugar =y, 


WOP 

P+y 


=  R,  relative  number  for  sucrose ; 


100  —  R  =/,  relative  number  for  invert-sugar; 
~w~-  =  per  cent,  of  invert-sugar. 

Z  facilitates  reading  the  vertical  columns;  and  the  ratio  of  R  to  7,  the 
horizontal  columns  of  the  table,  for  the  purpose  of  finding  the  factor  (F) 
for  calculation  of  copper  to  in  vert-  sugar. 

MEISSL   AND  HILLER's   FACTORS  FOR  THE  DETERMINATION  OF   MORE  THAN 
1    PER  CENT.   OF  INVERT-SUGAR. 


Ratio  of 
Sucrose  to 
Invert- 
sugar  =  R  :  I. 

Approximate  Absolute  Weight  of  Invert-sugar=Z. 

200  Milli- 
grammes. 

17  5  Milli- 
grammes. 

150  Milli- 
grammes. 

125  Milli- 
grammes. 

100  Milli- 
grammes. 

75  Milli- 
grammes. 

50  Milli- 
grammes. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

0:  100 

56.4 

55.4 

54.5 

53.8 

53.2 

53.0 

53.0 

10:90 

56.3 

55.3 

54.4 

53.8 

53.2 

52.9 

52.9 

20:80 

56.2 

55.2 

54.3 

53.7 

53.2 

52.7 

52.7 

30:70 

56.1 

55.1 

54.2 

53.7 

53.2 

52.6 

52.6 

40  :60 

55.9 

55.0 

54.1 

53.6 

53.1 

52.5 

52.4 

50:50 

55.7 

54.9 

54.0 

53.5 

53.1 

52.3 

52.2 

60:40 

55.6 

54.7 

53.8 

53.2 

52.8 

52.1 

51.9 

70:30 

55.5 

54.5 

53.5 

52.9 

52.5 

51.9 

51.6 

80:20 

55.4 

54.3 

53.3 

52.7 

52.2 

51.7 

51.3 

90:  10 

54.6 

53.6 

53.1 

52.6 

52.1 

51.6 

51.2 

91  :9 

54.1 

53.6 

52.6 

52.1 

51.6 

51.2 

50.7 

92:8 

53.6 

53.1 

52.1 

51.6 

51.2 

50.7 

50.3 

93:7 

53.6 

53.1 

52.1 

51.2 

50.7 

50.3 

49.8 

94:6 

53.1 

52.6 

51.6 

50.7 

50.3 

49.8 

48.9 

95:5 

52.6 

52.1 

51.2 

50.3 

49.4 

48.9 

48.5 

96:4 

52.1 

51.2 

50.7 

49.8 

48.9 

47.7 

46.9 

97:3 

50.7 

50.3 

49.8 

48.9 

47.7 

46.2 

45.1 

98    2 

49.9 

48.9 

48.5 

47.3 

45.8 

43.3 

40.0 

99:  1 

47.7 

47.3 

46.5 

45.1 

43.3 

41.2 

38.1 

1046 


APPENDIX    I. 


Example, — The  polarization  of  a  sugar  is  86-4,  and  3-256  grm.  of  it  (W) 
are  equivalent  to  0  •  290  grm.  of  copper.     Then : 
Cu     0-290  ~ 


W=°-U5X^  =  ^5 


Y, 


100P 


8640 


4.9, 


100-72  =  100-95-  1=7 

R  :  7  =  95-1  :4-9. 

By  consulting  the  table  (p.  1045)  it  will  be  seen  that  the  vertical  column 
headed  150  is  nearest  to  Z,  145,  and  the  horizontal  column  headed  95  :  5  is 
nearest  to  the  ratio  of  R  to  7,  95-1  :4-9.  Where  these  columns  meet  we 
find  the  factor  51-2,  which  enters  into  the  final  calculation: 

CuF  =  °'290X51'2  =  4-56  per  cent,  of  invert-sugar. 

(c)  ALLIHN'S  METHOD  FOR  THE  DETERMINATION  OP  DEXTROSE.  —  Reagents: 
34  •  639  *  grm,  of  CuSO4  •  5H2O,  dissolved  in  water  and  diluted  to  500  c.c. 
173  grm.  of  Rochelle  salts  )  dissolved  in  water  and  diluted  to  500 

125  grm.  of  potassium  hydroxide  }      c.c. 

Place  30  c.c.  of  the  copper  solution,  30  c.c.  of  the  alkaline  tartrate  solu- 
tion, and  60  c.c.  of  water  in  -a  beaker,  and  heat  to  boiling.  Add  25  c.c.  of  the 
solution  of  the  material  to  be  examined,  which  must  be  so  prepared  as  not 
to  contain  more  than  1  per  cent,  of  dextrose,  and  boil  for  two  minutes. 
Filter  immediately  without  diluting  and  obtain  the  weight  of  copper  by  one 
of  the  methods  given  on  page  1048.  The  corresponding  weight  of  dextrose 
is  found  by  the  following  table  : 

ALLIHN'S  TABLE  FOR  THE  DETERMINATION  OF  DEXTROSE,  f 


Mgrm. 
of 
Copper. 

Mgrm. 
of  Dex- 
trose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Dex- 
trose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Dex- 
trose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Dex- 
trose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Dex- 
trose. 

10 

6.1 

32 

17.0 

54 

27.9 

76 

38.8 

98 

49.9 

11 

6.6 

33 

17.5 

55 

28.4 

77 

39.3 

99 

50.4 

12 

7.1 

34 

18.0 

56 

28.8 

78 

39.8 

100 

50.9 

13 

7.6 

35 

18.5 

57 

29.3 

79 

40.3 

101 

51.4 

14 

8.1 

36 

18.9 

58 

29.8 

80 

40.8 

102 

51.9 

15 

8.6 

37 

19.4 

59 

30.3 

81 

41.3 

103 

52.4 

16 

9.0 

38 

19.9 

60 

30.8 

82 

41.8 

104 

52.9 

17 

9.5 

39 

20.4 

61 

31.3 

83 

42.3 

105 

53.5 

18 

10.0 

40 

20.9 

62 

31.8 

84 

42.8 

106 

54.0 

19 

10.5 

41 

21.4 

63 

32.3 

85 

43.4 

107 

54.5 

20 

11.0 

42 

21.9 

64 

32.8 

86 

43.9 

108 

55.0 

21 

11.5 

43 

22.4 

65 

33.3 

87 

44.4 

109 

55.5 

22 

12.0 

44 

22.9 

66 

33.8 

88 

44.9 

110 

56.0 

23 

12.5 

45 

23.4 

67 

34.3 

89 

45.4 

111 

56.5 

24 

13.0 

46 

23.9 

68 

34.8 

90 

45.9 

112 

57.0 

25 

13.5 

47 

24.4 

69 

35.3 

91 

46.4 

113 

57.5 

26 

14.0 

48 

24.9 

70 

35.8 

92 

46.9 

114 

58.0 

27 

14.5 

49 

25.4 

71 

36.3 

93 

47.4 

115 

58.6 

28 

15.0 

50 

25.9 

72 

36.8 

94 

47.9 

116 

59.1 

29 

15.5 

51 

26.4 

73 

37.3 

95 

48.4 

117 

59.6 

30 

16.0 

52 

26.9 

74 

37.8 

96 

48.9 

118 

60.1 

31 

16.5 

53 

27.4 

75 

38.3 

97 

49.4 

119 

60.6 

*  Using  the  atomic  weights  employed  in  this  book,  the  weight  should  be  34.669  grm. 
— TRANSLATOR. 

t  Principles  and  Practice  of  Agricultural  Analysis,  in,  pp.  156-158. 


OFFICIAL   METHODS   OF   ANALYSIS. 


1047 


ALLIHN'S  TABLE  FOR  THE  DETERMINATION  OF  DEXTROSE — Continued. 


Mgrm. 
of 
Copper. 

Mgrm. 
.of  Dex 
trose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Dex- 
trose. 

Mgnn. 
of 
Copper 

Mgrm 
of  Dex 
trose. 

Mgnn.     Mgrm. 
of        of  Dex 
Copper,     trose. 

Mgrm 
of 
I  Copper 

Merm. 
of  Dex- 
trose. 

120 

61.1 

189 

96.8 

258 

133.5 

327         171.4 

396 

210.6 

121 

61.6 

190 

97.3 

259 

134.1 

328 

172.0 

397 

211.2 

122 

62.1 

191 

97.8 

260 

134.6 

329 

172.5 

398 

211.7 

123 

62.6 

192 

98.4 

261 

135.1 

330 

173.1 

399 

212.3 

124 

63.1 

193 

98.9 

262 

135.7 

331 

173.7 

400 

212.9 

125 

63  7 

194 

99.4 

263 

136  2 

332 

174.2 

401 

213.5 

126 

64.2 

195 

100.0 

264 

136.8 

333 

174.8 

402 

214.1 

127 

64.7 

196 

100.5 

265 

137.3 

334 

175.3 

403 

214.6 

128 

65.2 

197 

101.0 

266 

137.8 

335 

175.9 

404 

215.2 

129 

65.7 

198 

101.5 

267 

138.4 

336 

176.5 

405 

215.8 

130 

66.2 

199 

102.0 

268 

138.9 

337 

177.0 

406 

216.4 

131 

66.7 

200 

102.6 

269 

139.5 

338 

177.6 

407 

217.0 

132 

67.2 

201 

103.1 

270 

140.0 

339 

178.1 

408 

217.5 

133 

67.7 

202 

103.7 

271 

140.6 

340 

178.7 

409 

218.1 

134 

68.2 

203 

104.2 

272 

141.1 

341 

179.3 

410 

218.7 

135 

68.8 

204 

104.7 

273 

141.7 

342 

179.8 

411 

219.3 

136 

69.3 

205 

105.3 

274 

142.2 

343 

180.4 

412 

219.9 

137 

ti9.8 

206 

105.8 

275 

142.8 

344 

180.9 

413 

220.4 

138 

70.3 

207 

106.3 

276 

143.3 

345 

181.5 

414 

221.0 

139 

70.8 

208 

106.8 

277 

143.9 

346 

182.1 

415 

221.6 

140 

71.3 

209 

107.4 

278 

144.4 

347 

182.6 

416 

222.2 

141 

71.8 

210 

107.9 

279 

145.0 

348 

183.2 

417 

222  ,8 

142 

72.3 

211 

108.4 

280 

145.5 

349 

183.7 

418 

223.3 

143 

72.9 

212 

109.0 

281 

146.1 

350 

184.3 

419 

223.9 

144 

73.4 

213 

109  5 

282 

146.6 

351 

184.9 

420 

224.5 

145 

73.9 

214 

110.0 

283 

147.2 

352 

185.4 

421 

225.1 

146 

74.4 

215 

110.6 

284 

147.7 

353 

186.0 

422 

225.7 

147 

74.9 

216 

111.1 

285 

148.3 

354 

186.6 

423 

226.3 

148 

75.5 

217 

111.6 

286 

148.8 

355 

187.2 

424 

226.9 

149 

76.0 

218 

112.1 

287 

149.4 

356 

187.7 

425 

227.5 

150 

76.5 

219 

112.7 

288 

149.9 

357 

188.3 

426 

228.0 

151 

77.0 

220 

113.2 

289 

150.5 

358 

188.9 

427 

228.6 

152 

77.5 

221 

113.7 

290 

151.0 

359 

189.4 

428 

229.2 

153 

78.1 

222 

114.3 

291 

151.6 

360 

190.0 

429 

229.8 

154 

78.6 

223 

114.8 

292 

152.1 

361     1    190.6 

430 

230.4 

155 

79.1 

224 

115.3 

293 

152.7 

362 

191.1 

431 

231.0 

156 

79.6 

225 

115.9 

294 

153.2 

363 

191.7 

432 

231.6 

157 

80.1 

226 

116.4 

295 

153.8 

364 

192.3 

433 

232.2 

158 

80.7 

227 

116.9 

296 

154.3 

365 

192.9 

434 

232.8 

159 

81.2 

228 

117.4 

297 

154.9 

366 

193.4 

435 

233.4 

160 

81.7 

229 

118.0 

298 

155.4 

367 

194  0 

436 

233.9 

161 

82  2 

230 

118.5 

299 

156.0 

368 

194.6 

437 

234.5 

162 

82.7 

231 

119.0 

300 

156.5 

369 

195.1 

438 

235.1 

163 

83.3 

232 

119.6 

301 

157.1 

370 

195.7 

439 

235.7 

164 

83.8 

233 

120.1 

302 

157.6 

371 

196.3 

440 

236.3 

165 

84.3 

234 

120.7 

303 

158.2 

372 

196.8 

441 

236.9 

166 

84.8 

235 

121.2 

304 

158.7 

373 

197.4 

442 

237.5 

167 

85.3 

236 

121.7 

305 

159.3 

374 

198.0 

443 

238  .  1 

168 

85.9 

237 

122.3 

306 

159.8 

375 

198.6 

444 

238.7 

169 

86.4 

238 

122.8 

307 

160.4 

376 

199.1 

445 

239.3 

170 

86.9 

239 

123.4 

308 

160.9 

377 

199.7 

446 

239.8 

171 

87.4 

240 

123.9 

309 

161.5 

378 

200.3 

447 

240.4 

172 

87.9 

241 

124.4 

310 

160.2 

379 

200.8 

448 

241.0 

173 

88.5 

242 

125.0 

311 

162.6 

380 

201.4 

449 

241.6 

174 

89.0 

243 

125.5 

312 

163.1 

381 

202.0 

450 

242.2 

175 

89.5 

244 

126.0 

313 

163.7 

382 

202.5 

451 

242.8 

176 

90.0 

245 

126.6 

314 

164.2 

383 

203.1 

452 

243.4 

177 

90.5 

246 

127.1 

315 

164.8 

384 

203.7 

453 

244.0 

178 

91.1 

247 

127.6 

316 

165.3 

385 

204.3 

454 

244.6 

179 

91.6 

248 

128.1 

317 

165.9 

386 

204.8 

455 

245.2 

180 

92.1 

249 

128.7 

318 

166.4 

387 

205.4 

456 

245.7 

181 

92.6 

250 

129.2 

319 

167.0 

388 

206.0 

457 

246.3 

182 

93.1 

251 

129.7 

320 

167.5 

389 

206.5 

458 

246.9 

183 

93.7 

252 

130.2 

321 

168.1 

390 

207.1 

459 

247.5 

184 

94.2 

253 

130.8 

322 

168.6 

391 

207.7 

460 

248.1 

185 

94.7 

254 

131.4 

323 

169.2 

392 

208.3 

461 

248.7 

186 

95.2 

255 

131.9 

324 

169.7 

393 

208.8 

462 

249.3 

187 

95.7 

256 

132.4 

325 

170.3 

394 

209.4 

463 

249.9 

188 

96.3 

257 

133.0         326 

170.9 

395 

210.0 

1048  APPENDIX  I. 

(2)  Methods  for  the  Determination  of  the  Copper  Contained  in  the  Precipitate 
of  Cuprous  Oxide  Obtained  in  the  Determination  of  Reducing  Sugars. 

(a)  METHOD  REQUIRING  REDUCTION  IN  HYDROGEN. — Filter  the  cuprous 
oxide  immediately  under  pressure  through  a  weighed  filtering  tube  made 
of  hard  glass.  The  asbestos  film  in  the  filtering  tube  is  supported  by  a  perfo- 
rated disk  or  cone  of  platinum,  and  should  be  washed  free  from  loose  fibres 
before  weighing,  and  moistened  previous  to  the  filtration.  The  tube  is  pro- 
vided with  a  detachable  funnel  during  the  filtration,  so  that  none  of  the  pre- 
cipitate accumulates  near  the  top,  where  it  could  be  removed  by  the  cork 
used  during  the  reduction  of  the  cuprous  oxide.  The  precipitate  is  all  trans- 
ferred to  tjie  filter  and  thoroughly  washed  with  hot  water,  following  the 
water  by  alcohol  and  ether  successively.  After  being  dried  the  tube  is  con- 
nected with  an  apparatus  for  supplying  a  continuous  current  of  dry  hydrogen, 
gently  heated  until  the  cuprous  oxide  is  completely  reduced  to  the  metallic 
state,  cooled  in  the  current  of  hydrogen,  and  weighed. 

(6)  ELECTROLYTIC  METHOD  BY  SOLUTION  IN  NITRIC  ACID  AND  SUBSE- 
QUENT EVAPORATION  WITH  EXCESS  OF  SULPHURIC  ACID. — The  filtration, 
after  reduction,  is  made  in  a  Gooch,  and  the  beaker  and  precipitate  thoroughly 
washed  with  hot  water  without  any  effort  to  transfer  the  precipitate  to  the 
filter.  Wash  the  asbestos  film  and  the  adhering  cuprous  oxide  into  the 
beaker  by  means  of  hot  dilute  nitric  acid.  After  the  copper  is  all  in  solution, 
refilter  through  a  Gooch  with  a  thin  film  of  asbestos  and  wash  thoroughly 
with  hot  water.  Add  10  c.c.  of  dilute  sulphuric  acid  (containing  200  c.c. 
of  sulphuric  acid — specific  gravity,  1  •  84 — per  litre)  and  evaporate  the  fil- 
trate on  the  steam-bath  until  the  copper  salt  has  largely  crystallized.  Heat 
carefully  on  a  hot  plate  or  over  a  piece  of  asbestos  board  until  the  evolution 
of  white  fumes  shows  that  the  excess  of  nitric  acid  is  removed.  Add  from 
8  to  10  drops  of  nitric  acid  (specific  gravity,  1  •  42)  and  rinse  into  a  platinum 
dish  of  from  100  to  125  c.c.  capacity.  Precipitate  the  copper  by  electrolysis.* 
Wash  thoroughly  with  water  before  breaking  the  current,  remove  the  dish 
from  the  circuit,  wash  with  alcohol  and  ether  successively,  dry  at  a  tempera- 
ture that  can  be  borne  by  the  hand,  and  weigh.  If  preferred,  the  electrolysis 
can  be  conducted  in  a  beaker,  the  copper  being  deposited  upon  a  weighed 
platinum  cylinder. 

(c)  ELECTROLYTIC  METHOD  BY  SOLUTION  IN  A  MIXTURE  OF  SULPHURIC 
AND  NITRIC  ACIDS. — The  filtration  and  washing  are  conducted  as  under 
(6).     Transfer  the  asbestos  film  from  the  crucible  to  the  beaker  by  means 
of  a  glass  rod  and  rinse  the  crucible  with  about  30  c.c.  of  a  boiling  mixture 
of  dilute  sulphuric  and  nitric  acids,  containing  65  c.c.  of  sulphuric  acid  (spe- 
cific gravity,  1-84)  and  50  c.c.  of  nitric  acid  (specific  gravity,  1 -42  per  litre). 
Heat  and  agitate  until  solution  is  complete:  filter  and  electrolyze  as  under  (6). 

(d)  ELECTROLYTIC  METHOD  BY  SOLUTION  TN  NITRIC  ACID. — Filter  and 
wash  as  under  (6).     Transfer  the  asbestos  film  and  adhering  oxide  to  the 
beaker.     Dissolve  the  oxide  still  remaining  in  the  crucible  by  means  of  2  c.c. 

*  Principles  and  Practice  of  Agricultural  Analysis,  in,  pp.  150-153. 


OFFICIAL   METHODS    OF    ANALYSIS.  1049 

of  nitric  acid  (specific  gravity,  1-42),  adding  it  with  a  pipette  and  receiving 
the  solution  in  the  beaker  containing  the  asbestos  film.  Rinse  the  crucible 
with  a  jet  of  water,  allowing  the  rinsings  to  flow  into  the  beaker.  Heat  the 
contents  of  the  beaker  until  the  copper  is  all  in  solution;  filter,  dilute  the 
filtrate  to  a  volume  of  100  c.c.,  or  more,  and  electrolyze.  According  to 
PORMANEK,  a  solution  of  copper  nitrate  can  be  successfully  electrolyzed  if 
it  contains  as  high  as  4  per  cent,  of  nitric  acid.  When  a  nitrate  solution  is 
electrolyzed,  the  first  washing  of  the  deposit  should  be  made  with  water 
acidulated  with  sulphuric  acid,  in  order  that  the  nitric  acid  may  be  all  re- 
moved before  the  current  is  interrupted. 

(e)  VOLUMETRIC  PERMANGANATE  METHOD  (ADOPTED  PROVISIONALLY). — 
Filter  and  wash  the  cuprous  oxide  as  described  for  method  (6).  Transfer 
the  asbestos  film  to  the  beaker,  add  about  30  c.c.  of  hot  water,  and  heat  the 
precipitate  and  asbestos  up  thoroughly.  Rinse  the  crucible  with  50  c.c.  of 
a  hot  saturated  solution  of  ferric  sulphate  in  20-per  cent,  sulphuric  acid,  re- 
ceiving the  rinsings  in  the  beaker  containing  the  precipitate.  After  the 
cuprous  oxide  is  dissolved,  wash  the  solution  into  a  large  ERLENMEYER 
flask  and  immediately  titrate  with  standard  solution  of  potassium  perman- 
ganate. One  c.c.  of  the  permanganate  solution  should  equal  0-010  gnn.  of 
copper.  In  order  to  determine  the  strength  of  this  solution  make  six  or 
more  determinations  with  the  same  sugar  solution,  titrating  one-half  of  the 
precipitates  obtained,  and  determining  the  copper  in  the  others  by  electroly- 
sis. The  average  weight  of  copper  obtained  by  electrolysis,  divided  by  the 
average  number  of  cubic  centimeters  of  permanganate  solutions  required 
for  the  titration,  is  equal  to  the  weight  of  copper  equivalent  to  1  cubic  centi- 
meter of  the  standard  permanganate  solution.  A  solution  standardized 
with  iron  or  oxalic  acid  will  give  too  low  results. 

5.  DETERMINATION  OF  SUCROSE. 

(a)    OPTICAL  METHODS. 

(1)  Preparation  of  Reagents. 

(a)  LEAD-SUBACETATE  SOLUTION. — Boil  an  aqueous  solution  of  lead 
acetate  with  an  excess  of  lead  oxide  (PbO)  for  half  an  hour  and  make  the 
filtered  solution  of  a  concentration  of  not  less  than  1  •  25  specific  gravity. 
Solid  lead  subacetate  may  be  substituted  for  the  normal  salt  and  oxide  in 
the  preparation  of  the  solution. 

(6)  ALUMINA  CREAM. — Prepare  a  cold  saturated  solution  of  alum  in 
water  and  divide  into  two  unequal  portions.  Add  a  slight  excess  of  ammo- 
nium hydrate  to  the  larger  portion,  and  then  add  by  degrees  the  remaining 
alum  solution  until  a  faintly  acid  reaction  is  secured. 

(2)  Determination. 

(a)  IN  SUGAR,  MASSECUITES,  ETC. — Place  in  a  tared  dish  the  normal 
weight  for  the  instrument  employed;  wash  into  a  100  c.c.  flask;  add  water 
until  the  volume  is  about  85  c.c.  When  the  crystals  are  all  dissolved  add 
sufficient  lead  subacetate  to  throw  down  all  precipitable  matter.  With 
molasses  and  massecuites  add  sufficient  acetic  acid  to  convert  the  subace- 


1050  APPENDIX   I. 

tate  into  the  neutral  acetate.  Make  up  to  the  mark,  using  a  little  ether 
spray  to  break  bubbles;  filter,  throwing  away  the  first  10  to  15  c.c.  ;  place 
in  the  observation  tube  and  polarize.  If  too  dark  to  read,  filter  through 
dry,  finely  powdered  bone  black,  rejecting  the  first  30  to  40  c.c. 

For  adjusting  the  polariscope,  graduating  flasks,  etc.,  the  usual  methods 
are  followed.* 

The  volumes  and  polarizations  should  be  made  as  nearly  as  possible  at 
the  temperature  at  which  the  instruments  are  graduated,  usually  17-5°. 
Variations  from  this  temperature  require  correction.  (See  Journ.  Amer. 
Chem.  Soc.,  May,  1899.) 

(6)  IN  JUICES,  ETC.  —  Transfer  by  means  of  a  pipette,  to  the  tared  sugar 
dish,  the  normal  or  multiple  normal  weight  of  the  juice  or  sirup  to  be  analyzed. 

In  the  cases  of  juices  and  thin  sirups,  the  contents  of  the  dish  are  at  once 
washed  into  the  100  c.c.  flask,  clarified,  completed  to  volume,  and  polarized 
as  in  (a). 

(6)    OPTICAL   METHODS   BY   INVERSION.  -  FOR   RAW   SUGAR,    MOLASSES,    ETC. 

(1)  Method  of  Clerget. 

Make  up  the  solution  as  above,  and  place  50  c.c.  of  the  filtrate  in  a  flask 
marked  at  50  and  55  c.c.  Fill  to  the  upper  mark  with  pure  fuming  hydro- 
chloric acid  and  mix  well;  place  in  water  and  heat  until  the  thermometer, 
with  the  bulb  as  near  the  center  of  the  sugar  solution  in  the  flask  as  possible, 
marks  68°,  consuming  about  fifteen  minutes  in  the  heating;  remove,  cool 
quickly  to  room  temperature,  and  polarize,  noting  the  temperature.  If 
the  sample  contained  originally  any  invert-sugar,  the  second  polarization 
should  be  made  at  approximately  the  same  temperature  as  the  first.  The 
percentage  of  sucrose  is  calculated  by  the  following  formula  : 
S  =  percentage  of  sucrose. 
a  =  first  polarization. 

b  =  second  polarization  (usually  to  the  left). 
a  —  b=  the  algebraic  difference  between  the  two  polarizations. 

t  —  temperature  of  observation. 
Then 


144  -- 

(c)    GRAVIMETRIC    METHOD. 

Determine  first  any  reducing  sugar  in  the  sample;  then  invert  the  su- 
crose according  to  (2)  under  optical  methods  by  inversion,  neutralize  the  free 
acid,  and  redetermine  the  reducing  sugar.  Deduct  the  percentage  of  reduc- 
ing sugar  obtained  at  first,  and  the  remainder  will  be  the  reducing  sugar 
derived  from  the  sucrose  ;  multiply  this  number  by  0-95  to  obtain  the  per- 
centage of  sucrose  in  the  sample. 

(2)  Creydt's  Method  for  Determining  Raffinose  and  Sucrose  Together. 

Let  Z  equal  the  percentage  of  sucrose,  R  the  percentage  of  raffinose, 
and  I  the  polarization  of  the  invert-sugar  at  20°.  When  the  normal  weight 

*  Principles  and  Practice  of  Agricultural  Analysis,  in,  pp.  93  et  seq. 


OFFICIAL   METHODS    OF   ANALYSIS.  1051 

of  26-048  gnn.  of  sucrose  polarizes  100°,  a  normal  weight  of  16-575  grm. 
of  hydrated  raffinose  will  polarize  100°.  After  inversion  at  20°  the  nor- 
mal weight  of  sucrose  will  polarize  —32°  and  the  normal  weight  of  raffinose 
50  •  7°.  Let  P  equal  the  direct  polarization  of  the  mixture  and  S  equal  the 
polarization  of  the  inverted  sucrose  and  raffinose  mixture  at  20°.  The  per- 
centages of  sucrose  and  raffinose  are  then  computed  by  the  following  f onnulae : 

1.  P  =  Z+1-57R 

2.  S  =  1-32  Z+  (1-57#)0- 493. 

S-0-493P        0-5070  P-I 


3.  Z 


0-827  0-827 


More  recent  researches  indicate  that  the  denominator  0  •  827  in  the  above 
formula  is  more  accurately  expressed  by  the  number  0-831.  The  inversion 
is  conducted  according  to  CLERGET'S  method.  According  to  HERZFELD, 
the  reading  of  pure  inverted  sugar  at  20°  is  —32-66°  V,  and  for  raffinose 
51-29°  V.  His  formula  for  calculating  the  sucrose  in  the  mixture  when 
the  polarizations  are  conducted  at  20°  is 

P-P' 


= 

0-8474 

In  the  above  formula  P'  equals  (z+0-0050Z+l-85#(r+  0-0020,  in 
which  z  and  r  represent  the  inversion  polarization  for  each  degree  of  the 
original  polarization  at  zero  for  sucrose  and  raffinose,  respectively,  and  t 
represents  the  temperature  of  observation. 

6.  DETERMINATION  OF  LACTOSE. 
(a)  OPTICAL  METHOD  FOR  THE  DETERMINATION  OF  LACTOSE  IN  MILK. 

(1)  Preparation  of  Reagents. 

(a)  ACID  MERCURIC  NITRATE.  —  Dissolve  mercury  in  double  its  <  -eight 
of  nitric  acid,  specific  gravity  1-42.  Add  to  the  solution  an  equal  volume 
of  water.  One  c.c.  of  this  reagent  is  sufficient  for  the  quantities  of  milk 
mentioned  below.  Larger  quantities  may  be  used  without  affecting  the 
results  of  polarization. 

(6)  MERCURIC  IODIDE  WITH  ACETIC  ACID.  —  Mix  33-2  grm.  of  potassium 
iodide,  13  •  5  grm.  of  mercuric  chloride,  20  c.c.  of  glacial  acetic  acid,  and  640 
c.c.  of  water. 

(2)  Apparatus. 

One  pipette  or  burette  of  100  c.c.  capacity,  graduated  in  cubic  centi- 
meters and  tenths  of  cubic  centimeters;  sugar  flasks,  marked  at  102  -4  c.c. 
when  a  polariscope  is  used  for  which  the  normal  weight  of  sucrose  is  16-19 
grm.,  marked  at  102-6  c.c.  when  the  normal  weight  of  sucrose  for  the  polari- 
scope used  is  26-048  grm.  ;  filters,  observation  tubes,  and  polariscope;  hydrom- 
eter and  cylinder;  thermometers. 

(3)  Determination. 

The  milk  should  be  at  a  constant  temperature  and  its  specific  gravity 
determined  with  a  delicate  hydrometer.  Where  greater  accuracy  is  required, 
a  pycnometer  is  used. 


1052 


APPENDIX   I. 


The  quantities  of  the  milk  measured  for  polarization  vary  with  the  specific 
gravity  of  the  milk  as  well  as  with  the  polariscope  used.  The  quantity  to 
be  measured  in  any  case  will  be  found  in  the  following  table: 


Volume  of  Milk  to  be  Used. 

Specific 
Gravity. 

For  Polariscopes 
of  which  the  Su- 

For Polariscopes 
of  which  the  Su- 

crose Normal 

crose  Normal 

Weight  is  16  19 

Weight  is  26  -048 

Grammes. 

Grammes. 

Cubic  Centimeters. 

Cubic  Centimeters. 

1-024 

60-0 

64-4 

1-026 

59-9 

64-3 

1-028 

59-8 

64-15 

1-030 

59-7 

64-0 

1-032 

59-6 

63-9 

1-034 

59-5 

63-8 

1-035 

59-35 

63-7 

Place  the  quantity  of  milk  indicated  in  the  table  in  a  flask  graduated  at 
102-4  c.c.  for  a  LAURENT  or  102-6  c.c.  for  a  VENTZKE  polariscope.  Add 
1  c.c.  of  mercuric-nitrate  solution  or  30  c.c.  of  mercuric-iodide  solution  (an 
excess  of  these  reagents  does  no  harm),  fill  to  the  mark,  agitate,  filter  through 
a  dry  filter,  and  polarize.  It  is  not  necessary  to  heat  before  polarizing.  In 
case  a  200  mm.  observation-tube  is  used,  the  polariscopic  reading  is  to  be 
divided  by  3  when  the  sucrose  normal  weight  of  the  instrument  employed  is 
16-19  grm.,  or  by  2  when  the  normal  weight  of  the  instrument  is  26-048 
grnio  When  a  400  mm.  tube  is  used,  these  divisors  become  6  and  4,  respect- 
ively. For  the  calculation  of  the  above  table,  the  specific  rotatory  power 
of  lactose  is  taken  as  52-53°,  and  the  corresponding  number  for  sucrose  as 
66-5°.  The  lactose  normal  weight  to  read  100°  on  the  sugar  scale  for  LAU- 
RENT instruments  is  20-496  grm.,  and  for  VENTZKE  instruments  32-975  grm. 
(6)  SOXHLET'S  METHOD  USING  ALKALINE  COPPER  SOLUTION. 
(1)  Preparation  of  the  Milk  Solution. 

Dilute  25  c.c.  of  the  milk  with  400  c.c.  of  water  and  add  10  c.c.  of  a  solu- 
tion of  copper  sulphate  of  the  strength  given  for  SOXHLET'S  modification 
of  FEHLING'S  solution,  page  1042;  add  about  7-5  c.c.  of  a  solution  of  potassium 
hydroxide  of  such  strength  that  one  volume  of  it  is  just  sufficient  to  completely 
precipitate  the  copper  as  suboxide  from  one  volume  of  the  solution  of  copper 
sulphate.  In  place  of  a  solution  of  potassium  hydroxide  of  this  strength, 
8«8  c.c.  of  a  half  normal  solution  of  sodium  hydroxide  may  be  used.  After 
the  addition  of  the  alkali  solution  the  mixture  must  still  have  an  acid  reaction 
and  contain  copper  in  solution  (p.  1042).  Fill  the  flask  to  the  mark,  agitate, 
and  filter  through  a  dry  filter. 

(2)  Determination. 

Place  50  c.c.  of  the  mixed  copper  reagent  in  a  beaker  and  heat  to  the 
boiling-point.  While  boiling  briskly  add  100  c.c.  of  the  milk,  prepared  as 


OFFICIAL    METHODS    OF   ANALYSIS. 


1053 


directed  in  the  preceding  paragraph,  and  boil  for  six  minutes.  Filter 
immediately  and  determine  the  amount  of  copper  reduced  by  one  of  the 
methods  given  under  reducing  sugars,  page  1048.  Obtain  the  weight  of 
lactose  equivalent  to  the  weight  of  copper  found  from  the  following  table : 

TABLE   FOR   THE    DETERMINATION    OF   LACTOSE.* 


Mgrm. 
of 
Copper. 

ofc 

lose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Lac- 
tose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Lac- 
tose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Lac- 
tose. 

Mgrm. 
of 
Copper. 

Mgrm. 
of  Lac- 
tose. 

100 

71.6 

160 

116.4 

220 

161.9 

280 

208.3 

340 

255.7 

101 

72.4 

161 

117.1 

221 

162.7 

281 

209.1 

341 

256.5 

102 

73.1 

162 

117.9 

222 

163.4  ! 

282 

209.9 

342 

257.4 

103 

73.8 

163 

118.6 

223 

164.2 

283 

210.7 

343 

258.2 

104 

74.6 

164 

119.4 

224 

164.9 

284 

211.5 

344 

259.0 

105 

75.3 

165 

120.2 

225 

165.7 

285 

212.3 

345          259.8 

106 

76.1 

166 

120.9 

226 

166.4 

286 

213.1 

346          260.6 

107 

76.8 

167 

121.7 

227 

167.2 

287 

213.9 

347           261.4 

108 

77.6 

168 

122.4 

228 

167.9 

288 

214.7 

348          262.3 

109 

78.3 

169 

123.2 

229 

168.6  i 

289 

215.5 

349 

263.1 

110 

79.0 

170 

123.9 

230 

169.4  1 

290 

216.3 

350 

263.9 

111 

79.8 

171 

124.7 

231 

170.1 

291 

217.1 

351           264.7 

112 

80.5 

172 

125.5 

232 

170.9  ! 

292 

217.9 

352 

265.5 

113 

81.3 

173 

126.2 

233 

171.6 

293 

218.7 

353          266.3 

114 

82.0 

174 

127.0 

234 

172.4 

294 

219.5 

354          267.2 

115 

82.7 

175 

127.8 

235 

173.1 

295 

220.3 

355          268.0 

116 

83.5 

176 

128.5 

236 

173.9 

296 

221.1 

356 

268.8 

117 

84.2 

177 

129.3 

237 

174.6 

297 

221.9 

357           269.6 

118 

85.0 

178 

130.1 

238 

175.4 

298 

222.7 

358          270.4 

119 

85.7 

179 

130.8 

239 

176.2 

299 

223.5 

359          271.2 

120 

86.4 

180 

131.6 

240 

176.9 

300 

224.4 

360          272.1 

121 

87.2 

181 

132.4 

241 

177.7 

301 

225.2 

361           272.9 

122 

87.9 

182 

133.1 

242 

178  .  5 

302 

225.9 

362 

273.7 

123 

88.7 

183 

133.9 

243 

179.3 

303 

226.7 

363 

274.5 

124 

89.4 

184 

134.7 

244 

180.1 

304 

227.5 

364 

275.3 

125 

90.1 

185 

135.4 

245 

180.8 

305 

228.3 

365 

276.2 

126 

90.9 

186 

136.2 

246 

181.6 

306 

229.1 

366 

277.1 

127 

91.6 

187 

137.0 

247 

182.4 

307 

229.8 

367 

277.9 

128 

92.4 

188 

137.7 

248 

183.2 

308 

230.6 

368 

278.8 

129 

93.1 

189 

138.5 

249 

184.0 

309 

231.4 

369 

279.6 

130 

93.8 

190 

139.3 

250 

184.8 

310 

232.2 

370 

280.5 

131 

94.6 

191 

140.0 

251 

185.5 

311 

232.9 

371 

281.4 

132 

95.3 

192 

140.8 

252 

186.3 

312 

233.7 

372 

282.2 

133 

96.1 

193 

141.6 

253 

187.1 

313 

234.5 

373 

283.1 

134 

96.9 

194 

142.3 

254 

187.9 

314 

235.3 

374          283.9 

135 

97.6 

195 

143.1 

255 

188.7 

315 

236.1 

375          284.8 

136 

98.3 

196 

143.9 

256 

189.4 

316 

236.8 

!      376          285.7 

137 

99.1 

197 

144.6 

257 

190.2 

317 

237.6 

377           286.5 

138 

99.8 

198 

145.4 

258 

191.0 

318 

238.4 

378          287.4 

139 

100.5 

199 

146.2 

259 

191.8 

319 

239.2 

379          288.2 

140 

101.3 

200 

146.9 

260     ' 

192.5 

320 

240.0 

380          289.1 

141 

102.0 

201 

147.7 

261 

193.3 

321 

240.7 

381           289.9 

142 

102.8 

202 

148.5 

262 

194.1 

322 

241.5 

382          290.8 

143 

103.5 

203 

149.2 

263 

194.9 

323 

242.3 

383          291.7 

144 

104.3 

204 

150.0 

264 

195.7 

324 

243.1 

384 

292.5 

145 

105.1 

205 

150.7 

265 

196.4 

325 

243.9 

;      385 

293.4 

146 

105.8 

206 

151.5 

266 

197.2 

326 

244.6 

386 

294.2 

147 

106.6 

207 

152.2 

,     267 

198.0 

327 

245.4 

;      387 

295  1 

148 

107.3 

208 

153.0 

268 

198.8 

328 

246.2 

388 

296.0 

149 

108.1 

209 

153.7 

269 

199.5 

329 

247.0 

389 

296  8 

150 

108.8 

210 

154.5 

270 

200.3 

330 

247.7 

390          297.7 

151 

109.6 

211 

155.2 

271 

201.1 

331 

248.5 

391           298.5 

152 

110.3 

212 

156.0 

272        201.9 

332 

249.2 

392     1      299  4 

153 

111.1 

213 

156.7 

273     I   202.7 

333 

250.0 

393          300.3 

154 

111.9 

214 

157.5 

274         203.5 

334 

250.8 

394     i      301  .  1 

155 

112.6 

215 

158.2 

275 

204.3 

335 

251.6 

395          302  0 

156 

113.4 

216 

159.0 

276        205.1 

336 

252.5 

396          302.8 

157 

114.1 

217 

159.7 

277         205.9 

337 

253.3 

397           303.7 

158 

114.9 

218 

160.4 

278        206.7 

338 

254.1 

398          304  6 

159 

115.6 

219 

161.2 

279        207.5 

339 

254.9 

?P9          305.4 

400 

306.3 

*  Principles  and  Practice  of  Agricultural  Analysis,  in,  pp.  163-165. 


1054  APPENDIX   I, 


IV.    METHODS  FOR  THE  ANALYSIS  OF  DAIRY  PRODUCTS. 
1.  BUTTER  ANALYSIS. 

(«)    PREPARATION   OF  SAMPLE. 

If  large  quantities  of  butter  are  to  be  sampled,  a  butter  trier  or  sampler 
may  be  used.  The  portions  thus  drawn,  abo.ut  500  grm.  are  to  be  perfectly 
melted  in  a  closed  vessel  at  as  low  a  temperature  as  possible,  and  when  melted 
the  whole  is  to  be  shaken  violently  for  some  minutes  till  the  mass  is  homo- 
geneous, and  sufficiently  solidified  to  prevent  the  separation  of  the  water 
and  fat.  A  portion  is  then  poured  into  the  vessel  from  which  it  is  to  be 
weighed  for  analysis,  and  should  nearly  or  quite  fill  it.  This  sample  should 
be  kept  in  a  cold  place  till  analyzed. 

(6)  DETERMINATION    OF  WATER. 

From  1-5  to  2-5  grm.  of  the  sample  are  dried  to  constant  weight  at  the 
temperature  of  boiling  water  in  a  dish  with  flat  bottom,  having  a  surface 
of  at  least  20  square  centimeters. 

The  use  of  clean  dry  sand  or  asbestos  with  the  butter  is  admissible,  and 
is  necessary  if  a  dish  with  round  bottom  be  employed. 

(C)  DETERMINATION  OF  ETHER  EXTRACT. 

(1)  Direct  Method. 

Water  may  be  determined  by  drying  the  butter  on  asbestos  or  sand,  and 
the  fat  extracted  by  anhydrous  alcohol-free  ether.  The  extract,  after  evapora- 
tion of  the  ether,  is  heated  to  constant  weight  at  the  temperature  of  boiling 
water  and  weighed. 

(2)  Indirect  Method. 

The  dry  butter  from  the  water  determination  is  dissolved  in  the  dish 
with  absolute  ether,  or  with  76°  petroleum  ether.  The  contents  of  the  dish 
are  then  transferred  to  a  weighed  Gooch  with  the  aid  of  a  wash-bottle  filled 
with  the'  solvent,  and  are  washed  till  free  from  fat.  The  crucible  and  con- 
tents are  heated  at  the  temperature  of  boiling  water  till  the  weight  is  constant. 
The  weight  of  fat  is  calculated  from  the  data  obtained. 

(d)  DETERMINATION  OF  CASEIN,  ASH,  AND  CHLORINE. 

The  crucible  containing  the  residue  from  the  fat  determination  is  covered 
and  heated,  gently  at  first,  gradually  raising  the  temperature  to  just  below 
redness.  The  cover  may  then  be  removed  and  the  heat  continued  till  the 
contents  of  the  crucible  are  white.  The  loss  in  weight  of  the  crucible  and 
contents  represents  casein,  and  the  residue  in  the  crucible  mineral  matter. 
In  this  mineral  matter,  dissolved  in  water  slightly  acidulated  with  nitric 
acid,  chlorine  may  be  determined  gravimetrically  with  silver  nitrate,  or 
volumetrically,  using  potassium  chromate  as  an  indicator. 

(e)  DETERMINATION    OF    SALT. 

Weigh  in  a  counterpoised  beaker  from  5  to  10  grm.  of  the  butter.  The 
butter  is  placed,  in  portions  of  about  1  grm.  at  a  time,  in  the  beaker,  these 


OFFICIAL    METHODS   OF   ANALYSIS.  1055 

portions  being  taken  from  different  parts  of  the  sample.  Hot  water  is  added 
(about  20  c.c.)  to  the  beaker  containing  the  butter,  and  after  it  has  melted 
the  liquid  is  poured  into  the  bulb  of  a  separating  funnel.  The  stopper  is 
inserted,  and  the  contents  shaken  for  a  few  moments.  After  standing  until 
the  fat  has  all  collected  on  top  of  the  water,  the  stopcock  is  opened  and  the 
water  is  allowed  to  run  into  an  ERLENMEYER  flask,  care  being  exercised 
to  let  none  of  the  fat  globules  pass.  Hot  water  is  again  added  to  the  beaker, 
and  the  extraction  is  repeated  from  10  to  15  times,  using  each  time  from  10 
to  20  c.c.  of  water.  The  resulting  washings  contain  all  but  a  mere  trace  of 
the  sodium  chloride  originally  present  in  the  butter.  The  sodium  chloride 
is  determined  in  the  filtrate  by  a  standard  solution  of  silver  nitrate,  using 
a  few  drops  of  *  solution  of  potassium  chromate  as  an  indicator. 

(/)  DETERMINATION    OF   VOLATILE   ACIDS. 

(1)  Preparation  of  Reagents. 

(a)  CAUSTIC-SODA  SOLUTION. — One  hundred  grm.  of  sodium  hydroxide 
are  dissolved  in  100  c.c.  of  distilled  water.  The  caustic  soda  should  be  as  free 
as  possible  from  carbonates  and  be  preserved  out  of  contact  with  the  air. 

(6)  CAUSTIC-POTASH  SOLUTION. — Dissolve  100  grm.  of  the  purest  potassium 
hydroxide  in  58  grm.  of  hot  distilled  water.  Allow  to  cool  in  a  stoppered 
vessel,  decant  the  clear  solution,  and  preserve  from  contact  with  the  air. 

(c)  ALCOHOL,  of  about  95-per  cent.,  redistilled  with  caustic  soda. 

(d)  ACID. — Solution  of  sulphuric  acid  containing  200  c.c.  of  strongest 
sulphuric  acid  in  1000  c.c.  of  water. 

(e)  BARIUM  HYDROXIDE. — An  accurately  standardized,   approximately 
decinormal  solution  of  barium  hydroxide. 

(/)  INDICATOR. — Dissolve  1  grm.  of  phenolphtalein  in  100  c.c.  of  alcohol. 

(g)  GLYCERIN-SODA^SOLUTION. — Add  20  c.c.  of  a  50-per  cent,  solution  of 
sodium  hydroxide  to  180  c.c.  pure  concentrated  glycerin.  The  soda  must 
be  as  free  from  carbonate  as  possible. 

(2)  Apparatus. 

(a)  SAPONIFICATION  FLASKS,  of  from  250  to  300  c.c.  capacity  of  hard,  well- 
annealed  glass,  capable  of  resisting  the  tension  of  alcohol  vapor  at  100°. 

(6)  A  PIPETTE  graduated  to  deliver  40  c.c. 

(c)  DISTILLING  APPARATUS. 

(d)  BURETTE. — An  accurately  calibrated  burette  reading  to  tenths  of  a 
cubic  centimeter. 

(3)  Determination. 

(a)  WEIGHING  THE  FAT. — The  butter  or  fat  to  be  examined  should  be 
melted  and  kept  in  a  dry,  warm  place  at  about  60°  for  two  or  three  hours, 
until  the  water  and  curd  have  entirely  deposited.  The  clear,  supernatant 
fat  is  poured  off  and  filtered  through  a  dry  filter-paper  in  a  jacketed  funnel 
containing  boiling  water.  Should  the  filtered  fat,  in  a  fused  state,  not  be 
perfectly  clear,  it  must  be  filtered  a  second  time. 

The  saponification  flasks  are  prepared  by  thoroughly  washing  with  water, 
alcohol,  and  ether,  wiping  perfectly  dry  on  the  outside,  and  heating  for  one 
hour  at  the  temperature  of  boiling  water  The  flasks  should  then  be  placed 


1056 


APPENDIX    I. 


in  a  tray  by  the  side,  of  the  balance  and  covered  with  a  silk  handkerchief  until 
they  are  perfectly  cool.  They  must  not  be  wiped  with  a  silk  handkerchief 
within  fifteen  or  twenty  minutes  of  the  time  they  are  weighed.  The  weight 
of  the  flasks  having  been  accurately  determined,  they  are  charged  with  the 
melted  fat  in  the  following  way : 

A  pipette  with  a  long  stem,  marked  to  deliver  5-75  c.c.,  is  warmed  to 
a  temperature  of  about  50°.  The  fat,  having  been  poured  back  and  forth 
once  or  twice  into  a  dry  beaker  in  order  to  thoroughly  mix  it,  is  taken  up 
in  the  pipette  and  the  nozzle  of  the  pipette  carried  to  near  the  bottom  of 
the  flask,  having  been  previously  wiped  to  remove  any  adhering  fat,  and 
5-75  c.c.  of  fat  are  allowed  to  flow  into  the  flask.  After  the  flasks  have  been 
charged  in  this  way  they  should  be  recovered  with  the  silk  handkerchief 
and  allowed  to  stand  fifteen  or  twenty  minutes,  when  they  are  again  weighed. 

The  fat,  prepared  as  above, 
may  also  be  weighed  into  the 
saponification  flask  from  a 
weighing  tube  marked  to  con- 
tain 5-75  c.c. 

(6)  SAPONIFICATION. 

(bj  In    the    Presence 

of   Alcohol. — Ten    c.c.    of 

95-per   cent,  alcohol    are 

added  to  the  fat  in  the 

flask,  and  then  2  c.c.  of 

the  caustic-soda  solution. 

A    soft    cork    stopper    is 

inserted  in  the  flask  and 

tied   down   with   a   piece 

of     twine.     The     saponi- 
fication is  then  completed 

by  placing  the  flask  upon 

the  water-  or  steam-bath 

(Fig.   1).     The  flask  dur- 
ing    the      saponification, 

which    should    last     one 

hour,    should    be    gently 

rotated     from     time     to 

time,    being    careful    not 

to   project   the   soap   for 

any  distance  up  its  sides. 

At  the  end  of  an  hour  the  flask,  after  having  been  cooled  to  near 

the  room  temperature,  is  opened. 

(&2)  Optional  Method  of  Saponification. — Using  the  same  amounts 

of  alkali  and  alcohol  as  described  above,  the  saponification  may  be 

conducted  on  a  steam-  or  water-bath,  the  flask  being  connected  with 

a  reflux  condenser  consisting  of  a  glass  tube  of  not  less  than  1  metre  in 

length,  or  of  a  shorter  condenser  cooled  by  a  current  of  water. 


FIG.  1.— Saponification  flask. 


OFFICIAL   METHODS    OF   ANALYSIS.  1057 

(&,j)  Optional  Method — Without  the  use  of  Alcohol. — To  avoid  the 
danger  of  loss  from  the  formation  of  ethers,  and  the  trouble  of  removing 
the  alcohol  after  saponification,  the  fat  may  be  saponified  with  a  solu- 
tion of  caustic  potash  in  a  closed  flask  without  using  alcohol  The 
operation  is  carried  on  exactly  as  indicated  above  for  saponification 
in  the  presence  of  alcohol,  using  caustic-potash  solution  instead  of 
caustic  soda,  and  omitting  the  operation  for  volatilizing  the  alcohol. 
For  the  saponification,  use  2  c.c.  of  the  caustic-potash  solution,  which 
are  poured  on  the  fat  after  it  has  solidified  in  the  flask.  Great  care 
must  be  taken  that  none  of  the  fat  be  allowed  to  rise  on  the  sides  of 
the  saponifying  flask  to  a  point  where  it  cannot  be  reached  by  the 
alkali.  During  the  process  of  saponification  the  flask  can  only  be 
very  gently  rotated  in  order  to  avoid  the  difficulty  mentioned.  This 
process  is  not  recommended  with  any  apparatus  except  a  closed  flask 
with  round  bottom.  Potash  is  used,  instead  of  soda,  so  as  to  form 
a  softer  soap,  and  thus  allow  a  more  perfect  saponification. 

The  saponification  may  also  be  conducted  as  follows:  The  alkali 
and  fat  in  the  melted  state  are  shaken  vigorously  in  the  saponifica- 
tion flask  until  a  complete  emulsion  is  secured.  The  rest  of  the  oper- 
ation is  then  conducted  as  above. 

(64)  LEFFMANN-BEAM  METHOD. — About  5  grm.  of  fat  are  placed  in  a 
ilask  and  20  c.c.  of  the  glycerin-soda  solution  are  added.  The  flask  is  heated 
until  complete  saponification  takes  place,  as  evidenced  by  the  mixture 
becoming  perfectly  clear,  the  whole  operation  requiring  less  than  five  minutes. 
The  soap  is  dissolved  in  135  c.c.  of  water,  preferably  previously  boiled,  the 
water  being  added  at  first  drop  by  drop  to  prevent  foaming;  5  c.c.  of  the 
dilute  sulphuric  acid  are  added,  and  the  distillation  is  begun  at  once  with- 
out previous  melting  of  the  free  fatty  acids. 

(c)  REMOVAL  OF  THE  ALCOHOL. — (When  method  (6^  has  been  used  for 
saponification.) 

The  stoppers  having  been  laid  loosely  in  the  mouth  of  the  flask,  the  alcohol 
is  removed  by  dipping  the  flask  into  a  steam-bath.  The  steam  should  cover 
the  whole  of  the  flask  except  the  neck.  After  the  alcohol  is  nearly  removed, 
frothing  may  be  noticed  in  the  soap,  and  to  avoid  anjr  loss  from  this  cause 
or  any  creeping  of  the  soap  up  the  sides  of  the  flask,  it  should  be  removed 
from  the  bath  and  shaken  to  and  fro  until  the  frothing  disappears.  The 
last  traces  of  alcohol  vapor  may  be  removed  from  the  flask  by  waving  it 
briskly,  mouth  down,  to  and  fro. 

(d)  DISSOLVING  THE  SOAP. — After  the  removal  of  the  alcohol  the  soap 
should  be  dissolved  by  adding  135  c.c.  of  recently  boiled  distilled  water,  or 
132  c.c.  when  method  (62)  has  been  used  for  saponification,  warming  on  the 
steam-bath  with  occasional  shaking  until  solution  of  the  soap  is  complete. 

(e)  SETTING  FREE  THE  FATTY  ACIDS. — When  the  soap  solution  has  cooled 
to  about  60°  or  70°,  the  fatty  acids  are  separated  by  adding  5  c.c.  of  the 
dilute  sulphuric  acid  solution  mentioned  above,  or  8  c.c.  when  method  (62) 
has  been  used  for  saponification. 

(f)  MELTING  THE  FATTY  ACID  EMULSION. — The  flask  should  now  be 


1058 


APPENDIX   I. 


restoppered  as  in  the  first  instance,  and  the  fatty  acid  emulsion  melted  by 
replacing  the  flask  on  the  steam-bath.  According  to  the  nature  of  the  fat 
examined,  the  time  required  for  the  fusion  of  the  fatty  acid  emulsions  may 
vary  from  a  few  minutes  to  several  hours. 

(0)  THE  DISTILLATION. — After  the  fatty  acids  are  completely  melted, 
which  can  be  determined  by  their  forming  a  transparent  oily  layer  on  the 
surface  of  the  water,  the  flask  is  cooled  to  room  temperature,  and  a  few  pieces 
of  pumice  stone  added.  The  pumice  stone  is  prepared  by  throwing  it,  at  a 
white  heat,  into  distilled  water,  and  keeping  it  under  water  until  used.  The 
flask  is  connected  with  a  glass  condenser  (Fig.  2),  slowly  heated  with  a  naked 


FIG.  2. — Apparatus  for  the  distillation  of  volatile  acids. 

flame  until  ebullition  begins,  and  then  the  distillation  continued  by  regu- 
lating the  flame  in  such  a  way  as  to  collect  110  c.c.  of  the  distillate  in,  as 
nearly  as  possible,  thirty  minutes.  The  distillate  should  be  received  in  a 
flask  accurately  graduated  at  110  c.c. 

(h)  TITRATION  OF  THE  VOLATILE  ACIDS.— The  110  c.c.  of  distillate,  after 
thorough  mixing,  are  filtered  through  perfectly  dry  filter-paper,  100  c.c.  of 
the  filtered  distillate  poured  into  a  beaker  holding  from  200  to  250  c.c.,  0-5 
c.c.  phenolphtalein  solution  added,  and  decinormal  barium  hydrate  run 
in  until  a  red  color  is  produced.  The  contents  of  the  beaker  are  then  returned 
to  the  measuring  flask  to  remove  any  acid  remaining  therein,  poured  again 
into  the  beaker,  and  the  titration  continued  until  the  red  color  produced 
remains  apparently  unchanged  for  two  or  three  minutes.  The  number  of 
cubic  centimetres  of  decinormal  barium  hydroxide  required  should  be 
increased  by  one-tenth. 


OFFICIAL   METHODS    OF   ANALYSIS.  1059 

(g)    DETERMINATION    OF   SOLUBLE   AND   INSOLUBLE   ACIDS. 

(1)  Preparation  of  Reagents. 

(a)  STANDARD  CAUSTIC-SODA  SOLUTION. — A  decinormal  solution  of 
caustic  soda  is  used.  Each  cubic  centimetre  contains  0-004  grm.  of  sodium 
hydroxide  and  neutralizes  0-0088  grm.  of  butyric  acid  (C4H8O2). 

(6)  ALCOHOLIC  POTASH  SOLUTION. — Dissolve  40  grm.  of  caustic  potash 
in  1  litre  of  95-per  cent,  redistilled  alcohol.  The  solution  must  be  clear  and 
the  potassium  hydroxide  free  from  carbonates. 

(c)  STANDARD  ACID  SOLUTION. — Prepare  accurately  a  half-normal  solu- 
tion of  hydrochloric  acid. 

(d)  INDICATOR. — Dissolve  1  grm.  of  phenolphtalein  in  100  c.c.  of  95- 
per  cent,  alcohol. 

(2)  Determination. 

(a)  SOLUBLE  ACIDS. — About  5  grm.  of  the  sample  are  placed  in  a  saponi- 
fication  flask,  50  c.c.  of  the  alcoholic  potash  solution  added,  and  the  flask 
stoppered  and  placed  in  the  steam-bath  until  the  fat  is  entirely  saponified. 
The  operation  may  be  facilitated  by  occasional  agitation.  The  alcoholic 
potash  is  always  measured  with  the  same  pipette,  and  uniformity  further 
secured  by  allowing  it  to  drain  the  same  length  of  time  (thirty  seconds). 
Two  or  three  blank  experiments  are  conducted  at  the  same  time. 

In  from  five  to  thirty  minutes,  according  to  the  nature  of  the  fat,  the 
liquid  will  appear  perfectly  homogeneous,  and  when  this  is  the  case  the 
saponification  is  complete  and  the  flask  is  removed  and  cooled.  When 
sufficiently  cool,  the  stopper  is  removed  and  the  contents  of  the  flask  rinsed 
with  a  little  95-per  cent,  alcohol  into  an  ERLENMEYER  flask  of  about  200  c.c. 
capacity,  which  is  placed  on  the  steam-bath  together  with  the  blanks  until 
the  alcohol  is  evaporated. 

Titrate  the  blanks  with  half-normal  hydrochloric  acid,  using  phenolphta- 
lein as  indicator.  Then  run  into  each  of  the  flasks  containing  the  fatty  acids 
1  c.c.  more  of  the  half-normal  hydrochloric  acid  than  is  required  to  neutralize 
the  potash  in  the  blanks.  The  flask  is  then  connected  with  a  reflux  con- 
denser and  placed  on  the  steam-bath  until  the  separated  fatty  acids  form 
a  clear  stratum  on  the  upper  surface  of  the  liquid.  The  flask  and  contents 
are  then  cooled  in  ice  water. 

The  fatty  acids  having  quite  solidified,  the  liquid  contents  of  the  flask 
are  poured  through  a  dry  filter  into  a  litre  flask,  care  being  taken  not  to 
break  the  cake.  Between  200  and  300  c.c.  of  water  are  next  brought  into 
the  flask,  the  cork  with  its  condenser  reinserted,  and  the  flask  placed  on 
the  steam-bath  until  the  cake  of  acids  is  thoroughly  melted.  During  the 
melting  of  the  cake  of  fatty  acids  the  flask  should  occasionally  be  agitated 
with  a  circulatory  motion  in  such  a  way  that  its  contents  are  not  allowed 
to  touch  the  cork.  When  the  fatty  acids  have  again  separated  into  an  oily 
layer,  the  flask  and  its  contents  are  cooled  hi  ice  water  and  the  liquid  filtered 
through  the  same  filter  into  the  same  litre  flask  as  before.  This  treatment 
with  hot  water,  followed  by  cooling  and  filtration  of  the  wash  water,  is 
repeated  three  times,  the  washings  being  added  to  the  first  filtrate.  The 


1060  APPENDIX   I. 

mixed  washings  and  filtrate  are  made  up  to  1  litre,  and  100  c.c.  in  duplicate 
are  titrated  with  decinormal  sodium  hydroxide.  The  number  of  cubic  centi- 
meters of  sodium  hydroxide  required  for  each  100  c.c.  of  the  filtrate  is  mul- 
tiplied by  10  to  correct  for  the  total  volume.  The  number  so  obtained 
represents  the  volume  of  decinormal  sodium  hydroxide  neutralized  by  the 
soluble  fatty  acids  of  the  butter  fat,  plus  that  corresponding  to  the  excess 
of  the  standard  acid  used,  viz.,  1  c.c.  The  number  is  therefore  to  be  dimin- 
ished by  5,  corresponding  to  the  excess  of  1  c.c.  of  half -normal  acid.  This 
corrected  volume  multiplied  by  0-0088  gives  the  weight  of  butyric  acid  in 
the  amount  of  butter  fat  saponified. 

(6)  INSOLUBLE  ACIDS. — The  flask  containing  the  cake  of  insoluble  fatty 
acids  from  (a),  and  the  paper  through  which  the  soluble  fatty  acids  have 
been  filtered,  are  allowed  to  drain  and  dry  for  twelve  hours,  when  the  cake, 
together  with  as  much  of  the  fatty  acids  as  can  be  removed  from  the  filter- 
paper,  are  transferred  to  a  weighed  glass  evaporating  dish.  The  funnel, 
with  the  filter,  is  then  placed  in  an  ERLENMEYER  flask,  and  the  paper  thor- 
oughly washed  with  absolute  alcohol.  The  flask  is  rinsed  with  the  washings 
from  the  filter-paper,  then  with  pure  alcohol,  and  these  transferred  to  the 
evaporating  dish.  The  dish  is  placed  on  the  steam-bath  until  the  alcohol 
is  evaporated,  dried  for  two  hours  at  100°,  cooled  in  a  desiccator,  and  weighed. 
It  is  again  placed  in  the  air-bath  for  another  two  hours,  cooled  as  before, 
and  weighed.  If  there  be  any  considerable  decrease  in  weight,  reheat  two 
hours  and  weigh  again.  This  gives  the  weight  of  insoluble  fatty  acids,  from 
which  the  percentage  is  easily  calculated. 

(k~)  DETERMINATION  OF  SAPONIFICATION  EQUIVALENT  (KOETTSTORFER 

NUMBER). 

(1)  Preparation  of  Reagents. 

The  reagents  used  in  this  determination  are  the  same  as  those  given  under 
(g)  (1),  page  1059,  except  that  the  standard  caustic  soda  solution  is  not 
required. 

(2)  Determination. 

Between  1  and  2  grm.  of  the  sample  are  placed  in  a  saponification  flask 
(2)  (a),  page  1055,  25  c.c.  of  the  alcoholic  potash  solution  added,  and  the  flask 
stoppered  and  placed  in  the  steam-bath  until  the  fat  is  entirely  saponified. 
The  operation  may  be  facilitated  by  occasional  agitation.  The  alcoholic 
potash  is  always  measured  with  the  same  pipette,  and  uniformity  further 
secured  by  allowing  it  to  drain  the  same  length  of  time  (thirty  seconds). 
Two  or  three  blank  experiments  are  conducted  at  the  same  time.  As  soon 
as  the  saponification  is  complete  the  flasks  are  removed  from  the  bath,  cooled, 
and  the  contents  are  titrated  with  the  half -normal  hydrochloric  acid,  using 
phenolphtalein  as  indicator.  The  KOETTSTORFER  number  (milligrammes  of 
potassium  hydroxide  required  to  saponify  1  grm.  of  the  fat)  is  obtained  by 
subtracting  the  number  of  cubic  centimeters  of  hydrochloric  acid  necessary 
to  neutralize  the  alkali  after  saponification  from  the  number  necessary  to 
neutralize  the  blank,  multiplying  the  result  by  28-06,  and  dividing  the  product 
by  the  number  of  grammes  of  fat  used  for  the  determination. 


OFFICIAL    METHODS   OF   ANALYSIS. 


1061 


(l)    DETERMINATION  OF   THE   REFRACTIVE    INDEX. 

The  refractive  index  is  conveniently  determined  by  ABBE'S  refractometer 
(fig.  3).  *  A  piece  of  fine  tissue-paper,  3  cm.  in  length  by  1  -5  cm.  in  width,  is 

*  A  later  and  much  improved  model  of  the  ABBE  instrument  in  which  arrangements 
are  made  for  controlling  the  temperature,  the  weakness  of  the  older  form,  is  described 
in  BENEDIKT  (Anal,  der  Fette  it.  Wach.,  3d  ed.,  p.  105).  For  the  mode  of  using  the  ZEISS 
butyro-refractometer  (WILEY,  Prin.  and  Prac.  Agr.  Anal.,  ni,  pp.  339-341)  which  is  here 
shown,  proceed  as  follows:  Place  the  instrument  upon  a  table  where  diffuse  daylight  or 
any  form  of  artificial  light  can  be  readily  admitted  for  illumination.  Supply  through 


ZEISS'  butyro-refractometer. 

nozzle  D  a  stream  of  water  of  constant  temperature.  Then  open  the  prism  casing  by 
giving  to  the  pin  F  a  half  turn.  The  surfaces  of  the  prism  must  now  be  cleaned  with 
the  greatest  care,  which  is  best  done  by  applying  soft  linen  moistened  with  ether.  Now 
melt  the  sample  of  fat  and  pour  the  clear  fat  through  a  filter,  allowing  the  first  two  or 
three  drops  to  fall  on  the  surface  of  the  prism  contained  in  casing  B  (oils  must  be  filtered 
if  turbid).  For  this  purpose  the  apparatus  should  be  raised  with  the  left  hand,  so  as  to 
place  the  prism  surface  in  a  horizontal  position.  Then  press  B  against  A  and  bring  F 
back  into  its  original  position  by  turning  it  in  the  opposite  direction.  Adjust  the  mirror 
until  it  gives  the  sharpest  reading.  If  the  reading  be  not  distinct  after  running  water 
of  a  const  ant  temperature  thro  ugh  the  instrument  for  some  time,  the  fat  is  not  evenly  dis- 
tributed on  the  surfaces  of  the  prism  and  the  process  must  be  repeated.  The  instrument 
should  be  carefully  adjusted  by  means  of  the  standard  fluid,  which  is  supplied.  As  the 


1062 


APPENDIX    I. 


placed  on  the  lower  of  the  two  glass  prisms  of  the  apparatus.  Two  or  three 
drops  of  oil  or  fat  are  placed  upon  the  paper,  and  the  upper  prism  carefully 
fixed  in  position,  so  as  not  to  move  the  paper  from  its  place.  In  charging 
the  apparatus  with  the  oil  in  this  way  it  is  placed  in  a  horizontal  position. 
After  the  paper  disk  holding  the  fat  is  secured,  by  replacing  the  upper  prism, 

the  apparatus  is  placed  in  its 
normal  position  and  the  index 
moved  until  the  light  directed 
through  the  apparatus  by  the 
mirror  shows  the  field  of  vision 
divided  into  dark  and  light  por- 
tions. The  dispersion  apparatus 
is  turned  until  the  rainbow  colors 
on  the  line  between  the  dark  and 
light  field  have  disappeared.  Be- 
fore doing  this,  however,  the  tele- 
scope is  so  adjusted  as  to  bring 
the  cross  lines  of  the  field  of  vision 
distinctly  into  focus.  The  index 
of  the  apparatus  is  now  moved 
back  and  forth  until  the  dark  edge 
of  the  field  of  vision  falls  exactly 
in  the  intersection  of  the  cross 
lines.  The  refractive  index  of  the 
fat  under  examination  is  then 
read  directly  upon  the  scale  by 

index  of  refraction  is  greatly  affected  by  temperature,  care  must  be  used  to  keep  it  con- 
stant. 

The  following  table  can  be  used  to  convert  the  degreas  of  the  instrument  into  refrac- 
tive indices: 

BUTYRO-REFRACTOMETER   READINGS   AND    INDICES    OF   REFRACTION. 
Winton,  Conn.,  Expt.  Sta.  Rept.,  1900,  pt.  2,  p.  143. 


FIG.  3. — ABBE'S  refractometer. 


Reading. 

Index  of 
Refrac- 
tion. 

Reading. 

Index  of 
Refrac- 
tion. 

Reading. 

Index  of 
Refrac- 
tion. 

Reading. 

Index  of 
Refrac- 
tion. 

40.0 

1.4524 

50.0 

1.4593 

60.0 

1.4659 

70.0 

.4723 

40.5 

1  .4527 

50.5 

1.4596 

60.5 

1.4662 

70.5 

.4726 

41.0 

1.4531 

51.0 

1.4600 

61.0 

1.4665 

71.0 

.4729 

41.5 

1.4534 

51.5 

1.4603 

61.5 

1.4668 

71.5 

.4732 

42.0 

1.4538 

52.0 

1.4607 

62.0 

1.4672 

72.0 

.4735 

42.5 

1.4541 

52.5 

1.4610 

62.5 

1.4675 

72.5 

.4738 

43.0 

1.4545 

53.0 

1.4613 

63.0 

1.4678 

73.0 

.4741 

43.5 

1.4548 

53.5 

1.4616 

63.5 

1.4681 

73.5 

.4744 

44.0 

1.4552 

54.0 

1.4619 

64.0 

1.4685 

74.0 

.4747 

44.5 

1.4555 

54.5 

1.4623 

64.5 

1.4688 

74.5 

.4750 

45.0 

1.4558 

55.0 

1.4626 

65.0 

1.4691 

75.0 

.4753 

45.5 

1.4562 

55.5 

1.4629 

65.5 

1.4694 

75.5 

.4756 

46.0 

1.4565 

56.0 

1.4633 

66.0 

1.4697 

76.0 

.4759 

46.5 

1.4569 

56.5 

1.4636 

66.5 

1.4700 

76.5 

.4762 

47.0 

1.4572 

57.0 

1.4639 

67.0 

1.4704 

77.0 

.4765 

47.5 

1.4576 

57.5 

1.4642 

67.5 

1.4707 

77.5 

1.4468 

48.0 

1.4579 

58.0 

1.4646 

68.0 

1.4710 

78.0 

.4771 

48.5 

1.4583 

58.5 

1.4649 

68.5 

1.4713 

78.5 

1.4774 

49.0 

1.4586 

59.0 

1.4652 

69.0 

1.4717 

79.0 

.4777 

49.5 

1.4590 

59.5 

1.4656 

69.5 

1.4720 

79.5 

1.4780 

OFFICIAL   METHODS    OF   ANALYSIS.  1063 

means  of  a  small  magnifying  glass.  To  check  the  accuracy  of  the  first  read- 
ing, the  dispersion  apparatus  should  be  turned  through  an  angle  of  180°  until 
the  colors  have  again  disappeared,  and  the  scale  of  the  instrument  again 
read.  These  two  readings  should  nearly  coincide,  and  their  mean  is  the  true 
reading  of  the  index  of  the  fat  under  examination. 

For  butter  fats  the  apparatus  should  be  kept  in  a  warm  place,  the  tempera- 
ture of  which  does  not  fall  below  30°.  For  reducing  the  results  obtained  to 
a  standard  temperature,  say  25°,  the  factor  0-000176  may  be  used.  As  the 
temperature  rises  the  refractive  index  falls. 

Example. — Refractive  index  of  a  butter  fat  determined  at  32-4°  = 
1-4540,  reduced  to  25°  as  follows:  32-4-25=7-4;  0-000176X7-4  = 
0-0013;  then  1-4540+0-0013=1-4553. 

The  instrument  used  should  be  set  with  distilled  water  at  25°,  the  theo- 
retical refractive  index  of  water  at  that  temperature  being  1  •  333.  In  the 
determination  above  given,  the  refractive  index  of  pure  water  measured 
1  •  33 ;  hence  the  above  numbers  should  be  corrected  for  theory  by  the  addition 
of  0-003,  making  the  corrected  index  of  the  butter  fat  mentioned,  at  the 
temperature  given,  1-4583. 

0")    DETERMINATION    OF   IODINE    ABSORPTION    NUMBER, 

(1)  Preparation  of  Reagents. 

,o)  IODINE  SOLUTION. — Dissolve  26  grm.  of  pure  iodine  in  500  c.c.  of  95- 
per  cent,  alcohol.  Dissolve  30  grm.  of  mercuric  chloride  in  500  c.c.  of  95-per 
cent,  alcohol.  The  latter  solution,  if  necessary,  is  filtered,  and  then  the  two 
solutions  mixed.  The  mixed  solution  should  be  allowed  to  stand  twelve 
hours  before  using. 

(6)  DECINORMAL  SODIUM-THIOSULPHATE  SOLUTION. — Dissolve  24-6  grm. 
of  chemically  pure  sodium  thiosulphate  freshly  pulverized  as  finely  as  pos- 
sible and  dried  between  filter-  or  blotting-paper,  and  dilute  with  water  to  1 
litre  at  the  temperature  at  which  the  titrations  are  to  be  made. 

(c)  STARCH  PASTE. — One  grm.  of  starch  is  boiled  in  200  c.c.  of  distilled 
water  for  ten  minutes  and  cooled  to  room  temperature. 

(d)  SOLUTION  OF  POTASSIUM  IODIDE. — One  hundred  and  fifty  grm.   of 
potassium  iodide  are  dissolved  in  water  and  the  volume  of  the  solution  made 
up  to  1  litre. 

(e)  SOLUTION    OF   POTASSIUM    DICHROMATE. — Dissolve    3-874    grm.    of 
chemically  pure  potassium  dichromate  in  distilled  water  and  make  the  volume 
up  to  1  litre  at  the  temperature  at  which  the  titrations  are  to  be  made. 

(2)  Determination. 

(a)  STANDARDIZING  THE  SODIUM-THIOSULPHATE  SOLUTION. — Place  20  c.c. 
of  the  potassium-dichromate  solution,  to  which  have  been  added  10  c.c.  of 
the  solution  of  potassium  iodide,  in  a  glass-stoppered  flask.  Add  to  this  5 
c.c.  of  strong  hydrochloric  acid.  Allow  the  solution  of  sodium  thiosulphate 
to  flow  slowly  into  the  flask  until  the  yellow  color  of  the  liquid  has  almost 
disappeared.  Add  a  few  drops  of  the  starch  paste,  and  with  constant  shaking 


1064  APPENDIX   I. 

continue  to  add  the  sodium-thiosulphate  solution  until  the  blue  color  just 
disappears.  The  number  of  cubic  centimeters  of  thiosulphate  solution 
used  multiplied  by  5  is  equivalent  to  1  grm.  of  iodine. 

Example. — Twenty  cubic  centimeters  K2O2O7  solution  required 
16-2  c.c.  sodium  thiosulphate;  then  16-2x5  =  81  =number  cubic 
centimeters  of  thiosulphate  solution  equivalent  to  1  grm.  of  iodine. 
Then  1  c.c.  thiosulphate  solution  =0-0124  grm.  of  iodine.  Theory 
for  decinormal  solution  of  sodium  thiosulphate,  1  c.c.  =0-0127  grm. 
of  iodine. 

(6)  WEIGHING  THE  SAMPLE. — About  1  grm.  of  butter  fat  is  placed  in  a 
glass-stoppered  flask  holding  about  300  c.c.,  with  the  precautions  mentioned 
for  weighing  the  fat  for  determining  volatile  acids  (/)  (3),  page  1055. 

(c)  ABSORPTION  OF  IODINE. — The  fat  in  the  flask  is  dissolved  in  10  c.c.  of 
chloroform.     After  complete  solution,  30  c.c.  of  the  iodine  solution  (1)  (a) 
are  added.     The  flask  is  now  placed  in  a  dark  place  and  allowed  to  stand, 
with  occasional  shaking,  for  three  hours. 

(d)  TITRATION  OF  THE  UN  ABSORBED  IODINE. — One  hundred  c.c.  of  distilled 
water  are  added  to  the  contents  of  the  flask,  together  with  20  c.c.  of  the  potas- 
sium-iodide solution.     Any  iodine  which  may  be  noticed  upon  the  stopper 
of  the  flask  should  be  washed  back  into  the  flask  with  the  potassium-iodide 
solution.     The  excess  of  iodine  is  taken  up  with  the  sodium-thiosulphate 
solution,  which  is  run  in  gradually,  with  constant  shaking,  until  the  yellow 
color  of  the  solution  has  almost  disappeared.     A  few  drops  of  starch  paste 
are  added,  and  the  titration  continued  until  the  blue  color  has  entirely  dis- 
appeared.    Toward  the  end  of  the  reaction  the  flask  should  be  stoppered 
and  violently  shaken,  so  that  any  iodine  remaining  in  solution  in  the  chloro- 
form may  be  taken  up  by  the  potassium-iodide  solution  in  the  water.     A  suffi- 
cient quantity  of  sodium-thiosulphate  solution  should  be  added  to  prevent  a 
reappearance  of  any  blue  color  in  the  flask  for  five  minutes. 

(e)  SETTING  THE  VALUE  OF  THE  IODINE  SOLUTION  BY  THE  THIOSULPHATE 
SOLUTION. — At  the  time  of  adding  the  iodine  solution  to  the  fat,  two  flasks 
of  the  same  size  as  those  used  for  the  determination  should  be  employed  for 
conducting  the  operation  described  above,  but  without  the  presence  of  any 
fat.     In   every   other  respect   the   performance   of   the   blank   experiments 
should  be  just  as  described.     These  blank  experiments  must  be  made  each  time 
the  iodine  solution  is  used. 

Example  Blank  Determinations. — 30  c.c.  iodine  solution  required 
46-4  c.c.  of  sodium-thiosulphate  solution.  30  c.c.  iodine  solution 
required  46  •  8  c.c.  of  sodium  thiosulphate  solution.  Mean,  46  •  6  c.c. 

Per  cent,  of  iodine  absorbed: 

Weight  of  fat  (grm.) 1 -04791 

Quantity  of  iodine  solution  (c.c.) 30-0 

Thiosulphate  equivalent  to  iodine  (c.c.) 46-6 

Thiosulphate  equivalent  to  remaining  iodine  (c.c.) 14-7 

Thiosulphate  equivalent  to  iodine  absorbed  (c.c.) 31-9 

Per  cent,  of  iodine  absorbed,  31  •  9  X  0  •  0124  X 100  -*•  1  •  0479  =  37  •  75. 


OFFICIAL   METHODS   OF   ANALYSIS.  1065 

(&)    DETERMINATION    OF   SPECIFIC    GRAVITY. 

(1)  Standardization  of  Flasks. 

Use  a  small  specific-gravity  flask  of  from  25  to  30  c.c.  capacity.  The 
flask  is  to  be  thoroughly  washed  with  hot  water,  alcohol,  and  ether,  and  then 
dried.  After  cooling  in  a  desiccator,  the  weight  of  the  flask  and  stopper 
is  accurately  determined. 

The  flask  is  filled  with  freshly  boiled  and  still  hot  distilled  water,  and 
placed  in  a  bath  of  pure  distilled  water.  The  water  of  the  bath  is  kept  in 
brisk  ebullition  for  thirty  minutes,  any  vaporation  from  the  flask  being 
replaced  by  the  addition  of  boiling  distilled  water.  The  stopper,  previously 
heated  to  100°,  is  then  inserted,  the  flask  removed,  wiped  dry,  and  after  it 
has  nearly  cooled  to  room  temperature  placed  in  the  balance  and  weighed 
when  balance  temperature  is  reached. 

OPTIONAL  METHOD  OF  STANDARDIZING  FLASKS. — The  following  formula 
may  be  used  for  calculating  the  volume  V,  in  c.c.,  of  a  glass  vessel  from  the 
weight  P  of  water  at  temperature  t  contained  therein,  and  the  volume  V  at 
any  other  temperature  t': 

eT 

v=  p?-n- 

p  =  weight  (brass  weights)  of  1  c.c.  of  water  in  vacuo  at  4°.  This  is  so 
nearly  1  that  it  will  not  affect  the  result  in  the  fifth  place  of  decimals,  and 
may  therefore  be  disregarded.  Hence  the  formula  stands: 


d  =  density  of  water  at  temperature  t . 
f  =  0-000025,  the  cubical  expansion  coefficient  of  glass. 
(2)  Determination. 

WEIGHT  OF  FAT  AT  THE  TEMPERATURE  OF  BOILING  WATER. — The  flask 
is  rinsed  with  alcohol  and  ether,  and  dried  for  a  few  minutes  at  the  tem- 
perature of  boiling  water.  It  is  filled  with  the  dry,  hot,  fresh-filtered  fat, 
which  should  be  entirely  free  from  air  bubbles,  replaced  in  the  water-bath, 
and  kept  for  thirty  minutes  at  the  temperature  of  boiling  water.  The 
stopper,  previously  heated  to  100°,  is  inserted,  the  flask  removed,  wiped 
dry,  placed  in  the  balance  after  it  has  nearly  cooled  to  room  temperature, 
and  weighed  when  the  balance  temperature  is  reached.  The  weight  of  fat 
having  been  determined,  the  specific  gravity  is  obtained  by  dividing  it  by 
the  weight  of  water  previously  found. 

Example: 

Gnn. 

Weight  of  flask  dry 10-0197 

Weight  of  flask,  plus  water 37-3412 

Weight  of  water 27-3215 

Weight  of  flask,  plus  fat 34-6111 

Weight  of  flask 24  -  5914 

Specific  gravity  =  24  •  5914  -i-  27  •  3215 = 0  •  90008. 


1066  APPENDIX   I. 

The  weight  of  the  flask  dry  and  empty,  and  the  weight  of  water  at  boiling 
temperature  contained  therein,  may  be  used  constantly  if  great  care  be 
taken  in  handling  and  cleaning  the  apparatus. 
Example: 

Grm. 

Weight  of  flask,  dry  and  empty 10  •  0028 

Weight  of  flask  after  three  weeks'  use 10-0030 

(1)  DETERMINATION  OF  MELTING-POINT.     WILEY'S  METHOD. 
(1)  Preparation  of  Reagents. 

(a)  A  piece  of  ice  floating  in  distilled  water  that  has  been  recently  boiled. 

(6)  A  mixture  of  alcohol  and  water  of  the  same  specific  gravity  as  the  fat 
to  be  examined.  This  is  prepared  by  boiling  distilled  water  and  95-per  cent, 
alcohol  to  remove  the  gases  which  they  may  hold  in  solution.  While  still 
hot,  the  water  is  poured  into  the  test-tube  described  below  (2)  (e)  until  it  is 
nearly  half  full.  The  test-tube  is  nearly  filled  with  the  hot  alcohol,  which 
is  carefully  poured  down  the  side  of  the  inclined  tube  to  avoid  too  much 
mixing.  If  the  alcohol  be  not  added  until  the  water  has  cooled,  the  mixture 
will  contain  so  many  air  bubbles  as  to  be  unfit  for  use.  These  bubbles  will 
gather  on  the  disk  of  fat  as  the  temperature  rises  and  finally  force  it  to  the  top, 

(2)  Apparatus. 

The  apparatus  for  determining  the  melting-point  (Fig.  4)  consists  of  (a) 
an  accurate  thermometer  reading  easily  tenths  of  a  degree;  (&)  a  cathe- 
tometer  for  reading  the  thermometer  (but  this  may  be  done  with  an  eye-glass, 
if  held  steadily,  and  properly  adjusted) ;  (c)  a  thermometer;  (d)  a  tall  beaker 
35  cm.  high  and  10  cm.  in  diameter;  (e}  a  test-tube  30  cm.  long  and  3-5  cm. 
in  diameter;  (/)  a  stand  for  supporting  the  apparatus;  (g)  some  method  of 
stirring  the  water  in  the  beaker  (for  example,  a  blowing  bulb  of  rubber,  and 
a  bent  glass  tube  extending  to  near  the  bottom  of  the  beaker) . 

(3)  Determination. 

The  disks  of  fat  are  prepared  as  follows.  The  melted  and  filtered  fat 
is  allowed  to  fall  from  a  dropping  tube  from  a  height  of  from  15  to  20  cm. 
on  a  smooth  piece  of  ice  floating  in  distilled  water  that  has  been  recently 
boiled.  The  disks  thus  formed  are  from  1  to  1  •  5  cm.  in  diameter,  and  weigh 
about  200  mg.  By  pressing  the  ice  under  the  water  the  disks  are  made  to 
float  on  the  surface,  whence  they  are  easily  removed  with  a  steel  spatula, 
which  should  be  cooled  in  the  ice  water  before  using. 

The  test-tube  containing  the  alcohol  and  water  is  placed  in  a  tall  beaker 
containing  water  and  ice,  until  cold.  The  disk  of  fat  is  then  dropped  into 
the  tube  from  the  spatula,  and  at  once  sinks  until  it  reaches  a  part  of  the 
tube  where  the  density  of  the  alcohol-water  is  exactly  equivalent  to  Vts  own. 
Here  it  remains  at  rest  and  free  from  the  action  of  any  force  save  that  inherent 
in  its  own  molecules. 

The  delicate  thermometer  is  placed  in  the  test-tube  and  lowered  until  the 
bulb  is  near  the  disk.  In  order  to  secur6  an  even  temperature  in  all  parts 


OFFICIAL   METHODS   OF   ANALYSIS. 


1067 


of  the  alcohoi  mixture  in  the  vicinity  of  the  disk,  the  thermometer  is  moved 
from  time  to  time  in  a  circularly  pendulous  manner. 

The  disk  having  been  placed  in  position,  the  water  in  the  beaker  is  slowly 
heated,  and  kept  constantly  stirred  by  means  of  the  blowing  apparatus 
already  described. 


Fro.  4. — Apparatus  for  the  determination  of  melting-point. 

When  the  temperature  of  the  alcohol-water  mixture  rises  to  about  6° 
below  the  melting-point,  the  disk  of  fat  begins  to  shrivel,  and  gradually  rolls  up 
into  an  irregular  mass. 

The  thermometer  is  lowered  until  the  fat  particle  is  even  with  the  center 
of  the  bulb.  The  bulb  of  the  thermometer  should  be  small,  so  as  to  indi- 
cate only  the  temperature  of  the  mixture  near  the  fat.  A  gentle  rotary  move- 
ment should  be  given  to  the  thermometer  bulb.  The  rise  of  temperature 
should  be  so  regulated  that  the  last  2°  of  increment  require  about  ten  min- 


1068  APPENDIX   I. 

utes.  The  mass  of  fat  gradually  approaches  the  form  of  a  sphere,  and  when 
it  is  sensibly  so  the  reading  of  the  thermometer  is  made.  As  soon  as  the 
temperature  is  read,  the  test-tube  is  removed  from  the  bath  and  placed  again 
in  the  cooler.  A  second  tube,  containing  alcohol  and  water,  is  at  once  placed 
in  the  bath.  The  test-tube  (ice  water  having  been  used  as  a  cooler)  is  of 
low  enough  temperature  to  cool  the  bath  sufficiently.  After  the  first  deter- 
mination, which  should  be  only  a  trial,  the  temperature  of  the  bath  should  be 
so  regulated  as  to  reach  a  maximum  of  about  1 . 5°  above  the  melting-point 
of  the  fat  under  examination. 

The  edge  of  the  disk  should  not  be  allowed  to  touch  the  sides  of  the  tube. 
This  accident  rarely  happens,  but  in  case  it  should  take  place,  and  the  disk 
adhere  to  the  sides  of  the  tube,  a  new  trial  should  be  made. 

Triplicate  determinations  should  be  made,  and  the  second  and  third 
results  should  show  a  near  agreement. 

Example. — Melting-point  of  sample  of  butter: 

Degrees. 

First  trial 33-15 

Second  trial 33-05 

Third  trial 33-00 

(m)    MICROSCOPIC   EXAMINATION. 

Place  a  small  portion  of  the  fresh  sample,  taken  from  the  inside  of  the 
mass,  on  a  slide,  add  a  drop  of  pure  sweet  oil,  cover  with  gentle  pressure, 
and  examine  with  a  one-half  to  one-eighth  inch  objective  for  crystals  of 
lard,  etc.  Examine  the  same  specimen  with  polarized  light  and  a  selenite 
plate  without  the  use  of  oil.  Pure  fresh  butter  will  neither  show  crystals 
nor  a  particolored  field  with  selenite.  Other  fats  melted  and  cooled  and 
mixed  with  butter  will  usually  present  crystals  and  variegated  colors  with  the 
selenite  plate. 

For  further  microscopic  study  dissolve  from  4  to  5  c.c.  of  the  fat  in  15  c.c. 
of  ether  in  a  test-tube.  Close  the  tube  with  a  loose  plug  of  cotton  wool  and 
allow  to  stand  from  twelve  to  twenty-four  hours  at  room  temperature  (20° 
to  25°).  When  crystals  form  at  the  bottom  of  the  tube,  they  are  removed 
with  a  pipette,  glass  rod,  or  tube,  placed  on  a  slide,  covered,  and  examined. 
The  crystals  formed  by  later  deposits  may  be  examined  in  a  similar  way. 

2.  MILK  ANALYSIS. 

(tt)    DETERMINATION  OF  WATER. 

Heat  to  constant  weight  at  the  temperature  of  boiling  water  from  1  to 
2  grm.  of  milk  in  a  tared  flat  dish  of  not  less  than  5  c.c.  diameter.  If  desired, 
from  15  to  20  grm.  of  pure  dry  sand  may  be  previously  placed  in  the  dish. 
Cool  in  a  desiccator,  and  weigh  rapidly  to  avoid  absorption  of  hygroscopic 
moisture. 

BABCOCK  Asbestos  Method. — Provide  a  hollow  cylinder  of  perforated 
sheet  metal,  60  mm.  long  and  20  mm.  in  diameter,  closed  5  mm.  from  one 
end  by  a  disk  of  the  same  material.  The  perforations  should  be  about  0-7 


OFFICIAL    METHODS   OF   ANALYSIS.  1069 

in  diameter  and  about  0-7  mm.  apart.  Fill  loosely  with  from  1-5 
to  2-5  grin,  of  freshly  ignited,woolly  asbestos,  free  from  fine  and  brittle  ma- 
terial, cool  in  a  desiccator,  and  weigh.  Introduce  a  weighed  quantity  of 
milk  (between  3  and  5  grm.)  and  dry  at  100°  to  constant  weight  for  the 
determination  of  total  solids. 

(6)    DETERMINATION    OF    FAT. 

(1)  Paper-coil  Method. 

Coils  made  of  thick  filter-paper,  cut  into  strips  6-25  by  62-5  cm.  are 
thoroughly  extracted  with  ether  and  alcohol,  or  the  weight  of  the  extract 
corrected  by  a  constant  obtained  for  the  paper.  If  the  latter  method  be  used, 
a  small  amount  of  anhydrous  sodium  carbonate  should  be  added.  From  a 
weighing  bottle  about  5  grm.  of  milk  are  transferred  to  the  coil  by  a  pipette, 
care  being  taken  to  keep  the  end  of  the  coil  held  in  the  fingers  dry.  The 
coil,  dry  end  down,  on  a  piece  of  glass,  is  dried  at  the  temperature  of  boiling 
water  for  one  hour,  or,  better,  dried  in  hydrogen  at  the  temperature  of  boiling 
water,  transferred  to  an  extraction  apparatus,  and  extracted  with  absolute 
ether  or  petroleum  ether  boiling  at  about  45°.  The  extracted  fat  is  dried 
in  hydrogen  and  weighed. 

(2)  BABCOCK  Asbestos  Method. 

Extract  the  residue  from  the  determination  of  water  by  the  BABCOCK 
asbestos  method  with  anhydrous  ether  until  the  fat  is  removed,  evaporate 
the  ether,  dry  the  fat  at  100°,  and  weigh.  The  fat  may  also  be  determined 
by  difference,  drying  the  extracted  cylinders  at  100°. 

(3)  Volumetric  Methods. 

Any  of  the  well-known  volumetric  methods,  such  as  BABCOCK'S  and 
GERBER'S  majr  be  used.  (See  Principles  and  Practice  of  Agricultural  Analy- 
sis. VoL  HI.,  pp.  499  et  seq.) 

(c)    DETERMINATION    OF   TOTAL   NITROGEN. 

Place  in  a  KJELDAHL  digestion  flask  a  known  weight  (about  5  grm.)  of 
milk,  and  proceed,  without  evaporation,  exacthr  as  described  for  this  method 
under  nitrogen,  page  1021.  Multiply  the  percentage  of  nitrogen  by  6-25 
for  nitrogen  compounds. 

1.  Official  Method  for  Determination  of  Casein  in  Cow's  Milk. — The  deter- 
mination of  casein  hi  milk  should  be  made  when  the  milk  is  fresh,  or  nearly 
so.  When  it  is  not  practicable  to  make  this  determination  within  twenty- 
four  hours,  add  1  part  of  formaldehyde  to  2500  parts  of  milk,  and  keep  hi  a 
cool  place.  Place  about  10  grm.  of  milk  in  a  beaker  with  about  90  c.c.  of 
water  at  40°-42°,  and  add  at  once  1-5  c.c.  of  a  solution  containing  10  per 
cent,  of  acetic  acid  by  weight.  Stir  with  a  glass  rod,  and  let  stand  from 
three  to  five  minutes  longer.  Then  decant  on  a  filter,  wash  two  or  three  tunes 


1070  APPENDIX   I. 

with  cold  water  by  decantation,  and  transfer  precipitate  completely  to  filter. 
Wash  once  or  twice  on  filter.  The  filtrate  should  be  clear,  or  very  nearly 
so.  If  it  be  not  clear  when  it  first  runs  through,  it  can  generally  be  made  so 
by  two  or  three  repeated  nitrations,  after  which  the  washing  of  the  precipi- 
tate can  be  completed.  The  washed  precipitate  and  filter-paper  are  digested  as 
in  the  regular  KJELDAHL  method  for  the  determination  of  nitrogen,  and  the 
process  is  completed  as  usual.  To  calculate  the  nitrogen  into  an  equiva- 
lent amount  of  casein,  multiply  by  6  •  25. 

In  working  with  milk  which  has  been  kept  with  preservatives,  the  acetic 
acid  should  be  added  in  small  proportions,  a  few  drops  at  a  time,  with  stir- 
ring and  the  addition  continued  until  the  liquid  above  the  precipitate  becomes 
clear,  or  very  nearly  so. 

2.  Provisional  Method  for  Determining  Albumin  in  Milk. — The  filtrate 
obtained  in  the  above  operation  is  neutralized  with  caustic  alkali,  three- 
tenths  c.c.  of  a  10-per-cent.  solution  of  acetic  acid  added  and  the  mixture 
heated  to  the  temperature  of  boiling  water  for  from  ten  to  fifteen  minutes. 
The  precipitate  is  collected  on  a  filter,  washed,  and  the  nitrogen  therein 
determined.     Nitrogen  multiplied  by  6-25  equals  albumin. 

3.  Official  Optional  Method  for  Determining  Casein  in  Milk. — To  5  grm. 
of  milk,  50  c.c.  of  a  solution  of  magnesium  sulphate  saturated  at  from  40°  to 
45°  are  added  and  the  mixture  heated  to  about  45°,  until  the  precipitate 
separates  and  subsides,   leaving  the   supernatant  liquid  clear.     The   pre- 
cipitate is  collected  on  a  filter,  washed  two  or  three  times  with  the  solution 
of  magnesium  sulphate  prepared  as  above  and  at  the  same  temperature, 
viz.,  about  45°,  and  the  nitrogen  therein  determined. 

4.  Provisional  Optional'  Method  for  Determining  Albumin  in  Milk. — To 
the  filtrate,  obtained  by  the  above  process,  are  added  three-tenths  c.c.  of 
a  10-per-cent.  solution  of  acetic  acid  and  the  mixture  is  boiled  until  the  albu- 
min is  completely  precipitated.     The  precipitate   is    collected  on  a    filter, 
washed  as  above  described,  and  the  nitrogen  therein  determined. 

(d)    DETERMINATION    OF   ASH. 

In  a  weighed  dish  put  about  20  grm.  of  milk,  add  6  c.c.  of  nitric  acid, 
evaporate  to  dryness,  and  burn  at  a  low  red  heat  until  the  ash  is  free  from 
carbon. 

(e)    DETERMINATION    OF   SUGAR. 

See  Determination  of  Carbohydrates  in  Agricultural  Products,  page  1051. 
3.  CHEESE  ANALYSIS. 

(a)    PREPARATION    OF   SAMPLE. 

When  the  cheese  can  be  cut,  a  narrow,  wedge-shaped  segment  reaching 
from  the  outer  edge  to  the  center  of  the  cheese,  is  secured.  This  is  to  be 
cut  into  strips  and  passed  through  a  sausage-grinding  machine  three  times. 
When  the  cheese  cannot  be  cut,  samples  are  obtained  by  a  cheese  trier.  If 


OFFICIAL   METHODS   OF  ANALYSIS.  1071 

only  one  plug  can  be  obtained,  this  should  be  taken  perpendicular  to  the 
surface  at  a  point  one-third  of  the  distance  from  the  edge  to  the  center  of 
the  cheese.  The  plug  should  reach  either  entirely  through  or  only  half- 
way through  the  cheese.  When  possible,  draw  three  plugs — one  from  the 
center,  one  from  a  point  near  the  outer  edge,  and  one  from  a  point  halfway 
between  the  other  two.  For  inspection  purposes,  the  rind  may  be  rejected; 
but  for  investigations  requiring  the  absolute  amount  of  fat  in  the  cheese 
the  rind  is  included  hi  the  sample.  It  is  preferable  to  grind  the  plugs  in  a 
sausage  machine,  but  when  this  is  not  done  they  are  cut  very  fine  and  care- 
fully mixed. 

(6)    DETERMINATION   OP  WATER. 

From  2  to  5  grm.  of  cheese  should  be  placed  in  a  weighed  platinum  or 
porcelain  dish  which  contains  a  small  quantity  of  porous  material  such  as 
ignited  asbestos  or  sand  to  absorb  the  fat  which  may  run  out  of  the  cheese. 
This  is  heated  in  a  water  oven  for  ten  hours  and  weighed;  the  loss  hi 
weight  is  considered  as  water.  Or,  if  preferred,  the  dish  may  be  placed  in  a 
desiccator  over  concentrated  sulphuric  acid  and  dried  to  constant  weight. 
In  some  cases  this  may  require  as  much  as  two  months.  The  acid  should 
be  renewed  when  the  cheese  has  become  nearly  dry. 

(c)    DETERMINATION    OF   FAT. 

Cover  the  perforations  in  the  bottom  of  the  extraction-tube  with  dry 
asbestos  felt,  and  on  this  place  a  mixture  containing  equal  parts  of  anhy- 
drous copper  sulphate  and  pure,  dry  sand  to  the  depth  of  about  5  cm.,  pack- 
ing loosely.  Cover  the  upper  surface  of  this  material  with  a  film  of  asbestos. 
On  this  are  placed  from  2  to  5  grm.  of  the  sample  of  cheese.  The  tube  is 
placed  in  a  continuous  extraction  apparatus,  and  treated  for  five  hours  with 
anhydrous  ether.  The  cheese  is  removed  and  ground  to  a  fine  powder  with 
pure  sand  in  a  mortar.  The  mixed  cheese  and  sand  are  replaced  in  the  extrac- 
tion-tube, the  mortar  washed  free  of  all  matters  with  ether,  the  washings 
being  added  to  the  tube,  and  the  extraction  is  continued  for  10  hours. 

(rf)    DETERMINATION  OF   NITROGEN. 

Make  a  determination  of  nitrogen  by  the  KJELDAHL  method,  using  about 
2  grm.  of  cheese,  and  multiply  the  percentage  of  nitrogen  found  by  6  •  25. 

(e)    DETERMINATION    OF   ASH. 

The  dry  residue  from  the  water  determination  may  be  used  for  the  ash. 
If  the  cheese  be  rich  in  fat,  the  asbestos  wiU  be  saturated  therewith.  This 
may  be  ignited  carefully  and  the  fat  allowed  to  burn  off,  the  asbestos  acting 
as  a  wick.  No  extra  heat  should  be  applied  during  this  operation,  as  there 
is  danger  of  spurting.  When  the  flame  has  died  out,  the  burning  may  be 
completed  in  a  muffle  at  low  redness.  When  desired,  the  salt  may  be  deter- 
mined hi  the  ash  in  the  manner  specified  under  butter  analysis,  page  1054. 


1072  APPENDIX   I. 

(/)    DETERMINATION    OF    OTHER    CONSTITUENTS. 

The  sum  of  the  percentages  of  the  different  constituents,  determined 
as  above,  subtracted  from  100  will  give  the  amount  of  organic  acids,  milk- 
sugar,  etc.,  in  the  cheese. 

(gr)    PROVISIONAL  METHOD   FOR  THE  DETERMINATION  OF  ACIDITY  IN  CHEESE. 

To  10  grm.  of  finely  divided  cheese  add  water,  at  a  temperature  of  40°, 
until  the  volume  equals  105  c.c. ;  agitate  vigorously  and  filter.  Titrate  por- 
tions of  25  c.c.  of  filtrate,  corresponding  to  2  •  5  grm.  of  cheese,  with  standard- 
ized solution  of  sodium  hydroxide,  preferably  one-tenth  normal.  Use 
phenolphtalein  as  indicator.  Express  amount  of  acid  as  lactic. 

V.— METHODS  FOR  THE  ANALYSIS  OF  FERMENTED  AND  DIS- 
TILLED LIQUORS. 

1.  DETERMINATION  OF  SPECIFIC  GRAVITY. 

The  specific  gravity  is  ascertained  at  15-5°  by  means  of  a  pycnometer 
or  a  Westphal  balance  controlled  by  pycnometer,  or  a  delicate  hydrometer 
may  be  used  which  has  been  carefully  calibrated  by  a  pycnometer. 

2.  DETERMINATION  OF  ALCOHOL, 
(a)  IN  FERMENTED  LIQUORS. 

(1)  By  Weight. 

One  hundred  c.c.  of  the  liquor  are  measured  into  a  flask  of  from  250  to 
300  c.c.  capacity,  50  c.c.  of  water  added,  the  flask  attached  to  a  vertical  con- 
denser by  means  of  a  bent  tube,  and  100  c.c.  distilled.  The  specific  gravity 
of  the  distillate  is  determined  as  in  1.  The  distillate  is  also  weighed,  or  its 
weight  calculated  from  the  specific  gravity.  The  corresponding  percentage 
of  alcohol  by  weight  is  obtained  from  the  appended  table,  and  this  figure 
multiplied  by  the  weight  of  the  distillate,  and  the  result  divided  by  the  weight 
of  the  sample  taken,  gives  the  per  cent,  of  alcohol  by  weight  contained  therein. 

(2)  By  Volume. 

The  percentage  of  alcohol  by  volume  of  the  liquor  is  the  same  as  that  of 
the  distillate,  and  is  obtained  from  the  appended  table. 

(&)     IN    DISTILLED    LIQUORS. 

(1)  By  Weight. 

About  30  grm.  of  the  liquor  are  diluted  to  150  c.c.,  100  c.c.  distilled,  and 
the  per  cent,  of  alcohol  by  weight  determined  as  under  fermented  liquors. 

(2)  By  Volume. 

The  percentage  of  alcohol  by  volume  in  the  distillate  is  obtained  from 
the  appended  table,  this  figure  divided  by  the  volume  of  the  liquor  taken 
for  the  determination  (calculated  from  the  specific  gravity),  and  the  result 
multiplied  by  100. 


OFFICIAL   METHODS   OF   ANALYSIS. 


1073 


PERCENTAGE   OF  ALCOHOL  BY  WEIGHT  AND   BY  VOLUME. 

[Recalculated  from  the  determinations  of  GILPIN   DRINKWATER,  and  SQUIBB,  by  EDGAB 

RICHARDS.] 


Specific 
Gravity 
at|8°F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at|8°F. 

Per 

Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent. 
Alco- 
hol 

Specific 
Gravity 

at|g°F. 

Per 

Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent. 
Alco- 
hol 

Specific 
Gravity 
at|»°F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

1.00000 

0-00 
.05 

°'8S 

0.99629 

2-50 
.55 

1:8 

0.99281 

5.00 

4-00 
.04 

0.98959 

7-50 
.55 

6.02 

984 

.10 

ios 

615 

.60 

.07 

268 

!io 

.08 

947 

.60 

!io 

976 

.15 

.12 

607 

.65 

.11 

261 

.15 

.12 

940 

.65 

.14 

968 

.20 

.16 

600 

.70 

.15 

255 

.20 

.16 

934 

.70 

.18 

961 

.25 

.20 

593 

.75 

.19 

248 

.25 

.20 

928 

.75 

.22 

953 

.30 

.24 

586 

.80 

.23 

241 

.30 

.24 

922 

.80 

.26 

945 

.35 

.28 

579 

.85 

.27 

235 

.35 

.28 

916 

.85 

.30 

937 

.40 

.32 

571 

.90 

.31 

228 

.40 

.35 

909 

.90 

.34 

930 

.45 

.36 

564 

.95 

.35 

222 

.45 

.36 

903 

.95 

.38 

.99923 

0-50 

0.40 

.99557 

3-00 

2-39 

.99215 

5.50 

4.40 

.98897 

8.00 

6-42 

915 

55 

.44 

550 

.05 

.43 

208 

55 

4A 

891 

05 

.46 

907 

'.60 

.48 

543 

.10 

.47 

202 

'.60 

'.48 

885 

.10 

.50 

900 

.65 

.52 

536 

.15 

.51 

195 

.65 

.55 

879 

.15 

.54 

892 

.70 

.56 

529 

.20 

.55 

189 

.70 

.56 

873 

.20 

.58 

884 

.75 

.60 

522 

.25 

.59 

182 

.75 

.6C 

867 

.25 

.62 

877 

.80 

.64 

515 

.30 

.64 

175 

.80 

.64 

861 

.30 

.67 

869 

.85 

.67 

508 

.35 

.68 

169 

.85 

.68 

855 

.35 

.71 

861 

.90 

.71 

501 

.40 

.72 

162 

.90 

.75 

849 

.40 

.75 

854 

.95 

.75 

494 

.45 

.76 

156 

.95  1     .76 

843 

.45 

.79 

.99849 

842 

i-oo 

0.79 
.83 

.99487 
480 

3-M 

2-|0 

.99149 
143 

6.00      4.80 
.05        .84 

.98J37 

8.50 

9:!73 

834 

'.10 

.87 

473 

.60 

'.88 

136 

.10  ;      .88 

825 

'.60 

.91 

827 

.15 

.91 

466 

.65 

.92 

130 

.15        .92 

819 

.65 

.95 

819 

.20 

.95 

459 

.70 

.96 

123 

.20        .96 

813 

.70 

.99 

812 

.25 

.99 

452 

.75 

3.00 

117 

.25      5.00 

807 

.75 

7.03 

805 

.30 

1.03 

445 

.80 

.04 

111 

.30        .05 

801 

.80 

.07 

797 

.35 

.07 

438 

.85 

.08 

104 

.35        .09 

795 

.85 

.11 

790 

.40 

.11 

431 

.90 

.12 

098 

.40        .13 

789 

.90 

.15 

782 

.45 

.15 

424 

.95 

.16 

091 

.45        .17 

783 

.95 

.19 

.99775 

768 

1-50 

1-19 

•99417 
410 

4-00 

3.20 

.99085 

6.50 

6.21 

.98777 

9.00 
.05 

7-23 

760 

'.60 

!27 

403 

!io 

.28 

072 

'.60  !    .29 

765 

.10 

'.31 

753 

.65 

.31 

397 

.15 

.32 

066      .65  I      .33 

759 

.15 

.35 

745 

.70 

.35 

390 

.20 

.36 

059       .70        .37 

754 

.20 

.39 

738 

.75 

.39 

383 

.25 

.40 

053       .75        .41 

748 

.25 

.43 

731 

.80 

.43 

376 

.30 

.44 

047  1      .80        .80 

742 

.30 

.48 

723 

.85 

.•47 

369 

.35 

.48 

040       .85        .4fl 

736 

.35 

.52 

716 

.90 

.51 

363 

.40 

.52 

034!      .90         .53 

730 

.40 

.56 

708 

.95 

.55 

356 

.45 

.56 

027 

.95        .57 

724 

.45 

.60 

.99701 

2.00 

1.59 

.99349 

4.50 

3-60 

.99021 

7.00 

5.61 

.98719 

9-50 

7.64 

694 

.05 

.63 

342 

55 

.64 

015 

05 

65 

713 

55 

.68 

687 

.10 

'.67 

335 

'.60 

.68 

009 

!io 

.'69 

707 

'.60 

!72 

679 

.15 

.71 

329 

.65 

.72 

002 

.15 

.73 

701 

.65 

.76 

672 

.20 

.75 

322 

.70 

.76 

.98996 

.20 

.77 

695 

.70 

.80 

665 

.25 

.79 

315 

.75 

.80 

990 

.25 

.81 

689 

.75 

.84 

658 

.30 

.83 

308 

.80 

.84 

984 

.30 

.86 

683 

.80 

.88 

651 

.35 

.87 

301 

.85 

.88 

978 

.35 

.90 

678 

.85 

.92 

643 

.40 

.91 

295 

.90 

.92 

971 

.40 

.94 

672 

.90 

.96 

636 

.45 

.95 

288 

.95 

.96 

965 

.45 

.98 

666 

.95 

8.00 

1074 


APPENDIX    I. 


PERCENTAGE  OF  ALCOHOL  BY  WEIGHT  AND  BY  VOLUME — Continued. 


[Recalculated  from  the  determinations  of  GILPIN,  DRINKWATER,  and  SQUIBB,  by  EDGAR 

RICHARDS.] 


Specific 
Gravity 
at  |g°  F. 

Per 

Cent. 
Alco- 
hol 

Per 

Cent. 
Alco- 
hol 
by 
Wgt, 

Specific 
Gravity 
at  |g°  F. 

Per 

ICent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at  |g°  F. 

Per 

Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent. 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at  |8°  F. 

Per 
Cent. 
Alco- 
hol 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

0.98660 
654 

10.00 

«.04 

0.98881 

12.50 

10-08 

.12 

0.98114 
108 

15-00 

12-13 
.17 

0.97859 
853 

17.50 

14-19 
.23 

649 

'10 

12 

370 

'.60 

.16 

104 

!io 

.21 

848 

'.60 

.27 

643 

,15 

.16 

364 

.65 

.20 

099 

.15 

.25 

843 

.65 

.31 

637 

.20 

20 

359 

.70 

.24 

093 

.20 

.29 

838 

.70 

.35 

632 

25 

.24 

353 

.75 

.28 

088 

.25 

.33 

833 

.75 

.40 

626 

.30 

.29 

348 

.80 

.33 

083 

.30 

.38 

828 

.80 

.44 

620 

.35 

33 

342 

.85 

.37 

078 

.35 

.42 

823 

.85 

.48 

614 

40 

.37 

337 

.90 

.41 

073 

.40 

.46 

818 

.90 

.52 

609 

.45 

.41 

331 

.95 

.45 

068 

.45 

.50 

813 

.95 

.56 

.98603 

•^0.50 

8-45 

.98326 

13-00 

10-49 

.98063 

15.50 

12-54 

.97808 

18-00 

14-60 

597 

.55 

4S 

321 

05 

.53 

057 

55 

58 

803 

.05 

.64 

592 

.60 

!53 

315 

!io 

.57 

052 

.'60 

!62 

798 

.10 

.68 

586 

.65 

.57 

310 

.15 

.61 

047 

.65 

.66 

793 

.15 

.73 

580 

.70 

.61 

305 

.20 

.65 

042 

.70 

.70 

788 

.20 

.77 

575 

.75 

.65 

299 

.25 

.69 

037 

.75 

.75 

783 

.25 

.81 

569 

.80 

.70 

294 

.30 

.74 

032 

.80 

.79 

778 

.30 

.85 

563 

.85 

.74 

289 

.35 

78 

026 

.85 

.83 

773 

.35 

.89 

557 

.90 

.78 

283 

.40 

.82 

021 

.90 

.87 

768 

.40 

.94 

552 

.95 

.82 

278 

.45 

.86 

016 

.95 

.91 

763 

.45 

.98 

.98546 

11-00 

8-86 

.98273 

13-50 

10-90 

.98011 

16-00 

12.95 

1  .97758 

18-50 

15-02 

540 

.05 

90 

267 

.55 

.94 

005 

.05 

.  99 

753 

.55 

.06 

535 

.10 

!94 

262 

.60 

.98 

001 

.10 

13.03 

748 

.60 

!io 

529 

.15 

.98 

256 

.65 

11.02 

.97996 

.15 

.08 

743 

.65 

.14 

524 

.20 

9.02 

251 

.70 

.06 

991 

.20 

.12 

738 

.70 

.18 

518 

.25 

.07 

246 

.75 

.11 

986 

.25 

.16 

733 

.75 

.22 

513 

.30 

.11 

240 

.80 

.15 

980 

.30 

.20 

728 

.80 

.27 

507 

.35 

.15 

235 

.85 

.19 

975 

.35 

.24 

723 

.85 

.31 

502 

.40 

.19 

230 

.90 

.23 

970 

.40 

.29 

718 

.90 

.38 

496 

.45 

.23 

224 

.95 

.27 

965 

.45 

.33 

713 

.95 

.39 

.98491 

11.50 

9-27 

.98219 

14.00 

11-31 

.97960 

16-50 

13-37 

•97708 

19-00 

15-43 

485 

55 

.31 

214 

.05 

35 

955 

55 

.41 

703 

05 

.47 

479 

!eo 

.35 

209 

.10 

!39 

950 

'.60 

.45 

698 

!io 

.51 

474 

.65 

.39 

203 

.15 

.43 

945 

.65 

.49 

693 

.15 

.55 

468 

.70 

.43 

198 

.20 

.47 

940 

.70 

.53 

688 

.20 

.59 

463 

.75 

.47 

193 

.25 

.52 

935 

.75 

.57 

683 

.25 

.63 

457 

.80 

.51 

188 

.30 

.56 

929 

.80 

.62 

678 

.30 

.68 

452 

.85 

.55 

182 

.35 

60 

924 

.85 

.66 

673 

.35 

.72 

446 

.90 

.59 

177 

.40 

.64 

919 

.90 

.70 

668 

.40 

.76 

441 

.95 

.63 

172 

.45 

.68 

914 

.95 

.74 

663 

.45 

.80 

98t!E 

12-01 

9:781 

.98167 
161 

M:K 

11-72 
.76 

.97909 
904 

17.00 
.05 

13-78 

•97658 

19-50 
.55 

15-84 

.88 

424 

!io 

.75 

156 

.60 

.80 

899 

.10 

'.86 

•  648 

.60 

.93 

419 

.15 

.79 

151 

.65 

.84 

894 

.15 

.90 

643 

.65 

.97 

413 

.20 

.83 

146 

.70 

.88 

889 

.20 

.94 

638 

.70 

16.01 

408 

.25 

.87 

140 

.75 

.93 

884 

.25 

.98 

633 

.75 

.05 

402 

.30 

.92 

135 

.80 

.97 

879 

.30 

14.03 

628 

.80 

.09 

397 

.35 

.96 

130 

.85 

12.01 

874 

.35 

.07 

623 

.85 

.14 

391 

.40 

10.00 

125 

.90 

.Or 

869 

.40 

.11 

618 

.90 

.18 

386 

.45 

.04 

119 

.95 

.09 

864 

.45 

.15 

613 

.95 

.22 

OFFICIAL    METHODS   OF   ANALYSIS. 


1075 


PERCENTAGE   OF  ALCOHOL  BY  WEIGHT  AND  BY  VOLUME — Continued. 


[Recalculated  from  the  determinations  of  GILPIN,  DRINKWATER,  and  SQUIBB,  by  EDGAR 

RICHARDS.] 


Specific 
Gravity 
at  18°  F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent. 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at  |{J°  F. 

Per 

Cent. 
Alco- 
hol 

Per 

Cent 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at|8°F. 

Per 

Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 

atI8°F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent. 
Alco- 
hol 
by 
Wgt. 

0.97608 
603 

20-00 
.05 

16-26 

0.97355 
350 

22  •  50 

18.34 

0.97097 
092 

25-00 
.05 

20.43 

0-96828 

27-50 
.55 

22:!t 

598 

.10 

'.34 

345 

.'eb 

'.42 

086 

.10 

.51 

816 

.60 

.62 

593 

.15 

.38 

340 

.65 

.47 

081 

.15 

.56 

811 

.65 

.67 

588 

.20 

.42 

335 

.70 

.51 

076 

.20 

.60 

805 

.70 

.71 

583 

.25 

.46 

330 

.75 

.55 

071 

.25 

.64 

800 

.75 

.75 

.       578 

.30 

.51 

324 

.80 

.59 

065 

.30 

.68 

794 

.80 

.79 

573 

.35 

.58 

319 

.85 

.63 

060 

.35 

.72 

789 

.85 

.83 

568 

.40 

.59 

314 

.90 

.68 

055 

.40 

.77 

783 

.90 

.88 

563 

.45 

.63 

309 

.95 

.72 

049 

.45 

.81 

778 

.95 

.92 

.97558 
552 

20:i§ 

16:76I 

.97304 
299 

23-00 
.05 

18-76 

.97044 
039 

25-50 

20-85 
.89 

-96772 
766 

2,.oo5 

22-96 
23.00 

547 

.60 

.75 

294 

.10 

'.84 

033 

6C 

.93 

761 

.10 

.04 

542 

.65 

.80 

289 

.15 

.88 

028 

!65 

.98 

755 

.15 

.09 

537 

.70 

.84 

283 

.20 

.92 

023 

.70 

21.02 

749 

.20 

.13 

532 

.75 

.88 

278 

.25 

.96 

018 

.75 

.06 

744 

.25 

.17 

527 

.80 

.92 

273 

.30 

19.01 

012 

.80 

.10 

738 

.30 

.21 

522 

.85 

.96 

268 

.35 

.05 

007 

.85 

.14 

732 

.35 

.25 

517 

.90 

17.01 

263 

.40 

.09 

001 

.90 

.19 

726 

.40 

.30 

512 

.95 

.05 

258 

.45 

.13 

.  96996 

.95 

.23 

721 

.45 

.34 

•97507 

21:8i 

17-09 
.13 

•97253 
247 

23:Ii 

19-17 
.21 

.96991 
986 

se.oo 

21-27 
.31 

.96715 
709 

28-50 
.55 

23-38 

497 

.10 

.17 

242 

.60 

.25 

980 

.10 

.35 

704 

.60 

.47 

492 

.15 

.22 

237 

.65 

.30 

975 

.15 

.40 

698 

.65 

.51 

487 

.20 

.26 

232 

.70 

.34 

969 

-.20 

.44 

692 

.70 

.55 

482 

.25 

.30 

227 

.75 

.38 

964 

.25 

.48 

687 

.75 

.60 

477 

.30 

.34 

222 

.80 

.42 

959 

.30 

.52 

681 

.80 

.'64 

472 

.35 

.38 

216 

.85 

.46 

953 

.35 

.56 

675 

.85 

.68 

467 

.40 

.43 

211 

.90 

.51 

949 

.40 

.61 

669 

.90 

.72 

462 

.45 

.47 

206 

.95 

.55 

942 

.45 

.65 

664 

.95 

.77 

.97457 
451 

21:B 

"•11 

.97201 
196 

24.00 
.05 

19-59 
.63 

•96937 
932 

26-50 
.55 

21-69 

.96658 
652 

29-00 

23-81 

.85 

446 

.60 

.59 

191 

.10 

.67 

926 

.60 

77 

646 

!ib 

.89 

441 

.65 

.63 

185 

.15 

.72 

921 

.65 

'.S2 

640 

.15 

.94 

436 

.70 

.67 

180 

.20 

.76 

915 

.70 

.86 

635 

.20 

.98 

431 

.75 

.71 

175 

.25 

.80 

910 

.75 

.90 

629 

.25 

24.02 

426 

.80 

.76 

170 

.30 

.84 

905 

.80 

.94 

623 

.30 

.06 

421 

.85 

.80 

165 

.35 

.88 

899 

.85 

.98 

617 

.35 

.10 

416 

.90 

.84 

159 

.40 

.93 

894 

.90 

22.03 

611 

.40 

.15 

411 

.95 

.88 

154 

.45 

.97 

888 

.95 

.07 

605 

.45 

.19 

.97406 

22.00 

17-92 

.97149 

24.50 

20.01 

.96883 

27-00 

22-11 

.96600 

29-50 

24-23 

401 

.05 

144 

.55 

877 

.05 

.15 

594 

.55 

.27 

396 

.10 

isioc 

139 

.60 

!os 

872 

.10 

.20 

587 

.60 

.32 

391 

.15 

.05 

133 

.65 

.14 

866 

.15 

.24 

582 

.65 

.36 

386 

.20 

.09 

128 

.70 

.18 

861 

.20 

.28 

576 

.70 

.40 

381 

.25 

.13 

123 

.75 

.22 

855 

.25 

.33 

570 

.75 

.45 

375 

.30 

.17 

118 

.80 

.26 

850 

.30 

.37 

564 

.80 

.49 

370 

.35 

.21 

113 

.85 

.30 

844 

.35 

.41 

559 

.85 

.53 

365 

.40 

.26 

107 

.90 

.35 

839 

.40 

.45 

553 

.90 

.57 

360 

.45 

.30 

102 

.95 

.39 

833 

.45 

.50 

547 

.95 

.62 

1076 


APPENDIX    I. 


PERCENTAGE   OF  ALCOHOL  BY  WEIGHT  AND   BY  VOLUME — Continued. 

[Recalculated  from  the  determinations  of  GII^PIN,  DRINK  WATER,  and    SQUIBB,  by  EDGAR 

RICHARDS.] 


Specific 
Gravity 
at  §8°  F. 
1    - 

Per 

Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at  g»°  F. 

Per 

Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

Specific 
Gravity 
at  |g°  F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent 
Alco- 
hol 
by 
Wgt, 

Specific 
Gravity 
at  |8°  F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 
by 
Wgt. 

0.96541 
535 

30.0024-66 

0-96235 

32.50 
.55 

26-80 

.84 

0-95910 
903 

35-00 
.05 

28-96 
29.00 

I 
0.95560!  37-50 
552         .  55 

sl:H 

529 

.10 

.74 

222 

.60 

.89 

896 

.10 

.05 

545 

.60 

.23 

523 

.15 

.79 

216 

.65 

.93 

889 

.15 

.09 

538 

.65 

.27 

517 

.20 

.83 

210 

.70 

.97 

883 

.20 

.13 

531 

.70 

.32 

511 

.25 

.87 

204 

.75 

27.02 

876 

.25 

.18 

523 

.75 

.36 

505 

.30 

.91 

197 

.80 

.06 

869 

.30 

.22 

516 

.80 

.40 

499 

.35 

.95 

191 

.85 

•1Q 

862 

.35 

.26 

509 

.85 

.45 

493 

.40 

25.00 

185 

.90 

.14 

855 

.40 

.30 

502 

.90 

.49 

487 

.45 

.04 

178 

.95 

.19 

848 

.45 

.35 

494 

.95 

.54 

.98481 

30.5025-08 
.55       .12 

.96172 

33.00 

»  •$ 

•95f4i 

35-50 
.55 

29.39 

.95487!  38-00 
480         .05 

31-58 
.63 

469         .60 

.17 

159 

.10 

.32 

828 

.60 

.48 

472         .  10 

.67 

463         .65 

.21 

153 

.15 

.36 

821 

.65 

.52 

465         .  15 

.72 

457 

.70 

.25 

146 

.20 

.40 

814 

.70 

.57 

457 

.20 

.76 

451 

.75 

.30 

140 

.25 

.45 

807 

.75 

.61 

450 

.25 

.81 

445         .80 

.34 

133 

.30 

.49 

800 

.80 

.65 

442 

.30 

.85 

439         .85 

.38 

127 

.35 

.53 

794 

.85 

.70 

435 

.35 

.90 

433         .90 

.42 

120 

.40 

.57 

787 

.90 

.74 

427 

.40 

.94 

427 

.95 

.47 

114 

.45 

.62 

780 

.95 

.79 

420 

.45 

.99 

.96421 
415 

31-0025.51 
.05       .55 

.96108 

33  :fi 

»;JJ 

"Ml 

36.00 

29-83 

.87 

•95to! 

38.50 
.55 

32.03 

409 

.10' 

.60 

095 

.60 

.75 

759 

.10 

.92 

398 

.60 

.12 

403 

.15 

.64 

088 

.65 

.79 

752 

.15 

.96 

390 

.65 

.16 

396         .  20 

.68 

082 

.70 

.83 

745 

.20 

30.00 

383 

.70 

.20 

390         .25 

.73 

075 

.75 

.88 

738 

.25 

.05 

375 

.75 

.25 

384 

.30 

.77 

069 

.80 

.92 

731 

.30 

.09 

368 

.80 

.29 

378         .35 

.81 

062 

.85 

.96 

724 

.35 

.13 

360 

.85 

.33 

372         .40 

.85 

056 

.90 

28.00 

717 

.40 

.17 

353 

.90 

.37 

366 

.45 

.90 

049 

.95 

.05 

710 

.45 

.22 

345 

.95 

.42 

•96111 

31:ii25:§4 

•9684I 

34:8§ 

28.09 

.95703 
695 

38.50 

30.28 

.95338 
330 

39.00 

32-46 
.50 

347 

.60 

26.03 

030 

.10 

.18 

688 

.60 

.35 

323 

.10 

.55 

341 

.65 

.07 

023 

.15 

.22 

681 

.65 

.39 

315 

.15 

.59 

335 

.70 

.11 

016 

.20 

.26 

674 

.70 

.44 

307 

.20 

.64 

329 

.75 

.16 

010 

.25 

.31 

667 

.75 

.48 

300 

.25 

.68 

323 

.80 

.20 

003 

.30 

.35 

660 

.80 

.52 

292 

.30 

.72 

316         .85 

.24 

95.996 

.35 

.39 

653 

.85 

.57 

284 

.35 

.77 

310l        .90 

.28 

990 

.40 

.43 

646 

.90 

.61 

277 

.40 

.81 

304 

.95 

.33 

983 

.45 

.48 

639 

.95 

.66 

269 

.45 

.86 

-    .96298 

32.00 

26-37 

•95977 

34-50 

28-52 

.95632 

37-00 

30-70 

.95262 

39-50 

32-90 

292 

.05 

.41 

970 

.55 

.56 

625 

.05 

.74 

254 

.55 

.95 

285 

.10 

.46 

963 

.60 

.61 

618 

.10 

.79 

246 

.60 

.99 

279 

.15 

.50 

957 

.65 

.65 

610 

.15 

.83 

239 

.65 

33.04 

273 

.20 

.54 

950 

.70 

.70 

603 

.20 

.88 

231 

.70 

.08 

267 

.25 

.59 

943 

.75 

.74 

596 

.25 

.92 

223 

.75 

.13 

260 

.30 

.63 

937 

.80 

.78 

589 

.30 

.96 

216 

.80         .17 

254 

.35 

.67 

930 

.85 

.83 

581 

.35 

31.01 

208 

.851        .22 

248 

.40 

.71 

923 

.90 

.87 

574 

.40 

.05 

200 

.90         .27 

241 

.45 

76 

917 

.95 

.92 

567 

.45 

.10 

193 

.95         .31 

OFFICIAL    METHODS    OF   ANALYSIS. 


1077 


PERCENTAGE   OF  ALCOHOL  BY  WEIGHT  AND   BY  VOLUME Continued. 


[Recalculated  from  the  determinations  of  GILPIN,  DRINKWATER,  and  SQUIBB,  by  EDGAK 

RICHARDS.] 


Specific 
Gravity 
at  |§°  F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

!   Per 
Cent 
Alco- 
hol 
by 

wjt. 

Specific 
Gravity 
at|8°F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent 
Alco- 
hol 

& 

Specific 
Gravity 
atfS<>F. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 
Cent. 
Alco- 
hol 

&. 

Specific 
Gravity 

atirr. 

Per 
Cent. 
Alco- 
hol 
by 
Vol. 

Per 

Cent. 
Alco- 
hol 

,&. 

0.95185    40-0033-35 

0.94786 

42-50 

35-58 

0.94364 

45-00 

37-84 

0.93916 

47-50 

40-13 

177  i        .05 

.39 

778 

.55 

.6? 

355 

.05 

.89 

906 

.18 

169         .10 

.44 

770 

.60 

.67 

346 

.10 

.93 

898 

leo 

.22 

161         .15 

.48 

761 

.65 

.72 

338 

.15 

.98 

888 

.65 

.27 

154 

.20 

.53 

753 

.70 

.76 

329 

.20 

38.02 

879 

.70 

.32 

146         .  25 

.57 

745 

.75 

.81 

320 

.25 

.07 

870 

.75 

.37 

138         .30 

.61 

737 

.80 

.85 

311 

.30 

.12 

861 

.80 

.41 

130         .35 

.66 

!  729 

.85 

.90 

302 

.35 

.16 

852 

.85 

.46 

122         .40 

.70 

720 

.90 

.94 

294 

.40 

.21 

842 

.90 

.51 

114         .45 

.75 

712 

.95 

.99 

285 

.45 

.25 

833 

.95 

.55 

.95107    40-5033-79 
099         .55       .84 

•94704 
696 

43-00 
.05 

36:81 

'"IT6 

45  -M 

38:1§ 

.93824 
815 

48:8i 

40.60 
.65 

09i;        .60 

.88 

687 

.10 

.12 

258 

.60 

.39 

805 

.10 

.69 

083  i        .65 

.93 

679 

.15 

.17 

250 

.65 

.44 

796 

.15 

.74 

075         .70 

.97 

670 

.20 

.21 

241 

.70 

.48 

786 

.20 

.78 

067 

.7534.021 

662 

.25 

.23 

232 

.75 

.53 

777 

.25 

.83 

059 

.80 

.06 

654 

.30 

.30 

223 

.80 

.57 

768 

.30 

.88 

052 

.85 

.11 

645 

.35 

.35 

214 

.85 

.62 

758 

.35 

.92 

044 

.90 

.15 

637 

.40 

.39 

206 

.90 

.66 

749 

.40 

.97 

036 

.95 

.20 

628 

.45 

.44 

197 

.95 

.71 

739 

.45 

41.01 

.95028 
020 

41:8i 

34-24 

.94620 

43-50 
.55 

••:« 

•»«»! 

46.00 
.05 

38:ia 

.937320 

48:!E 

41.0, 

012 

.10 

.33 

603 

.60 

.57 

170 

.10 

.84 

711 

.60 

.15 

004 

.15 

.37 

595 

.65 

.62 

161 

.15 

.89 

702 

.65 

.20 

.94996 

.20 

.42 

586 

.70 

.66 

152 

.20 

.93 

692 

.70 

.24 

988 

.25 

.46 

578 

.75 

.71 

143 

.25 

.98 

683 

.75 

.29 

980 

.30 

.50 

570 

.80 

.75 

134 

.30 

39.03 

679 

.80 

.34 

972 

.35 

.55 

561 

.85 

.80 

125 

.35 

.07 

664 

.85 

.38 

964 

.40 

.59 

553 

.90 

.84 

116 

.40 

.12 

655 

.90 

.43 

956 

.45 

.64 

544 

.95 

.89 

107 

.45 

.16 

645 

.95 

.47 

.94948 
940 

41:ii 

3t:tt 

.94536 

U:!S 

36.9| 

•  .94098 
089 

46:i? 

39-i 

•»3636 

49:8i 

41  •% 

932 

.60 

.77 

519 

.10 

37.02 

080 

.60 

.30 

617 

.10 

.61 

924 

.65 

.82 

510 

.15 

.07 

071 

.65 

.35 

607 

.15 

.66 

916 

.70 

.86 

502 

.20 

.11 

062 

.70 

.39 

598 

.20 

.71 

908 

.75 

.91 

493 

.25 

.16 

053 

.75 

.44 

588 

.25 

.76 

900 

.80 

.95 

484 

.30 

.21 

044 

.80 

.49 

578 

.30 

.80 

892 

.8535.00 

476 

.35 

.25 

035 

.85 

.53 

569 

.35 

.85 

884 

.90 

.04 

467 

.40 

.30 

026 

.90 

.58 

559 

.40 

.90 

876 

.95 

.09 

459 

.45 

.34 

017 

.95 

.62 

550 

.45 

.94 

-94868 
860 

*:S 

35:il 

•94450 
441 

44  -  50 
.55 

37.35 

•94008 
.  93999 

47:8§ 

39-67 

-93540 
530 

49-50    41-99 
.55    42.04 

852 

.10 

.22 

433 

.60 

At 

990 

.10 

'.76 

521 

.60         .08 

843 

.15 

.27 

424 

.65 

.53 

980 

.15 

.81 

511 

.65         .13 

835 

.20 

.31 

416 

.70 

.57 

971 

20 

.85 

502 

.70         .18 

827 

.25 

.36 

407 

.75 

.62 

962 

.25 

.90 

492 

.75         .23 

819 

.30 

.40 

398 

.80 

.66 

953 

.30 

.95 

482 

.80 

.27 

811 

.35 

.45 

390 

.85 

.71 

944 

.35 

.99 

473 

.85 

.32 

802 

.40 

.49 

381 

.90 

.76 

934 

.40 

40.04 

463 

.90 

.37 

794 

.45 

.54 

373 

.95 

.80 

925 

.45 

.08 

454 

.95 

.41 

1078  APPENDIX   I. 

3.  DETERMINATION  OF  EXTRACT. 

(a)  IN  DISTILLED  LIQUORS,  DRY  WINES,  BEERS,  ALES,  ETC. 
(1)  Direct  Method. 

Fifty  c.c.  of  the  sample  are  weighed  in  a  flat  platinum  dish  about  85 
mm.  in  diameter  and  capable  of  holding  about  75  c.c.  and  evaporated  on  the 
water-bath  to  a  sirupy  consistence.  The  residue  is  heated  for  two  and  a 
half  hours  in  a  drying  oven  at  the  temperature  of  boiling  water  and  weighed. 

(6)  IN  SWEET  WINES. 

Ten  c.c.  of  the  liquor  are  weighed  and  diluted  to  100  c.c.  with  water. 
Fifty  c.c.  of  this  solution  are  evaporated  as  described  under  (1). 

4.  DETERMINATION  OF  TOTAL  ACIDITY. 

Expel  any  carbon  dioxide  that  is  present  by  continued  shaking.  Trans- 
fer 10  c.c.  of  the  sample  to  a  beaker  and,  in  the  case  of  white  wines,  add  about 
10  drops  of  a  neutral  litmus  solution.  Add  decinormal  sodium-hydroxide 
solution  until  the  red  color  changes  to  violet.  Continue  adding  a  few  drops 
at  a  time  until  a  drop  of  the  mixture,  placed  on  delicate  red  litmus  paper, 
shows  an  alkaline  reaction.  The  result  is  expressed  in  terms  of  tartaric  acid. 

One  c.c.  of  decinormal  sodium-hydroxide  solution  =  0  •  0075  grm.  tartaric 
acid. 

5.  DETERMINATION  OF  VOLATILE  ACIDS. 

Fifty  c.c.  of  wine,  to  which  a  little  tannin  has  been  added  to  prevent 
foaming,  are  distilled  in  a  current  of  steam.  The  flask  is  heated  until  the 
liquid  boils,  when  the  lamp  under  it  is  turned  down,  and  the  steam  passed 
through  until  200  c.c.  have  been  collected  in  the  receiver.  The  distillate  is 
titrated  with  decinormal  sodium-hydroxide  solution  and  the  result  ex- 
pressed as  acetic  acid. 

One  c.c.  of  decinormal  sodium-hydroxide  solution  =  0  •  006  grm.  acetic  acid. 

6.  DETERMINATION  OF  GLYCERIN. 

(a)  IN  DRY  WINES. 

One  hundred  c.c.  of  wine  are  evaporated  in  a  porcelain  dish  to  about 
10  c.c.,  a  little  quartz  sand  and  milk-of-lime  added,  and  the  evaporation 
carried  almost  to  dryness.  The  residue  is  mixed  with  50  c.c.  of  90-per  cent, 
alcohol,  using  a  glass  pestle  or  spatula  to  break  up  any  solid  particles,  heated 
to  boiling  on  the  water-bath,  allowed  to  settle,  and  the  liquid  filtered  into  a 
small  flask.  The  residue  is  repeatedly  extracted  in  a  similar  manner  with 
small  portions  of  boiling  alcohol  until  the  filtrate  in  the  flask  amounts  to  about 
150  c.c.  A  little  quartz  sand  is  then  added  to  it,  the  flask  connected  \\ith  a 
condenser,  and  the  alcohol  slowly  distilled  until  about  10  c.c.  remain.  The 
evaporation  is  then  continued  in  the  water-bath  until  the  residue  becomes 
simpy.  It  is  cooled  and  dissolved  in  10  c.c.  of  absolute  alcohol.  The  solution 
mav  be  facilitated  by  gentle  heating  on  the  water-bath.  Fifteen  c.c.  of 
anhvdrous  ether  are  added  and  the  flasks  stoppered  and  allowed  to  stand 
until  the  precipitate  has  collected  on  the  sides  and  bottom  of  the  flask. 


OFFICIAL    METHODS    OF    ANALYSIS.  1079 

The  clear  liquid  is  decanted  into  a  tared  weighing  bottle,  the  precipitate 
repeatedly  washed  with  a  few  cubic  centimeters  of  a  mixture  of  1  part  abso- 
lute alcohol  and  1  •  5  parts  anhydrous  ether  and  the  washings  added  to  the 
solution.  The  ether-alcohol  is  evaporated  on  the  water-bath  and  the  residue 
dried  one  hour  in  a  water-oven,  weighed,  the  amount  of  ash  determined, 
and  its  weight  deducted  from  that  of  the  weighed  residue. 

(6)    IN   SWEET   WIXES. 

One  hundred  c.c.  of  wine  are  evaporated  on  the  water-bath  to  a  sirupy 
.•on.-sistence,  a  little  quartz  sand  being  added  to  render  subsequent  extraction 
easier.  The  residue  is  repeatedly  extracted  with  absolute  alcohol  until  the 
united  extracts  amount  to  from  100  to  150  c.c.  The  extract  is  collected  in  a 
flask,  and  for  every  part  of  alcohol  1-5  parts  of  ether  are  added,  the  liquor 
well  shaken,  and  allowed  to  stand  until  it  becomes  clear.  The  supernatant 
liquid  is  decanted  into  a  beaker,  and  the  precipitate  washed  with  a  few  cubic 
centimeters  of  a  mixture  of  1  part  alcohol  and  1  •  5  parts  ether.  The  united 
liquids  are  distilled,  the  evaporation  being  finished  on  the  water-bath,  the 
residue  is  dissolved  in  water,  transferred  to  a  porcelain  dish,  and  treated  as 
under  (a). 

It  is  necessary  to  test  the  glycerin  from  sweet  wines  for  sugar,  and  if  any 
be  present,  it  must  be  estimated  by  methods  already  described  and  its  weight 
subtracted  from  that  of  the  glycerin. 

7.  DETERMINATION  OF  REDUCING  SUGARS. 

The  reducing  sugars  are  estimated  as  dextrose,  and  may  be  determined 
by  any  of  the  methods  given  for  the  estimation  of  dextrose. 

S.  POLARIZATION. 

All  results  are  to  be  stated  as  the  polarization  of  the  undiluted  wine. 
The  VEXTZKB  scale  saccharimeter  is  to  be  used,  and  the  results  expressed 
in  terms  of  the  sugar  scale  of  this  instrument.  If  any  other  instrument  be 
used,  or  if  it  be  desirable  to  convert  to  angular  rotation,  the  folio  wing  factors 
may  be  employed: 

1°  VENTZKE  =  0  •  3468°  angular  rotation  D. 

1°  angular  rotation  D.          =2-8835°  VENTZKE. 

1  °  VENTZKE  =  2  -  6048°  Wild  (sugar  scale) . 

1  °  Wild  (sugar  scale)  =  0  •  3840°  VENTZKE. 

1°  Wild  (sugar  scale)  =0- 1331°  angular  rotation  D. 

1°  angular  rotation  D.          =0-7511°  Wild  (sugar  scale). 

1°  LAURENT  (sugar  scale)    =0-2167°  angular  rotation  D. 

1°  angular  rotation  D.          =4-6154°  LAURENT  (sugar  scale). 

(a)    IN   WHITE    WINES. 

Sixty  c.c.  of  wine  are  clarified  with  3  c.c.  of  lead-subacetate  solution  and 
filtered  after  adding  3  c.c.  of  water.  Thirty-three  c.c.  of  the  filtrate  are  treated 
with  3  c.c.  of  a  half-saturated  solution  of  sodium  carbonate,  filtered  and 
polarized.  This  gives  a  dilution  of  10  to  11,  which  must  be  considered  hi 


1080  APPENDIX   I. 

the  calculation,  and  the  polariscope  reading  must  accordingly  be  increased 
one-fifth. 

(6)  IN  RED  WINES. 

Sixty  c.c.  of  wine  are  clarified  with  6  c.c.  of  lead-subacetate  solution  and 
filtered.  To  33  c.c.  of  the  filtrate  3  c.c.  of  a  saturated  solution  of  sodium 
carbonate  are  added,  filtered,  and  the  filtrate  polarized.  The  dilution  in 
this  case  is  5  to  6,  and  the  polariscope  reading  must  accordingly  be  increased 
one-fifth. 

(c)  IN  SWEET  WINES. 

(1)  Before  Inversion. 

One  hundred  c.c.  are  clarified  with  2  c.c.  of  lead-subacetate  solution,  and 
filtered  after  the  addition  of  8  c.c.  of  water.  One-half  c.c.  of  a  saturated 
solution  of  sodium  carbonate  and  4-5  c.c.  of  water  are  added  to  55  c.c.  of  the 
filtrate,  and  the  liquid  mixed,  filtered,  and  polarized.  The  polariscope 
reading  is  multiplied  by  1-2. 

(2)  After  Inversion. 

Thirty-three  c.c  of  the  filtrate  from  the  lead  subacetate  in  (1)  are  placed 
in  a  flask  with  3  c.c.  strong  hydrochloric  acid.  After  mixing  well,  the  flask 
is  placed  in  water  and  heated  until  a  thermometer,  placed  in  the  flask  with 
the  bulb  as  near  the  center  of  the  liquid  as  possible,  marks  68°,  consuming 
about  fifteen  minutes  in  the  heating  It  is  then  removed,  cooled  quickly  to 
room  temperature,  filtered,  and  polarized,  the  temperature  being  noted. 
The  polariscope  reading  is  multiplied  by  1-2. 

(3)  After  Fermentation. 

Fifty  c.c.  of  wine,  which  have  been  dealcoholized  and  made  up  to  the 
original  volume  with  water,  are  mixed  in  a  small  flask  with  well-washed 
beer  yeast  and  kept  at  30°  until  fermentation  has  ceased,  which  requires 
from  two  to  three  days.  The  liquid  is  then  washed  into  a  100  c.c.  flask, 
a  few  droDS  of  a  solution  of  acid  mercuric  nitrate  and  then  lead-subacetate 
solution,  followed  by  sodium  carbonate,  added.  The  flask  is  filled  to  the 
mark  with  water,  shaken,  and  the  solution  filtered  and  polarized 

(d)    APPLICATION   OF   ANALYTICAL   METHODS, 

(1)  The  Wine  shows  no  Rotation. 

This  may  be  due  to  the  absence  of  any  rotatory  body,  to  the  simulta- 
neous presence  of  the  dextrorotatory  non-fermentable  constituents  of  com- 
mercial dextrose  and  levorotatory  sugar,  or  to  the  simultaneous  presence 
of  dextrorotatory  cane-sugar  and  levorotatory  invert-sugar. 

(a)  THE  WINE  is  INVERTED. — A  levorotation  shows  that  the  sample 
contains  cane-sugar. 

(6)  THE  WINE  is  FERMENTED. — A  dextrorotation  shows  that  botli  levo- 
rotatory sugar  and  the  unfermentable  constituents  of  commercial  dextrose 
are  present. 


OFFICIAL   METHODS   OF  ANALYSIS.  1081 

If  no  change  take  place  in  either  (a)  or  (6)  in  the  rotation,  it  proves  the 
absence  of  unfermented  cane  sugar,  the  unfermen table  constituents  of  com- 
mercial dextrose,  and  of  levorotatory  sugar. 

(2)  The  Wine  Rotates  to  the  Right. 

This  may  be  caused  by  unfermented  cane  sugar,  the  unfennentable  con- 
stituents of  commercial  dextrose,  or  both, 
(a)  THE  WINE  is  INVERTED. 

(at)  It  rotates  to  the  left  after  inversion. — Unfermented  cane  sugar 
is  present. 

(a2)  It  rotates  more  than  2-30°  to  the  right.— The  unfennentable 
constituents  of  commercial  dextrose  are  present 

(a3)  It  rotates  less  than  2  •  30°  and  more  than  0  •  9°  to  the  right. — It  is 
in  this  case  treated  as  follows : 

Two  hundred  and  ten  c.c.  of  the  wine  are  evaporated  in  a  porce- 
lain dish  to  a  thin  sirup  with  a  few  drops  of  a  20-per  cent,  solution  of 
potassium  acetate.  To  the  residue  200  c.c.  of  90-per  cent,  alcohol  are 
added  with  constant  stirring.  The  alcoholic  solution  is  filtered  into  a 
flask,  and  the  alcohol  removed  by  distillation  until  about  5  c.c.  remain. 
The  residue  is  mixed  with  washed  bone  black,  filtered  into  a  gradu- 
ated cylinder,  and  washed  until  the  filtrate  amounts  to  30  c.c.  When 
the  filtrate  shows  a  dextrorotation  of  more  than  1-5°,  it  indicates 
the  presence  of  the  unfennentable  constituents  of  commercial  dextrose 

(3)   The  Wine  Rotates  to  the  Left. 

It  contains  unfermented  levorotatory  sugar,  derived  either  from  the 
must  or  from  the  inversion  of  added  cane  sugar.  It  may,  however,  also  con- 
tain unfermented  cane  sugar  and  the  unfennentable  constituents  of  com- 
mercial dextrose. 

(a)  The  wine  is  fermented  according  to  8  (c),  (3). 

(aj  It  polarizes  3°  after  fermentation. — It  contains  only  levo- 
rotatory sugar. 

M  It  rotates  to  the  right. — It  contains  both  levorotatory  sugar 
and  the  unfennentable  constituents  of  commercial  dextrose. 

(b)  The  wine  is  inverted  according  to  8  (c),  (3). 

(6,>  It  is  more  strongly  levorotatory  after  inversion.— It  contains 
both  levorotatory  sugar  and  unfermented  cane  sugar. 

9.  DETERMINATION  OF  TANNIN  AND  COLORING  MATTER. 

(a)    PREPARATION    OF    REAGENTS. 

DeTinarmal  Solution  of  Oxalic  Acid.— 10  c.c.  =0-04157  grm.  tannin. 

Potassium --permanganate  Solution.  — I  •  333  grm.  of  potassium  perman- 
ganate are  dissolved  in  1  litre  of  water  and  the  solution  standardized  by 
means  of  the  decinormal  oxalic-acid  solution. 

Tndiqo  Solution. — 6  grm.  of  sodium  sulphindigotate  are  dissolved  in  500  c.c. 
of  water  with  the  aid  of  heat,  cooled.  50  c.c.  of  concentrated  sulphuric  acid 
added,  and  the  solution  made  up  to  1  litre  and  filtered. 


1082  APPENDIX    I. 

Purified  Bone-black.  —Finely  pulverized  bone-black  is  extracted  with 
hydrochloric  acid  and  washed  with  distilled  water  until  the  acid  is  entirely 
removed.  The  bone  black  is  kept  covered  with  water. 

(6)    LETERMINATION. 

(1)  One  hundred  c.c.  of  wine  are  dealcoholized  by  evaporation,  and  the 
original  volume  restored  with  water.     Ten  c.c.  are  measured  into  a  porce- 
lain casserole  having  a  capacity  of  about  a  litre,  and  750  c.c.  of  water  and 
20  c.c.  of  the  indigo  solution  added,  the  latter  being  measured  from  a  burette. 
The  potassium -permanganate   solution  is  added,   a  cubic  centimeter  at    a 
time,  until  the  blue  color  changes  to  green ,  then  a  few  drops  at  a  time  until 
the  liquid  becomes  golden  yellow.     Designate  by  a  the  number  of  cubic 
centimeters  of  permanganate  solution  used. 

(2)  Ten  c.c.  of  the  dealcoholized  wine,  obtained  as  in  (1),  are  treated 
with  bone-black  for    fifteen  minutes,  filtered,  and  the  bone-black    washed 
carefully.     The  filtrate  is  diluted  with  750  c.c.  of  water,  20  c.c.  of  indigo 
solution  added,  and  the  titration  carried  out  as  in  (1).     Designate  burette 
reading  by  b. 

Then  a  —  6=c=the  number  of  cubic  centimeters  of  the  potassium  per- 
manganate solution  required  for  the  oxidation  of  the  tannin  and  coloring 
matter  in  10  c.c.  of  wine. 

10.  DETERMINATION  OF  POTASSIUM  BITARTRATE. 

The  determination  of  potassium  bitartrate  is  necessary  when  an  esti- 
mation of  the  tartaric  acid  is  desired. 

Fifty  c.c.  of  wine  are  placed  in  a  porcelain  dish  and  evaporated  to  a  sirupy 
consistence,  a  little  quartz  sand  being  added  to  render  subsequent  extrac- 
tion easier.  After  cooling,  70  c.c.  of  96-per  cent,  alcohol  are  added  with 
constant  stirring.  After  standing  for  twelve  hours  at  as  low  a  tempera- 
ture as  practicable,  the  solution  is  filtered  and  the  precipitate  washed  with 
alcohol  until  the  filtrate  is  no  longer  acid.  The  alcoholic  filtrate  is  preserved 
for  the  estimation  of  the  tartaric  acid.  The  filter  and  precipitate  are  returned 
to  the  porcelain  dish  and  repeatedly  treated  with  hot  water,  each  extraction 
being  filtered  into  a  flask  or  beaker  until  the  washings  are  neutral.  The 
combined  aqueous  filtrates  and  washings  are  titrated  with  decinormal  sodium- 
hydroxide  solution. 

One  c.c.  decinormal  sodium -hydroxide  solution  =0-0188  grm.  potassium 
bitartrate. 

11.  DETERMINATION  OF  TARTARIC  ACID. 

(a)    IN    THE    ALCOHOLIC    FILTRATE   FROM   THE  POTASSIUM   BITARTRATE. 

The  filtrate  is  made  up  to  a  definite  volume  with  water  and  divided  into 
two  equal  portions.  One  portion  is  exactly  neutralized  with  decinormal 
sodium-hydroxide  solution,  the  other  portion  added,  the  alcohol  evaporated, 
the  residue  washed  into  a  porcelain  dish,  and  treated  as  under  10. 

One  c.c.  decinormal  sodium -hydroxide  solution  =0-0075  grm.  tartaric  acid. 


OFFICIAL   METHODS    OF   ANALYSIS.  1083 

As,  however,  only  half  of  the  free  tartaric  acid  is  determined  by  this 
method — 

One  c.c.  decinormal  sodium  hydroxide  =0-015  gnn.  of  tartaric  acid, 

(6)    MODIFIED    BERTHELOT-FLEURY    METHOD. 

Ten  c.c.  of  wine  are  neutralized  with  potassium-hydroxide  solution  and 
mixed  in  a  graduated  cylinder  with  40  c.c.  of  the  same  sample.  To  one- 
fifth  of  the  volume,  corresponding  to  10  c.c.  of  wine,  50  c.c.  of  a  mixture  of 
equal  parts  of  alcohol  and  ether  are  added  and  allowed  to  stand  twenty-four 
hours.  The  precipitated  potassium  bitartrate  is  separated  by  filtration, 
dissolved  in  water  and  titrated.  The  excess  of  potassium  bitartrate  over 
the  amount  of  that  constituent  present  in  the  wine  corresponds  to  the  free 
tartaric  acid. 

12.  DETERMINATION  OF  TARTARIC,  MALIC,  AND  SUCCINIC  ACIDS. 

[SCHMIDT  and  HIEPE'S  method.] 

Two  hundred  c.c.  of  wine  are  evaporated  one-half,  cooled,  and  lead-eub- 
acetate  solution  added  until  the  reaction  is  alkaline.  The  precipitate  is 
separated  by  filtration  and  washed  with  cold  water  until  the  filtrate  shows 
only  a  slight  reaction  for  lead.  The  precipitate  is  washed  from  the  filter  into 
a  beaker  by  means  of  hot  water,  and  treated  hot  with  hydrogen  sulphide  until 
all  the  lead  is  converted  into  sulphide.  It  is  then  filtered  hot  and  the  lead 
sulphide  washed  with  hot  water  until  the  washings  are  no  longer  acid.  The 
filtrate  and  washings  are  evaporated  to  50  c.c.  and  accurately  neutralized 
with  potassium  hydroxide.  An  excess  of  a  saturated  solution  of  calcium 
acetate  is  added  and  the  liquid  allowed  to  stand  from  four  to  six  hours  with 
frequent  stirring.  It  is  then  filtered  and  the  precipitate  washed  until  the 
filtrate  amounts  to  exactly  100  c.c.  The  precipitate  of  calcium  tartrate 
is  converted  into  calcium  oxide  by  igniting  in  a  platinum  crucible.  After 
cooling,  from  10  to  15  c.c.  of  normal  hydrochloric  acid  are  added,  the  solution 
washed  into  a  beaker,  and  accurately  titrated  with  normal  potassium- 
hydroxide  solution.  Every  cubic  centimeter  of  normal  acid  saturated  by 
the  calcium  oxide  is  equivalent  to  0-075  grm.  tartaric  acid.  To  the  amount 
so  obtained  0-0286  grm.  must  be  added,  representing  the  tartaric  acid  held 
in  solution  in  the  filtrate  as  calcium  tartrate.  The  sum  represents  the  total 
tartaric  acid  in  the  wine. 

The  filtrate  from  the  calcium  tartrate  is  evaporated  to  about  25  c.c.,  cooled, 
and  mixed  with  three  times  its  volume  of  96-per  cent,  alcohol.  After  standing 
several  hours  the  precipitate  is  collected  on  a  weighed  filter,  dried  at  100°, 
and  weighed.  It  represents  the  calcium  salts  of  malic,  succinic,  and  sul- 
phuric acids  and  of  the  tartaric  acid  which  remained  in  solution.  This  pre- 
cipitate is  dissolved  in  a  minimum  quantity  of  hydrochloric  acid,  filtered,  and 
the  filter  washed  with  hot  water.  Potassium-carbonate  solution  is  added 
to  the  hot  filtrate  and  the  precipitated  calcium  carbonate  separated  by  filtra- 
tion and  washed.  This  filtrate  contains  the  potassium  salts  of  the  above- 
named  acids.  It  is  neutralized  with  acetic  acid,  evaporated  to  a  small  volume, 
and  precipitated  hot  with  barium  chloride.  The  precipitate  of  barium 


1084  APPENDIX   I. 

succinate  and  sulphate  is  separated  by  filtration,  washed  with  hot  water,  and 
treated  on  the  filter  with  dilute  hydrochloric  acid.  The  barium  sulphate 
remaining  is  washed,  dried,  ignited,  and  weighed.  In  the  filtrate  which  con- 
tains the  barium  succinate,  the  barium  is  precipitated  hot  with  sulphuric  acid, 
washed,  dried,  ignited,  and  weighed.  Two  hundred  and  twenty-three  parts 
barium  sulphate  equal  118  parts  succinic  acid.  The  succinic  and  sulphuric 
acids,  as  well  as  the  tartaric  acid  remaining  in  solution  which  is  equal  to 
0  •  0286,  are  to  be  calculated  as  calcium  salts  and  the  result  deducted  from  the 
total  weight  of  the  calcium  precipitate.  The  remainder  is  the  calcium  ma- 
late,  of  which  172  parts  equal  134  parts  malic  acid. 

13.  DETECTION  OF  COLORING  MATTER, 
(a)  CAZENEUVE  REACTION. 

Add  0-2  grm.  of  precipitated  mercuric  oxide  to  10  c.c.  of  wine,  shake  for 
one  minute,  and  filter. 

Pure  wines  give  filtrates  which  are  colorless  or  light  yellow,  while  the 
presence  of  a  more  or  less  red  coloration  indicates  that  an  aniline  color  has 
.been  added  to  the  wine. 

(6)  METHOD  OP  SOSTEGNI  AND  CARPENTIERI. 

Evaporate  the  alcohol  from  200  c.c.  of  wine,  add  from  2  to  4  c.c.  of  a  10- 
per  cent,  solution  of  hydrochloric  acid,  immerse  some  threads  of  fat-free  wool, 
and  boil  for  five  minutes.  Remove  the  threads,  wash  them  with  cold  water 
acidified  with  hydrochloric  acid,  then  with  hot  water  acidified  with  hydro- 
chloric acid,  then  with  pure  water,  and  dissolve  the  color  in  a  boiling  mixture 
of  50  c.c.  of  water  and  2  c.c.  of  concentrated  ammonia.  Replace  the  threads 
by  new  ones,  acidify  with  hydrochloric  acid,  and  boil  again  for  five  minutes. 
In  the  presence  of  aniline  colors  to  the  amount  of  2  mgrm.per  litre,  the 
threads  are  dyed  as  follows 

Safranin light  rose-red. 

Vinolin rose-red  to  violet. 

Bordeaux  red rose-red  to  violet. 

Ponceau  red rose-red. 

Fuchsin dirty  white. 

Tropa?olin  00 straw-yellow. 

Tropseolin  000 light  orange. 

Corallin dirty  white. 

This  method  is  not  suitable  for  the  detection  of  fuchsin  or  corallin. 

(c)  DETECTION  OF  FUCHSIN  AND  ORSEILLE. 

To  20  c.c.  of  wine  add  10  c.c.  of  lead-subacetate  solution,  heat  slightly, 
and  mix  by  shaking.  Filter  into  a  test-tube,  add  2  c.c.  of  amyl  alcohol,  and 
shake.  If  the  amyl  alcohol  be  colored  red,  separate  it  and  divide  it  into  two 
portions.  To  one  portion  add  hydrochloric  acid,  to  the  other  ammonia. 
When  the  color  is  due  to  fuchsin,  the  amyl  alcohol  will  in  both  cases  be  de- 
colorized; when  due  to  orseille,  the  ammonia  will  change  the  color  of  the 
amyl  alcohol  to  purple-violet. 


OFFICIAL    METHODS   OF   ANALYSIS.  1085 

14.  DETERMINATION  OF  ASH. 

The  residue  from  the  direct  extract  determination  is  ineinerated  at  as 
low  a  heat  as  possible.  Repeated  moistening,  drying,  and  heating  to  redness 
is  advisable  to  get  rid  of  all  organic  substances. 

15.  DETERMINATION  OF  POTASH. 

(a)  KAYSER'S  METHOD. 

Dissolve  0.7  grm.  of  pure  sodium  hydroxide  and  2  grm.  of  tartaric  acid  in 
100  c.c.  of  wine,  add  150c.  c.  of  92-  to  94-per  cent,  alcohol,  and  allow  the  liquid 
to  stand  twenty-four  hours.  The  precipitated  potassium  bitartrate  is  col- 
lected on  a  small  filter  and  washed  with  50-per  cent,  alcohol  until  the  filtrate 
amounts  to  260  c.c.  The  precipitate  and  filter  are  transferred  to  the  beaker 
in  which  the  precipitation  was  made,  the  precipitate  dissolved  in  hot  water, 
the  volume  made  up  to  200  c.c.  and  50  c.c.  titrated  with  decinormal  sodium- 
hydroxide  solution ;  0  •  004  grm.  must  be  added  to  the  final  result, this  represent- 
ing the  potash  which  remains  in  solution  as  bitartrate. 

(6)  PLATINUM  CHLORIDE  METHOD. 

Evaporate  100  c.c.  of  wine  to  dryness,  incinerate  the  residue,  and  de- 
termine potash  as  given  under  methods  for  ash. 

16.  DETERMINATION  OF  SULPHUROUS  ACID. 

One  hundred  c.c.  of  wine  are  distilled  in  a  current  of  carbon  dioxide 
after  the  addition  of  phosphoric  acid  until  about  50  c.c.  have  passed  over. 
The  distillate  is  collected  in  accurately  standardized  iodine  solution.  When 
the  distillation  is  finished,  the  excess  of  iodine  is  determined  with  standard- 
ized sodium-thiosulphate  solution. 

17.  DETECTION  OF  SALICYLIC  ACID. 
(a)  SPICA'S  METHOD. 

Acidify  100  c.c.  of  the  liquor  with  sulphuric  acid  and  extract  with  ether. 
Evaporate  the  extract  to  dry-ness,  warm  the  residue  carefully  with  1  drop 
of  concentrated  nitric  acid,  and  add  2  or  3  drops  of  ammonia.  The  presence  of 
salicylic  acid  in  the  liquor  is  indicated  by  the  formation  of  the  yellow  color 
of  ammonium  picrate,  and  may  be  confirmed  by  dyeing  a  thread  of  fat-free 
wool. 

(5)  BIGELOW'S  METHOD. 

Place  100  c.c.  of  the  wine  in  a  separatory  funnel,  add  5  c.c.  of  sulphuric 
acid  (1-3),  and  extract  with  a  sufficient  quantity  of  a  mixture  of  eight  or 
nine  parts  of  ether  to  one  part  of  petroleum  ether.  Throw  away  the  aqueous 
portion,  wash  the  other  once  with  water,  then  shake  thoroughly  with  about 
50  c.c.  of  water,  to  which  from  6  to  8  drops  of  0-5  per  cent,  solution  of  ferric 
chloride  have  been  added.  Discard  the  aqueous  portion,  which  contains 
the  greater  part  of  the  tannin  in  combination  with  iron,  wash  again  with 
water,  transfer  the  ethereal  solution  to  a  porcelain  dish,  and  allow  to  evapo- 
rate spontaneously.  Heat  the  dish  on  the  steam-bath,  take  up  the  residue 


1086  APPENDIX   I. 

•with  1  or  2  c.c,  of  cold  water,  transfer  quickly  to  a  test-tube  without  stirring, 
and  add  1  or  2  drops  of  0-5  per  cent,  solution  of  ferric  chloride.  The  pres- 
ence of  salicylic  acid  is  indicated  by  the  appearance  of  a  violet-red  colora- 
tion. In  the  case  of  red  wines  a  second  extraction  of  the  residue  with  ether 
mixture  is  sometimes  necessary.  This  is  indicated  by  the  amount  of  residue 
left  in  the  dish  on  the  evaporation  of  the  ether. 

This  method  cannot  be  used  in  the  examination  of  beers  and  ales. 

(c)  GIRARD'S  METHOD. 

Extract  a  portion  of  the  acidified  liquor  with  ether  as  in  the  preceding 
methods,  evaporate  the  extract  to  dryness,  and  extract  the  residue  with 
petroleum  ether.  The  residue  from  the  petroleum-ether  extract  is  dissolved 
in  water  and  treated  with  a  few  drops  of  a  very  dilute  solution  of  ferric  chloride. 
The  presence  of  salicylic  acid  is  indicated  by  the  appearance  of  a  violet-red 
coloration. 

18.  DETECTION  OF  GUM  AND  DEXTRIN. 

Four  c.c.  of  wine  are  mixed  with  10  c.c.  of  96-per  cent,  alcohol.  When 
gum  arable  or  dextrin  is  present,  a  lumpy,  thick,  and  stringy  precipitate 
is  produced,  whereas  pure  wine  becomes  at  first  opalescent  and  then  gives  a 
flocculent  precipitate. 

19.  DETERMINATION  OF  FUSEL  OIL. 

The  apparatus  recommended  for  this  determination  is  BROMWELL'S 
modification  of  ROESE'S  fusel-oil  apparatus. 

This  apparatus  consists  of  a  pear-shaped  bulb  holding  about  200  c.c., 
stoppered  at  the  upper  end  and  sealed  at  the  lower  to  a  graduated  stem 
about  4  mm.  in  internal  diameter.  To  the  lower  end  of  this  graduated  stem 
is  a  sealed  bulb  of  20  c.c.  capacity,  the  lower  end  of  which  bears  a  stop-cock 
tube.  The  apparatus  is  graduated  to  0-02  c.c.,  from  20  c.c.  to  22-5  c.c. 

The  reagents  required  are  fusel-free  alcohol  that  has  been  prepared  by 
fractional  distillation  over  caustic  potash,  and  diluted  to  exactly  30  per 
cent,  by  volume  (specific  gravity,  0-96541);  chloroform  freed  from  water 
and  redistilled;  and  sulphuric  acid  (specific  gravity,  1-2857  at  15-6°). 

Distill  slowly  200  c.c.  of  the  sample  under  examination  till  about  175  c.c. 
have  passed  over,  allow  the  distilling  flask  to  cool,  add  25  c.c.  of  water,  and 
distill  again  till  the  total  distillate  measures  200  c.c.  Dilute  the  distillate 
to  exactly  30  per  cent,  by  volume  (specific  gravity,  0-96541  at  15-6°). 

The  following  is  an  accurate  method  for  diluting  any  given  alcohol  solu- 
tion to  a  weaker  solution  of  definite  percentage:  Designate  the  volume  per- 
centage of  the  stronger  alcohol  by  V  and  that  of  the  weaker  alcohol  by  v. 
Mix  v  volumes  of  the  stronger  alcohol  with  water  to  make  V  volumes  of  the 
product.  Allow  the  mixture  to  stand  till  full  contraction  has  taken  place, 
and  till  it  has  reached  the  temperature  of  the  original  alcohol  and  water 
and  make  up  any  deficiency  in  the  V  volumes  with  water. 

Example. — It  is  desired  to  dilute  a  distillate  containing  50  per  cent,  of 
alcohol  by  volume  until  it  contains  30  per  cent.  To  30  volumes  of  the  50 


OFFICIAL    METHODS   OF    ANALYSIS.  1087 

per  cent,  alcohol  add  enough  water  to  make  50  volumes  or  place  150  c.c. 
of  the  distillate  in  a  250  c.c.  flask,  fill  to  the  mark  with  water,  mix,  cool,  and 
ml  to  tne  mark  again. 

Prepare  a  water-bath,  the  contents  of  which  are  kept  at  exactly  15°,  and 
place  in  it  the  apparatus  (covering  the  end  of  the  tube  with  a  rubber  cap 
to  prevent  wetting  the  inside  of  the  tube)  and  ffasks  containing  the  30-per 
cent,  fusel-free  alcohol,  chloroform,  sulphuric  acid,  and  the  distillate  diluted 
to  30  per  cent,  by  volume.  When  the  solutions  have  all  attained  the  tem- 
perature of  15°,  fill  the  apparatus  to  the  20  c.c.  mark  with  the  chloroform, 
drawing  it  through  the  lower  tube  by  means  of  suction,  add  100  c.c.  of  the 
30-per  cent,  fusel-free  alcohol  and  1  c.c.  of  the  sulphuiic  acid,  invert  the 
apparatus,  and  shake  vigorously  for  two  or  three  minutes,  interrupting  once 
or  twice  to  open  the  stop-cock  for  the  purpose  of  equalizing  pressure.  Allow 
the  apparatus  to  stand  ten  or  fifteen  minutes  in  water  that  is  kept  at  the 
temperature  of  15°,  turning  occasionally  to  hasten  the  separation  of  the 
reagents,  and  note  the  volume  of  the  chloroform.  After  thoroughly  cleansing 
and  drying  the  apparatus,  repeat  this  operation,  using  the  diluted  distillate 
from  the  sample  under  examination  in  place  of  the  fusel-free  alcohol.  The 
increase  in  the  chloroform  volume  with  the  sample  under  examination  over 
that  with  the  fusel-free  alcohol  is  due  to  fusel  oil,  and  this  difference  (expressed 
hi  cubic  centimeters),  multiplied  by  the  factor  0-€63,  gives  the  volume  of 
fusel  oil  in  100  c.c.,  which  is  equal  to  the  percentage  of  fusel  oil  by  volume 
in  the  30-per  cent,  distillate.  This  must  be  calculated  to  the  percentage 
of  fusel  oil  by  volume  in  the  original  liquor. 

Example. — A  sample  of  liquor  contains  50  per  cent,  of  alcohol  by  volume. 
The  increase  in  the  chloroform  volume  with  the  30-per  cent,  fusel-free  alcohol, 
is  1-42  c.c. ;  the  increase  in  the  chloroform  volume  with  the  distillate  from 
the  liquor  under  examination,  diluted  to  30  per  cent.,  is  1-62  c.c.;  differ- 
ence, 0  •  20  c.c.  The  volume  of  fusel  oil  in  100  c.c.  of  the  30-per  cent,  distillate 
then  is  0-20x0-663=0-1326  c.c.,  and  by  the  proportion  30  :  50  ::  0-1326  : 
0-  221,  we  obtain  the  percentage  of  fusel  oil  by  volume  in  the  original  liquor. 

20.  DETERMINATION  OF  ALDEHYDES. 

(a)  Preparation  of  Reagents.— Eighty  c.c.  of  a  saturated  solution  of  sodium 
disulphite  are  mixed  with  a  solution  of  0- 12  grm.  of  fuchsin  in  about  * 
of  water,  12  c.c.  of  sulphuric  acid  added,  the  solution  thoroughly  mixed, 
and  diluted  with  water  to  1  l:tre. 

(V)  Determination.— A  portion  of  the  sample  is  diluted  with  water,  or 
strengthened  with  aldehyde-free  alcohol  until  it  contains  50  per  cent,  of  ; 
hy  volume,  and  25  c.c.  of  this  solution  are  treated  with  10  c.c.  of  the  reager 
?nd  allowed  to  stand  twenty  minutes.     At  the  same  time  25  c.c.  of  a  s< 
tion  of  0-05  grm.  of  acetic  aldehyde  in  1000  c.c.  of  50- per  cent,  alcohol  i 
treated  in  the  same  manner  and  allowed  to  stand  the  same  length  of  t 
The  relative  intensity  of  the  colors  of  the  two  solutions  is  then  determined 
bv  means  of  a  colorimeter,  and  from  the  figure  thus  obtained  the  weight 
of  aldehvde  is  estimated  as  acetic  aldehyde,  and  calculated  to  percentage  of 
the  original  liquor. 


1088  APPENDIX   I. 

21.  DETERMINATION  OF  ETHEREAL  SALTS. 

After  the  determination  of  the  volatile  acids,  the  neutralized  distillate 
is  transferred  to  a  flask  connected  with  a  reflux  condenser,  treated  with  25  c.c. 
of  tenth-normal  sodium  hydroxide,  and  boiled  one-half  hour.  The  flask 
and  contents  are  then  cooled,  25  c.c.  of  tenth-normal  hydrochloric  acid  added, 
and  the  excess  of  acid  titrated  with  sodium  hydroxide,  using  phenolphtalein 
as  indicator.  The  number  of  cubic  centimeters  of  tenth-normal  alkali  used 
in  this  titration.  multiplied  by  0  •  0088,  is  equal  to  the  weight  in  grm.  of  ethereal 
salts  (calculated  as  ethyl  acetate)  in  the  volume  of  liquor  taken  for  the  deter- 
mination. 

VI.— METHODS  FOR  THE  ANALYSIS  OF  SOILS. 

1.  PREPARATION  OF  SAMPLE. 

Surface  accumulations  of  decaying  leaves,  etc.,  should  be  removed  and 
a  slice  of  uniform  thickness  from  the  surface  to  the  desired  depth  should  be 
secured.  To  eliminate  the  effects  of  accidental  variations  in  the  soil,  select 
specimens  from  five  or  six  places  in  the  field  and  remove  several  pounds  of 
the  soil,  to  the  depth  of  6  inches,  or  to  the  change  between  the  surface  soil 
and  the  subsoil,  in  case  such  change  occurs  between  the  depth  of  6  and  12 
inches.  In  no  case  is  the  sample  to  be  taken  to  a  greater  depth  than  12 
inches.  If  the  surface  soil  extends  to  a  greater  depth,  a  separate  sample  below 
the  depth  of  12  inches  is  to  be  obtained.  If  the  surface  soil  extends  to  a 
depth  of  less  than  6  inches,  and  the  difference  between  it  and  the  subsoil  is 
unusually  great,  a  separate  sample  of  the  surface  soil  should  be  secured, 
besides  the  one  to  the  depth  of  6  inches. 

The  depth  to  which  the  sample  of  subsoil  should  be  taken  will  depend 
on  circumstances.  It  is  always  necessary  to  know  what  constitutes  the 
foundation  of  a  soil,  to  the  depth  of  3  feet  at  least,  since  the  question  of  drain- 
age, resistance  to  drought,  etc.,  will  depend  essentially  upon  the  nature  of 
the  substratum.  But  in  ordinary  cases  10  or  12  inches  of  subsoil  will  be  suffi- 
cient for  the  purpose  of  examination  in  the  laboratory.  The  specimen  should 
be  obtained  in  other  respects  precisely  like  that  of  the  surface  soil,  while 
that  of  the  material  underlying  this  subsoil  may  be  taken  with  less  exact- 
ness, perhaps  at  some  ditch  or  other  easily  accessible  point,  and  should  not 
be  broken  up,  but  left,  as  nearly  as  possible,  in  its  original  state.  Mix  these 
soils  intimately,  remove  any  stones,  shake  out  all  roots  and  foreign  matters, 
expose  in  thin  layers  in  a  warm  room  till  thoroughly  air-dry,  or  dry  it  in  an 
air-bath  at  a  temperature  of  40°. 

The  soil  is  rapidly  driect  to  arrest  nitrification.  It  is  not  heated  above 
40°  lest  there  be  dissipation  of  ammonium  compounds,  or  a  change  in  the 
solubility  of  the  soil.  The  normal  limit  to  which  the  soil  may  be  heated  in 
place  by  the  sun's  rays  should  not  be  exceeded  in  preparing  a  soil  for  an 
agricultural  chemical  analysis. 

Five  hundred  grm.  or  more  of  the  air-dried  soil,  which  may  be  either  the 
original  soil  or  that  which  has  been  passed  through  a  sieve  of  coarser  mesh. 


OFFICIAL    METHODS    OF    ANALYSIS.  1089 

are  sifted  through  a  sieve  with  circular  openings  one-half  mm.  in  diameter, 
rubbing,  if  necessary,  with  a  rubber  pestle  in  a  mortar  until  the  fine  earth 
has  been  separated  as  completely  as  possible  from  the  particles  that  are  too 
coarse  to  pass  the  sieve.  The  fine  earth  is  thoroughly  mixed  and  preserved 
in  a  tightly  stoppered  bottle,  from  which  the  portions  for  analysis  are  weighed. 

The  coarse  part  is  weighed  and  examined  microscopically  or  with  THOU- 
LET'S  solution.* 

It  may  sometimes  be  necessary  to  wash  the  soil  through  the  one-half- 
mm.  sieve  with  water;  but  this  is  to  be  avoided  whenever  possible. 

2.  DETERMINATION  OF  MOISTURE. 

Heat  from  2  to  5  grm.  of  the  air-dried  soil  in  a  flat-bottomed,  tared  plati- 
num dish  for  five  hours  in  a  water-oven  kept  briskly  boiling ;  cover  the  dish, 
cool  in  a  desiccator  and  weigh.  Repeat  the  heating,  cooling,  and  weighing 
at  intervals  of  two  hours  till  nearly  constant  weight  is  found,  and  estimate 
the  moisture  by  the  loss  of  weight.  Weigh  rapidly,  to  avoid  absorption  of 
moisture  from  the  air. 

3.  DETERMINATION  OF  VOLATILE  MATTER. 

Heat  the  dish  and  dry  soil  from  the  above  determination  to  full  redness, 
until  all  organic  matter  is  burned  away.  If  the  soil  contains  appreciable 
quantities  of  carbonates,  the  contents  of  the  dish,  after  cooling,  are  moistened 
with  a  few  drops  of  a  saturated  solution  of  ammonium  carbonate,  dried,  and 
heated  to  dull  redness  to  expel  salts  of  ammonium,  cooled  in  the  desiccator, 
and  weighed.  The  loss  in  weight  represents  the  organic  matter,  water  of 
combination,  salts  of  ammonium,  etc. 

4.  DETERMINATION  OF  ACID-SOLUBLE  MATERIALS. 

In  the  following  scheme  for  soil  analysis  it  is  intended  to  use  the  air-dried 
soil  from  the  sample  bottle  for  each  separate  investigation.  The  determina- 
tion of  moisture,  made  once  for  all  on  a  separate  portion  of  air-dried  soil, 
will  afford  the  datum  for  calculating  the  results  of  analysis  upon  the  soil 
dried  at  the  temperature  of  boiling  water.  It  is  not  desirable  to  ignite  the 
soil  before  analysis,  or  to  heat  it  so  as  to  change  its  chemical  properties. 

The  acid  digestion  is  jib  be  performed  in  a  flask  so  arranged  that  the  evap- 
oration of  acid  shall  be  reduced  to  a  minimum,  but  under  atmospheric  pres- 
sure and  at  the  temperature  ot  boiling  water.  The  digestion  is  easily  accom- 
plished in  a  flat-bottomed  conical  flask  of  hard  glass,  earning  a  stopper  and 
hard-glass  condensing  tube  at  least  18  inches  long.  Where  sulphuric  acid  is 
to  be  determined,  a  rubber  stopper  cannot  be  used.  A  flask  with  ground- 
glass  stopper,  carrying  a  condensing  tube,  is  useful  in  such  cases. 

The  flask  must  be  immersed  in  the  water-bath  up  to  the  neck,  or  at  least 
to  the  level  of  the  acid,  and  the  water  must  be  kept  boiling  continuously 
during  the  digestion. 

In  the  following  scheme  10  grm.  of  soil  are  used,  this  being  a  convenient 
quantity  of  most  soils,  in  which  the  insoluble  matter  is  about  80  per  cent. 

*  Principles  and  Practice  of  Agricultural  Analysis,  i,  p.p.  268,  269. 


1090  APPENDIX   I. 

If  desired,  a  larger  quantity  of  such  soil  may  be  used,  with  a  proportionately 
larger  quantity  of  acid,  and  making  up  the  soil  solution  to  a  proportionately 
larger  volume.  In  very  sandy  soils,  where  the  proportion  of  insoluble 
matter  is  90  per  cent,  or  more,  20  grm.  of  soil  are  to  be  digested  with  100  c.c. 
of  acid  and  the  solution  made  up  to  500  c.c. ;  or  a  larger  quantity  may  be  used, 
preserving  the  same  proportions.  It  is  very  important  that  the  analyst 
assure  himself  of  the  purity  of  all  the  reagents  to  be  used  in  the  analysis 
of  soils  before  beginning  the  work. 

(a)  ACID  DIGESTION  OF  THE  SOIL. 

Place  10  grm.  of  the  air-dried  soil  in  an  ERLENMEYER  glass  flask  of  from 
150  to  200  c.c.  capacity,  add  100  c.c.  of  pure  hydrochloric  acid  of  specific 
gravity  1:115,  insert  the  stopper  with  condensing- tube,  place  in  a  water- 
or  steam-bath,  and  digest  for  ten  hours  continuously  at  the  tempera- 
ture of  boiling  water,  shaking  once  each  hour.  Pour  the  clear  liquid  from 
the  flask  into  a  small  beaker  and  wash  the  residue  out  of  the  flask  with  dis- 
tilled water  on  a  filter,  adding  the  washings  to  the  contents  of  the  beaker. 
The  residue,  after  washing  until  free  from  acid,  is  dried  and  ignited,  as  directed 
below.  Oxidize  the  organic  matter  present  in  the  filtrate  with  nitric  acid 
and  evaporate  to  dryness  on  the  water-bath,  finishing  on  a  sand-  or  air-bath  to 
complete  dryness;  take  up  with  hot  wa,er  and  a  few  cubic  centimeters  of 
hydrochloric  acid  and  again  evaporate  to  complete  dryness.  Take  up  as 
before,  filter,  and  wash  thoroughly  with  cold  water,  or  with  hot  water 
slightly  acidified  at  first  with  hydrochloric  acid.  Cool  and  make  up  to  500 
c.c.  This  is  solution  A.  The  residue  is  to  be  added  to  the  main  residue  and 
the  whole  ignited  and  weighed,  giving  the  " insoluble  matter."  (See  5, 
p.  1094.) 

(6)  DETERMINATION    OF    FERRIC    OXIDE,    ALUMINA,    AND    PHOSPHORIC    ACID, 

COLLECTIVELY. 

To  100  or  200  c.c.  of  solution  A,  according  to  the  probable  amount  of  iron 
and  alumina  present,  add  ammonium  hydroxide  to  slightly  alkaline  reaction 
to  precipitate  ferric  and  aluminic  hydrates  and  phosphates.  Expel  the  excess 
of  ammonia  by  boiling,  allow  to  settle,  and  decant  the  clear  solution  through 
a  filter;  add  to  the  flask  50  c.c.  of  hot  distilled  wditer,  boil,  settle,  and  de- 
cant as  before.  After  pouring  off  all  the  clear  solution  possible,  dissolve 
the  residue  with  a  few  drops  of  hydrochloric  acid  and  precipitate  again  with 
ammonium  hydroxide  exactly  as  before;  transfer  all  the  precipitate  to  the 
filter  and  wash  with  hot  distilled  water  till  the  washings  become  free  from 
chlorides.  Save  the  filtrates  and  washings  which  form  solution  B.  Dry 
the  filtrate  and  precipitate,  transfer  the  precipitate  to  a  tared  platinum 
crucible,  burn  the  filter,  and  add  the  ash  to  the  precipitate ;  ignite  to  bright 
redness,  cool  in  a  desiccator,  and  weigh.  The  increase  of  weight,  minus 
the  ash  of  filter  and  the  phosphoric  acid  (found  in  a  separate  process),  repre- 
sents the  weight  of  the  Fe2O3  and  A12O3. 

(c)   DETERMINATION  OF  MANGANESE. 

Concentrate  the  filtrates  and  washings  (solution  B)  to  100  c.c:  or  less; 
add  ammonium  hydroxide  to  alkalinity;  add  bromine  water  and  heat  to 


OFFICIAL  METHODS  OF  ANALYSIS.  1091 

boiling,  keeping  the  beaker  covered  with  a  watch  crystal;  as  the  bromine 
escapes  the  beaker  is  allowed  to  cool  somewhat,  more  ammonia  and  bromine 
water  being  added  and  heated  as  before.  This  process  is  continued  until 
the  manganese  is  completely  precipitated,  which  requires  from  fifteen  to 
thirty  minutes.  The  solution  is  then  to  be  slightly  acidified  with  a  few 
drops  of  acetic  acid  and  filtered  while  still  boiling  hot,  the  precipitate  washed 
with  hot  water,  dried,  ignited,  and  weighed  as  Mn3O4. 

(d)   DETERMINATION   OF  CALCIUM. 

If  no  manganese  be  precipitated,  evaporate  solution  B  or  the  filtrates 
and  washings  from  (c)  to  about  50  c.c.,  make  slightly  alkaline  with  ammonia, 
and  add,  while  still  hot,  ammonium-oxalate  solution  so  long  as  any  precipi- 
tate is  produced,  adding  a  few  cubic  centimeters  in  excess  to  convert  the  mag- 
nesium also  into  oxalate.  Heat  to  boiling,  allow  the  precipitate  to  settle, 
decant  the  clear  solution  on  a  filter,  pour  from  15  to  20  c.c.  of  hot  distilled 
water  on  the  precipitate,  and  again  decant  the  clear  solution  on  the  filter. 
Dissolve  the  precipitate  in  the  beaker  with  a  few  drops  of  hydrochloric  acid, 
add  a  little  water,  and  reprecipitate,  boiling  hot,  by  adding  ammonium 
hydroxide  to  slight  alkalinity  and  a  little  ammonium-oxalate  solution ;  filter 
through  the  same  filter,  transfer  the  precipitate  to  the  filter,  and  wash  it  free 
from  chlorides;  dry,  ignite  the  precipitate  over  the  blast  lamp  until  it  ceases 
to  lose  weight,  weigh,  and  estimate  as  CaO. 

0)  DETERMINATION  OF  MAGNESIUM. 

Slightly  acidify  the  filtrate  and  washings  from  (d)  with  hydrochloric 
acid  and  concentrate  to  about  50  c.c.,  place  in  a  small  ERLENMEYER  flask 
or  beaker,  make  slightly  alkaline  with"  ammonium  hydroxide,  and  add 
sufficient  acid-sodium-phosphate  solution  to  precipitate  the  magnesium; 
then  add  gradually  10  c.c.  strong  ammonium  hydroxide,  cover  closely  to 
prevent  escape  of  ammonia,  and  let  stand  in  the  cold.  Filter  after  twelve 
hours,  wash  the  precipitate  free  from  chlorides,  dry,  burn  at  first  at  a  moderate 
heat,  finally  igniting  intensely,  and  weigh  as  Mg2P2O7. 

(/)    DETERMINATION   OF   FERRIC    OXIDE. 

Evaporate  100  c.c.  of  solution  A,  with  the  addition  of  about  10  c.c.  of  sul- 
phuric acid,  until  all  hydrochloric  acid  is  expelled;  dilute  with  water,  reduce 
with  zinc,  and  estimate  ferric  oxide  by  a  standard  solution  of  potassium 
permanganate.  To  prepare  potassium-permanganate  solution,  dissolve  3-156 
grm.  of  the  pure  salt  in  2000  c.c.  of  distilled  water,  and  preserve  in  a 
glass-stoppered  bottle,  shielded  from  the  light.  Standardize  this  solution, 
after  it  has  stood  twenty-four  hours  with  pure  ammonio-ferrous  sulphate, 
oxalic  acid,  or  metallic  iron. 

Instead  of  using  another  portion  of  the  solution,  the  weighed  precipi- 
tate from  (6)  may  be  dissolved  by  digestion  on  the  water-bath  in  a  covered 
beaker  or  flask  with  from  10  to  20  c.c.  of  a  mixture  of  one  part  H^O,  with 
four  parts  of  water. 

Deduct  the  per  cent,  of  ferric  oxide  obtained  from  the  per  cent,  of  ferric 


1092  APPENDIX    I. 

oxide  and  alumina  (6),  and  make  corrections  for  filter  ash  and  phosphoric 
acid,  to  obtain  the  per  cent,  of  alumina. 

(0)  DETERMINATION  OF  PHOSPHORIC  ACID. 

Evaporate  100  or  200  c.c.  of  solution  A  to  about  25  or  30  c.c. ;  nearly 
neutralize  with  ammonium  hydroxide,  add  about  10  grm.  pure  crystallized 
ammonium  nitrate,  and  gradually  add  about  20  c.c.  molybdic  solution  ((1)  (6), 
p.  1018)  and  set  in  water-bath  at  a  temperature  of  40°.  When  the  precipitate 
has  settled  sufficiently,  draw  out  with  a  pipette  about  5  c.c.  of  the  clear 
liquid,  and  test  it  by  allowing  it  to  run  into  5  c.c.  of  warm  molybdic  solu- 
tion. If  any  precipitate  be  produced,  the  test  liquid  is  returned  to  the  main 
portion  and  more  molybdic  solution  is  added  and  the  operation  repeated 
until  all  the  phosphoric  acid  is  precipitated.  After  standing  from  eight 
to  twelve  hours  at  a  temperature  not  above  40°,  the  ammonium  phospho- 
molybdate  is  filtered  off  and  the  phosphoric  acid  determined  as  magnesium 
pyrophosphate,  as  directed  under  total  phosphoric  acid  in  fertilizers  (page 
1018).  It  is  recommended  to  redissolve  the  magnesium-ammonium  phosphate 
precipitate  in  acetic  acid,  after  it  has  been  washed  once  or  twice,  and  re- 
precipitate  with  ammonia  and  a  fresh  quantity  of  magnesia  mixture,  giving 
the  usual  time  for  the  separation  of  the  precipitate.  If  there  be  any  residue 
of  phosphates  remaining  on  dissolving  the  phosphomolybdate  in  ammonia, 
or  the  magnesium-ammonium  phosphate  in  acetic  acid,  this  residue  is  dis- 
solved in  a  little  hydrochloric  acid,  neutralized  with  ammonium  hydroxide, 
and  precipitated  with  molybdic  solution,  and  the  phosphomolybdate  ob- 
tained added  to  the  main  quantity. 

(/l)    PROVISIONAL    METHOD     FOR     DETERMINING    AVAILABLE     PHOSPHORIC    ACID. 

Ten  grm.  of  the  air-dried  soil,  passed  through  a  sieve  of  one-millimetre 
mesh,  are  placed  in  a  small  KJELDAHL  flask  marked  at  250  c.c.  From  20 
to  30  c.c.  concentrated  sulphuric  acid  and  approximately  0-7  grm.  yellow 
oxide  of  mercury  are  added,  the  contents  of  the  flask  well  mixed  by  shaking, 
and  oxidized  over  the  open  flame,  as  in  the  determination  of  nitrogen,  for  an 
hour.  After  cooling,  about  100  c.c.  of  water,  5  c.c.  of  concentrated  hydro- 
chloric acid  and  2  c.c.  of  concentrated  nitric  acid  are  added,  and  the  mixture 
reboiled  to  oxidize  the  iron,  cooled,  the  volume  completed  to  the  mark  with 
water,  and  the  contents  of  the  flask  filtered  through  a  dry,  folded  filter-paper. 
One  hundred  cubic  centimetres  of  the  filtrate  are  placed  in  a  flask  of  about 
450  c.c.  capacity,  strong  ammonia  added  until  a  permanent  precipitate  is 
formed,  which  is  dissolved  by  the  addition  of  about  7  c.c.  of  nitric  acid,  and 
the  mixture  boiled  until  clear.  The  flask  is  removed  from  the  flame  and 
cooled  at  room  temperature  for  exactly  two  minutes,  75  c.c.  molybdate 
solution  added,  and  the  flask  placed  in  a  water-bath  kept  at  80°  for  15  minutes, 
shaking  vigorously  four  or  five  times  meanwhile.  After  removing  from  the 
bath,  the  flask  is  allowed  to  stand  for  ten  minutes  until  the  precipitate  has 
settled,  and  the  supernatant  liquid  is  poured  onto  the  filter-paper  under  pres- 
sure, the  precipitate  being  partially  brought  upon  the  paper.  The  flask 
and  precipitate  are  thoroughly  washed  with  ammonium-nitrate  solution, 


OFFICIAL   METHODS   OF  ANALYSIS.  1093 

the  precipitate  either  by  decantation  or  on  the  filter-paper.  The  flask  is 
placed  under  the  funnel,  the  precipitate  is  dissolved  in  ammonia,  and  the 
phosphoric  acid  estimated  by  the  usual  processes.  Details  of  the  manipula- 
tion are  given  in  Bulletin  No.  43  of  the  Division  of  Chemistry,  pp.  58-60. 

(l)    PROVISIONAL    METHOD    FOR     THE     DETERMINATION    OF     THE    MORE     ACTIVE 
FORMS    OF   THE    PHOSPHORIC    ACID    IN   SOILS. 

(a)  Prepare  a  large  stock  solution  of  normal  HC1  by  titrating  against  a 
standard  KOH  solution  containing  little  or  no  carbonate,  using  phenol- 
phtalein  as  the  indicator. 

(6)  Digest  10  grm.  of  air-dried  soil,  in  a  stoppered  flask,  with  100  c.c. 
of  N/5  HC1,  for  exactly  five  hours  in  a  water-bath  kept  at  a  temperature 
of  40°.  Filter  the  solution  through  a  dry  paper,  cool  to  the  room  tempera- 
ture, and  titrate  20  c.c.  of  the  filtrate  with  standard  carbonate-free  KOH 
solution,  using  phenolphtalein  as  the  indicator.  From  the  data  thus  se- 
cured, calculate  the  exact  number  of  cubic  centimeters  of  normal  acid  of  the 
stock  solution  and  of  water  to  make  exactly  one  or  two  litres  of  acid  of  N/5 
strength  after  allowing  for  the  amount  neutralized  by  the  amount  of  soil  to 
be  used  in  (c). 

(c)  Place  200  grm.  of  the  air-dried  soil  in  a  large,  dry.  glass-stoppered 
bottle  and  add  exactly  2000  c.c.  of  X/5  HC1  corrected  for  neutralization 
as  in  (6).  In  the  case  of  soils  known  to  be  rich  in  available  phosphoric  acid 
100  grm.  of  soil  and  1000  c.c.  of  acid  will  be  sufficient.  Place  the  bottle  in 
a  large  water-bath  and  keep  at  a  temperature  of  40°  for  exactly  five  hours, 
shaking  thoroughly  each  half  hour.  At  the  end  of  the  digestion  shake  con- 
tents of  bottle  well  and  pour  quickly  upon  a  large,  dry,  ribbed  filter  of  two 
thicknesses  of  paper  and  of  sufficient  size  to  receive  the  entire  contents  of 
the  bottle.  The  filtrate  is  to  be  received  in  a  dry  vessel  and  the  solution 
poured  back  through  the  paper  until  entirely  clear.  Evaporate  1000  c.c.  of 
the  filtrate  if  200  grm.  of  soil  be  used,  or  500  c.c.  if  100  grm.  be  employed, 
to  dryness  in  a  porcelain  dish,  after  adding  a  few  c.c.  of  nitric  acid  to  oxidize 
organic  matter,  etc.,  moisten  the  residue  with  HC1,  take  up  with  water,  and 
filter  into  a  flask  of  about  500  c.c.  capacity.  Add  15  grm.  of  ammonium 
nitrate  in  solution,  add  strong  ammonia  until  a  permanent  precipitate  forms, 
and  then  concentrated  nitric  acid  until  the  precipitate  dissolves.  Dilute 
the  solution  to  about  100  c.c.,  if  not  already  of  that  volume,  place  a  ther- 
mometer in  the  flask,  and  heat  to  exactly  85°.  Add  75  c.c.  of  recently  pre- 
pared molybdate  solution,  digest  in  a  water-bath  at  80°  for  fifteen  minutes, 
with  occasional  shaking,  remove  from  the  bath  and  allow  to  stand  at  least 
10  minutes  before  filtering.  Continue  the  determination  in  the  usual  way. 

(/)    DETERMINATION    OF    SULPHURIC    ACID. 

Evaporate  100  or  200  c.c.  of  solution  A  nearly  to  dryness  on  a  water- 
bath  to  expel  the  excess  of  acid;  then  add  50  c.c.  of  distilled  water;  heat 
to  boiling  and  add  from  2  to  3  c.c.  of  a  solution  of  barium  chloride,  and  con- 
tinue the  boiling  for  five  minutes.  When  the  precipitate  has  settled  pour 
the  liquid  on  a  tared  Gooch,  treat  the  precipitate  with  from  15  to  20  c.c.  of 


1094  APPENDIX   I. 

boiling  water,  and  transfer  to  the  filter  and  wash 'with  boiling  water,  at  first 
slightly  acidified  with  a  few  drops  of  hydrochloric  acid,  finally  with  pure 
water,  till  the  filtrate  is  free  from  chloride.  Dry  the  filter,  ignite,  and  weigh 
as  barium  sulphate,  which  multiplied  by  0-34331  equals  SO3. 

(K)    DETERMINATION    OF    POTASH   AND    SODA. 

Treat  the  filtrate  from  (/)  with  ammonium  hydroxide  exactly  as  in  (6). 
Evaporate  the  filtrate  and  washings  to  dryness,  heat  below  redness,  until 
ammonium  salts  are  expelled,  dissolve  in  about  25  c.c.  of  hot  water,  add  5  c.c. 
of  baryta  water,  and  heat  to  boiling;  let  settle  a  few  minutes,  and  test  a 
little  of  the  clear  liquid  with  more  baryta  water  to  be  sure  that  enough  has 
been  added.  When  no  further  precipitate  is  produced,  filter  and  wash  thor- 
oughly with  hot  water.  Add  ammonia  and  ammonium  carbonate  to  com- 
plete the  precipitation  of  the  barium,  let  stand  a  short  time  on  the  water- 
bath,  filter  and  wash  the  precipitate  thoroughly  with  hot  water,  evaporate 
nitrate  and  washings  to  dryness  in  a  porcelain  dish,  expel  ammonium  salts 
by  heat  below  redness,  take  up  with  a  little  hot  water,  add  a  few  drops  of 
ammonium  hydroxide  and  a  drop  or  two  of  ammonium  carbonate,  let  stand 
a  few  minutes  on  the  water-bath,  filter  into  a  tared  platinum  dish,  evaporate 
to  dryness  on  the  water-bath  and  heat  to  dull  redness,  until  all  ammonium 
salts  are  expelled  and  the  residue  is  nearly  or  quite  white.  The  heat  must 
not  be  sufficient  to  fuse  the  residue.  The  weight  of  the  residue  represents 
potassium  and  sodium  chlorides.  Determine  the  potassium  present  with 
platinum  chloride  in  the  usual  manner.  The  sodium  chloride  is  obtained 
by  subtracting  potassium  chloride  thus  found  from  the  total  weight  of  the 
two  chlorides. 

Instead  of  this,  a  fresh  aliquot  portion  of  solution  A  may  be  evaporated 
to  dryness,  redissolved  in  water  and  treated  directly  with  milk-of-lime  as 
in  ash  analysis,  but  without  previous  addition  of  barium  chloride. 

5.  DETERMINATION  OF  ACID-INSOLUBLE  MATERIALS. 

The  residue  from  4  (a)  may  be  analyzed  by  the  usual  methods  for  sili- 
cates. If  it  be  desired  to  determine  the  silica  soluble  in  alkalies,  the  residue 
must  be  dried  at  100°  and  an  aliquot  portion  removed  before  ignition,  for 
treatment  with  sodium-carbonate  solution,  as  described  under  ash  analysis, 
page  1097.  Another  aliquot  portion,  or  the  rest  of  the  residue,  is  ignited 
and  weighed. 

6.  DETERMINATION  OF  TOTAL  ALKALIES. 

Determine  in  a  separate  portion  of  the  soil  by  J.  LAWRENCE  SMITH'S 
method,  given  in  CROOKES'S  Select  Methods,  second  edition,  pp.  28-40,  and 
Principles  and  Practice  of  Agricultural  Analysis,  Vol.  I,  pp.  378-381;  or, 
preferably,  determine  by  this  method  the  alkalies  in  the  insoluble  residue 
from  4  (a)  and  add  the  amount  obtained  from  the  hydrochloric-acid  solution. 


OFFICIAL   METHODS    OF   ANALYSIS.  1095 

7.  IDENTIFICATION  OF  LITHIUM,  CESIUM,  AND  RUBIDIUM. 

The  salts  of  these  elements  are  occasionally  ioimd  in  very  small  amounts 
in  soils.  Their  agricultural  uses  are  still  in  question,  and  their  amount  is 
too  small  to  admit  of  quantitative  estimation.  A  qualitative  examination 
may  be  made  by  the  spectroscope  with  the  water-soluble  materials  evapor- 
ated to  dryness  and  dissolved  with  two  or  three  drops  of  hydrochloric  acid 
or  with  the  alkaline  chlorides  separated  as  in  4  (i)  or  6. 

8.  DETERMINATION  OF  TOTAL  NITROGEN. 

From  7  to  14  grm.  of  the  soil  are  placed  in  a  small  KJELDAHL  digesting 
flask,  about  250  c.c.  capacity,  with  30  c.c.  of  strong  sulphuric  acid,  or  more, 
if  necessary,  and  0-7  grm.  yellow  oxide  of  mercury,  and  boiled  for  an  hour. 
The  residue  is  oxidized  with  potassium  permanganate  in  the  usual  way. 
After  cooling,  the  flask  is  half  filled  with  water,  vigorously  shaken,  the  heavy 
matters  allowed  to  subside,  and  the  supernatant  liquid  poured  into  a  flask 
of  from  1000  to  1200  c.c.  capacity.  This  operation  is  repeated  until  the 
ammonium  sulphate  is  practically  all  removed  and  the  digestion  flask  is  a 
little  more  than  half  full,  and  the  ammonia  distilled  hi  the  usual  manner. 
If  a  sample  be  known  to  contain  a  considerable  amount  of  nitrate,  use  method 
p.  1024  (c). 

9.  DETERMINATION  OF  CARBON  DIOXIDE. 

Determine  as  in  ash  analysis,  page  1098,  using  from  5  to  10  grm.  of 
the  sample. 

10.  DETERMINATION  OF  HUMUS. 

Ten  grm.  of  the  sample  are  placed  in  a  Gooch,  extracted  with  1-per  cent, 
hydrochloric  acid  until  the  filtrate  gives  no  reaction  with  ammonia  and 
ammonium  oxalate,  and  the  acid  removed  by  washing  with  water.  The 
contents  of  the  crucible  (including  the  asbestos  filter)  are  then  washed  into 
a  glass-stoppered  cylinder  with  500  c.c.  of  4-per  cent,  ammonia  and  allowed 
to  remain,  with  occasional  shaking,  for  twenty-four  hours.  During  this 
time  the  cylinder  is  inclined  as  much  as  possible  without  bringing  the  con- 
tents in  contact  with  the  stopper,  thus  allowing  the  soil  to  settle  on  the  side 
of  the  cylinder,  and  exposing  a  very  large  surface  to  the  action  of  the  ammonia. 
The  cylinder  is  then  placed  in  a  vertical  position  and  left  for  twelve  hours, 
to  allow  the  sediment  to  settle  to  the  bottom.  The  supernatant  liquid  is 
filtered  and  an  aliquot  portion  evaporated,  dried  at  100°,  and  weighed.  The 
residue  is  then  ignited  and  again  weighed.  The  humus  is  calculated  from 
the  difference  in  weights  between  the  dried  and  the  ignited  residues. 

11.  DETERMINATION  OF  HUMUS  NITROGEN. 

Digest  the  soil  with  2  per  cent,  hydrochloric  acid  and  wash  as  nearly 
free  of  acid  as  possible  with  distilled  water.  Extract  the  humus  with  a  3-per 
cent,  solution  of  sodium  hydrate  and  determine  nitrogen  in  the  extract  in 
the  usual  wav. 


1096  APPENDIX  I. 

12.  STATEMENT  OF  RESULTS. 

All  results  of  soil  analysis  are  to  be  calculated  as  per  cent,  of  the  soil  dried 
to  constant  weight  in  the  water-oven  (see  determination  of  moisture,  p.  1089), 
and  are  to  be  stated  in  the  following  order : 

Insoluble  matter ) 

Soluble  silica ) 

Potash  (K2O) 

Soda  (Na2O) 

Lime  (CaO) 

Magnesia  (MgO) 

Manganese  oxide  (MnO) 

Ferric  oxide  (Fe2O3) 

Alumina  (A12O3) 

Phosphorus  pentoxide  (P2O6) 

Sulphur  trioxide  (SO3) 

Carbon  dioxide  (CO2) 

Water  and  organic  matter 


Total 

Humus 

Ash 

Phosphorus  pentoxide. 

Silica 

Nitrogen  (organic) 

Hygroscopic  moisture 

Moisture  absorbed  at  t°.  . 


VII.    METHODS  FOR  THE  ANALYSIS  OF  ASHES. 

1.  PREPARATION  OF  THE  ASH. 

Before  combustion  the  material  must  be  thoroughly  cleaned  from  all 
foreign  matter,  especially  from  adhering  soil.  The  combustion  should  be 
carried  on  at  a  comparatively  low  temperature,  never  reaching  a  full  red  heat, 
because  of  the  danger  of  volatilizing  alkaline  chlorides,  etc.,  and  of  fusing 
the  ash ;  nor  in  a  strong  draft  of  air,  lest  the  lighter  part  of  the  ash  be  carried 
away.  Combustion  is  best  carried  on  in  a  flat  platinum  dish  in  a  muffle. 
With  substances  rich  in  silica  and  alkalies  it  is  better  to  first  char  the  sub- 
stance, wash  with  distilled  water  to  remove  soluble  salts,  then  dry  and 
incinerate  the  residue.  Evaporate  the  aqueous  extract  and  add  this  to  the 
rest  of  the  ash.  With  substances  rich  in  phosphates,  e.g.,  seeds  and  animal 
substances,  char  the  material,  remove  salts  by  acetic  acid,  decant  the  acetic 
solution,  wash  with  distilled  water,  and  then  complete  the  combustion.  Add 
the  acetic  solution  and  washings  to  the  final  ash,  evaporate  to  dryness,  and 
gently  ignite  the  whole  to  decompose  the  acetates.  In  whatever  way  obtained, 
the  whole  of  the  ash  should  be  pulverized  and  intimately  mixed  while  still 
warm,  and  preserved  in  a  tight,  dry  bottle  for  analysis.  If  after  incineration 
the  ash  has  absorbed  moisture,  dry  thoroughly  at  low  redness  before  bottling. 


OFFICIAL   METHODS   OF    ANALYSIS.  1097 

It  is  intended  that  the  preliminary  preparation  of  the  ash  shall  bring  it  to  a 
perfectly  dry  condition,  rendering  a  moisture  determination  unnecessary,  and 
that  the  portions  for  analysis  shall  be  weighed  from  the  prepared  sample  in 
this  condition.  As  it  is  sometimes  difficult  or  impossible  to  prepare  an  ash 
for  analysis  in  large  quantity,  the  following  method  has  been  arranged  so 
that  a  small  amount  of  ash  may  be  used.  Where  the  ash  is  to  be  had  in  abun- 
dance larger  quantities  and  more  portions  may  be  used,  but  the  proportion 
of  acid  to  substance  taken  is  to  be  preserved.  Much  latitude  must  be  left 
to  individual  judgment  in  adapting  the  method  to  particular  cases. 

2.  SOLUTION  AND  DETERMINATION  OF  CARBON,  SAND,  AND  SILICA. 

Five  grm.  of  ash  are  treated  hi  a  beaker,  covered  with  a  watch-glass,  with 
50  c.c.  of  hydrochloric  acid  of  specific  gravity  1-115,  and  digested  on  the 
water-bath  until  ah1  effervescence  has  ceased.  The  watch-glass  is  then  re- 
moved to  allow  the  liquid  to  evaporate,  any  adhering  substance  washed  back 
into  the  beaker,  and  the  residue  is  thoroughly  dried  and  pulverized  to  render 
silica  insoluble.  The  dry  residue  is  moistened  with  from  5  to  10  c.c.  of  hydro- 
chloric acid,  taken  up  with  about  50  c.c.  of  water,  allowed  to  stand  on  the  water- 
bath  a  few  minutes,  filtered  through  a  parchment-paper  filter  (S.  and  S. 
"hardened"  filters),  and  thoroughly  washed.  The  solution  and  washings 
are  to  be  made  up  to  250  c.c.  or  other  convenient  volume  and  preserved  for 
analysis. 

(a)  The  residue  is  washed  from  the  filter  (which  may  be  used  again)  into 
a  platinum  dish  and  boiled  about  five  minutes  with  about  20  c.c.  of  a  satu- 
rated solution  of  pure  sodium  carbonate,  a  few  drops  of  pure  sodium- 
hydroxide  solution  are  added,  the  solids  are  allowed  to  settle,  and  the  liquor 
decanted  through  a  tared  Gooch.  The  residue  in  the  dish  is  to  be  boiled  with 
sodium-carbonate  solution  and  decanted  as  before,  and  the  process  repeated 
a  third  time,  after  which  the  residue  is  brought  upon  the  filter  and 
thoroughly  washed,  first  with  hot  water,  then  with  a  little  dilute  hydrochloric 
acid,  and  finally  with  hot  water  until  free  from  chlorides.  The  Gooch  and 
contents  are  dried  to  constant  weight  at  110°,  and  the  combined  weight 
of  carbon  and  sand  determined.  After  incineration  the  loss  in  weight  gives 
the  carbon.  It  is  advisable  to  examine  the  residue  under  the  microscope  to 
ascertain  if  it  be  really  sand.  The  alkaline  filtrates  and  washings  are  to 
be  united,  acidified  with  hydrochloric  acid,  evaporated  to  dryness,  and  the 
silica  separated  and  determined  in  the  usual  way. 

(6)  Instead  of  determining  directly  the  silica  dissolved  by  the  sodium- 
carbonate  solution,  as  described  above,  another  portion  of  the  ash  may  be 
treated  as  in  (2),  and  the  residue  of  silica,  sand,  and  carbon  filtered  on  an 
ordinary  filter,  washed,  burned,  and  weighed,  giving  the  combined  weight 
of  silica  and  sand,  from  which  the  weight  of  sand  found  in  (a)  is  to  be  deducted 
to  obtain  the  silica.  It  is  inadmissible  to  separate  the  soluble  silica  from 
the  residue  after  ignition. 

3.  DETERMINATION  OF  MANGANESE,  CALCIUM,  AND  MAGNESIUM. 
To  an  aliquot  portion  of  the  solution  of  the  ash  prepared  as  in  (2),  corres- 
ponding to  0  •  5  to  2  grm.,  add  a  quantity  of  pure  ferric-chloride  solution,  more 


1098  APPENDIX   I. 

than  equivalent  to  the  phosphoric  acid  which  may  be  present,  neutralize  with 
ammonia,  add  one  or  two  grm.  of  sodium  acetate  and  boil  one  or  two  minutes, 
filter  and  wash  with  boiling  water.  Evaporate  the  filtrate  and  washings 
to  about  50  c.c.,  and  determine  manganese,  calcium,  and  magnesium  as  in 
the  analysis  of  soils  (pp.  1090  and  1091,  c,  d,  and  e). 

4.  DETERMINATION  OF  PHOSPHORIC  ACID. 

An  aliquot  portion  of  the  hydrochloric-acid  solution  (see  2)  correspond- 
ing to  0  •  2  to  1  grm.  is  to  be  used  for  the  determination  by  any  of  the  methods 
described  for  total  phosphoric  acid  in  fertilizers. 

5.  DETERMINATION  OF  SULPHURIC  ACID  AND  ALKALIES. 

An  aliquot  part  of  the  hydrochloric-acid  solution  (see  2)  corresponding  to 
0  •  5  to  1  grm.  of  ash  is  heated  to  boiling,  and  barium-chloride  solution  added 
in  small  quantities  until  no  further  precipitation  is  produced.  Let  stand 
on  the  water-bath  until  clear,  filter  on  a  tared  Gooch,  wash  thoroughly  with 
hot  water,  at  first  slightly  acidified  with  hydrochloric  acid,  finally  with  pure 
water  until  free  from  chlorides,  dry,  burn,  and  weigh  the  barium  sulphate. 
Evaporate  the  filtrate  and  washings  from  the  barium  sulphate  to  dryness, 
redissolve  the  residue  in  about  50  c.c.  of  water, and  add  milk-of-lime  or  barium- 
hydroxide  solution,  which  must  be  perfectly  free  from  alkalies,  until  no  further 
precipitation  is  produced  and  it  is  certain  that  there  is  an  excess  of  calcium 
or  barium  hydroxide  present;  boil  for  two  or  three  minutes,  filter  hot,  wash 
thoroughly  with  boiling  water,  precipitate  the  lime  and  baryta  from  the 
solution  with  ammonia  and  ammonium  carbonate,  filter  after  standing  at 
least  one-half  hour  on  the  water-bath,  evaporate  filtrate  and  washings  to 
dryness,  and  drive  off  the  ammonium  salts  by  careful  heating  below  red- 
ness. When  cold,  redissolve  the  residue  in  about  10  c.c.  of  water,  add  a  few 
drops  of  ammonia  and  ammonium-carbonate  solution,  let  stand  a  few  minutes 
on  the  water-bath,  filter  into  a  tared  platinum  dish,  evaporate  to  dryness, 
expel  the  ammonium  salts  by  heating  to  just  perceptible  dull  redness  and 
weigh  the  chlorides  of  potassium  and  sodium.  If  on  dissolving  the  chlorides 
in  a  little  water  any  residue  be  left  the  precipitation  with  ammonia  and  am- 
monium carbonate  may  be  repeated  before  the  final  weighing,  or  the  residue 
may  be  collected  on  a  small  ashless  filter,  burnt,  and  weighed  back  with 
the  dish. 

6.  DETERMINATION  OF  CARBON  DIOXIDE. 

Use  from  1  to  5  grm.  of  ash  in  any  of  the  usual  forms  of  apparatus,  de- 
termining the  carbon  dioxide  evolved  either  by  increase  of  weight  of  potash 
bulbs  or  loss  of  weight  of  the  apparatus. 

7.  DETERMINATION  OF  CHLORINE. 

Determine  as  silver  chloride,  either  gravimetrically  or  by  one  of  the 
standard  volumetric  processes,  in  a  nitric-acid  or  aqueous  solution  of  the 
ash.  Nitric  acid  may  be  used  in  (e)  and  the  solution  employed  for  this  pur- 
pose. 


OFFICIAL   METHODS   OF  ANALYSIS.  1099 


VIII.    METHODS  FOR  THE  ANALYSIS  OF  TANNING  MATERIALS. 

I.  PREPARATION  OF  SAMPLE. 

Barks,  woods,  leaves,  dry  extracts,  and  similar  tanning  materials  should 
be  ground  to  such  a  degree  of  fineness  that  they  can  be  thoroughly  extracted. 
Fluid  extracts  must  be  heated  to  50°  C.,  well  shaken,  and  allowed  to  cool 
to  room  temperature. 

II.  QUANTITY  OF  MATERIAL. 

In  the  case  of  bark  and  similar  material  use  such  quantity  as  will  give 
about  0-8  grm.  solids  per  100  c.c.  of  solution,  extract  in  SOXHLET  or  similar 
apparatus  at  steam  heat  for  non-starchy  materials.  For  canaigre  and 
substances  containing  like  amounts  of  starch  use  temperature  of  50°  to  55°  C. 
until  near  complete  extraction,  finishing  the  operation  at  steam  heat.  In  the 
case  of  extract  weigh  such  quantity  as  will  give  0-8  grm.  solids  per  100  c.c. 
of  solution,  dissolve  in  900  c.c.  of  water  at  80°,  let  stand  twelve  hours,  and 
make  up  to  1000  c.c. 

III.  MOISTURE. 

(a)  Place  2  grm.,  if  it  be  an  extract,  into  a  flat-bottomed  dish  not  less  than 
6  cm.  in  diameter,  add  25  c.c.  of  water,  warm  slowly  till  dissolved,  continue 
evaporation,  and  dry. 

(6)  All  dryings  called  for,  after  evaporation  to  dryness  on  water-bath 
or  others,  shall  be  done  by  one  of  the  following  methods,  the  soluble  solids 
and  non-tannins  being  dried  under  similar,  and,  so  far  as  possible,  identical 
conditions : 

1.  For  twenty-four  hours  at  the  temperature  of  boiling  water  hi  a  steam- 
bath. 

2.  For  eight  hours  at  100°  to  103°  in  an  air-bath. 

3.  To  constant  weight  in  vacuo  at  70°. 

IV.  TOTAL  SOLIDS. 

Shake  the  solution,  and  without  filtering  immediately  measure  out  100 
c.c.  with  a  pipette,  evaporate  in  a  weighed  dish,  and  dry  to  constant  weight, 
at  the  temperature  of  boiling  water.  Dishes  should  be  flat-bottomed  and 
not  less  than  6  cm.  in  diameter. 

V.  SOLUBLE  SOLIDS. 

Filtration  shall  take  place  through  a  double-folded  filter  (S.  and  S.  No. 
590),  the  first  150  c.c.  passing  through  shall  be  rejected,  100  c.c.  next  passing 
through  shall  be  evaporated  and  dried.  When  a  clear  filtrate  cannot  be 
otherwise  obtained  the  use  of  10  grm.  of  kaolin  previously  washed  in  a  portion 
of  the  tanning  solution  is  permissible.  Evaporation  during  filtration  must  be 
guarded  against. 

VI.  NON-TANNINS. 

Propare  20  grm.  of  hide-powder  by  washing  in  a  No.  7  beaker  with  from 
800  to  1000  c.c.  of  water,  stir  well  and  let  stand  one  hour,  filter  the  magma 


1100  APPENDIX  I. 

through  linen,  squeeze  thoroughly  by  hand,  and  remove  as  much  water  as 
possible  by  means  of  a  press,  weigh  the  pressed  hide,  and  take  approximately 
one-fourth  of  it  for  moisture  determination.  Weigh  this  fourth  carefully 
and  dry  to  constant  weight.  Weigh  the  remaining  three-fourths  carefully 
and  add  them  to  200  c.c.  of  the  original  solution;  shake  ten  minutes,  and 
squeeze  the  tanned  hide  through  linen.  Collect  this  nitrate,  add  5  gnu.  of 
kaolin,  free  from  soluble  salts,  stir  well  and  filter  through  folded  filter  (S.  and 

5.  No.  590,  15  cm.),  returning  the  first  25  c.c.     Evaporate  100  c.c.  of  the  clear 
filtrate.     The  weight  of  this  residue  must  be  corrected  for  the  dilution  caused 
by  the  water  contained  in  the  pressed  hide-powder.     The  shaking  must  be 
done  in  some  form  of  mechanical  shaker.     The  simple  machine  used  by 
druggists,  and  known  as  the  milk-shake,  is  recommended. 

VII.  TANNINS. 

The  amounts  of  these  is  shown  by  the  difference  between  the  soluble 
solids  and  the  corrected  non-tannins. 

VIII.  TESTING  HIDE-POWDER. 

(a)  Shake  10  grm.  of  hide-powder  with  250  c.c.  of  water  for  five  minutes, 
strain  through  linen,  squeeze  the  magma  thoroughly  by  hand ;  repeat  this 
operation  three  times,  pass  the  last  filtrate  through  paper  (S.  and  S.  No.  590, 
15  cm.)  till  clear,  evaporate  100  c.c.,  and  dry.  If  this  residue  amounts  to  more 
than  10  mg.  the  hide  must  be  rejected. 

(fe)  Prepare  a  solution  of  pure  gallo-tannin  by  dissolving  5  grm.  in  1000 
c.c.  of  water.  Determine  the  total  solids  by  evaporating  100  c.c.  of  this 
solution  and  drying  to  constant  weight.  Treat  200  c.c.  of  the  solution 
with  hi  Je -powder  exactly  as  described  in  paragraph  6.  The  hide-powder 
must  absorb  at  least  95  per  cent,  of  the  total  solids  present.  The  gallo- 
tannin  used  must  be  completely  soluble  in  water,  alcohol,  acetone,  and  acetic 
ether,  and  should  not  contain  more  than  1  per  cent,  of  substances  not  re- 
moved by  digesting  with  excess  of  yellow  mercuric  oxide  on  steam-bath  for 
two  hours. 

IX.  TESTING  NON-TANNIN  FILTRATE. 

(a)  For  Tannin. — Test  a  small  portion  of  the  clear  non-tannin  filtrate 
with  a  few  drops  of  a  1-per  cent,  solution  of  NELSON'S  gelatin.  A  cloudiness 
indicates  the  presence  of  tannin,  in  which  case  repeat  the  process  described 
under  6,  using  25  instead  of  20  grm.  of  hide  powder. 

(6)  For  Soluble  Hide. — To  a  small  portion  of  the  clear  non-tannin  filtrate 
add  a  few  drops  of  the  filtered  tannin  solution.  A  cloudiness  indicates  the 
presence  of  soluble  hide,  in  which  case  repeat  the  process  described  under 

6,  giving  the  hide-powder  a  more  thorough  washing. 

The  temperature  of  solutions  shall  be  between  16°  and  20°  when  measured 
or  filtered.  All  dryings  should  be  made  in  flat-bottomed  dishes  of  at  least 
6  cm.  diameter.  S.  and  S.  No.  590,  15  cm.  filter-paper  should  be  used  on  all 
filtrations. 


APPENDIX     II. 

SOME  PRINCIPLES  AND  METHODS  OF  ROCK  ANALYSIS. 

(Bulletin  of  the  United  States  Geological  Survey,  No.  176,  1900.) 

BY  WILLIAM  FRANCIS  HILLEBRAND. 

TART  I.     INTRODUCTION. 

I.  IMPORTANCE  OF  COMPLETE  AND  THOROUGH  ANALYSES. 

The  composition  of  the  ultimate  ingredients  of  the  earth's  crust — the 
different  mineral  species  which  are  there  found  and  of  many  of  which  its 
rocks  are  made  up — was  the  favorite  theme  of  the  great  workers  in  chemistry 
of  the  earlier  half  of  this  century,  and  for  the  painstaking  care  and  accuracy 
of  BERZELIUS,  WOHLER,  and  others  the  mineralogists  and  geologists  of  to-day 
have  need  to  be  thankful.  Considering  the  limited  facilities  at  their  dis- 
posal in  the  way  of  laboratory  equipment  and  quality  of  reagents,  the  general 
excellence  of  their  work  is  little  short  of  marvelous.  As  an  outgrowth  of 
and  closely  associated  with  the  analysis  of  minerals  came  that  of  the  more 
or  less  complex  mixtures  of  them — the  rocks — to  aid  whose  study  by  the 
petrographer  and  geologist  a  host  of  chemists  have  for  many  decades  annually 
turned  out  hundreds  of  analyses  of  all  grades  of  quality  and  completeness. 
With  the  growth  and  extraordinary  development  of  the  so-called  organic 
chemistry,  inorganic  chemistry  gradually  fell  into  a  sort  of  disfavor.  In 
many,  even  the  best,  European  laboratories,  the  course  in  mineral  analysis, 
while  maintained  as  a  part  of  the  curriculum  of  study,  became  but  a  sub- 
ordinate prelude  to  the  ever-expanding  study  of  the  carbon  compounds, 
whose  rapid  multiplication,  offering  an  easy  and  convenient  field  for 
original  research  and  possible  profit,  proved  a  more  tempting  opening  to 
young  chemists  than  the  often-worked-over  and  apparently  exhausted 
inorganic  pasture.  For  one  student  devoting  his  time  to  higher  research 
on  inorganic  lines  were  perhaps  fifty  engaged  in  erecting  the  present 
enormous  structure  of  carbon  chemistry.  The  instruction  afforded  the 
student  in  mineral  analysis  was  confined  to  the  ordinary  separations  of  the 
commoner  ingredients  occurring  in  appreciable  quantities,  with  little  regard 
to  supposed  traces  and  with  still  less  attempt  to  find  out  if  the  tabulated 
list  really  comprised  all  that  the  mineral  or  rock  contained. 

With  the  introduction  of  improved  methods  of  examination  by  the  petrog- 
rapher, especially  as  applied  to  thin  rock  sections,  and  the  use  of  heavy 

1101 


1102  APPENDIX   II. 

solutions,  whereby,  on  the  one  hand,  the  qualitative  mineral  composition 
of  a  rock  could  be  preliminarily  ascertained  with  considerable  certainty, 
and  on  the  other,  chemical  examination  of  the  more  or  less  perfectly  separated 
ingredients  was  rendered  possible,  a  great  help  and  incentive  was  afforded 
to  t>he  few  chemists  engaged  in  rock  analysis.  The  microscope  often  obviated 
in  part  the  necessity  for  tedious  and  time-wasting  qualitative  tests,  and  the 
heavy  solutions,  by  permitting  the  concentration  and  separation  of  certain 
components,  facilitated  the  detection  of  elements  whose  existence  had  long 
been  overlooked. 

Meanwhile  in  the  progress  of  chemistry  new  methods  and  reagents  for 
qualitative  detection  and  quantitative  separation  and  estimation  were  gradu- 
ally being  discovered  and  devised.  The  supposed  adequacy  of  some  well- 
established  methods  was  shown  to  be  unwarranted;  some  had  to  be  dis- 
carded altogether;  others  were  still  utilizable  after  modification.  In  the 
light  thus  shed  it  became  possible  to  explain  many  hitherto  incomprehensible 
variations  in  the  composition  of  some  rock  species  or  types,  as  shown  in 
earlier  analyses,  and  in  not  a  few  cases  it  appeared  that  the  failure  to  report 
the  presence  of  one  or  more  elements  had  obscured  relations  and  differences 
which  more  thorough  examination  showed  to  exist-  (see  pp.  1103  and  1104). 
Consequently  there  arose  a  feeling  of  distrust  of  much  of  the  older  work  in  the 
minds  of  those  chemists  and  petrographers  best  fitted  to  judge  of  its  probable 
qualities.  This,  and  the  incompleteness  of  nearly  ah1  the  earlier  work  (and 
much  of  that  of  to-day,  unfortunately),  as  shown  by  the  largely  increased 
list  of  those  elements  now  known  to  enter  into  the  normal  composition  of 
rocks,  is  rendering  the  old  material  less  and  less  available  to  meet  the  increas- 
ing demands  of  the  petrographer. 

And  yet  these  demands  on  his  part  are,  with  few  exceptions,  by  no  means 
so  exacting  as  they  should  be.  Often  the  analysis  is  intrusted  to  the  hands 
of  a  student  without  other  experience  than  that  gained  by  the  analysis  of 
two  or  three  artificial  salts  and  as  many  comparatively  simple  natural  minerals, 
and  with  a  laboratory  instructor  as  adviser  whose  experience  in  rock  analysis 
may  be  little  superior  to  his  own.  In  other  words,  one  of  the  most  difficult 
tasks  in  practical  analysis  is  expected  to  be  solved  by  a  tyro,  and  his  results 
are  complacently  accepted  and  published  broadcast  without  question.  Even 
to  those  thoroughly  familiar  with  the  subject  rock  analysis  is  a  complex  and 
often  trying  problem.  Although  long  practice  may  have  enabled  one  to 
do  certain  parts  of  it  almost  mechanically,  one  is  still  from  time  to  time  con- 
fronted with  perplexing  questions  which  require  trained  judgment  to  properly 
meet  and  answer,  and  there  is  still  room  for  important  work  in  some  of  the 
supposedly  simplest  quantitative  determinations.  If  the  results  are  to  have 
any  decided  value  for  purposes  of  scientific  interpretation  and  comparison, 
they  should  be  the  product  of  one  competent  to  find  his  way  through  the 
intricacies  of  an  analysis  in  which  from  fifteen  to  twenty-five  different  com- 
ponents are  to  be  separated  and  estimated  with  close  approach  to  accuracy, 
and  this  a  beginner  cannot  hope  to  do  in  the  majority  of  cases.  The  con- 
scientious chemist  should  have  a  live  interest  in  this  matter.  He  should 
work  with  a  two-fold  purpose  in  view — that  of  lightening  the  labors  of  those 


SOME    PRINCIPLES   AND   METHODS  OF   ROCK    ANALYSIS.    1103 


who  come  after  him  by  enabling  them  to  use  his  work  with  less  supple- 
mentary examination,  and  of  thereby  enhancing  his  own  reputation  by  merit- 
ing encomiums  on  work  that  has  stood  the  test  of  time. 

The  petrographer,  again,  should  seek  to  have  his  analyses  made  as  com- 
plete as  possible,  and  not,  as  is  so  often  the  case,  be  content  with  determina- 
tions of  silica,  alumina,  the  oxides  of  iron,  lime,  magnesia,  the  alkalies,  and 
water.  The  latter,  it  is  true,  are  entirely  justifiable  at  times,  and  may  serve 
the  immediate  purpose  for  which  they  were  intended,  but  their  incomplete- 
ness may,  on  the  other  hand,  not  only  conceal  points  fruitful  of  suggestion 
to  the  attentive  mind,  but,  what  is  of  still  greater  importance,  they  may  be 
actually  misleading.  Enough  instances  of  totally  inaccurate  conclusions  to 
be  drawn  from  them  have  fallen  under  my  own  observation  to  fully  justify 
this  plea  in  favor  of  greater  completeness  in  rock  and  mineral  analyses  made 
for  purely  scientific  purposes. 

The  importance  of  the  points  indicated  in  the  foregoing  paragraph  is 
shown  by  the  difference  between  the  analyses  given  in  the  following  tables. 
The  specimens  were  taken  and  analyzed  at  widely  separated  times  and  by 
different  persons,  it  is  true,  but  they  were  unquestionably  from  the  same 
rock  mass,  in  which,  however  much  the  relative  proportions  of  the  different 
mineral  constituents  might  vary  within  certain  limits,  there  can  be  no  reason 
to  doubt  the  general  distribution  of  all  the  elements  shown  by  the  second 
analysis. 


Earlier 
Analysis. 

Later 

Analysis.* 

Earlier 
Analysis. 

Later 
Analysis. 

SiO2.  . 

54-42 

53-70 

Li2O.  . 

Trace 

Trace 

TiO2 

1-92 

H2O  below  110°C 

•80 

AljO3 

13-37 

11-16 

H2O  above  1  10°  C 

J2-76 

2-61 

O2O3            .  .      . 

•  04 

CO2  . 

1-82 

FeX>,  . 

t  -61 

3-10 

P9OV 

1-75 

Feo  3:  : 

13-52 

1-21 

s63.  . 

•06 

MnO  

•  04 

F..V. 

•44 

CaO 

4-38 

3-46 

Cl 

•03 

SrO             .    .      . 

•19 

BaO 

-62 

99-58 

100  •  40 

MgO  

6-37 

6-44 

Less  O  for  F.  .... 

•19 

K,O  

10-73 

11-16 

Na^O  

1-60 

1-67 

100-21 

*  A  still  more  recent  analysis  of  another  of  the  series  of  rocks  of  which  this  is  an  ex- 
ample has  shown  that  this  "later  analysis"  is  itself  probably  incomplete  and  incorrect 
in  part — incomplete  because  of  the  probable  presence  of  0'2  per  cent,  or  more  of  ZrO2, 
incorrect  because  of  the  error  in  A12O3  resulting  from  having  counted  ZrO2  as  A12O3,  and 
from  the  fact  that  titanium  is  not  fully  precipitable  in  presence  of  zirconium  by  GOOCH'S 
method  (the  one  employed).  The  latter  error  involves  both  the  TiOo  and  the  Al^Oj. 
(See  pp.  1153  and  1154.) 

t  From  the  fact  that  repeated  determinations  of  the  iron  oxides  in  this  and  related 
rocks  from  the  same  region  show  always  a  great  preponderance  of  ferric  oxide,  it  is  not 
improbable  that  the  figures  given  for  the  two  oxides  in  the  first  analysis  were  accidentally 
transposed. 

t  In  the  published  analysis  it  does  not  appear  whether  this  is  total  water  or,  as 
seems  probable,  only  that  remaining  above  100°  C. 


1104 


APPENDIX    II. 


Another  instance  of  similar  kind  is  given  below.  Here,  again,  certain 
differences  -are  explainable  by  natural  variations  in  the  proportions  of  the 
constituent  minerals,  but  it  can  hardly  be  doubted  that  TiO2,  BaO,  SrO, 
P2O5,  and  SO3  were  present  in  both  specimens  in  approximately  the  same 
amounts.  In  the  earlier  analysis  determinations  of  some  supposed  unim- 
portant constituents  were  purposely  omitted,  or  made  only  qualitatively, 
with  results  that  cannot  be  otherwise  than  fatal  to  a  full  comprehension  of 
the  mineralogical  nature  of  the  rock. 


Earlier 

Analysis. 

Later 

Analysis. 

Earlier 
Analysis. 

Later 
Analysis. 

SiO, 

44-31 

44-65 

Na2O.  . 

4-45 

5-67 

TiO2 

Not  est 

95 

Li2O  

Trace. 

A12O3 

17-20 

13-87 

H2O  below  1  10°  C. 

•77 

-95 

Fe,Oo 

4-64 

6-06 

H2O  above  1  10°  C 

2-10 

FeO     I 

3-73 

2-94 

H2O  by  ignition.  .  . 

3-30 

MnO 

•10 

•17 

CO2  

•11 

CaO 

10-40 

9-57 

P,O,.  . 

1-50 

SrO 

*-37 

d... 

Trace. 

BaO 

•76 

so,  

•61 

Mo-O 

fi.  ^7 

K.I  pj 

K2O 

3-64 

4-49 

99-11 

99-92 

*  Not  entirely  free  from  CaO. 

Prof.  F.  W.  CLARKE  has  shown  that  the  combined  percentages  of  titanic 
and  phosphoric  oxides  in  rock  of  the  earth's  crust,  averaged  from  hundreds  of 
analyses,  is  0-8  per  cent.  When  the  determination  of  these  is  neglected 
the  error  falls  upon  the  alumina.  If  the  latter  is  then  used  as  a  basis  for 
calculating  the  feldspars,  it  is  easy  to  see  that  a  very  large  average  error  in  the 
latter  may  result,  amounting  to  several  per  cent,  of  the  rock. 

In  order  to  more  strongly  emphasize  the  importance  of  completeness  in 
analysis,  a  few  facts  brought  out  by  the  hundreds  of  rock  analyses  made 
in  this  laboratory  may  be  cited.  It  has  been  demonstrated  most  conclu- 
sively that  barium  and  strontium  are  almost  never-failing  constituents  of 
the  igneous  rocks  of  the  United  States  and  of  many  of  their  derivatives.  These 
amounts  are  usually  below  0-1  per  cent,  for  each  of  the  oxides  of  those 
metals,  but  higher  amounts  are  by  no  means  uncommon.  Furthermore,  the 
weight  of  barium  is  almost  without  exception  in  excess  of  that  of  strontium. 
But  a  still  more  important  point  is  that  the  igneous  rocks  of  the  Rocky 
Mountain  region,  so  far  as  examined,  show  far  higher  average  percentages 
of  both  metals  than  the  rocks  from  the  eastern  and  the  more  western 
portions  of  the  United  States.  The  following  examples  serve  to  illustrate 
certain  types  of  Rocky  Mountain  igneous  rocks:  Of  seven  rocks  forming 
a  Colorado  series,  six  held  from  0-13  to  0-18  per  cent,  of  BaO,  while  in  the 
seventh  the  percentage  was  0-43.  The  SrO  ranged  from  0-07  to  0-13  per 
cent,  for  six,  and  was  0-28  for  that  one  highest  in  BaO.  Of  thirteen  geo- 
logically related  rocks  from  Montana,  embracing  basic  as  well  as  acid  and 
intermediate  types,  the  range  of  BaO  was  from  0-19  to  0-37  per  cent.,  with 


SOME   PKINCIPLES   AND   METHODS   OF  ROCK  ANALYSIS.    1105 

an  average  of  0-30  per  cent.  Three  others  of  the  same  series  contained 
0-10  per  cent,  or  less,  while  the  seventeenth  carried  0-76  per  cent.  BaO. 
The  SrO  ranged  from  0-37  per  cent,  in  the  last  instance  to  an  average  of 
0-06  for  the  other  sixteen.  Certain  peculiar  rocks  from  Wyoming  carry 
from  0  •  62  to  1  •  25  per  cent.  BaO,  and  from  0  •  02  to  0  •  33  per  cent.  SrO.  Surely 
this  concentration  of  certain  chemical  elements  in  certain  geographic  zones 
has  a  significance  which  future  geologists  will  be  able  to  interpret,  if  those 
of  to-day  are  not. 

Again,  vanadium  is  an  element  which  few  chemists  have  ever  thought  of 
looking  for  in  igneous  rocks,  though  it  has  long  been  known  to  occur  in  mag- 
netites and  other  iron  ores.  HAYES,  in  1875,  reported  its  occurrence  in  a 
great  variety  of  rocks  and  ores.  Quoting  from  THORPE'S  Dictionary  of  Chem- 
istry: "It  is  said  to  be  diffused  with  titanium  through  all  primitive  granite 
rocks  (DIEULAFAIT),  and  has  been  found  by  DEVILLE  in  bauxite,  rutile,  and 
many  other  minerals,  and  by  BECHI  and  others  in  the  ashes  of  plants  and  in 
argillaceous  limestones,  schists,  and  sands."  It  is  further  reported  to  com- 
prise, as  the  pentoxide,  up  to  0  •  1  per  cent,  of  many  French  and  Australian 
clays,  0  •  02-0  •  03  per  cent,  of  some  basalts,  0  •  24  per  cent,  of  a  coal  of  unknown 
origin,  and  0  •  45  per  cent,  of  one  from  Peru.  Still  later  examinations  in  this 
laboratory  of  about  100  rocks,  chiefly  igneous,  covering  the  whole  territory 
of  the  United  States,  show  not  only  its  general  qualitative  and  qualitative 
distribution,  but  that  it  predominates  in  the  less  siliceous  igneous  rocks  and 
is  absent,  or  nearly  so,  in  those  high  in  silica.  In  some  of  the  more  basic 
rocks  it  occurs  in  sufficient  amount  to  seriously  affect  the  figures  for  the 
oxides  of  iron  unless  separately  estimated  and  allowed  for  (see  p.  1175) — a 
matter  of  considerable  importance,  since  the  petrographer  lays  great  stress 
on  accuracy  in  their  determinations. 

This  same  investigation  has  also  thrown  some  light  on  the  distribution  of 
molybdenum,  which  seems  to  be  confined  to  the  more  siliceous  rocks  and  to 
occur  in  quantities  far  below  those  commonly  found  for  vanadium. 

Finally,  had  it  not  been  the  writer's  practice  of  late  years  to  look  for 
sulphur  in  rocks,  even  when  no  sulphides  were  visible  to  the  eye,  its  almost 
invariable  presence  in  the  form  of  sulphide,  and  consequent  connection  with 
the  long  mystifying  lack  of  agreement  between  results  for  ferrous  iron  ob- 
tained by  the  MITSCHERLICH  and  the  hydrofluoric -acid  methods,  might  not 
have  been  suspected.  (See  p.  1169.) 

While  strongly  upholding  the  necessity  for  more  thorough  work,  necessar- 
ily somewhat  at  the  expense  of  quantity,  it  is  far  from  the  writer's  intention 
to  demand  that  an  amount  of  time,  although  disproportionate  to  the  im- 
mediate objects  to  be  sought,  should  be  expended  on  every  analysis.  But  it 
is  maintained  that  in  general  the  constituents  which  are  likely  to  be  present 
in  sufficient  amount  to  admit  of  determination  in  the  weight  of  sample  usually 
taken  for  analysis— say  1  grm.  for  SiO2,  A12O3,  etc.,  to  2  grm.  for  certain 
other  constituents— should  be  sought  for,  qualitatively  at  least,  in  the  ordi- 
nary course  of  quantitative  work,  and  their  presence  or  absence  noted  among 
the  results.  If  present  in  little  more  than  traces,  that  knowledge  alone 
may  suffice,  for  it  is  often  more  important  to  know  whether  or  not  an  ele- 


1106  APPENDIX   II. 

ment  is  present  than  to  be  able  to  say  that  it  is  there  in  amount  of  exactly 
0-02  or  0-06  per  cent.  In  the  tabulation  of  analyses  a  special  note  should 
be  made  in  case  of  intentional  or  accidental  neglect  to  look  for  substances 
which  it  is  known  are  likely  to  be  present.  Failure  to  do  this  may  subject 
the  analyst  to  unfavorable  criticism,  when  at  some  future  time  his  work  is 
reviewed  and  the  omissions  are  discovered  by  new  analyses. 

Finally,  whenever  possible,  a  thorough  microscopical  examination  of 
the  rocks  in  thin  section  should  precede  the  chemical  analysis.  This  may 
be  of  the  greatest  aid  to  the  chemist  in  indicating  the.  presence  of  unusual 
constituents,  or  of  more  than  customary  amounts  of  certain  constituents, 
whereby,  possibly,  necessary  modifications  in  the  analytical  procedure 
may  be  employed  without  waste  of  time  or  labor.* 

II.  OBJECT  AND  SCOPE  OF  THE  PRESENT  TREATISE. 

The  literature  relating  to  analysis  of  silicates  is  extensive  but  scattered, 
and  in  no  single  article  is  there  to  be  found  a  satisfactory  exposition  of  the 
methods  to  be  followed  or  the  precautions  to  be  observed,  especially  in  the 
search  for  some  of  the  rarer  constituents  or  those  which,  without  being  rare, 
have  been  of  late  years  recognized  as  occurring  persistently  in  small  amounts. 
It  is  not  intended  to  make  this  little  volume  a  treatise  on  mineral  analysis, 
but  it  is  believed  that  the  experience  gained  by  the  chemists  of  this  Survey 
during  the  twenty  years  since  the  establishment  of  its  first  chemical  labora- 
tory in  Denver  may  be  useful  to  most  chemists  interested  in  mineral  and 
especially  rock  analysis. 

The  original  publication  of  these  data  in  Bulletin  No.  148  was  primarily 
intended  to  show  the  principles  and  methods  according  to  which  the 
major  part  of  the  very  many  hundreds  of  analyses  therein  brought  together 
had  been  executed,  and  thus  to  furnish  a  partial  measure  of  the  trustworthi- 
ness of  those  analyses,  rather  than  to  serve  as  a  practical  manual  of  rock 
analysis.  But  the  use  which  has  been  made  by  mineral  chemists  of  that 
bulletin  has  seemed  to  render  it  advisable  to  amplify  somewhat  in  detail 
and  to  add,  besides  a  few  new  methods,  a  number  of  alternative  ones  which  are 
known  or  believed  to  be  good,  in  order  that  those  who  may  wish  to  use  this 
treatise  as  a  practical  guide  shall  have  a  choice  from  which  to  select  in  case 
the  rather  expensive  apparatus  or  complicated  arrangements  sometimes 
preferred  are  not  available.  Where  silicate  analyses  are  very  frequently 
made,  however,  it  is  a  saving  of  time  and  of  money  in  the  end  to  set  up  per- 
manent arrangements  for  convenience  in  estimating  water,  carbon  dioxide, 
ferrous  iron,  making  reductions  in  hydrogen,  etc. 

Stress  will  be  laid  on  those  points  meriting  particular  attention,  and  now 

*  The  foregoing  tables  and  accompanying  remarks,  including  several  sentences  pre- 
ceding the  tables,  have  been  largely  taken  from  the  writer's  papers  entitled  "A  Plea  fcr 
Greater  Completeness  in  Chemical  Rock  Analysis,"  published  in  the  Journal  of  the  Ameri- 
can Chemical  Society,  xvi,  pp.  90-93.  1894;  also  in  the  Chemical  News,  LXIX,  p.  163,  1894. 
See  also  "Distribution  and  Quantitative  Occurrence  of  Vanadium  and  Molybdenum  in 
Rocks  of  the  United  States,"  in  the  American  Journal  of  Science,  4th  Series,  vi.  p.  209, 
1898,  and  Chemical  News,  LXXVIII,  p.  216.  1898. 


SOME   PRINCIPLES  AND   METHODS   OF   ROCK   ANALYSIS.    1107 

and  then  a  brief  discussion  or  criticism  of  methods  elsewhere  in  vogue  may 
be  entered  into. 

In  the  earlier  years  of  the  existence  of  the  Washington  laboratory  oppor- 
tunity was  afforded  for  the  testing  of  novel  methods  and  the  devising  of  new 
ones,  with  most  excellent  results,  as  shown  especially  by  the  methods  for 
separation  of  titanium,  of  lithium,  and  of  boron,  due  to  Prof.  F.  A.  GOOCE, 
to  whose  inventive  skill  chemists  owe  likewise  the  perforated  filtering  crucible 
and  the  tubulated  platinum  crucible  arrangement  for  the  estimation  of  water. 
Of  late  years  the  press  of  routine  work  has  been  such  as  to  more  fully  fill  up 
the  time  of  the  much-reduced  chemical  force,  and  as  a  consequence  it  has 
been  found  impossible  to  subject  to  critical  trial  several  separation  methods  of 
recent  origin,  some  of  which  seem  to  be  full  of  promise,  or  to  follow  out  certain 
lines  of  investigation  which  have  been  suggested  by  the  observations  made 
in  this  laboratory.  This,  then,  must  be  offered  in  explanation  if,  in  the 
following  discussion,  it  may  seem  to  some  that  any  of  the  methods  followed 
are  too  conservative.  In  general  the  discussion  will  be  confined  strictly  to 
such  separations  as  may  be  required  in  the  analysis  of  an  igneous,  metamor- 
phic,  or  sedimentary  silicate  rock  of  complex  mineralogical  composition,  in 
which  the  majority  and  possibly  all  of  the  ingredients  in  the  list  given  below 
may  occur  hi  weighable  or  readily  discoverable  quantities : 

SiO.,,  TiO2,  ZrO2,  A1A,  Fe2O3,  Cr2O3,  V2O3,  FeO,  MnO,  NiO,  CoO,  MgO, 
CaO,  SrO,  BaO,  ZnO,  CuO,  K2O,  Na2O,  Li2O,  H2O,  P2O5,  S,*  SO3  C,f  CO9 

Fl,  Cl,  N. 

The  special  problems  often  arising  in  the  analysis  of  rocks  of  extra- 
terrestrial origin — the  more  or  less  stony  meteorites — will  not  be  considered^ 
An  analysis  of  that  kind  should  never  be  intrusted  to  the  novice,  but  only  to 
the  chemist  who  has  a  knowledge  of  the  composition  and  properties  of  the 
peculiar  mineral  constituents  of  those  bodies  and  a  judgment  fit  to  cope 
with  the  oftentimes  difficult  problems  presented  by  them. 

Thorium,  cerium,  and  other  rare  earths  are  seldom  encountered  in  quan- 
tities sufficient  to  warrant  the  expenditure  of  the  time  necessary  for  their 
isolation.  A  search  for  them  qualitatively,  even,  is  at  present  rarefy  justi- 
fiable unless  there  is  microscopic  or  other  evidence  of  the  presence  of  min- 
erals likely  to  contain  them.  Tantalum,  columbium,  boron,  and  glucinum 
have  never  been  certainly  met  with  in  the  writer's  experience,  and  yet  they 
must  be  present  in  certain  rocks,  and  doubtless  traces  have  been  overlooked 
at  times.  There  is  no  reason  to  suppose  that  other  elements  may  not  be 
tound  by  careful  search,  possibly  all  in  the  known  category,  and,  indeed, 
SAXDBERGER'S  icsearches  have  shown  to  what  an  extent  this  is  true  of  a 
large  number  of  those  elements  contributing  to  the  filling  of  metalliferous 
veins.  But  those  in  the  above  list  may  usually  be  estimated  with  ease  in 
weights  of  from  one-half  to  2  grm. 

If  the  point  be  raised  that  many  of  the  published  analyses  emanating 
from  the  Survey  laboratories,  even  the  earlier  ones  of  the  writer,  are  not  in 

*  Usually  as  pyrite  not  infrequently  as  pyrrhotite.         t  As  graphite  or  coaly  matter. 


1108  APPENDIX    II. 

accord  with  the  advocacy  of  completeness  contained  in  the  foregoing  pages, 
it  may  be  remarked  that  these  ideas  have  been  to  a  considerable  degree 
evolved  during  a  personal  experience  of  twenty  years  in  this  line  of  work, 
and  that  frequently  the  exigencies  were  such  as  to  compel  restriction  in  the 
examination.  Where  the  latter  has  been  the  case  subsequent  developments 
have  in  some  cases  shown  it  to  be  bad  policy  in  every  respect.  It  is  better, 
both  for  the  geologist  and  the  chemist,  to  turn  out  a  limited  amount  of  thor- 
ough work  than  a  great  deal  of  what  may  prove  to  be  of  more  than  doubtful 
utility  in  the  end. 

III.    STATEMENT  OF  ANALYSES. 

Until  recently  it  has  been  the  practice  in  this  laboratory  to  tabulate  the 
constituents  of  a  rock  somewhat  in  the  order  of  their  determination,  begin- 
ning with  SiO2  as  the  chief  constituent  and  grouping  together  all  chemically 
related  oxides,  as  shown,  for  instance,  on  pages  1103  and  1104. 

From  a  strictly  scientific  point  of  view  a  chemical  classification  founded 
on  a  separation  into  basic  and  acidic  atoms  or  radicals  would  be  more  satis- 
factory, but  until  we  learn  to  find  out  what  silicic  radicals  are  present  and 
in  what  relative  amounts,  also  how  much  free  silica  there  may  be,  it  is  useless 
to  think  of  employing  the  arrangement  so  valuable  in  stating  water  analyses. 

Of  late  petrographers  have  begun  to  demand,  with  considerable  reason, 
an  arrangement  ''which  shall  bring  the  essential  chemical  features — both 
the  percentage  figures  and  the  molecular  ratios — prominently  and  compactly 
before  the  eye,  so  that  the  general  chemical  character  and  the  relations  of 
the  various  constituents  may  be  seen  at  a  glance."  * 

In  accordance  with  this  demand  it  is  now  our  practice  to  follow  pretty 
closely  the  arrangement  proposed  by  PIRSSON  and  very  recently  strongly 
advocated  by  WASHINGTON  (loc.  cit.},  namely: 

SiO2,  A12O3,  Fe2O3,  FeO,  MgO,  CaO,  Na2O,  K2O,  H2O  (above  105-110°  C.), 
H2O  (below  105-110°  C.),  CO2,  TiO2,  ZrO2,  P2O5,  SO3,  Cl,  Fl,  S  (FeS2),  Cr2O8, 
V2O3>  NiO,  CoO,  CuO,  MnO,  SrO,  BaO,  Li2O,  C,  NH3. 

By  this  arrangement  the  nine  constituents  which  in  the  great  majority  of 
cases  determine  the  character  of  the  rock  are  placed  at  the  head  of  the  list, 
thus  greatly  facilitating  the  comparison  of  different  analyses  similarly  ar- 
ranged, especially  when,  as  WASHINGTON  recommends,  the  molecular  ratios 
are  calculated  for  these  leading  constituents  and  placed  immediately  after  the 
corresponding  oxides.  The  order  of  the  remaining  members  is  determined 
somewhat  by  the  following  considerations:  CO2  is  placed  next  after  H.,0, 
since  these  two  are  generally  a  measure  of  the  alteration  the  rock  may  have 
undergone.  TiO2  and  ZrO2  naturally  follow  CO2  on  chemical  grounds,  and 
SO3  and  Cl,  being  common  constituents  of  the  sodalite  group,  are  conveniently 
placed  together. 


*  H.  S.  WASHINGTON  "  The  Statement  of  Rock  Analysis,"  Am.Journ.  Sci.,  4th  Series, 
,  p.  61,  1900. 


SOME    PRINCIPLES   AND    METHODS    OF    ROCK    ANALYSIS.    1109 


IV.  TIME  NEEDED  FOR  MAKING  AN  ANALYSIS. 

The  question  has  often  been  put,  ' '  How  long  does  it  take  to  complete  an 
analysis  of  this  kind?"  This  will  depend,  of  course,  on  the  mineral  com- 
plexity of  the  sample  and  on  the  personal  factor  of  the  individual  worker. 
If  there  is  a  competent  assistant  to  do  the  grinding,  and  specific-gravity 
determinations  are  not  required,  it  is  quite  possible  after  long  experience 
for  a  quick  worker  to  learn  to  so  economize  every  moment  of  time  in  a  working 
day  of  seven  hours,  with  an  abundance  of  platinum  utensils  and  continuous 
use  of  air-  and  Crater-baths  through  the  night,  as  to  finish  every  three  days, 
after  the  completion  of  the  first  analysis,  barring  accidents  and  delays,  one 
of  a  series  of  rocks  of  generally  similar  character,  each  containing  from  eight- 
een quantitatively  determinable  constituents,  excluding,  for  instance, 
fluorine,  carbon  as  such,  nitrogen,  metals  of  the  hydrogen-sulphide  group, 
and  cobalt.  On  one  occasion  a  series  of  fourteen  rocks,  of  comparatively 
simple  composition,  was  completed  in  one  month,  with  the  help  of  an  assist- 
ant who  made  the  phosphorus  and  ferrous  iron  determinations.  But  such 
an  output  of  work  is  more  than  exceptional  and  implies  an  unusual  freedom 
from  those  occasional  setbacks  to  which  every  chemist  is  exposed. 

It  should  here  be  remarked  that  the  Survey  laboratory  is  most  excep- 
tionally well  supplied  with  all  kinds  of  platinum  vessels  and  utensils,  so  that 
it  is  rare  indeed  for  delay  to  arise  through  lack  of  dishes  of  even  the  largest 
sizes. 


V.    TWO  USEFUL  AIDS  IN  CHEMICAL  MANIPULATION. 

In  connection  with  the  foregoing  remarks  it  is  in  place  to  mention  two 
aids  to  the  chemist  which  are  in  constant  use  in  this  laboratory  and  have 
come  to  be  well-nigh  indispensable.  Neither  is  novel  in  principle  and  both 
are  in  use  elsewhere,  but  they  are  not  so  commonly  known  as  they  deserve 
to  be,  hence  this  allusion  to  them. 

Fig.  1  represents  a  form  of  platinum-tipped  crucible  tongs  devised  by 
Dr.  A.  A.  BLAIR  many  years  ago.  With  them  a  crucible  can  be  securely 
grasped  and  brought  into  any  desired  position  while  still  hot.  To  the  con- 
tents, if  in  fusion  over  the  blast  flame,  can  be  imparted  the  rotatory  motion 
so  often  desirable.  Above  all,  the  cover  need  not  be  in  the  slightest  degree 
displaced,  as  when  using  the  common  form  of  platinum-tipped  tongs. 

Fig.  2  represents  a  very  useful  adjunct  to  the  work-table  and  especially 
to  the  draught  cupboard,  whereby  the  liquid  contents  of  crucibles  can  be 
speedily  evaporated  at  almost  any  desired  temperature  and  the  dehydration 
of  many  solids  effected  much  more  safely  than  on  an  iron  plate  or  sand-bath. 
I  do  not  recall  who  originated  this  form  of  air-bath,  but  it  has  been  in  use 
here  for  over  fifteen  years  and  is  identical  in  principle  with  the  later  Xickel- 
becher  of  JANNASCH.  Nickel  undoubtedly  has  a  certain  advantage  in  not 
rusting  as  does  iron,  but  the  form  depicted  in  R  of  Fig.  2  can  easily  be  made 
anywhere  of  sheet  iron  riveted  at  the  joint,  the  bottom  (not  shown  in  the 


1110 


APPENDIX   II. 


figure)  being  securely  held  by  a  flange  at  the  extremity  of  the  truncated 
cone.     A  crucible  placed  on  the  platinum  triangle  becomes  uniformly  heated 


FIG.  1.  FIG.  2. 

FIG.  !• — Platinum-tipped  crucible  tongs.     The  parts  AB,  also  of   heavy  platinum,  are 

hollow,  to  serve  as  sockets  for  the  cheaper  metal  of  the  handles. 
FlQ-  2. — Radiator  for  rapid  and  safe  evaporation.     R  is  of  sheet  iron,  also  nickel  (JAN- 

NASCH).     Various  sizes.     A  convenient  height  is  7  cm.,  width  at  top  7  cm.,  and  at 

bottom  5  cm. 

by  hot  air,  and  large  quantities  of  liquid,  even  sulphuric  acid,  can  be  thus 
volatilized  in  a  short  time  without  ebullition  or  spattering. 


SOME    PRINCIPLES   AND    METHODS   OF  ROCK  ANALYSIS.    1111 


VI.  LIMITS  OF  ALLOWABLE  ERROR  IN  SUMMATION  OF 
ANALYTICAL  RESULTS. 

As  is  well  known,  a  complete  silicate  rock  analysis  which  foots  up  less 
than  100  per  cent,  is  generally  less  satisfactory  than  one  which  shows  a 
summation  somewhat  in  excess  of  100.  This  is  due  to  several  causes. 
Nearly  all  reagents,  however  carefully  purified,  still  contain,  or  extract  from 
the  vessels  used,  traces  of  impurities,  which  are  eventually  weighed  in  part 
with  the  constituents  of  the  rock.  The  dust  entering  an  analysis  from  first 
to  last  is  very  considerable,  washings  of  precipitates  may  be  incomplete, 
and  if  large  filters  are  used  for  small  precipitates  the  former  may  easily  be 
insufficiently  washed. 

Given  the  purest  obtainable  reagents,  an  ample  supply  of  platinum, 
facilities  for  working,  and  a  reasonably  clean  laboratory,  there  is  no  excuse 
for  failure  on  the  part  of  a  competent  chemist  to  reach  a  summation  within 
the  limits  99-75  and  100-50.  Failure  to  attain  100  per  cent,  in  several  of 
a  series  of  analyses  of  similar  nature  should  be  the  strongest  evidence  that 
something  has  been  overlooked.  Excess  above  100-5  per  cent,  should  be 
good  ground  for  repeating  portions  of  the  analysis  in  order  to  ascertain  where 
the  error  lies,  for  it  is  not  proper  to  assume  that  the  excess  is  distributed 
over  all  determined  constituents.  It  is  quite  as  likely,  in  fact  more  than 
likely  to  affect  a  single  determination  and  one  which  may  be  of  importance 
in  a  critical  study  of  the  rock  from  the  petrographic  side. 

VII.  QUALITY  OF  REAGENTS. 

It  is  due  to  say  that  all  analyses  performed  in  the  Survey  laboratories  have 
been  made  with  the  purest  reagents  obtainable,  either  by  purchase  in  the 
open  market  or  by  special  preparation  on  the  part  of  manufacturers  or  in 
the  laboratory.  The  best  acids  made  in  this  country  are  of  a  high  grade  and 
need  no  redistillation  except  for  special  experiments.  Ammonia  has  always 
been  redistilled  at  short  intervals;  and  no  sodium  carbonate  which  exceeds 
2*  mg.  of  total  impurity  (see  p.  1134)  in  20  grm.  (0-012  per  cent.)  is  used  for 
the  main  portions,  in  which  silica,  alumina,  etc.,  are  to  be  estimated.  For 
other  portions,  as  phosphoric  acid,  fluorine,  sulphur,  a  poorer  grade  is  entirely 
allowable,  provided  it  is  free  from  the  elements  to  be  determined,  and  from 
any  other  which  might  interfere  with  its  estimation. 

Hydrofluoric  acid  was  always  freshly  distilled  with  potassium  permanga. 
nate  imtil  the  introduction  of  ceresine  bottles  afforded  an  article  sufficiently 
pure  for  all  but  the  most  exacting  work.  Care  must  be  exercised  even  yet? 
however,  that  no  particles  of  paraffin  or  ceresine  are  floating  on  the  acid,  and 
that  the  latter  is  free  from  traces  of  chlorine  whenever  it  is  to  be  used  for 
attacking  silicates  with  a  view  to  estimating  chlorine  (p.  1182). 

Potassium  bisulphate  has  usually  been  prepared  in  the  laboratory  from 
sulphuric  acid  and  potassium  sulphate,  since  it  is  not  always  to  be  bought 
of  satisfactory  quality.  Even  then  the  normal  sulphate  had  first  to  be 


1112  APPENDIX   II. 

examined,  for  it  has  been  found  to  contain,  on  different  occasions,  notable 
amounts  of  lead,  calcium,  and  silica. 

The  phosphorus  salt  used  for  precipitating  magnesium  has  been  found  to 
contain  iron,  and  calcium  is  almost  always  a  constituent  of  ammonium 
oxalate.  The  latter  has  therefore  to  be  purified  or  specially  prepared,  as  also 
oxalic  acid,  ammonium  chloride  (in  which  latter  manganese  has  been 
observed),  and  occasionally  other  reagents.  Some  hydrogen  peroxide  con- 
tains fluorine,  which  renders  it  unfit  for  use  as  a  chemical  reagent. 

A  "C.  P."  label  is  no  guaranty  whatever  of  the  purity  of  a  reagent;  hence 
no  chemicals  should  be  taken  on  trust  because  of  bearing  such  a  label.  Every 
new  purchase  should  be  examined,  if  it  is  one  in  which  purity  is  a  desidera- 
tum. In  general  all  so-called  "C.  P."  chemicals  should  at  least  stand  the 
tests  laid  down  by  KRAUCH.* 

Of  late  years  the  appearance  upon  the  market  of  so-called  guaranteed 
reagents  promised  to  meet  a  long-felt  want.  But  experience  has  shown  that 
with  the  pioneer  in  this  line  at  least  the  guaranty  amounts  to  nothing,  the 
reagents  being  sometimes  worse  than  the  "C.  P."  articles  emanating  from 
sources  which  make  no  claim  to  special  purity  for  their  goods,  and  redress 
being  unobtainable.  The  "guaranteed  reagent"  needs  checking  as  much  as 
any  other. 

VIII.  PRELIMINARY  QUALITATIVE  ANALYSIS. 
A  complete  qualitative  analysis  of  a  rock,  preceding  the  quantitative 
examination,  is  in  most  cases  a  sheer  waste  of  time.  A  few  constituents 
may  now  and  then  be  specially  looked  for,  but  in  general  time  is  saved  by 
assuming  the  presence  of  most  of  them  and  proceeding  on  that  assumption 
in  the  quantitative  analysis. 

PART   II.     METHODS. 

I.    INTRODUCTORY  REMARKS. 

The  order  hereinafter  followed  in  describing  the  various  chemical  sepa- 
rations has  little  relation  to  the  affinities  of  the  constituents  of  the  rock, 
but  those  are  grouped  together  which  can  be  conveniently  determined  in  the 
same  portion  of  rock  powder.  Thus,  in  the  main  portion  are  usually  de- 
termined SiO2,  TiO2,  MnO,  NiO,  CaO,  SrO,  MgO,  total  iron,  and  the  com- 
bined weight  of  all  the  following:  A12O3,  TiO2,  P2O5,  ZrO2,  all  iron  as  Fe203, 
and  nearly  if  not  quite  all  vanadium  as  V2O5,  also  perhaps  rare  earths  if 
present.  In  a  separate  portion  is  estimated  FeO;  and  also  the  total  iron, 
as  well  as  BaO,  if  these  last  are  desired  as  checks.  The  alkalies  need  a  por- 
tion for  themselves.  In  another,  ZrO2,  BaO,  and  total  sulphur  are  very  con- 
veniently determined.  For  V2O3  and  Cr2O3  still  another  and  usually  much 
larger  portion  is  to  be  used.  Determinations  of  CO2,  C,  H2O,  Fl,  Cl,  are  all 
best  made  in  separate  portions  of  substance,  though  various  combinations 
are  possible,  as  CO2  and  H2O,  C  and  H2O,  or  H2O,  Fl,  and  Cl.  In  fact,  by  a 

*  Die  Prufung  der  chemischen  Reagentien,  3d  ed.,  Berlin,  JULIUS  SPRINGER,  1896.  S^e 
also  the  English  translation  of  RRAUCH'S  work  by  J.  A.  WILLIAMSON  and  L.  W.  DUPRE. 


SOME    PRINCIPLES   AND    METHODS    OF   ROCK   ANALYSIS.    1113 

judicious  selection  and  combination  of  methods  a  very  satisfactory  analysis 
can  sometimes  be  made  on  4  grm.  of  material  without  omission  of  anything 
of  importance,  though  the  time  consumed  will  be  greater  than  if  ample 
material  is  available. 

As  an  illustration  of  the  advantage  to  be  gained  by  a  little  judgment  in 
the  combination  of  methods,  the  case  of  sulphur,  barium,  and  zirconium 
may  serve.  Many  chemists  never  look  for  the  second  and  third  of  these, 
but  by  following  the  procedure  given  on  pages  1155  to  1157  very  little  more 
labor  is  expended  in  confirming  their  presence  or  absence  than  that  of 
sulphur  alone. 

With  only  occasional  exceptions,  nearly  all  the  constituents  mentioned 
on  page  1108  can  be  estimated  if  present  in  portions  of  powder  not  exceed- 
ing 1  grm.  each  in  weight. 

This  is  a  convenient  weight  to  take  for  the  main  portion  in  which  silica, 
alumina,  etc.,  the  alkaline  earths,  and  magnesia  are  to  be  sought;  but  it 
should,  in  general,  be  a  maximum,  because  if  larger,  the  precipitate  of  alumina, 
etc.,  is  apt  to  be  unwieldy.  Its  weight  cannot  often  be  much  reduced  with 
safety  if  satisfactory  determinations  of  manganese,  nickel,  and  strontium  are 
to  be  expected.  For  the  alkali  portion  one-half  grm.  is  a  very  convenient 
weight.  In  general,  it  may  be  made  a  rule  not  to  use  more  than  2  grm.  for 
any  portion  which  has  to  be  fused  with  an  alkali  carbonate,  as  for  sulphur, 
fluorine,  and  chlorine.  For  carbon  dioxide  the  weight  may  rise  to  5  grm.,  or 
even  more,  if  the  amount  of  this  constituent  is  very  small,  without  expen- 
diture of  any  more  time  than  is  required  by  1  grm.,  and  with  correspondingly 
greater  approach  to  correctness  in  the  result.  For  vanadium  also  a  larger 
weight  than  2  grm.  is  usually  demanded. 

II.     SPECIFIC  GRAVITY. 
BY  SUSPENSION  IN  WATER. 

Ordinary  Method. — This  determination,  when  required,  is  best  made 
upon  one  or  several  fragments  weighing  up  to  20  grm.  They  are  held  together 
by  a  fine  platinum  wire  ready  for  suspension  from  the  balance,  and  thus  held 
are  placed  in  a  small  beaker  to  soak  over  night  in  distilled  water  under  the 
exhausted  receiver  of  an  air-pump,  side  by  side  with  a  similar  beaker  of 
water.  Boiling  is,  of  course,  a  much  less  effective  means  of  removing  air 
than  the  air-pump,  and  the  boiling  water  may  exert  an  undesirable  solvent  and 
abrading  effect.  In  the  morning  the  wire  is  attached  to  the  balance-arm,  the 
rock  fragm'ents  remaining  immersed  in  the  water;  a  thermometer  is  placed 
in  the  companion  beaker  of  water,  now  likewise  in  the  balance  case,  and 
the  weight  is  at  once  taken.  Both  vessels  of  water  having  precisely  the  same 
temperature,  it  is  quite  unnecessary  to  wait  for  the  water  to  assume  that  of 
the  balance  should  it  not  already  possess  it.  The  fragments  are  now  lifted 
out,  without  touching  the  vessel,  and  carefully  transferred  to  a  tared  crucible 
or  dish;  the  wire  is  removed  and  at  once  reweighed  with  the  precaution 
that  it  dips  just  as  far  into  the  water  now  as  when  weighed.  Hereby  a 
special  weighing  of  the  wire  out  of  water  is  avoided.  The  sample  may  now 


1114  APPENDIX   II. 

be  dried  on  the  water-bath  and  then  at  110°  C.  for  some  hours  to  certainly 
expel  all  absorbed  water,  and  weighed  after  prolonged  cooling  in  the  desic- 
cator. It  is  better  to  ascertain  the  weight  of  the  dry  rock  after  soaking  in 
water  than  before,  in  order  to  avoid  the  error  due  to  possible  breaking  off 
a  few  grains  between  the  two  weighings.  Should  the  density  of  the  rock  in 
air-dry  condition  be  required,  it  may  be  left  exposed  to  the  air  for  a  long 
period  after  drying  and  before  weighing;*  but  the  difference  will  only  in 
exceptional  cases  affect  the  second  decimal  by  more  than  a  single  unit.  For 
instance,  an  undried  rock  of  2-775  specific  gravity  containing  in  the  un- 
crushed  sta.te  the  high  percentage  of  0-3  hygroscopic  moisture  will  have  a 
density  of  2-79  when  dry ;  a  rock  of  2  •  982  specific  gravity,  undried,  will 
have  a  density  of  3-00  after  removal  of  0-3  per  cent,  of  moisture.  The 
difference  becomes  greater  as  the  density  of  the  rock  increases. 

This  method  of  ascertaining  the  specific  gravity  of  rocks  is  certainly 
more  convenient  than,  and  for  compact  rocks  is  believed  to  be  decidedly 
preferable  to,  that  of  the  pycnometer,  in  which  the  fragments  must  be  re- 
duced to  small  size  with  consequent  formation  of  more  or  less  powder,  which 
is  subject  to  slight  loss  in  the  various  manipulations.  To  exclude  this  powder 
and  employ  only  small  fragments  would  introduce  a  possible  source  of  error, 
since  it  is  likely  to  consist  largely  of  the  most  easily  abraded  minerals  and 
consequently  not  to  have  the  average  composition  of  the  mass.  By  following 
the  instructions  given  above,  loss  of  material  is  absolutely  avoided,  a  decided 
saving  in  time  is  effected,  and  considerable  weights  can  be  easily  employed 
with  consequent  lower  probable  error  in  the  results.  To  vesicular  rocks, 
however,  notably  certain  lavas,  the  above  procedure  is,  of  course,  inapplicable, 
unless  the  datum  is  desired  for  certain  considerations  in  which  the  relative 
density  of  large  rock  masses  as  they  occur  in  nature  is  sought,  as  for  the 
comparison  of  building-stones  or  the  calculation  of  large  known  or  acsumed 
areas  of  particular  rocks. 

PENFIELD'S  Method  for  Mineral  Fragments. — PENFIELD  f  recommends  the 
following  modification  of  the  suspension  method  as  more  convenient  than 
that  by  the  pycnometer  in  many  cases  for  small  fragments  of  minerals. 

After  boiling  in  water,  the  substance  is  transferred  with  water  to  a  small 
glass  tube  about  8  mm.  by  35  mm.,  provided  with  a  fine  platinum  wire  for 
suspension.  This  is  weighed  full  of  water  in  another  vessel  of  water,  and 
again  after  the  removal  of  the  mineral,  the  weight  of  which  is  found  after 
drying. 

This  method  is,  of  course,  more  applicable  to  homogeneous  minerals  than 
to  rock  fragments,  and  will  therefore  be  applied  in  rock  analysis  chiefly 

*  In  view  of  the  uncertainty  as  to  what  constitutes  hygroscopic  water  (see  p.  1117  et  seq.), 
this  course  is  perhaps  more  to  be  commended  than  the  former,  and  seems  imperative 
for  certain  zeolitic  rocks.  In  such  cases  it  is  best  to  weigh  the  fragments  before  putting 
to  soak,  and  afterwards  to  collect  on  a  GOOCH  crucible  the  grains  which  may  have  fallen 
off  in  the  water.  Should  no  crucible  of  this  kind  be  available,  a  paoer  filter  may  un- 
hesitatincrlv  be  used  and  incinerated  with  the  powder,  owing  to  the  small  amount  of  which 
the  error  due  to  loss  of  even  all  its  water  during  ignition  is  quite  negligible, 
t  Am.  Journ.  Sci.,  3d  Series,  L,  p.  448,  1895. 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1115 

to  the  determination  of  the  specific  gravity  of  the  mineral  grains  separated 
by  heavy  solutions  or  acids. 

PYCNOMETER  METHOD. 

If  the  pycnometer  has  to  be  used,  as  is  generally  the  case  when  the  den- 
sity of  any  one  of  the  mineral  ingredients  of  a  rock  is  desired  after  separation 
by  one  of  the  approved  methods,  it  being  then  in  a  more  or  less  finely  divided 
state,  the  most  accurate  procedure  is  that  adopted  in  this  laboratory  by  Mr. 
L.  G.  EAKINS  a  number  of  years  ago.  The  pycnometer  used  is  one  with  a  capil- 
lary stopper,  provided  with  a  millimeter  scale  etched  in  the  glass,  the  divisions 
being  numbered  both  ways  from  the  centre  and  calibrated  by  mercury  so  that 
the  value  of  each  one  in  weight  of  water  is  known.  The  capacity  of  the 
flask  filled  with  water  to  the  zero  division  is  then  calculated  for  every  half 
degree  of  temperature  from  0°  C.  to  30°  C.,  by  making  a  series  of  careful 
weighings,  in  which  the  capacity  of  the  stem  being  known,  it  is  quite  imma- 
terial at  what  level  the  water  stands  provided  it  is  within  the  limits  of  the 
scale.  The  exact  temperature  is  obtained  by  an  accurate  thermometer 
placed  in  a  companion  vessel  of  similar  shape  to  the  pycnometer  and  con- 
taining a  like  amount  of  water,  both  being  left  in  the  balance-case  till  its 
temperature  has  been  nearly  or  quite  assumed,  as  shown  by  a  second  ther- 
mometer. The  weighing  must  of  course  be  made  before  the  thread  of  water 
has  sunk  beneath  the  lowest  division,  which  it  will  do  after  a  time,  even 
though  at  first  filling  the  bore  to  the  top  of  the  stopper;  and  the  corrected 
weight  when  full  of  water  to  the  zero  mark  is  found  by  adding  or  subtracting 
the  needed  amount,  as  shown  by  the  height  of  the  thread  on  the  scale. 

For  each  pycnometer  in  use,  and  these  are  of  different  sizes,  is  prepared  a 
table  showing  its  weight,  the  value  of  each  scale  division  in  grm.  of  water, 
and  the  capacity  of  the  flask  at  different  temperatures,  as  indicated  above. 
The  preparation  of  such  a  series  of  flasks  is  time  saved  in  the  end,  for  the 
weighing  of  the  flask  full  of  water  each  time  a  density  determination  is  made 
is  rendered  superfluous.  All  that  is  necessary  is  to  look  up  in  the  table  the 
weight  corresponding  to  the  temperature. 

The  density  of  the  previously  weighed  substance  in  this  case  is  now  de- 
termined in  much  the  same  way,  after  the  unstoppered  pycnometer  con- 
taining it  and  nearly  filled  with  water  has  stood  with  its  companion  vessel  of 
water  under  the  air-pump  the  necessary  length  of  time.  The  water  needed 
to  fill  the  flask  is  taken  from  its  companion. 

All  who  have  used  the  pycnometer  method  for  fine  substances  know  the 
difficulty  experienced  in  preventing  a  portion  from  being  held  at  the  surface, 
despite  all  attempts  at  making  it  sink.  Hence  it  often  happens  that  a  very 
small  portion  runs  out  around  the  sides  of  the  stopper  on  inserting  it.  If 
the  flask  rests  in  a  small  tared  dish  the  grains  thus  forced  out  may  be  washed 
down  into  it  and  weighed  after  evaporation  in  order  to  get  the  correct  weight 
of  that  in  the  flask ;  or,  after  weighing,  the  contents  of  the  flask  may  be  emptied 
into  a  tared  dish  and  the  water  slowly  evaporated  off  in  order  to  get  the  weight 
of  the  mineral  Usually  this  way  is  less  to  be  recommended  than  the  other. 


1116  APPENDIX   II. 

HEAVY  SOLUTIONS  NOT  SUITABLE  FOR  ROCKS. 

Because  of  their  roughness,  porosity,  and  complex  mineral  composition 
the  density  of  rock  fragments  cannot  be  accurately  determined  by  that  of 
heavy  solutions  in  which  they  may  remain  suspended. 


III.     PREPARATION  OF  SAMPLE  FOR  ANALYSIS. 

QUANTITY  OF  ROCK  TO  BE  CRUSHED. 

In  the  great  majority  of  cases  a  few  chips  from  a  hand  specimen  will 
well  represent  the  average  of  the  mass,  but  with  rocks  in  which  a  porphyritic 
structure  is  strongly  developed  the  case  is  different.  Here  a  large  sample 
should  be  provided,  gauged  according  to  the  size  of  the  crystals,  and  the 
whole  of  this  should  be  crushed  and  quartered  down  for  the  final  sample, 
Unless  this  is  done,  it  is  manifest  that  the  analysis  may  represent  anything  but 
the  true  average  composition  of  the  rock. 

.    CRUSHING. 

Mechanical  appliances  for  reducing  samples  to  fine  powder  are  much 
in  use  in  technical  laboratories,  where  they  answer  their  purpose  more  or 
less  satisfactorily,  and  something  similar  is  needed  in  those  scientific  labora- 
tories where  rock  analysis  is  of  daily  occurrence  and  many  samples  must  be 
reduced  to  fine  powder  in  a  short  space  of  time.  For  accurate  analyses  the 
use  of  steel  crushers  and  mortars  is  out  of  the  question,  because  of  the  danger 
of  contamination  by  particles  of  metal  and  the  impossibility  of  cleansing 
the  roughened  surfaces  after  they  have  been  in  use  a  short  time.  Extraction 
by  the  aid  of  a  magnet  of  steel  particles  thus  introduced  into  the  powder  is 
quite  inadmissible,  since  the  rocks  themselves,  almost  without  exception, 
contain  magnetic  minerals.  The  method  of  rough  crushing  on  a  small  scale 
found  to  be  most  satisfactory  in  practice  is  to  place  each  fragment  as  received 
on  a  hard  steel  plate  about  4 £  cm.  thick  and  10  cm.  square,  on  which  is  like- 
wise placed  a  steel  ring  2  cm.  high  and  of  about  6  cm.  inner  diameter,  to 
prevent  undue  flying  of  fragments  when  broken  by  a  hardened  hammer.  In 
this  way  a  considerable  sample  can  soon  be  sufficiently  reduced  for  transfer  to 
the  agate  grinding  mortar  with  a  minimum  of  metallic  contamination. 

For  breaking  large  pieces  of  rock  to  small  sizes  a  thick  iron  plate  with 
specially  hardened  surface  and  a  similarly  hardened  pounder,  such  as  street- 
pavers  use,  will  probably  render  the  best  service,  but  the  hardening  must  be 
done  with  extreme  care. 

GRINDING. 

Of  the  various  grinding  arrangements  on  the  market  purporting  to  fulfill 
their  purpose  few,  if  any,  observed  have  met  the  conditions  required  by  the 
work  in  hand.  Either  the  mechanical  arrangement  is  complicated  or  cum- 
bersome, requiring  more  power  or  space  than  is  usually  at  disposal  or  csusirg 
too  much  noise,  or  thorough  cleansing  is  difficult  and  troublesome,  or  there 
is  likelihood  of  contamination  from  oil  or  grease  or  lack  of  facility  for  the 


SOME    PRINCIPLES   AND    METHODS    OF   ROCK   ANALYSIS.    1117 

removal  of  all  powder  from  the  mortar.  These  last  defects  are  especially 
prominent  in  those  forms  in  which  the  mortar  is  fixed  in  its  setting. 

All  rock  samples  have  therefore  been  reduced  to  powder  by  hand,  involv- 
ing a  great  expenditure  of  time  and  labor.  Ordinarily  an  extremely  fine 
state  of  division  is  unnecessary,  except  in  the  case  of  those  portions  in  which 
alkalies  and  ferrous  iron  are  to  be  estimated  or  where  soluble  constituents 
are  to  be  removed  by  acids,  etc.,  and  in  such  cases  the  final  grinding  can  be 
doae  at  the  balance-table  on  a  small  portion  slightly  in  excess  of  the  quantity 
to  be  weighed  off. 

The  process  of  sifting  through  fine  cloth,  the  German  ' '  Beuteln,"  is  not  one 
always  to  be  commended,  because  of  the  time  required  and,  more  especially, 
because  of  the  certainly  of  contamination  by  cloth  fiber,  which  in  the  ferrous- 
iron  portion  might  affect  the  result.  Still  less  should  metal  sieves  be  used. 

WEIGHT  OF  GROUND  SAMPLE. 

The  sample  when  ground  should  weigh  not  less  than  10  grm.,  and  prefer- 
ably 20  in  case  it  should  be  necessary  to  repeat  or  advisable  to  employ  un- 
usually large  portions  for  certain  determinations,  notably  carbonic  acid. 
Rock  analysis  has  in  this  respect  an  advantage  over  mineral  analysis,  since 
material  is  almost  always  available  in  ample  quantity  and  any  desired  num- 
ber of  separate  portions  may  be  used,  whereas  with  a  mineral  the  analyst 
is  frequently  compelled  to  determine  many  or  all  constituents  in  a  single,  often 
very  small,  portion  of  the  powder.  This  course  often  involves  delay  and  the 
employment  of  more  complicated  methods  of  separation  than  are  usually 
necessary  in  rock  analysis. 


IV.     WATER— HYGROSCOPIC,   ZEOLITIC,  CRYSTAL. 

Importance  of  Employing  Air-dry  Powder  for  Analysis. — The  time- 
honored  custom  of  drying  a  powdered  specimen  before  bottling  and  weighing 
has  long  seemed  to  the  writer  one  that  has  no  sound  basis  in  reason.  Its  object 
is  of  course  plain,  namely,  that  of  securing  a  uniform  hygroscopic  condition 
as  a  basis  for  convenient  comparison  of  analytical  results,  since  some  rocks 
contain  more  hygroscopic  moisture  than  others.  Nothing,  however,  is  more 
certain  than  that  by  the  time  the  substance  is  weighed  it  has  reabsorbed 
a  certain  amount  of  moisture,  small,  indeed,  in  most  cases,  but  very  appre- 
ciable in  others;  and  further,  with  every  opening  of  the  tube,  moisture-laden 
air  enters  and  is  inclosed  with  the  remainder  of  the  dry  powder.  It  therefore 
may  very  well  happen  that  a  powder  at  first  dry  will,  after  several  openings 
of  the  tube,  especially  at  considerable  intervals,  be  nearly  as  moist  as  when 
first  inclosed. 

It  is  preferable  to  weigh  the  air-dry  powder  and  to  make  a  special  deter- 
mination of  moisture.  If  all  the  portions  necessary  for  an  analysis  are  weighed 
out  one  after  another,  or  even  at  different  times  on  the  same  day,  the  error 
due  to  difference  of  hygroscopicity  in  dry  and  moist  weather,  which  for  most 
of  the  separate  portions  is  an  entirely  negligible  quantity,  is  eliminated.  Onlv 


1118 


APPENDIX   II. 


in  the  main  portion,  in  which  silica  and  the  majority  of  the  bases  are  to  be 
estimated,  can  it  ever  be  an  appreciable  factor. 

Temperature  of  Drying. — As  to  the  temperature  to  be  adopted  for  drying 
in  order  to  determine  so-called  hygroscopic  moisture,  the  practice  has  varied 
at  different  times  and  with  different  workers,  ranging  from  100°  to  110°  C. 
For  the  great  majority  of  rock  specimens  it  is  quite  immaterial  which  of  these 
temperatures  is  adopted,  since  no  greater  loss  is  experienced  at  the  higher 
than  at  the  lower  temperature,  given  a  sufficient  time  for  the  latter.  It  is 
the  present  practice  in  this  laboratory  to  employ  a  toluene-bath  giving  a  tem- 
perature of  about  105°  C.  Should  the  results  show  a  very  unusually  high  loss, 
the  powder  is  reheated  at,  say,  125°,  in  order  to  leaiai  if  the  loss  is  progressive 
with  increased  temperature  In  the  affirmative  case  it  may  be  well  to  repeat 
the  drying  at  100°,  for  a  portion  of  the  loss  at  105°  was  probably  due  to  com- 
bined water  from  a  mineral  or  minerals  in  the  rock;  but  in  that  case  even  the 
loss  at  100°  may  sometimes  very  well  include  combined  water,  in  which  case 
drying  over  sulphuric  acid  alone  may  be  desirable,  or  over  dry  sand. 

Cautionary  Hints. — In  this  latter  connection  it  is  proper  to  point  out  cer- 
tain pitfalls  in  the  path  of  the  unwary,  which,  however,  are  far  more  likely  to 
be  encountered  in  the  analysis  of  minerals,  where  their  influence  may  be  of 
far-reaching  consequence 

A  mineral  which  loses  a  great  deal  of  water  over  sulphuric  acid — "2  or  3  per 
cent,  for  instance — may  need  an  exposure  of  several  days  or  even  weeks  for 
its  complete  extraction.  If  the  weighings  are  made  from  day  to  day,  the 
apparent  limit  may  be  reached  long  before  all  water  really  removable  has 
been  taken  up  by  the  acid.  Whenever  the  crucible,  after  weighing,  is  re- 
placed in  the  desiccator  it  is  no  longer  in  a  dry  but  a  more  of  less  moist  atmos- 
phere, and  its  contents,  even  when  covered,  sometimes  absorb  a  part  of  this 
moisture  and  retain  it  so  persistently  that  the  acid  is  unable  to  bring  the 
powder  beyond  its  previous  state  of  dryness  in  the  next  twenty-four  hours. 
In  fact,  it  may  be  unable  even  to  reach  it  unless  greater  time  is  allowed.  An 
experiment  on  1  grm.  of  tyrolite,  made  and  published  some  years  ago,  seems 
to  illustrate  this  point  in  part? 


Hours 
Exposed. 

Loss. 

Hours 
Exposed. 

Loss. 

18 
26 
23 
24 
23 
24 
25 

Grm. 

0.0231 
•0083 
•0029 
•0012 
•0008 
•0001 
•0003 

24 

24 
48 
24 

Grm. 
0-0002 
•0003 
•0006 
•0002 

283 

•0380 

The  experiment  might  reasonably  have  been  considered  ended  after  the  one 
hundred  and  fifty-eighth  hour,  when  a  loss  of  but  0  •  1  mgrm.  was  shown 
during  twenty-four  hours;  but  nevertheless  a  nearly  steady  loss  of  0-3 


SOME   PRINCIPLES   AND    METHODS   OF   ROCK  ANALYSIS.    1119 

mgrm.  per  day  took  place  for  six  days  more,  and  might  have  been  longer  ob- 
served but  for  the  interruption  of  the  experiment. 

Again,  it  is  a  common  practice  to  determine  the  water  given  off  by  hydrous 
minerals  in  an  air-bath  at  temperatures  far  above  100°  C.  To  insure  accuracy 
this  experiment  should  not  be  made  in  crucibles  or  dishes  which  must  be 
cooled  in  a  desiccator.  One  instance  will  suffice :  A  gramme  of  a  mineral  mix- 
ture containing  about  17  per  cent,  of  water,  of  which  about  3  per  cent,  was 
driven  off  at  100°  and  8  or  9  per  cent,  at  280°,  was,  after  several  hours'  heat- 
ing at  the  latter  temperature,  placed  in  a  desiccator  over  sulphuric  acid  and 
weighed  as  soon  as  cold,  then  replaced  and  again  weighed  the  next  day.  It 
had  regained  1£  per  cent,  of  its  original  weight,  although  the  desiccator  was 
tightly  closed  and  the  crucible  covered,  showing  apparently  a  drying  power 
superior  to  that  of  the  acid. 

A  specimen  of  tyrolite  was  found  on  one  occasion  to  lose  10  •  34  per  cent, 
at  280°  C.,  and  on  another  occasion  14-33  per  cent.  In  the  latter  case  the 
drying  and  heating  at  progressive  temperatures  had  continued  during  a 
period  of  528  hours,  the  weighings  being  made  usually  from  day  to  dayj 
whereas  in  the  former  the  duration  of  the  experiment  was  much  shorter  and 
the  intervals  between  weighings  were  but  a  few  hours  each. 

Procedure  in  Special  Cases. — For  experiments  of  the  kind  just  indicated 
the  powder  should  be  heated  in  a  weighed  tube,  through  which  a  current  of 
dry  air  can  be  passed,  and  allowed  to  cool  therein,  or  else  the  water  given  off 
should  be  collected  and  directly  weighed  in  suitable  absorption  tubes,  even 
though  the  long  time  often  required  is  an  objection  to  this  latter  method, 
since  the  absorption  tube  may  gain  weight,  other  than  that  of  the  water  from 
the  mineral,  sufficient  to  introduce  an  appreciable  error. 

The  recent  important  research  of  FRIEDEL  *  well  shows  what  errors  are 
possible  in  the  determination  of  this  easily  removable  water,  since  he  found 
that  certain  zeolites  which  had  been  largely  dehydrated  but  not  heated  to 
the  point  of  rupture  of  the  molecular  net,  could  then  absorb,  instead  of  water, 
various  dry  gases  in  which  they  might  be  placed,  as  carbon  dioxide,  ammonia, 
carbon  disulphide,  and  others,  even  air  in  large  quantities,  and  certain  liquids. 
In  the  light  of  this  observation  the  cause  of  the  great  increase  of  1J  per  cent, 
in  weight  of  the  partially  dehydrated  mineral  mentioned  above  may  very 
possibly  be  attributed  to  air  from  the  desiccator  instead  of  moisture,  as  was 
at  the  time  supposed.  At  any  rate,  as  FRIEDEL  says,  the  danger  of  accepting 
a  loss  in  weight  as  an  index  of  the  amount  of  water  lost  is  clearly  shown,  and 
thus  that  method  of  determining  water  is  for  many  cases  fully  discredited. 
Just  what  method  to  adopt  must  be  largely  left  to  the  judgment  of  the  oper- 
ator, who  will  often  be  guided  by  the  mineral  composition  of  the  rock  as 
revealed  by  the  unaided  eye  or  the  microscope, 

FRIEDEL  (loc.  cit}.  indicates  a  means  for  determining  the  true  weight  of 
water  lost  by  minerals  behaving  like  the  zeolites,  even  without  collecting  the 
water  lost,  namely,  by  driving  out  of  the  dehydrated  and  weighed  mineral, 
under  proper  precautions,  any  air  it  may  have  absorbed  in  the  process  of 

*  Bull.  Soc.  Min.,  xix,  pp.  14,  94,  1896;  Couples  rendus,  cxxn,  p.  1006,  1896. 


1120  APPENDIX   II. 

drying  and  cooling,  and  collecting  and  measuring  this  air  and  thus  finding 
its  weight,  which,  added  to  the  apparent  loss,  gives  the  true  contents  in 
water. 

Argument  in  Favor  of  Including  Hygroscopic  Water  in  Summation. — The 
question  has  been  asked :  ''  If  the  so-called  hygroscopic  water  is  not  always 
such,  but  not  infrequently  includes  combined  water,  why  is  not  its  deter- 
mination and  separate  entry  in  the  analysis  entirely  unnecessary?  Why 
make  a  distinction,  which,  after  all,  may  not  be  a  true  one?"  The  question 
involves  the  further  consideration  of  the  advisability  of  including  in  the 
analysis  at  all  the  loss  at  100°  or  110°  C.  Many  petrographers  desire  to  have 
all  analyses  referred  to  a  moisture-free  basis,  in  order  that  they  shall  be 
strictly  comparable,  and  therefore  would  omit  the  "hygroscopic"  water 
from  the  list  of  constituents.  This  would  be  eminently  proper  were  it  always 
possible  to  be  sure  that  the  loss  at  100°  truly  represents  mechanically  held 
water.  Since  it  very  often  represents  more,  and  the  determination  as  to 
whether  or  not  it  does  in  each  case  is  not  always  possible,  and  would  add  to 
the  time  required  for  the  analysis,  it  seems  necessary  to  include  this  water. 
What  errors  may  arise  from  its  exclusion  the  following  rather  extreme  case 
well  illustrates:  Certain  rocks  of  Wyoming  in  powder  form  lost  from  1  to  2 
per  cent,  of  moisture  at  110°.  That  not  even  an  appreciable  fraction  of  this 
was  truly  hygroscopic  the  fact  of  the  uncrushed  rocks  losing  the  same  amount 
fully  demonstrates;  yet  the  rule  followed  by  many  chemists  and  petrographers 
would  have  involved  the  removal  of  all  this  water  as  a  preliminary  to  begin- 
ning the  analysis,  and  not  only  would  a  most  important  characteristic  have 
passed  unnoticed,  but  the  analyst  would  have  reported  an  incorrect  analysis, 
inviting  to  false  conclusions  and  possibly  serious  confusion. 

Separate  Entry  of  Hygroscopic  and  Combined  Water. — To  revert  now  to  the 
primary  question,  it  may  be  said  that  the  estimation  of  the  loss  at  100°  or 
110°  C.  and  its  separate  entry  in  the  analysis  is  advisable  as  not  infrequently 
affording  at  once  to  the  lithologist  an  indication  of  the  mineral  character  of 
one  or  more  of  the  rock  constituents,  thus  perhaps  confirming  the  micro- 
scopical evidence  or  suggesting  further  examination  in  that  line.  An  un- 
usually high  loss  at  100°  would  be  regarded  as  probable  evidence  of  the  pres- 
ence of  zeolites  or  other  minerals  carrying  loosely  combined  water.  It  has  been 
objected  that  the  true  hygroscopic  moisture  varies  with  the  degree  of  com- 
minution of  the  sample  and  with  the  condition  of  the  air  at  the  time  of  weigh- 
ing, and  that  it  is  therefore  improper  to  incorporate  it  in  the  analysis;  but 
this  variation  is  ordinarily  not  at  all  great.  Perhaps  the  time  may  come 
when  it  will  be  the  rule  to  ascertain  by  additional  heating  at  a  higher  tem- 
perature whether  the  water  lost  at  100°  is  to  be  regarded  as  purely  hygro- 
scopic. In  such  case  it  would  be  proper  to  omit  it,  and  a  distinct  advance 
would  undoubtedly  be  scored. 

Is  all  True  Hygroscopic  Water  Expelled  at  100°? — It  has  been  tacitly  assumed 
in  the  foregoing  that  true  hygroscopic  water  can  all  be  expelled  at  100°, 
which  perhaps  is  not  to  be  accepted  as  universally  true.  Eminent  authority 
holds  that  it  is  impossible,  in  the  cases  of  certain  foliaceous  minerals,  notably 
the  micas,  to  thus  entirely  remove  it,  but  that  a  part  is  only  driven  off  at 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1121 

higher  temperatures.  If  this  is  true  a  further  uncertainty  is  introduced  in 
its  determination,  which  not  only  strengthens  the  argument  hi  favor  of  enter- 
ing all  water  in  the  tabulation,  but  also  serves  to  emphasize  the  difficulties  of 
the  situation. 

APPARATUS   FOR  THE   DIRECT  DETERMINATION   OF  WATER  AT  DIFFERENT 
TEMPERATURES. 

A  form  of  drying -oven  devised  by  Dr.  T.  M.  CHATARD  *  is  in  use  in  this 
laboratory  for  determining  water  at  different  temperatures  up  to  350°  C., 
and  gives  entire  satisfaction.  It  is  an  asbestos-covered  copper  box  B,  shown 
in  different  aspects  and  parts  in  the  accompanying  Fig.  3.  The  box  is  so  con- 


n 


FIG.  3. — CHATARD'S  form  of  drying  oven  for  water  determinations.  B,  copper  box 
18  cm.  long,  1(H  cm.  high,  9  cm.  wide,  open  in  front,  its  sides  and  top  covered  with 
asbestos  board;  S,  two  slides  of  different  sizes  to  close  the  openings  O,  after  the  tube 
is  in  position;  F,  asbestos-board  front  stiffened  by  an  interlaid  sheet  of  copper; 
R,  metal  rod  to  hold  front  in  place;  A,  calcium-chloride  absorption  tube. 

structed  that  the  tube  with  its  contents  can  be  removed  without  detaching 
from  either  the  drying  or  collecting  tubes,  which  is  a  great  advantage  if  it  is 
desired  to  afterwards  apply  the  direct  heat  of  a  lamp  in  order  to  expel  the 
water  retained  at  300°  to  350°.  To  facilitate  this  removal  the  stand  is  on 
rollers,  so  that  after  clamping  the  projecting  end  of  the  tube  and  removing 
the  front  of  the  box  F  and  the  little  side  pieces  S  closing  the  horizontal  slits, 
the  oven  can  be  rolled  bodily  backward,  leaving  the  tube  and  its  attachments 


*  Am.  Chem.  Journ..  xm,  p.  110.  1891;  Bull.  U.  S.  Geol.  Survey,  No.  78,  p.  84. 


1122  APPENDIX   II. 

in  their  original  position,  ready  for  further  heating  over  a  burner  or  blast. 
The  removable  front  F  of  the  oven  is  made  of  two  pieces  of  sheet  asbastos 
board  stiffened  by  an  interlaid  piece  of  sheet  copper.  The  inner  piece  of 
asbestos  board  fits  snugly  into  the  box,  while  the  outer  one,  being  slightly 
larger,  by  its  projecting  edges  hinders  the  door  from  falling  in  and  helps  to 
prevent  air  currents.  This  door  is  held  in  place  by  the  metal  rod  R.  The 
little  slides  S  are  made  in  a  somewhat  similar  manner,  and  are  intended  to 
slip  in  from  the  front  and  close  the  two  openings  0  after  the  tube  is  in  place, 
but  before  closing  the  front. 

For  other  forms  of  tubes  adapted  to  similar  determinations,  see  pages 
1124  and  1130. 

V.  WATER— TOTAL  OR  COMBINED. 

ARGUMENTS   AGAINST    "LOSS    ON    IGNITION"    METHOD. 

In  a  few  cases  the  simple  loss  on  ignition  of  a  rock  will  give  the  total 
water  with  accuracy,  but  in  the  great  majority  there  are  so  many  possible 
sources  of  error  that  this  old-time  method  can  rarely  be  used  with  safety. 
Only  when  the  rock  is  free  from  fluorine,  chlorine,  sulphur,  carbon,  carbon 
dioxide,  and  fixed  oxidizable  constituents  can  the  loss  be  accepted  as  the 
true  index  of  the  amount  of  water  present,  and  it  is  rarely  that  a  rock  is  met 
with  fulfilling  these  conditions,  especially  as  to  the  absence  of  ferrous  iron. 
Blast  ignition  in  presence  of  carbon  dioxide  alone  of  the  above  list  may  give 
a  correct  result,  after  separate  estimation  of  the  carbon  dioxide,  provided 
this  emanates  from  carbonates  of  the  earths  and  not  from  those  of  iron  or 
manganese.  The  long-maintained  and  still  upheld  idea  that  in  presence  of 
ferrous  iron  a  sufficiently  correct  result  is  obtainable  by  adding  to  the  observed 
loss  an  amount  needed  for  oxidizing  all  ferrous  iron  is  not  justifiable.  There 
can  be  no  certainty  that  the  oxidation  has  been  complete,  especially  in  the 
case  of  readily  fusible  rocks,  and  at  the  high  temperature  of  the  blast  a  par- 
tial reduction  ot  higher  oxides  is  not  only  possible,  but  sometimes  certain. 
The  inability  to  insure  complete  oxidation  by  simple  ignition  is  illustrated 
in  the  case  of  precipitated  ferric  hydroxide  which  has  been  ignited  in  contact 
with  its  filter-paper.  If  the  quantity  was  in  any  degree  large  it  is  sometimes 
decidedly  magnetic,  presumably  from  presence  of  magnetic  oxide,  which  no 
amount  of  heating  wholly  oxidizes,  especially  in  the  larger  grains.  Neither 
is  evaporation  with  nitric  acid  and  reignition  sufficient  to  destroy  the  mag- 
netic property  of  the  oxide,  as  has  been  claimed. 

Direct  weighing  of  the  water  evolved  is  then  imperative  in  most  cases, 
and  of  the  numerous  methods  advocated,  or  in  general  use,  several  will  now  be 
considered. 

DIRECT  WEIGHING  OF  THE  WATER  WITHOUT  THE  USE  OF  ABSORPTION 
TUBES — PENFIELD'S  METHODS. 

For  Minerals  Easily  Deprived  of  their  Water. — If  no  other  volatile  constitu- 
ents than  water  are  present,  the  beautifully  simple  method  first  used  by 


SOME    PRINCIPLES   AND    METHODS   OF   ROCK   ANALYSIS.    1123 


Prof.  G.  J.  BRUSH  and  extended  by  Prof.  S.  L.  PENFIELD  *  leaves  nothing  to 
be  desired  for  accuracy.  It  consists  simply  in  heating  the  powder  in  a  nar- 
row tube  of  hard  glass,  enlarged  at  the  closed  end  and  provided  with  one  or 
two  further  enlargements  in  the  middle  to  hold  the  water  and  prevent  its 
running  back  and  cracking  the  hot  glass.  A  capillary  glass  stopper  fitted 
in  with  rubber  tubing  prevents  loss  of  water  by  circulating  air  currents. 
The  tube  being  held  horizontally,  the  bulb  is  heated  to  any  required  degree 
by  the  BUNSEN  or  blast  flame.  Moistened  filter-paper  or  cloth  wound  about 
the  cooler  parts  of  the  tube  insures  condensation  of  all  water.  The  heated 
end  being  finally  pulled  off,  the  tube  is  weighed  after  cooling  and  external 
cleansing,  and  again  after  the  water  has  been  removed  by  aspiration.  For 
most  rocks,  as  they  contain  little  water,  central  enlargements  of  the  tube 
are  hardly  needed. 

Various  forms  of  tubes  used  by  PENFIELD  are  shown  in  Fig.  4. 

Before  using,  even  if  apparently  dry,  "these  tubes  must  be  thoroughly 
dried  inside,  wrhich  is  best  accomplished  by  heating  and  aspirating  a  current 
of  air  through  them  by  means  of  a  glass  tube  reaching  to  the  bottom." 

How  this  simple  tube  is  made  to  afford  entirely  satisfactory  results  with 


C 


•f 


FIG.  4 — PENFIELD'S  tubes  for  water  determination  in  minerals,     a,  b,  c,  different  forms 
of  tubes;  d,  thistle  tube  for  introducing  the  powder;  e,  capillary-tipped  stopper. 

minerals,  even  when  carbonates  are  present,  is  fully  set  forth  in  the  paper 
cited. 

Few  rocks,  comparatively,  are  altogether  free  from  other  volatile  con- 
stituents. Hence,  for  refined  work  the  application  of  this  apparatus  in  the 
simple  manner  above  set  torth  is  limited.  It  may,  however,  be  used  with 
the  addition  of  a  retainer  for  fluorine,  sulphur,  etc.,  in  the  shape  of  calcium, 
lead,  or  bismuth  oxides. 

Far  Minerals  not  Easily  Deprived  o/  their  Water. — When  minerals  are  pres- 
ent which  do  not  give  up  their  water  wholly,  even  over  the  blast,  as  talc, 

*  Am.  Journ.  Sci.,  3d  Senes,  XLVIII,  p.  31,  1894;  Zetfsch.  fur  anorg.  Chemie,  vii,  p.  22 
1894. 


1124  APPENDIX    II. 

topaz,  chondrodite,  staurolite,  etc.,  PENFIELD'S  simple  combination  of  fire- 
brick and  charcoal  oven,  depicted  in  Fig.  5,  must  be  used,  either  with  or 
without  a  retainer  for  fluorine,  as  circumstances  demand.  The  part  of  the  tube 
in  the  fire  is  to  be  protected  by  a  cylinder  of  platinum  foil  tightly  sprung 
about  its  end,  and  the  part  outside  by  asbestos  board,  as  well  as  by  wet  cloth 
or  paper.  A  piece  of  charcoal  is  likewise  laid  on  the  tube,  as  well  as  beneath 
and  behind,  and  the  blast  flame  is  given  a  horizontal  direction,  so  as  to  play 
upon  the  side  of  the  apparatus.  In  this  way  a  most  intense  temperature  can 
be  reached. 

In  'whichever  way  the  apparatus  may  be  used,  the  water  found  is  the 


FIG.  5. — PENFIELD'S  fire-brick  and  charcoal  oven  for  use  in  determining  water, 
total  water,  from  which  that  found  separately  at  105°  may  be  deducted  if 
desired. 

DIRECT    WEIGHING    OF    THE    WATER    IN    ABSORPTION    TUBES. 

Penfield's  Procedure. — The  simplest  of  these  methods  as  to  apparatus, 
and  one  permitting,  by  the  use  of  auxiliary  arrangements  such  as  are  shown 
and  described  on  page  1121,  the  determination  of  the  hygroscopic  as  well  as 
any  other  fraction  of  the  water,  is  the  following  glass-tube  arrangement 
(Fig.  6)  of  Dr.  PENFIELD'S,*  whereby  the  brick  and  charcoal  oven  already 
referred  to  (Fig.  5)  comes  again  into  play,  but  without  the  half-brick  shown 
in  that  figure. 


u 


16  C.Mr A 11  C.M.- + 16C.M.-- 


Fio.  6— Tube  for  water  determination  according  to  PENFIELD.  A  outer  protecting 
covering  of  platinum  foil.  A  second  similar  foil  on  the  inside  prevents  the  glass 
from  collapsing  when  heated  to  softness.  6,  cross-section  of  platinum  boat. 

The  tube  is  of  about  15  mm.  internal  diameter,  and  is  fitted  with  two 
platinum  cylinders  at  A,  one  inside,  the  other  outside,  where  the  heat  expo- 
sure  is  to  be  most  intense. 

These  cylinders  are  made  from  pieces  of  platinum  foil,  about  0-07  mm.  in 
thickness  and  8  by  11  cm.  in  diameter,  which  have  been  previously  bent  around 
glass  tubes  of  such  a  size  that  when  applied  to  the  combustion  tubing  the 

*  Am.  Journ.  Sci.,  3d  Series,  XLVIII,  p.  37.  1894;  Zeitsch.  fur  anorg.  Chemie,  vx,  p.  2? 


SOME    PRINCIPLES   AND    METHODS    OF    ROCK    ANALYSIS.    1125 

spring  of  the  metal  will  hold  them  in  place.  A  large  platinum  boat,  7  to 
8  cm.  long  and  11  to  12  mm.  in  diameter,  with  a  cross-section  like  6,  should  be 
used,  since  this  will  readily  hold  a  gramme  of  mineral  mixed  with  5  grm.  of 
sodium  carbonate.  The  tube  is  placed  in  the  angle  formed  by  the  char- 
coal lining,  some  pieces  of  charcoal  are  placed  at  the  sides  in  front,  leaving 
an  opening  through  which  the  flame  may  be  directed,  and  an  additional  piece 
is  laid  on  top.  The  tube  can  readily  be  brought  to  a  full  white  heat,  and  by 
forcing  a  slow  current  of  dry  air  through  the  apparatus  the  carbon  dioxide 
resulting  from  the  decomposition  can  be  removed  and  the  water  carried 
over  into  the  weighed  absorption  tube.  The  glass  fuses  between  the  plati- 
num casings,  and  in  a  number  of  experiments  that  have  been  tried  there  has 
not  been  a  single  instance  where  the  glass  tube  has  broken  or  shown  any 
indication  of  breaking.  After  heating  the  tube  will  not  crack  if  it  is  left  to 
cool  slowly  on  the  charcoal,  but  it  cannot  be  used  a  second  time. 

At  the  high  temperature  to  which  the  glass  is  subjected  it  of  course  becomes 
very  soft  and  the  ends  must  be  properly  supported;  also  the  rubber  connec- 
tions and  absorption  apparatus  must  be  carefully  screened  by  asbestos  board. 
By  constructing  a  cover  for  the  boat  no  material  need  be  lost  by  spattering, 
and  after  making  the  water  determination  the  contents  may  be  used  for  the 
remainder  of  the  analysis. 

The  inner  cylinder  of  platinum  serves  to  prevent  the  glass  from  collapsing 
as  it  softens,  whereby  distortion  of  the  boat  would  result  and  its  withdrawal 
for  further  examination  of  its  contents  would  be  impossible. 

Gooch's  Apparatus. — Of  more  elaborate  apparatus,  designed  to  be  used 
with  fluxes,  the  tubulated  platinum  crucible  invented  by  Dr.  GOOCH  *  is 
capable  of  affording  most  excellent  service,  and  it  is  the  one  by  which  far  the 
larger  number  of  water  determinations  in  this  laboratory  have  been  made. 

Fig.  7,  which  hardly  needs  detailed  description,  shows  it  in  a  modified 
form,  which  differs  from  the  original  forms  of  GOOCH  in  that  the  tubes  for 
connecting  with  both  the  drying  and  absorption  vessels  are  constructed 
wholly  of  platinum  instead  of  lead  glass,  the  vertical  one  being  bent  hori- 
zontally at  right  angles  for  convenient  attachment  to  the  drying  towers,  and 
the  side  one  also  bent  at  right  angles,  but  downward,  and  having  its  end 
slightlv  drawn  in  at  E  (Fig.  7)  so  as  to  admit  of  easy  insertion  in  the  rubber 
stopper  of  a  U-shaped  calcium-chloride  tube  as  shown  in  Fig.  9  (page  1128). 
With  tubes  of  the  lengths  shown  in  the  figure  there  is  absolutely  no  danger 
of  their  ends  becoming  hot  enough  by  conduction  to  scorch  or  soften  the 
rubber  stopper  or  other  connection. 

The  extra  first  cost  of  the  platinum  extension  to  these  tubes  over  the  lead- 
jrlass  ends  of  GOOCH'S  original  and  modified  forms  need  hardly  enter  as  a 
factor  into  the  question  of  emplovment  of  this  apparatus  The  glass  ends 
often  break,  and  onlv  a  rich  lead  glass,  not  easily  obtainable,  can  be  used, 
since  it  alone  will  not  crack  at  the  joint  with  the  platinum  after  cooling.  In 
its  present  form  the  whole  apparatus  weighs  aDproximately  88  grammes. 

As  an  adjunct  to  its  convenient  use  there  is  needed  an  ordinary  upright 

*  Am.  Chem.  Jour.,  n,  p.  247,  1880;  Chemical  News,  XLH,  p.  326.  1880. 


1126 


APPENDIX    II. 


iron  ring-stand,  with  two  small  sliding  rings,  and  a  sliding  ring-burner  pro- 
vided with  entering  ducts  for  gas  and  air  blast.     Across  the  uppermost  ring 


FIG.  7. — Modified  form  of  the  GOOCH  tubulated  platinum  crucible  for  the  determination 
of  water,  about  one-half  natural  size.     Weight  about  88  grm. 

there  is  an  arrangement  of  stout  platinum  wire  (S,  Fig.  8),  forming  at  the 
center  of  the  ring  a  secure  seat  for  the  upturned  flange  of  the  crucible  proper. 
Both  rings  and  burner  can  be  clamped  firmly  at  any  height. 

The  rock  powder,  having  been  placed  in  the  cylindrical  crucible  (C,  Fig.  7), 
is  there  mixed  with  not  more  than  3  or  4  grammes  of  fully  dehydrated  sodium 
carbonate,*  or  more  of  lead  chromate  if  carbon  is  to  be  likewise  determined. 
The  crucible  is  sunk  in  its  seat  S  (Fig.  8)  in  the  upper  ring  R'  and  the  tubu- 
lated cap  T  (Fig.  7)  is  fitted  on  and  attached  to  the  calcium-chloride  drying 
towers— preceded  by  one  containing  potassium  hydroxide  if  carbon  is  like- 
wise to  be  estimated— on  the  one  side,  and  to  a  sulphuric-acid  bulb  tube  B 
(Fig.  9)  on  the  other.  Powdered  sodium  tungstate— free  from  arsenic, 
which  would  soon  ruin  the  crucible  lips— is  now  poured  into  the  flanged  lip  L 
fFig.  7)  in  which  the  cap  rests,  and  a  metal  vessel  of  cold  water  having  been 

*  This  has  been  heated  for  a  length  of  time  to  near  its  fusing-point  over  a  free  flame 
or  in  an  air-bath,  to  decompose  the  bicarbonate  it  usually  contains,  and  then  placed  in 
a  desiccator.  Thus  heated  it  is  not  very  hygroscopic.  PENFIELD  found  that  2-5  grm. 
of  it,  spread  out  on  a  watch-glass,  gained  only  .0002  grm.  in  15  minutes.  Potassium 
carbonate  and  potassium-sodium  carbonate  are  too  hygroscopic  by  far  to  be  available. 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1127 


raised  up  by  the  lower  ring  R"  (Figs.  8  and  9)  until  the  platinum  crucible 
is  sufficiently  immersed,  the  flame  of  an  ordinary  blast-lamp  is  turned  on  to 
melt  the  tungstate.  As  soon  as  this  is  fused  the  flame  is  removed  and  the 
salt  solidifies  and  makes  an  air-tight  joint,  the  test  of  which  is  the  perma- 


FIG.  8. — Details  of  the  GOOCH  crucible  for  determining  water.  S,  seat  of  stout  platinum 
wire  resting  on  ring  R' ,  and  serving  as  a  support  for  the  crucible;  R'",  blast -fed  ring 
burner;  R" ,  support  for  air-  or  toluene-bath  O. 

nence  of  the  column  of  sulphuric  acid  in  the  bulb  tubes  caused  by  the  contrac- 
tion of  the  air  in  the  platinum  apparatus  as  it  cools. 

After  drying  by  a  current  of  air  at  105°  for  two  hours,  more  or  less  (see 
below,  page  1129),  by  means  of  an  air-  or  toluene-bath  as  shown  in  Fig.  8,  the 
absorption  tube  A  (Fig.  9)  is  interposed  between  the  sulphuric-acid  bulbs 
and  the  apparatus,  being  fitted  to  the  latter  by  its  stopper,  which  is  at  other 


1128 


APPENDIX   II. 


times  closed  b}'  a  glass  plug,  and  while  a  slow  current  of  air  continues  to  pass 
the  gradual  heating  and  subsequent  fusion  of  the  flux  is  brought  about  by 
the  blast-fed  sliding  ring-burner  R'"  (Figs.  8  and  9).  The  sodium-tungstate 
joint  is  shielded  from  the  flame  by  small  pieces  of  asbestos  board  P  (Fig.  9), 
cut  out  so  as  to  fit  the  crucible.  When  fusion  is  complete,  as  shown  in  the 
case  of  sodium-carbonate  flux  by  the  decided  slackening  of  the  gas  current 
through  the  safety  bulbs  attached  to  the  drying  tube,  the  flame  is  extin- 
guished and  a  current  of  air  is  allowed  to  continue  until  the  apparatus  is 
cold. 

This  apparatus  suffers  from  the  drawback  of  being  slightly  permeable  to 
combustion  gases  at  high  temperature.     The  defect  can  be  overcome  by 


Fio.  9. — Arrangement  during  fusion  of  GOOCH  apparatus  for  determining  water.  R'" 
blast -fed  ring  burner;  P,  protective  asbestos-board  shield  resting  on  ring  R" ;  FF, 
board  forming  end  of  frame  and  covered  with  asbestos  board  to  prevent  being  set 
on  fire  by  the  heat  of  the  blast.  This  serves  at  the  same  time  as  an  efficient  shield 
for  the  absorption  tube  A.  In  it  there  is  bored  a  round  hole  at  hh,  through  which 
passes  the  outlet  tube  from  the  crucible.  B,  sulphuric-acid  bulbs  serving  to  show 
the  rate  of  gas  currrent  through  the  absorption  tube  and  at  the  same  time  to  prevent 
back  entry  of  moisture  from  the  air  into  A.  > 

causing  the  flame  to  play  upon  an  outer  ordinary  platinum  crucible,  kept 
permanently  filled  with  sodium-potassium  carbonate.  This  protective  cm- 
ciblp,  However,  is  soon  ruined  for  other  purposes,  being  distorted  by  the 
alternate  expansion  and  contraction  of  the  carbonate. 

It  has  been  found  that  if  the  operation  is  carried  out  expeditiously  and 
the  final  full  heat  applied  for  but  a  few  minutes,  the  error  due  to  penetrating 


SOME    PRINCIPLES   AND    METHODS   OF   ROCK   ANALYSIS.    1129 

water  gases  is  inappreciable.  This  hastening  may  be  rendered  safer  by  using 
rather  finely  powdered  calcium  chloride  in  the  central  section  of  the  U-shaped 
absorption  tube  to  avoid  large  air  channels.  Through  this,  or  any  apparatus 
based  on  similar  principles,  the  air  current  should  always  be  forced,  not 
drawn.  A  warm  blast  directed  upon  the  exit  tube  near  its  entrance  into 
the  absorption  tube  greatly  shortens  the  time  required  and  is  to  be  recom- 
mended. 

In  this  apparatus  only  the  water  expelled  above  100°  to  1 10°  should  as  a 
rule  be  determined,  and  to  effect  drying  of  the  mixed  mineral  powder  and 
sodium  carbonate,  after  luting  the  tubulated  cap  on  the  cylindrical  crucible 
with  sodium  tungstate,  the  tube  is  sunk  through  a  round  hole  in  the  cover 
into  a  small  cylindrical  air-bath  (Fig.  8),  which  can  be  heated  from  beneath 
by  the  same  ring-burner  which  is  subsequently  to  fuse  the  flux.  A  slow  cur- 
rent of  air  is  then  forced  through  and  the  drying  satisfactorily  accomplished. 

The  reason  why  it  is  unsafe  to  attempt  estimation  of  'hygroscopic"  mois- 
ture in  this  apparatus  is,  that  the  luting  of  the  two  parts  must  be  done  by 
direct  application  of  a  flame  to  the  tungstate,  and  considerable  water-vapor 
may  enter  the  apparatus  and  be  in  part  retained  by  the  dried  sodium  car- 
bonate. 

CHATARD'S  A  pparatus. — The  platinum  apparatus  devised  by  Dr.  CHATARD* 
overcomes  the  permeability  of  the  metal  to  gases  and  affords  sharp  results, 
moreover  permitting  of  determining  by  direct  absorption  not  only  the  hygro- 
scopic water,  but  that  which  may  be  driven  off  at  any  desired  temperature, 
either  with  or  without  fluxes.  It  is,  however,  perhaps  even  more  costly  than 
the  GOOCH  apparatus,  and  the  supposed  non-liability  to  injury  by  warping, 
because  of  the  protective  layer  of  borax  and  asbestos,  can  hardly  be  considered 
as  proved. 

Merits  of  the  above  Three  Forms  of  A  pparatus.— All  of  these  apparatus,  except 
the  glass  tube  of  the  modified  BRUSH  method,  permit  of  the  estimation  of 
other  constituents  besides  water  in  the  same  portion  if  necessary,  and  by  the 
use  of  lead  chromate  or  potassium  chromate,  instead  of  sodium  carbonate, 
graphite,  or  the  carbon  of  organic  matter,  can  be  simultaneously  determined 
with  the  water. 

To  one  accustomed  to  its  use,  and  with  a  drying  and  suspension  attach- 
ment permanently  set  up,  the  GOOCH  apparatus,  considering  its  limitations 
above  set  forth,  offers  perhaps  the  most  handy  and  convenient  means  for  the 
determination  of  water  in  rocks.  Its  high  first  cost,  in  comparison  with  the 
glass  tube,  is  fully  made  up  in  time  by  its  durability. 

JANNASCH'S  Methods. — This  zealous  deviser  of  methods  for  mineral  analysis 
has  published  in  the  Zeitschrift  fur  anorganische  Chemie  and  the  Berichte  der 
deutschen  chtmischen  Gesettschaft  several  papers  dealing  with  the  problem 
of  water  determination  in  minerals,  and  in  his  text-book  f  these  are  collected 
in  more  or  less  modified  form. 

For  the  majority  of  silicates  he  finds  dehydrated  borax  powder  a  most 

*  Am.  Chem.  Journ.,  xm,  p.  110,  1891;  Bull.  U.  S.  Geol.  Survey,  No.  78,  p.  84,  1891. 
*t  Praktischer  Leitfaden  der  Gewichtsanalyse,  Leipzig,  vov  VEIT  &  Co.,  1897. 


1130 


APPENDIX   II. 


efficacious  flux,  usually  at  a  very  moderate  temperature.  The  fusion  is 
accomplished  either  in  a  platinum  boat  within  a  glass  tube  or  in  a  tube  of 
the  form  and  dimensions  shown  in  the  accompanying  Fig.  10. 

For  rocks  or  minerals  containing  not  much  fluorine  a  retaining  layer  of 
granular  lead  chromate,  or  of  previously  fused  and  powdered  lead  oxide,  is 
used  as  shown  at  a.  Plugs  of  glass  wool  are  used  at  c,  c.  Whether  or  not 


FIG.  10. — Glass  tube  for  determination  of  water  (JANNASCH).  6,  mixture  of  mineral 
powder  with  borax;  c.  c,  plugs  of  glass  wool;  a,  layer  of  lead  chromate  or  lead  oxide. 
Total  length  of  the  tube,  33  cm. ;  inside  diameter,  12-14  mm. 

the  boat  is  employed  the  borax  is  first  introduced  and,  together  with  the  re- 
tainer, is  thoroughly  dried  out  in  an  asbestos  oven  by  a  hot-air  current. 
Then,  after  cooling,  the  mineral  powder  is  added  and  thoroughly  mixed  with 
the  borax.  Heat  is  applied  by  a  flat  flame  to  the  mixture,  which  soon  melts 
and  forms  a  clear  fusion,  when  the  action  is  complete.  The  blast  may  be 
used  in  extreme  cases.  The  layer  of  retainer  must  be  kept  warm  by  an 
auxiliary  flame,  and  the  absorption  tube  must  be  removed  before  the  flame 
under  the  fused  mass  is  extinguished,  for  the  glass  breaks  as  soon  as  this  is 

A  A 


Fio.  11. — Glass  tube  for  determination  of  water  in  special  cases  (JANNASCH).  Length 
from  a  to  e,  26  cm.;  inside  diameter  somewhat  over  1  cm. ;  volume  of  bulb  6,25  c.c.; 
c,  d,  retaining  layer  of  lead  oxide  between  plugs  of  glass  wool;  /,  calcium-chloride 
absorption  tube;  g,  protective  tube. 

done.  Carbon  dioxide  can  simultaneously  be  determined  by  attaching  a 
soda-lime  tube  to  the  calcium-chloride  tube.  For  one-half  to  1  grm.  of 
silicate  JANNASCH  uses  1£  to  2  grm.  of  borax. 

Regarding  the  borax  method,  its  inventor  insists  upon  the  following  points 
as  essential  to  success,  especially  when  the  blast  cannot  be  applied:  Most 
thorough  mixing  of  flux  and  mineral  powder  and  a  most  impalpable  fine- 
ness of  the  latter. 

The  borax  itself  is  prepared  by  heating  pure  crystallized  borax  in  a  plati- 
num dish  till  a  small  portion  has  melted.  That  remaining  unfused  is  pow- 
dered and  again  heated  in  the  dish  to  dull  redness  for  fifteen  minutes,  with 
constant  stirring.  The  powder  is  placed  in  a  tube  with  tightly  fitting  glass 
stopper,  and  kept  over  sulphuric  acid.  It  must  not  be  kept  long  without 
reheating,  because  of  being  hygroscopic. 

Another  form  of  tube  used  by  JANNASCH  for  special  purposes  is  shown  in 
Fig.  11.  Minerals,  such  as  topaz,  which  is  not  fully  decomposed  by  the 
borax  method  and  ^hich  contains  a  large  amount  of  fluorine,  are  fused  at 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    3131 

b  with  about  six  times  their  weight  of  lead  oxide.     A  layer  of  lead  oxide 
between  c  d  serves  to  retain  any  fluorine  escaping  from  the  fusion, 

VL     SILICA,  SEPARATION  FROM  ALUMINA,  ETC. 
ALTERNATIVE  METHODS  OF  DECOMPOSITION. 

PRELIMINARY  REMARKS. 

The  practice  of  separating  alumina,  etc.,  by  the  usual  method,  after  first 
attacking  the  rock  powder  with  hydrofluoric  and  sulphuric  acids — silica  being 
estimated  in  a  separate  portion — while  attractive .  in  principle,  was  aban- 
doned by  the  writer  after  fair  trial,  owing  to  the  disturbance  sometimes 
occasioned  by  incomplete  expulsion  of  fluorine  and  to  a  less  degree  by  the 
presence  of  sulphates  instead  of  chlorides.  With  exception  of  the  compar- 
atively few  analyses  made  thus,  the  sodium-carbonate  method  has  always 
been  employed.  In  the  case  of  rocks  rich  in  fluorine  strict  accuracy  would 
require  the  separation  of  silica  to  be  made  as  in  the  BERZELIAN  method  for 
fluorine  estimation  (see  toot-note,  page  1133),  but  in  practice  it  is  not  often 
necessary  to  resort  to  this  tedious  procedure,  since  the  amount  of  fluorine  is 
usually  small  and  it  can  by  no  possibility  cause  a  loss  of  much  more  than 
three-fourths  its  own  weight  of  silica  by  volatilization  as  silicon  fluoride  when 
the  sodium-carbonate  fusion  is  evaporated  directly  with  hydrochloric  acid. 
Probably  the  loss  is  less,  since  some  fluorine  perhaps  escapes  as  hydrofluoric 
acid.  However  this  may  be,  the  error  is  of  comparatively  slight  importance, 
since  it  attaches  to  the  constituent  always  present  in  greatest  amount. 

Various  fluxes  other  than  alkali  carbonates  have  been  recommended  for 
breaking  up  silicates  insoluble  in  ordinary  acids,  such  as  lead  and  bismuth 
oxides,  lead  carbonate,  borax,  and  boric  oxide.  Professor  JANNASCH  and  his 
pupils  have  been  especially  active  of  recent  years  in  this  line  of  work,  as 
evidenced  by  their  numerous  published  papers.  One  of  the  advantages  these 
fluxes  possess  over  the  alkali  carbonates  is  their  removability  after  serving 
their  purpose,  thus  allowing  the  various  separations  to  be  made  more  perfectly 
and  without  the  annoying  interference  of  several  grammes  of  foreign  fixed 
salts,  wrhich  are  most  troublesome  in  that  part  of  the  analysis  devoted  to  the 
separation  of  silica,  alumina,  iron,  lime,  and  magnesia. 

Another  of  their  advantages  is  that  with  some  of  them  it  is  possible  to 
estimate  in  one  portion  the  alkalies,  in  addition  to  those  constituents  usually 
determined  in  the  silica  portion.  Where  the  material  is  limited,  as  it  so  often 
is  in  mineral  analysis,  this  is  a  most  important  advantage,  sufficient  to  out- 
weigh all  possible  objections;  but  in  rock  analysis,  where  the  supply  of  ma- 
terial is  usually  ample,  it  is  rarely  worth  considering.  A  still  further  point 
in  their  favor  is  that  it  is  probably  more  easy  to  obtain  them  entirely  free 
from  fixed  impurities  than  an  alkali  carbonate. 

There  are,  however,  objections  to  their  use.  With  some  of  them  an  ex- 
traordinary amount  of  time  must  be  devoted  to  grinding  the  mineral  to  an 
impalpable  powder,  and  the  flux  itself  may  need  considerable  hand  pulveri- 
zation. Once  introduced,  they  must  be  removed  before  the  analysis  can  be 


1132  APPENDIX   II. 

proceeded  with,  and  this  removal  takes  much  time  and  is  always  a  possible 
source  of  error. 

In  mineral  analysis  these  objections  are  entitled  to  far  less  weight  than  in 
rock  analysis,  since  the  object  sought — usually  the  deduction  of  a  formula — 
warrants  the  expenditure  of  much  time  and  painstaking  care.  Finally,  it 
has  been  found  that  one  or  more  of  these  fluxes  are  not  available  for  altogether 
general  use,  since  certain  minerals  do  not  fully  succumb  to  their  attack  under 
simple  conditions,  as  andalusite  with  boric  oxide  and  others  with  lead  oxide 
(JANNASCH).  Therefore,  however  well  adapted  one  or  the  other  of  these 
methods  may  be  for  the  analysis  of  homogeneous  minerals,  it  is  very  im- 
probable that  the  vivid  anticipations  of  Professor  JANNASCH,  to  the  effect 
that  the  boric-oxide  method  will  soon  supersede  the  alkali-carbonate-fusion 
method  in  rock  as  well  as  in  mineral  analysis,  will  be  speedily  realized.  Never- 
theless, the  boric-oxide-fusion  method,  owing  to  its  evident  merit,  will  be 
described  in  detail  after  brief  reference  to  a  means  of  bringing  refractory 
silicates  into  solution  without  employing  any  solid  reagent. 

DECOMPOSITION    OF  REFRACTORY    SILICATES   BY  HYDROCHLORIC  ACID 
UNDER    PRESSURE. 

JANNASCH  *  pours  upon  the  finely  ground  rock  powder  contained  in  a 
platinum  tube  of  about  26  c.c.  capacity  a  somewhat  diluted  hydrochloric 
acid  (4  acid  to  1  water),  places  over  the  open  end  a  cap  which  does  not  her- 
metically close  the  tube,  inserts  the  latter  in  a  larger  one  of  potash  glass  like- 
wise partially  filled  with  the  diluted  acid,  seals  the  glass  tube,  and  places  it 
hi  turn  in  an  inclined  position  in  a  steel  MANNESMANN  tube  containing  ether 
or  benzene  to  equalize  the  pressure,  and  heats  to  any  desired  temperature 
up  to  400°  C. 

The  chief  drawback  seems  to  be  a  somewhat  incomplete  decomposition 
doubtless  due  to  the  necessarily  inclined  position  of  the  tube,  which  causes 
the  powder  to  collect  at  the  lower  end,  and  thus  renders  decomposition  less 
complete  than  if  the  material  were  spread  evenly  throughout  the  length  of 
the  tube.  Further,  the  acid  strongly  attacks  the  platinum  unless  the  air 
in  both  the  platinum  and  the  glass  tubes  is  replaced  by  carbon  dioxide.  Even 
when  this  is  done,  several  milligrammes  of  platinum  are  found  in  the  silicate 
solution. 

Nevertheless,  to  those  possessing  the  necessary  platinum  and  steel  tubes 
the  method  can  render  efficient  service  in  special  cases  when  economy  of 
material  is  imperative. 

THE    BORIC    OXIDE    METHOD    OF  JANNASCH   AND    HEIDENREICH.f 

Preparation  of  the  Boric  Oxide. — This  demands,  if  the  alkalies  are  to  be 
estimated  in  the  same  proportion  as  silica,  etc.,  an  absolutely  alkali-free  boric 
acid,  which  can  be  prepared  by  two  or  three  recrystallizations  of  a  good 
commercial  article.  The  purified  crystals  are  dehydrated  and  fused  in  a 

*  Ber.  deutsch.  chem.  Gesell.,  xxiv,  p.  273.  1891,  and  Zeitschr.  fur  anorg.  Chem.  VI, 
p.  72,  1894. 

t  Zeitschr.  fur  anorg.  Chem.,  xn,  p.  208,  1896. 


SOME    PRINCIPLES   AND    METHODS   OF  ROCK   ANALYSIS.    1133 

large  platinum  crucible.  This  is  then  suddenly  cooled  to  cause  the  anhydride 
to  crack  into  pieces  of  a  size  convenient  for  powdering,  which  are  to  be  kept 
in  a  tight  glass  and  powdered  as  needed,  since  the  anhydrous  oxide  is  hygro- 
scopic. 

Treatment  of  Easily  Decomposable  Silicates. — To  this  flux  JANNASCH  and 
HEIDEXREICH  find  that  nearly  all  silicates  readily  succumb  over  the  ordinary 
blast-lamp.  The  fusion  is  made  in  a  large  crucible  holding  40-65  c.c.,  and 
the  proportion  of  flux  to  be  used  is  gauged  according  to  the  nature  of  the 
silicate,  ranging  from  3  to  8  and  more  parts  to  1  of  mineral.  This  last  must 
be  finely  powdered,  especially  the  most  resistant,  the  authors  recommend- 
ing the  expenditure  of  one-half  to  one  hour's  time  for  the  grinding  of  one- 
half  to  1  grm.  of  powder.  A  low-burner  heat  is  applied  for  five  to  ten  minutes 
till  water  is  expelled,  which  is  then  gradually  increased  till  the  gas  is  fully 
turned  on.  Bubbling  and  rising  in  the  crucible  is  prevented  so  far  as  pos- 
sible by  using  a  short  platinum  rod  which  does  not  reach  above  the  edge  of 
the  crucible.  When  the  mass  has  been  in  quiet  fusion  for  a  time  in  the 
covered  crucible  the  blast-flame  is  applied.  The  average  duration  of  the 
entire  operation  is  twenty  to  thirty  minutes,  but  depends  much  on  the  char- 
acter of  the  mineral. 

Treatment  of  Refractory  Silicates. — For  those  minerals  which,  like  anda- 
lusite,  cyanite,  and  topaz,  are  not  fully  decomposable  by  the  heat  of  the  ordi- 
nary blast-flame,  JANNASCH  and  WEBER  *  use  a  flame  fed  by  oxygen  instead 
of  air.  The  blast-lamp,  of  2£  mm.  opening,  is  supplied  with  gas  from  at 
least  five  or  six  ordinary  gas  cocks,  and  the  flame  is  made  broad  and  free 
from  luminosity.  The  mineral  having  been  first  heated  as  above  described 
but  with  a  much  larger  proportion  of  flux — as  high  as  30  to  1 — a  few  grm. 
additional  of  boric  oxide  are  added  and  the  oxygen  blast  is  applied  till,  in 
ten  or  fifteen  minutes,  the  fusion  is  as  transparent  as  glass,  f 

Further  Treatment  After  Fusion. — From  this  point  the  further  treatment 
is  the  same  in  both  cases,  and  as  modified  by  JANNASCH  and  WEBER  (loc.  cit.) 
is  as  follows: 

The  hot  crucible  is  cooled  in  cold  water  and  the  contents  are  turned  into 
a  very  large  porcelain  or  platinum  dish,  to  which,  after  covering  with  a  glass, 
a  saturated  solution  of  hydrochloric-acid  gas  in  methyl  alcohol  is  added. J 
The  cover  being  then  removed,  the  liquid  is  heated  to  boiling  over  asbestos 
board  by  an  inch-high  flame,  stirring  constantly,  or  it  is  left  without  atten- 
tion over  a  lower  flame  or  on  a  water-bath  heated  short  of  boiling.  The 
crucible  is  cleansed  in  a  similar  manner,  and  its  contents  are  added  to  the 
dish.  In  ten  to  fifteen  minutes,  with  occasional  addition  of  the  methyl 
chloride,  solution  is  complete  and  the  liquid  is  then  boiled  down  to  a  small 

*  Her.  deutsch.  chem.  Geaell.,  xxxn,  p.  1670.  1899. 

t  An  interesting  and  important  observation  reported  by  JANNASCH  and  WEBER  is 
that  when  the  oxygen  blast  has  been  used  fo-  ;hcates  carrying  fluorine  or  mixed  with 
H'londes.  the  fluorine  seems  to  be  wholly  expelled  as  boric  fluoride,  without  loss  of  silica. 
If  this  should  prove  to  be  generally  true,  an  easy  way  is  at  last  afforded  for  estimating 
silica  in  such  cases,  where  even  its  detection,  when  present  in  small  amount,  has  hereto- 
fore been  difficult. 

t  Made  by  passing  dry  HC1  into  cooled  CH4O  for  from  one  to  two  hours. 


1134  APPENDIX   II. 

volume  and  evaporated  to  dryness  on  the  bath.  The  residue  is  then  digested 
on  a  bath  at' 80°  to  85°  three  or  four  times  in  succession,  with  the  ether 
solution,  in  order  to  remove  the  last  traces  of  boron  as  boric  ether.  Care 
should  be  taken  to  wash  down  from  the  sides  of  the  dish,  with  methyl-chloride 
solution,  the  boric  acid  formed  and  deposited  thereon  during  the  evaporation. 
Possible  Objections  to  the  Boric-oxide  Method. — Very  much  is  claimed 
by  JANNASCH  for  this  method,  but  with  all  its  undoubted  merit  there  are 
two  points  which  may  militate  against  it  in  time.  The  boric  ether,  driven 
off  in  such  enormous  quantities,  at  once  decomposes  in  contact  with  mois- 
ture, and  boric  acid  settles  over  all  objects  with  which  it  comes  in  contact. 
The  hood  must  become  thickly  coated.  Hence  a  special  hood  for  these 
evaporations  alone  seems  to  be  called  for,  otherwise  boric  acid  may  at  any 
time  fall  into  other  dishes  and  cause  untold  trouble.  The  second  objection 
attaches  to  the  use  of  the  oxygen  flame  when  alkalies  are  to  be  estimated 
in  the  fusion,  and  the  ability  to  so  determine  them  is  one  of  JANNASCH'S  chief 
claims  in  favor  of  the  method,  for  it  cannot  be  doubted  that  at  the  high 
temperature  of  this  flame  alkalies  are  volatilized  in  part.  Borax  can  be 
slowly  but  wholly  volatilized  over  the  ordinary  blast,  hence  there  is  great 
reason  to  fear  sufficient  loss  at  this  much  higher  temperature  to  give  rise 
to  serious  error  at  times. 

THE    SODIUM-CARBONATE    METHOD. 

Purity  of  the  Sodium  Carbonate  used  as  a  Flux. — Notwithstanding  the  most 
earnest  efforts  for  years,  it  has  been  impossible  to  procure,  either  in  the  open 
market  or  by  special  arrangement  with  manufacturers,  an  article  of  sodium 
carbonate  which  can  be  called  chemically  pure.  With  special  precautions 
small  lots  can  be  prepared  in  the  laboratory  that  will  contain  less  than  1 
mgrai.  total  impurity  in  10  grm. ;  but  such  an  article  cannot  be  purchased 
in  the  market,  and  rarely  will  the  so-called  chemically  pure  dry  sodium 
carbonate  contain  as  little  as  1  mgrm.  in  10  grm.  The  invariable  contam- 
inating substances,  aside  from  sand  and  straw,  which  have  sometimes  been 
found  in  large  amount,  are  silica,  alumina,  iron,  lime,  and  magnesia,  all  of 
these  going  into  aqueous  solution  with  the  carbonate.  The  chief  of  these 
impurities  are  usually  silica,  alumina,  and  lime.  An  article  of  the  above 
degree  of  purity  is  satisfactory  in  almost  all  imaginable  cases,  since  the  use 
of  the  usually  extravagant  amount  of  10  grm.  for  a  fusion  would  introduce 
an  error  of  but  0-1  per  cent,  in  the  analysis,  supposing  1  grm.  of  mineral  to 
be  operated  on,  and  it  would,  moreover,  be  distributed  over  several  con- 
stituents. This  error  is  undoubtedly  fully  equalled  by  the  introduction  of 
dust  from  the  air  in  the  various  long  evaporations. 

Precautions  in  Fusing.— Special  directions  with  regard  to  the  fusion  and 
its  first  treatment  are  unnecessary,  except  to  say  that  ordinarily  from  4  to  6 
parts  of  flux  should  be  used  to  1  of  rock  and  that  the  flame  should  not  be 
,  directed  vertically  against  the  bottom  of  t.he  crucible,  but  at  an  angle  against 
the  side  and  bottom,  nor  should  the  flame  be  allowed  to  envelop  the  whole 
crucible.  These  precautions  apply  in  all  ignitions  of  reducible  substances, 
and  yet  they  are  rarely  observed.  In  neither  case,  if  neglected,  will  there  be 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1135 

the  necessary  oxidizing  atmosphere  within  the  crucible;  on  the  contrary, 
reduction  may  occur  fraught  with  serious  consequences.  This  is  especially 
true  if  the  rock  contains  more  than  traces  of  pyrite  or  other  sulphide,  when, 
after  cleansing  and  igniting  the  crucible,  there  may  appear  on  its  interior  a 
darkening  due  to  oxidation  of  reduced  iron  which  had  alloyed  with  the 
platinum.  This  may  in  exceptional  cases  amount  to  several  milligrammes 
in  weight,  and  can  be  removed  only  by  repeated  ignitions,  followed  each 
time  by  scouring  or  treatment  with  hydrochloric  acid  or  acid  potassium 
sulphate.  In  order  to  avoid  the  use  of  nitre  in  case  of  pyritiferous  rocks,  it 
is  well  to  first  roast  the  weighed  powder  in  the  crucible  in  which  the  fusion  is 
to  be  made. 

Treatment  after  Fusion. — When  fusion  is  complete,  the  crucible  is  seized 
with  the  tongs  (Fig.  1,  p.  1110)  and  the  contents  are  caused  to  solidify  in  a  thin 
sheet  over  the  sides  and  bottom  by  imparting  an  appropriate  rotating  motion 
with  the  arm  during  the  cooling  process.  This  is  far  preferable  to  allowing 
the  melt  to  form  a  thick  cake  at  the  bottom,  since  much  less  time  is  required 
for  disintegration,  and  separation  from  the  crucible  is  usually  much  easier. 

It  sometimes  happens  that  the  cooled  flux,  and  even  its  solution,  will 
indicate  absence  of  manganese  when  it  is  really  present  in  quantity  to  give 
normally  a  strong  coloration.  Two  fusions  made  side  by  side  or  successively, 
under  apparently  similar  conditions,  may  in  one  case  show  little  or  no  man- 
ganese, in  the  other  considerable.  This  observation  has  been  frequently 
made,  and  therefore  the  absence  of  a  bluish-green  color  in  the  fusion  is  not 
to  be  taken  as  proof  of  the  absence  of  manganese.  This  difference  of  behav- 
ior I  can  ascribe  to  no  other  cause  than  that  of  a  reducing  atmosphere  in 
one  of  the  crucibles  and  an  oxidizing  one  in  the  other,  even  though  the  con- 
ditions were  apparently  alike. 

The  contents  of  the  crucible  are  placed  in  a  rather  tall  covered  beaker 
with  some  water,  and  hydrochloric  acid  of  1-1  specific  gravity  is  added  in 
excess.  The  depth  of  the  pink  color  usually  produced  on  addition  of  the 
acid  allows  of  judging  approximately  as  to  the  amount  of  manganese  present. 
The  beaker  is  placed  on  the  water-bath,  and  when  disintegration  is  complete, 
having  been  assisted  by  gentle  pressure  with  a  blunt  glass  rod,  the  contents 
are  transferred  to  a  large  platinum  dish  and  evaporated  on  the  bath. 

SUBSEQUENT    TREATMENT. 

From  this  point  the  treatment  will  ordinarily  be  the  same  whether  the 
boric-oxide  or  the  sodium-carbonate  method  of  decomposition  has  been 
employed. 

Drying  and  Testing  of  Silica. — As  to  the  best  way  of  rendering  silica  insolu- 
ble by  evaporation,  the  writer's  predilection  is  for  a  double  evaporation 
instead  of  a  single  one  on  the  water-bath.  By  fusing  with  sodium  carbonate 
in  the  forenoon  the  silica  is  ready  for  the  first  filtration  in  the  afternoon.  It 
is  quite  unnecessary  to  carry  the  evaporation  beyond  approximate  dryness. 
The  filtrate  is  again  evaporated,  always  in  platinum,  and  is  ready  for  final 
filtration  the  following  morning  when  approximately  1  per  cent,  of  silica  is 
recovered  and  added  to  the  main  portion.  The  writer's  experience  is  that 


1136  APPENDIX    II. 

a  better  separation  of  silica  is  effected  hereby,  and  in  no  more  time  than  bv  a 
single  long  evaporation.  That  which  is  subsequently  recovered  from  the 
precipitate  of  alumina,  etc.  (p.  1139),  rarely  exceeds  a  half  or,  at  the  most, 
1  mgrm. 

Drying  in  an  air-bath  at  110°  or  higher,  or  on  a  hot  plate  or  sand-bath, 
or  over  a  free  flame,  in  order  to  render  silica  insoluble,  offers  no  advantage 
unless  much  magnesium  is  present,  and  then  the  most  favorable  tempera- 
ture, according  to  GILBERT,*  is  120°.  The  presence  of  much  calcium 
chloride  seems  to  facilitate  dehydration  of  the  silica,  while  magnesium  chlo- 
ride above  120°,  on  the  other  hand,  by  decomposing,  forms  a  silicate  which 
dissolves  in  hydrochloric  acid  and  increases  the  amount  of  silica  carried 
into  the  filtrate.  It  does  not  appear  from  GILBERT'S  paper  that  the  blast- 
furnace slags,  on  which  he  experimented,  contained  titanium,  phosphorus, 
or  iron  in  appreciable  amounts.  Basic  magnesian  rocks  usually  do,  and  in 
such  cases  it  is  probable  that  the  employment  of  a  drying  temperature  of 
120°  would  materially  add  to  the  large  impurity  always  to  be  expected  with 
the  silica.  In  other  cases  he  confirms  the  earlier  belief  that  drying  tempera- 
tures higher  than  that  of  the  water-bath  increase  the  amount  of  insoluble 
impurity,  chiefly  alumina,  in  the  s'lica,  and  that  this  amount  cannot  be 
reduced  by  long  digestion  with  hydrochloric  acid.  Further,  he  confirms 
LINDO'S  statement  that  evaporation  with  sulphuric  acid  till  the  appearance 
of  white  fumes  gives  a  higher  result  in  silica  than  with  hydrochloric  acid. 
But  for  general  rock  analysis  the  use  of  sulphuric  acid  at  this  stage  must  be 
rejected  utterly. 

Blasting  for  twenty  to  thirty  minutes  f  is  necessary  to  expel  all  moisture 
from  the  silica,  and  it  is  then  not  hygroscopic.  Its  weight  should  always 
be  corrected  for  impurities,  which  are  never  absent,  by  evaporating  with 
hydrofluoric  and  sulphuric  acids  and  again  blasting.  If  toward  the  end  of 
evaporation  with  these  acids,  when  the  hydrofluoric  acid  has  been  driven 
off  and  the  sulphates  begin  to  appear  in  solid  form,  the  residue  has  a  pecu- 
Jiar  milky  or  enamel-like  appearance,  it  may  be  taken  as  evidence  of  much 
phosphorus  and  titanium.  This  appearance  is  possibly  due  to  zirconium 
with  the  phosphorus  and  titanium,:}:  and  is  so  unusual  and  striking  that  it 
is  worth  while  calling  attention  to  it.  With  basic  rocks  very  rich  in  titanium 
and  phosphorus  the  residue  may  amount  to  2  or  even  3  per  cent,  of  the  rock. 

The  subsequent  precipitate  of  alumina,  etc.,  is  usually  ignited  in  the 
crucible  containing  the  residue  from  the  silica. 

It  might  be  supposed  that  this  residue  would  contain  most  of  the  barium 
of  those  rocks  carrying  that  element,  together  with  sulphur  or  sulphates, 

*  Technology  Quarterly,  in,. p.  61,  1890.  Abstract  in  FRESENIUS'S  Zeitschr.  fur  anal. 
Chemie,  xxix,  p.  688,  1890. 

t  It  must  be  borne  well  in  mind  that  some  platinum  crucibles  lose  weight  steadily 
and  very  appreciably  on  long  blasting,  not  only  when  new  but  even  after  long  use.  When 
a  crucible  suffers  from  this  defect  the  rate  of  loss  should  be  ascertained  from  time  to  time 
and  allowance  made  accordingly,  or  else  the  weight  of  the  crucible  should  be  taken  after 
and  not  before  ignition  of  the  precipitate.  (See  on  this  subject  HALL,  Journ,  Am.  Chem. 
Soc.,  xxn,  p.  494,  1900.) 

J  See  second  foot-note,  p.   1133. 


SOME   PRINCIPLES   AND   METHODS   OF   ROCK   ANALYSIS.    1137 

but  the  reverse  is  true  as  a  rule.  Only  when  there  is  a  considerable  excess 
of  SO3  over  the  BaO  will  much  of  the  latter  be  found  there,  and  in  the  vast 
majority  of  cases  there  is  none  at  all.  Should  some  be  present,  its  removal 
and  estimation  at  this  stage  is  not  necessary,  as  it  can  be  more  conveniently 
recovered  later,  together  with  the  silica  accompanying  the  alumina,  etc., 
precipitate  (p.  1139). 

The  separation  of  silica  in  rocks  containing  fluorine  has  been  touched 
upon  in  commenting  on  the  boric-oxide  and  sodium-carbonate  methods 
of  fusion,*  and  will  be  considered  further  under  the  head  of  Fluorine  (p.  1182). 

Platinum  in  Filtrates. — The  filtrates  from  the  silica  always  contain  nota- 
ble amounts  of  platinum.  This  arises  in  very  small  degree  from  the  crucible 
fusion,  in  a  larger  one  indirectly  from  the  action  of  hydrochloric  acid  on 
manganate,  vanadate,  and  sometimes  chromate  of  sodium,  and,  if  much 
iron  is  present,  in  no  small  degree  from  the  reduction  of  ferric  chloride  to 
ferrous  by  the  platinum  of  the  dish.  This  last  reaction  is  little  known, 
apparently,  but  is  mentioned  in  GMELIN-KRAUT,|  and  can  be  readily  de- 
monstrated by  evaporation  of  ferric  chloride  in  platinum. 

The  removal  of  this  platinum  before  precipitating  alumina  and  iron 
is  not  necessary  (but  see  first  foot-note,  p.  1140),  and  to  do  so  involves  the 
reoxidation  of  all  iron  and  subsequent  boiling  to  remove  or  destroy  the 
excess  of  oxidizing  agent,  together  with  the  expenditure  of  much  valuable 
time.  The  iron  is  already  oxidized  by  the  fusion,  and  needs  no  further  help 
in  that  direction.  Nevertheless,  if  time  is  not  a  prime  object,  its  removal 
by  hydrogen  sulphide  is  to  be  recommended.  In  the  following  descriptions, 
however,  it  is  assumed  that  the  platinum  has  not  been  gotten  rid  of  at  this 
stage. 

VII.     METALS  PRECIPITABLE  BY  HYDROGEN  SULPHIDE. 

The  presence  in  appreciable  amounts  of  metals  precipitable  by  hydro- 
gen sulphide,  except  perhaps  copper,  is  of  such  infrequent  occurrence  in 
most  rocks  that  discussion  is  unnecessary  in  their  connection.  In  case  it 
is  necessary  to  precipitate  them  at  this  stage,  however,  it  is  always  well  to 
bear  in  mind  that  a  little  titanium  may  be  thrown  down  along  with  them. 
Separations  of  the  silica  should  be  made  in  porcelain,  to  eliminate  platinum, 
or,  better  still,  the  quantitative  estimation  of  these  metals  should  be  made 
in  a  separate  portion  of  the  rock  broken  up  by  the  action  of  hydrofluoric 
and  sulphuric  acids. 

VIII.     ALUMINIUM.    TOTAL  IRON. 
INDIRECT  METHOD  FOR  ALUMINIUM. 

The  common  practice  in  this  laboratory  is  to  find  alumina  by  difference, 
after  deducting  from  the  precipitate  produced  by  ammonia  or  sodium  ace- 
tate the  sum  of  all  other  oxides  this  precipitate  may  contain.  Of  these, 
only  ferric  oxide,  titanic  oxide,  and  the  trace  of  silica  are  determined  in  this 

*  See  p.  1131,  and  foot-note,  p.  1133. 

t  Anorg.  Chem.,  in,  p.  359.     Sixth  revised  edition. 


1138  APPENDIX   II. 

portion  (see  also  first  foot-note,  p.  1140),  those  of  phosphorus,  vanadium, 
chromium,  and  zirconium  being  looked  for  in  other  portions  of  the  rock 
powder.  This  throws  upon  the  alumina  all  errors  involved  in  their  separate 
determinations:  but  these  may  balance,  and  in  any  case  the  probable  error 
can  hardly  be  as  high  as  that  involved  in  the  direct  weighing  of  the  alumina 
itself,  considering  the  difficulty  of  effecting  a  satisfactory  separation  of  it 
from  all  the  other  admixtures,  an  operation  which  would,  moreover,  immod- 
erately extend  the  time  required  for  each  analysis. 

PRECIPITATION    OF   ALUMINIUM,    IRON,    ETC. 

Precipitation  by  Ammonia. — Two  precipitations  by  ammonia  at  boiling 
heat  are  usually  quite  sufficient  to  separate  iron,  aluminium,  phosphorus,  vana- 
dium, chromium,  titanium,  and  zirconium,  if  all  these  are  present,  from 
nickel,  manganese,  the  alkaline-earth  metals,  and  magnesium,  provided 
ammoniacal  salts  are  present  in  sufficient  quantity.  This  last  point  is  of 
special  importance  as  regards  magnesium,  and  failure  to  observe  it  is  doubtless 
the  reason  why  many  old  analyses,  and  sometimes  modern  ones,  show  utterly 
improbable  percentages  of  alumina,  especially  as  chemists  were  formerly 
often  satisfied  with  a  single  precipitation.  The  necessary  ammonium  chloride 
is  better  obtained  by  the  use  of  purified  ammonia  water  and  hydrochloric 
acid  than  by  the  addition  of  the  solid  salt,  which  is  seldom  pure. 

Precipitation  by  the  Basic  Acetate  Method. — But  it  will  occasionally  happen 
that  the  separation  from  even  very  small  amounts  of  manganese  is  alto- 
gether incomplete,  and  the  uncertainty  of  insuring  this  separation  has  led  the 
writer  of  late  to  employ  the  basic  acetate  method  for  the  first  precipitation  in 
all  cases  where  manganese  is  present — and  the  exceptions  are  few — even 
though  the  precipitation  of  alumina  is  sometimes  less  complete  than  by 
ammonia,  and  in  spite  of  other  admitted  defects,  as,  for  instance,  a  tendency 
of  the  precipitate  to  run  through  the  filter  on  washing.*  Not  more  than  2, 
or  at  most  3,  grm.  of  sodium  acetate  need  be  used.  After  slight  washing 
and  sucking  dry  at  the  pump,  the  precipitate  is  redissolved  in  a  large  excess 
of  hydrochloric  acid  and  reprecipitated  by  ammonia  in  slight  excess.  The 
complete  boiling  off  of  this  excess  is  unnecessary,  as  pointed  out  by  GENTH 
and  PENFIELD,  since  it  is  apparently  the  washing  with  pure  water  and  not 
the  free  ammonia  which  carries  small  amounts  of  alumina  into  the  filtrate. 
PENFIELD  and  HARPER  f  recommend  washing  with  a  dilute  solution  of  ammo- 
nium nitrate  (20  c.c.  nitric  acid,  neutralized  by  ammonia,  to  the  liter),  and 
also  the  solution  of  the  first  precipitate  in  nitric  instead  of  hydrochloric 
acid,  in  order  to  shorten  the  washing,  there  being  no  chloride  to  remove. 

The  filtrates  are  strongly  concentrated  separately  J  in  platinum,  a  drop 

*  The  fact  must  not  be  overlooked  that  certain  of  the  rare  earths  may  pass  completely 
into  the  nitrate  if  the  basic  acetate  method  is  followed.  If  then,  later,  on  rendering 
the  combined  filtrates  ammoniacal,  an  unexpectedly  large  precipitate  appears,  this  should 
b#  carefully  examined  as  to  its  nature.  In  an  analysis,  of  piedmontite  from  Maryland 
cover  2  per  cent",  of  rare  earths,  including  cerium  and  others  not  identified,  were  quanti- 
tatively separated  in,  this  way  from  iron,  alumina,  etc. 

t  Am.  Journ.  Sci.,  3d  Series,  xxxn,  p.  112,  1886. 

t  If.  instead  of  sodium  acetate,  ammonia  alone  has  been  used  to  precipitate  alumina 
etc.,  it  has  sometimes  happened  in  the  experience  of  others  than  the  writer  that  on  con- 


SOME    PRINCIPLES    AND    METHODS    OF    ROCK    ANALYSIS.    1139 

or  two  of  ammonia  being  added  toward  the  end  to  the  second  one,  and  fil- 
tered successively  through  the  same  small  filter  into  a  flask  of  150  to  200  c.c. 
capacity,  tte  ammoniacal  filtrate  serving  as  wash  water  for  the  first  dish  and 
containing:  enough  ammoniacal  salt  to  prevent  precipitation  of  magnesium 
in  the  first  filtrate  when  mixed  with  it.  If  manganese  has  been  deposited 
upon  the  surface  of  the  dish  it  is  removed  by  hydrochloric  and  a  drop  or  two 
of  sulphurous  acids,  which  mixture  is  then  passed  hot  through  the  filter.  A 
reprecipitation  by  ammonia  is  then  made,  and  the  precipitate  collected  again 
on  the  filter  and  added  to  the  main  one,  the  filtrate  passing  into  the  flask 
containing  the  previous  one.  If  much  manganese  is  present,  of  course  a 
second  precipitation  by  ammonia  of  the  small  precipitate  may  be  required. 
In  these  cases  there  is  no  difficulty  in  getting  all  the  manganese  into  the 
filtrate. 

IGNITION    OF    THE    PRECIPITATE. 

The  combined  precipitates  of  alumina,  etc.,  are  ignited  moist,  in  the 
paper,  unless  considerable  iron  is  present,  when  the  main  one  is  dried,  removed 
so  far  as  possible  from  the  paper,  and  the  latter  ignited  separately  to  prevent 
partial  reduction  of  a  portion  of  the  iron,  which  cannot  then  be  wholly  reoxi- 
dized  by  heating  or  by  treatment  with  nitric  acid  (see  p.  1122). 

Alumina  in  the  quantities  ordinarily  found  cannot  be  fully  dehydrated 
by  the  full  heat  of  the  BUNSEN  burner.  It  must  be  blasted  for  five  or  ten 
minutes.  If  iron  is  present  in  large  amount  this  last  operation  must  be 
conducted  so  as  to  insure  free  access  of  air  to  the  crucible  (p.  1134). 

RECOVERY    OF    SILICA    AND    POSSIBLE    BARIUM    IN    THE    ALUMINA    PRECIPITATE. 

The  precipitate  is  dissolved  by  fusion  with  acid  potassium  sulphate, 
an  operation  which  is  accomplished  without  trouble  in  from  two  to  four 
hours  if  the  temperature  is  kept  low  and  the  acid  salt  has  been  properly 
made  free  from  water  and  excess  of  acid.  The  melt  is  taken  up  with  hot 
water  and  considerable  dilute  sulphuric  acid,  the  residue  collected,  weighed, 
and  corrected  by  hydrofluoric  and  sulphuric  acids  for  silica,  which,  as  said 
before,  rarely  amounts  to  1  mgrm.  in  weight,  and  further  examined  for 
barium  (see  p.  1136)  by  dissolving  any  remaining  residue  in  hot,  strong  sul- 
phuric acid  and  diluting  with  cold  water.* 

oentration  of  the  first  filtrate  a  pale  straw-colored  precipitate  appeared,  which  remained 
on  the  filter  with  the  traces  of  alumina  that  may  also  separate,  although  it  is  slowly  solu- 
ble in  hot  water.  This  is  said  to  be  some  compound  of  platinum,  and  attention  is  called 
to  it  here  for  the  guidance  of  others  who  may  notice  it  and  be  unaware  of  its  character. 

*  Some  years  ago,  in  a  series  of  analyses  of  rocks  from  the  Leucite  Hills,  in  Wyoming, 
there  was  obtained  at  this  stage,  when  it  was  customary  to  dissolve  the  melt  in  cold  water 
preliminary  to  precipitation  of  titanium  by  boiling  the  neutralized  sulphuric  solution  in 
presence  of  sulphur  dioxide,  a  white,  more  or  less  flocculent  residue  amounting  to  1  to 
3  per  cent,  of  the  rock,  which  was  at  first  taken  to  be  a  mixture  of  tantalic  and  Columbia 
acids.  Eventually  it  was  found  to  consist  apparently  of  nothing  but  TiO2  and  P-2Os, 
with  perhaps  a  little  ZrO2.  By  repeated  fusion  with  acid  potassium  sulphate  and  leach- 
ing with  cold  water  it  could  be  gradually  brought  into  solution.  It  was  these  rocks 
which  furnished  the  most  striking  instance  of  the  peculiar,  milky,  sulphate  residues  men- 
tioned on  p.  1136,  as  derived  from  the  ignited  silica. 

KXOP  (Zeitschr.  fur  Kryst.,  x,  p.  73,  1885)  seems  to  have  obtained  a  similar  mixture 
in  analyzing  minerals  from  the  Kaiserstuhl  in  Baden,  but  its  nature  was  not  ascertained, 
though  suspected  to  be.  if  not  silica,  columbiferous  titanic  acid. 


1140  APPENDIX    II. 

ESTIMATION  OF  IRON  IN  THE  PRECIPITATE  OF  ALUMINA,  ETC. 

Without  Regard  to  the  Presence  of  Vanadium. — The  filtrate  obtained  in 
the  preceding  paragraph  is  reduced,  hot,  by  hydrogen  sulphide,  boiled  to 
collect  sulphur  and  the  platinum  sulphide  *  resulting  from  the  bisulphate 
fusion,  the  hydrogen  sulphide  being  allowed  to  pass  for  a  short  time  after 
boiling.  It  is  then  filtered  f  hot  into  a  flask  attached  to  a  carbonic-acid 
apparatus  and  brought  to  boiling  to  expel  hydrogen  sulphide.  When  this 
is  fully  effected  the  flask  is  cooled  in  water  while  the  carbon  dioxide  still 
passes,  and  the  solution  is  then  titrated  by  potassium  permanganate.  The 
results  are  strictly  accurate,  with  the  limitations  set  forth  in  the  paragraph 
below,  when  care  is  taken  with  the  reduction  by  hydrogen  sulphide.  The 
method  is  altogether  superior  to  that  involving  the  use  of  zinc,  since  no 
foreign  impurity  affecting  the  result  is  introduced  and  the  ever-present 
titanium  is  not  affected,  nor  is  vanadium  reduced  below  the  condition  of 
V2O4,  whereas  nascent  hydrogen  converts  it,  in  part  at  least,  to  V2O3.  Tita- 
nium can  be  conveniently  estimated  by  adding  hydrogen  peroxide  to  the 
titrated  iron  solution  (see  p.  1149). 

Having  Regard  to  the  Presence  of  Vanadium. — If  vanadium  is  present 
the  value  found  for  iron  will  be  in  error  by  the  amount  of  permanganate 
required  to  oxidize  V2O4  to  V2O5.  The  amount  of  the  correction  will  differ 
according  as  titration  of  the  iron  is  made  after  reduction  by  hydrogen  sul- 
phide or  by  nascent  hydrogen.  If  the  former  is  used,  as  should  always  be 
the  case,  because  of  the  ever-present  titanium,  the  vanadium  is  reduced  by  it 
to  V2O4,  which  in  its  action  on  permanganate  is  equivalent  to  two  molecules 
of  FeO,  while  the  reduction  goes  further  with  hydrogen.  After  the  first 
transitory  pink  blush  throughout  the  liquid,  the  slower-acting  vanadium 
may  require  the  addition  of  a  drop  or  two  more  of  permanganate  before  a 
comparatively  permanent  coloration  appears. 

*  It  may  be  mentioned  that  the  precipitation  of  platinum  from  a  hot  sulphate  solution 
is  far  quicker  and  cleaner  than  from  hydrochloric  acid.  Further,  this  platinum  sulphide, 
when  ignited  in  the  crucible  in  which  the  bisulphate  fusion  was  made,  should  weigh  together 
with  the  crucible  itself  what  the  latter  weighed  before  the  main  silica  precipitate  was 
ignited  in  it;  in  other  words,  the  weight  of  the  platinum  recovered  by  hydrogen  sulphide 
should  equal  the  loss  in  weight  of  the  crucible  due  to  attack  by  the  bisulphate.  In  some- 
what rare  instances  this  will  not  be  so,  but  the  weight  will  be  greater,  showing  again  in 
platinum  which  may  amount  to  a  milligramme.  Tests  have  shown  that  this  is  not  due  to 
retention  of  platinum  by  the  main  A^Oa,  etc. ,  precipitate ;  hence  it  must  come  from  platinum 
mechanically  loosened  from  the  dish  during  the  drying  and  powdering  of  the  silica  pre- 
paratory to  its  collection  on  the  filter,  or  to  some  insoluble  compound  of  platinum  formed 
during  evaporation  and  drying  of  the  silica.  It  may  also  be  in  part  or  wholly  due  to 
contamination  from  reduction  of  platinum  during  evaporation  of  the  filtrate  from  the 
basic  acetate  separation.  It  will  be  remembered  that  from  this  filtrate  a  small  amount 
of  iron  and  alumina  is  recovered  and  added  to  the  main  precipitate.  Hence  it  is  always 
well  in  fine  work  to  collect  the  sulphide  and  weigh  the  platinum  in  the  original  crucible, 
deducting  any  excess  from  the  alumina,  or  else  to  get  rid  of  the  platinum  by  hydrogen 
sulphide  before  proceeding  to  the  precipitation  of  alumina,  etc.  (see  p.  1137). 

t  Filtration  is  not  necessary  if  only  precipitated  sulphur  and  no  sulphides  are  in  sus- 
pension, since  this  is  without  reducing  action  on  cold  permanganate  solution,  as  WELLS 
tiid  MITCHELL,  and  others  before  them,  have  pointed  out.  The  above  authors  used  this 
method  of  reducing  ferric  iron  in  titanic  iron  ores.  (Journ.  Am.  Chem.  Soc.,  xvii,  p.  78, 
1895;  also  Chemical  News,  LXXIII,  p.  123,  1896.) 


SOME    PRINCIPLES   AND    METHODS   OF   ROCK   ANALYSIS.    1141 

When  the  amount  of  vanadium  in  the  rock  is  known,  a  correction  can 
be  applied  on  the  assumption  that  practically  all  the  vanadium  is  here  col- 
lected, a  p:>int  that  needs  further  investigation.  Various  authors  assert 
its  precipitability  with  alumina  and  iron  by  ammonia  and  ammonium 
acetate,  though  CARNOT  *  states  that  repeated  precipitation  by  ammonia, 
ammonium  carbonate,  or  ammonium  sulphydrate,  separates  it  from  iron. 
The  writer'?  experience  with  ores  very  rich  in  vanadium  shows  that  precipi- 
tation along  with  iron  and  aluminium  is  only  partial.  RIDSDALE  f  has  deter- 
mined its  precipitability  with  various  metals  and  gives  numerous  figures 
which  show  an  approximation  to  90  per  cent,  thus  thrown  down  under  the 
conditions  prevailing  in  analysis  of  iron  slags,  the  remainder  passing  into 
the  filtrates  and  appearing  in  small  part"  with  the  lime  and  to  a  greater  extent 
with  the  magnesium  phosphate.  For  all  practical  purposes  it  is  probably 
safe  to  assume  that  the  small  amounts  of  vanadium  met  with  in  rocks  are 
wholly  in  the  alumina  precipitate. 

If  the  amount  of  vanadium  in  the  rock  is  not  known,  and  great  accuracy 
is  necessary,  caution  requires  the  determination  of  the  total  iron  to  be  made 
either  in  a  separate  portion  or  after  reprecipitation  from  the  above  solution, 
as  follows:  Fuse  with  sodium  carbonate,  extract  with  water,  bring  the  insolu- 
ble residue  into  sulphuric  solution,  reduce  and  titrate  as  above  directed. 
But  unless  a  certain  precaution  is  here  observed  an  error  greater  than  that 
which  it  is  designed  to  avoid  will  be  committed.  Contrary  to  general  belief,  the 
aqueous  extract  from  the  sodium-carbonate  fusion  carries  a  small  but  appre- 
ciable fraction  of  a  per  cent,  of  iron,  as  the  writer  has  repeatedly  found  by 
actual  test.  This  iron  is  thrown  out  with  the  alumina  (and  silica,  if  present) 
by  the  usual  methods  of  neutralizing  the  alkaline  solution,  and  can  be  brought 
to  light  when  the  precipitate  thus  formed  is  treated  with  a  fixed  caustic- 
alkali,  or  again  fused  with  sodium  carbonate  and  leached  with  water,  when 
it  remains  wholly  or  in  part  undissolved.  Hence  it  is  necessary  to  collect 
this  iron  and  add  it  to  the  main  portion  before  titration. 

DETERMINATION    OF   THE   TRUE    VALUE    FOR   FERRIC   IRON. 

Having  in  one  way  or  another  found  the  total  iron  in  the  rock,  it  remains 
to  deduct  an  amount  equivalent  to  the  ferrous  oxide  the  rock  contains,  and 
a  further  amount  corresponding  to  the  sulphides  often  present,  in  order  to 
get  what  may  pass  for  the  true  value  for  ferric  iron.  That  this  is  often  only 
an  approximation  appears  from  the  difficulties  due  to  the  presence  of  vana- 
dium and  the  generally  indeterminable  effect  of  sulphides  on  the  ferrous- 
oxide  determination.  (See  pp.  1173  to  1175.) 

METHODS  AIMING  AT  THE  MORE  OR  LESS  DIRECT  ESTIMATION  OF  ALUMINIUM 
AFTER  FIRST  REMOVING  IRON  AS  SULPHIDE. 

Should  it  be  defeirable  for  any  reason  to  effect  an  actual  separation  of 
aluminium,  this  may  best  be  done,  up  to  a  certain  point,  after  the  bisulphate 

*  Comptea  rendus,  crv,  p.  1803,  1887 ;  Zeitschr.  fur  anal.  Chem.,  xxxii,  p.  223,  1893. 
t  Journ.  Soc.  Chem.  Industry,  vn,  p.  73,  1888. 


1142  APPENDIX   II. 

fusion  (p.  1139),  by  removal  of  the  iron*  by  ammonium  sulphide  in  ammo- 
nium- tartrate  solution,  evaporation  of  the  filtrate,  ignition  of  the  residue  with 
sodium  carbonate  and  nitrate,  and  extraction  with  water,  whereby  titanium 
and  zirconium  are  left  on  the  filter  as  sodium  salts,  while  chromium  and  vana- 
dium are  carried  into  the  filtrate  as  chromate  and  vanadate  along  with 
aluminium  and  phosphorus.  The  further  separation  of  the  two  last  from 
the  chromium  and  vanadium  is  outlined  under  Phosphorus,  p.  1160.  This  is 
as  far  as  the  separation  can  well  be  carried,  and  the  A12O3  must  still  be  found 
by  subtracting  the  P2O5  from  the  combined  weights  of  the  A12O3  and  P2O5. 
The  possibility  of  loss  of  some  P2O5  by  volatilization  f  during  the  bisulphate 
fusion  must  be  borne  in  mind  here,  for  if  it  takes  place  the  final  weight  of 
A12O3+P2O5  will  not  contain  all  the  P2O5. 

Some  writers  recommend  dissolving  the  ignited  alumina,  iron  oxide,  etc., 
in  hydrochloric  acid,  but  when  the  precipitate  has  been  heated  over  the 
blast,  as  it  should  be,  this  is  very  ineffective. 

BY   EXTRACTION   WITH   A   FIXED    CAUSTIC   ALKALI. 

A  favorite  practice  in  some  countries  of  Europe  is  to  fuse  the  ignited 
precipitate  containing  A12O3,  Fe2O3,  TiO2,  P2O5,  etc. — or  that  of  the  A12O3 
TiO2,  P2O5,  etc.,  after  separation  of  iron  by  ammonium  sulphide  in  tartrate 
solution — with  sodium  hydroxide  in  a  silver  crucible,  or  to  boil  the  freshly 
precipitated  mixture  with  a  solution  of  the  alkali,  on  the  assumption  that 
the  titanium  oxide  is  hereby  rendered  wholly  insoluble  and  thus  separated 
from  the  alumina.  This,  however,  is  in  part  an  error  long  since  pointed 
out  by  GoocH,J  who  showed  that  pure  titanic  oxide  is  markedly  soluble 
under  both  conditions  of  treatment.  Experiments  very  recently  made  by  the 
writer  to  test  the  extent  of  this  error  brought  out  the  following  interesting 
results: 

When  0-045  grm.  of  titanic  oxide  was  fused  by  itself  with  sodium  hy- 
droxide, the  clear  aqueous  extract  of  the  fusion  held  0-0031  TiO2,  or  about 
7  per  cent.,  determined  colorimetrically.  When  freshly  precipitated  and 
boiled  with  the  alkali  the  solubility  was  less.  When  fused  with  sodium, 
carbonate  but  an  infinitesimal  trace  was  dissolved,  which  required  strong 
concentration  for  its  detection.  When  mixed  with  a  large  excess  of  alumina 
and  fused  with  the  caustic  alkali,  the  solubility  was  still  very  marked,  though 
less  than  when  alumina  was  absent.  With  a  large  excess  of  ferric  oxide, 
with  or  without  alumina,  no  titanium  could  be  detected  in  the  unconcen- 
trated  filtrate. 

It  thus  appears  that  fusion  with  caustic  alkali  after  first  removing  iron 
involves  an  error  in  the  gravimetric  determination  of  both  aluminium  and 
titanium  which  does  not  appear  if  the  iron  has  not  been  removed. 

*  This  being  first  reduced  to  the  ferrous  condition  by  hydrogen  sulphide  in  acid  solu- 
tion in  order  to  obviate  the  possibility  of  precipitating  some  titanium,  which  otherwise 
is  likely  to  happen.  (CiTHREiN,  Zeitschr.  fur  Kryst.,  vi,  p.  246,  1882,  and  vn,  p.  250, 
1883.) 

t  H.  ROSE  speaks  of  such  loss  when  volatilizing  sulphuric  acid  in  presence  of  phos- 
phoric acid.  (Handb.  f.  quant.  Anal.,  FINKENER  edition,  n,  p.  575,  and  elsewhere.) 

J  Proc.  Am.  Acad,  Arts  and  Sci.,  xn,  p.  436,  1885;  Bull.  U.  S.  Geol.  Survey,  No.  27, 
pp.  16  and  17. 


SOME    PRINCIPLES   AND    METHODS   OF  ROCK   ANALYSIS.    1143 
DIRECT   PRECIPITATION    OF  ALUMINA. 

A  recent  and  promising  method  for  the  "direct  determination  of  alumina 
«  presence  of  iron,  manganese,  calcium,  and  magnesium  "  is  that  of  HESS 
and  CAMPBELL,*  but,  as  with  the  methods  just  considered,  it  involves  finally 
weighing  aluminum  and  phosphorus  together,  and  the  behavior  of  titanium 
has  not  been  investigated.  For  this  latter  reason  the  details  of  the  method 
will  not  be  given.  Suffice  it  to  say  that  precipitation  of  the  aluminium  and 
phosphorus  is  made  by  phenylhydrazine,  after  first  neutralizing  the  (prefer- 
ably chloride)  solution  by  ammonia  and  reducing  iron  by  a  saturated  solution 
of  ammonium  bisulphite.  Phenylhydrazine  "precipitates  aluminium  from 
its  solutions  quantitatively  as  the  hydroxide  without  a  trace  of  the  precipi- 
tate being  redissolved  in  excess  of  the  precipitant." 

IX.  MANGANESE/NICKEL,  COBALT,  COPPER,  ZINC. 

Ammonia  is  added  to  the  flask  containing  manganese,  the  earths,  etc. 
(p.  1139),  and  hydrogen-sulphide  gas  is  introduced,  whereby  manganese, 
nickel,  cobalt,  copper,  zinc,  and  a  small  part  of  the  platinum  from  the  dish 
are  precipitated.  The  flask  is  set  aside,  corked,  for  at  least  twelve  hours, 
and  preferably  twenty-four,  or  even  longer;  the  precipitate,  collected  and 
washed  on  a  small  filter  with  water  containing  ammonium  chloride  and  sul- 
phide, is  extracted  by  hydrogen-sulphide  water  acidified  with  one-fifth  its 
volume  of  hydrochloric  acid  (sp.  gr.  l-ll),  manganese  and  zinc,  if  present, 
going  into  solution. 

MANGANESE  AND  ZINC. 

The  filtrate  is  evaporated  to  dryness,  ammonium  salts  are  destroyed 
by  evaporation  with  a  few  drops  of  sodnjm-carbonate  solution,  hydrochloric 
and  a  drop  of  sulphurous  acids  are  added  to  decompose  excess  of  carbonate 
and  to  dissolve  precipitated  manganese,  and  the  latter  is  reprecipitated  at 
boiling  heat  by  sodium  carbonate  after  evaporation  of  the  hydrochloric 
acid.  If  zinc  is  present,  it  can  be  separated  from  the  manganese  after  weigh- 
ing. For  the  small  quantities  of  manganese  usually  found  the  sodium-car- 
bonate method  of  precipitation  is  to  be  preferred  to  that  by  bromine  or  sodium 
phosphate,  as  equally  accurate  and  a  great  time  saver. 

The  precipitation  of  manganese  in  alkaline  solution  by  hydrogen  per- 
oxide, as  proposed  by  JANNASCH  and  CLOEDT,*  a  method  which  appeared 
to  be  simple  and  accurate,  besides  affording  a  separation  from  zinc,  has  been 
shown  by  FRIEDHEIM  and  BRUHL  •}•  to  be  valueless,  as  also  other  separation 
methods  of  JANNASCH  based  on  the  use  of  hydrogen  peroxide. 

The  employment  of  ammonium  sulphide  instead  of  bromine  for  the  sep- 
aration of  manganese  from  the  alkaline  earths  and  magnesia  has  the  advan- 
tage that,  by  a  single  operation,  nickel,  copper,  and  zinc  are  likewise  removed 

*  Journ.  Am.  Chem.  Soc.,  xxi,  p,  776,  1899;  Chemical  News,  LXXXI,  p.  158,  1900. 

*  Zeitschr.  fur  anorg.  Chemie,  x,  p.  405,  1895. 

t  Zeitschr.  fur  anal.  Chemie,  xxxvm,  p.  681,  1899. 


1144  APPENDIX   II. 

if  present.  There  need  be  no  fear  of  overlooking  nickel  or  copper,  for  under 
the  conditions  of  the  precipitation  they  are  not  held  in  solution.  Now  and 
then  a  trace  of  alumina  may  be  found  in  the  precipitate,  and  magnesia,  too, 
would  contaminate  it  if  ammonium  salts  were  not  present  in  sufficient  quan- 
tity. Regard  must  therefore  be  had  to  these  possibilities,  and  also  to  the 
rather  remote  possibility  of  the  presence  of  rare  earths  which  were  not  thrown 
out  by  the  basic  acetate  precipitation  (see  foot-note,  p.  1138). 

NICKEL,  COBALT,  COPPER. 

The  paper  containing  these  is  incinerated  in  porcelain,  dissolved  in  a 
few  drops  of  aqua  regia,  evaporated  with  hydrochloric  acid,  the  copper  and 
platinum  thrown  out  warm  by  hydrogen  sulphide,  and  nickel  and  cobalt 
thrown  down  from  the  ammoniacal  filtrate  by  hydrogen  sulphide.  This 
is  then  rendered  faintly  acid  by  acetic  acid  and  allowed  to  stand.  The  sul- 
phide of  nickel  is  simply  burned  and  weighed  as  oxide,  its  weight  being  always 
very  small,  and  is  then  tested  for  cobalt  in  the  borax  bead. 

It  is  somewhat  unsafe  to  consider  traces  of  copper  found  at  this  stage 
to  belong  to  the  rock  if  the  evaporations  have  been  conducted,  as  is  usually 
the  case,  on  a  copper  water-bath,  or  if  water  has  been  used  which  has  been 
boiled  in  a  copper  kettle,  even  if  tinned  inside.  Therefore,  and  because 
of  its  contamination  by  a  little  platinum,  it  is  better  to  determine  copper 
in  a  separate  portion  if  its  presence  is  indicated  with  certainty.  (See  p.  1137). 

X.    CALCIUM  AND  STRONTIUM  (BARIUM). 
SEPARATION  FROM  MAGNESIUM. 

Precipitation  and  Ignition  of  the  Oxalates  Together. — The  platinum  derived 
from  the  dish  in  the  silica  evaporation,  except  for  the  small  portion  precipi- 
tated with  the  manganese  sulphide,  is  now  wholly  in  the  nitrate  from  the 
latter.  Its  separation  at  this  or  any  other  stage  is  quite  unnecessary,  nor 
is  the  removal  of  ammonium  chloride  usually  demanded,  since  there  is 
no  undue  amount  present  in  most  cases,  the  first  precipitation  of  alumina, 
etc.,  having  been  by  sodium  acetate.*  Therefore,  without  lestroying  ammo- 
nium sulphide  the  calcium  and  strontium  are  thrown  out  by  ammonium 
oxalate  at  boiling  heat,  the  precipitate,  often  darkened  by  deposited  platinum 
sulphide,  is  ignited  and  redissolved  in  hydrochloric  acid,  boiled  with  ammo- 
nia to  throw  out  traces  of  alumina  sometimes  present  and  reprecipitated 
as  before,  but  in  a  small  bulk  of  solution.  It  is  weighed  as  oxide,  trans- 
ferred to  a  small  flask  of  20  c.c.  capacity,  dissolved  in  nitric  acid,  evapor- 
ated to  dryness  at  150°  to  160°,  and  the  separation  of  strontium  from  cal- 
cium effected  by  ether-alcohol  f  as  described  below. 

*  If  two  or  three  precipitations  by  ammonia  alone  are  depended  on,  the  second  and 
third  filtrates  are  evaporated  rapidly  to  dryness  and  the  ammonium  salts  removed  by 
ignition. 

t  See  FRESENITTS,  Zeitschr.  fur  anal.  Chemie,  xxxn,  pp.  189,  312,  1893,  for  the  latest 
improvements  in  this  method. 


SOME  PRINCIPLES   AND    METHODS    OF   ROCK   ANALYSIS.    1145 

The  weight  of  strontia  found  deducted  from  that  of  the  two  oxides  gives 
that  of  the  lime. 

Necessity  for  Two  Precipitations  by  Ammonium  Oxalate. — It  may  be  said 
with  regard  to  the  separation  of  calcium  from  magnesium  that  two  precipi- 
tations by  ammonium  oxalate  are  essential  to  the  attainment  of  correct 
results,  not  only  for  the  complete  removal  of  magnesium  but  of  sodium  as 
well,  the  retention  of  compounds  of  the  latter  element  by  calcium  oxalate 
being  now  generally  known.  For  the  treatment  of  the  filtrates,  see  Mag- 
nesium, p.  1146. 

SEPARATION  OP  STRONTIUM  (BARIUM)  FROM  CALCIUM  BY  ETHER- 
ALCOHOL. 

The  thoroughly  dried  nitrates  are  treated  with  as  little  (rarely  over  2  c.c., 
of  a  mixture  in  equal  parts  of  absolute  alcohol  and  ether  as  may  be  needed 
to  dissolve  the  calcium  salt,  solution  being  hastened  by  occasional  gentle 
agitation.  After  standing  over  night  in  a  corked  flask  the  insoluble  matter 
is  collected  on  the  smallest  possible  filter  and  washed  with  more  of  the  above 
mixture  of  alcohol  and  ether.  After  drying,  a  few  cubic  centimetres  of  hot 
water  are  passed  through  the  filter,  on  which  may  remain  a  few  tenths  of 
a  milligramme  of  residue  which  does  not  usually  contain  any  lime  or  other  alka- 
line earth  and  whose  weight  is  therefore  to  be  deducted  from  that  of  the  lime, 
unless  it  can  be  shown  that  it  is  derived  from  the  glass  of  the  little  flask  in 
which  the  nitrates  of  calcium  and  strontium  were  evaporated.  To  the  solu- 
tion of  strontium  nitrate  in  a  small  beaker  sulphuric  acid  and  then  alcohol 
is  added,  whereby  the  strontium  is  precipitated  as  sulphate,  in  which  form 
it  is  weighed  and  then  tested  spectroscopically  as  to  freedom  from  calcium 
and  barium. 

Because  of  the  slight  solubility  of  strontium  nitrate  in  amyl  alcohol,  the 
method  of  BROWNING  *  does  not  appear  to  be  adapted  for  the  separation  from 
calcium  of  the  small  amounts  of  strontium  met  with  in  rocks,  though  with 
barium  the  case  is  different,  since  its  nitrate  according  to  BROWNING  is  insolu- 
ble in  absolute  amyl  alcohol. 

BEHAVIOR  OF  BARIUM. 

Barium  will,  after  two  ammonium-oxalate  precipitations,  never  be  found 
with  the  ignited  calcium  and  strontium  in  more  than  spectroscopic  traces, 
unless  originally  present  in  excess  of  3  or  4  mgrm.,  and  very  often  only  when 
in  considerable  ex  cess,  f  If  present  with  them,  however,  it  will  be  separated 
with  the  strontium  by  ether-alcohol  or  amyl  alcohol,  and  these  two  must 
then  be  treated  by  the  ammonium-chromate  method,  given  below,  in  order 
to  arrive  at  the  strontium.  The  barium  is  best  estimated  hi  a  separate  por- 
tion. (See  Barium,  p.  1155.) 

*  Am.  Journ.  Sci.,  3d  Series,  XLIII,  pp.  50,  314,  1892. 

t  W.  F.  HILLEBRAND,  Journ.  Am.  Chem.  Soc.,  xvi.  p.  83,  1894;  Chemical  News,  LXIX, 
p.  147,  1894. 


1146  -  APPENDIX    II. 


SEPARATION  OF  BARIUM  FROM  STRONTIUM. 

FRESENIUS  has  shown  *  in  what  manner  only  a  correct  separation  of 
barium  and  strontium  can  be  made  by  the  ammonium-cnromaie  metnod, 
involving  double  precipitation  when  tne  amounts  are  at  all  large,  ims 
procedure  is  here  given  for  the  amounts  used  by  him,  but  a  single  precipi- 
tation will  suffice  for  the  small  amounts  met  with  in  rock  analysis,  ine 
volumes  of  solutions  used  should  be  largely  reduced  and  the  operations  other- 
wise shortened. 

The  chlorides  corresponding  to  0-2774  grm.  BaO  and  0-4864  grm.  SrO 
were  dissolved  in  300  c.c.  of  water  with  addition  of  6  drops  of  acetic  acid 
(1-065  sp.  gr.).  To  the  hot  solution  was  added  an  excess  (10  c.c.)  of  ammo- 
nium-chromate  solution  (1  c.c.  =0-1  grm.  neutrarchrohiate).  After  settling 
and  cooling  for  an  hour  the  precipitate  was  washed,  mainly  by  decantation, 
with  water  holding  ammonium  chromate  till  the  nitrate  gave  no  precipitate 
with  ammonia  and  ammonium  carbonate  (100  c.c.  used).  The  washing 
was  continued  with  warm  water  till  silver  nitrate  gave  but  a  very  slight  red- 
dish coloration  (110  c.c.).  The  precipitate  was  then  washed  into  the  pre- 
cipitating dish,  the  filter  rinsed  with  warm  dilute  nitric  acid  (1  2  sp.  gr.) 
and  more  nitric  acid  (2  c.c.  in  all)  added  to  the  dish.  The  solution  having 
been  diluted  to  200  c.c.  and  heated,  5  c.c.  of  ammonium- acetate  solution 
(1  c.c.  =0-31  grm.  ammonium  acetate)  were  very  gradually  added,  and  then 
ammonium  chromate  till  the  odor  of  acetic  acid  had  wholly  disappeared 
(10  c.c.).  After  one  hour  the  supernatant  liquid  was  passed  through  the 
filter  and  the  precipitate  digested  with  hot  water,  which  was  then  cooled; 
thereupon  the  precipitate  itself  was  brought  on  the  filter  and  washed  with 
cold  water  till  silver  nitrate  gave  a  scarcely  perceptible  reaction.  The 
strontium  was  thrown  down  from  the  filtrate  by  ammonia  and  ammonium 
carbonate,  after  concentration  in  presence  of  a  little  nitric  acid,  and  weighed 
as  carbonate;  or  the  carbonate  can  be  redissolved,  precipitated  by  sulphuric 
acid  and  alcohol,  and  weighed  as  sulphate.  The  barium  is  weighed  as  chro- 
mate after  ignition,  the  filter  being  burned  separately. 

XI.  MAGNESIUM. 

PRECIPITATION. 

The  first  precipitation  of  magnesium  is  made  without  special  precau- 
tions in  the  filtrate  from  the  first  calcium-oxalate  separation  (p.  1144)  by 
sodium-ammonium-hydrogen  phosphate  (microcosmic  saltf)  in  indefinite 
decided  excess  and  without  the  great  excess  of  ammonia  usually  prescribed. 
It  is  not  necessary  to  first  remove  ammoniacal  salts  unless  very  little  mag- 
nesium is  present,  and  then  only  in  order  to  hasten  precipitation.  NEU- 
BAUER  |  has  shown  that  precipitation  is  complete  even  in  presence  of  large 

*  Zeitachr.  fur  anal.  Chemie,  xxix,  p.  428,  1890. 

t  The  objection  that  has  been  made  by  one  writer  to  the  use  of  this  salt  instead  of 
disodium-hydrogen  phosphate  is,  so  far  as  our  experience  teaches,  entirely  groundless. 
J  Zeitschr.  fur  angew.  Chemie,  1896,  p.  435. 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK    ANALYSIS.    1147 

quantities  of  salts  of  ammonium,  including  the  oxalate.  He  has,  however, 
also  shown  that  the  composition  of  the  precipitate  is  largely  affected  by 
ammonium  salts,  and  also  by  the  way  in  whicn  the  precipitation  is  made. 
These  points  are  only  of  importance  when  a  single  precipitation  is  to  be 
made  or  in  the  final  of  two  or  more,  as  will  be  discussed  later. 

Hatinum  sulphide  usually  strongly  contaminates  the  separated  phos- 
phate, but  this  matters  not,  as  it  remains  on  the  filter  when  the'  phosphate 
id  redissolved  in  hydrochloric  acid,  of  which  not  more  than  the  amount  really 
needed  should  be  used.  The  solution  thus  obtained  is  united  with  that  of 
tne  residue  from  evaporation  and  ignition  of  the  second  filtrate  from  calcium 
oxalate,  and  is  diluted  if  necessary.  A  few  drops  of  sodium-ammonium- 
phosphate  solution  are  now  added,  and  ammonia  in  slight  excess,  with  con- 
stant stirring  till  the  crystalline  precipitate  has  well  formed.  'The  laree 
excess  of  ammonia  of  0-96  specific  gravity  (one-third  the  original  volume) 
usually  prescribed  has  been  shown  by  GOOCH  and  AUSTIN  *  to  be  quite  unnec- 
essary, in  fact,  disadvantageous. 

XEUBAUER  hi  the  above-cited  paper  has  shown,  and  GOOCH  and  AUSTIN 
(toe.  cit.}  have  confirmed  his  statements,  that  it  is  only  by  working  under 
these  conditions — absence  of  any  large  excess  of  precipitant,  of  ammoniacal 
salts,  and  of  ammonia — that  a  precipitate'of  normal  composition  is  obtain- 
ble.  It  usually  differs  from  the  normal  in  containing  relatively  more  ammo- 
nium and  less  magnesium — for  instance,  an  admixture  of  such  a  molecule  as 
Mg(XH4)4(PO4)2— the  result  being  that  when  ignited  in  the  ordinary  way  too 
much  magnesium  is  found,  because  of  formation  of  some  metaphosphate. 
To  obviate  this  error  NEUBAUER  considers  it  absolutely  necessary  to  blast 
the  precipitate  for  half  an  hour,  and  then  to  repeat  the  blasting  for  a  second 
half  hour  to  see  if  a  constant  weight  has  been  reached.  The  phosphate  is 
then  entirely  pyrophosphate,  which  is  quite  unaffected  by  further  blasting. 
The  intense  heat  has  caused  a  decomposition  of  the  metaphosphate  with 
volatilization  of  P2O6,  as  follows:  2Mg(PO,)2  =  Mg2P,O7  +  P2O5.  NEUBAUER 
worked  with  the  usual  excess  of  ammonia,  and  it  remains  to  be  seen  whether 
by  precipitating  and  working  according  to  GOOCH  and  AUSTIN  the  com- 
position of  the  precipitate  is  always  close  enough  to  the  ideal  MgXH4PO4  to 
obviate  the  necessity  for  blasting. 

From  the  labors  of  XEUBAUER  and  of  GOOCH  and  AUSTIN  it  is  clear  that 
the  common  way  of  adding  the  phosphate  precipitant  to  the  ammoniacal 
solution  of  the  magnesium  salt  is  not  calculated  to  produce  a  precipitate  of 
normal  composition.  The  precipitant  should  be  added  to  the  acid  solution 
of  the  magnesium,  and  ammonia  should  then  be  added  in  slight  excess. 

GOOCH  and  AUSTIN  call  attention  to  a  modification  proposed  some  years 
ago  by  WOLCOTT  GIBBS,*  whereby  the  phosphorus  and  magnesium  salts  ate 
first  boiled  together  in  neutral  solution  for  a  few  minutes  and  to  the  cooled 
solution  ammonia  is  added.  The  results  are  said  to  be  remarkably  exact. 


*  Am.  Journ.  Sci..  4th  Series,  vii,  p.  187,  1899;   Chemical  News,  LXXIX,  pp.  233,  244, 
555,  1899;   Zeitschr.  fur  anorg.  Chemie,  xx,  p.  121,  1899. 
t  Am.  Journ.  Sci.,  3d  Series,  v,  p.  114,  1873. 


1148  APPENDIX   II. 


METHODS  OF  COLLECTING  AND  IGNITING  THE  PRECIPITATE. 

If  the  blast  has  not  to  be  employed,  the  weight  of  the  pyrophosphate  can 
doubtless  be  most  accurately  arrived  at  by  collecting  and  igniting  the  pre- 
cipitate in  a  GCOCH  crucible,  provided  the  asbestos  felt  is  well  constructed 
and  not  of  the  serpentine  variety  so  largely  on  the  market. 

NEUBAUER  ignites  slowly  in  platinum  after  drying,  without  removing 
from  the  paper,  applying  the  blast  only  when  the  carbon  has  been  wholly 
burned  off.* 

Almost  as  exact  are  the  two  modifications  of  the  method  in  use  for  phos- 
phate analyses  at  the  agricultural  experiment  stations  at  Danzig  and  Lisbon, 
described  by  SCHMOEGER  f  and  MASTBAUM.  J  According  to  the  former  the 
precipitate  after  drying  is  detached  from  the  paper  and  placed  in  a  platinum 
crucible,  followed  by  the  folded  filter.  To  the  covered  crucible  the  full  flame 
of  a  burner  is  applied,  and  after  a  short  time  the  burning  off  of  the  carbon  is 
accomplished  with  the  crucible  open.  A  short  blasting  follows.  In  a  num- 
ber of  experiments  on  quantities  ranging  from  0-06  to  0-28  grm.  of  pyro- 
phosphate the  results  were,  with  a  few  exceptions,  naturally  lower  than 
those  obtained  on  duplicates  by  the  ordinary  method  of  igniting,  but  only 
by  0-0013  grm.  in  maximum. 

MASTBAUM,  to  shorten  time,  applies  the  full  flame  to  the  moist  precipi- 
tate wrapped  in  its  filter.  Later,  when  most  of  the  carbon  is  burned  off,  he 
moistens  the  residue  with  two  or  three  drops  of  strong  nitric  acid,  evaporates 
this  carefully,  heats  with  full  burner  for  a  few  minutes,  then  blasts  for  half  a 
minute.  He  describes  the  results  as  irreproachable.  In  this  laboratory 
only  the  MASTBAUM  modification  has  been  tried,  and  it  certainly  seems  to  be 
satisfactory  when  the  extreme  of  accuracy  is  not  required. 

At  one  time  the  procedure  first  recommended  by  ULBRICHT,  later  by 
BROOCKMANN,  and  also  by  L.  L.  DE  KONINCK,  was  used.  It  consists  in  dis- 
solving the  ammonium-magnesium  phosphate  off  the  filter  with  nitric  acid, 
collecting  the  filtrate  in  a  weighed  crucible,  evaporating  the  contents  to  dry- 
ness,  §  and  subsequently  igniting,  the  product  being  presumably  pyrophos- 
phate. But  it  was  soon  observed  that  the  ignited  salt,  especially  when  large 
in  amount,  does  not  always  dissolve  completely  in  hydrochloric  acid,  but 
that  sometimes  a  white  residue  is  left  in  light  lumps  which  appears  to  be 
quite  insoluble  in  acids.  This  residue  contains  no  silica,  but  only  the  con- 
stituents of  a  magnesian  phosphate,  and  it  may  be  a  peculiar  metaphosphate. 
Whether  its  appearance  is  due  to  an  abnormal  composition  of  the  original 
magnesian  precipitate  or  to  conceivable  change  during  evaporation  in  the  . 
crucible  with  nitric  acid  remains  to  be  determined.  Until  this  is  done  the 
employment  of  this  method  of  igniting  is  not  to  be  recommended. 

*  Zeitschr.  fur  anal.  Chentie,  xxxin,  p.  362,  1894. 

t  Ibid.,  xxxvn,  p.   308,   1898. 

t  Ibid.,  p.  581,  1898. 

§  A  pink  color  of  varying  intensity  almost  invariably  becomes  apparen'  as  the  mass 
approaches  dryness,  a  most  delicate  test  for  the  traces  of  manganese  which  always  escape 
precipitation  by  ammonium  sulphide  or  bromine. 


SOME    PRINCIPLES   AND   METHODS    OF    ROCK  ANALYSIS.    1149 


CONTAMINATION  BY  AND  REMOVAL  OF  BARIUM  AND  CALCIUM. 

Barium  phosphate  will  not  contaminate  the  second  magnesian  precipi- 
tate unless  there  are  notable  amounts  of  barium  in  the  rock,  in  which  case  it 
must  be  removed  by  sulphuric  acid  prior  to  the  final  precipitation  of  the 
magnesium  Calcium,  however,  is  probably  never  absent,  and  has  to  be 
estimated  and  allowed  for  as  follows : 

To  the  ignited  pyrophosphate,  dissolved  in  but  slight  excess  of  hydro- 
chloric acid,  ammonia  is  added  to  alkalinity,  and  then  acetic  acid,  drop 
by  drop,  till  the  solution,  which  should  not  be  hot,  clears.  It  now  and  then 
happens  that  a  little  flocculent  matter  fails  to  dissolve.  This  is  to  be  re- 
moved, ignited,  and  subtracted  from  the  original  weight.  It  is  likely  to 
consist,  in  great  part  or  wholly,  of  phosphates  of  iron  or  manganese,  or  both, 
and  shows  often  a  reddish  color  on  ignition.  If  an  excess  of  acetic  acid  has 
been  used,  this  is  cautiously  removed  by  ammonia.  Then  a  drop  or  two  of 
solution  of  ammonium  oxalate  is  added,  and  the  small  beaker  is  set  aside 
for  twelve  hours  if  necessary.  Almost  invariably  a  small  precipitate  soon 
shows  itself,  which  if  fine-grained  and  non-adherent  to  the  glass  may  be 
regarded  as  pure  calcium  oxalate ;  otherwise  it  contains,  or  may  largely  con- 
sist of,  magnesium  oxalate.  It  is  in  that  case  to  be  collected,  ignited, 
redissolved,  and  reprecipitated.  Its  final  weight,  averaging  perhaps  one- 
half  milligramme,  is  to  be  added  to  that  of  the  lime  already  found,  and 
subtracted  as  tricalcium  phosphate  from  that  of  the  magnesium  pyrophos- 
phate in  order  to  arrive  at  the  true  figure  for  magnesia.  This  separation,  to 
be  satisfactory,  requires  great  care. 

XII.     TITANIUM. 

COLORIMETRIC  ESTIMATION  WITH  HYDROGEN  PEROXIDE  (WfiLLER'S  METHOD).* 

The  method  consists  in  comparing  the  color  of  a  known  bulk  of  solution 
to  be  tested  with  that  of  a  standard  solution  of  titanium  sulphate,  both 
having  been  fully  oxidized  by  hydrogen  peroxide.  The  strength  of  the  per- 
oxide should  be  approximately  measured  by  titration  with  permanganate 
on  opening  a  fresh  bottle,  and  again  after  a  few  weeks,  otherwise  very  serious 
error  may  arise  through  its  deterioration. 

Mere  traces  of  hydrofluoric  acid,  either  in  the  peroxide  or  the  titanium 
solution,  render  this  method  inexact  ,f  hence  care  should  be  exercised  as 
to  the  character  of  the  peroxide,  which,  as  sold  in  the  market,  often  contains 
fluorine. 

DUNNINGTONJ  has  pointed  out  the  necessity  for  the  presence  of  at  least 
5  per  cent,  of  sulphuric  acid  in  solutions  which  are  to  be  thus  tested  for  tita- 
nium, in  order,  as  he  concludes,  to  prevent  partial  reversion  to  metatitanic 

*  Ber.  deutsch.  chem.  Gesell..  xv,  p.  2593,  1882. 

t  HILLEBRAXD,  Journ.  Am.  Chem.  Soc.,  xvn,  p.  718,  1895;    Chemical  News,  LXXH, 
p.  158-  1895:  Butt.  U.  S.  Geol.  Survey,  No.  167,  p.  56. 
J  Journ.  Am.  Chem.  Soc.,  xin,  p.  210,  1891. 


1150  APPENDIX   II. 

acid,  which  does  not  give  a  color  with  hydrogen  peroxide.  The  standard 
solution  of  titanium  sulphate,  holding  conveniently  about  1  centigramme  TiO2 
in  10  c.c.,  equivalent  to  1  per  cent,  of  TiO2  in  1  grm.  of  rock,  contains,  there- 
fore, 5  per  cent,  or  more  of  sulphuric  acid.  Of  this,  10  c.c.  are  mixed  with 
a  sufficiency  of  hydrogen  peroxide  (2  c.c.  of  most  commercial  brands  is 
ample)  and  diluted  to  100  c.c.  in  a  measuring  flask. 

Titanium  can  be  estimated,  as  a  rule,  most  conveniently  in  the  solution 
which  has  served  for  the  tit-ration  of  total  iron  (p.  1140).  This,  having  been 
evaporated,  if  necessary,  to  less  than  100  c.c.  is  to  be  fully  oxidized  with 
hydrogen  peroxide,  and  if  the  color  is  less  intense  than  that  of  the  standard, 
is  made  up  to  100  c.c.  with  dilute  sulphuric  acid  in  a  measuring  flask  and 
mixed;  otherwise,  in  a  flask  of  sufficient  size  to  insure  that  its  color  shall  be 
less  intense.  One  of  the  rectangular  'glasses  described  below  being  filled 
with  the  solution  to  be  tested,  10  c.c.  of  the  diluted  standard  are  run  into 
the  other  from  a  burette,  and  water  is  added  from  a  second  burette  until 
there  is  no  distinction  as  to  color.  A  second  and  a  third  portion  of  the  stand- 
ard can  be  run  in  and  diluted  and  the  mean  of  several  determinations  struck, 
when  a  simple  calculation  gives  the  percentage  of  TiO2  in  the  rock. 

If  the  convenient  but  expensive  SOLEIL-DUBOSCQ  colorimeter  is  used,  or  the 
simple  NESSLER  tubes,  it  is  of  course  unnecessary  to  dilute  the  rock  solution 
to  the  extent  above  required,  should  it  be  stronger  than  the  standard.  Ex- 
perience has  shown,  however,  that  differences  cannot  be  sharply  estimated 
in  strongly  colored  solutions,  and  that  the  results  are  much  more  satisfactory 
when  the  color  intensity  is  not  much,  if  any,  greater  than  that  given  by  a 
standard  of  the  above  concentration.  For  the  percentages  of  titanium 
found  in  rocks,  clays,  and  soils,  usually  under  1  per  cent.,  but  rising  to  2  or 
even  3  per  cent,  or  more  occasionally, the  colorimeter  method  gives  results 
which  are  fully  equal  to  those  of  the  best  gravimetric  method,  besides  being 
a  great  time -saver.  The  error  introduced  by  iron,  in  consequence  of  the 
yellowish  color  of  its  sulphate  solution,  is  practically  negligible  unless  its 
percentage  is  very  high;  then  either  the  iron  must  be  removed  prior  to  making 
the  color  test,  or  correction  should  be  applied  for  known  amounts  of  ferric 
sulphate  in  solutions  of  the  requisite  dilution. 

The  exact  correction  to  be  applied  in  such  cases  is  difficult  of  determina- 
tion because  of  the  impossibility  of  matching  the  colors  of  titanium- peroxide 
solutions  with  those  of  ferric  sulphate;  but  tests  made  go  to  show  that  the 
coloring  effect  of  0-1  grm.  of  Fe2O3  in  100  c.c.  5  per  cent,  sulphuric-acid 
solution  is  about  equal  to  0-2  mgrm.  of  TiO2  in  100  c.c.  when  oxidized  by 
hydrogen  peroxide.  This  amounts  to  a  correction  of  only  0  •  02  per  cent,  on 
1  grm.  of  rock  containing  the  unusual  amounts  of  10  per  cent.  Fe2O3.  It 
will  be  more  satisfactory,  when  much  iron  is  present,  to  remove  this  as  de- 
scribed on  page  1153  and  to  colorimetrically  estimate  the  uranium  thus  froed 
from  iron! 

ALTERNATIVE  MODE  OF  PREPARING  THE  TEST  SOLUTION. 

As  said  above,  and  on  p.  1140,  the  solution  that  has  been  used  for  volu- 
metric estimation  of  total  iron  can  most  conveniently  be  used  for  the  colori- 


SOME    PRINCIPLES   AND    METHODS    OF    ROCK    ANALYSIS.    1151 

metric  determination  of  titanium,  but  if  desired  this  can,  of  course,  be  made 
on  some  other  portion  of  rock  powder.  At  one  time  it  was  the  practice  in 
this  laboratory  to  combine  it  with  the  determination  of  barium,  as  described  in 
Bulletin  148  of  the  United  States  Geological  Survey,  by  decomposing  th*: 
powder  by  sulphuric  and  hydrofluoric  acids,*  expelling  the  latter  by  repeated 
evaporations  with  sulphuric  acid,  taking  up  with  dilute  sulphuric  acid,f  fil- 
tering from  barium  sulphate,  etc.,  and  estimating  the  titanium  colorimetric- 
ally  in  the  filtrate.  The  expulsion  of  fluorine  must  be  thorough,  or  else  the 
titanium  result  will  be  low,  as  already  stated  (p.  1149),  and  it  is  not  always  easy 
to  effect  this  complete  removal,  though  the  time  required  to  do  so  seems  to  be 
in  no  slight  degree  dependent  on  the  nature  of  the  fluorides  to  be  decom- 
posed. Long  after  every  trace  of  fluorine  seems  to  be  gone,  the  formation 
of  a  crust  on  the  evaporating  solution  sometimes  allows  an  accumulation  of 
enough  hydrofluoric-acid  gas  to  become  plainly  manifest  to  the  smell  on 
breaking  the  crust. 


THE  COLORIMETRIC  APPARATUS  AND  ITS  USE. 

The  glasses  G  (Fig.  12)  may  be  of  square  or  rectangular  section,  8  to 
12  cm.  high  and  3  to  3£  cm.  inside  measurement  between  those  sides  through 
which  the  liquid  is  to,  be  observed. i  These  sides  should,  of  course,  be  exactly 
parallel;  the  others  need  not  be,  but  should  be  blackened  externally.  In 
order  to  further  exclude  the  effect  of  side  light  in  this  and  other  similar  methods 
(chromium,  for  instance,  p.  1161),  it  is  very  convenient  to  have  a  simple,  light 
box  (B,  Fig.  12)  that  can  be  easily  held  in  one  hand,  about  35  cm.  long  and 
12  cm.  square,  stained  black  inside  and  out,  and  with  one  'end  closed  by  a 
piece  of  ground  glass  W,  the  other  open.  For  a  space  equal  to  the  width 
of  the  glasses  the  cover  is  removed  at  the  top  next  the  glass  end  to  permit 
of  the  insertion  of  the  glasses  side  by  side  in  such  a  way  that  no  light  shall 
penetrate  around  their  sides  or  between  them.  Immediately  back  of  the 

*  It  is  to  be  borne  in  mind  that  evaporation  with  hydrofluoric  acid  alone  results  in 
loss  of  titanium  by  volatilization,  but  that  there  is  no  loss  if  excess  of  sulphuric  acid  is 
also  present. 

t  With  acid  rocks  solution  is  very  complete,  and  it  can  be  made  nearly  so  with  the 
most  basic  by  transference  to  a  small  beaker  and  gentle  boiling.  The  residue  thus  ob- 
tained may  contain,  besides  barium  sulphate,  a  little  calcium  sulphate,  zircon,  andalu- 
site.  topaz,  and  possibly  a  trace  of  titanium  in  some  form.  It  is  therefore  to  be  thor- 
oughly fused  with  sodium  carbonate,  leached  with  water,  fused  with  potassium  bisul- 
phate,  dissolved  in  dilute  sulphuric  acid,  filtered,  and  the  filtrate  added  to  the  main  one. 
The  insoluble  matter  will  now  be  chiefly  barium  sulphate,  for  the  furthei  treatment  of 
which,  see  p.  1155. 

J  The  allowable  error  in  distance  between  the  corresponding  pairs  of  sides  of  the  two 
glasses  should  not  in  any  case  exceed  1  per  cent.  Unfortunately  there  seems  to  be  a 
disinclination  or  inability  on  the  part  of  dealers  in  this  country  to  furnish  glasses  fulfilling 
this  requirement,  and  held  together  by  a  durable  cement  which  shall  be  proof  acain?t 
dilute  sulphuric  acid.  Cadada  balsam  answers  well  for  a  time,  but  sooner  or  later  it 
cracks,  leaks  then  appear,  and  the  sides  soon  drop  off.  It  is,  however,  but  a  simple  matter 
to  cement  them  on  again. 

A  pair  of  entirely  satisfactory  glasbes  can  be  made  from  a  couple  of  square  or  rectan- 
gular 3  to  4  ounce  bottles  by  cutting  off  one  pair  of  sides  from  each  and  grinding  down 
till  the  calipers  show  that  agreement  is  perfect.  The  tops  are  then  to  be  sawed  off  and 
pieces  of  plate  glass  cemented  on  the  sides. 


1152 


APPENDIX   II. 


glasses  is  a  partition  P,  with  openings  of  appropriate  size  cut  in  it.  A  stiffly 
sliding  black  cardboard  shutter  S  is  movable  up  and  down  immediately 
back  of  the  partition,  so  that  all  light  can  be  cut  off  except  that  which  comes 
through  the  liquid. 

Precautions  of  this  kind  are  necessary  if  accurate  results  are  to  be  counted 
on.  Except  for  mere  traces,  this  combination  of  glasses  and  darkened  box 
insures  greater  accuracy  and  rapidity  of  work  than  NESSLER  tubes,  and  is 
preferable  likewise,  so  far  as  the  writer's  experience  goes,  to  expensive  instru- 


FIG.  12. — Apparatus  for  colorimetric  determinations,  in  different  aspects.  G,  one  of 
two  glasses  of  square  or  rectangular  section,  8  to  12  cm.  high  and  3  to  3£  cm.  inside 
measurement  between  those  sides  through  which  the  liquid  is  to  be  observed.  The 
other  sides  are  blackened  on  the  outside.  B,  rectangular  box  about  35  cm.  long 
and  12  cm.  square,  stained  black  inside  and  out,  one  end  closed  by  a  ground-glass 
window,  W,  the  other  open,  and  a  portion  of  the  top  removed.  P,  blackened  parti- 
tion, with  openings  corresponding  to  the  interior  dimensions  of  the  glasses  when  in 
position.  S,  blackened  cardboard  shutter  sliding  stiffly  up  and  down  between  parti- 
tion and  glasses,  so  as  to  shut  off  all  light  above  the  lowest  surface  of  the  liquid  in 
the  glasses. 

ments  like  the  colorimeter  of  SOLEIL-DUBOSCQ,  etc.  In  making  the  color 
comparisons  the  box  is  best  held  close  to  a  window,  so  as  to  get  a  full,  strong 
light.  Daylight  is  far  preferable  to  artificial  light. 

GOOCH'S  GRAVIMETRIC  METHOD. 

When  titanium  is  present  in  excess  of  4  to  5  per  cent,  and  whenever  for 
any  reason  it  is  desired  to  employ  a  gravimetric  method,  among  the  few 
that  have  been  thoroughly  tested  that  of  Dr.  GOOCH  *  is  unequaled.  With 

*  Proc.  Am.  Acad.  Arts  and  Sci.,  n.  s.,  xn,  p.  435;  Bull.  U.  S.  Geol.  Survey,  No.  27. 
p.  16,  1886;  Chemical  News,  LII,  pp.  55  and  68,  1885. 


SOME   PRINCIPLES   AND    METHODS   OF   ROCK    ANALYSIS.    1153 

one  or  two  minor  modifications  introduced  by  Dr.  T.  M.  CHATARD,*  it  is 
as  follows : 

.  Any  solution  of  the  rock  freed  from  silica  can  be  used,  and  the  first  step 
is  to  remove  the  iron.  This  is  best  done,  after  adding  tartaric  acid  and  re- 
ducing the  iron  by  means  of  hydrogen  sulphide  to  the  ferrous  condition,  by 
rendering  the  solution  ammoniacal  and  introducing  more  hydrogen  sulphide. 
If  the  iron  is  not  thus  reduced  before  precipitation,  titanium  will  be  in  part 
thrown  down  also.f  The  amount  of  tartaric  acid  is  to  be  gauged  according 
to  the  combined  weights  of  the  oxides  to  be  held  by  it  in  solution,  and  three 
times  this  weight  is  ample.  After  removing  the  iron  sulphide  by  filtration — • 
little  washing  suffices,  because  of  the  relatively  small  amount  of  titanium 
commonly  present — the  tartaric  acid  is  destroyed  as  follows: 

Potassium  permanganate  to  the  extent  of  two  and  one-half  tunes  the 
weight  of  the  tartaric  acid  used  is  made  into  a  strong  solution,  and  to  the 
ammoniacal  filtrate  from  the  iron  sulphide  enough  sulphuric  acid  is  intro- 
duced to  leave  some  excess  after  all  the  permanganate  has  been  reduced. 
After  expulsion  of  hydrogen  sulphide  by  boiling,  the  permanganate  is  added 
gradually  to  the  hot  solution  contained  in  a  large  beaker  or  flask.  A  vigor- 
ous reaction  ensues.  When  a  permanent  brown  precipitate  of  manganic 
hydrate  appears  the  tartaric  acid  has  been  fully  broken  up,  and  the  precipi- 
tated manganese  is  to  be  redissolved  by  a  few  drops  of  ammonium-bisulphite 
or  of  sulphurous-acid  solution. 

.  Ammonia  is  then  added  in  slight  excess,  followed  at  once  by  acetic 
acid  in  considerable  excess,  and  the  boiling  is  continued  for  a  few  minutes. 
Thereby  the  titanium  is  freed  from  most  of  the  alumina,  and  from  lime  and 
magnesia  if  they  had  not  been  earlier  removed,  also  from  most  of  the  manga- 
nese introduced.  The  precipitate  is  filtered  and  washed  with  water  con- 
taining acetic  and  sulphurous  acids,  then  ignited,  fused  thoroughly  with 
sodium  carbonate,  and  leached  with  water  to  remove  phosphoric  acid  and 
most  of  the  remaining  alumina.  The  residue  is  again  ignited  and  fused 
with  sodium  carbonate.  To  the  cooled  melt  in  the  crucible  strong  sulphuric 
acid  is  to  be  added,  wherein  it  dissolves  readily  by  aid  of  gentle  heat.  This 
solution  is  to  be  poured  into  a  small  volume  of  cold  water  and  the  platinum 
it  contains  precipitated  by  hydrogen  sulphide  at  or  near  boiling  tempera- 
ture. After  filtering  and  cooling,  ammonia  is  added  till  the  titanium  is  just 
precipitated,  and  a  measured  volume,  containing  a  known  weight  of  absolute 
sulphuric  acid,  is  then  added— just  enough  to  redissolve  the  precipitate. 
The  solution  is  then  made  up  with  acetic  acid  in  such  amount  that  the  final 
bulk  shall  contain  from  7  to  11  per  cent,  of  absolute  acid,  and  then  enough 
solid  sodium  acetate  is  stirred  in  to  more  than  take  up  the  sulphuric  acid 
introduced.  Upon  rapidly  bringing  the  liquid  to  ebullition  the  titanium 
is  precipitated  in  flocculent  and  easily  filterable  condition,  and  the  precipi- 
tation is  complete  after  a  minute's  boiling,  provided  all  the  prescribed  con- 
ditions have  been  followed  and  zirconium  is  absent. 

*  Am.  Chem.  Journ.,  xra,  p.  106, 1891;  Butt.  U.  S.  Geol.  Survey,  No.  78,  Pr.87;_ 
col  News,  Lxm,  p.  267,  1891. 

t  CATHREIN,  Zeitschr.  fur  Kryst.,  vi,  p.  243,  1882;  vii,  p.  250,  1883. 


1154  APPENDIX   II. 

The  precipitate  is  washed  first  with  acetic  acid  of  7  per  cent,  strength 
and  then  with  hot  water.  After  15  to  20  minutes'  ignition  over  a  good  burner 
it  is  in  condition  for  weighing,  and  will  lose  no  more  weight  over  the  blast- 
lamp.  For  large  amounts  of  titanium  a  repetition  of  the  sodium-carbon- 
ate fusion,  etc.,  should  be  made.  The  actual  carrying  out  of  all  these  oper- 
ations, when  once  the  method  is  understood,  requires  much  less  time  than 
the  detailed  description  would  indicate. 

GOOCH'S   METHOD   NOT   DIRECTLY    APPLICABLE    TO   ROCKS    CONTAINING 
ZIRCONIUM. 

Prior  to  the  adoption  of  the  colorimetric  method,  Dr.  GOOCH'S  was  invari- 
ably used  in  this  laboratory.  Occasional  inability  to  secure  clean  and  com- 
plete precipitation  by  it  was  experienced,  especially  with  a  certain  series 
of  rocks  rather  poor  in  titanium.  Long  research  showed  the  difficulty  to 
be  due  to  the  presence  of  zirconium,  which  acts  as  a  marked  preventive  of 
the  precipitation  of  titanium  by  boiling  in  an  acetic-acid  solution  under  the 
conditions  of  the  GOOCH  method. 

The  above  rocks  were  found  to  contain  up  to  0-2  per  cent,  of  ZrO2,  and 
this  amount  was  able  to  prevent  precipitation  of  0-3  per  cent,  of  TiO2.  The 
titanium  which  came  down  in  excess  of  this  amount  did  not  settle  out  in 
flocculent  condition,  as  happens  when  zirconium  is  not  present,  and  it  was 
difficult  to  filter.  After  the  removal  of  the  zirconium  in  the  manner  to  be 
hereafter  described  (p.  1156),  however,  no  difficulty  was  experienced  in  pre- 
cipitating all  the  titanium  with  the  usual  ease. 

SUPERIORITY  OF  THE  COLORIMETRIC  AND  GOOCH  METHODS  OVER  THE 
OLDER  ONES. 

In  view  of  the  good  results  obtainable  by  the  colorimeter  method  in  all 
cases  and  by  the  GOOCH  method  in  the  absence  of  zirconium,  it  is  incom- 
prehensible that  the  old  method  of  precipitation  by  many  hours'  boiling 
in  a  nearly  neutral  sulphate  solution  in  presence  of  sulphurous  acid  should 
still  find  adherents  in  any  part  of  the  world. 

Attention  has  been  directed  (p.  1142)  to  the  error  resulting  from  attempt- 
ing to  separate  aluminium  from  titanium  by  either  fused  or  dissolved  sodium 
hydroxide. 

BASKERVILLE'S    METHOD. 

BASKERVILLE  *  has  proposed  the  separation  of  titanium  from  iron  and 
aluminium  by  boiling  the  neutralized  solution  of  the  chlorides  for  a  few  min- 
utes in  presence  of  sulphurous  acid.  The  test  separations  as  given  by  him 
are  sharp,  and  a  single  precipitation  is  said  to  suffice,  the  titanium  being  free 
from  iron  and  easily  filterable.  This  last  statement  and  the  ready  precipi- 
tability  are  fully  confirmed  by  the  experiments  of  the  writer  on  titaniferous 
iron  ores,  but,  although  the  titanium  is  completely  thrown  out,  it  carries 
with  it  a  little  iron,  for  instance,  about  0-25  per  cent.  Fe2O3  with  8  to  10  per 

*  Journ.  Am.  Chem.  Soc.,  xvi,  p.  427,  1894. 


SOME    PRINCIPLES  AND   METHODS   OF   ROCK  ANALYSIS.    1155 

cent.  TiO-j.  Zirconium  would  probably  be  likewise  precipitated  (see  p.  1158) 
and  phosphorus  perhaps  also,  but  this  last  point  has  not  been  investigated, 
neither  has  the  applicability  of  the  method  to  aluminous  rocks  been  tested. 

XIII.    BARIUM  (ZIRCONIUM,  TOTAL  SULPHUR). 

Reasons  for  Estimating  Barium  in  a  Separate  Portion  of  Rock  Powder. — It 
has  been  said  above  (p.  1 145)  that  only  in  very  exceptional  cases  will  barium 
be  found  with  the  calcium  and  strontium  after  two,  or  possibly  three,  precipi- 
tations of  the  latter  as  oxalate,  since  it  passes  into  the  filtrates  with  the  mag- 
nesium, whence  it  may  be  obtained  as  sulphate  after  removal  of  ammoniacal 
salts.  Addition  of  some  alcohol  insures  also  the  recovery  of  traces  of  stron- 
tium if  the  rocks  are  very  rich  in  it.  But  it  is  unsafe  to  regard  the  amount 
thus  separated  from  the  magnesium  as  representing  the  total  amount  of 
barium  in  the  rock.  It  will  almost  always  be  found  lower  than  the  truth, 
probably  for  the  reason  that  there  are  opportunities  during  the  analysis  for 
slight  losses.  It  is  best  to  estimate  it  in  a  separate  2-grm.  portion,  which 
may  also  serve  with  advantage  for  the  estimation  of  zirconium  and  total 
sulphur. 

Modes  of  Attack  and  Subsequent  Treatment. — If  zirconium  and  sulphur  are 
not  to  be  looked  for,  the  simplest  procedure  is  to  decompose  the  powder  by 
sulphuric  and  hydrofluoric  acids  (see  p.  1151,  under  Titanium),  and  to  com- 
plete the  purification  of  the  barium  sulphate  thus  obtained  in  the  manner 
described  in  the  third  paragraph  below. 

If  zirconium  and  sulphur  are  both  to  be  likewise  determined,  decomposi- 
tion is  effected  by  fusing  over  the  BUNSEN  flame  and  then  over  the  blast 
with  sulphur-free  sodium  carbonate  and  insufficient  nitre  to  injure  the  cruci- 
ble, first  fitting  the  latter  snugly  into  a  hole  in  asbestos  board  (LUNGE)  to 
prevent  access  of  sulphur  from  the  gas-flame.  In  case  sulphur  is  not  to  be 
regarded,  the  nitre  and  asbestos  board  are  omitted.  After  thorough  disin- 
tegration of  the  melt  in  water,  to  which  a  drop  or  two  of  methyl-  or  ethyl- 
alcohol  has  been  added  for  the  purpose  of  reducing  manganese,  the  solution 
is  filtered  and  the  residue  washed  with  a  very  dilute  solution  of  sodium  car- 
bonate free  from  bicarbonate.  This  is  to  prevent  turbid  washings.  A  yel- 
low colof  in  the  filtrate  indicates  chromium. 

For  the  further  treatment  of  the  filtrate  see  Sulphur,  p.  1184,  and  Chro- 
mium (colorimetric  method),  p.  1161. 

The  residue  is  dissolved  in  quite  dilute  warm  sulphuric  acid  (stronger 
acid  may  be  used  if  barium  only  is  sought)  and  filtered  through  the  original 
filter.  This,  with  its  contents,  is  ignited,  evaporated  with  hydrofluoric  and 
sulphuric  acids,  and  taken  up  with  hot  dilute  sulphuric  acid.  The  filtrate, 
added  to  the  former  one,  now  contains  all  the  zirconium  (see  pp.  1156  and 
1157  for  its  further  treatment).  The  residue  contains  all  the  barium,  besides 
some  of  the  strontium,  and  perhaps  a  good  deal  of  calcium.  It  is  fused  with 
sodium  carbonate,  leached  with  water,  the  residue  dissolved  off  the  filter  by 
a  few  drops  of  hydrochloric  acid,  from  which  solution  the  barium  is  thrown 
out  by  a  large  excess  of  sulphuric  acid.  A  single  solution  of  the  barium  sul- 


1156  APPENDIX   II. 

phate  in  concentrated  sulphuric  acid  and  reprecipitation  by  water  suffices 
to  remove  traces  of  calcium  which  might  contaminate  it  if  the  rock  was  one 
rich  in  calcium,  and  even  strontium  is  seldom  retained  by  it  in  quantity 
sufficient  to  give  concern.  Should  this  be  the  case,  however,  which  will 
occur  when  the  SrO  and  BaO  are  together  in  the  rock  in,  roughly  speaking, 
0-2  and  0-4  per  cent.,  respectively,  ftie  only  satisfactory  way  is  to  convert 
the  sulphates  into  chlorides  and  to  apply  to  the  mixture  the  ammonium- 
chromate  method  of  separation  (p.  1146). 

Barium  and  srontium  sulphates  can  be  brought  into  a  condition  for  testing 
spectroscopically  by  reducing  for  a  very  few  moments  the  whole  or  part  of 
the  precipitate  on  a  platinum  wire  in  the  luminous  tip  of  a  BUNSEN  burner, 
and  then  moistening  with  hydrochloric  acid.  This  should  be  known  to 
every  one,  but  probably  is  not. 

The  procedure  outlined  in  the  foregoing  paragraphs  for  the  estimation 
of  calcium,  stronium,  and  barium  in  silicate  rocks  is  the  one  which  long  expe- 
rience has  shown  to  be  best  adapted  for  securing  the  most  satisfactory  results 
with  a  minimum  expenditure  of  time.*  Even  where  no  attempt  is  made 
to  separate  contaminating  traces  of  SrO  and  BaO  one  from  the  other,  the 
error  is  usually  of  no  great  consequence,  for  an  absolute  error  of  25  per  cent., 
even,  in  a  substance  constituting  only  one  or  two  tenths  per  cent,  of  a  rock, 
is  ordinarily  of  small  moment  compared  with  the  ability  to  certify  to  its 
presence  with  approximate  correctness. 

With  such  small  amounts  of  barium  as  are  usually  found  in  rocks  it  is 
doubtful  if  MAR'S  f  method  for  the  separation  of  barium  from  calcium  and 
magnesium,  by  the  solvent  action  of  concentrated  hydrochloric  acid  mixed 
with  10  per  cent,  of  ether  on  the  chlorides,  could  be  conveniently  applied 
here,  although  for  larger  amounts  the  method  would  seem  to  be  accurate 
and  easily  executed.  Moreover,  it  would  probably  not  entirely  remove 
contaminating  strontium,  and  hence  offers  no  advantage. 

XIV.    ZIRCONIUM. 

This  element  is  rarely  looked  for  by  chemists,  though  shown  by  the  micro- 
scope to  be  one  of  the  most  constant  rock  constituents,  usually  in  the  form 
of  zircon,  in  which  occurrence  its  amount  can  be  approximately  judged  of 
and  a  chemical  test  rendered  almost  unnecessary;  but  sometimes  it  occurs 
in  other  minerals,  and  is  then  unrecognizable  under  the  microscope.  It 
may  rarely  be  present  up  to  a  few  tenths  of  1  per  cent,  of  the  rock. 

AUTHOR'S  METHOD. 

For  its  detection  and  estimation  in  such  cases,  or  whenever  a  search  for 
it  seems  called  for,  the  following  procedure,  based  on  a  method  by  G.  H. 
BAILEY,J  has  been  devised,  which  serves,  when  carried  out  with  care,  to 

*  For  details  consult  W.  F.  HILLEBRAND,  Journ.  Am.  Chem.  Soc.,  xn,  p.  83,  1894; 
Chemical  News,  i,xix,  p.  147,  1894. 

t  Am.  Journ.  Sci..  3d  Series,  XLIII,  p.  521,  1892. 
t  Journ.  Chem.  Soc.,  XLIX,  pp.  149,  481,  1886. 


SOME   PRINCIPLES    AND   METHODS   OF   ROCK   ANALYSIS.    1157 

detect  with  certainty  the  merest  trace — 0-02  per  cent.,  for  instance — in  1 
grm. 

The  preliminary  treatment  of  the  rock  power  has  been  fully  given  under 
Barium  (p.  1155),  where  the  separation  from  barium  has  been  described  and 
also  the  concentration  of  the  zirconia  in  a  small  amount  of  very  dilute  sul- 
phuric solution.  This  should  probably  not  contain  much  above  1  per  cent, 
of  sulphuric  acid,  though  the  actually  permissible  limit  has  not  been  estab- 
lished. To  the  solution,  which  should  be  in  a  small  flask,  is  now  added 
hydrogen  peroxide  to  oxidize  the  titanium,  and  then  a  few  drops  of  a  soluble 
orthophosphate  solution.  The  flask  is  set  aside  in  the  cold  for  twenty-four 
to  forty-eight  hours.  If  the  color  bleaches  after  a  time,  more  hydrogen 
peroxide  should  be  added.  Under  these  circumstances  the  zirconium  is 
thrown  out  as  phosphate  and  collects  as  a  flocculent  precipitate,  which  at 
this  stage  is  not  always  pure.  No  matter  how  small  or  insignificant,  it  is 
collected  on  a  filter,  ignited,  fused  with  sodium  carbonate,  leached  with 
water,  the  filter  again  ignited,  fused  with  very  little  acid  potassium  sulphate, 
brought  into  solution  in  hot  water  with  a  few  drops  of  dilute  sulphuric  acid, 
poured  into  a  flask  of  about  20  c.c.  capacity,  a  few  drops  of  hydrogen  per- 
oxide and  of  sodium  phosphate  added,  and  the  flask  skt  aside.  Titanium  is 
now  almost  never  present,  and  the  zirconium  appears  after  a  time  as  a  white 
flocculent  precipitate,  which  can  be  collected  and  weighed  as  phosphate. 
For  the  small  amounts  usually  met  with  it  is  safe  to  assume  that  it  contains 
50  per  cent,  of  ZrOf(51-8  by  theory).  If  the  amount  is  rather  large,  it  may 
be  fused  with  sodium  carbonate,  leached,  ignited,  fused  with  acid  potassium 
sulphate,  reprecipitated  by  ammonia,  and  weighed  as  ZrOj.  Certainty  as 
to  its  identity  can  be  had  by  again  bringing  it  into  solution,  precipitating 
by  ammonia,  dissolving  in  hydrochloric  acid,  evaporating  to  a  drop  or  two, 
and  testing  with  turmeric  paper  or  by  a  microchemical  reaction.  With  the 
very  smallest  amounts  no  color  can  be  obtained  by  this  turmeric-paper  test,, 
which,  however,  responds  readily  to  as  little  as  1  mgrm.  of  dioxide,  and 
with  proper  care  for  as  small  an  amount  as  0-3  mgrm.  (Dr.  H.  N.  STOKES). 
No  element  other  than  thorium  is  ever  likely  to  contaminate  the  zirconium 
thus  precipitated. 

In  BAILEY'S  experiments  the  precipitation  was  not  made  by  addition  of 
a  phosphate,  but  is  said  to  be  due  solely  to  the  hydrogen  peroxide,  the  pre- 
cipitate being  a  hydrated  peroxide,  Zr2O5,  or  ZrO2.*  My  own  efforts  to 
secure  a  precipitate  in  acid  solutions  of  zirconium  sulphate  by  hydrogen 
peroxide  alone  were  unsuccessful,  perhaps  for  lack  of  a  sufficiently  strong 
peroxide.  The  ability  to  obtain  the  zirconium  free  from  phosphoric  acid 
would  certainly  be  a  great  improvement  on  the  method  described  above. 

Were  it  not  for  the  necessity  of  working  in  a  weakly  acid  solution,  the 
separation  of  zirconium  could  be  made  in  the  same  portion  in  which  the  tita- 
nium is  colorimetrically  determined. 


*  BAILEY,  Chemical  News,  LX.  p.  6.  1889. 


1158  APPENDIX   II. 


OTHER  METHODS  OF  SEPARATING  ZIRCONIUM. 

STREIT  and  FRANZ  *  claim  to  secure  complete  separation  of  titanium  from 
iron  and  zirconium  by  boiling  the  neutralized  solutions  of  the  sulphates  with 
a  large  excess  (50  per  cent.)  of  acetic  acid.  The  method  has  been  from  time 
to  time  recommended,  but  without  any  data  showing  its  value.  The  single 
separation  made  by  STREIT  and  FRANZ  was  far  from  perfect. 

DAVIS  f  separated  zirconium  sharply  from  aluminium,  but  not  from  iron, 
by  precipitation  as  an  oxyiodate  in  a  boiling  neutralized  solution  of  chlorides, 
but  the  method  is  hardly  applicable  for  rock  analysis. 

BASKERVILLE  J  has  proposed  a  method  for  the  separation  of  zirconium 
from  iron  and  aluminium  similar  to  his  method  for  the  separation  of  titanium 
from  those  elements  (p.  1154).  It  is  based  on  the  precipitability  of  ZrO2  by 
boiling  the  neutralized  chloride  solution  for  two  minutes  in  presence  of  sul- 
phurous acid,  and  seems  to  be  excellent.  As  titanium  is  always  present 
and  is  presumably  quantitatively  thrown  down  also,  the  two  would  have  to  be 
separated  by  hydrogen  peroxide.  No  tests  as  to  the  availability  of  the  method 
for  separating  the  small  amounts  met  with  in  rock  analysis  have  been  made. 

XV.  RARE  EARTHS  OTHER  THAN  ZIRCONIA. 

For  the  few  cases  in  which  it  may  be  necessary  to  look  for  rare  earths 
other  than  zirconia,  the  following  procedure  is  suggested  as  likely  to  prove 
satisfactory : 

The  rock  powder  is  thoroughly  decomposed  by  several  partial  evapora- 
tions with  hydrofluoric  acid,  the  fluorides  of  all  earth  metals  except  zirconium 
are  collected  on  a  platinum  cone,  washed  with  water  acidulated  by  hydro- 
fluoric acid,  and  the  precipitate  washed  back  into  the  dish  or  crucible  and 
evaporated  with  enough  sulphuric  acid  to  expel  all  fluorine.  The  filter  is 
burned  and  added,  By  careful  heating  the  excess  of  sulphuric  acid  is  re- 
moved and  the  sulphates  are  taken  up  by  dilute  hydrochloric  acid.  The 
rare  earths,  with  perhaps  some  alumina,  are  then  separated  by  ammonia, 
washed,  redissolved  in  hydrochloric  acid,  and  evaporated  to  dryness,  then 
taken  up  with  water  and  a  drop  of  hydrochloric  acid,  and  only  enough  ammo- 
nium acetate  to  neutralize  the  latter  added,  followed  by  oxalic  acid  (not 
ammonium  oxalate,  which  would  fail  to  precipitate  thorium) .  In  'this  way 
as  little  as  0-03  per  cent,  of  rare  earths  have  been  found  when  working  on  not 
more  than  2  grm.  of  materials. 

This  method  eliminates  at  once  most  of  the  aluminium,  all  the  iron,  phos- 
phorus, titanium,  and  zirconium,  and  has  the  further  advantage  of  collecting 
with  the  earthy  fluorides,  as  UF4,  any  uranous  uranium  that  the  rock  might 
have  held. 

An  alternative  method  would  be  to  fuse  with  sodium  carbonate,  leach 
with  water  to  get  rid  of  phosphorus  so  far  as  possible,  dissolve  the  residue  in 

*  Journ.  fur  prakt.  Chemie,  cvui,  p.  65,  1869. 

t  Am.  Chem.  Journ.,  xi,  p.  27    1889. 

t  Journ.  Am.  Chem.  Soc..  xvi,  p.  475   1894;  Chemical  News,  LXX,  p.  57 ,'1894. 


SOME   PRINCIPLES  AND    METHODS   OF   ROCK  ANALYSIS.    1159 

hydrochloric  acid,  separate  silica  as  usual,  precipitate  alumina,  etc.,  by 
ammonia,  dissolve  the  precipitate  again  in  hydrochloric  acid,  evaporate, 
and  proceed  as  by  the  former  method,  which  in  most  cases  would  undoubtedly 
give  better  results  than  this  one. 

XVI.    PHOSPHORUS. 

It  is  sometimes  possible  to  extract  all  phosphorus  from  a  rock  by  simple 
digestion  with  nitric  acid,  but  quite  as  often,  if  not  oftener,  this  fails;  hence 
the  necessity  for  resorting  to  one  of  the  longer  methods  of  extraction  detailed 
below. 

PROCEDURE  WHEN  MATERIAL  is  AMPLE. 

When  material  is  ample  it  is  best  to  use  one  portion  for  phosphorus  only 
and  to  proceed  as  follows: 

Fuse  with  sodium  carbonate,  separate  silica  by  a  single  evaporation  with 
nitric  acid,  treat  the  ignited  silica  with  hydrofluoric  and  a  drop  or  two  of 
sulphuric  acids,  evaporate  to  expel  hydrofluoric  acid,  bring  the  small  residue 
into  solution  by  boiling  with  nitric  acid  and  add  it  to  the  main  portion,  hi 
which,  after  addition  of  considerable  ammonium  nitrate,  precipitate  the 
phosphorus  by  molybdate  solution. 

The  turbidity  often  observed  on  dissolving  the  precipitated  and  washed 
phospho-molybdate  in  ammonia  is  due  to  a  compound  of  phosphorus.  If 
the  addition  of  a  small  fragment  of  a  crystal  of  citric  or  tartaric  acid  fails  to 
dissolve  it,  this  should  always  be  re-fused  with  sodium  carbonate,  extracted 
with  water  and  the  filtrate  otherwise  treated  as  above,  in  order  to  secure  the 
phosphorus  in  it. 

According  to  GOOCH  and  AUSTIN,*  in  order  to  secure  a  magnesium- 
ammonium  phosphate  of  normal  composition,  the  procedure  at  this  point 
should  be  as  follows:  To  the  phosphate  solution,  containing  not  more  than  5 
to  10  per  cent,  of  ammonium  chloride  and  a  slight  excess  of  magnesia  mix- 
ture, a  little  ammonia  is  added,  and  the  precipitate  is  washed  in  due  time 
with  weak  ammonia  water.  In  general,  however,  as  these  conditions  can 
seldom  be  fulfilled,  they  recommend  to  decant  the  supernatant  liquid  through 
the  filter  which  is  later  to  receive  the  precipitate,  to  dissolve  this  in  as  little 
hydrochloric  acid  as  possible,  to  reprecipitate  by  dilute  ammonia  without 
further  addition  of  magnesia  mixture,  and  to  wash  finally  with  weakly  ammo- 
niacal  water.  Excess  of  ammonia,  of  ammonium  salts,  and  of  precipitant 
are  all  objectionable.  In  rock  analysis  the  second  precipitation  will  seldom 
be  necessary.  For  ignition,  etc.,  of  the  precipitate,  see  this  subject  under 
Magnesium  (p.  1148). 

PROCEDURE  WHEN  MATERIAL  is  SCANTY. 

The  following  procedure  admits  of  determining  in  the  same  portion,  be- 
sides phosphorus,  barium,  iron,  vanadium,  chromium,  and  titanium,  the  last 

*  Am,  Journ.  Sci.,  4th  Series,  vrr,  p.  187,  1899;  Zeitschr.  fur  anorg.  Chemie  xx,  p.  121 1 
1899;  Chemical  News,  LXXIX,  pp.  233,  244,  255,  1899. 


1160  APPENDIX   II. 

two  either  colorimetrically  or  gravimetrically,  and  is  in  large  part  extracted 
from  a  paper  by  Dr.  T.  M.  CHATARD.* 

Silica  is  removed  by  hydrofluoric  and  sulphuric  acids,  excess  of  fluorine 
expelled,  the  residue  brought  into  solution  so  far  as  possible  with  sulphuric 
or  hydrochloric  acid  and  hot  water,  filtered,  the  residue  ignited,  fused  with 
sodium  carbonate,  dissolved  in  hydrochloric  acid,  and  the  solution,  after 
precipitation  of  barium,  added  to  the  main  one,  which  is  now  precipitated  by 
ammonia  to  get  rid  of  the  magnesium  salts  usually  present  and  thus  insure  a 
cleaner  subsequent  fusion  with  sodium  carbonate. 

The  precipitated  A12O3,  P2O5,  Cr2O3,  Fe2O3,  and  TiO2  is  dissolved  in  hot 
hydrochloric  acid  and  filtered  into  a  large  platinum  crucible,  the  filter  burned 
and  added,  the  solution  evaporated  to  pastiness,  a  little  water  added  to  dissolve 
the  salts,  and  dry  sodium  carbonate  added  in  portions  and  stirred  in  thor- 
oughly to  prevent  lumpiness  in  the  fusion  to  follow,  which  is  continued  for 
half  an  hour.  Addition  of  sodium  nitrate  is  not  necessary. 

The  fused  mass  is  boiled  out  with  water  and  washed  with  very  dilute 
sodium-carbonate  solution.  In  the  residue  iron  and  titanium  can  be  deter- 
mined by  the  methods  already  described.  In  the  filtrate  chromium  can  be 
determined  colorimetrically  if  present  in  sufficient  amount  to  give  a  pro- 
nounced color  (see  p.  1161).  Afterwards,  or  immediately  if  the  chromium  is 
not  to  be  thus  estimated,  enough  ammonium  nitrate  is  added  to  react  with 
all  the  carbonate,  and  the  solution  is  digested  on  the  bath  till  most  of  the 
ammonium  carbonate  is  gone.  Nearly  if  not  quite  all  alumina  is  thus  thrown 
out,  carrying  with  it  all  phosphorus.  The  precipitate  is  washed  with  dilute 
ammonium-nitrate  solution  till  the  yellow  color  wholly  disappears,  after 
which  it  is  dissolved  in  nitric  acid  and  the  phosphorus  thrown  out  by  molyb- 
date  solution.  The  filtrate,  containing  chromium  and  vanadium,  can  be 
treated  as  detailed  in  the  next  following  sections. 

XVII.     CHROMIUM. 

If  vanadium  is  absent,  or  nearly  so,  as  is  apt  to  be  the  case  in  those  highly 
magnesian  rocks  (peridotites)  usually  carrying  a  good  deal  of  chromium, 
the  following  separation  and  gravimetric  method  for  chromium  gives  good 
and  concordant  results,  but  in  presence  of  vanadium,  and  it  is  best  generally 
to  assume  its  presence,  the  colorimetric  method  should  always  be  adopted. 

GRAVIMETRIC  METHOD. 

Having  obtained  chromium  in  solution  as  chromate  and  free  from  all 
else  but  a  little  alumina,  as  at  the  conclusion  of  the  preceding  section  on 
phosphorus,  proceed  as  follows : 

Concentrate  if  necessary  and  add  fresh  ammonium  sulphide,  or  intro- 
duce hydrogen  sulphide.  The  chromium  is  reduced  and  appears  as  a  pre- 
cipitate of  sesquioxide  mixed  with  the  rest  of  the  alumina.  This  precipi- 

*  Am.  Chem.  Joum.,  xm,  p.  106, 1891 ;  Bull.  U.  S.  Geol.  Survey,  No.  78,  p.  87 ;  Chemi- 
cal News,  ucxin,  p.  267,  1891. 


SOME   PRINCIPLES  AND    METHODS   OF   ROCK  ANALYSIS.    1161 

tate  is  now  treated  according  to  BAUBIGNY  *  by  dissolving  in  nitric  acid, 
evaporating  to  near  dryness,  and  heating  with  strong  nitric  acid  and  potas- 
sium chlorate,  finally  evaporating  to  dryness  to  get  rid  of  the  acid.  Oxida- 
tion is  complete  and  very  speedy.  On  dilution  with  cold  water,  acid  sodium 
carbonate  is  added  in  slight  excess,  and  after  two  or  three  hours  the  pre- 
cipitated alumina  is  filtered  off.  From  the  filtrate  the  chromium  is  then 
thrown  out  by  fresh  ammonium  sulphide,  redissolved  and  reprecipitated 
to  free  from  alkali,  and  weighed. 

The  separation  of  aluminium  from  chromium  by  hydrogen  peroxide  in 
ammoniacal  solution,  as  recommended  by  JANNASCH  and  CLOEDT,-}-  has  been 
shown  by  FRIEDHEIM  and  BRUHL,!  together  with  most  of  the  other  separa- 
tions of  JANNASCH  based  on  the  use  of  hydrogen  peroxide  and  from  which 
so  much  was  hoped,  to  be  valueless. 

COLORIMETRIC    METHOD. 

For  this  very  accurate  and  by  far  the  quickest  method  §  for  determin- 
ing chromium  in  rocks  and  ores  where  the  amount  does  not  exceed  a  few 
per  cent.,  there  is  needed  the  aqueous  extract  of  a  sodium-carbonate  fusion 
of  the  rock  (as  obtained,  for  instance,  under  Phosphorus,  p.  1160)  in  order 
to  compare  its  color  with  that  of  a  standard  solution. 

Preparation  and  Strength  of  Standard  Solution. — This  standard  solution 
is  made  by  dissolving  0  •  25525  grm.  or  double  that  amount  of  pure  potassium 
monochromate  in  one  liter  of  water  made  alkaline  by  a  little  sodium  carbonate- 
Each  cubic  centimeter  then  corresponds  to  one-tenth  mgrm.  or  two-tenths 
mgrm.  of  chromic  oxide  (Cr2O3),  in  which  condition  chromium  is  usually 
reported  in  rocks  and  ores.  It  is  probably  'inadmissible  to  increase  the 
strength  of  the  standard  much  above  the  figure  given. 

Preparation  of  the  Test  Solution. — Before  filtering  the  aqueous  extract 
of  the  sodium-carbonate  fusion  a  few  drops  of  alcohol  (ethyl  or  methyl) 
are  added  to  destroy  the  color  of  sodium  manganate.  If  the  yellow  color 
of  the  filtrate  is  very  faint,  concentration  by  evaporation  will  strengthen  it, 
and  less  than  2  mgrm.  of  chromic  oxide  in  1  grm.  of  rock  can  then  be  exactly 
measured.  For  smaller  amounts  it  is  best  to  employ  from  3  to  5  grm.  of 
powder,  and  then  to  concentrate  the  chromium  by  precipitation  by  mer- 
curous  nitrate,  as  detailed  in  the  nexts  ection  under  VANADIUM  (p.  1163); 
otherwise  it  may  be  difficult  or  impossible,  because  of  the  large  amount  of 
alkali  carbonate  present,  to  obtain  a  filtrate  of  sufficiently  small  bulk  to 
show  a  decided  color. 

If  nitre  has  been  used  in  the  fusion,  and  the  crucible  has  been  at  all  attacked 
by  it,  a  yellow  coloration  of  the  filtrate  may  be  due  to  dissolved  platinum, 

*  Bull.  Soc.  Chimique  (n.  s.),  XLII,  p.  291,  1884;  Chemical  News,  L,  p.  18,  1885. 

+  Zeitschr.  fur  anarg.  Chemie,  x,  p.  402,  1895. 

t  Zeitschr.  fur  anal.  Chemie,  xxxvni,  p.  681,  1899. 

§  W.  F.  HII.I.EBRAND,  Journ.  Am.  Chem.  Soc.,  xx,  p.  454,  1898;  Chemical  Newt, 
LXXVTII,  pp.  227,  239,  1898;  Bull.  U.  S.  Geol.  Survey,  No.  167,  p.  37.  First  applied  by 
L.  DE  KOXIXGH  (Nederl.  Tyds.  voor  Pharm.  Chem.  and  Tox..  1889)  for  the  estimation  of 
chromium  in  foodstuffs. 


1162 


APPENDIX    II. 


but  neither  the  proportion  of  nitre  nor  the  temperature  of  the  blast  should 
ever  be  high  enough  to  permit  the  crucible  to  be  attacked. 

Comparison  of  Colors. — The  final  solution  is  transferred  to  a  graduated 
flask  of  such  size  that  its  color  shall  be  weaker  than  that  of  the  standard 
chromium  solution.  Definite  amounts  of  the  latter  are  then  diluted  with 
water  from  a  burette  until  of  the  same  strength  as  the  test  solution,  exactly 
as  described  on  page  1150  for  the  colorimetric  estimation  of  titanium.  For 
very  minute  amounts  it  is  necessary  to  use  NESSLER  tubes,  as  in  ammonia 
estimations,  instead  of  the  glasses  and  apparatus  described  and  depicted 
under  Titanium  (p.  1152). 

As  with  colorimetric  methods  in  general,  this  one  gives  better  results 
with  small  than  with  large  percentages  of  chromium,  yet  it  can  be  applied 
in  the  latter  cases  with  satisfactory  results  by  making  a  larger  number  of 
consecutive  comparisons  with  the  same  solution. 

A  FEW  COMPARATIVE  DATA. 

A  few  comparisons  between  colorimetric  and  gravimetric  determina- 
tions of  chromium  are  here  given  to  show  the  order  of  agreement,  the  former 
having  been  made  several  months  and  even  years  after  the  latter. 


Gravimetric 

Colorimetric 

Gravimetric 

Colorimetric 

per  cent.  Cr^Gg. 

per  cent.  C^Oa. 

per  cent.  Cr2O3. 

per  cent.  Cr2O3. 

Trace. 

0-018 

Trace. 

•013 

0-05 

•051 

None. 

•0086 

•  14 

•12 

None. 

•0067 

•08 

•083 

The  outcome  was  somewhat  surprising,  for  it  was  hardly  to  be  expected 
that  the  long  and  laborious  quantitative  separations  should  have  resulted  so 
well  as  they  are  shown  to  have  done.  It  should  be  mentioned  that  for  the 
gravimetric  tests  but  1  or  2  grm.  at  most  were  used,  which  accounts 
for  the  reported  absence  of  chromium  in  two  instances,  this  report  being 
based  on  the  lack  of  color  in  the  aqueous  extract  of  the  alkali  fusion  after 
removal  of  manganese. 


XVIII.  VANADIUM  (CHROMIUM)  AND  MOLYBDENUM. 
DISTRIBUTION  OF  VANADIUM  AND  MOLYBDENUM. 

The  wide  distribution  of  vanadium  throughout  the  earth's  crust  has  in 
recent  years  been  clearly  established  (see  ante,  p.  1105),  not  only  in  ores  and 
in  coals,  but  in  clays,  limestones,  sandstones,  and  igneous  rocks.*  The 
writer  has  shown  (loc.  cit.)  that  vanadium  occurs  in  quite  appreciable  amounts 

*  W.  F.  HILLEBRAND,  "Distribution  and  Quantitative  Occurrence  of  Vanadium  and 
Molybdenum  in  Rocks  of  the  United  States,"  Am.  Journ.Sci.,4ih  Series,  vi,  p.  209,  1898; 
Chemical  News,  LXXVIII,  p.  216,  1898:  Bull.  U.  S.  Geol.  Survey,  No.  167,  p.  49. 


SOME   PRINCIPLES   AND    METHODS    OF   ROCK   ANALYSIS.    1163 

in  the  more  basic  igneous  and  metamorphic  rocks  up  to  0-08  per  cent,  or 
more  of  V2O3,  but  that  it  seems  to  be  absent,  or  nearly  so,  from  the  highly 
siliceous  ones.  Some  of  their  ferric  aluminous  silicate  constituents  carry 
still  higher  percentages — up  to  0-13  per  cent.  V2O3  in  a  biotite  separated 
from  a  pyroxenic  gneiss.  Molybdenum,  on  the  other  hand,  appears  to  be 
confined  in  quantities  susceptible  of  detection  to  the  more  siliceous  rocks, 
and,  except  perhaps  in  rare  instances,  is  not  present  hi  them  in  quantitatively 
determinable  amount  when  operating  on  5  grm.  of  material.  Hence  the 
quantitative  search  for  vanadium  will  usually  be  limited  to  rocks  with  less 
than  60  per  cent,  of  silica.  The  search  for  it  even  then  will  perhaps  not  often 
warrant  the  necessary  expenditure  of  time,  but  in  this  connection  it  is  to  be 
remembered  that  neglect  to  estimate  it  introduces  an  error  in  the  figures 
for  both  ferrous  and  ferric  oxides,  which  in  extreme  cases  met  with  may  be 
of  considerable  moment.  (See  p.  1140,  and  also  pp.  1174  and  1175.) 

DESCRIPTION  OF  METHOD. 

In  the  following  method  there  is  nothing  absolutely  novel  except  that 
chromium  and  vanadium,  when  together,  need  not  be  separated,  but  are 
determined,  the  former  colorimetrically,  as  already  described  (p.  1161),  the 
latter  volumetrically,  in  the  same  solution.* 

Five  grm.  of  the  rock  are  thoroughly  fused  over  the  blast  with  20  grm.  of 
sodium  carbonate  and  3  grm.  of  sodium  nitrate.  After  extracting  with  water 
and  reducing  manganese  with  alcohol  it  is  probably  quite  unnecessary,  if  the 
fusion  has  been  thorough,  to  remelt  the  residue  as  above,  though  for  some 
magnetites  and  other  ores  containing  larger  amounts  of  vanadium  than  the 
generality  of  rocks,  this  may  be  necessary,  as  EDO  CLAASSEN  has  shown.f  The 
aqueous  extract  is  next  nearly  neutralized  by  nitric  acid,  the  amount  to  be  used 
having  been  conveniently  ascertained  by  a  blank  test  with  exactly  20  grm.  of 
sodium  carbonate,  etc.,  and  the  solution  is  evaporated  to  approximate  dry- 
ness.  Care  should  be  taken  to  avoid  overrunning  neutrality,  because  of 
the  reducing  action  of  the  nitrous  acid  set  free  from  the  nitrite  produced 
during  fusion,  but  when  chromium  is  present  it  has  been  my  experience  that 
some  of  this  will  invariably  be  returned  by  the  precipitated  silica  and  alumina, 
though  only  in  one  case  have  I  observed  a  retention  of  vanadium,  it  being 
then  large.  The  use  of  ammonium  nitrate  instead  of  nitric  acid  for  con- 
verting the  sodium  carbonate  into  nitrate  does  not  seem  to  lessen  the  amount 
of  chromium  retained  by  the  silica  and  alumina. 

As  a  precautionary  measure,  therefore,  and  always  when  chromium  is 
to  be  estimated  also,  the  silica  and  alumina  precipitate  should  be  evaporated 
with  hydrofluoric  and  sulphuric  acids,  the  residue  fused  with  a  little  sodium 
carbonate  and  the  aqueous  extract  again  nearly  neutralized  with  nitric  acid 
and  boiled  for  a  few  moments,  the  filtrate  being  added  to  the  main  one. 

Mercurous  nitrate  is  now  added  to  the  cold  alkaline  solution  in  some 

*W.  F.  HILLEBRAND,  Journ.  Am.  Soc.,  xx,  p.  461,  1898;    Chemical  News,  LXXVIII, 
p.  295,  1898;  Bull.  U.  S.  Geol.  Survey,  No.  167,  p.  44. 
t  Am.  Chem.  Journ.,  vm,  p.  437,  1886. 


1164  APPENDIX   II. 

quantity,  so  as  to  obtain  a  precipitate  of  considerable  bulk,  containing, 
besides  mercurous  carbonate,  chromium,  vanadium,  molybdenum,  tung- 
sten, phosphorus,  and  arsenic,  should  all  happen  to  be  in  the  rock.  The 
mercurous  carbonate  serves  to  counteract  any  acidity  resulting  from  the 
decomposition  of  the  mercurous  nitrate.  Precipitating  in  a  slightly  alkaline 
instead  of  a  neutral  solution,  renders  the  addition  of  precipitated  mercuric 
oxide  unnecessary  for  correcting  this  acidity.  If  the  alkalinity,  as  shown 
by  the  formation  of  an  unduly  large  precipitate,  should  have  been  too  great, 
it  may  be  reduced  by  careful  addition  of  nitric  acid  until  an  added  drop  of 
mercurous  nitrate  no  longer  produces  a  cloud. 

After  heating  and  filtering,  the  precipitate  is  ignited  in  a  platinum  cru- 
cible, after  drying  and  removing  from  the  paper  to  obviate  any  chance  of 
loss  of  molybdenum  and  of  injury  to  the  crucible  by  reduction  of  arsenic. 
The  residue  is  fused  with  a  very  little  sodium  carbonate,  leached  with  water 
and  the  solution,  if  colored  yellow,  filtered  into  a  graduated  flask  of  25  or 
more  cubic  centimeters  capacity.  The  chromium  is  then  estimated  accurately 
in  a  few  minutes  by  comparing  with  a  standard  alkaline  solution  of  potassium 
monochromate  (p.  1161).  Then,  or  earlier  in  absence  of  chromium,  sulphuric 
acid  is  added  in  slight  excess  and  molybdenum  and  arsenic,  together  with 
occasional  traces  of  platinum,  are  precipitated  by  hydrogen  sulphide,  prefera- 
bly in  a  small  pressure  bottle.*  If  the  color  of  the  precipitate  indicates 
absence  of  arsenic  the  filter,  with  its  contents,  is  carefully  ignited  in  porcelain, 
and  the  delicate  sulphuric-acid  test  for  molybdenum  is  applied  as  follows: 
The  molybdenum  compound  is  heated  in  porcelain  with  a  single  drop  of 
strong  sulphuric  acid  till  the  acid  is  nearly  volatilized.  On  cooling  a  beau- 
tiful blue  color  is  proof  of  the  presence  of  molybdenum. 

The  filtrate,  in  bulk  from  25  c.c.  to  100  c.c.  is  boiled  to  expel  hydro- 
gen sulphide,  and  titrated  at  a  temperature  of  70°  to  80°  with  a  very 
dilute  solution  of  permanganate  representing  about  1  mgrm.  V2O5  per  cubic 
centimeter  as  calculated  from  the  iron  strength  of  the  permanganate,  one 
molecule  of  V2O5  being  indicated  for  each  one  of  Fe2O3.  One  or  two  checks 
are  always  to  be  made  by  reducing  again  by  means  of  a  current  of  sulphur 
dioxide  gas,  boiling  this  out  again,f  and  repeating  the  titration.  The  latter 
results  are  apt  to  be  a  very  little  lower  than  the  first,  and  are  to  be  taken  as 
the  correct  ones. 

In  case  the  volume  of  permanganate  used  is  so  small  as  to  make  doubtful 

*  From  a  sulphuric  solution  the  separation  of  platinum  and  molybdenum  by  hydro- 
gen  sulphide  is  much  more  rapid  and  satisfactory  than  from  a  hydrochloric  solution. 

t  The  direct  use  of  a  solution  of  sulphur  dioxide  or  of  an  alkali  sulphite  is  inadmissible 
unless  these  have  been  freshly  prepared  since  after  a  lapse  of  time  they  contain  other 
oxidizable  bodies  than  sulphurous  acid  or  a  sulphite.  The  sulphur  dioxide  is  best  ob- 
tained as  wanted  by  heating  a  flask  containing  a  solution  of  sulphur  dioxide,  or  of  a  sul- 
phite to  which  sulphuric  acid  has  been  added. 

The  expulsion  of  the  last  traces  of  sulphur  dioxide  is  said  to  be  more  effectively  ac- 
complished by  boiling  with  simultaneous  passage  of  a  rapid  current  of  carbon  dioxide 
for  a  few  minutes  at  the  last  than  by  boiling  alone.  Because  of  the  small  amount  of  air 
carried  with  it,  long  passage  of  the  gas  is  said  to  result  in  slight  oxidation  of  the  vana- 
dium (MANASSE,  Ann.  Chem.  u.  Pharm.,  CCXL,  p.  23,  1887;  Zeitschr.  fur  anal.  Chemie* 
xxxii,  p.  225,  1893.) 


SOME   PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1165 

the  presence  of  vanadium,  it  is  necessary  to  apply  a  qualitative  test,  which 
is  best  made  as  follows:  The  solution  is  evaporated  arid  heated  to  expel  excess 
of  sulphuric  acid,  the  residue  is  taken  up  with  two  or  three  cubic  centimetres 
of  water  and  a  few  drops  of  dilute  nitric  acid,  and  a  couple  of  drops  of  hydro- 
gen peroxide  are  added.  A  characteristic  brownish  tint  indicates  vanadium. 
Unless  the  greater  part  of  the  free  sulphuric  acid  has  been  removed,  the  ap- 
pearance of  this  color  is  sometimes  not  immediate  and  pronounced,  hence  the 
above  precaution.  It  is  also  necessary  that  the  nitric  acid  shall  be  hi  con- 
siderable excess,  since  in  a  neutral  or  only  faintly  acid  solution  the  color 
does  not  appear  strongly. 

The  above  is  a  surer  test  to  apply  than  the  following:  Reduce  the  bulk 
to  about  10  c.c.,  add  ammonia  in  excess  and  introduce  hydrogen  sulphide  to 
saturation.  The  beautiful  cherry-red  color  of  vanadium  in  ammonium- 
sulphide  solution  is  much  more  intense  than  that  caused  by  hydrogen  per- 
oxide in  acid  solution,  but  the  action  of  ammonia  is  to  precipitate  part  or  all  of 
the  vanadium  with  the  chromium  or  aluminium  that  may  be  present  or  with 
the  manganese  used  in  titrating,  and  ammonium  sulphide  is  unable  to  extract 
the  vanadium  wholly  from  these  combinations.  Usually,  however,  the 
solution  will  show  some  coloration,  and  addition  of  an  acid  preciptiates 
brown  vanadium  sulphide,  which  can  be  collected,  ignited,  and  further  tested 
if  desired. 

APPLICATION  OF  THE  METHOD  IN  PRESENCE  OF  RELATIVELY  MUCH  CHROMIUM. 

The  application  of  the  method  in  its  foregoing  simplest  form  is  subject 
to  one  limitation — the  chromium  must  not  be  present  above  a  certain  mod- 
erate amount.  This  limitation  is  due  to  the  considerable  amount  of  per- 
manganate then  required  to  produce  a  clear  transition  tint  when  titrating 
in  a  hot  solution,  as  is  advisable  with  vanadium.  In  a  cold  solution  of  chromic 
sulphate  much  less  permanganate  is  needed  to  produce  the  peculiar  blackish 
tint  without  a  shade  of  green,  which  affords  a  sure  indication  of  excess  of 
permanganate,  but  in  a  hot  and  especially  a  boiling  solution,  the  oxidation 
of  the  chromium  itself  takes  place  so  rapidly  that  a  very  large  excess  of  the 
reagent  may  be  added  before  a  pronounced  end  reaction  is  obtained.  Never- 
theless, quite  satisfactory  determinations  of  as  little  as  1  or  2  mgrm.  of  vana- 
dium pentoxide  can  be  made  in  presence  of  as  much  as  30  mgrm.  of  chromic 
oxide.  To  accomplish  this  it  is  only  necessary  to  apply  a  simple  correction 
obtained  by  adding  permanganate  to  a  like  bulk  of  equally  hot  chromic-sul- 
phate solution  containing  approximately  the  same  amount  of  chromium. 

RIDSDALE*  titrated  the  cold  solution  to  avoid  oxidation  of  chromium, 
and  obtained  accurate  results,  but  in  the  writer's  experience  the  end  reaction 
is  then  uncertain. 

The  following  tables  contain  the  results  of  a  considerable  number  of 
tests,  those  in  Table  II  being  tabulated  separately  in  order  to  show  the 
degree  of  accuracy  attainable  with  a  large  excess  of  chromium  by  applying 
the  correction  above  mentioned  and  also  the  amount  of  this  correction : 

*  Journ.  Chem.  Soc.,  vn,  p.  73,  1888. 


1166 


APPENDIX   II. 


TABLE  I. 

TESTS   FOR   VANADIUM   IN   THE   PRESENCE    OF  CHROMIUM. 


No. 

Chromic 
Oxide. 

Vanadium 
Pentoxide. 

Vanadium 
Pentoxide 
Found. 

Error. 

Milligrams. 

Milligrams. 

Milligrams. 

Milligram. 

1 

1 

9-87 

9-22 

-0-15 

2 

1 

•94 

1-04 

+    -10 

-98 

+    -04 

3 

1-5 

5-25 

5-49 

+    -24 

5-43 

+    -19 

4 

2 

5-62 

5-5 

-    -12 

5-5 

-    -12 

5 

3 

4-68 

4-78 

+  -10 

4-78 

+    -10 

4-83 

+    -15 

6 

3 

5-62 

5-58 

-    -04 

5-58 

-    -04 

7 

3-5 

18-74 

18-89 

+    -15 

18-97 

+    -23 

8 

6 

5-6 

6-1 

+    -50 

9 

6 

4-68 

4-78 

+    -10 

10 

6 

5-62 

5-58 

-    -04 

11 

10 

5-62 

5-58 

-    -04 

12 

10 

23-52 

23-81 

+    -29 

23-71 

+    -19 

13 

10 

46-85 

46-98 

+    -13 

47-20 

+    -35 

14 

25 

23-52 

23-65 

+    -13 

23-75 

+    -23 

15 

87-5 

23-52 

23-71 

+    -19 

TABLE  II. 

SHOWING  APPLICATION  OF  CORRECTION  FOR  LARGER  AMOUNTS  OF  CHROMIUM, 
OBTAINED  BY  ADDING  POTASSIUM  PERMANGANATE  TO  AN  EQUAL  BULK  OF 
SOLUTION  CONTAINING  A  LIKE  AMOUNT  OF  CHROMIC  SULPHATE. 


No. 

Chromic 
Oxide. 

Vanadium 
Pentoxide. 

Vanadium 
Pentoxide 
Found. 

Vanadium 
Pentoxide 
Found. 

Error. 

Volume  of 
Solution. 

Milligrams. 

Milligrams. 

Uncorrected. 

Corrected. 

Milligram. 

16 

20 

0-94 

1-59 

0-99 

+  0-05 

50-100  c.c. 

17 

20 

1-87 

2-69 

2-09 

+    -22 

50-100  c.c. 

2-39 

1-79 

-    -08 

2-59 

1-99 

+    -12 

18 

20 

18-74 

19-4 

18-73 

-    -01 

50-100  c.c. 

19-3 

18-63 

-    -11 

19-3 

18-63 

-    .11 

19 

30 

1-87 

2-99 

2-14 

+    -27 

About  100  c.c. 

2-79 

1-94 

+    -07 

2-79 

1-94 

+    -07 

2-69 

1-84 

-    -03 

2-69 

1-84 

-    -03 

20 

30 

1-87 

2-69 

1-79 

-    -08 

200  c.c. 

2-89 

2-09 

+    -22 

2-89 

2-09 

+    -22 

2-79 

1-99 

+    -12 

21 

62 

46-85 

48-60 

47-60 

+    -75 

200  c.c. 

SOME  PRINCIPLES   AND   METHODS   OF   ROCK   ANALYSIS.    1167 

In  spite  of  the  fact  that  the  correction  in  most  of  the  trials  of  this  last 
table  represents  a  large  proportion  of  the  permanganate  used,  the  results 
must  be  considered  satisfactory  in  view  of  the  small  amount  of  vanadium 
present,  and  they  show  that  the  method  in  competent  hands  after  a  little 
experience  affords  trustworthy  figures. 

The  method  of  T.  FISCHER* — digestion  of  the  precipitated  lead  salts 
with  a  strong  solution  of  potassium  carbonate — appears  to  offer  the  long- 
needed  satisfactory  quantitative  separation  of  arsenic,  phosphorus,  chro- 
mium, tungsten,  and  molybdenum  from  vanadium,  the  normal  lead  meta- 
vanadate  remaining  quite  unattacked,  according  to  the  author,  while  the 
other  lead  salts  are  wholly  decomposed,  but  the  applicability  of  this  method 
to  the  separation  of  the  minute  amounts  often  found  in  rocks  and  ores 
has  not  been  tested.  The  object  has  been  in  the  present  case  to  reach  satis- 
factory results  with  the  greatest  expedition,  and  when  chromium  is  not  present 
in  considerable  amount  this  is  accomplished. 

Fortunately,  chromium  is  almost  never  a  prominent  constituent  of  clays, 
coals,  iron  ores,  and  those  rocks  in  which  vanadium  has  thus  far  been  re- 
ported, for  although  it  is  usually  certain  of  the  most  basic  of  the  silicate 
rocks  that  are  highest  in  chromium — as  the  peridotites — yet  in  these,  so  far 
as  present  experience  teaches,  vanadium  is  lacking,  a  fact  doubtless  connected 
with  the  simultaneous  absence  from  them  of  ferric-aluminous  silicates. 

CONDITION  OF  VANADIUM  IN  ROCKS. 

The  above  and  elsewhere  mentioned  connection  of  vanadium  with  the 
ferric-aluminous  silicates  of  rocks,  taken  in  connection  with  the  existence 
of  the  mineral  roscoelite,  classed  as  a  vanadium  mica,  indicates  a  condi- 
tion of  the  vanadium  corresponding  to  aluminium  and  ferric  iron,  and  that 
it  is  to  be  regarded  as  replacing  one  or  both  of  these  elements.  Hence  it 
should  be  reported  as  V2O3  and  not  as  V2O5. 

What  its  condition  may  be  in  matter  of  secondary  origin,  like  clays, 
limestones,  sandstones,  coals,  and  ores  of  iron,  is  yet  open  to  discussion. 
It  was  the  writer's  opinion  until  recently,  that  it  should  then  be  regarded 
as  in  the  pentavalent  state  (V2O5),  but  his  work  upon  certain  remarkable 
vanadiferous  sandstones  f  of  Western  Colorado,  in  which  it  unquestionably 
occurs  as  trivalent  vanadium,  (V2O3),  has  led  to  a  decided  unsettling  of  this 
view.  It  is  but  proper  to  recall  that  CZUDNOWICZ,!  because  of  the  extreme 
difficulty  in  completely  extracting  it  from  iron  ores  by  an  alkali-carbonate 
fusion  and  because  of  the  easy  reducibility  of  vanadic  acid  by  ierrous  salts, 
under  the  conditions  in  which  brown  iron  ores  are  supposed  to  form,  con- 
sidered the  vanadium  in  such  ores  to  be  in  a  lower  condition  of  oxidation, 
(V2O3).  LINDEMANN'S  §  contrary  conclusion  with  regard  to  certain  iron 
ores,  because  the  vanadium  was  extracted  as  V2O5  by  sodium-carbonate 


*  Inaugural  Dissertation,  ROSTOCK,  1894. 

t  HILLEBRAND  and  RANSOME,  Am.  Journ.  Sci.,  4th  Series,  x,  p.  120,  1900. 

1  POGG.  Ann.,  cxx,  p.  20,  1863. 

§  Dissertation,  Jena,  1878,  through  Zeitschr.  fur  anal.  Chemie,  xvin,  p.  99,  1879. 


1168  APPENDIX   II. 

fusion  without  niter,  is  not  valid,  since  this  would  probably  be  the  case 
even  if  it  existed  in  the  ore  as  V2O3. 


XIX.  FERROUS  IRON. 

COMPARISON    OF   SEALED-TUBE    AND    HYDROFLUORIC-ACID    METHODS — COM- 
PARATIVE  WORTHLESSNESS   OF  THE   FORMER   IN   ROCK   ANALYSIS. 

No  point  in  rock  analysis  has  been  the  cause  of  greater  solicitude  to 
the  chemist,  and  especially  to  the  mineralogist  and  petrographer,  than  the 
determination  of  iron  in  ferrous  condition.  The  sealed-tube  or  MITSCHER- 
LICH  method  with  sulphuric  acid,  for  a  long  time  the  only  available  one. 
is  in  theory  perfect,  since  complete  exclusion  of  oxygen  is  easily  attainable, 
Its  chief  hitherto  recognized  defect  lies  in  the  inability  to  always  secure 
complete  decomposition  of  the  iron-bearing  minerals,  and  even  to  ascertain 
oftentimes,  whether  or  not  the  decomposition  has  been  complete.  The 
addition  of  hydrofluoric  acid  to  the  sulphuric  in  the  tube,  in  order  to  insure 
this  breaking  up,  is  to  be  regarded  as  of  very  doubtful  utility  in  most  cases, 
since  the  glass  may  be  so  strongly  attacked  as  to  add  an  appreciable  amount 
of  iron  to  the  solution,  and  the  hydrofluoric  acid  may  have  exhausted  itself 
in  attacking  the  glass  before  the  more  refractory  minerals  succumb.  Never- 
theless, if  decomposition  can  be  effected  by  sulphuric  acid  alone  the  results 
obtained  are  sharp  and  concordant,  and  what  has  seemed  especially  re- 
markable, and  up  to  almost  the  present  moment  without  a  satisfactory 
explanation,  they  are  in  rock  analysis  usually  higher  than  when  made  by 
any  of  the  modifications  of  the  hydrofluoric-acid  method  now  so  extensively 
practiced.  This  difference  is  not  very  marked  with  rocks  containing  but  1 
or  2  per  cent,  of  ferrous  iron,  but  it  increases  with  rising  percentage  to  such 
an  extent  that  where  the  sealed-tube  method  will  show  12  per  cent.  FeO  the 
other  may  indicate  no  more  than  10  per  cent.  This  is  a  fact  of  which  the 
writer  has  long  been  cognizant,  but  it  does  not  seem  to  be  known  to  chemists 
or  petrographers  at  large,  though  WULFING  *  has  noticed  this  difference 
in  certain  analyses  without  appreciating  its  significance.  Experiments 
with  soluble  iron  salts  of  known  composition,  like  ferrous  sulphate  and 
ferrous-ammonium  sulphate,  throw  no  light  on  the  subject,  for  both  methods 
give  with  them  the  same  sharp  and  accurate  results. 

In  spite  of  several  attempts  to  find  a  solution  to  the  problem,  none  pre- 
sented itself  until  very  recently,  when,  as  a  result  of  observations  made  in 
this  laboratory  by  Dr.  H.  N.  STOKES  in  a  pending  investigation  on  the  action 
of  ferric  salts  on  pyrite  and  other  sulphides,  the  clue  was  given.  Dr.  STOKES 
found  that  ferric  salts  exercise  a  most  marked  oxidizing  effect  on  pyrite  and 
probably  other  sulphides.f  The  reaction  is  not  new  (see  J.  H.  L.  VOGT  in 
Zeitschr.  fur  prakt.  Geol.,  1899,  pp.  250,  251),  but  the  ease  with  which  the 

*  Ber.  deutach.  chem.  Gesell.,  xxxn,  p.  2217,  foot-note,  1899. 

tThis  effect  had,  however,  been  already  pointed  out  by  Prof.  L  L.  de  KONINCK  in 
a  communication  (Ann.  soc.  geolog.  Belg.  x  [1882-83]  101),  which,  from  lack  of  publicity, 
was  overlooked. 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1169 

change  takes  place  and  the  completeness  of  the  oxidation  of  the  pyrite, 
not  only  of  its  iron  but  of  the  greater  part  of  the  sulphur  as  well,  were 
entirely  unexpected.  Pure  pyrite  itself  is  attacked  with  extreme  slowness 
by  boiling  dilute  sulphuric  and  hydrofluoric  acids,  either  alone  or  mixed, 
but  the  moment  a  ferric  salt  is  introduced  the  case  is  altogether  differant. 

However,  experiment  has  shown  (p.  1174)  that  with  the  amounts  of  sul- 
phides usually  found  in  igneous  rocks  their  effect  upon  the  estimation  of 
ferrous  iron  by  the  hydrofluoric-acid  method  at  atmospheric  pressure  and 
boiling  heat  is  negligible,  though  by  increasing  the  amount  of  sulphide  the 
effect  becomes  more  and  more  apparent,  because  of  the  greater  surface  of 
pyrite  exposed  to  the  action  of  the  ferric  iron  of  the  rock. 

Under  the  conditions  of  the  MITSCHERLICH  method,  on  the  other  hand — 
a  temperature  of  150°  to  200°  C.,  and  even  higher,  high  pressure,  much 
longer  time  of  action,  and  impossibility  of  escape  of  any  hydrogen  sulphide 
that  may  be  formed — the  sulphur  of  the  sulphides  becomes  nearly,  if  not 
fully,  oxidized  to  sulphuric  acid  at  the  expense  of  the  ferric  iron  in  the  rock, 
with  the  production  of  an  equivalent  amount  of  ferrous  iron  in  addition  to 
that  resulting  from  the  sulphide  itself.  Now,  rocks  with  hardly  an  exception, 
and  many  minerals,  carry  pyrite  or  pyrrhotite,  or  both,  often  in  consider- 
able amount,  often  in  traces  only.  My  own  experience  has  been  that  sul- 
phur can  almost  always  be  detected  in  2  grm.  of  rock  powder. 

Let  us  now  see  what  the  effect  of  these  traces  when  fully  oxidized  amounts 
to.  One  atom  of  sulphur  (32)  requires  for  its  complete  conversion  to  tri- 
oxide  the  oxygen  of  three  molecules  of  ferric  oxide  (480),  which  then  becomes 
six  molecules  of  ferrous  oxide  (432).  In  other  words  0-01  per  cent,  of  sul- 
phur may  cause  the  ferrous  oxide  to  appear  too  high  by  0- 135  per  cent,  and 
0-10  per  cent,  of  sulphur  may  bring  about  an  error  of  1  •  35  per  cent,  in  ferrous 
oxide.  The  case  is  still  worse  if  the  sulphur  is  set  free  as  hydrogen  sulphide 
from  a  soluble  sulphide,  for  then  the  above  percentages  of  sulphur  produce 
errors  of  0-18  and  1-8  per  cent.,  respectively,  in  the  ferrous  oxide  deter- 
mination. 

The  error  caused  by  sulphides  tends  to  become  greater  the  more  there 
is  present  of  either  or  both  sulphide  and  ferric  salt.  Now,  the  highly  fer- 
ruginous rocks  usually  carry  more  ferric  iron  than  the  less  ferruginous  ones, 
and  they  are  often  relatively  high  in  pyrite  and  pyrrhotite ;  hence  the  increas- 
ing discrepancy  between  the  results  by  the  two  methods  as  the  iron  con- 
tents of  the  rocks  rise  is  fully  in  accord  with  the  above  explanation.* 

Notwithstanding  that  the  MITSCHERLICH  method  has  thus  been  dis- 
credited in  its  general  applicability  to  rocks  and  minerals,  it  is  still  capable 
of  affording  valuable  assistance  with  those  which  are  totally  free  from  sul- 
phides. Hence  the  conditions  under  which  success  can  best  be  achieved 
by  it  are  set  f ort-h  in  the  following  paragraphs : 

*  For  details  of  experiments  showing  the  worthlessness  of  the  MITSCHERLICH  method 
for  rocks  and  minerals  which  contain  even  a  trace  of  free  sulphur  or  sulphides,  see  HILLE- 
BRAND  and  STOKES,  in  and  as  yet  unpublished  paper  in  Journ.  Am.  Chem.  Soc.,  xxn,  and 
Zeiischr.  fur  anorg.  Chem.,  xxv,  1900,  entitled.  "Relative  Value  of  the  MITSCHERLICH  and 
hydrofluoric-acid  methods  for  ferrous  iron  deteminations. 


1170  APPENDIX   II. 


THE  MODIFIED  MITSCHERLICH  METHOD. 

Strength  of  Acid. — The  method  in  its  original  and  usual  application  calls 
for  a  mixture  of  three  parts  of  sulphuric  acid  and  one  of  water  by  weight, 
or  about  three  to  two  by  volume,  though  a  still  stronger  acid  is  sometimes 
used.  In  some  cases,  however,  perhaps  in  most,  much  better  decomposi- 
tion of  the  silicates  is  effected  by  reversing  the  proportions  of  water  and 
acid,  or  at  any  rate  by  diluting  considerably  beyond  the  above  proportion. 
Hereby  the  separation  of  salts  difficultly  soluble  in  the  stronger  acid  is  avoided 
and  the  actual  solvent  effect  on  the  minerals  seems  to  be  in  nowise  diminished. 

Filling,  Sealing,  and  Heating  of  the  Tube. — The  very  finely  powdered 
mineral  having  been  introduced  into  a  tube  of  resistant  glass  free  from  fer- 
rous iron,  the  open  end  is  drawn  out,  so  as  to  leave  a  funnel  for  the  intro- 
duction of  the  acid.  A  very  little  water  is  then  introduced  and  carefully 
heated  to  boiling  for  a  moment  to  expel  all  air  from  the  powder.  The  diluted 
acid — which  has  just  been  boiled  down  from  a  state  of  greater  dilution  in 
order  to  have  it  free  from  air — is  then  poured  in  until  the  tube  is  about  three- 
fourths  filled.  Carbon  dioxide  is  then  introduced  from  a  generator  which 
has  been  in  active  operation  for  some  time,  through  a  narrow  glass  tube 
drawn  out  of  the  same  kind  of  glass  as  that  of  which  the  decomposing  tube 
consists.  In  a  few  moments  the  air  is  expelled,  and  the  small  tube  is  then 
sealed  into  the  large  one  over  the  blast-lamp  without  interrupting  the  gas- 
current  until  the  very  last  instant,  when  to  prolong  it  would  perhaps  cause 
a  blowing  out  of  the  softened  glass.  The  interruption  of  the  current  at  the 
proper  moment  is  easily  effected  by  the  pressure  of  the  thumb  and  finger 
holding  the  small  tube  at  the  point  where  it  enters  the  rubber  tube  leading 
from  the  gas-generator.  No  breakage  in  the  oven  ever  occurs  as  a  conse- 
quence of  thus  fusing  one  tube  into  the  other. 

The  heating  is  done  in  a  bomb  oven  at  any  desired  temperature  up  to, 
say,  200°  and  continued  at  intervals  until  examination  by  aid  of  a  low- 
power  lens  shows  that  decomposition  is  complete  or  has  progressed  as  far 
as  can  be  hoped  for.  By  inclosing  the  glass  in  an  outer  tube  of  strong  steel, 
properly  capped  *  and  containing  a  little  ether  or  benzin  to  equalize  the 
pressure  on  both  sides  of  the  glass,  the  temperature  can  be  elevated  far  be- 
yond what  is  otherwise  permissible,  and  the  decomposition  will  then  doubt- 
less be  more  complete  with  refractory  silicates. 

Reason  for  Introducing  Gas  and  Sealing  as  Above  Directed. — The  usual 
practice  in  employing  the  above  method  has  been  to  expel  air  before  sealing 
by  introducing  a  few  crystals  or  lumps  of  an  alkali  carbonate  or  bicarbonate, 
the  gas  set  free  on  their  contact  with  the  acid  being  supposed  to  effectively 
expel  all  air.  That  this  is  not  accomplished  the  following  series  of  compara- 
tive results  long  since  published  elsewhere  f  fully  show.  The  material  used 
was  the  oxide  of  uranium,  U3O8,  requiring  by  theory  32-07  per  cent,  of  UO2. 

*  ULLMANN,  Zeitschr.  fiir  angew.  Chemie,  1893.  p.  274;  Zeit.  fur.  anal.  Chemie,  xxxni 
p.  582.  1894. 

t  Bull.  U.  S.  Geol.  Survey,  No.  78,  p.  50;  Chemical  News,  LXIV,  p.  232,  1891. 


SOME    PRINCIPLES    AND    METHODS   OF  ROCK   ANALYSIS.    1171 
Operating  as  just  above  described  on  from  0-3  to  0-5  gnn.,  the  results  were 

31-06,  31-07,  29-72,  29-33,  29-89,  30-69, 

whereas  after  filling  the  tube  with  gas  from  a  generator  there  was  found 
32-11,  31-90,  32-15,  32-12,  32-06,  32-17,  32-28, 

the  average  error  of  the  former  series  being  1  •  78  per  cent.  The  percentage 
error  would,  of  course,  be  reduced  by  increasing  the  weight  of  mineral  operated 
on.  An  average  error  equal  to  the  above  when  employing  1  grm.  of  ferrous 
minerals  would  make  the  percentage  for  FeO  about  0-3  per  cent,  too  low. 
While  the  absolute  error  might  be  the  same  in  all  cases,  the  relative  error 
would  increase  with  minerals  low  in  ferrous  iron. 

THE  HYDROFLUORIC-ACID  METHOD. 

This  method  is  the  one  which  has  been  almost  exclusively  used  since  the 
earliest  years  of  the  Survey's  existence. 

The  specially  ground  powder,  in  a  capacious  crucible,  is  placed,  after 
stirring  up  with  dilute  sulphuric  acid,  on  a  small  water-bath  of  a  single  open- 
ing (Fig.  13)  and  covered  with  a  glass  funnel,  the  stem  of  which  has  been  cut 
off  near  the  flare,  resting  in  a  depression  of  the  specially  made  cover,  into 
which  water  constantly  drops  from  a  tubulated  bottle,  thus  securing  a  per- 
fect water  joint  and  serving  to  keep  the  bath  full.  Through  a  small  metal 
pipe  carbonic-acid  gas  flows  into  the  bath  above  the  surface  of  the  water, 
and  rising  through  orifices  in  the  cover  fills  the  funnel  and  crucible.*  The 
lamp  under  the  bath  is  lighted  and  hydrofluoric  acid  is  poured  into  the  cru- 
cible through  a  platinurn  funnel,  which  is  left  in  place  to  serve  as  an  occa- 
sional starrer,  for  which  a  rod  or  wire  may  be  substituted.  After  boiling 
commences  the  rapid  gas  current  can  be  safely  interrupted,  to  be  restored 
when  the  lamp  is  extinguished  after  one-half  to  one  or  more  hours.  A  full 
stream  of  cold  water  is  then  caused  to  flow  from  the  tubulated  bottle  into 
the  bath,  the  overflow  from  the  outlet  tube  being  caught  in  a  receiver.  As 
soon  as  cool  the  contents  of  the  crucible  are  emptied  into  a  platinum  dish 
containing  cold  water  and  titrated  till  the  first  permanent  color  appears, 
which  usually  will  last  for  only  a  few  seconds.  Duplicate  determinations  are 
to  be  advised  whenever  possible,  since  even  with  the  utmost  care  the  results 
will  occasionally  differ  more  than  is  allowable. 

In  absence  of  a  suitable  water-bath  an  ordinary  one  can  be  used  covered 
with  a  beaker,  through  a  hole  in  the  bottom  of  which  a  strong  current  of 
carbon  dioxide  is  introduced,  or  the  crucible  may  be  set  in  a  sand-bath  and 
covered  in  the  same  way  with  a  broken  beaker  (DOELTER). 

The  cause  of  the  rapid  disappearance  of  the  first  pink  blush  when  titrating 
in  hydrofluoric-sulphuric  solution  appears  to  be  the  ready  oxidizability  of 
manganous  fluoride  by  permanganate.  The  latter  can  be  added  by  the  cubic 

*  J.  P.  COOKE,  Am.  Journ.  Sci.,  2d  Series,  xuv,  p.  347.  1867. 


1172 


APPENDIX   II. 


centimeter  to  solutions  already  containing  manganous  sulphate  in  presence 
of  hydrofluoric  acid  without  producing  a  more  than  passing  pink  blush.  The 
solution,  however,  takes  on  in  ever-increasing  intensity  the  red-brown  color 


Fio.  13. — COOKE'S  apparatus  for  the  determination  of  ferrous  iron. 


characteristic  of  manganic  salts.  The  decolorization  due  to  this  cause  is 
hence  much  more  pronounced  in  the  case  of  rocks  high  in  ferrous  iron  than 
of  those  low  in  this  constituent,  because  of  the  greater  amount  of  manganous 


SOME   PRINCIPLES  AND   METHODS   OF   ROCK  ANALYSIS.    1173 

salt  resulting  from  reduction  of  a  correspondingly  larger  amount  of  perman- 
ganate. 

When  pyrite  is  present  the  bleaching  is  hi  part  due  to  its  action  on  any 
permanganate  added  in  excess  of  the  requirements  of  the  ferrous  oxide.  But 
this  action  is  not  so  immediate  as  to  affect  the  ferrous  oxide  determination 
if  the  end  point  hi  the  latter  has  been  properly  observed. 

PRATT'S  MODIFICATION  OF  THE  HYDROFLUORIC-ACID  METHOD. 
J.  H.  PRATT  *  has  shown  that  very  satisfactory  ferrous-iron  determinations 
can  be  secured  by  simple  boiling  of  the  rock  powder  with  hydrofluoric  and 
sulphuric  acids  hi  a  large  crucible  fitted  with  a  cover  and  platinum  tube  for 
introduction  of  carbon  dioxide.  His  test  experiments  on  ferrous  sulphate 
show  that  there  need  be  practically  no  oxidation,  even  if  the  heating  lasts 
several  hours.  The  directions  given  on  page  150  of  his  paper,  with  reference 
to  the  treatment  of  very  refractory  minerals  which  are  not  fully  decomposed 
by  this  treatment,  must  be  understood  as  referring  only  to  homogeneous 
minerals  and  not  to  rocks,  where  the  relations  of  ferrous  and  ferric  iron  in  the 
undecomposed  portion  are  certainly  different  from  those  in  the  part  dissolved. 

INFLUENCE  OF  SULPHIDES,  VANADIUM,  AND  CARBONACEOUS  MATTER  ON  THE 
DETERMINATION  OF  FERROUS  IRON  BY  THE  HYDROFLUORIC-ACID  METHOD. 

A  dark  color  of  the  undissolved  residue  may  be  due  to  pyrite,  graphite,  or 
carbonaceous  matter.  The  first  of  these  affects  the  result  but  little,  the 
second  probably  not  at  all,  and  they  can  be  distinguished  by  their  behavior 
toward  nitric  acid.  Organic  matter  of  course  renders  impossible  the  esti- 
mation of  ferrous  iron. 

Sulphides. — Pyrite,  in  the  quantities  usually  met  with  in  igneous  rocks, 
is  probably  without  serious  effect  on  the  ferrous-iron  determination  by  any  of 
the  hydrofluoric-acid  methods.  This  sulphide  is  very  resistant  toward  attack 
in  the  absence  of  oxygen,  as  is  shown  by  the  fact  that  if  present  in  any  quan- 
tity it  can  be  readily  recognized  in  the  residue  after  titration.  In  any  case 
it  is  impossible  to  allow  for  an  error  introduced  by  its  possible  decomposition, 
and  the  result  of  titration  must  count  as  ferrous  iron.  In  the  case  of  soluble 
sulphides  two  sources  of  error  are  introduced — that  of  reduction  of  ferric  iron 
by  hydrogen  sulphide  evolved,  and  that  due  to  the  ferrous  iron  which  the  sul- 
phides themselves  may  contain,  especially  if  pyrrhotite  is  present.  The  first 
of  these  is  perhaps  negligible,  since  most  of  the  hydrogen  sulphide  would 
probably  be  expelled  without  reducing  iron.  The  second  is  approximately 
measurable  if  it  is  known  that  pyrrhotite  is  the  only  soluble  sulphide  present 
and  its  amount  has  been  ascertained  by  determining  the  hydrogen  sulphide 
sot  free  on  boiling;  with  hydrochloric  acid  in  a  current  of  carbon  dioxide.  In 
this  case  a  correction  is  to  be  applied  to  the  result  of  titration  for  total  ferrous 
iron.  (See  also  page  1184,  under  Sulphur.) 

In  order  to  obtain  quantitative  data  regarding  the  effect  of  pyrite  on  the 
ferrous-iron  estimation  by  the  hydrofluoric-acid  method  the  following  tests 

*  Am.  Journ.  Sci.,  3d  Series,  XLVIII,  p.  149,  1894. 


1174  APPENDIX    II. 

were  recently  made:  Part  of  a  fine  crystal  of  pyrite  was  rather  finely  pow- 
dered and  boiled  with  dilute  sulphuric  acid,  which  extracted  considerable 
ferrous  iron,  derived  presumably  from  admixed  or  intergrown  pyrrhotite, 
since  a  second  boiling  with  fresh  acid  gave  a  negative  test  for  ferrous  iron. 
After  washing  by  decantation  with  water,  followed  by  alcohol  and  ether,  the 
powder  was  dried  and  further  pulverized.  A  quarter  of  a  gramme,  of  it  when 
treated  with  hydrofluoric  and  sulphuric  acids  in  a  large  crucible  by  the 
COOKE  method  for  ferrous  iron,  then  rapidly  filtered  through  a  very  large 
perforated  platinum  cone  fitted  with  filter-paper,  required  but  2  drops  of  a 
permanganate  solution  representing  only  0  •  0032  grm.  FeO  to  the  cubic  centi- 
meter. 

Since,  however,  Dr.  H.  N.  STOKES  has  found  in  a  pending  investigation 
that  the  oxidizing  effect  of  ferric  salts  on  pyrite  and  other  sulphides  is  vastly 
greater  than  seems  to  have  been  suspected  (see  page  1168),  the  following  tests 
were  made  in  order  to  ascertain  the  probable  error  due  to  this  action  under 
the  conditions  prevailing  in  rock  analysis :  Successive  portions  of  1  grm.  each 
of  a  hornblende-schist,  free  from  sulphur  and  carrying  10-09  per  cent.  FeO 
as  the  mean  of  several  determinations  and  4-00  percent.  Fe2O3,  were  mixed 
in  a  large  (50  c.c.)  platinum  crucible  with  0-02,  0-025,  and  0-10  grm., 
respectively,  of  the  above  purified  pyrite  powder,  and  treated  with  hydro- 
fluoric and  sulphuric  acids  by  the  COOKE  method,  the  water-bath  being  at 
boiling  heat  for  one  hour.  The  cooled  contents  of  the  crucible  were  poured 
into  a  platinum  dish  containing  water  and  titrated  rapidly  nearly  to  an  end. 
Then,  in  order  to  get  rid  of  the  pyrite,  which  would  obscure  the  end  reaction 
by  its  reducing  effect  on  the  permanganate,  the  solution  was  filtered  as  above 
and  in  the  clear  filtrate  the  titration  was  carried  to  completion.  The  results 
were  10  •  02,  10  •  16,  and  10  •  70.  Inasmuch  as  the  smallest  of  these  three  charges 
of  pyrite  was  several  times  greater  than  what  may  be  considered  an  unusually 
high  amount  for  an  igneous  rock,  it  is  very  evident  that  for  all  practical  pur- 
poses the  influence  of  pyrite  on  the  ferrous  estimation  by  the  COOKE  method 
is  negligible.  At  the  same  time  it  is  to  be  borne  in  mind  that  with  increased 
content  in  ferric  iron  an  increased  amount  of  pyrite  will  be  attacked,  and 
that  the  extent  of  this  attack  is  undoubtedly  influenced  by  the  degree  of 
fineness  of  the  pyrite  powder. 

Vanadium. — If  vanadium,  when  present,  exists  in  the  trivalent  condition, 
it  necessarily  affects  with  an  error  varying  with  its  amount  the  result  of  titra- 
tion for  ferrous  iron.  Knowing  the  amount  of  vanadium  a  correction  can  be 
applied  as  follows:  One  molecule  of  V2O3  (150-8)  in  oxidizing  to  V2O5  requires 
as  much  oxygen  as  four  molecules  of  FeO  (288)  when  oxidized  to  Fe2O.  The 
proportion,  150-8  :  288  : :  V2O3  present  :  x,  therefore  gives  the  figure  to  be 
deducted  from  the  unconnected  value  for  FeO.  That  this  correction  is  very 
needful  with  many  of  the  basic  rocks  becomes  at  once  evident  from  the  fol- 
lowing perhaps  extreme  example : 

Found  2-50  per  cent,  apparent  FeO  in  a  rock  containing  0-13  per  cent. 
V203. 

Deduct  0  •  25  per  cent.  FeO  equivalent  in  its  action  on  KMnO4  to  0  •  13  V2O3. 

Leaving  2  •  25  per  cent.  FeO  corrected. 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK   ANALYSIS.    1175 

Found  5  •  00  per  cent,  apparent  total  iron  as  Fe2O3  in  the  same  rock. 

Deduct  •  14  per  cent.  Fe2O3  corresponding  to  0-13  per  cent.  V2O3. 

Leaving  4  •  86  per  cent,  corrected  total  iron  as  Fe2O3. 

Deduct  2  •  50  per  cent.  Fe2O3  equivalent  to  2  •  25  per  cent.  FeO. 

Leaving  2  36  per  cent.  Fe2O3  in  the  rock. 

Failure  to  correct  for  the  vanadium  in  both  cases  would  have  made  the 
figures  for  FeO  and  Fe2O3,  respectively,  2-50  and  2-22  instead  of  2-25  and 
2  •  36  as  shown  above. 

Carbonaceous  Matter. — As  said  before  (page  1173),  matter  of  organic  origin 
other  than  graphic  carbon  lenders  the  results  from  the  ferrous  iron  determi- 
nation altogether  unreliable. 

UNCERTAINTIES  OF  THE  FERROUS  IRON  DETERMINATION. 

From  the  foregoing  it  is  apparent  that,  despite  the  utmost  care  in  prac- 
tical manipulation,  the  exact  estimation  of  ferrous  iron  in  rocks  is  one  fraught 
with  extraordinary  difficulties  and  uncertainties.  Only  in  absence  of  de- 
composable sulphides,  and  when  the  amount  and  condition  of  vanadium  are 
known,  can  the  result  be  regarded  as  above  suspicion. 

XX.  ALKALIES. 

THE  LAWRENCE  SMITH  METHOD. 

The  various  methods  for  getting  at  the  alkalies  in  insoluble  silicates  differ 
more  in  the  mode  of  attack  of  the  mineral  powder  and  in  the  immediately 
subsequent  treatment  than  in  the  final  stages.  With  very  few  exceptions, 
since  the  early  days  of  the  Survey's  existence,  all  alkali  determinations  have 
been  made  by  the  method  of  J.  LAWRENCE  SMITH,*  which  is  far  more  conven- 
ient than  and  fully  as  accurate  as  those  in  which  decomposition  is  effected 
by  hydrofluoric  and  sulphuric  acids,  or  by  bismuth,  lead,  or  boric  oxides. 
One  of  its  chief  advantages  is  the  entire  elimination  of  magnesia  at  the  start. 

Decomposition  of  the  powder  is  effected  by  heating  it  with  its  own  weight 
of  ammonium  chloride  and  eight  times  as  much  precipitated  calcium  car- 
bonate. 

The  ammonium  chloride  used  must  be  purified,  preferably  by  sublima- 
tion, or  made  by  neutralizing  pure  ammonia  by  pure  hydrochloric  acid,  and 
the  calcium  carbonate  is  best  obtained  from  pure  calcite  by  solution  and 
reprecipitation.  However  obtained,  this  last  is  rarely  free  from  alkalies, 
which  must  be  estimated  once  for  all  in  a  blank  test  in  order  to  apply  a  cor- 
rection. Eight  grm.  of  the  carbonate  will  contain  usually  from  0-0012  to 
0-0016  grm.  of  alkali  chlorides,  almost  entirely  the  sodium  salt,  but  the 
amount  has  been  brought  down  to  half  the  above  by  very  long  washing.  This 
correction  may  be  admitted  at  once  to  be  a  defect  of  the  method,  but  it  is 
one  easily  applied  with  safety.  41 

The  ignition  may  be  made  in  a  covered  crucible  of  ordinary  shape  and 

*  Am.  Journ.  Sci.,  2d  Series,  L,  p.  269,  1871;  Am.  Chemist,  x,  1871;  Annalen  Chem. 
vnd  Pharm.,  CLIX,  p.  82,  1871. 


1176 


APPENDIX    II. 


of  about  20  to  30  c.c.  capacity,  heated  to  dull  redness  for  not  more  than 
two-fifths  of  its  height,  but  the  heat  has  to  be  kept  so  low  in  this  case  to 
avoid  loss  by  volatilization  that  perfect  decomposition  is  not  always  assured. 
Hence,  to  avoid  waste  of  time,  in  very  fine  grinding,  the  form  of  crucible  with  cap 
originally  advocated  by  SMITH  is  very  much  to  be  preferred,  since  it  permits, 
when  set  at  an  angle  through  an  opening  in  the  side  of  a  fire-clay  cylinder, 
of  the  application  of  the  full  heat  of  two  burners,  and  perfect  decomposi- 
tion invariably  results  without  the  need  of  extraordinary  care  in  grinding. 
The  crucible  used  in  this  laboratory  (Fig.  14)  for  one-half  grm.  of  rock  pow- 
der and  4  grm.  calcium  carbonate  is  8  cm.  long,  1  •  8  cm.  wide  at  the  mouth, 


FIG.  14. — The  J.  LAWRENCE  SMITH  crucible  for  alkali  determinations, 
dimensions  see  text. 


For 


and  1*5  at  the  bottom.     For  double  the  amounts  or  more  the  dimensions 
are  8  cm.,  2-5  cm.,  and  2-2  cm.     The  weights  are  25  and  40  grm. 

Treatment  of  the  Mineral  Powder. — Perfectly  satisfactory  results  are 
to  be  obtained  with  but  a  half  gramme  of  rock  powder.  This  is  weighed  out, 
ground  down  somewhat  finer  in  a  large  agate  mortar,  mixed  with  its  own 
weight  of  sublimed  ammonium  chloride,  and  the  two  thoroughly  ground 
together.  Then  nearly  all  of  4  grm.  of  calcium  carbonate  is  added  and  the 
grinding  continued  till  a  thorough  mixing  has  resulted.  The  contents  of 
the  mortar  are  transferred  to  the  long  crucible,  the  rest  of  the  carbonate 
being  used  for  rinsing  off  mortar  and  pestle.  The  crucible  is  then  capped 
and  placed  in  a  clay  cylinder  (Fig.  14),  or  through  a  hole  in  a  piece  of  stout 
asbestos  board  clamped  in  a  vertical  position,  and  heated  for  about  ten 
minutes  by  a  low,  flat  flame  placed  at  considerable  distance  beneath.  As 
soon  as  the  odor  of  ammonia  is  no  longer  perceptible,  the  nearly  full  flame 
of  two  BUNSEN  burners  is  applied,  and  continued  for  forty  to  fifty  minuses. 
The  sintered  cake  *  detaches  readily  from  the  crucible  as  a  rule ;  if  not,  it  is 


*  To  avoid  the  formation  of  a  melted  cake  with  silicates  very  high  in  iron  it  is  advisable 
to  increase  the  proportion  of  calcium  carbonate. 


SOME    PRINCIPLES  AND    METHODS   OF   ROCK   ANALYSIS.    1177 

softened  up  in  a  few  minutes  by  hot  water  and  digested  in  a  dish  until  thor- 
oughly disintegrated.  It  is  first  washed  by  decantation,  and  any  lumps 
are  broken  up  by  a  pestle,  then  thrown  on  the  filter  and  well  washed  with 
hot  water.  The  residue  should  dissolve  completely  in  hydrochloric  acid 
without  showing  the  least  trace  of  unattacked  mineral,  not  even  of  quartz. 

Separation  of  Calcium  and  Sulphuric  Acid. — All  but  a  trifling  amount 
of  the  calcium  is  separated  at  boiling  heat  in  a  large  platinum  dish  by  double 
precipitation  by  ammonia  and  ammonium  carbonate.  The  combined 
filtrates  are  evaporated  to  dryness  and  the  ammonium  salts  are  carefully 
driven  off.  From  the  aqueous  solution  of  the  residue — but  a  few  cubic 
centimetres  in  bulk — the  rest  of  the  calcium  is  thrown  out  by  ammonia 
and  ammonium  oxalate,  this  last  being  more  effective  than  the  carbonate. 
The  filtrate,  caught  in  an  untared  platinum  crucible  or  small  dish,  is  evapo- 
rated to  dryness  and  gently  ignited;  the  residue  is  moistened  with  hydro- 
chloric acid  to  decompose  any  alkali  carbonate  that  may  have  been  formed, 
again  evaporated,  ignited,  and  weighed.  On  solution  in  water  a  few  tenths 
of  a  milligramme  of  fixed  residue  is  invariably  left,  which  should  be  collected, 
ignited,  and  weighed  in  the  same  crucible  or  dish  in  order  to  arrive  at  the 
weight  of  the  chlorides. 

If  the  rock  contains  sulphur  this  will  be  in  part  found  with  the  chlorides 
as  sulphate.  Therefore,  if  the  sulphur  is  at  all  considerable  in  amount  it 
must  be  removed  by  a  drop  of  barium  chloride  before  the  final  precipitation 
of  the  calcium.  The  excess  of  barium  is  removed  by  ammonium  carbonate 
and  the  last  of  the  calcium  by  ammonium  oxalate,  as  above.  If  the  sul- 
phur is  not  thus  removed  there  is  danger,  if  not  certainty,  of  the  potassium- 
platinic  chloride  carrying  sodium  sulphate.  A  faint  reaction  for  sulphate 
can  usually  be  obtained,  anyway,  if  the  evaporations  have  been  made  on 
a  water-bath  heated  by  gas. 

Precipitation  of  Potassium. — To  the  solution  of  the  chlorides  in  a  small 
porcelain  *  dish  an  excess  of  platinic-chloride  solution  is  added.  The  dilu- 
tion should  be  such  that  when  heated  on  the  water-bath  any  precipitate 
that  may  form  wholly  redissolves.  Evaporation  is  then  carried  on  till  the 
residue  solidifies  on  cooling.  It  is  then  drenched  with  absolute  alcohol  f 
or  with  that  of  80-per  cent,  strength,  filtered  by  decantation  through  a  very 
small  filter  and  washed  by  decantation  with  alcohol  of  the  same  strength, 
The  precipitate  is  not  brought  onto  the  filter  more  than  can  be  avoided. 
Dish  and  filter  are  then  dried  for  a  few  minutes  to  remove  adhering  alcohol; 
the  contents  of  the  former  are  transferred  to  a  weighed  platinum  crucible 
or  very  small  dish,  and  what  still  adheres  to  the  porcelain  is  washed  through 
the  filter  with  hot  water  into  the  weighed  receptacle.  This  is  now  placed 

*  Preferred  to  platinum  because  of  the  possibility,  under  certain  rare  and  ill-under- 
stood conditions,  of  the  formation  of  an  insoluble  subchloride  of  platinum,  probably  by 
reaction  between  the  platinum  of  the  dish  and  that  of  the  salt.  (See  also  BOHX,  Zeitschr. 
fiir  anal.  Chemie,  xxxvm,  p.  349,  1899.) 

t  PRECHT  (Zeitschr.  fiir  anal.  Chemie,  xvin,  p.  513,  1879)  claims  that  this  is  to  be 
preferred  to  80-per  cent,  alcohol,  especially  if  evaporation  has  been  carried  to  dehydra- 
tion of  the  sodium  salt.  ATTERBERG  disputes  this  final  statement  and  says  that  80-per 
cent,  alcohol  gives  better  results. 


1178  APPENDIX   II. 

on  the  water-bath  and  afterwards  heated  to  135°  in  an  air-bath.     The  factor 
used  for  reduction  of  K2PtCl6  to  2KC1  is  0-307  of  2KC1  to  K2O,  0-632. 

LITHIUM. 

After  separation  of  the  potassium-platinic  chloride,  the  alcoholic  filtrate 
is  evaporated  and  tested  spectroscopically  for  lithium.  This  element  is  al- 
most invariably  present,  but  almost  never  in  amount  to  warrant  quantita- 
tive estimation.  Should  it  be  so,  however,  the  very  excellent  GOOCH  method 
(summarized  below)  of  separation  by  amyl  alcohol  is  to  be  followed,  after 
removal  of  the  platinum  by  hydrogen  gas.*  In  rock  analysis  there  need  be 
no  fear  of  enough  lithium  falling  with  the  potassium  to  cause  any  concern. 

If  ammonium  carbonate  alone  has  been  relied  on  to  separate  all  calcium 
(ante,  page  1177)  the  few  tenths  of  a  milligramme  of  calcium  chloride  that 
escaped  precipitation  can  now  be  found  with  the  sodium. 

GOOCH'S   METHOD  f    FOR    SEPARATING    LITHIUM. 

To  the  concentrated  solution  of  the  chlorides  amyl  alcohol  is  added  and 
heat  is  applied,  gently  at  first,  to  avoid  danger  of  bumping,  until,  the  water 
disappearing  from  solution  and  the  point  of  ebullition  rising  and  becoming 
constant  for  some  minutes  at  a  temperature  which  is  approximately  that  at 
which  the  alcohol  boils  by  itself,  the  chlorides  of  sodium  and  potassium  are 
deposited  and  lithium  chloride  is  dehydrated  and  taken  into  solution.  At 
this  stage  in  the  operation  the  liquid  is  cooled  and  a  drop  or  two  of  strong 
hydrochloric  acid  added  to  reconvert  traces  of  lithium  hydrate  in  the  deposit, 
and  the  boiling  continued  until  the  alcohol  is  again  free  from  water.  If  the 
amount  of  lithium  chloride  present  is  small,  it  will  now  be  found  in  solution 
and  the  chlorides  of  sodium  and  potassium  will  be  in  the  residue,  excepting 
the  traces  for  which  correction  will  be  made  subsequently.  If,  however,  the 
weight  of  lithium  chloride  present  exceeds  10  or  20  mgrm.,  it  is  advisable 
at  this  point,  though  not  absolutely  essential  to  the  attainment  of  fairly 
correct  results,  to  decant  the  liquid  from  the  residue,  wash  the  latter  a  little 
with  anhydrous  amyl  alcohol,  dissolve  in  a  few  drops  of  water,  and  repeat 
the  separation  by  boiling  again  in  amyl  alcohol.  For  washing,  amyl  alcohol 
previously  dehydrated  by  boiling  is  to  be  used,  and  the  filtrates  are  to  be 
measured  apart  from  the  washings.  In  filtering  it  is  best  to  make  use  of  the 
perforated  crucible  and  asbestos  felt,  and  apply  gentle  pressure.  The  cruci- 
ble and  residue  are  ready  for  the  balance  after  drying  for  a  few  minutes 

*  When  haste  is  not  an  object,  this  way  of  BUNSEN'S  for  removing  platinum  from  the 
chlorides  of  the  alkalies  is  by  far  the  neatest  and  most  satisfactory.  The  small  flask 
containing  the  solution  is  placed  in  a  water-bath  and  attached  to  a  hydrogen  generator. 
After  expelling  all  air  the  flask  is  closed,  without  breaking  connection  with  the  generator, 
and  left  to  itself,  except  for  occasional  light  shaking  up,  till  reduction  is  accomplished. 
A  more  expeditious  and  very  satisfactory  reduction  is  effected  by  evaporating  the  solu- 
tion to  dryness  with  metallic  mercury,  then  heating-to  expulsion  of  the  excess  of  mercury 
and  of  its  chloride  (SONSTADT,  Journ.  Chem.  Soc.,  LXVTI,  p.  984,  1895),  who  thus  reduces 
potassium-platinic  chloride  in  order  to  weigh  its  platinum. 

t  Proc.  Am.  Acad.  Arts  and  Sci.,  p.  177,  1886;  Bull.  U.  S.  Geol.  Survey,  No.  42,  p.  73, 
1887;  Chemical  News,  LV,  pp.  18,  29,  40,  56,  78,  1887;  Am.  Chem.  Journ.,  ix,  p.  33,  1887. 


-  SOME    PRINCIPLES   AND    METHODS   OF   ROCK   ANALYSIS.    1179 

directly  over  a  flame  turned  low.  The  weight  of  insoluble  chlorides  actually 
obtained  in  this  manner  is  to  be  corrected  by  the  addition  of  0-00041  grm. 
for  every  10  c.c.  of  amyl  alcohol  in  the  filtrate,  exclusive  of  washings,  if  the 
insoluble  salt  is  entirely  sodium  chloride,  0-00051  grm.  for  every  10  c.c.  if 
potassium  chloride  constitutes  the  residue,  and  if  both  sodium  and  potassium 
chlorides  are  present,  0-00092  grm.;  but  the  entire  correction  may  in  any 
case  be  kept  within  very  narrow  limits  if  due  care  be  given  to  the  re- 
duction of  the  volume  of  residual  alcohol  before  filtration.  The  filtrate  and 
washings  are  evaporated  to  dryness,  treated  with  sulphuric  acid,  the  excess 
of  the  latter  driven  off,  and  the  residue  ignited  to  fusion  and  weighed.  From 
the  weight  thus  found  the  subtraction  of  0  •  0005  grm.  is  to  be  made  if  sodium 
chloride  constitutes  the  precipitate,  0-00059  grm.  if  potassium  chloride  alone 
is  present  in  the  residue,  and  0-00109  grm.  if  both  these  chlorides  are  present, 
for  every  10  c.c.  of  filtrate,  exclusive  of  washings. 

Amyl  alcohol  is  not  costly,  the  manipulations  of  the  process  are  easy,  and 
the  only  objectionable  feature  —the  development  of  the  fumes  of  amyl  alcohol 
— is  one  which  is  insignificant  when  good  ventilation  is  available. 

The  process  has  been  used  for  some  months  frequently  and  successfully, 
by  others  as  well  as  by  myself,  for  the  estimation  of  lithium  hi  waters  and 
minerals. 

SEPARATION  OF  ALKALIES  BY  OTHER  METHODS. 

When,  as  may  happen  in  rare  instances,  it  is  necessary  to  estimate  alka- 
lies in  the  main  portion  after  elimination  of  silica,  alumina,  lime,  etc.,  in 
one  of  the  usual  ways,  the  question  of  a  suitable  method  for  separating  mag- 
nesium becomes  important. 

The  Mercuric-oxide  Method. — The  old  barium-hydroxide  method  is  not 
to  be  recommended.  The  mercuric- oxide  method  of  ZIMMERMANX,  whereby 
the  magnesia  is  precipitated  from  solution  of  the  chlorides  by  moist,  freshly 
precipitated,  and  alkali-free  mercuric  oxide,  can  give  satisfactory  results. 
The  oxide  is  added  in  excess  to  the  solution  in  a  platinum  crucible  and  evapo- 
rated to  dryness.  Then  the  mercuric  chloride  and  most  or  all  of  the  excess 
of  oxide  are  expelled  by  cautious  heating.  On  leaching  with  water  the  mag- 
nesia remains  on  the  filter.  With  more  than  1  per  cent,  of  magnesia  the 
operation  must  be  repeated  (DITTRICH). 

The  Ammonium-Carbonate  Method. — Lately  the  once-favored  method 
of  precipitating  the  magnesium  by  neutral  ammonium  carbonate  in  con- 
centrated solution  has  been  again  recommended.*  The  magnesium  solu- 
tion must  be  as  strongly  concentrated  as  possible,  and  a  great  excess  of  ammo- 
nium-carbonate solution  must  be  used.  A  voluminous  precipitate  forms, 
which  dissolves  on  vigorous  stirring  if  enough  of  the  precipitant  was  used. 
After  a  time  a  crystalline  precipitate  falls — a  double  carbonate  of  magnesium 
and  ammonium — which  is  insoluble  in  a  concentrated  solution  of  ammonium 
carbonate.  Allow  to  stand  for  six  to  twenty-four  hours.  Wash  with  the 

*  WtLFixo,  d .  Ber.  deutsch.  Chem.  Gesell.,  xxxn,  p.  2214,  1899.  The  neutral  carbonate 
is  prepared  by  dissolving  230  grm.  of  ammonium  carbonate  in  180  c.c.  of  ammonia  of 
0-92  specific  gravity  and  enough  water  to  make  1  litre. 


1180  APPENDIX   II. 

concentrated  ammonium-carbonate  solution.  It  is  probably  no  exercise 
of  undue  caution  to  redissolve  and  reprecipitate  to  make  sure  of  getting  all 
alkali  in  the  filtrate. 

The  Amyl-olcohol  Method. — Under  certain  circumstances,  notably  ab- 
sence of  lithium,  the  method  of  GOOCH  developed  by  RIGGS  *  may  be  satis- 
factory. It  is  similar  to  that  of  GOOCH  for  separating  lithium  from  sodium 
and  potassium  chlorides  by  amyl  alcohol,  and  involves  the  same  solubility 
corrections  for  the  alkali  chlorides  above  noted  (p.  1179)  in  the  description 
of  GOOCH'S  method.  RIGGS'S  summary  is  as  follows: 

Evaporate  the  solution  nearly  or  quite  to  dryness.  Dissolve  the  residue 
in  as  little  water  as  possible  and  add  a  few  drops  of  hydrochloric  acid.  Then 
add  30  to  40  c.c.  of  amyl  alcohol  and  expel  the  water  by  bringing  the  alcohol 
to  boiling.  Continue  the  boiling  until  the  volume  of  the  solution  is  reduced 
to  10  c.c.,  or  even  considerably  less.  In  filtering,  it  is  of  great  advantage 
to  use  a  perforated  crucible  and  an  asbestos  felt  and  to  filter  under  pressure. 
In  case  the  total  chlorides  exceed  0-2  grm.  it  may  be  advisable  to  decant  the 
liquid,  wash  the  residue,  redissolve,  and  repeat  the  precipitation.  If  this 
be  not  done,  the  precipitate  should  be  redissolved  with  the  least  possible 
quantity  of  water,  a  few  drops  of  hydrochloric  acid  added,  and  the  pre- 
cipitation repeated  in  the  original  solution.  The  filtrate  is  transferred  to  a 
weighed  platinum  dish  and  evaporated.  Water  is  added  before  the  alcohol 
has  been  expelled  and  the  evaporation  continued.  The  residue  is  dis- 
solved in  water.  Sulphuric  acid  is  added  in  slight  excess.  This  solution 
is  evaporated  to  dryness,  the  residue  ignited  and  weighed,  and  the  treatment 
with  sulphuric  acid  is  repeated.  The  residue  of  insoluble  chlorides  may 
be  transferred  to  the  weighed  perforated  crucible  and  dried  at  a  tempera- 
ture below  their  melting-points,  or  it  may  be  dissolved  and  the  solution 
transferred  to  a  weighed  platinum  dish,  evaporated,  and  the  residue  dried 
as  above  and  weighed. 

As  with  the  GOOCH  method  for  lithium,  the  numerous  test  results  are 
good. 

XXI.    CARBON  DIOXIDE,  CARBON. 

For  this  estimation  an  apparatus  (Fig.  15)  permanently  set  up  is  used, 
of  which  several  forms  have  been  described  by  different  writers.  The  rock 
powder  is  boiled  with  dilute  hydrochloric  acid  in  a  small  ERLENMEYER  flask 
attached  to  an  upward-inclined  condenser,  whence,  after  passing  through 
a  compact  arrangement  of  drying-tubes — first,  one  of  calcium  chloride, 
then  one  of  anhydrous  copper  sulphate  to  retain  hydrogen  sulphide  from 
decomposable  sulphides  and  any  hydrochloric  acid  that  may  pass  over, 
and  finally  a  second  calcium-chloride  tube — the  carbon  dioxide  is  retained 
by  absorption  tubes  filled  with  soda-lime  followed  by  calcium  chloride. 
Of  course,  arrangement  is  made  for  a  current  of  CO,-free  air  with  which  to 
sweep  out  the  apparatus  before  and  after  the  experiment,  and  for  a  slow 

*  Am.  Journ.  Sci.,  3d  Series,  XLIV,  p.  103,  1892. 


SOME    PRINCIPLES    AND    METHODS   OF   ROCK   ANALYSIS.    1181 

current  during  its  continuance.     The  results  are  very  accurate  and  the  deter- 
mination can  be  quickly  carried  out. 

In  the  preliminary  qualitative  test  for  carbon  dioxide,  it  must  be  re- 
membered that  while  calcite  gives  off  its  carbon  dioxide  on  treatment  with 


FIG.  15. — Compact  form  of  apparatus  for  estimation  of  carbon  dioxide. 

cold  acid,  dolomite  and  siderite  do  not,  and  hence  warming  should  not  be 
omitted;  otherwise,  a  few  tenths  per  cent,  of  carbon  dioxide  can  very  well 
be  overlooked.  Moreover,  the  powder  should  first  be  stirred  up  with  a  little 
hot  water,  to  remove  all  entangled  air  which  might  otherwise  be  mistaken 
for  carbon  dioxide. 

It  has  been  already  shown  under  water  (p.  1129)  how,  in  case  of  need, 


1182  APPENDIX   II. 

the  determination  of  carbon  dioxide  can  be  combined  with  that  of  water 
by  fusion  with  lead  chromate  or  potassium  chromate.  This  latter  method 
must  always  be  resorted  to  when  the  carbon  of  graphite  or  carbonaceous 
matter  has  to  be  estimated.  If  carbonates  are  present  at  the  same  time  the 
result  of  the  test  includes  the  carbon  from  both  sources,  and  a  separate  deter- 
mination by  the  wet  way  of  that  of  the  carbonates  is  necessary. 

XXII.    CHLORINE. 

To  make  sure  of  getting  all  the  chlorine,  it  is  best  to  fuse  with  chlorine- 
free  sodium-potassium  carbonate,  or  even  sodium  carbonate  alone,  first 
over  the  full  burner,  then  for  a  moment  or  two  over  the  blast,  leach  with 
water,  acidify  with  nitric  acid,  and  precipitate  by  silver  nitrate  without 
preliminary  separation  of  silica.  If  1  grm.  of  material  has  been  used  no 
precipitation  of  silica  need  be  feared  on  acidifying  or  on  standing. 

In  many  cases  it  is  quite  sufficient  to  attack  the  powder  by  chlorine- 
free  hydrofluoric  acid  and  a  little  nitric  acid,  with  occasional  stirring,  and 
after  filtering  through  paper  fitted  into  a  large  platinum  cone  or  rubber 
funnel,  to  throw  down  the  chlorine  by  silver  nitrate.  The  presence  of  nitric 
acid  is  necessary,  since  otherwise  ferrous  fluoride  reduces  silver  nitrate  with 
deposition  of  crystallized  silver.  When  coagulated  by  heating  and  stirring, 
the  precipitate  is  collected  on  the  filter,  washed,  dissolved  by  a  little 
ammonia,  and  reprecipitated  by  nitric  acid,  when  it  can  be  collected  in  a 
GOOCH  crucible  and  weighed,  or,  if  very  small  in  quantity,  on  a  small  filter- 
paper,  which  is  then  dried,  wound  up  in  a  tared  platinum  wire,  and  care- 
fully ignited.  The  increased  weight  of  the  wire  is  due  to  the  metallic  silver 
of  the  chloride  which  has  alloyed  with  it. 

XXIII.    FLUORINE. 

Fluorine  can  only  be  estimated  by  the  method  of  ROSE,  care  being  taken 
to  use  sodium -potassium  carbonate  as  a  flux,  and  to  avoid  use  of  the  blast 
if  possible.  For  minerals  rich  in  fluorine  and  low  in  silica  it  may  be  neces- 
sary to  add  pure  silica  before  the  fusion  in  order  to  effect  complete  decom- 
position of  the  fluoride  just  as  with  the  alkaline-earth  phosphates.  To  the 
hot  aqueous  extract  several  grammes  of  ammonium  carbonate  are  added,  and 
more  on  cooling.  After  twelve  hours  the  solution  is  filtered,  ammonium 
carbonate  is  expelled,  and  an  ammoniacal  solution  of  zinc  oxide  added, 
whereupon  evaporation  is  carried  on  till  the  odor  of  ammonia  is  entirely 
gone.  After  filtering,  add  nitric  acid  in  insufficient  quantity  to  fully 
neutralize. 

The  use  of  ammonium  nitrate  or  chloride,  instead  of  carbonate,  for 
throwing  out  the  silica  and  alumina  is  not  to  be  recommended,  because 
of  loss  of  fluorine  on  evaporation  (ROSE).  If  the  rocks  are  very  basic  it 
may  happen  that  the  amount  of  silica  in  the  alkaline  solution  is  so  small 
that  ammonium  carbonate  may  be  dispensed  with  and  the  ammoniacal 
zinc- oxide  solution  added  at  once. 


SOME    PRINCIPLES   AND    METHODS   OF   ROCK   ANALYSIS.    1183 

By  whatever  modification  of  the  method  the  silica  and  alumina  may 
have  been  separated,  the  alkali  carbonate  must  be  converted  into  nitrate 
and  not  chloride  if  phosphorus  or  chromium,  or  both,  are  present.  To 
remove  the  chromium  and  the  last  of  the  phosphorus,  silver  nitrate  in  excess 
is  added  to  the  solution  containing  still  enough  alkali  carbonate  to  cause 
a  copious  precipitate  of  silver  carbonate,  which  shall  take  up  the  acid  set 
free  and  thus  insure  a  neutral  solution  and  consequent  complete  precipita- 
tion of  phosphorus  and  chromium.  After  heating  and  filtering,  the  excess 
of  silver  is  to  be  removed  by  sodium  or  potassium  chloride,  and  sodium 
carbonate  is  to  be  added,  in  order  to  furnish  by  addition  of  calcium  chloride 
in  excess  to  the  hot  solution  a  sufficient  admixture  of  calcium  carbonate 
with  the  fluoride.  At  this  stage  there  must  be  no  ammoniacal  salts  in  solu- 
tion, otherwise  calcium  fluoride  may  be  held  up. 

The  next  operation  is  perhaps  best  conducted  as  recommended  by  PEN- 
FIELD  and  MINOR.*  To  the  gently  ignited  precipitate  of  carbonate  and 
fluoride  of  calcium,  at  most  1  to  2  c.c.  of  acetic  acid  are  added  in  the  crucible, 
which  is  then  placed  for  a  time  on  the  water-bath  and  afterwards  its  con- 
tents are  evaporated  to  dryness.  They  are  then  taken  up  with  hot  water, 
the  solution  is  decanted  through  a  small  filter,  likewise  the  washings.  The 
filter  is  burned  in  the  same  crucible,  more  acetic  acid  is  added,  and  the  various 
operations  are  repeated  until  all  calcium  oxide  and  carbonate  have  been 
extracted.  The  above  authors  find  that  if  a  great  excess  of  acetic  acid  is 
used  at  the  start,  the  results  are  low.  While  their  experiments  related 
to  the  determination  of  fluorine  in  a  mineral  rich  in  that  element — topaz — 
their  precautions  are  probably  not  needless  with  the  small  amounts  of 
fluorine  met  with  in  rocks. 

The  well-washed  and  gently  ignited  calcium  fluoride  finally  obtained  in 
the  course  of  this  method  should  be  converted  into  sulphate  as  a  check  upon  its 
purity,  and  at  the  same  time  as  a  qualitative  test  to  ascertain  if  it  really  is 
calcium  fluoride  by  the  characteristic  odor  of  the  gas  given  off.  Should 
fluorine  be  found,  and  the  weight  of  sulphate  not  correspond  to  that  of  the 
fluoride,  the  former  should  be  dissolved  in  hot  nitric  acid  and  tested  for 
phosphorus  by  ammonium-molybdate  solution.  If  phosphate  is  absent 
the  impurity  may  have  been  silica  or  calcium  silicate — which  of  these  it  would 
be  difficult  to  decide.  In  the  former  case  the  fluorine  might  be  safely  deduced 
from  that  of  the  sulphate,  but  not  in  the  latter.  If  the  rock  were  rich  in 
sulphur  it  might  happen  that  calcium  sulphate  would  be  thrown  down  with 
the  fluoride,  but  this  should  be  removed  by  thorough  washing.  If  not,  and 
it  were  certainly  the  only  impurity  present,  the  fluorine  could  be  calculated, 
after  conversion  of  the  fluoride  into  sulphate,  by  the  formula : 

CaSO4— CaF2 :  2F  : :  Diff.  between  impure  CaSO4  and  CaF2 :  x. 

It  is  an  exceptional  case  when  there  is  exact  agreement  between  the 
weight  of  fluoride  and  sulphate,  and  with  the  small  amounts  usually  met  in 

*  Am.  Journ.  Sci.,  3d  Series,  XLVII,  p.  389,  1894. 


1184  APPENDIX    II. 

rocks  the  error  may  be  an  appreciable  one  in  percentage  of  fluorine,  though 
of  no  great  significance  otherwise. 

There  is  no  qualitative  test  which  will  reveal  with  certainty  the  presence 
of  fluorine  in  rocks.  Heating  the  powder  before  the  blow-pipe  with  sodium 
metaphosphate  on  a  piece  of  curved  platinum  foil  inserted  into  one  end  of 
a  glass  tube,  or  in  a  bulb  tube,  is  not  to  be  relied  on  in  all  cases.  While  as 
little  as  one-tenth  of  1  per  cent,  of  fluorine  can  sometimes  be  thus  detected 
with  ease,  much  larger  amounts  in  another  class  of  rocks  may  fail  to  show. 

XXIV.     SULPHUR. 

Before  proceeding  to  the  estimation  of  sulphur,  its  condition,  if  present, 
should  be  ascertained. 

Evolution  of  hydrogen  sulphide  on  boiling  with  hydrochloric  acid  is 
evidence  of  a  soluble  sulphide,  usually  pyrrhotite,  but  possibly  lazurite. 
Extraction  of  magnetic  particles  reacting  for  sulphur  shows  pyrrhotite  to 
have  been,  in  part  at  least,  the  source  of  the  hydrogen  sulphide.  A  reaction 
for  sulphuric  acid  in  the  filtered  solution  indicates  a  soluble  sulphate,  usually 
noselite  or  hauynite.  If  the  residue,  when  well  washed  and  treated  with 
aqua  regia  or  hydrochloric  acid  and  bromine,  gives  more  sulphuric  acid,  the 
probable  presence  of  pyrite  is  shown.  Should  this  solution  likewise  show 
arsenic,  the  sulphide  may  be  arsenopyrite,  which,  however,  is  of  very  rare 
occurrence  in  igneous  rocks,  if,  indeed,  it  is  ever  found  there. 

For  the  quantitative  extraction  of  the  sulphur  of  soluble  sulphates,  simple 
boiling  with  hydrochloric  acid  suffices,  which  should  be  done  in  an  atmos- 
phere of  carbonic  acid  if  pyrites  or  other  oxidizable  sulphides  are  present, 
and  should  be  finished  as  quickly  as  possible  in  order  to  minimize  the  error 
resulting  from  oxidation  to  sulphuric  acid  of  the  sulphur  of  sulphides,  if 
present,  by  any  ferric  salts  that  may  have  been  dissolved. 

The  sulphur  of  sulphides  may  sometimes  be  correctly  determined  by 
extraction  with  aqua  regia  or  some  other  powerful  oxidizer,  but  not  always, 
so  that  it  is  better  by  far  to  fuse  with  sulphur-free  sodium  carbonate  and  a 
little  nitre  over  the  BUNSEN  burner,  and  for  a  few  moments  over  the  blast, 
fitting  the  crucible  into  a  hole  in  asbestos  board  (LUNGE)  to  prevent  access 
of  sulphur  from  the  flame.  After  thorough  disintegration  of  the  fusion  in 
water,  to  which  a  d/op  or  two  of  alcohol  has  been  added  for  the  purpose  of 
reducing  manganese,  the  solution  is  filtered  and  the  residue  washed  with  a 
dilute  solution  of  sodium  carbonate.  In  the  filtrate  (100-250  c.c.  in  bulk) 
the  sulphur  is  precipitated  at  boiling  heat  by  barium  chloride  in  excess  after 
slightly  acidifying  by  hydrochloric  acid.  Evaporation  to  dryness  first 
with  acid,  in  order  to  eliminate  silica,  is  needless,  for  in  the  above  bulk  of 
solution  there  will  almost  never  be  the  least  separation  of  silica  with  the 
barium  sulphate.  It  is  well  that  this  is  so,  for  evaporation  on  the  water- 
bath  heated  by  gas  to  remove  silica  would  in  many  cases  involve  an  error 
fully  equal  to  the  sulphur  present  by  contamination  from  the  sulphur  of  the 
gas  burned. 

Owing  to  the  small  amount  of  sulphur  in  rocks,  special  purification  ol 


SOME    PRINCIPLES   AND    METHODS    OF    ROCK   ANALYSIS.    1185 

the  barium  sulphate  obtained  is  hardly  ever  needful,  especially  as  it  has  been 
precipitated  in  absence  of  iron.  Should  there  be  fear  of  a  trace  of  silica 
being  present,  it  can  be  removed  by  a  drop  of  hydrofluoric  and  sulphuric 
acids  before  weighing  the  barium  sulphate. 

This,  of  course,  gives  the  total  sulphur  in  the  rock.  If  soluble  sulphates 
and  sulphides  as  well  as  insoluble  sulphates  and  sulphides  are  present  together, 
the  sulphur  of  the  first  is  found  in  solution  after  extraction  by  hydrochloric 
acid  in  a  carbon-dioxide  atmosphere,  and  that  of  the  decomposable  sulphides 
by  collecting  the  hydrogen  sulphide  evolved.*  In  the  residue  the  sulphur 
of  the  insoluble  sulphides  can  be  estimated,  or  from  the  total  sulphur  found 
in  another  portion  its  amount  can  be  calculated.  The  error  involved  in  the 
above  estimation  of  the  sulphur  of  soluble  sulphides,  due  to  the  possible 
reducing  effect  of  hydrogen  sulphide  on  ferric  salts,  is  probably  negligible. 
Most  of  the  hydrogen  sulphide  would  be  expelled  before  any  such  action 
could  take  place,  and  probably  before  the  ferric  salts  were  largely  attacked, 
but  of  course  the  small  proportion  of  sulphur  set  free  as  such  from  pyrrhotite 
would  escape  estimation  and  introduce  further  uncertainty.  In  general,  it 
would  be  safe  enough  to  assume  the  composition  FejSg  for  pyrrhotite.  How- 
ever carefully  all  these  separate  determinations  may  be  carried  out,  the  final 
figures  for  ferrous  and  ferric  oxides  can  hardly  be  regarded  as  more  than 
approximations  when  much  sulphide  is  present.  (See  pp.  1173  and  1174.) 

XXV.     BORON. 

To  the  best  of  the  writer's  belief,  it  has  never  been  found  necessary  in 
this  laboratory  to  estimate  boron  in  a  silicate  rock.  Should  the  determina- 
tion be  required,  since  most  silico-borates  are  insoluble  minerals,  it  would 
probably  be  necessary  to  fuse  with  sodium  carbonate,  extract  with  water, 
faintly  acidify  with  nitric  or  acetic  acid,  expel  the  boron  by  distillation  with 
methyl  alcohol,  and  collect  the  boric  ether  in  a  suitable  manner.  For  simple 
borates,  artificial  or  native,  this  method,*  first  devised  by  ROSENBLADT  and 
GOOCH  independently,  gives  entire  satisfaction  when  all  needful  precautions 
are  carefully  observed,  but  its  application  to  boro-silicates  yet  needs  investi- 
gation, in  view  of  the  as  yet  unexplained  very  discordant  results  obtained 


*  With  pyrrhotite  a  small  fraction  of  its  sulphur — one-eighth  if  the  formula  Fe7S8  is 
adopted — is  liberated  as  free  sulphur  and  not  as  hydrogen  sulphide. 

*  ROSENBLADT  (Zeitschr.  fur  anal.  Chemie,  xxiv,  p.  217.  188)  used  magnesia  for  bind 
ing  the  boron,  while  GOOCH  (Proc.  Am.  Acad.  Arts  and  Sci.,  p.  167,  1887;    Bull.  U.  S. 
Geol.  Survey,  No.  42,  p.  64;   Chemical  News,  LV,  p.  7,  1887)  preferred  lime,  as  more  active 
and  reliable.     GOOCH  and  JONES  have  later  (Am.  Journ.  Sci.,  4th  Series,  vn,  p.  34,  1899; 
Chemical  News,  LXXIX,  pp.  99,  111,  1899)  upheld  the  use  of  lime,  and  proposed,  as  a  con- 
venient  though  perhaps  not   quite   so   perfect   substitute,   sodium  tungstate  containing 
an  excess  of  tungstic  oxide.     In  this  article  they  likewise  indicate  the  precautions  now 
used  to  insure  complete  collection  and  retention  of  the  boron. 

For  a  useful  modification  in  the  way  of  collecting  the  boric  ether  in  ammonia  before 
bringing  in  contact  with  the  lime,  see  PENFIELD  and  SPERRT  (Am.  Journ.  Sci.,  3d  Series, 
xxxiv,  p.  222,  1887);  also  MOISSAN  (Comptes  rendus,  cxvi,  p.  1087,  1893,  and  Bull.  Soc. 
Chim.,  xii,  p.  955,  1894),  who  modifies  the  GOOCH  distilling  apparatus  in  certain  respects 


1186  APPENDIX   II. 

some  years  ago  by  J.  E.  WHITFIELD  in  this  laboratory  on  the  mineral  war- 
wickite,  a  boro-titanate  of  magnesium  and  iron. 

It  is  nlso  quite  possible  that  the  accurate  estimation  of  but  a  few  milli- 
grammes or  even  less  of  boric  oxide  by  the  use  of  a  large  excess  of  lime  as  a 
retainer  would  not  be  feasible.  Fluorine  would  have  to  be  first  removed  by 
calcium  nitrate  or  acetate  before  freeing  the  boron. 

XXVI.    NITROGEN. 

Nitrogen  has  been  found  in  igneous  rocks  or  the  minerals  occurring  in 
them  by  several  observers.  Thus,  H.  ROSE  *  says  that  pitchstone  gives  off 
ammoniacal  water  on  heating;  SILVESTRI|  mentions  a  nitride  of  iron  in 
lavas  from  Etna;  SANDBERGER  finds  ammonium  carbonate  to  be  given  off 
from  certain  rocks  of  Pribram;  the  writer  has  shown  nitrogen  to  exist  in 
uraninite;  RAMSAY  and  others  have  noted  it  in  traces  with  or  without  helium, 
etc.,  in  numerous  minerals;  and  later  ERDMANN!  found  it  to  be  given  off  as 
ammonia  on  treating  various  minerals  of  "ancient  igneous  rocks"  with  a 
caustic  alkali.  LUEDEKING  also  found  ammonium  sulphate  in  a  barite  from 
Missouri,  the  presence  of  which  the  writer  was  able  to  confirm. 

It  has  been  noted  in  this  laboratory  on  three  separate  occasions,  when 
series  of  ores,  roofing  slates,  and  eruptive  rocks  were  analyzed,  that  ammonia, 
either  in  the  form  of  chloride  or  sulphate,  or  even  as  free  ammonia,  was 
given  off  on  heating.  Its  appearance  was  not  limited  to  one  or  a  few  speci- 
mens of  a  series,  but  seemed  to  be  characteristic  cf  all,  and  to  be  afforded  by 
the  unbroken  rock  as  well  as  by  the  powdered  sample.  The  precise  condi- 
tions under  which  the  specimens  were  collected  not  being  known,  it  is  impossi- 
ble to  affirm  positively  that  the  ammonia  may  not  have  been  due  to  recent 
organic  contamination  of  some  sort,  especially  in  the  case  of  the  slates,  but 
it  is  believed  that  a  more  critical  collection  of  material  wrill  not  alter  the  gen- 
eral result.  Its  amount  was  sometimes  readily  determinable  by  Nessleriza- 
tion  being  as  high  as  0-04  per  cent,  in  some  slates.  Carbonaceous  organic 
matter  was  absent  from  most  of  these,  but  doubtless  existed  in  them  in  their 
early  history.  In  their  case  the  ammonia  was,  in  part  at  least,  evolved  as 
such,  imparting  a  strong  alkaline  reaction  to  the  water  in  the  upper  part  of 
the  tube.  The  presence  of  sulphides,  fluorides,  or  chlorides  in  the  rock 
might  cause  the  ammonia  to  appear  as  a  sublimate  of  sulphate,  fluoride,  or 
chloride.  Speculation  on  this  matter  would  be  altogether  premature,  but 
attention  is  called  to  it  in  the  hope  that  other  observers  may  be  led  to  look 
for  and  investigate  similar  appearances.  It  should  be  borne  in  mind  that 
the  nitrogen  present  would  not  necessarily  appear  as  ammonia  or  ammonium 
salts,  since  it  might  be  given  off  in  the  elemental  condition,  as  with  the  gases 
obtained  from  uraninite. 

*  Quantitative  Analyse,  p.  673.     FINKENER  edition, 

t  Gazz.  Chim.  ital.,  v,  p.  303,  1875. 

J  Ber.  d.  deutsch.  chem.  Gesell.,  xxix,  p.  1710,  1896. 


SOME    PRINCIPLES  AND   METHODS   OF  ROCK   ANALYSIS.    1187 


XXVII.    SPECIAL  OPERATIONS. 

The  problem  often  presents  itself  of  ascertaining  the  composition  of 
that  portion  of  a  rock  powder  which  is  soluble  in  special  reagents  or  hi  a 
reagent  of  a  particular  concentration.  No  precise  directions  can  be  for- 
mulated to  meet  such  cases.  The  procedure  must  vary  with  the  character 
of  the  constituents  of  the  rock  and  with  the  object  which  it  is  sought  to 
attain,  and  only  in  exceptional  cases  can  a  separation  of  this  kind  be  sharp. 
Much  depends  on  the  degree  of  fineness  of  the  powder  and  on  the  length 
of  time  it  is  exposed  to  the  action  of  the  reagent. 

DETECTION  OF  NEPHELINE  IN  PRESENCE  OF  OLTVTNE. 

For  confirmation  of  the  microscopic  diagnosis.  Prof.  L.  V.  PIRSSON* 
has  indicated  a  means  of  detecting  nepheline  in  presence  of  olivine,  as  in 
nepheline  basalts,  based  on  the  very  ready  solubility  of  nepheline,  as  com- 
pared with  olivine,  when  boiled  for  but  one  minute  with  a  sufficiency  of  very 
dilute  nitric  acid  (1  :  40).  Gelatinization  of  the  filtrate  on  evaporation 
is  taken  as  evidence  of  the  presence  of  nepheline.  If  olivine  is  present  hi 
quantity,  however,  this  test  must  not  be  accepted  at  once  as  final,  for  some, 
if  not  all,  olivines  are  much  more  soluble  in  nitric  acid  of  the  above  strength 
than  Professor  PIRSSON  was  led  to  believe  from  his  original  tests.  If,  there- 
fore, on  evaporation  of  the  filtrate,  much  iron  is  indicated,  the  gelatiniza- 
tion  may  well  be  due  to  olivine  alone  or  in  part,  and  then  the  quantitative 
relation  of  silica  to  iron  plus  magnesium  should  be  ascertained.  It  must 
also  be  borne  in  mind  that  any  other  very  soluble  silicates  present  will  be 
more  or  less  affected,  and  that  apatite  is  largely  or  wholly  dissolved.  It  is 
possible  that  still  more  dilute  nitric,  or  perhaps  some  other,  acid  may  exert 
a  slighter  solvent  action  on  olivine  without  being  appreciably  less  effective 
in  dissolving  nepheline,  etc.  In  combination  with  a  quantitative  analysis 
of  the  extract  the  method  is  perhaps  susceptible  of  a  wider  application  than 
the  particular  case  for  which  it  was  first  used.  It  is  well  worth  further 
study. 

ESTIMATION  OF  SOLUBLE  SILICA. 

Very  often  hi  treatment  by  acids  silica  is  separated  hi  gelatinous  or 
granular  form  mixed  with  the  unattacked  minerals,  and  it  becomes  neces- 
sary to  remove  or  estimate  this  silica,  or  else  to  discriminate  between 
soluble  and  insoluble  silica  already  existing  together.  Usually  a  boiling 
solution  of  sodium  carbonate  has  been  employed  for  this  purpose,  though  the 
caustic  alkalies  have  found  advocates. 

LUNGE  and  MiLLBERof  have  lately  conclusively  shown  that  quartz  is 
not  nearly  so  insoluble  in  solutions  of  the  caustic  alkalies  as  has  been  sup- 
posed, but  that  given  a  sufficient  degree  of  subdivision  it  can  be  brought 
wholly  into  solution-,  that  it  is  impossible  to  secure  correct  separation  of 

*  Am.  Jvum.  Sci.   4th  Series   n   p.  142.  18%. 

t  Zeitschr.  fur  angewandte  Chemie,  1897.  pp.  393,  425. 


1188  APPENDIX    II. 

quartz  and  opaline  silica  by  the  use  of  either  caustic  or  carbonated  alkalies, 
and  that  digestion  on  the  water-bath  for  15  minutes  with  5-per  cent,  solu- 
tion of  sodium  carbonate  is  the  only  way  to  secure  exact  separation  of  un- 
ignited  precipitated  silica  from  quartz,  and  then  only  when  the  finest  flour 
has  been  removed  by  levigation.  The  authors  say : 

"  If,  however,  no  more  of  such  flour  is  present  than  is  produced  in  the 
ordinary  operations  of  powdering  and  sifting  through  cloth  of  the  finest 
mesh,  the  error  arising  from  the  above  mentioned  treatment  is  so  slight 
that  it  can  generally  be  neglected;  it  reaches  0- 1  to  at  the  most  0-2  per  cent 
of  the  total  silica,  by  which  amount  the  quartz  will  appear  too  low,  the 
amorphous  silica  too  high." 

The  above  authors  also  show,  however,  that  the  solvent  action  of  the 
caustic  alkalies  on  quartz  becomes  very  apparent  only  when  the  material 
has  been  reduced  to  such  an  utterly  impalpable  degree  of  fineness  as  is  prac- 
tically never  reached  in  the  preparation  of  samples  for  rock  analysis.  For 
this  reason  I  have  no  hesitation  hi  recommending  the  employment  of  a 
dilute  solution  of  sodium  hydroxide  when  the  silica  separated  by  acid  from 
one  of  several  mineral  constituents  of  a  rock  is  to  be  estimated.  Even 
when  dilution  is  considerable,  solution  is  almost  immediate,  and  as  soon 
as  this  is  accomplished — the  point  being  known  by  the  change  in  appear- 
ance of  the  residue — the  solution  should  be  diluted  with  cold  water  and 
filtered  at  once.  The  difficulty  met  with  in  filtration  may  often  be  over- 
come by  faintly  acidifying,  which  has  the  added  advantage  of  at  once  arrest- 
ing any  further  action  of  the  alkali.  If  the  dilution  is  sufficient  no  separa- 
tion of  silica  results  from  so  doing.  Very  dilute  acid  should  also  be  used 
for  washing.  LUNGE,  when  using  sodium  carbonate,  washes  with  hot  car- 
bonate solution  to  which  alcohol  has  been  added,  thus  obtaining  clear  fil- 
trates. 

XXVIII.     ESTIMATION   OF   MINUTE   TRACES  OF  CERTAIN 
CONSTITUENTS 

If,  as  sometimes  may  happen,  the  problem  is  presented  of  examining 
rocks  for  traces  of  gold,  silver,  and  other  elements  which  are  not  ordinarily 
looked  for,  as  in  SANDBERGER'S  investigations  bearing  on  the  origin  of  the 
metalliferous  contents  of  veins,  large  weights  of  material  must  be  taken, 
up  to  50  grm.  or  more.  This  involves  the  use  also  of  large  quantities  of 
reagents,  the  purity  of  which  must  then  be  looked  to  with  the  utmost  care. 
Special  directions  to  meet  such  cases  cannot  now  be  given,  nor  even  a  com- 
plete reference  list  of  the  scanty  and  scattered  literature  on  this  subject. 
SANDBERGER'S  own  writings  deal  but  little  with  its  analytical  side,  and  from 
its  inaccessibility  in  the  Washington  libraries  the  writer  is  as  yet  unacquainted 
with  the  report  by  VON  FOULLON,  "Ueber  den  Gang  und  die  Ausfuhrung 
der  chemischen  Untersuchung,"*  following  SANDBERGER'S  own  paper  in 
the  general  report,  "  Untersuchungen  der  Nebengesteine  der  Pribramer 

*  Jahrbuch  der  Bergakademie,  Leoben  u.  Pribram,  1887,  p.  363. 


SOME    PRINCIPLES   AND    METHODS   OF    ROCK    ANALYSIS.    1189 

Gange."*  The  present  writer  has  published  a  few  data  as  to  gold,  silver, 
lead,  zinc,  etc.,f  in  Mr.  S.  F.  EMMON'S  report  on  "The  Geology  and  Mining 
Industry  of  Leadville";  and  Mr.  J.  S.  CURTIS,^  in  his  report  on  "The  Silver- 
Lead  Deposits  of  Eureka,  Nevada,"  has  given  his  method  of  assaying  rocks 
for  traces  of  gold  and  silver. 

*  From  SANDBERGER'S  report  it  appears  that  the  rocks  were  treated  successively  with 
water,  acetic  acid,  boiling  dilute  hydrochloric  acid  for  two  days,  and  finally  hydrofluoric 
acid,  the  several  extracts  and  final  residue  of  fluorides  (and  pyrite)  being  separately  ex- 
amined for  heavy  metals.  The  products  of  distillation  were  also  examined.  A  striking 
fact  observed  in  all  cases  was  the  complete  insolubility  of  the  pyrite.  even  after  the  severe 
treatment  mentioned.  This  speaks  strongly  in  favor  of  the  correctness  of  ferrous-iron 
estimations  in  silicates  by  the  hydrofluoric  and  sulphuric  acid  method  when  pyrite  is 
present  unaccompanied  by  other  sulphides.  (See  p.  1173.) 

t  Man.  U.  S.  Geol.  Survey,  xn,  Appendix  B.  pp.  592-596,  1886. 

t  Man.  U.  8.  Geol.  Survey,  vn,  pp.  12O-138,  1884. 


TABLES  FOR  THE  CALCULATION  OF  ANALYSIS. 


TABLE  I. 

ATOMIC    WEIGHTS     OF   THE    ELEMENTS    CONSIDERED    IN   THE    PRESENT    WORK.* 


Name. 

Sym- 
bol. 

Atomic  Weight. 

Name. 

Sym 
bol. 

Atomic  Weight. 

O  =  16. 

H  =  l. 

O  =  16. 

H  =  l. 

Aluminium  
Antimony  

Al 
St. 
As 
Ba 
Bi 
B 
Br 
Cd 
Cs 
Ca 
C 
Ce 
Cl 
Cr 
Co 
Cb 
Cu 
Er 
Fl 

Ga 
Ge 
Gl 
Au 
H 
In 
I 
Ir 
Fe 
La 
Pb 
Li 
Mg 
Mn 

ss 

27.1 
120.4 
75.0 
137.40 
208  .  1 
11.0 
79.95 
112.4 
132.9 
40.1 
12.0 
139.0 
35.45 
52.1 
59.00 
93.7 
63.6 
166.0 
19.05 
157.0 
70.0 
72.5 
9.1 
197.2 
1.008 
114.0 
126.85 
193  .  1 
55.9 
138.6 
206.92 
7.03 
24.3 
55  .  0 
200.0 
96.0 

26.9 
119.5 
74.45 
136.4 
206.5 
10.9 
79.34 
111.55 
131.9 
39.8 
11.9 
138.0 
35.18 
51.7 
58.55 
93.0 
63.1 
164.7 
18.9 
155.8 
69.5 
71.9 
9.0 
195.7 
1.00 
113.1 
125.89 
101  .7 
55.5 
137.6 
205.36 
6.97 
24.1 
54.6 
198.50 
95.3 

Neodymium.  .  .  . 
Nickel  
Nitrogen 

'Ni" 
N 
Oa 
O 
Pd 
P 
Pt 
K 

'Rh 
Rb 
Ru 
Sm 
Sc 
Se 
Si 
Ag 
Na 
Sr 
S 
Ta 
Te 
Tb 
Tl 
Th 
Tu 
Sn 
Ti 
W 
U 
V 
Yb 
Yt 
Zn 
Zr 

143.6 
58.70 
14.04 
191.0 
16.00 
107.0 
31.0 
194.9 
39.11 
140.5 
103.0 
85.4 
101.7 
150.3 
44.1 
79.2 
28.4 
107  .92 
23.05 
87.60 
32.07 
182.8 
127.52 
160.00 
204.15 
232.6 
170.7 
119.0 
48.15 
184.00 
239.6 
51.4 
173.2 
89.0 
65.4 
90.4 

142  .  5 
58.25 
13.93 
189.6 
15.88 
106.2 
30.75 
193.4 
38.82 
139.4 
102.2 
84.75 
100.9 
149.2 
43.8 
78.6 
28.2 
107.11 
22.88 
86.95 
31.83 
181.5 
126.5 
15S.8 
202.61 
230.8 
169.4 
118.1 
47.8 
182.5 
237.8 
51.0 
171.9 
88.3 
64.9 
89  7 

Osmium  
Oxygen.  .  . 

Bismuth  
Boron  
Bromine  

Palladium  
Phosphorus.  .  .  . 
Platinum  
Potassium  
Praseodymium  . 
Rhodium  .  . 

Cadmium  
Csesium  

Calcium  
Carbon 

Cerium  
Chlorine  

Rubidium.  . 

Ruthenium  

Cobalt  

Columbium 

Selenium  

Copper  

Erbium  

Silver  

Fluorine  
Gadolinium.  .  .  . 

Sodium  
Strontium  
Sulphur  
Tantalum  
Tellurium  
Terbium  
Thallium  
Thorium  

TTiiiliiim 

Gallium.  
Germanium.  .  .  . 

Glucinum  
Gold  

Hydrogen 

Indium  
Iodine  

Iridium    
Iron  

Tin  
Titanium  
Tungsten 

Lanthanum  
Lead  
Lithium  
Magnesium  
Manganese  
Mercury.  .  . 

Uranium.  .  .  . 

Vanadium 

Ytterbium  
Yttrium  

Zinc 

Molybdenum  

Zirconium  

*  Journal  of  the  American  Chemical  Society,  March,  1902. 


1190 


TABLE   II.  1191 

TABLE  II. 

COMPOSITION    OF   THE    BASIC   AND   ACID    OXIDES. 

GROUP  I.       a.  BASIC  OXIDES. 

€sesia. Cs^ 265-80 94-32 

O. .  .   16-00..  5-68 


Cs2O 281-80 100.00 

Rubidia Rb2 170-80 91-43 

O  ..  .   16-00..  8-57 


Rb2O 186-80 100-00 

Potassa K, 78-22 83-02 

O  ..  .   16-00..  .   16-98 


94-22  ........  100-00 


Soda  .......................  Na,..  ..............  46-10  ........  74-24 

O  ..  .   16-00..  .  25-76 


Na.,0 62-10 100-00 

Lithia Li 14-06 46-77 

O  ..  .   16-00..  .   53-23 


L 


Li20 30-06.... 100-00 

Ammonium  oxide (NH4)2 36-144 69-32 

O  ..  .   16-00..  .  30-68 


(NH4)aO 52-144 100-00 

GROUP  IL 

Baryta Ba 137-40 89-57 

O  ..  .   16-00..  .   10-43 


BaO 153-40 100-00 

Strontia. . . .  :Sr 87-60 84-56 

O  ..  .   16-00..  .   15-44 


SrO.  ;; 103-60 100-00 

Lime Ca 40-10 71-48 

O  ..  .   16-00..  .  28-52 


CaO 56-10 100-00 

Magnesia. Mg 24-30 60-30 

O  ..  .   16-00..  .  39-70 


MgO 40-30 100-00 


1192          TABLES  FOR  THE   CALCULATION   OF   ANALYSIS. 

TABLE  II.— Continued. 
GROUP  III. 

Alumina A12 54-20 53-03 

O3 48-00 46-97 


A12O3 102-20. ..... .  .100-00 

Chromic  oxide O2 104-20 68-46 

O3 48-00 31-54 

Cr2O3 152-20 100-00 

GROUP  IV. 

Zinc  oxide. Zn 65-40 80-34 

O 16-00 19-66 

ZnO 81-40 100-00 

Manganous  oxide .Mn 55-00 77-46 

O 16-00..  .  22-54 


MnO 71-00 100-00 

Manganic  oxide Mn2 110-00 69-62 

O3 48-00 30-38 


Mn2O3 158-00 100-00 

Nickelous  oxide Ni 58-70. ... 78-58 

O  .;  .   16-00..  .  21-42 


NiO 74-70 100-00 

Cobaltous  oxide Co 59-00 78-67 

O  ,,  .    16-00..  .  21-33 


CoO 75-00 100-00 

Cobaltic  oxide Co2 118-00 71-08 

03..  .   48-00..  .  28-92 


Co2O3 166-00 100-00 

Ferrous  oxide Fe 55-90 77-75 

O  ..  .   16-00..  .  22-25 


FeO .  71-90..         ..100-00 


Ferric  oxide ,.,.,Fe2., 111-80 69-96 

O3 48-00 30-04 


Fea03 159-80 100-00 


TABLE    II. 


1193 


TABLE  II. — Continued. 
GROUP  V. 


Ag 

215-84. 

93-10 

O  

16-00. 

6-90 

Lead  oxide  

Ag20.... 

...Pb  
O  

231-84. 

206-92. 
16-00. 

100-00 

92-82 
7-18 

Mercurous  oxide  

PbO.... 

222-92. 
400-00. 

100-00 
96-15 

O  

16-00. 

3-85 

Mercuric  oxide  

Hg20... 

...Hg  
O  

416-00. 

200-00. 
16-00. 

100-00 

92-59 
7-41 

Cuprous  oxide  

HgO  .  .  . 

...Cu2  
O  

216-00. 

127-20. 
16-00. 

100-00 

88-83 
11-17 

Cupric  oxide  

0X1,0.... 

...Cu  
O    

143-20. 

63-60. 
16-00 

100-00 

79-90 
20-10 

Bismuth  trioxide  

CuO.... 

79-60. 
416-20. 

100-00 
89-66 

02  

48-00. 

10-34 

Cadmium  oxide  

Bi203... 
...Cd.  .... 

464-20. 
112-40. 

100-00 
87-54 

O  

16-00. 

12-46 

\uric  oxide.    

CdO.  .  .  . 

GROUP 

.  Au0  .  . 

128-40. 

VL 
394-40 

100-00 
89-15 

03  

48-00. 

10-85 

Au,O,  . 

442-40 

100-00 

Platinic  oxide  

...Pt  
02  

194-90. 
32-00. 

85-90 
14-10 

Antimonous  oxide  

PtO2  .  .  . 

...Sb2  
03  

226-90. 

240-80. 
48-00. 

100-00 

83-38 
16-62 

.288-80. 


100-00 


1194  TABLES    FOR   THE    CALCULATION   OF   ANALYSIS. 

TABLE  II. — Continued. 
GROUP  VI. — Continued. 

Stannous  oxide Sn 119-00 88-15 

O 16-00..  .   11-85 


SnO 135-00 100-00 

Stannic  oxide Sn 119-00 78-81 

O2 32-00 21-19 

SnO2 151-00 100-00 

Arsenous  oxide As2 150-00 75-76 

O3 48-00..  .   24-24 


>3 198-00 100-00 

Arsenic  oxide As2 150-00 65-22 

O6 80-00.  .  .  34-78 


As2O5 230-00 100-00 

6.  ACID  OXIDES  (ANHYDRIDES). 


Chromic  anhydride  

..Cr.  .. 
03... 

Cr03. 

52-10... 
48-00... 

52-05 
47-95 

100-10... 

100-00 

Sulphuric  anhydride  

..S.  .. 
03... 

SO3. 

32-07... 
48-00... 

40-05 
.....   59-95 

100-00 

80-07... 

Phosphoric  anhydride  

"<c; 

PA. 

62-00... 
80-00... 
142-00... 

43-66 
56-34 
100-00 

Boric  anhydride  

..B2... 
03... 

B208. 

22-00... 
48-00... 

31-43 
68-57 

70-00... 

100-00 

Oxalic  anhydride  

..C2... 

24-00... 

33-33 

0.-.' 

0,0,. 

48-00... 

.....  66-67 

72-00... 

100-00 

Carbonic  anhydride  

..c..  . 

12-00... 

27-27 

02... 

32-00... 

72-73 

CO, 44-00..          ..100-00 


TABLE   III.  1195 

TABLE  II. — Continued. 

GROUP  VI. — Continued. 

Silicic  anhydride Si 28-40 47-02 

O2 „.  32-00........   52-98 


SiO2 60-40 100-00 

Nitric  anhydride N2 28-08 25-98 

O5 80-00 74-02 

N2O5 108-08 100-00 

Chloric  anhydride CLj 70-90 46-99 

O5 80-00 53-01 

CIA 150-90 100-00 


TABLE  III. 

REDUCTION    OP    COMPOUNDS    FOUND    TO    CONSTITUENTS    SOUGHT    BY     SIMPLE 
MULTIPLICATION    OR    DIVISION. 

This  Table  contains  only  some  of  the  more  frequently  occurring    com- 
pounds. 

FOR  INORGANIC  ANALYSIS. 

CARBON  DIOXIDE. 
Calcium  carbonate  X  0  •  43956  =  Carbon  dioxide. 

CHLORINE. 

Silver  chloride  X  0  •  24726  =  Chlorine. 

COPPER. 
Cupric  oxide  X  0-79899  =  Copper. 

IRON. 

Ferric  oxide  X  0  •  6996  =  Iron. 
Ferric  oxide  XO- 9= Ferrous  oxide. 

LEAD. 
Lead  oxide  X  0  -  92823  =  Lead. 

MAGNESIA. 

Magnesium  pyrophosphate  X  0  •  36208  =  Magnesia. 

MANGANESE. 

Protosesquioxide  of  manganese  X  0  •  72052  =  Manganese. 
Protosesquioxide  of  manganese  X  0  •  93013  =  Manganous  oxide. 

PHOSPHORIC    ANHYDRIDE    (P2O5). 

Magnesium  pyrophosphate  X  0  •  63792  =  Phosphoric  acid. 
Uranyl  pyrophosphate ((UO2)2P2O7)  XO- 19799  =  P2O5. 


1196          TABLES   FOR   THE   CALCULATION   OF   ANALYSIS. 
TABLE  III.— Continued. 

POTASSIUM. 

Potassium  chloride  X  0  •  52454  =  Potassium. 
Potassium  sulphate  X  0  •  54059  =  Potassa  (KjO). 
Potassium  platinic  chloride  X  0  •  30695 

.  or  I-  =  Potassium  chloride. 

Potassium  platinic  chloride 

3-2579 


Potassium  platinic  chlorideXO- 19394 


or 


Potassium  platinic  chloride 
5-1562 


=  Potassa  (K2O). 


SODA. 

Sodium  chlorideXO- 53077  =  Soda  (Na2O). 
Sodium  sulphate  X  0  •  4368  =  Soda  (Na2O). 

SULPHUR. 

Barium  sulphate  X  0  •  13736  =  Sulphur. 

SULPHURIC   ACID. 

Barium  sulphate  X  0-34296  =  Sulphuric  anhydride 

FOR  ORGANIC  ANALYSIS. 
CARBON. 

Carbon  dioxide  X  0  •  2727 

or 
Carbon  dioxide 


3-6667 

or 

Carbon  dioxide  X  3 
11 

HYDROGEN. 

WaterXO-1119  " 


=  Carbon. 


or 


—  Hydrogen. 


Water 
8-9365 

NITROGEN. 

Ammonium  platinic  chloride  X  0  •  06328  -  Nitrogen. 
Platinum  X  0  •  1441  —  Nitrogen. 


TABLE   IV. 


1197 


^5        00        00 

oo      o      co 


CO        Jt1**        CO 


CO 

^C 


00*0 

iC          Oi          CO 

IN      d      d 


CO        l>        00 
CO       1C        CO 


~    ~ 

II 

til 

S.§  d 

H       -«H 


t™^       — 


-^  - 

II 

43      C3 


§  § 


f! 


CO        (M        CO 
<N        O        O 


CO  *O  CO 

Oi  O 

!-H  O  CO 

i-H  O  O 


S    5    §    i 


^  00  O          r-t 

O        CO 


CO 


Oi      oo      oo 

1C        »O        CO 

i-H  O  O 


CO         ^          -^          ^y^          CO 


00        00        O5        CO        O        Tt* 

3       S       t^       O       ^       0» 
CO        »C        <N        OS        O       t>- 


»-i         O         O 


CO 
'O 


CO 

l-H  CO 


o 


<N      cs      (M      ^H      <N 


co      co      *o 

odd 


CO  i—  i  CO  C5 
OOO5»O 
T-iT^<NcO 


C3 
cN 


coo 


00       l^       00       C3i       CO       t^ 

o      o      o      o      o      d 


O  O  CD 

•g  _-^  T3 


fll 


fell 

II 'SO 


t£ 

5 


oo    o>      -2    .  ,-H    .  I-H 

7    ^^^  II 

'I          O  fS    O  ^     »  TJH  ^2 

H-T  -2  "5  •-    „  -S    ..  GQ 


Alum 
A12O3= 


fflllf|HwPl5 

4      4-1^1  ^  -3 


1198 


TABLE    IV. 


o       i> 

tliflr- 

•^        10  ^         *     TO 

•aoeog -Lg  -  = 


§      1 

CO  rH 

O  OS 


00        »0        CO 


CO        00 

§    S 


TABLE    IV. 

CO  t^        00 


O        CO 
00        t>- 


(M 


1199 


8  3 

00        <N 


N  O 

oo  co 

CO  rH 

?*  CO 

co  ^f 


»O       CO 

cq o_ 


CO 


i-i         CO 

Ei     £2 

CO         Cv 


<N        C 


CO        O 


CO        OS        CO 


00        »O 
rn'        o 


1C        00 

oo      co 

00        *>• 


CO        CM        CO        (M 


£    $ 

rH  O 


8  S 

CO        (N 


g  s  « 
i  i  S 

<N  rH  (N 


CO        CO 


g        | 
CS?         rH 


§|| 
S  rH  IO 


OS 
t>. 


CO          rH 
O          O 


00 


CO        O 


£    3 


o 

OS 


CO 


O  O  CO 

t^  O  rH  CO 

^O  t^»  t^*  t^* 

OS  iO  t>.  -^ 

00  O  t^-  iO 


CO        O 

o      o 


OS  1> 

CO  rH 

10  os 

t^»  co 

00  «3 


i  ||  5  II  S  II  £  II 

PQ  ^WOPQOPQO 

rn         03*3303 

cq     «     « 


§7  §7 


^ 

.—  OS 

gt- 

o  II 

&& 


-  8 


PQ 


la 


*-    PQ       2 


1 


Cadmium  oxide 
CdO=128.4 
admium  sulphat 
CdSO4=208.47 


1200 


TABLE  IV. 


CO  l>  CO 

rH  GO  OS 

%  s  $ 

rt |  1>  O 

CO  CO  to 


i—  I    OS 
l>   C<l 


£   l 

£  S 


co 


CO   i—  i 

CO    rH 


CO     1C 


S 


iO    (N    CO 


OS       O 

rH  CO 


g  S 

8  S 

CO  CO 

tO  TjH 


t^   OS 


CO 
CO 


GO 
CO 


l>        iO        O 

to      p      oo 

CO        <N        C* 


CO 


CO  CO 

tO  (N 

IO  rH 

co  co 


00  ^  CO 

OS  t^  i-H 

tO  Tt<  Tf 

00  CO  (N 

<N  rH  (N 


(N 
CO 


1-1    (N    <N 


oo      oo 

rH  CO 

oo  oo 
—  — 
oo  co 

d ^ 


00 


os   t^ 

10   os 
os   co 


CO  (N 

iO  OS 

"?  oo 

d  d 


c<j      to      oo 

<N        OS        (N 


(N 


rH  00  CO 

00  t>  rjn 

t^  (N  CO 

OS  CO  O 


(N 


CO 

oo 


s§ 


CO  "H^  H^ 

CO  C^l  rH 

(N        CO        (N 


0  OS  rH 

OS  CO  l> 

00  rH  rH 

os  co  o 


OS  »O 

Tfl  00 

t>.  OS 

o  d 


(N 

to 


t^  OS 

OS  iO 

^    CO  00 

OS   »O  O 

rt<   CO  to 


<N        OS 

1Q          1^ 

OS       00 


S  I 

00        CO 


% 


OS          i-H 

CO        tO 


s 


rH  t^  (N 

O^        4s*        ^D 

S    §8    S 

CO        00        1> 

odd 


N        CO 

d     d 


'SO 


ss 


ti 

s 


ilili! 

°^   6   6 


6    8 


'C  to'C  to  o  «g 
o  co  o  COTS  co 

3  II  3  II      II 


TABLE    IV. 


1201 


CO        CO         00        *O 

rH  00  N.  >0 

CO  rH  (N  CO 


S       3 


t^  rH  rH  rH  rH 


5 


§ 


CO          CO 


co      o      o      to 

rH        00        <N        <N 


^  O 


§  2 

rH  C5 

OS  00 

co  co 


rH  rH  Q 


OS 


« 


O       1-1 


t^        CO 

OS        00 


OS        OS 
t>       l>- 


OS 


ol 


CO  rH 


DC 


'M 


cc 


O        to        OS 
tO         to        Tt< 

rH  OS  OS 

t>. 

1C 


Tj<  rH  f"*  CO  00 

l>  CO  CO  to  CQ 

00  CO  ^f  C^  C*^ 

O  OS  rH  CO  t^ 

tO  rH  CO  O  O 


s 


to  to  oo  ^ 

Os  ^2  OS  Os 

CO  CO  rH  00 

CO  CO  CO  t^ 


8    § 


CO        OS 

10  TF 


-s  -s 


0 

666 


O^  Ot^ 


66        66 


—       — 

-6-3 


s 


Il 


a 

™ 


II  24  ^^3  SM-5  SW  ico 


-*^  •'"/^    cfi  i 


>i  ^ — N 

+  SO" 


of- 

1.9  loo 

a»|^ 


16 


1202 


TABLE    IV. 


8 


rH  05 


O 
iO 


O5         00 

TH  O 


CO 


00  TH 


IO  IO  CO 

t>  C<1  CO 

l>  O5  <M 

O3  O5  TH 

rH  CO  00 


CO 


<N         GO        <N 

TH         CO        (M 

00         O5         t^ 


CO 


CO          TH 


O        O        00 
IO        iO        l>- 

0:0^ 

t>        iO        IO 

CM        CO        (M 


i 

co      oo 

^     TH 


CO 


CM         1>         00 

§        §        g 
CO        1>        CM 


O 

CO 


0        0 


<M      r-  ^ 

CO         00  "f 

§O5  CO 

00  CO 

o      o  o 


bfiO 

ww 


.Sco.S 

T3  <N  T3 


o 


g0^  g 


I 


I 


""O^r/iCO  WlOX1^ 

.2SS  S:8      :    07  STH 


TABLE   IV. 


1203 


3    & 

co      oo 


»O        CO        CO 


w  t^  o 

-H  O  CO 

CO  W  00 

CO  CO  to 

•^  ^  Oi 

»o  t^  «o 


<N  l-H 

CO        <N 


CO        CO 


o  «o  o 

-^  00  »O 

T}<  ^  1> 

^H  C5  O5 


CO        CN        <N 


8 


CO        iO 

g  SB 


(N  ^H 

»C        CO 


00        »O 

o     o" 


£    § 

o     o 


T-4  O  ^ 

O5  (N  CO 

i-H  O5  00 

53  CO  rf 


<N         CO 

co      co 

00        O 


o> 


S3    § 


l- 

§    ^    §8 


co      co      co 
odd 


-       - 


^      «  I 

II  13      a 

be  -^t-  £co 

8  s  'ilSla 


M   —          I         *"H     II      ^^       I' 

IIP. 


1204 


TABLE    IV. 


CO          CD 


s 


CO 


<N        00 

i>      os 

5      So 


(N        r-i        GO 
O        OS       I-H 


O        r-i 
-*        CO 


g     So 

<N        i-i 


•^        Oi 
CO       t- 

00        CO 


OS        id 

^        O 
(N        CO 


«  ^ 

CO         CO 


25    28 


§    § 


§ 


O        CO 

C<J  l-H 


(N        CO 

OS       OS 


»O        CN 

CO        10 

e  g 


s 


O 


CO 
00         00 


§    II    3<N 

§0  S  II 
BHifi  wi 

S^sw 


TABLE    IV. 


1205 


tO        O*        t>-        GO 

O  ^  ^H  1-5 


§        I 


i-i  (N  CO 

CO  •*  <M 

O}  Tt<  t>. 

GO  CO  <N 

t^  ou  CO 


CO  "-,  rH 


3     9 

O  I—I 


O         OC 
Is*          CO 

o       eo 


^H        1-1        (N 


odd 


»O  CO 

oc  -^ 

^  tO 

t»  co 


co      co 

d      d 


^        (N 


l-i  t> 

odd 


t>.        CO 

CO         O5 


CO        t> 

d     d 


o»     o 

d     i-I 


1-4     i- 


00         CO 


l> 

(M         to 

d      d 


t^        O 

t>         QO 

d      d 


^»      co 

1— I         — 

d     d 


O        <N 

CO        CO 

1-1  Tj^ 

_d d 


CO        CO 

rH  t>* 

CO        to 

%  s 

d o_ 


i— i  i— i  CO 

O  (N  GC 

(N  O  CO 

i-i  i— i  !>. 

CO  CO  CO 


i- 


to      i>      c^ 

i-t          l>          30 


o      o 


s 


>0        CO 

GO         •* 
CO        to 


X        Tt<        to 

i-l          i-l          O5 


lO        <N 

S    R 


i-l  C<l 

d      d 


CO 

ao 


O        O        (N 
1— I        1— I        1— I 

d     d     d 


. 

« 


ss 


fc  a*. 

g^  ^ 

3?3S 


13  1.  IS 


: |§|l8S|8«g||1 
=  S'»sAldid^''-a"a 


e^  C  -^ 

S'sS 


I 


1206 


TABLE    IV. 


§8 


fo  t* 

<N  rH 

CO  GO 

l>  <N 

iO        iO  O 

C^         CO  CN 


8 


9 


O  ^  00 

<N  CO  rH 

t^  00  t£ 

1C  <M  rH 


£ 


(N 

(N 


O 

O 


CO         O 
CO        00 


Ou        <N 

C75          rH 


CO'OrH 


1-HOOOi—lOi—  1  rH  O 


co  co      c  o  T-H 


cB 

1 

d      o'      o' 


§ 


S  I 


o  o 


z 


00 
CO 


OS  rH 

CO  »O 


WCOCO 


CO 

CO 


00  CO  r- 1 

rH  rH  O 

CO       <N        <N 

odd 


gcogcogcogcogcogcogcogcogco 

^~\\  >^\  ^7  ^7  ^  ii  S  ii  ^7  >^7  >^7 


50 


rn      eo'1 


u 


«   -S 

•  1 

0  'I  a 
§f  N^ 


2  rf.8 


S     O  3' 

g    I    |S' 
tao    S 


TABLE    IV. 


1207 


CO        CO 


O        1-1        i-H 


CO 


1-1  t> 

O  1-H 


*H       f-*       CQ 


25    S 

i-        O 


(N        CO 

,-i        1C 


t^  It} 


»c 

to 


O  ^H 


O  TH 


l>  CO 

—  — 

CO  00 

<N  •* 

CO  O5 


Is*        Oi 

O        1-1 


o 


iO        to 

d     d 


S     i 

2       ^ 

d         d 


>»  II 


>>  II  >»  II  >»  II  >»  II  >»  II  >»  II  >» 


Ss-IM-  a|*-8s-     ^^s  s^^ 
IT  s?  Ss  lasisla  -gsil  |7lal? 
''^Uiliiild^TU 

5   £3       O  •**   d 


g 


1208 


TABLE    IV. 


C 


co 

10 


1  8 

^         CO 

l>      l> 


TH1       Si 


s 


^        *O        CO 

"5nr~S 
£    8    8 


CO  TH 

TH  <N 


TH        CO 
TH        1C 


TH  00 

O  TH 


S  c^  § 

l>  TH  Tt* 

^  OS  05 

TH  t^  l> 


•^        CO        CO        CO        <M 


CO  TH 

<M'      co 


00         CO  OO 

§(N  CO 

»o  oo 

<M          <N  rH 


OO 
t^» 


(N  <M        CO 

CO  10        (N 

co  "5 

t^  O5 

»C  OO 


OS 

CO 


TH      o 

CO        (M 
"5        OS 


§00 
CO 

5   @ 

O        (M 


1>        CO 

00  TH 

CO        CO 


O  oj 

«B    g 

II 


TH        00 
OS        <N 


os      TH      10 

t^        CO        TH 
OS        O        00 


^        ^ 
t^        t^ 

8    § 


*o      oo      t> 

•HH  TH  1C 

<N         CO         CO 

odd 


~^- 


§ 


<M 

Szl  ^^ 

Si    ^HH' 


(M        (N^ 


TABLE   IV. 


1209 


to     *-* 


co  t>- 

"t  «O 

t$  <N 

CO  »Q 


O  1C  O 

o  CD  t>. 

co  p  co 

t^  to  cd 


g  s 

CO       CO 


<N        tO 

1-*  1-H 

to       CO 


co 


(N        CO 


CO 


§ 

i-H  CO 


to »0 

"ci — cT 


I-H  oo  os  o 

CO  CO  <N  W 

t^  tO  rt<  00 

1C  I-H  to  to 

O  t>  to  b- 


CO        CO 


<N    (N 


»O        CO 


_o w_ 

e:   ss 


os   oo   co   I-H 

rH    r-H    CO    tO 


co  co  oo 

CO  CO  CO 

CO  "*  1-1 

1>  OO  i-H 

O  CO  <N 


<N    (N 


_CO_ 


oo   co 
d  <N' 


s 


co  ^^  to  os 

i>  o  oo  -^ 

I-H  ^  CO  ^  o  co 

»-H  00  tO  (N  t^  (N 

b-  I-H  CO  00  OS  OS 

co  <N  c<i  I-H  I-H  c<j 


V, 

§ 


oo   to 

(N CO 


CO         05 

d      I-H 


0    (N 

CO   CO 


(N     i-H     rH 


CO        (N 


OJ    Tj< 
(M    (N 


»O 


CO        O5        O 
tO         CO          i-H 

(M        ^H        <N 


O        i- 


^  5 

tO   t» 


^H  O  i-l 


1-H  OS 


O  TH 


to  O 

i  £ 

l>  O 

00  OS 


Ct 


b-  (N  00 

»-H  tO  CO 

Tf    (N  to  t» 

C^    CO  O^  ^O 


-*   ^ 


O  I>  O  CQ   O 

oo  t^*  os  ^2   co 

co  o  ^f  ^   to 

co  co  co  os   oo 

Tf  to  CO  CO        tO 

d  d  o  o d 


CO  CO  ^^ 

tO  O  OS 

oc  to  i> 

d  o  o 


-Ji 


ifi« 

(O 


S^.2?  co  .25  co* 


loBO 

I  I 


s  n  z  ii 
1^1% 


<D        -S  <N 

•g.       S3  CO 

^C^O^  || 

«^    '-gt-  02 


I 


'gag1 

£    -z 


l-s- 

l'-as 


a  »  5 1 

S^"o    « 
< 


30  §« 


1210 


TABLE    IV. 


1>- 
(M 


c 


i       c 


(M  CO 

01  CO 

tO  t^ 

CO  CO 


o      oo 


>o 


a    2 

00        O 

Tt<  tO 


O 
(M 


CO 
iO 


£  8 

2  i 

(N  CO 

CO  CO 


(N       O 

§   $ 
3    S 


.  o  A 


O5          »O 
00        O5 


O 

os 


^3       1 

a.: 

•If 

f: 

cc 


T^ 


Tin 
Sn=119 
nnous  oxi 
SnO=135 


^  * "  ^«i^ 4 


Ba 
Ba 


Stannic  ox 
SnO2=  15 
Stannic  ox 
SnO2=15 


N 


TABLE   V. 


1211 


TABLE  V.— INTERNATIONAL  ATOMIC  WEIGHTS,  1903. 


O  =  in. 

H  =  l. 

O  =  16. 

H  =  l. 

Aluminium.  .  . 
Antimony.  .  .  . 
Argon. 

Al 
Sb 
A 

27-1 
120-2 
39-9 

26-9 
119-3 
39-6 

Molybdenum.  . 
Neodymium.  . 
Neon  

Mo 
Nd 

Ne 

96-0 
143-6 
20-0 

95-3 
142-5 
19-9 

Arsenic 

As 

75-0 

74-4 

Nickel  

Ni 

58-7 

58-3 

Barium  .  .  . 

Bi 

137-4 

136-4 

Nitrogen.  .  . 

N 

14-04 

13-93 

Bismuth. 

Bi 

203-5 

206-9 

Osmium.  .  . 

Os 

191-0 

189-6 

Boron.  . 

B 

11-0 

10-9 

Oxygen.  . 

o 

16-00 

15-88 

Bromine. 

Br 

79-96 

79-36 

Palladium 

Pd 

106-5 

105-7 

Cadmium.  . 

Td 

112-4 

111-6 

Phosphorus  . 

p 

31-0 

30-77 

Caesium.  .  . 

Cs 

133  -O 

132-0 

Platinum 

Pt 

194-8 

193-3 

Calcium  
Carbon.  .  . 

Ca 

c 

40-1 
12-00 

39-8 
11-91 

Potassium.  .  .  . 
Praseodymium 

K 
Pr 

39-15 
140-5 

38-86 
139-4 

Cerium  

Ce 

140-0 

139-0 

Radium   .    . 

R^ 

225-0 

223-3 

Chlorine.  .  .  . 

Cl 

35-45 

35-18 

Rhodium 

Rh 

103-0 

102-2 

Chromium.  .  .  . 
Cobalt.  .  . 

Cr 
Co 

52-1 
59-0 

51-7 
58-56 

Rubidium.  .  .  . 
Ruthenium 

Rb 
Ru 

85-4 
101-7 

84-8 
100-9 

Columbium 
(Niobium).  . 
Copper  

Cb 
Cii 

94-0 
63-6 

93-3 
63-1 

Samarium.  .  .  . 
Scandium.  .  .  . 
Selenium 

Sm 
Sc 
Se 

150-0 
44-1 
79-2 

148-9 
43-8 
78-6 

Erbium  

F, 

166-0 

164-8 

Silicon 

Si 

28-4 

28-2 

Fluorine.  .    .    . 

F 

19-0 

18-9 

Silver 

Ag 

107-93 

107-12 

Gadolinium.  .  . 

Gd 

156-0 

155-0 

Sodium 

Na 

23-05 

22-88 

Gallium. 

Ga 

70-0 

69-5 

Strontium 

Sr 

87-6 

86-94 

Germanium.  .  . 
Glucinum 
(Beryllium). 
Gold 

Ge 

Gl 
Au 

72-5 

9-1 
197-2 

71-9 

9-03 
195-7 

Sulphur  
Tantalum.  .  .  . 
Tellurium.  .'  .  . 
Terbium 

S 
Ta 
Te 
Tb 

32-06 
183-0 
127-6 
160-0 

31-83 
181-6 
126-6 

158-8 

Helium  

HP 

4-0 

4-0 

Thallium. 

Tl 

204-1 

202-6 

Hydrogen.  .  .  . 
Indium  

H 
In 

1-008 
114-0 

1-000 
113-1 

Thorium.  .... 
Thulium.  . 

Th 
Tm 

232-5 
171-0 

230-8 
169-7 

T 

126-85 

125-90 

Tin       

Sn 

119-0 

118-1 

Iridium 

Tr 

193-0 

191-5 

Titanium 

Ti 

48-1 

47-7 

Iron  

Fe 

55-9 

55-5 

Tungsten  

W 

184-0 

182-6 

Krypton 

Kr 

81;8 

81-2 

Uranium.  . 

u 

238-5 

236-7 

Lanthanum.  .  . 
Lead  . 

La 
Pb 

138-9 
206-9 

137-9 
205-35 

Vanadium.  .  .  . 
Xenon.  . 

V 

x 

51-2 
128-0 

50-8 
127-0 

Lithium  .  .  . 

T,i 

7-03 

6-98 

Ytterbium.  .  .  . 

Yb 

173-0 

171-7 

Magnesium 

Mff 

24-36 

24-18 

Yttrium 

Yt 

89-0 

88-3 

Manganese 

Mn 

55-0 

54-6 

Zinc 

Zn 

65-4 

64-9 

Hr 

200-0 

198-5 

Zirconium.  .  .  . 

7,T 

90-6 

89-9 

1212 


TABLE    VI. 


TABLE  VI. 

SPECIFIC   AND   ABSOLUTE   WEIGHTS   OF   SOME   GASES. 


Calculated  on  the  Values  used 
in  this  Work. 

Values  used  in  the  German 
Edition. 

Specific 
Weight, 
Air—I. 

1000  c.c.  of  Gas  at 
0°  and  760  mm. 
Pressure  Weighs 
in  Grammes. 

Specific 
Weight, 
Air  —I. 

Specific 
Weight, 
Air=l. 

1000  c.c. 
Gas  at  0° 
and 
760  mm. 
Pressure 
Weighs 
in 
Grammes. 

Atmospheric  air 

1.00000 
1  .  10526 

1  .  2930 
1.4291* 

1.2930 
1.4291* 

1.00000 
1  .  10563 
(Renault) 

1.00000 
1  .  10563 

1.293635* 
1.430282 

O=16. 

O  =  16. 

H-l. 

Cal- 
culated.! 

Deter- 
mined .1 

Hydrogen  . 

0.069651 
0.622256 
0.828937 
1.519718 
0.967093 
0.553730 
0.968199 
4.282842 
2.215335 
1  .  177298 
8.762557 
5.522794 
2.448819 
0.969857 
1.037553 
0.589374 
1.796031 

0.08988* 
0.80458 
1.07183 
1.96502 
1  .  25047 
0.71598 
1.25189 
5  .  53778 
2.85824 
1.52227 
11.33012 
7.14105 
3.16636 
1.25403f 
1.34157 
0.76207 
2.32587 

0.08988* 
0.80353 
1.06957 
1.96208 
1.24843 
0.71455 
1.24933 
5.52762 
2.86088 
1.52032 
11.31499 
7.13108 
3.16198 
1.25203f 
1  .  33966 
0.76083 
2.32160 

0.06910 
0.62191 
0.82922 
1.52024 
0.96742 
0.55281 
0.96742 
4.28432 
2.2112611 
1  .  17473 
8.76557 
5.52470 
2.45035 
0.97019 
1.03791 
0.58875 
1.79941 

0.06927 
1  .  52908 

0.97136 

0.089610 
1  .  978071 

1  .  256585 

Water  vapor  
Carbon  vapor. 

Carbonic  acid  
Carbonic  oxide  
Marsh-gas  (methane)  .  . 
Ethylene  
Phosphorus  Vapor  
Sulphur  vapor  
Hydrogen  sulphide.  .  .  . 
Iodine  vapor.  .  . 

Bromine  vapor 

Chlorine.  .  . 

Nitrogen  . 

Nitric  oxide. 

Ammonia,  NHs  
Cyanogen  

*  These  are  the  most  probable  values  for  oxygen  and  hydrogen,  according  to 
RAYLEIGH,  and  are  in  close  agreement  with  the  values  obtained  by  others  (REGNAULT, 
JOLLY,  MORLEY,  etc.);  they  are  calculated  for  0°,  760  mm.,  and  lat.  45°. 

t  RAYLEIGH  gives  1.2507  as  the  most  probable  value  for  nitrogen,  and  this  figure  is 
in  close  concordance  with  that  obtained  by  other  investigators  (MORLEY.  JOLLY,  etc.). 

J  For  Berlin,  calculated  by  W.  Lasch  (Chem.  Pharm.  Centralbl.,  1852.  p.  148. 

§  The  specific  weights  here  given  are  calculated  from  the  equivalents  used  in  the 
German  edition  and  are  based  on  the  specific  weight  of  oxygen,  1 . 10563,  as  determined 
by  REGNAULT. 

II  Sulphur  vapor  has  not  this  specific  weight  below  800°  to  1000°;  at  450°  to  500° 
it  is  6.6. 

1  The  values  of  hydrogen,  carbonic  acid,  and  nitrogen  as  determined  by  REGNAULT 
are  given  for  comparison  with  the  calculated  values.  From  these  the  weights  of  a  litre 
of  the  different  gases  at  Berlin  are  reckoned,  taking  the  weight  of  a  litre  of  atmospheric 
air  in  Berlin  as  the  standard. 


TABLE    VII.  1213 


TABLE  VIT. 

COMPARISON    OF    DEGREES    OF    THE    MERCURIAL     THERMOMETER    WITH    THOSE 
OF   THE    AIR-   OR    HYDROGEN-THERMOMETER. 

(According  to  CRAFTS.*) 

Degrees  of  the  Degrees  of  the 

Mercurial  Thermometer.  Air-thermometer. 

110 110-02 

120 120-04 

130 130-09 

140 140-16 

150 150-25 

1 60 160-33 

170 170-35 

180 180-34 

190 190-32 

200 200-27 

210 210-18 

220 .- 220-08 

230 229-98 

?40 239-86 

250 249-74 

260 259-61 

270 269-50 

280 279  37 

290 289 • 1 2 

300 298-79 

310 308-40 

320 317-97 

330 327-52 

*  Comptes  rendus,  xcv,  836  and  910:  Zeitschr.  f.  analyt.  Chem.,  xxin,  526.  The 
figures  are  the  mean  of  experiments  with  fifteen  thermometers.  They  hold  good  for 
lead  glass  containing  18  per  cent,  of  lead  oxide,  as  well  as  for  German  soda-glass. 
CRAFTS  found  no  important  difference  between  the  two  kinds  of  glass;  the  differences 
between  his  values  and  those  arrived  at  by  REGNAITLT  and  others  are  accounted  for  by 
him  from  the  circumstances  that  the  composition  of  the  glass  of  which  thermometers 
were  formerly  made  was  very  different  from  that  of  the  glass  now  employed  for  this 
purpose. 


INDEX. 


PAGE 

Abbe  refractometer ii,  1062 

Absorption  bulbs  for  carbonic  acid ii,  53 

for  water ii,  51 

Acid  apocrenic,  determining  in  mineral  waters ii,  261 

boric,  determination.  . i.  465 

as  potassium  borofluoride       i,  466 

separation  from  basic  radicals i,  468 

arsenic,  separation  from  alkalies,  alkali  earths,  zinc  etc        .......  i.  711 

arsenous  acid        i,  716.  721,  729 

barium,  strontium  calcium,  and  lead   .  .  if  713 
copper,  cadmium  iron  (ic):  manganese, 

etc i,  712 

manganese,  iron,  zinc,  copper,  nickel,  and 

cobalt     i,  710 

tin  and  antimony     i,  721 

metals  of  groups  i  and  n i,  713 

of  groups  i-iv       .     i.  712 

arsenous,  determination  gravimetrically,  indirectly i.  419 

by  Rose's  method , i.  419 

by  Vohl's  method  .    i.  419 

separation  from  arsenic  acid i.  716,  721,  729 

carbonic,  apparatus  for  absorbing     ii,  53 

determination  by  Dietrich's  method    v  504 

by  Kolbe's  method i.  493 

by  measuring  the  gas    i.  500 

by  Pettenkofer  s   method     i.  484 

by  Rose's  method i,  496 

by  Scheibler's  method.  , i.  500 

by  weighing ii,  31 6 

in  carbonates it  487 

in  gases , i.  479 

in  mineral  waters ii  227,  232,  236,  251 

in  water ii,  199 

gravimetrically i,  482 

1215 


1216  INDEX. 

PAGES 

Acid  carbonic,  determination  volumetrically i,  483 

with  barium  chloride  or  calcium  chloride 

and  ammonia i,  481 

with  calcium  hydroxide i,  480 

Geissler's  apparatus  for  determining i,  491 

separation  from  all  other  acids i,  733 

from  basic  radicals i,  487 

table  of  absorption  of i,  508 

of  weight  of  1  c.c.  at  various  temperatures  and  pres- 
sures   i,  506 

Well's  apparatus  for  determining i,  499 

chloric,  determination i,  593 

in  chlorates i,  593 

separation  from  bases i,  593 

from  other  acids i,  757 

chromic,  determination  as  barium  chromate i,  423 

as  lead  chromate ! i,  423 

as  oxide i,  422 

by  Bunsen's  method i,  424 

by  oxalic  acid i,  423 

by  Schwarz's  method i,  424 

by  Vohl's  method i,  423 

volumetrically i,  424 

separation  from  aluminium i,  427 

from  basic  radicals i,  426 

from  chromium i,  427 

crenic,  determining  in  mineral  waters ii,  261 

determination  acidimetrically ii,  295 

hydrochloric i,  129 

normal • ii,  299 

hydrofluoric i,  130 

determination  as  calcium  fluoride i,  472 

separation  from  other  acids i,  735 

hydrofluosilicic,  determination  of i,  442 

by  Stolba's  method i,  443 

iodic,  determination  of i,  432 

molybdic,  determination  as  dioxide,  lead  molybdate,  or  disulphide,  i,  420 

by  Pisani's  method i,  421 

nitric i,  128 

determination. i,  571 

as  ammonia i,  584 

as  ammonia  by  Harcourt's  method i,  585 

as  ammonia  by  Siewert's  method i,  587 

as  nitrogen i,  592 

by  distillation i,  573 

by  decomposition  with  alkalies i,  574 


INDEX  1217 


Acid  nitric,  determination  by  decomposition  with  ferrous  chloride  by 

Pelouze's  method i,  575 

by  Schlosing's  method. i,  579 

by  Tiemann-Schulze's  method i,  532 

from  loss  of  hydrogen,  by  Schulze's  method,  i,  588 

in  mineral  waters ii,  261 

in  water ii,  186 

separation  from  basic  radicals.  . i,  572 

from  other  acids i,  757 

nitrous,  determination i,  433 

in  water ii,  192 

in  water  by  permanganate  method ii,  195 

in  water  by  starch-iodide  method ii,  193 

normal,  for  acidimetry ii,  293,  297 

oxalic,  crystallized,  pure i,  144 

determination  as  calcium  carbonate i,  470 

as  carbonic  acid i,  471 

with  gold,  by  Rose's  method i,  470 

with  permanganate i,  470 

normal ii,  300 

separation  from  basic  radicals i.  471 

phosphoric,  determination  as  ferric  phosphate i,  452 

as  lead  phosphate i,  445 

as  magnesium  phosphate  by  Schulze's 

method i,  453 

as  magnesium  pyrophosphate i,  445 

as  uranyl  pyrophosphate i,  451 

by  Chancel's  method i,  450 

by  Girard's  method i,  449 

by  Neubauer's  method i,  454 

by  Reissig's  method i,  448 

by  Rose's  method i,  448 

by  Sonnenschein's  method i,  446 

by  Weeren's  method i,  452 

in  manures ii,  854,  856 

in  mineral  waters ii,  259 

in  superphosphates ii,  863 

volumetrically i,  453 

separation  from  alkalies,  barium,  calcium,  lead,  and 

strontium i,  457 

from  all  bases i,  464 

from  aluminium,  and  magnesium i,  458 

from  basic  metals i,  462 

from  chromium i,  460 

from   metals   of    the    second,  third,  and 

fourth  groups i,  460 


1218  INDEX. 


Acid  phosphoric,  separation  from  metals  of  fifth  and  sixth  groups i,  462 

rosolic ii,  311 

salicylic,  determination  in  wines. ii,  1085 

selenous,  determination ii,  429 

silicic *t  233 

determination i,  505 

by  fusion  with  alkali  carbonates i,  511 

by  Mitscherlich's  method i,  521 

by  Smith's  method i,  519 

in  compounds  decomposable  by  HC1  or  HNO3,  i,  509 

in  mineral  waters ii,  246 

in  water ii,  196 

with  ammonium  fluoride i,  516 

with  barium  hydroxide  or  carbonate i,  517 

with    calcium    carbonate    and    ammonium 

chloride .  i,  518 

with  hydrofluoric  acid i,  513 

with  hydrogen  potassium  fluoride i,  516 

separation  from  all  other  acids i,  737 

from  basic  radicals i,  509 

sulphuric,  determination i,  434 

by  Bohlig's  method i,  436 

by  Clemm's  method i,  436 

by  Mo.hr's  method i,  435 

by  Wildenstein's  method i,  437 

in  mineral  waters ii,  249 

in  presence  of  sulphates i,  442 

in  sulphur  water ii,  272 

in  water ii,  186 

fuming,  analysis  of ii,  706 

normal ii,  299 

separation  from  all  other  acids i,  731 

from  barium,  calcium,  lead,  and   strontium,  i,  441 

from  mercury  in  mercurous  sulphate i,  442 

sulphurous i,  149 

determination i,  431 

tartaric,  determination  in  wines ii,  1082 

thiosulphuric,  determination  of i,  432 

Acidimetry ii,  284 

Acids  arsenous  and  arsenic,  separation  from  all  other  acids i,  730 

combined,  determining  acidimetrically ii,  313 

free,  determination  acidimetrically ii,  301 

organic,  volatile,  determination  in  mineral  waters ii,  261 

in  saline  waters ii,  272 

separation  of i,  739 

volatile,  determination  in  butter ii,  1055 


INDEX.  1219 

PAGE 

Air,  atmospheric,  analysis  of ii,  928 

Air-baths i,  63 

Albuminoid  nitrogen  in  water,  determination  as  ammonia ii,  207 

Alcohol,  determination  in  liquors ii,  1072 

in  mixtures ii,  763 

Aldehydes,  determination  in  liquors ii,  1037 

Alkali,  caustic  with  carbonate,  determining ii,  323,  332 

normal ii,  293 

Alkali-earths,  determination  alkalimetrically ii,  334 

Alkalies,  determination  alkalimetrically  by  Descroizilles-Gay-Lussac's 

method ii,  323 

by  Mohr's  method ii,  329 

hi  carbonates  by  Fresenius-WilPs  method. ...  ii,  331 

in  ferrocyanides i,  554 

in  minerals ii,  1 175 

Alkalimetry ii,  319 

Allihn's  method  of  determining  grape-sugar ii,  741 

solution  (modified  Fehling's) ii,  741 

table  for  determining  dextrose ii,  1046 

Alumina i,  180 

cream  for  sucrose  determination ii,  1049 

Aluminium,  determination  as  oxide i,  278 

in  cast  iron ii,  543 

in  minerals ii,  1137 

in  mineral  waters ii,  246 

hydroxide i,  179 

oxide i,  180- 

separation  from  alkali-earth  metals i,  623 

from  ammonium i,  622 

from  barium  and  strontium : . .  i,  627 

from  calcium .» i,  627 

from  chromium i,  630 

from  iron  (ic) i,  646 

from  iron  (ic  and  ous),  cobalt,  and  nickel i,  643 

from  magnesium  and  calcium i,  628 

from  potassium  and  sodium i,  622 

from  radicals  of  the  fourth  group i,  640 

from  uranyl i,  674 

from  zinc,  cobalt,  and  nickel i,  656 

sulphate ii,  403 

Ammonia,  determination  by  the  zinc-iron  method ii,  1030 

in  mineral  waters ii,  260 

hi  saline  waters ii,  272 

in  water ii,  207,  211 

colorimetrically ii,  207 

with  potassium-mercuric  iodide.  .  .  ii,  212 


1220  INDEX. 

PAGE 

Ammonia-iron  alum i,  147 

Ammonium,  arseno-molybdate i,  224 

carbonate i,  142 

chloride i,  143,  167 

determination  as  ammonia i,  253 

as  ammonium-platinic  chloride i,  252 

as  chloride i,  252 

as  nitrogen i,  256 

-ferrous  sulphate i,  146 

-hydrogen  fluoride ii,  142 

-magnesium  arsenate i,  222 

phosphate i,  177 

-manganese  phosphate i,  188 

molybdate i,  136 

nitrate i,  142 

phosphate .  r i,  135 

phospho-molybdate .- i,  230 

-platinic  chloride i,  167 

salts,  determination  in  manures ii,  883 

separation  from  metals  of  the  fourth  group i,  631 

from  potassium  and  sodium i,  604 

from  sodium i,  603 

succinate.  ......... i,  135 

Analyses,  calculation  of ii,  158 

Analysis,  volumetric i,  122 

Analytical  experiments ii,  985 

Animal  charcoal,  analysis  of ii,  918 

Anthracene,  determination  in  crude  anthracene ii,  785 

Antimony i,  218 

alloys,  analysis  of ii,  674 

determination  as  sulphide  (ous) i,  396 

as  tetroxide '.  .  .  i,  398 

by  decomposing  the  sulphide i,  403 

by  Kessler's  method i,  400 

by  Mohr's  method i,  400 

by  Schneider's  method i,  403 

electrolytically ii,  673 

volumetrically i,  400 

with  dichromate i,  401 

with  permanganate i  402 

•   -nickel,  analysis  of ii,  474 

ores,  analysis  of ii.  669 

separation  from  antimonic  acid i.  729 

from  arsenic i,  720 

from  lead i.  714 

from  mercury. i,  708 


INDEX.  1221 


Antimony,  separation  from  metals  of  groups  iv  and  v  in  alloys i.  707 

from  tin i  716 

from  tin  and  arsenic . . .  i,  718 

sulphide i,  217 

tetroxide i,  21 3 

Apparatus  for  absorbing  carbonic  acid ii.  53 

water ii,  5 

Argentan.  analysis  of ii,  6G'» 

Arsenic,  see  also  acid  arsenous. 

compounds,  analysis  of ii,  690 

determination  as  ammonium-magnesium  arsenate. i,  412 

as  arsenate i,  41 1 

as  sulphide  (ous) i,  414 

as  uranyl  pyroarsenate i,  413 

by  Bunsen's  method i.  41V 

by  Kessler's  method i.  417 

by  Mohr's  method i,  416 

by  Werther's  method i,  413 

in  iron ii,  527 

in  organic  matter ii,  693 

in  pigments ii.  691 

in  tin i,  726 

volumetrically i,  416 

separation  from  antimony i.  720 

from  antimony  and  tin i,  722 

from  antimony  in  alloys i,  718 

from  copper i,  714 

from  metals  of  groups  n,  iv,  and  v I  708 

from  tin i,  717,  728 

sulphide,  determination  in  antimony  sulphide i,  720 

Arsenous  acid,  see  acid  arsenous. 

oxide i,  149 

sulphide i,  221 

Asbestos  filters i,  120;    ii,  503  (foot-note) 

Ash  analysis , ii,  789,  798,  1096 

Aspirator,  Bunsen's i,  103 

Azotometer.  SchifFs ii.  76 

Azotimetric  method  of  determining  ammonia  in  manures ii,  885 

in  soils ii,  845 

Babcock  asbestos  method  of  determining  fat  in  milk ii,  1069 

water  in  milk ii,  1069 

Balance,  testing,  etc i,  12 

Barium  acetate i,  137 

carbonate i.  138,  170 

chloride.  .  i,  137 


1222  INDEX. 


Barium  chromate i,  226 

compounds,  analysis  of ii,  375 

determination  as  carbonate ii,  264 

as  sulphate i,  263 

in  minerals .  ii,  1144,  1155 

in  mineral  waters ii,  246,  252 

in  saline  waters ii,  271 

separation  from  calcium i,  617 

from  potassium  and  sodium i,  607,  608 

from  strontium  and  calcium i,  616,  617 

silicofluoride i,  171 

sulphate i,  168 

Baskerville's  method  of  separating  titanium  from  iron  and  aluminium 

in  mineral  analysis ii,  11 54 

Bearing  metal,  white,  analysis  of ii,  686 

Beet-juice,  determining  sugar  in ii,  758 

Beilstein-Jawein's  method  of  determining  zinc  electrolytically ii,  449 

Bell  metal,  analysis  of ii,  680 

Belohoubeck's  method  of  determining  uranium i,  336 

Berthelot-Fleury's  modified  method  of  determining  tartaric  acid  in 

wines ii,  1083 

Berzelius'  method  of  determining  carbon  in  cast  iron ii,  502 

of  separating  phosphoric  acid  from  aluminium i,  459 

-Rose's  method  of  determining  sulphur i,  564 

Bigelow's  method  of  determining  salicylic  acid  in  wines ii,  1085 

Bismuth i,  212 

alloys,  analysis  of ii,  665 

and  copper,  separation  from  lead  and  cadmium i,  692 

carbonate i,  212 

chloride,  basic i,  212 

chromate i,  212 

determination  as  arsenate i,  387 

as  carbonate i,  383 

as  chromate i,  385 

as  metal i,  386 

as  trioxide i,  383 

as  trisulphide i,  383,  384 

by  Lowe's  method i,  385 

ores,  analysis  of ii,  661 

salts,  analysis  of ii,  666 

separation  from  all  other  metals i,  684,  690 

from  cadmium i,  694 

from  copper . i,  692 

from  copper,  cadmium,  and  mercury  (ic) i,  692 

from  lead  and  cadmium i,  692 

from  silver,  lead,  and  copper. i,  696 


INDEX.  1223 

PAGE 

Bismuth  trioxide i,  211 

trisulphide i,  213 

-white,  determination  of  bismuth  in ii,  668 

Black  ash,  analysis  of ii,  361 

Blair's  method  of  determining  phosphorus  in  iron ii,  529 

Bog-iron  ore,  analysis  of ii,  493 

Bohlig's  method  of  determining  chlorine i,  526 

ferrocyanides i,  557 

sulphuric  acid i,  436 

Bohmer's  method  of  analysis  of  Chili  saltpetre ii,  881 

Boisbaudran's  method  of  determining  copper  electrolytically ii,  624 

Bone-black,  analysis  of ii,  917 

manures,  analysis  of ii,  916 

-meal,  analysis  of ii,  917 

Boussingault's  method  of  determining  ammonia  in  mineral  waters ii,  260 

carbon  in  cast  iron ii,  505,  515 

Borax i,  140 

Boric  acid,  see  acid  boric. 

anhydride,  determination  of ii,  465 

Boron,  determination  in  minerals ii,  1185 

Brass,  analysis  of ii,  655 

Britannia  metal,  analysis  of ii,  685 

Britton's  method  of  analysis  of  chromium  ores ii,  422 

Bromine  containing  chlorine,  analysis  of i,  754 

determination  as  silver  bromide i,  532 

colorimetrically  by  Heine's  method i,  534 

gravimetrically  and  volumetrically i,  532 

in  free  state i,  536 

in  mineral  waters ii,  252 

in  organic  compounds ii,  121 

in  saline  waters ii,  271 

with  chlorine  water  and  chloroform  by  Rei- 

mann's  method i,  532 

with   chlorine   water   and   heat   by    Figuier's 

method i,  533 

In  organic  bodies,  testing  for ii,  7 

separation  from  chlorine i,  744 

from  chlorine  and  iodine i,  750 

from  metals i,  535 

Brominized  soda  solution  for  nitrogen  determinations ii,  888 

Bronze,  antique,  analysis  of ii,  680 

coin,  analysis  of ii,  680 

medal,  analysis  of.  .  . ii,  680 

patent,  analysis  of ii,  680 

Brugelmann's  method  of  determining  chlorine  in  organic  compounds. .  ii,  126 

sulphur  in  organic  compounds. .  ii,  111 


1224  INDEX. 

PAGB 

El-miner's  method  of  determining  water  and  carbonic  acid  in  air ii,  929 

Buisson-Ferray's  method  of  determining  bismuth  in  bismuth- white . . . .  ii,  668 

Bunsen's  aspirator i,  103 

method  of  determining  arsenic i,  417 

chlorine  volumetrically i,  530 

chromic  acid i,  424 

manganese  dioxide ii,  465 

sulphur i,  566 

vapor  densities ii,  156 

modification  of  Liebig's  combustion  method. ii,  30 

Burette,  Gay-Lussac's i,  48 

Geissler's i,  49 

Mohr's i,  42 

Burettes i,  42 

Butter,  analysis  of ii,  1054 

determination  of  casein,  ash,  and  chlorine  in ii,  1054 

of  salt  in ii,  1054 

of  soluble  and  insoluble  acids  in ii,  1059 

of  volatile  acids  in ii,  1055 

Cadmium  carbonate i,  214 

determination  as  oxide.  .     i,  388 

as  sulphate i,  389 

as  sulphide i,  388 

oxide i,  213 

separation  trom  copper i,  693 

from  zinc i,  684 

sulphide i,  214 

Calamine,  analysis  of. ii,  428 

electric,  analysis  of ii,  428 

Calcium i,  132 

acetate,  analysis  of ii,  387 

carbonate. i,  173 

chloride i,  155 

tubes ii,  14 

determination  as  carbonate i,  269 

as  oxide i,  269 

as  sulphate.    .  .  , i,  269 

by  volumetric  methods i,  273 

in  minerals ii,  1144 

in  mineral  waters ii,  246 

in  saline  waters ii,  268 

in  water ii,  196 

fluoride i,  232 

oxalate i,  175 

separation  from  aluminium. .    i,  627 


INDEX.  1225 

PACK 

Calcium,  separation  from  magnesium i,  618,  619 

from  nickel  and  cobalt i,  633,  638 

from  potassium  and  sodium i,  607,  609 

from  strontium i,  619 

sulphate i,  173 

Calculation  of  analyses ii,  158 

Cane-sugar,  determination  of ii,  730 

by  fermentation ii,  759 

by  inversion ii,  751 

Carbohydrates,  determination  by  Soxhlet's  method ii,  1042, 1043 

in  agricultural  products. ii,  1037 

in  grains  and  cattle  foods ii,  1034 

Carbon  and  hydrogen,  determination  in  nitrogenous  substances ii,  56 

in  organic  substances  by  CloeV 

method ii,  14Q 

in  organic    substances  by  War- 
ren's method ii,  145 

determination  in  minerals ii,  1180 

dioxide,  see  also  acid  carbonic. 

determination  in  minerals ii,  118fr 

disulphide i,  128 

in  cast  iron ii,  502,  517 

determining  as  carbonic  acid ". ii,  509 

by  Berzelius'  method ii,  502 

by  Boussingault's  method ii,  505 

by  oxidation  with  chromic  acid ii,  510 

by  Ullgren's  method ii,  505 

by  Weyl's  method ii,  505 

by  Wohler's  method ii,  508 

hi  steel,  determining ii,  548 

colorimetrically  by  Eggertz'  method ii,  550 

Carbonic  acid,  see  acid  carbonic. 

Cairus'  method  of  determining  chlorine,  bromine,  and  iodine  in  organic 

compounds ii,  124 

sulphur  in  organic  compounds ii,  lid 

Casein,  ash,  and  chlorine  hi  butter ii,  1054 

Cast  iron,  analysis  of ii,  501 

determining  iron  in ii,  536 

Caustic  lime,  method  of  preparing ii,  111 

Cazeneuve's  reaction  for  coloring-matter  in  wine ii,  1084 

Cement  copper,  analysis  of ii,  633 

Cements,  analysis  of ii,  393,  400 

Chancel's  method  of  determining  phosphoric  acid i,  450 

Chamber  acid,  analysis  of ii,  715 

Charcoal,  animal,  analysis  of ii,  918 

Chatard's  apparatus  for  determining  water  in  minerals ii,  1129- 


1226  INDEX. 

PAGE 

Chatard's  drying-oven  for  determining  moisture ii,  1121 

Cheese  analysis ii,  1070 

determination  of  fat  in ii,  1071 

of  nitrogen  in ii,  1071 

of  water  in ii,  1071 

Chili  saltpetre,  analysis  of ii,  875 

Chlorates,  see  acid  chloric. 
Chloric  acid,  see  acid  chloric. 

"Chloride  of  lime,"  analysis  of ii,  376 

Chlorides,  determining,  in  presence  of  fluorides i,  741 

Chlorinated  lime,  analysis  of ii,  376 

Chlorine i,  143 

determining,  alkalimetrically  by  Bohlig's  method i,  526 

as  chloride i,  521 

by  silver  nitrate  (volumetrically) i,  522 

gravimetrically.  .  . ! i,  531 

in  free  state i,  529 

in  minerals ii,  1182 

in  organic  compounds ii,  121 

in  silicates i,  740 

in  water ii,  185 

volumetrically  with  potassium  iodide  by  Bun- 
sen's  method i,  530 

with  mercuric  nitrate,  by  Liebig's  method i,  525 

with  silver  nitrate  and  starch  iodide,  by  Pisani's 

method i,  524 

in  organic  bodies,  testing  for ii,  7 

separation  from  bromine i,  744 

from  iodine i,  748 

from  iodine  and  bromine i,  750 

from  metals i,  527 

Christomanos'  method  of  analyzing  chromite ii,  423,  425 

Chrome-iron  ore ii,  421 

Chromic  acid,  see  acid  chromic. 

Chromite,  analysis  by  Christomanos'  method ii,  423,  425 

Chromium,  see  also  acid  chromic. 

determination  as  oxide i,  281 

in  cast  iron ii,  543 

in  minerals ii,  1160, 1162 

hydroxide i,  181 

separation  from  alkali-earth  metals i,  628 

from  aluminium i,  630 

from  ammonium i,  622 

from  barium,  strontium,  and  calcium i,  629 

from  metals  of  fourth  group i,  653 

from  potassium  and  sodium ...  i,  622 


INDEX.  1227 


Chromium,  separation  from  radicals  of  the  fourth  group i,  640 

Citrate-soluble  phosphoric  acid,  determination  in  superphosphates.  . . .  ii,  871 

Clamond  thermopile ii,  613 

Classen-Reis'  method  of  determining  copper  electrolytically ii ,  623 

Classen's  method  of  analysis  of  zinc  blende ii,  434 

of  determining  manganese  electrolytically ii,  472 

silver  electrolytically ii,  573 

tin  in  fine  solder  electrolytically ii,  684 

tin  alloys  electrolytically ii,  683 

of  nickel  analysis ii,  480 

Clays,  analysis  of ii,  413 

Clemm's  method  of  determining  sulphuric  acid i,  436 

Clennell's  method  of  zinc  determination ii,  440 

Clerget's  method  of  determining  sucrose ii,  1050 

Clips i,  43,  44 

Cloez'  method  of  determining  carbon  and  hydrogen  in  organic  sub- 
stances  ii,  140 

Coal,  analysis  of ii,  721 

determination  of  sulphur  in ii,  115 

Cobalt i,  192 

and  nickel,  separation  from  barium  and  strontium.  . .  .  i,  633,  634,  638 

from  manganese i,  651 

frotffmanganese  and  iron i,  651 

from  manganese  and  zinc i,  659 

from  zinc i,  659 

determination  as  hydroxide i,  306 

as  metal i,  306 

in  minerals ii,  1 144 

hydroxide  (ous) i,  191 

separation  from  alkalies i,  632 

from  nickel i,  654,  656,  665 

from  nickel,  manganese,  and  zinc i,  655 

from  zinc i,  657 

sulphate  (ous) i,  193 

sulphide i,  192 

-tripotassium  nitrite i,  193 

Cochineal  tincture ii,  309 

Coin  bronze,  analysis  of ii,  680 

Coke,  analysis  of ii,  721 

determination  of  sulphur  in ii,  115 

method  of  combustion  for ii,  105 

Colorimetric  determination  of  copper ii,  630 

Coloring  matter,  determination  of,  in  wines ii,  1081 

hi  wines,  Cazeneuves  reaction  for ii,  1084 

Combustion  by  Cloez'  method ii,  140 

furnaces ii;  18-22 


1228  INDEX. 

PAGE 

Combustion  of  difficultly  combustible  non-volatile  matters ii,  33 

of  extractive  matters ii,  33 

of  hygroscopic  substances ii,  44 

of  liquids ii,  46 

of  oils ii,  49 

of  resinous  matters ii,  33 

of  substances  yielding  little  vapor  and  no  sulphur  on  heat- 
ing  ii,  105 

of  volatile  substances ii,  108 

tube ii,  13 

with  cupric  oxide  and  oxygen ii,  37 

and  potassium  chlorate  or  perchlorate.  . .  ii,  36 

by  Liebig's  method ii,  12 

with  lead  chromate,  or  with  lead  chromate  and  potassium 
dichromate,  or  with  potassium  chromate  and  cupric 

oxide ii,  33 

Oooke's  apparatus  for  determining  ferrous  iron ii,  1172 

Copper i,  133, 154,  203 

alloys,  analysis  of ii,  655 

coarse,  analysis  of ii,  636 

determination  as  metal i,  373 

as  oxide  (ic) i,  371 

as  sulphide i,  375,  379 

as  sulpho-cyanate i,  376,  382;  ii,  628 

by  De  Haen's  method i,  377 

by  Fleck's  modification  of  Parkes'  method i,  378 

by  Fleischer's  method i,  382 

by  Fleitmann's  method i,  382 

by  Parkes'  method i,  378 

by  reduction  with  stannous  chloride i,  380 

by  Rivot's  method i,  376 

by  Schwarz's  method i,  381,  382 

by  Weil's  method i,  380 

colorimetrically ii,  630 

electrolytically i,  375;  ii,  611 

in  cuprous  oxide  in  sugar  determination ii,  1048 

in  iron ' ii,  527 

in  minerals ii,  1144 

in  ores ii,  624 

volumetrically i,  377 

electrolytic  separation  of ii,  621 

-nickel,  analysis  of ii,  474 

ores,  analysis  of ii,  605 

oxide  (ic) i,  151,  208 

preparing  for  combustions ii,  17 

oxides,  determination  of  copper  in ii,  624 


INDEX.  1229 

PAGE 

Copper  phosphate  (ic),  determining  copper  in ii,  624 

pyrites,  analysis  of ii,  605 

refined ii,  636 

separation  from  arsenic i,  714 

from  arsenic  and  antimony i,  714 

from  bismuth i,  692 

from  cadmium i,  693,  694 

from  iron i,  683 

from  mercury  (ic)  and  cadmium i,  691 

from  nickel i,  683 

from  other  metals i,  680 

from  zinc i,  683 

(ic)  from  (ous) i,  697 

(ous)  from  (ic) i,  697,  698 

sulphide  (ic) i,  210 

sulphide  (ous) i,  211 

sulphocyanate  (ous) i,  210 

Corallin . ii,  311 

Cretier's  method  of  determining  constituents  of  organic  substances. . . .  ii,  140 

Creydts'  method  of  determining  raffinose  and  sucrose ii,  1050 

Crucible  tongs ii,  1109 

Crude  lead,  analysis  of ii,  592 

Crum's  method  of  analysis  of  nitrose ii,  711 

Crushing  rocks  for  analysis ii,  1116 

Cupellation  of  lead  buttons ii,  581 

Cupric-oxide  method  of  determining  nitrogen  in  fertilizers ii,  1025 

Cyanides,  see  also  cyanogen. 

Cyanogen,  determining  by  Liebig's  volumetric  method i,  549 

in  mercuric  cyanide  by  Rose-Finkener's  method i,  552 

separation  from  chlorine,  bromine,  or  iodine i,  755 

from  the  metals i,  551 

volumetric  determination  by  Fordos-Gelis's  method i,  550 

Dairy  products ii,  1054 

Daw's  method  of  determining  manganese  dioxide ii,  467 

Debu's  method  of  determining  sulphur  in  organic  compounds ii,  98 

Decantation i,  93 

De  Haen's  method  of  determining  copper i,  377 

ferro-  and  ferricyanides i,  554 

Descroizilles-Gay-Lussac's  method  of  determining  caustic  alkali  and 

carbonate  alkalimetrically ii,  323 

Desiccation i,  54 

Desiccators i,  56 

Dextrin,  determination  of ii,  730,  760 

Dextrose,  determination  of ii,  730 

Diastase,  preparation  of  for  determining  starch ii,  763 


1230  INDEX. 

PAGtt 

Dietrich's  method  of  determining  carbonic  acid i,  504 

Distilled  liquors,  analysis  of ii,  1072 

Dittmar's  method  of  analysis  of  chromium  ores ii,  423 

Dittmar-Robinson's  method  of  determining  organic  matter  in  water .  . .  ii,  200- 

Dolomite,  analysis  of ii,  393 

Drewsen's  method  of  zinc-dust  analysis ii,  455 

Drying i,  54 

Drying-disk i,  67 

Dufty's  method  of  determining  carbon  in  steel. ii,  550 

Duflos'  method  of  determining  iodine i,  540 

Dumas'  method  of  determining  nitrogen  from  the  volume ii,  66 

vapor  densities ii,  147 

Dupasquier's  method  of  determining  hydrogen  sulphide i,  558 

Eggertz'  method  of  determining  carbon  in  steel  colorimetrically ii,  550 

Electrode,  revolving,  Gooch-Medway ii,  617 

Electrodes  for  electrolytic  determinations ii,  615 

Electrolytic  determination  of  zinc ii,  448 

Elements  in  organic  bodies,  determination  of .  . ii,  9 

Elutriation i,  53 

Engel's  method  of  determining  manganese  electrolytically ii,  473 

Equivalent  of  organic  compounds,  determining ii,  145 

Erdmann's  float i,  47 

Eschka's  method  of  determining  mercury  in  ores ii,  601 

sulphur  in  coal  and  coke ii,  115 

Eudiometer i,  28 

Evaporation i,  81 

Exercises  for  practice ii,  953 

Extract  logwood  indicator ii,  310 

Extractive  matters,  combustion  of ii,  33 

determination  in  mineral  waters ii,  263 

Fahlberg's  method  of  determining  zinc  volumetrically ii,  443 

Fahlerz,  analysis  of ii,  608 

Faulenbach's  diastase  solution  for  determining  starch ii,  762 

Feldhau's  method  (modified  by  Lunge)  of  analysis  of  nitrose ii,  711 

Fehling's  solution ii,  732,  735 

Fermentation  method  of  determining  sugar ii,  754 

Fermented  liquors,  analysis  of ii,  1072 

Ferricyanides,  determination  by  Lenssen's  method i,  556 

by  Bohlig's  method i,  557 

by  Rheineck's  method i,  557 

Ferrocyanogen,  separation  from  hydrochloric  acid i,  756 

volumetric  determination  by  De  Haen's  method. . : i,  554 

Fertilizers,  analysis  of ii,  1017 

determination  by  absolute  or  cupric-oxide  method ii,  1025 


INDEX.  1231 

PAGE 

Fertilizers,  determination  of  phosphoric  acid  hi ii,  1017 

Fiber,  crude,  determination  of ii.  1036 

Figuier's  method  of  determining  bromine i,  533 

Filter,  Gooch i,  120 

Filtering i,  94 

Filters,  asbestos i,  120 

Fine  solder,  analysis  of ii,  683 

Fish  guano,  analysis  of ii.  926 

Fixed  constituents  of  mineral  waters,  determining ii,  244 

Fleck's  method  of  determining  organic  matter  in  water ii,  205 

modification  of  Parkes'  method  of  determining  copper i,  378 

Fleischer's  method  of  decomposing  sulphuretted  ores ii,  626 

of  detennining  copper i,  382 

Fleitmann's  method  of  determining  copper i.  382 

Flesh-meal  guano,  analysis  of ii.  926 

Float,  Erdmann's i.  47 

Fluid  bodies,  combustion  of i.  46 

Fluids,  measuring i.  36 

Fluorides,  determination  by  decomposition  with  alkali  carbonates. i.  474 

with  sulphuric  acid i,  474 

from  silicon  fluoride  evolved i,  475 

Fluorine,  determination  in  minerals ii.  1182 

separation  from  metals i,  473 

Foods,  analysis  of ii,  1032 

determination  of  albuminoid  nitrogen  in,  by  Stutzer's  method,  ii,  1033 

of  carbohydrates  in ii,  1034 

of  crude  fibre  hi ii,  1034 

of  crude  protein  in ii,  1033 

Fordos-Gelis's  method  of  determining  cyanogen  volumetrically i,  550 

Frankland- Armstrong's   method    of    determining   organic    matter   in 

water ii,  200 

Fresenius- Will's  method  of  determining  alkalies  in  carbonates ii.  331 

manganese-dioxide ii,  458 

Fruit-sugar,  determination  of ii,  730 

Fuch's  method  of  determining  ferric  iron i.  334 

Fuchsin.  detection  in  wine ii,  1084 

Fusel  oil,  determination  in  liquors ii,  1087 

Galactan,  determination  of ii,  1036 

Galena,  analysis  of ii,  574 

determining  lead  in ii,  576 

silver  in ii,  577 

Galletti's  method  of  determining  zinc  volumetrically ii,  442 

Gas,  illuminating,  determination  of  sulphur  in ii,  114 

-lamp „ i,  82 

Gases  in  mineral  waters,  examination  of ii,  265 


1232  INDEX. 


Gases,  measuring.. i,  27 

reading-off i.  30 

total,  determining  in  mineral  waters ii.  232 

Gautier's  method  (Johnson-Chittenden's  modification)  of  determining 

arsenic  in  organic  matter ii,  693 

Gay-Lussac's  burette. i .  48 

method  of  chlorimetric  analysis ii.  377 

of  determining  silver.  . i.  342 

vapor  densities.  .  .  , ii.  151 

Geissler's  apparatus  for  determining  carbonic  acid i,  491 

burette ii,  49 

German  silver,  analysis  of.  . ii,  660 

Gibbs'  method  of  determining  nitrogen  in  organic  matter ii,  74 

Gintl's  method  of  combustion.      ii,  35 

of  determining  phosphorus  and  sulphur  in  iron ii,  531 

sulphur  in  iron ii,  522 

Girard's  method  of  determining  phosphoric  acid i,  449 

salicylic  acid  in  wines ii,  1086 

Glaser's  magnesia  mixture ii,  861 

method  of  determining  phosphoric  acid  in  manures ii,  860 

Glycerin,  determination  in  liquors ii.  1078 

Gold i:  215 

determination  as  metal. i   391 

as  sulphide  (ic) i  393 

in  platinum  ore i.  727 

separation  from  lead  and  bismuth i,  715 

from  metals  of  group  i i ,  705 

from  metals  of  groups  iv  and  v  in  alloys i.  703 

from  platinum i.  716.  727 

from  silver j    713 

from  tin i.  727 

sulphide i  215 

Gooch  apparatus  for  determining  water  in  minerals ii,  1 125 

filters i.  120 

-Medway  revolving  electrode , ii,  617 

method  of  determining  titanium  in  minerals    ii,  1152 

of  separating  lithium  from  alkalies  in  rock  analysis.  .  .  ii   1178 

Goppelsroder-Trechsel's  method  of  analysis  of  stannous  chloride ii.  689 

Grabowski's  method  of  determining  vapor  densities ii    155 

Granat  guano,  analysis  of   ii,  926 

Grape-sugar,  determination  of ii,  730,  735,  740 

Graphite,  analysis  of    , ii.  717 

determination  in  cast  iron ii,  516 

Grinding  rocks  for  analysis ii,  1116 

Guano,  analysis  of ii  921 

Gunning  method  of  determining  nitrogen.  .  .    ii,  1024 


INDEX.  1233 


PAGE 


Gunpowder,  analysis  of ii  349 

residues,  examination  of  by  Werthers  method    i,  742 

Hager's  method  of  determining  sugar    ii,  753 

solution  for  determining  mercury ii  ,  753 

Hammer's  method  of  determining  tannin ii,  775 

Hampe's  method  of  analysis  of  soft  or  refined  lead       ii.  590 

of  zinc  blende ii,  432 

of  determining  copper  in  coarse  and  refined  copper.,  .ii,  649 

refined  copper  electrolytically ii,  644 

Handy' s  method  of  determining  zinc  volumetrically ii,  446 

Harcourt's  method  of  determining  nitric  acid  as  ammonia       i    5S5 

Hard  lead,  analysis  of ii.  592 

Hardness  of  water,  determining .  ii    215 

Heat  radiator  for  evaporations ii.  1110 

Heavy  spar,  analysis  of ii,  375 

Heine's  method  of  determining  bromine  colorimetrically i,  534 

copper  colorimetrically  . ii,  630 

Hematite,  analysis  of ii.  486 

Hertzfeld's  table  for  determining  invert-sugar ii,  1044 

Hide-powder,  preparation  of ii   776 

testing    ii,  1100 

Hillebrand's  method  of  determining  zirconium  in  minerals ii   1156 

Hlasiwetz'  method  of  incinerating  plant  tissues      ii,  796 

Hofmann's  method  of  determining  vapor  densities ii,  151 

Hollard's  method  of  determining  lead  electrolytically. ii,  594 

Horn  cartilage ii,  769  770 

Horn-meal  guano,  analysis  of ii   926 

Hornschlaiiche ii,  769 

Hunt-Genth's  method  of  analysis  of  chrome-iron  ore ii,  424 

Hydrofluoric  acid,  see  acid  hydrofluoric. 
Hydrofluosilicic  acid,  see  acid  hydrofluosilicic. 

Hydrogen i,  143 

-ammonium  fluoride i,  142 

dioxide,  analysis  of ii,  728 

peroxide,  see  hydrogen  dioxide. 

-potassium  fluoride i,  141 

sulphide,  determination  by  Motif's  method i    560 

in  mineral  waters       ii,  229,  240 

with  iodine  by  Dupasquier's  method,  i,  558 

Hygroscopic  substances,  combustion  of ii,  44 

Hypobromite  solution ii.  888 

Inorganic  constituents  of  plants,  determination  of ii.  787 

substances,  determination  »n  organic  substances ii,  129 

in  organic  bodies,  testing  for ii^  8 


1234  INDEX. 

PAGE 

Invertin,  for  determining  sugar  by  inversion ii,  758 

Invert-sugar,  determination  of ii,  730,  745 

lodic  acid,  see  acid  iodic. 

Iodine i,  148 

absorption  number ii,  1063 

containing  chlorine,  analysis  of i,  753 

determination  as  palladious  iodide  by  Lassaigne's  method i,  536 

as  silver  iodide i,  536 

colorimetrically  by  Struve's  method i,  541 

in  free  state  by  Schwarz's  method i,  542,  543 

in  mineral  waters ii,  252 

in  organic  compounds ii,  121 

in  saline  waters ii,  271 

with  ferric  chloride  by  Duflos'  method .  i,  540 

with  nitrous  acid  and  carbon  disulphide i,  537 

with  palladious  chloride  by  Kersting's  method.  ..  i,  540 

with  permanganate  by  Reinige's  method i,  538 

with  silver  solution  and  starch  iodide  by  Pisani's 

method i,  539 

volumetrically i,  537 

in  organic  bodies,  testing  for ii,  7 

separation  from  chlorine i,  748 

from  chlorine  and  bromine i,  750 

from  metals i,  541 

lodometric  methods  in  chlorimetry ii,  382 

Iron  acetate,  basic  (ic) i,  197 

-alum i,  147 

-ammonium  sulphate  (ous) i,  146 

arsenate  (ic) i,  224 

carbonate,  ferrous,  determining  in  mineral  waters ii,  232 

cast,  analysis  of ii,  501 

determining  iron  in ii,  536 

converting  ferrous  into  ferric i,  31 1 

determination  gravimetrically ii,  499 

in  iron  ores,  volumetrically ii,  495 

in  minerals ii,  1137 

in  mineral  waters ii,  246 

ferric,  determination  as  oxide  or  hydroxide i,  323 

as  sulphide i,  323,  325 

by  Oudeman's  method i,  332 

by  reduction  with  hydrogen  sulphide i,  326 

by  reduction  with  stannous  chloride i,  327 

by  reduction  with  zinc i,  325 

volumetrically i,  325 

with  thiosulphate i,  331 

with  thiosulphate  and  copper  sulphate i,  332 


INDEX.  1235 

PAGE 

Iron,  ferric,  Fuch's  method  of  determining i,  334 

separation  from  aluminium i,  646,  652,  650 

from  aluminium  and  chromium i,  652 

from  barium  and  strontium i,  633,  634 

from  calcium  and  magnesium i,  633,  634 

from  ferrous  iron i,  664,  666 

from  ferrous  iron,  zinc,  and  nickel i,  661 

from  manganese,  nickel,  cobalt,  and  zinc  . .  i,  644,  649 
from  manganese,  zinc,  cobalt,  nickel,  and  fer- 
rous iron i,  647 

from  potassium  and  sodium i,  632 

from  radicals  of  the  fourth  group i,  640 

from  uranium i,  675 

ferrous,  determination i,  31 1 

as  metal i,  313 

by  Penny's  method i,  319 

in  minerals ii,  1168 

volumetrically i,  312 

with  ammonium-ferrous  sulphate i,  315 

with  oxalic  acid i,  316 

with  permanganate i,  313 

separation  from  ferric  iron i,  645 

formate,  basic  (ic) i,  197 

hydroxide  (ic) i,  194 

ore,  chrome ii,  421 

magnetic,  analysis  of ii,  494 

spathic,  analysis  of ii,  494 

ores,  analysis  of ii,  486 

oxide  (ic) i,  195 

phosphate  (ic) i,  227 

separation  from  copper i,  683 

succinate,  basic  (ic) i,  196 

sulphide  (ous) i,  195 

Jannasch's  methods  of  determining  water  in  minerals ii,  1129 

Jannasch-Heidenreich's  method  of  decomposing  silicates ii,  1132 

Johnson-Chittenden's   simplified    Gautier's    method  of    determining 

arsenic  in  organic  matter ii,  693 

Kaeppel's  method  of  determining  manganese  electrolytically ii,  473 

Kayser's  method  of  analysis  of  chromium  ores ii,  422 

of  determining  potash  in  wines ii,  1085 

Kersting's  method  of  determining  iodine i,  540 

Kessler's  method  of  determining  antimony i,  400 

arsenic i,  417 

manganese  in  iron ii,  537 

phosphorus  in  iron ii,  530 


1236  INDEX. 

PAGH 

Kjeldahl  method  of  determining  nitrogen ii,  879,  899,  1021 

modifications  of ii,  902 

Knapp's  method  of  sugar  determination ii,  749 

mercury  solution  for  sugar  determination ii,  749 

Knop's  method  and  apparatus  for  azotimetrically  determining  ammo- 
nia in  manures ii,  885 

Knop-Arendt's  method  of  determining  sulphur  in  plants ii,  811 

Knublauch's  apparatus  for  determining  ammonia  in  manures ii,  883 

Koettstorfer  number,  determination  of ii,  1060 

Kolbe's  method  of  determining  carbonic  acid , i,  493 

sulphur  in  organic  compounds ii,  97 

Kolb's  method  of  determining  sulphur  in  pyrites ii,  567 

Konig's  method  of  determining  iron ii,  500 

Kopp's  method  of  determining  chlorine,  bromine,  and  iodine  in  organic 

compounds ii,  124 

Kiinzel-GrolTs  method  of  zinc  determination ii,  439 

Lactose,  determination ii,  1051 

by  Soxhlet's  method ii,  1052 

in  milk ii,  1051 

Ladenburg's  method  of  determining  constituents  of  organic  compounds,  ii,  139 

Lamp,  Haste's i,  82 

Langmuir's  method  of  determining  zinc  volumetrically ii,  447 

Lassaigne's  method  of  determining  iodine i,  536 

Lead  acetate,  analysis  of ii,  599 

-acetate  paper ii,  213 

arsenate i,  221 

carbonate,  normal i,  201 

chloride. i,  203 

chromate i,  152,  225 

crude,  analysis  of ii,  592 

determination  as  chloride i,  357 

as  chromate i,  356 

as  metal .' i,  358 

as  oxide i,  353 

as  oxide  +  lead i,  357 

as  sulphate i,  355 

as  sulphide i,  354 

by  Schwarz's  method i,  360 

electrolytically ii,  594 

in  galena ii,  576 

volumetrically i,  359 

hard,  analysis  of ii,  592 

ores,  analysis  of ii,  574 

oxalate i,  202 

oxide i,  134,  202 


INDEX.  1237 

PAGE 

Lead  oxides,  analysis  of ii,  597 

phosphate i,  227 

refined,  analysis  of ii,  534 

salts,  analysis  of r ii,  597 

separation  from  antimony i,  714 

from  bismuth i,  697 

from  other  metals i,  689,  690 

from  silver i,  693 

soft,  analysis  of ii,  584 

-subacetate  solution  for  sucrose  determination ii,  1049 

sulphate i,  202 

sulphide i,  203 

Leffmann-Beam  method  of  saponification ii,  1057 

Lenssen's  method  of  determining  ferricyanides i,  556 

tin i,  403 

Levigation i,  52 

Levulose,  determination  of ii,  730 

Liebig's  method  of  combustion,  modified  by  Bunsen ii,  30 

with  cupric  oxide ii,  12 

of  determining  chlorine i,  525 

cyanogen  volumetrically i,  549 

lead  dioxide  in  minium ii,  600 

nitrogen  from  the  volume ii,  59 

oxygen  in  air ii,  948 

sulphur  hi  organic  compounds ii,  96 

potash  bulbs ii,  53 

Lime i,  132 

caustic,  method  of  preparing ii,  111 

chlorinated  ("chloride"),  analysis  of *.  ii,  376 

Limestone,  analysis  of ii,  392 

Limonite,  analysis  of ii,  488 

Lindo-Gladding  method  of  determining  potash  in  fertilizers ii,  1030 

Link's  method  of  analysis  of  gunpowder ii,  353 

Liquids,  reading-off .  i,  46 

Liquors,  analysis  of ii,  1072 

determination  of  alcohol  in ii,  1072 

of  aldehydes  in ii,  1087 

of  ethereal  salts  in ii,  1088 

of  fusel-oil  in ii,  1037 

of  glycerin  in ii,  1078 

of  volatile  acids  in ii,  1078 

Lithium,  determination  of i,  253 

in  mineral  waters ii,  252 

separation  from  other  alkalies i,  605 

Litmus,  tincture i,  145;  ii,  307 

Loge's  method  of  determining  organic  carbon  in  soils ii,  838 


1238  INDEX. 

PAGE 

Logwood,  extract  and  tincture ii,  310 

Lowe's  method  of  determining  bismuth i,  385 

iron ii,  499 

Lowenthal's  method  of  determining  tannin ii,  767 

Luck-Fresenius'  method  of  analysis  of  red  phosphorus ii,  700 

Lunge's  modification  of  Feldhaus'  method  of  nitrose  analysis ii,  711 

nitrometer ii,  712 

Magnesia  mixture  for  determining  phosphoric  acid  in  manures ii,  1018 

Glaser's ii,  861 

Magnesium-ammonium  arsenate i,  222 

phosphate ii,  177 

chloride ii,  138 

mixture  for  determining  phosphoric  acid ii,  858 

determination  as  oxide i,  276 

as  pyrophosphate i,  275 

as  sulphate i,  275 

in  minerals ii,  1146 

in  mineral  waters ii,  246 

in  saline  waters ii,  268 

in  water ii,  196 

oxide i,  179 

phosphate - i,  227 

pyroarsenate i,  223 

pyrophosphate. i,  178 

separation  from  barium  and  strontium i,  617 

from  calcium i,  619 

from  potassium  and  sodium i,  610 

from  uranium i,  674 

sulphate i,  176 

Magnetic  iron  ore,  analysis  of ii,  494 

Malachite,  determining  copper  in ii,  624 

Maltose,  determination  of ii,  730,  747 

Maly's  method  of  determining  bromine  and  iodine ii,  128 

Manganese-ammonium  phosphate i,  188 

carbonate i,  185 

determination  as  carbonate i,  293 

as  dioxide i,  294 

as  hydroxide i,  294 

as  protosesquioxide i,  293 

as  pyrophosphate i,  297 

as  sulphate i,  297 

as  sulphide i,  295 

electrolytically ii,  472 

of  hydrochloric  acid  required  for  decomposi- 
tion of.  .  , ii,  469 


INDEX.  1239 

PAGE 

Manganese,  determination  of  moisture  in. .  .  .  ii,  468 

in  iron ii,  537 

in  minerals ii,  1143 

in  mineral  waters ii,  246 

volumetrically i,  298 

with  potassium  ferricyandide i,  298 

permanganate i,  300 

dioxide i,  186 

determination  of ii,  458 

hydroxide  (ous) i,  186 

ores,  analysis  of ii,  470 

oxide,  black,  analysis  of ii,  456 

protosesquioxide i,  186 

pyrophosphate i,  189 

(ous)  preparing ii,  539 

separation  from  alkalies i,  632 

from  aluminium  and  iron i,  665 

from  barium  and  strontium i,  633,  634,  635,  636 

from  cobalt  and  nickel i,  651 

from  lead,  bismuth,  cadmium,  and  copper i,  685 

from  nickel  and  cobalt i,  633,  638 

from  nickel  and  zinc i,  644 

from  zinc i,  665 

sulphate,  anhydrous  (ous) i,  188 

sulphide i,  187 

Mann's  method  of  determining  zinc  volumetrically ii,  444 

Manures,  analysis  of ii,  850 

Marcker's  method  of  determining  grape-sugar ii,  740 

Marguerite's  method  of  ferrous  determination i,  312 

Marie's  method  of  determining  lead  electrolytically ii,  595 

Marl,  analysis  of ii,  393 

Marx's  method  of  determining  nitric  acid  in  water ii,  189 

Maste's  lamp ii,  82 

Maumen^'s  method  of  determining  oxygen  in  organic  compounds ii,  139 

Measuring i,  26 

Mechanical  division i,  51 

Medal  bronze,  analysis ii,  680 

Meinecke's  method  of  determining  sulphur  in  iron ii,  522 

Meissl-Hiller's  factors  for  determining  invert-sugar ii,  1045 

Melting-point  of  fat,  determination  by  Wiley's  method ii,  1066 

Mercury i,  205 

analysis  of ii,  602 

chloride  (ous) i,  205 

chromate  (ous) i,  226 

mercuric,  determination  as  chloride  (ous) i,  366 

determination  as  metal i,  364 


1240  INDEX. 

PAGE 

Mercury,  mercuric  determination  as  oxide i,  367 

as  sulphide i,  366 

by  Scherer's  method i,  369 

volumetric i,  367 

ores,  analysis  of ii,  601 

separation  from  mercury  (ous),  copper,  cadmium,  and  lead.  . .  i,  688 

mercurous,  determination  as  chloride i,  361 

determination  volumetrically i,  362 

separation  from  mercury   (ic),   copper,  cadmium, 

bismuth,  and  lead i,  688 

oxide  (ic) V. .  ..r. i,  134,  207 

phosphate  (ous) i,  230 

separation  from  antimony , i,  708 

from  arsenic  and  antimony  oxides i,  713 

from  gold  and  silver i,  710 

from  metals i,  679 

from  silver,  bismuth,  copper,  cadmium,  and  lead.  . .  i,  694 

sulphide  (ic) i,  206 

Metals  in  cyanides,  determination  of i,  553 

Meteorites,  analysis  of ii,  412 

Milk,  analysis  of ii,  1068 

determination  of  fat  in ii,  1069 

of  fat  in  by  the  paper-coil  method ii,  1069 

of  lactose  in ii,  1051 

of  water  in ii,  1068 

-sugar,  determination  of » ii,  730,  746 

Mineral  waters,  analysis  of ii,  221 

calculation,  control,  and  arrangement  of  results  of  anal- 
yses of ii,  274 

taking  samples  of ii,  225,  226 

Minium,  analysis  of ii,  597 

Mitscherlich's  absorption  bulbs ii,  53 

method  of  determining  all  the  constituents  in  organic 

compounds ii,  137 

of  determining  silicic  acid i,  521 

(modified)    of    determining    ferrous    iron    in 

minerals ii,  1 170 

Mixter's  method  of  determining  sulphur  in  organic  substances ii,  100 

modification  of  Sauer's  combustion  method ii,  106 

Mohr's  burette i,  42 

method  of  determining  alkalies  alkalimetrically ii,  329 

antimony i,  400 

arsenic i,  416 

carbonic  acid  in  air ii,  946 

copper  in  ores ii,  624 

hydrogen  sulphide i,  560 


INDEX.  1241 

PACK. 

Mohr's  method  of  determining  lead  in  galena ii,  576 

sulphuric  acid i,  435 

modified  Penot's  method  of  chlorimetric  analysis ii,  331 

Moisture,  determining  in  rocks  by  Chatard's  drying  oven ii,  1121 

influence  of  upon  gases,  in  reading-off i,  34 

Molasses,  determination  of ii,  1050 

Molybdenum,  determining  in  minerals ii,  1 162 

method  of  determining  phosphoric  acid  in  manures  ....  ii,  856 
solution  for  determining  phosphoric  acid  in  manures  ...  ii,  856- 
Molybdic  acid,  see  acid  molybdic. 

Mortreux's  method  of  determining  sulphur  in  free  state i,  570 

Miiller's  modified  Schulze's  method  of  determining  phosphoric  acid  as 

ferric  phosphate i,  452 

Muntz-Ramspacher's    modified    Hammer's    method    of    determining 

tannin ii,  780 

Nepheline,  determination  in  presence  of  olivine ii,  1187 

Neubauer's  method  of  determining  phosphoric  acid i,  454 

Nessler's  reagent ii,  207 

Neutralization,  methods  of ii,  294 

Nickel i,  190 

and  cobalt,  determining  electrolytically ii,  481 

separation  from  barium  and  strontium. .  .  .  i,  633,  634,  638 

-coinage  metal,  analysis  of ii,  659 

cubes,  analysis  of ii,  483 

determination  as  metal i,  304 

as  nickel  tripotassium  nitrate i,  307 

as  oxide  and  hydroxide i,  302 

as  sulphate i,  304,  308 

as  sulphide i,  303,  307 

electrolytically ii,  481 

in  minerals ii,  1144 

volumetrically i,  305,  308 

granular,  analysis  of ii,  483 

hydroxide  (ous) i,  189 

metallic,  analysis  of ii,  483 

ores,  analysis  of ii,  474 

oxide  (ous) i,  189 

separation  from  alkalies i,  632 

from  copper i,  683 

from  zinc i,  653 

sulphide,  hydrated  (ous) i,  190 

Nickelstein,  analysis  of ii,  474 

Nickelstibine,  analysis  of ii,  474 

Nicol's  method  of  determining  sugar  by  inversion . .  ii,  757 

Nitrates,  determining  in  manures ii,  914 


1242  INDEX. 


Nitrates,  see  also  acid  nitric. 

Nitrogen    i,  168 

albuminoid,  in  water,  determination  as  ammonia ii,  207 

determination  by  absolute  or  cupric-oxide  method ii,  1025 

by  conversion  into  ammonia  by  Varrentrapp- 

Will's  method r ii,  82 

by  Gunning's  method ii,  1024 

by  Kjeldahl's  method ii,  1021 

by  magnesium-oxide  method ii,  1029 

by  Ruffle's  method ii,  1027 

by  soda-lime  method ii,  102S 

by  Stutzer's  method ii,  1033 

by  Ulsch's  method,  modified  by  Street ii,  1029 

in  air ii,  948 

in  cheese ii,  1071 

in  iron ii,  524 

in  manures ii,  909 

in  milk ii,  1069 

in  minerals ii,  1 186 

in  organic  compounds ii,  58 

by  Dumas'  method ii,  66 

by  Gibbs'  method ii,  74 

by  Liebig's  method  ...  .  ii,  59 
by  Simpson's  method.  . .  ii,  69 
by  Thibault's  method  .  .  ii,  94 

testing  for,  in  organic  bodies ii ,  4 

table  of  absorption i,  259 

table  of  weight  of  1  c.c.  at  different  temperatures  and  pressures,  i,  260 
Nitric  acid,  see  acid  nitric. 

"Nitrose,"  analysis  of ii,  710 

Nitrous  acid,  see  acid  nitrous. 

Non-tannins,  determination  of ii,  1099 

Official  methods  of  analysis  adopted  by  the  Ass'n  of  Official  Agric. 

Chemists ii,  1017 

Oil-baths i,  66 

Oils,  combustion  of ii,  49 

Operations i,  11 

Organic  acids,  volatile,  determining  in  mineral  waters ii,  261 

analysis ii,  1 

compounds  containing  sulphur,  analysis  of ii,  95 

determination  of  all  constituents  in ii,  137 

of  inorganic  substances  in i,  129 

qualitative  examination  of ii,  4 

matter,  determination  in  water ii,  199 

by  permanganate  method.  ...  ii,  202 


INDEX.  1243 

PAGE 

Organic  matter,  determination  in  water  with  alkaline  silver  solution  . .  ii,  205 

Ore-furnace  regulus,  determination  of  copper  in ii,  625 

Orseille,  detection  in  wine ii,  1034 

O'Sullivan's  method  of  preparing  pure  diastase  for  determining  starch,  ii,  763 

Otto's  chlorimetric  method ii,  3?3 

method  of  separating  phosphoric  acid  from  aluminium i,  459 

Oudeman's  method  of  determining  ferric  iron i,  332 

Oxalic  acid,  see  acid  oxalic. 

Oxgyen i,  153 

determination  in  air ii,  948 

hi  organic  substances ii,  131 

Palladium,  determination  as  chloride  (ic) i,  390 

as  metal i,  390 

iodide  (ous) i,  237 

Parodi-Mascazziiii's  method  of  determining  zinc  electrolytically ii,  448 

Patera's  method  of  analysis  of  uranium  ores ii,  567 

Pattinson's  method  of  determining  manganese  dioxide .  .  .  ii,  466 

in  cast  iron ii,  541 

Pearlash,  determination  of ii,  336 

Pearson's  method  of  determining  sulphur  hi  organic  compounds ii,  119 

Peligot's  modification  of  Varrentrapp- Will's  method ii,  91,  894 

Pelouze's  method  of  determining  nitric  acid  with  ferrous  chloride i,  573 

sulphur  in  pyrites ii,  565 

Penfield's  method  of  determining  silicon  fluorides  evolved  from  fluorides,  i,  478 

specific  gravities  of  rock  fragments,  ii,  1114 

water  in  minerals ii,  1123 

oven  for  determining  water  in  minerals ii,  1124 

tubes  for  determining  water  in  minerals ii,  1123 

Penny's  method  of  ferrous-iron  determination i,  319 

Penot's  method  of  chlorimetric  analysis ii,  379 

Pentosans,  determination  by  phloroglucin ii,  1035 

Permanganate  method  of  determining  nitrous  acid  in  water ii,  195 

organic  matter  in  water ii,  202 

Pettenkofer's  method  of  determining  carbonic  acid i,  484 

in  air ii,  938 

modifications  of,  for  determining  carbonic  acid  in 

air ii,  941 

Pettersson's  method  of  determining  water  and  carbonic  acid  in  ah-. . .  ii,  932 

Pewter,  analysis  of ii,  685 

Phenolphtalein ii,  311 

Phosphates,  see  also  acid  phosphoric 

Phosphor-bronze,  analysis  of ii,  680 

Phosphoric  acid,  see  acid  phosphoric. 

Phosphorus,  determination  in  iron ii,  527 

in  minerals ii,  1 159 


1244  INDEX. 

PAGB 

Phosphorus,  determination  in  organic  compounds.... ii,  120 

hi  organic  bodies,  testing  for ii,  7 

red,  analysis  of ii,  700 

Pigments,  determination  of  arsenic  in ii,  691 

Pinch-cocks i,  43,  44 

Pipettes i,  39 

Pisani's  method  of  determining  chlorine i,  524 

iodine i,  539 

molybdic  acid i,  421 

silver i,  349 

Vogel's  modification  of i,  351 

Plants,  determination  of  inorganic  constituents  of ii,  787 

Platinum i,  216 

determination  as  metal i,  393 

as  potassium-platinic  chloride i,  394 

as  sulphide  (ic) i,  395 

separation  from  gold i,  716,  727 

from  metals  of  groups  iv  and  v  in  alloys i,  705 

sulphide  (ic) i,  216 

and  gold,  separation  from  tin,  antimony,  and  arsenic i,  716 

Polarization  of  wines ii,  1079 

Poquillon's  method  of  determining  clay  in  soils ii,  822 

Potash  bulbs ii,  14 

Liebig's ii,  53 

determination ii,  336 

in  fertilizers  by  Lindo-Gladding's  method ii,  1030 

in  wino ii,  1035 

Potassa i,  131 

fused ii,  155 

solution i,  155 

Potassium  bitartrate,  analysis  of ii,  357 

determination  in  wines ii,  1032 

borofluoride i,  232 

chloride i,  162 

analysis  of ii,  341 

cyanide i,  136 

determination  as  chloride i,  245 

as  nitrate i,  244 

as  potassium-platinic  chloride i,  245 

as  silicofluoride i,  248 

as  sulphate i,  243 

in  manures ii,  873 

in  mineral  waters ii,  249 

dichromate i,  156 

disulphate i,  141 

-ferrocyanide  method  of  determining  zinc ii,  442 


INDEX.  1246 

PAGE 

Potassium  hydroxide i,  131 

-hydrogen  fluoride i,  141 

iodide i,  148 

-starch  paper ii,  379 

nitrate i,  162 

analysis  of ii,  346 

permanganate i,  145 

-platinic  chloride i,  163 

separation  from  sodium i,  599,  604 

silicofluoride i,  164 

sulphate i,  161 

analysis  of ii,  341 

Pratt' s  modified  hydrofluoric-acid  method  of  determining  ferrous  iron,  ii,  1173 

Precipitates,  drying i,  110 

igniting i,  112 

washing i,  98 

Precipitation,  effecting i,  91 

Pressure,  influence  of,  upon  gases  in  reading-off i,  33 

Pycnometer  method  of  determining  specific  gravities  of  rock  fragments,  ii,  1115 
Pyrites,  analysis  of ii,  553 

Qualitative  examination  of  organic  bodies ii,  4 

Quicklime,  analysis  of ii,  400 

Radicals,  determination  of i,  239 

Raffinose  and  sucrose,  determination  by  Creydt's  method ii,  1050 

Rare  earths,  determination  hi  minerals ii,  1158 

Reagents i,  127 

Red  phosphorus,  analysis  of ii,  700 

Reducing  action  of  different  sugars  on  Fehling's  solution ii,  734 

Refined  lead,  analysis  of .  . ' ii,  584 

Refractometers ii,  1061 

Regnault's  method  of  determining  carbon  in  cast  iron ii,  515 

Reimann's  method  of  determining  bromine i,  532 

Reinige's  method  of  determining  iodine i,  538 

Reitmair's  method  of  determining  nitrates  in  manures ii,  915 

Reissig's  method  of  determining  phosphoric  acid i,  448 

Resinous  matters,  combustion  of ii,  33 

Reverted  phosphoric  acid,  determination  in  superphosphates ii,  869 

Rheineck's  method  of  determining  ferrocyanides ii,  557 

Riche's  method  of  determining  copper  electrolytically ii,  623 

zinc  electrolytically ii,  449 

Rivot's  method  of  determining  copper i,  376 

Rivot-Beudant-Daguin'c  method  of  determining  sulphur i,  568 

Rock  analysis ii,  1101 

Rocks,  crushing  and  grinding ii,  1116 

determining  water  hi ii,  1117, 1122 


1246  INDEX. 

PAGE 

Rose's  method  of  determining  arsenous  acid i,  419 

carbonic  acid i,  496 

oxalic  acid i,  470 

phosphoric  acid i,  448 

of  incinerating  plant  tissues ii,  797 

Rose-Finkener's  method  of  determining  cyanogen  in  mercuric  cyanide,  i,  552 

Rosolic  acid ii,  311 

Ruffle's  method  of  determining  nitrogen  in  fertilizers.  .  .  .1 ii,  1027 

Russel's  method  of  determining  sulphur  in  organic  compounds ii,  99 

Saccharose,  determination  of ii,  730 

Sachsse's  mercury  solution  for  determining  sugar ii,  751 

method  of  determining  dextrin  and  starch ii,  760 

sugar ii,  751 

Saline  waters,  examination  of ii,  268 

Salt  cake,  analysis  of ii,  373 

Saltpetre,  Chili,  analysis  of ii,  875 

Samples,  selection  of i,  50 

Saponification ii,  1056 

equivalent,  determination  of ii,  1060 

Leffmann-Beam  method  of ii,  1057 

Sauer's  method  of  combustion,  modified  by  Mixter ii,  106 

Schaffner's  method  of  determining  zinc  volumetrically ii,  436 

Scheibler's  method  of  determining  carbonic  acid i,  500 

Scherer's  method  of  determining  mercury  (ic). .  ; i,  369 

Schiff's  azotometer ii,  76 

Schlosing's  method  of  analysis  of  soils ii,  824 

of  determining  ammonia  in  soils ii,  843 

nitric  acid i,  579 

Schmidt-Hiepe's  method  of  determining  tartaric,  malic,  and  succinic 

acids  in  wine ii,  1083 

Schneider's  method  of  determining  antimony i,  403 

Schober's  method  of  determining  zinc ii,  446 

Schoffel's  method  of  determining  chromium  in  cast  iron ii,  543 

tungsten  in  cast  iron ii,  545 

Schulze's  method  of  determining  nitric  acid i,  582 

from  loss  of  hydrogen.  .  .  .  i,  588 

in  water ii,  186 

phosphoric  acid  as  magnesium  phos- 
phate  i,  453 

of  incinerating  plant  tissues ii,  795 

Schulze-Trommsdorff's  method  of  determining  organic  matter  in  water,    ii,  203 

Schwarz's  method  of  determining  chromic  acid i,  424 

copper i,  381,  382 

free  iodine i,  542^  543 

lead i,'360 


INDEX.  1247 

PAGE 

Scorification  of  galena ii,  578 

Selenium,  determination ii,  429 

Selenous  acid,  see  acid  selenous. 

Sifting i,  53 

Silica  (see  also  acid  silicic) i,  233 

separation  from  alumina  in  rock  analysis ii,  1131 

soluble,  determination  in  minerals ii,  1187 

Silicates,  analysis ii,  405 

boric-oxide  method  of  decomposing  in  rock  analysis ii,  1132 

decomposition  by  sodium  carbonate  in  rock  analysis ii,  1134 

method  of  decomposing  in  rock  analysis ii,  1132 

Silicic  acid,  see  acid  silicic. 

Silicon  determination  in  iron ; ii,  535 

Siewert's  method  of  determining  nitric  acid  as  ammonia i,  587 

Silver i,  150, 198 

alloys,  analysis  of ii,  569 

bromide i,  236 

chloride i,  198 

cyanide i,  201 

determination  as  chloride i,  338 

as  cyanide i,  341 

as  metal i,  341 

as  sulphide i,  340 

by  cupellation ii,  581 

by  Gay-Lussac's  method i,  342 

by  Pisani's  method i,  349 

electrolytically ii,  573 

in  galena ii,  577,  583 

volumetrically i,  342 

iodide i,  236 

method  of  determining  organic  matter  hi  water ii,    205 

ores,  analysis  of ii,  568 

phosphate,  normal i,  230 

separation  by  cupellation i,  698 

from  copper,  cadmium,  bismuth,  mercury,  and  lead. .  .  i,  686 

from  gold i,  713 

from  lead .- i,  693 

from  mercury  (ic),  copper,  and  cadmium i,  690 

from  metals i,  679 

sulphide i,  200 

Simpson's  method  of  determining  nitrogen  in  organic  substances ii,  69 

Smith's  crucible  for  alkali  determinations  hi  minerals ii,  1176 

method  of  determining  alkalies  in  minerals ii,  1175 

silicic  acid i,  519 

Soap  solution  for  determining  hardness  of  water ii,  217,  218 

Soda i,131 


1248  INDEX. 

PAGE 

Soda,  analysis  of ii,  360 

commercial,  analysis  of ii,  368 

-lime i,  153,  154 

method  of  determining  nitrogen  in  fertilizers ii,  1028 

preparation  of ii,  85 

solution,  normal ii,  293 

iSodium  carbonate i,  135 

anhydrous i,  166 

analysis  of ii,  360 

as  standard  for  acidimetry ii,  294 

determining  in  presence  of  potassium  carbonate.  . .  ii,  333 
method  of  decomposing  silicates  in  rock  analysis,   ii,  1134 

chloride i,  150,  165 

analysis  of ii,  371 

determination  as  carbonate i,  250 

as  chloride ii,  250 

as  nitrate i,  249 

as  sulphate i,  249 

in  mineral  waters ii,  249 

in  water ^ ii,  196 

disulphate i,  141 

hydroxide i,  131 

nitrate i,  165 

-platinic  chloride i,  166 

separation  from  ammonium i,  603 

from  potassium : i,  599,  604 

silicofluoride i,  167 

sulphate,  analysis  of .  ii,  373 

anhydrous. i,  164 

thiosulphate i,  135 

Soft  lead,  analysis  of ii,  584 

Soils,  analysis  of ii,  1088 

chemical  analysis  of ii,  825 

mechanical  analysis  of ii,  815 

Solder,  fine,  analysis  of ii,  683 

"Soluble"  phosphoric  acid,  determination  in  superphosphates ii,  870 

Solution,  Allihn's  modification  of  Fehling's ii,  741 

ammonium  citrate  for  determining  phosphoric  acid  in  fer- 
tilizers  ii,  1017 

arsenous  acid  for  chlorimetric  analysis ii,  379 

barium  chloride  for  determining  hardness  of  water ii,  217 

chlorinated  lime  for  chlorimetry ii,  378 

citric  acid  for  dissolving  "  soluble  phosphoric  acid"  in  super- 
phosphates  ii,  871 

Faulenbach's  diastase  for  determining  starch ii,  762 

Fehling's ii,  732 


INDEX.  1249 


PAGE 

Solution,  hypobromite ii,  888 

Knapp's,  for  sugar  determination ii,  749 

lead  subacetate  for  sucrose  determination ii,  1049 

magnesium  nitrate  for  determining  phosphoric  acid  in  fertil- 
izers  ii,  1018 

mercury,  Hager's,  for  determining  sugar ii,  753 

iodide,  alkaline,  for  determining  sugar ii,  751 

molybdic  for  phosphoric-acid  determination  hi  fertilizers.  . .  ii,  1018 

of  substances i,  79 

potassa i,  155 

potassium  arsenite  for  chlorimetric  analysis ii,  381 

permanganate  for  determining  organic  matter  in 

water ii,  204 

silver  nitrate,  alkaline,  for  determining  organic  matter  in 

water ii,  205 

soap,  for  determining  hardness  of  water ii,  217,  218 

soda,  brominized,  for  nitrogen  determinations ii,  888 

for  acidimetry ii,  293,  294,  298 

sodium  sulphide,  for  Schaffner's  method  of  zinc  determina- 
tion  ii,  436 

thiosulphate  for  determining  the  iodine  absorption 

number ii,  1036 

Soxhlet's  modification  of  Fehling's ii,  738,  1042 

stannous  chloride  for  ferric  iron  determination i,  329 

uranium  for  determining  phosphoric  acid  in  superphosphates,  ii,  865 

zinc,  for  Schaffner's  method  of  determination ii,  436 

zinc  iodide-starch ii,  193 

Sonnenschein's  method  of  determining  phosphoric  acid i,  446 

Sostegni-Carpentieri's  method  of  detecting  coloring-matter  in  wine.  .  .  ii,  1084 

Soxhlet's  method  of  determining  carbohydrates.  . ii,  1043 

lactose ii,  1052 

sugar ii,  738 

modified  Fehling's  solution t ii,  738 

solution ii,  1042 

Spathic-iron  ore,  analysis  of ii,  494 

Specific  gravity,  determining  in  rock  analysis ii,  1113 

of  mineral  waters ii,  242 

Speculum  metal ii,  680 

Spica's  method  of  determining  salicylic  acid  in  wines ii,  10S5 

Spring-Roland's  method  of  determining  carbonic  acid  in  air ii,  942,  945 

Starch,  determination ii,  760 

by  the  diastase  method •  ii,  1034 

in  commercial  starches  and  potatoes ii,  1034 

iodide i,  349 

method  of  determining  nitrous  acid  in  water ii,  193 

Stein's  method  of  combustion  of  hygroscopic  or  volatile  substances  ....  ii,  44 


1250  INDEX. 

PAGE 

Stockmann's  method  of  determining  phosphorus  in  iron ii,  527 

Stolba'    method  of  determining  hydrofluosilicic  acid i,  443 

Storer-Pearson's  method  of  determining  copper ii,  625 

Strecker's  method  of  incinerating  "plant  tissues ii,  796 

Stromeyer's  method  of  determining  oxygen  in  organic  compounds.  ...  ii,  135 

Strontium  carbonate i,  172 

determination  as  carbonate i,  267 

as  sulphate i,  266 

in  minerals ii,  1144 

in  mineral  waters ii,  246,  252 

in  saline  waters ii,  271 

separation  from  calcium i,  619,  621 

from  potassium  and  sodium i,  607,  609 

sulphate i,  171 

Struve's  method  of  determining  iodine  colorimetrically i,  541 

Stutzer's  method  of  determining  albuminoid  nitrogen ii,  1033 

Substances,  converting  into  weighable  forms i,  81 

Sucrose,  determination ii,  1034,  1049 

by  Clerget's  method. ii,  1050 

Sugar,  determination  by  fermentation ii,  754 

of  lead,  analysis  of ii,  599 

Sugars,  different  reducing  effect  on  Fehling's  solution ii,  734 

reducing,  determination ii,  1042 

Sulphates,  see  acid  sulphuric. 

Sulphides,  determining  in  presence  of  carbonates i,  742 

in  silicates i,  742 

Sulphur,  commercial,  analysis  of ". ii,  703 

determination  as  hydrogen  sulphide i,  558,  562,  569 

by  Berzelius-Rose's  method i,  564 

by  Bunsen's  method i,  566 

by  Rivot-Beudant-Daguin's  method i.  568 

in  cast  iron ii,  519 

in  coal  and  coke ii,  115 

in  free  state  by  Mortreux's  method i,  570 

in  illuminating  gas ii,  114 

in  minerals ii,  1155,  1184 

in  organic  compounds ii,  95 

in  pyrites ii,  561 

in  sulphides i,  562,  569 

in  sulphur  "water ii,  272 

in  organic  bodies,  testing  for ii,  5 

in  sulphides,  separation  from  chlorine.  , i,  756 

water,  examination  of ii,  272 

Sulphuretted  copper  ores,  analysis  of ii,  605 

ores,  determination  of  copper  in ii,  625 

Sulphuric  acid,  see  acid  sulphuric. 


INDEX.  1251 

PAGE 

Sulphurous  acid,  see  acid  sulphurous i,  431 

Superphosphates,  analysis  of ii,  862 

Table  for  calculating  grape-sugar  from  copper  determined  gravimetri- 

cally ii,  743 

for  determining  dextrose,  Allihn's ii,  1046 

invert-sugar,  Hertzfeld's ii,  1044 

for  comparison  of  specific  gravities,  degrees  Brix,  and  degrees 

Baume ii,  1039 

for  correction  of  readings  of  the  Brix  spindle ii,  1040 

for  determination  of  lactose ii,  1053 

of  absorption  of  carbonic  acid i,  508 

of  absorption  of  nitrogen  by  brominized  lye ii,  892 

of  butyro-refractometer  readings ii,  1062 

of  International  atomic  weights,  1903 ii,  1211 

of  weight  of  1  c.c.  of  carbonic  acid  at  various  temperatures  and 

pressures i,  506 

of  weight  in  mgrms.  of  1  c.c.  nitrogen  at  various  pressures,  etc. .  .  ii,  890 
showing  amount  of  the  constituent  sought  for  every  number 

of  the  compound  found ii,  1197 

comparison  of  degrees  of  mercurial  thermometer  with 

those  of  the  air-  or  hydrogen-thermometer ii,  1213 

percentage  of  alcohol  by  weight  and  volume ii.  1073 

of  ammonia  at  different  specific  gravities.    .  ii,  323 
of  anhydrous  acetic  acid  at  various  specific 

gravities ii,  318 

of   anhydrous   phosphoric   acid   at   various 

specific  gravities ii,  290 

of  free  sulphuric  acid  and  sulphuric  anhy- 
dride at  various  specific  gravities ii,  285 

of  hydrated  acetic  acid  at  various  specific 

gravities ii,  291 

of    hydrochloric    acid    at    various    specific 

gravities ii ,  287 

of  nitric  acid  at  various  specific  gravities ...  ii  289 
of  potassa  in  potassa  solution  at  different 

specific  gravities ii,  321 

of  soda  in  soda  solutions  at  different  specific 

gravities ii,  321 

of  tartaric  and  citric  acids  in  solutions  of 

various  specific  gravities ii,  292 

the  quantity  of  ammonia  hi  solutions  of  various  specific 

gravities' ii,  322 

of  anhydrous  potassium  and  sodium  car- 
bonates hi  solutions  at  various  specific 
gravities ii,  322 


1252  INDEX. 

PAGE 

Table  showing  the  quantity  of  hydrochloric  acid  at  various  degrees 

Baume ii,  288 

of  potassa  and  potassium  hydroxide  at 

various  specific  gravities ii,  319 

of  soda  and  sodium  hydroxide  at  various 

specific  gravities ii,  320 

of  sulphuric  acid  and  sulphuric  anhydride 

in  mixtures  with  water ii,  286 

specific  and  absolute  weights  of  some  gases ii,  1212 

Tamm's  method  of  determining  antimony  in  ores ii,  672 

Tannin  determination ii,  767,  1099 

by  methods,  decided  upon  by  the  Amer.  Assn. 

Off.  Agric.  Chemists,  1900 ii,  781 

hi  wines ii,  1081 

Tartar,  analysis  of ii,  357 

Tate's  method  of  analysis  of  chrome-iron  ore ii,  426 

Temperature,  influence  of  on  gases,  in  reading-off i,  33 

Tendon-meal  guano,  analysis  of ii,  926 

Thermopile,  Clamond ii,  613 

Thibault's  method  of  determining  nitrogen ii,  94 

Thiosulphuric  acid,  see  acid  thiosulphuric. 

Tiemann-Schulze's  method  of  determining  nitric  acid i,  582 

Tin  alloys,  analysis  of.  ... ii,  6SO 

chloride  (ous),  analysis  of ii,  689 

determination  as  oxide  (ic) i,  405 

as  stannic  (or  metastannic)  acid i,  405 

as  sulphide  (ous  or  ic) i,  406 

by  alkaline  iodine  solution i,  408 

by  Lenssen's  method i,  408 

in  fine  solder ii,  683 

with  ferric  chloride i,  408 

volumetrically i,  407 

ores,  analysis  of ii,  675 

oxide  (ic) i,  219 

phosphate  (ic) i;  230 

preparations,  analysis  of ii,  689 

pyrites,  analysis  of ii,  676 

separation  from  antimony i,  716,  725 

from  antimony  and  arsenic i.  723,  726,  728 

from  arsenic i,  717,  728 

from  gold i,  727 

from  metals  of  groups  i,  IT,  and  in i,  707 

from  metals  of  groups  iv  and  v i,  706 

from  stannic  tin i,  730 

sulphide,  hydrated  (ous) i,  220 


INDEX.  1253 


Tin  sulphide,  hydrated  (ic) i,  220 

varieties,  analysis  of ii,  677 

Tincture  cochineal ii,  309 

litmus ii,  307 

logwood ii,  310 

Tinstone,  analysis  of ii,  675 

Titanium,  colorimetric  determination  in  minerals ii,  1151 

determination i,  284 

in  iron ii,  535 

in  minerals ii,  1149 

Tripotassium  cobaltic  nitrite i,  193 

Trommsdorff  s  method  of  determining  nitrous  acid  in  water ii,  193 

Tropseolin  OO  and  OOO ii,  312 

Tungsten  in  cast  iron,  determining ii,  545 

Ulsch  method  modified  by  Street,  of  determining  nitrogen ii,  1029 

Ullgren's  method  of  determining  carbon  in  cast  iron ii,  505 

nitrogen  in  iron ii,  525 

Uranium  acetate i,  139 

determination ii,  335 

by  Belohoubeck's  method i,  336 

method  of  determining  phosphoric  acid  in  superphosphates  ii,  864 

ores,  analysis  of ii,  567 

separation  from  aluminium i,  674 

from  barium,  calcium,  and  strontium i,  673 

from  chromium i,  674 

from  cobalt,  nickel,  and  zinc i,  675 

from  iron  (ic) i,  675 

from  magnesium i,  674 

from  other  metals  of  groups  i-rv i,  672 

Uranyl  pyroarsenate i,  223 

pyrophosphate i,  229 

Vanadium  determination  in  cast  iron ii,  546 

in  minerals ii,  1 162 

Vapor  density  of  compounds,  determining ii,  147 

Varrentrapp- Will's  method  of  determining  nitrogen ii,  82 

modifications  of,  for  determining  nitrogen,  ii,  911 

Peligot's  modification  of ii,  91,  894 

Vogel's  modification  of  Pisani's  method i,  351 

Vohl's  method  of  determining  arsenous  acid i,  419 

chromic  acid i,  423 

von  Baumhauer's  method  of  determining  oxygen  in  organic  substances  ii,  131 

Volhard's  method  of  determining  copper  as  sulphocyanate ii,  623 

manganese  in  iron ii,  539 


1254  INDEX. 

PACE 

Wackenroder-Fresenius'  method  of  separating  phosphoric  acid  from 

aluminium i,  459 

Wagner's  method  of  analysis  of  Chili  saltpetre ii,  878 

of  determining  phosphoric  acid  in  manures ii,  859 

Wanklyn-Chapman-Smith's  method  of  determining  albuminoid  nitro- 
gen as  ammonia ii,  207 

Warren's  method  of  determining  carbon  and  hydrogen  in  organic  sub- 
stances   ii,  145 

chlorine  in  organic  compounds ii,  125 

Water,  analysis  of ii,  185 

apparatus  for  absorbing ii,  51 

-bath i,  58 

determining  hardness  of ii,  217 

distilled i,  127 

estimating i,  72 

sulphur,  examination  of ii,  272 

Waters,  mineral  analysis  of, ii,  221 

calculation,  control,  and  arrangement  of    results  of 

analyses  of, ii,  274 

saline,  examination  of ii,  268 

taking  samples  of '. ii,  225,  226 

Weeren's  method  of  determining  phosphoric  acid  by  Miiller's  modified 

Schulze's  method i,  452 

Weighing,  process  of i,  21,  70 

Weights,  testing,  etc i,  19 

Weil's  method  of  decomposing  sulphuretted  ores ii,  627 

of  determining  antimony  in  ores ii,  672 

copper i,  380 

Weldon  mud,  determination  of  effective  oxygen  value  of ii,  470 

Well's  apparatus  for  determining  carbonic  acid i,  499 

Werther's  method  of  determining  arsenic  as  uranyl  pyroarsenate i,  413 

of  examining  gunpowder  residues i,  742 

Weyl's  method  of  determining  carbon  in  cast  iron ii,  505 

White-bearing  metal,  analysis  of ii,  686 

Wichelhaus'  apparatus  for  determining  vapor  densities ii,  154 

Wildenstein's  method  of  determining  sulphuric  acid i,  437,  438 

Wiley's  method  of  determining  melting-point  of  fats ii,  1066 

Wines,  detecting  coloring  matter  in ii,  1084 

detection  of  fuchsin  and  orseille  in ii,  1084 

determination  of  dextrin  in ii,  1086 

of  gum  in ii,  1086 

of  coloring  matters  in ii,  1081 

glycerin,  etc.,  in ii,  1079 

of  potash  in ii,  1085 

of  potassium  bitartrate  in ii,  1082 

of  salicylic  acid  in .  ii,  10S5 


INDEX.  1255 

PAGE 

Wines,  determination  of  sulphurous  acid  in ii,  1085 

of  tannin  in ii,  1081 

of  tartaric  acid  in ii,  1082 

of   tartaric,    malic,   and   succinic   acids   in,   by 

Schmidt-Hiepe's  method ii,  1  083 

Winkler's  method  of  determining  tin  in  alloys ii,  685 

Wohler's  method  of  determining  carbon  hi  cast  iron ii,  508 

silicon  fluoride,  evolved  from  fluorides  i,  478 
Wolff's  method  of  determining  sulphuric  acid  and  chlorine  in  plants. . .  ii,  812 

modified  Knapp's  method  of  mechanical  analysis  of  soils ii,  819 

Wood's  metal,  analysis  of ii,  665 

WTrightson's  method  of  determining  copper  electrolytically ii,  623 

Zeiss'  butyro-refractometer ii,  1061 

Zimmermann's  method  of  analysis  of  zinc  blende ii,  431 

Zinc  i,  132 

blende,  analysis  of ii,  430 

carbonate,  basic i,  182 

determination  as  carbonate i,  287 

as  oxide i,  287 

as  sulphide i,  288,  289 

electrolytically ii,  448 

in  minerals ii,  1143 

volumetrically ii,  435 

-dust,  analysis  of ii,  452 

-iodide-starch  solution ii,  193 

metallic,  analysis  of ii,  450 

ores,  analysis  of ii,  435 

oxide i,  183 

separation  from  aluminium  and  manganese i,  649 

from  barium  and  strontium i,  633,  ii,  634 

from  cadmium i,  684 

from  calcium i,  633,  634 

from  copper i,  683 

from  iron  in  alloys i,  660 

from  nickel,  cobalt,  and  manganese i,  650 

from  potassium  and  sodium i ,  632 

sulphide i,  184 

Zirconium,  determination  hi  minerals ii,  1155, 1156 


R  A 

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UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


DEC  22   1947 


1953 


REC'D 


LD  21-100m-9,'47(A5702sl6)476 


ro 
8 

4 


THE 


ORNIA  LIBRARY 


